DE69232385T2 - Temperature control for thermal ink jet recording head - Google Patents

Description

GENERAL STATE OF THE ART Field of the invention

The present invention relates to an ink jet recording apparatus for performing a recording operation by ejecting an ink from a recording head onto a recording medium and to a temperature control method of the ink jet recording apparatus.

State of the art

Recording devices such as printers, copiers, facsimile machines and the like record an image consisting of a dot pattern on a recording medium such as a sheet of paper or a thin plastic plate based on image information.

The recording devices can be classified into ink-jet printers, dot matrix printers, thermal printers, laser beam printers and the like according to their recording systems. Of these devices, an ink-jet printer (ink-jet recording device) causes a recording head to eject a flying ink droplet (recording liquid droplet) from an ejection port and deposits the ink droplet on a recording medium to perform the recording operation.

Recently, a large number of recording devices are used, and the demand is directed to requirements such as high speed recording, resolution, high image quality, low noise and the like. As a recording apparatus that satisfies these requirements, the aforementioned ink jet recording apparatus is known. In the ink jet recording apparatus, since a recording operation is performed by discharging an ink from a recording head, stabilization control of an ink discharging operation and an ink discharging amount required to satisfy the aforementioned requirements is largely influenced by the temperature of the recording head.

For this reason, the conventional ink jet recording apparatus uses a so-called closed loop control, that is, a method in which an expensive temperature sensor is provided for a recording head unit, and based on the detected temperature of the recording head, the temperature of the recording head is controlled within a desired range or ejection recovery processing is controlled. A heater for temperature control, a heater connected to the recording head unit, or an ejection heater is used in the ink jet recording apparatus which generates a flying droplet using thermal energy to perform recording, that is, a device for ejecting an ink droplet by growing a bubble due to film boiling of an ink. When the ejection heater is used, it must be energized to reach a temperature corresponding to a non-bubble generation temperature.

In the recording apparatus for obtaining a discharge ink droplet by forming a bubble in a solid or liquid ink using heat energy, in particular, closed-loop temperature control is generally carried out because the discharge characteristics are remarkably dependent on the temperature of the recording head as is well known. Otherwise, only a printer of the inexpensive type which completely ignores the print quality, density unevenness and the like and is used in a compact electronic calculator.

However, with the advent of a portable OA device represented by laptop type personal computers, a portable printer having high quality is also required. Regarding the portable printer, a cartridge type replaceable head in which a head and an ink tank are integrated is expected to become increasingly popular due to compact construction structures. In addition, a cartridge type replaceable head is also expected to become popular from the viewpoint of maintenance due to the popularity of home/personal type word processors, personal computers and facsimile machines.

However, in this case, since a temperature sensor, a heater and the like for temperature control are built into the replaceable cassette, the following disadvantages arise.

(1) Variation of the temperature control measurement value due to the variation in the temperature sensor

Since replaceable heads are an indispensable supply, each time the head is replaced, a sensor is connected, which suffers from a variation in its characteristics, seen from the side of the printer main body.

Since a recording head for generating a flying droplet using a heat energy to perform recording has an ejection heater manufactured in a semiconductor process, it is essential to construct a diode sensor for detecting the temperature of the recording head in the same process from the viewpoint of cost reduction. Since the diode sensor suffers from a variation in manufacturing, it does not have the precision as a temperature sensor as a selected product. Thus, the temperatures measured by the diode sensors different production sometimes a difference of 15ºC or more.

For this reason, in closed-loop temperature control using a temperature sensor of the recording head, a variation in the temperature sensor of the recording head must be adjusted by an extra adjustment step, or, after a temperature sensor selected by measurement is connected to the main body, it is corrected by an adjustment switch, thus requiring cumbersome adjustment operations.

These adjustment operations significantly increase manufacturing costs and degrade manageability. An increase in signal processing volume due to these adjustment operations and a large increase in the processing volume of an MPU due to the closed loop control itself poses severe hurdles to the device design of compact portable printer main parts.

(2) Countermeasures against electrostatic interference

Since replaceable heads are a dispensable supply, a user repeatedly attaches and detaches the head from the base body. For this reason, contacts on the base body device side are always exposed.

Since the output signal from a temperature transmitter is delivered directly from the replaceable head to a circuit on a board of the main body through a carriage and flexible wires, a temperature measuring circuit is very susceptible to electrostatic interference. This weak point is exacerbated because the housing of a compact portable printer cannot provide adequate shielding.

Therefore, in a conventional temperature detection method, electrostatic shields and parts must be added as a countermeasure against electrostatic noise for the only one temperature sensor, and a compact structure, a Costs are reduced and quality is significantly reduced.

(3) Time delay

The purpose of the temperature detection of the recording head is to control the temperature of the recording head within a desired range and to carry out stabilization control and the recording ink ejection operation and ejection amount as described above. More specifically, the temperature detection of the recording head means to detect the ink temperature with respect to the ejection heater in a strict sense. However, since it is difficult to directly measure the ink temperature in the ejection heater, the temperature sensor is mounted near the heater (or nozzle) (the mounting position of the temperature sensor will be described in detail later). In an ink jet recording apparatus, since the heat conduction speed of a heater board is lower than the speed of change in temperature near the ejection heater, a time lag from the actual temperature is generated even if the temperature of the head is continuously measured. Since the control described above serves to feed back a temperature detected by the temperature sensor for an amount of heat through the heating element, the time delay interferes with the precise control.

(4) Temperature detection error

When detecting temperature by the temperature sensor, a temperature may be falsely detected due to thermal flow or electrical noise entering the temperature sensor. To prevent this, a method of averaging several detection values of head temperature and determining an average value as the current head temperature is adopted.

However, if several detection temperatures are averaged, the following problems arise:

[1] Dynamic changes in the temperature of the recording head are averaged; and

[2] a time delay is created between the current temperature and a set point.

Thus, these problems interfere with accurate feedback control.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentioned problems and has an object to provide a recording apparatus that can detect the temperature of a recording head without providing a temperature sensor in the recording head.

Canadian Patent Application No. CA-A-2025506 discloses a recording head for ejecting ink from an ejection port using thermal energy in response to a drive signal. A controller controls the energy supplied to a heating means to heat the head based on the measured ambient temperature.

According to a first aspect of the present invention there is provided a recording apparatus as set out in claim 1.

According to a second aspect, a method is provided as specified in claim 10.

Thus, after performing a recording operation by ejecting an ink droplet from a recording head, an ambient temperature sensor for measuring the ambient temperature is provided in the main body of the device side, and a change in the temperature of the head from the past to the present time is assumed and the change from the present time to the Future are both predicted by computational processing so that optimum temperature control can be carried out without providing a temperature sensor in the current head which has a correlation with the temperature. In short, a change in the temperature of the head is assumed or predicted by evaluating it using a matrix calculated in advance within a range of a thermal time constant of the head and an applicable energy.

SHORT DESCRIPTION OF THE DRAWING

Fig. 1 is a perspective view showing an arrangement of an ink jet recording apparatus to which the present invention is suitably applied or employed;

Fig. 2 is a perspective view showing a replaceable cartridge;

Fig. 3 is a cross-sectional view of a recording head;

Fig. 4 is a perspective view showing a recovery system unit;

Fig. 5 is a block diagram showing a control arrangement for executing a recording control process;

Fig. 6 is a view showing the positional relationship between a sub-heater and an ejection heater (main heater) of the head used in this embodiment;

Fig. 7 is an explanatory view of a sub-pulse width modulation driving method;

8A and 8B are a schematic longitudinal cross-sectional view and a schematic front view, respectively, showing an arrangement along an ink channel of a recording head to which the present invention can be applied;

Fig. 9 is a graph showing a preheat pulse dependency of the ejection amount;

Fig. 10 is a graph showing the temperature dependence of the ejection amount;

Figs. 11 to 13 are flow charts related to the temperature correction control;

Fig. 14 shows a temperature guess/prediction table;

Figs. 15A to 16E are explanatory views related to the temperature guessing/prediction control;

Fig. 17 is a graph showing temperature dependence of vacuum holding time and humidification amount;

Fig. 18 is a diagram showing a sub-tank system;

Figs. 19A and 19B are explanatory views showing another arrangement for presuming the head temperature;

Fig. 20 is a flow chart showing a schematic printing sequence;

Figs. 21 to 23 are flow charts related to the temperature prediction control;

Fig. 24 is a block diagram showing another control arrangement for executing a recording control flow;

Fig. 25 is a view showing a head in detail; and

Fig. 26 to 28 are flow charts related to another temperature prediction control.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a perspective view showing the arrangement of an ink jet recording apparatus IJRA in which to which the present invention is suitably applied or employed. In Fig. 1, a recording head (IJH) 5012 is coupled to an ink tank (IT) 5001. As shown in Fig. 2, the ink tank 5001 and the recording head 5012 form an integrated replaceable cartridge (IJC). A carriage (HC) 5014 is used to mount the cartridge (IJC) on a printer body and is scanned along a guide 5003 in a sub-scanning direction.

A platen roller 5000 scans a printing medium P in the main scanning direction. A temperature sensor 5024 measures the ambient temperature in the apparatus. Note that the carriage 5014 is connected to a board (not shown) having a plurality of electric circuits (such as the temperature sensor 5024) to control a printer via a flexible cable (not shown) for supplying a drive signal pulse current and a head temperature control current to the recording head 5012.

Fig. 2 shows the replaceable cartridge. The cartridge has a nozzle portion 5029 for ejecting an ink droplet. The ink jet recording apparatus IJRA having the above structure will be described in detail below. In the recording apparatus IJRA, the carriage HC is engaged with a spiral groove 5004 of a lead screw 5005 which is rotated by driving force transmission gears 5011 and 5009 upon normal or reverse rotation of a driving motor 5013. The carriage HC has a pin (not shown) and is reciprocated in directions shown by arrows a and b. A paper pressing plate 5002 presses a sheet of paper against the plate 5000 along a carriage moving direction. Photocouplers 5007 and 5008 serve as a home position detecting means for confirming the presence of a lever 5006 of the carriage HC in a corresponding zone and, for example, switching the rotation direction of the motor 5013. A member 5016 supports a cap member 5022 for capping the front surface of the recording head. A suction means 5015 attracts the inside of the cap by vacuum suction and performs a Suction recovery operation of the recording head 5012 through an inner cap opening 5023.

A link 5019 enables forward/backward movement of a cleaning blade 5017. The link 5019 and the cleaning blade 5017 are supported on a body support plate 5018. The blade of this embodiment is not limited to the cleaning blade 5017, any known cleaning blade may be used. A lever 5021 is used to start a suction recovery operation. The lever 5021 is moved after moving a comb 5020 engaged with the carriage HC, and is subjected to movement control based on a driving force from the driving motor through a known transmission means (for example, by clutches).

These capping, cleaning and suction recovery operations can be performed at their respective positions by operating the lead screw 5005 when the carriage HC reaches a home position zone. However, this embodiment is not limited to this, as long as desired operations are performed at known timings.

Fig. 3 shows the recording head 5012 in detail. A heater board 5100 formed in a semiconductor manufacturing process is provided on the surface of a support member 5300. A temperature control heater (temperature raising heater) 5110 formed in the same semiconductor manufacturing process for maintaining and controlling the temperature of the recording head 5012 is provided on the heater board 5100. A wiring board 5200 is provided on the support member 5300. The wiring board 5200, the temperature control heater 5110 and the ejection heater (main heater) 5113 are connected via wiring lines (not shown) such as by wire bonding. The temperature control heater 5110 can be prepared by Adhering a heating member to the support member 5300 or the like which is formed in a process different from that of the heating board 5100.

A bubble 5114 is generated by heating from the ejection heater 5113. An ink is ejected as an ink droplet 5115. The head has a common ink chamber 5112 through which an ink to be ejected flows into the recording head.

Fig. 4 is a schematic view of an ink jet recording apparatus to which the present invention is applicable. In Fig. 4, each ink jet cartridge 8a has an ink tank portion in the upper portion and a recording head 8b (not shown) in the lower portion, and also has a connector for receiving a signal for driving the recording head 8b. A carriage 9 can align and hold four cartridges (each storing inks of different colors, i.e., black, cyan, magenta, yellow, and the like). The carriage has a connector holder for supplying signals for driving the associated recording heads, and the holder is connected to each of the recording heads 8b.

The apparatus includes a scanning track 9a extending in the main scanning direction of the carriage 9 to slidably support the carriage 9, a drive belt 9c for transmitting a driving force for reciprocating the carriage 9, a pair of transport rollers 10c and 10d arranged in front of and behind the recording position of the recording head for clamping and transporting a recording medium, and a recording medium 11 such as a sheet of paper pressed against a platen (not shown) to make the recording surface of the recording medium 11 flat. The recording heads 8b of the ink jet cartridges 8a mounted on the carriage 9 extend downward from the carriage 9 and are located between the recording medium transport rollers 10c and 10d so that the The exit surface of each recording head unit faces parallel to the recording medium pressed against the guide surface of the platen (not shown). Note that the drive belt 9c is driven by a main scanning motor 63, and the pair of transport rollers 10c and 10d are driven by a sub-scanning motor (not shown).

In the ink jet recording apparatus of this embodiment, a recovery system unit 400 is arranged on the home position side of the left side in Fig. 1. The recovery system unit 400 includes cap units 300 arranged in accordance with the plurality of ink jet cartridges 8a each having a recording head 8b. The cap units 300 are arranged to be slidable in the left and right directions in Fig. 4 and to be vertically moved upon movement of the carriage 9. When the carriage 9 is at the home position, the cap units 300 are coupled to the corresponding recording heads 8b to cap them, thus preventing ejection failures that occur when an ink in the ejection port of each recording head 8b becomes highly viscous and remains stuck at the port after evaporation.

The recovery system unit also includes a pump unit 500 that communicates with the capping units 300. The pump unit 500 is used for generating a negative pressure in the suction recovery processing that is carried out by coupling the capping units 300 to the recording heads 8b when the recording heads 8b suffer from an ejection failure. Furthermore, the recovery system unit 400 includes a blade 401 and a wiping member made of an elastic member such as rubber, and a blade holder 402 that holds the blade 401. Reference numeral 403 denotes an absorber.

The four ink cartridges mounted on the carriage 9 use a black ink (hereinafter abbreviated to K), a cyan ink (hereinafter abbreviated to C), a magenta ink (hereinafter abbreviated to M) and a yellow ink (hereinafter abbreviated to Y), and the inks overlap in this order. Intermediate colors can be realized by accurately overlapping C, M and Y ink dots. More specifically, red can be realized by overlapping M and Y; blue by C and M, and green by C and Y. Although black can be realized by overlapping three colors C, M and Y, since the development of black at this time is poor and it is difficult to make the three colors overlap accurately, a chromatic color edge is undesirably formed and the ink ejection density per unit time becomes too high. Thus, only black is ejected separately (black ink is used).

(Control arrangement)

A control arrangement for carrying out the recording control of respective units in the apparatus arrangement described above will be described below with reference to Fig. 5. As shown in Fig. 5, the recording apparatus includes a CPU 60, a program ROM 61 storing a control program which the CPU 60 executes, an EEPROM 62 storing various data, the main scanning motor 63 for moving the recording heads, and the sub-scanning motor 64 for conveying a recording sheet. The sub-scanning motor 64 is also used in the suction operation by a pump. This device also includes a wiping solenoid 65, a paper feed solenoid 66 used for paper feed control, a cooling fan 67, a paper width detection LED 68 which is turned on in a paper width detection operation, a paper width sensor 69, a paper flutter sensor 70, a paper feed sensor 71, a paper ejection sensor 72, a pump position sensor 73 which detects the position of a suction pump, a carriage HP sensor 74 which detects the initial position of the carriage, a door open sensor 75 which detects the opening/closing state of a door, and a temperature sensor 76 which detects the ambient temperature of the device.

The apparatus further includes a gate array 78 which performs supply control of recording data for the heads of four colors, a head driver 79 for driving the head, the ink cartridges 8a for four colors, and the recording heads 8b for four colors. Fig. 5 shows only the cartridge 8a and the head 8b for black (Bk). The ink cartridge 8a has a remaining ink sensor 8f which detects the remaining amount of ink. The head 8b has a main heater 8c for ejecting an ink, a sub-heater 8d for performing temperature control of the head, and a ROM 854 which stores various data for the head.

Fig. 6 shows a heater board (H. B) 853 of the head used in this embodiment. An ejection unit assembly 8g in which the temperature control heaters (temperature control sub-heaters) 8d and the ejection heaters (main ejection elements) 8c are arranged, and driving elements 8h are arranged on a single board to have the positional relationship shown in Fig. 6. Since these elements are arranged on a single board, the head temperature can be efficiently detected and controlled. Thus, the head can be further downsized and the manufacturing process can be further simplified. Fig. 6 also shows the positional relationship of an outer shield surface 8f of a top plate for separating H. B into a zone filled with ink and a zone not filled with ink.

(First embodiment)

The first embodiment in which the present invention is applied is the one described above Recording device, which will now be described in detail using the attached drawing.

(Summary of temperature assumption)

After performing a recording operation in this embodiment by ejecting an ink droplet from a recording head, an ambient temperature sensor for measuring the ambient temperature is provided for the main body side to detect a change in the head temperature from the past to the present time by calculation processing, so that optimal temperature control can be carried out without providing a head temperature sensor having a correlation with the head temperature. In short, a change in the head temperature is assumed (presumed) by evaluating it using a matrix calculated in advance within a range of the thermal time constant of the head and the energy supplied to the head.

The thermal time constant or thermal capacity of the recording head is essentially a ratio determined by the amount of heat required to raise the temperature of the head by a specific amount.

Based on this assumed change in temperature, the head is controlled by a divided pulse width modulation (PWM) driving method for a heater (sub-heater) for increasing the temperature of the head and for an ejection heater. In a driving method of this control, when a difference from a temperature control target value is large, the temperature is increased to a temperature near the target value using the sub-heater, and the remaining temperature difference is controlled by PWM ejection amount control so that the ejection amount can become constant. After using PWM as a means of ejection amount control for a short response time head, no response delay time is required in the Temperature detection based on the sensor position is used, as in the case where the temperature sensor is used in the head, generated due to the calculation processing, and the control can be carried out which can make full use of this advantage.

More specifically, the density unevenness in a row or in a page can be eliminated. PWM can thus be realized in a row without arranging a temperature sensor in the head as described previously.

(PWM control)

The discharge amount control method of this embodiment is described below with reference to the accompanying drawing.

Fig. 7 is a view for explaining divided pulses according to the embodiment of the present invention. In Fig. 7, VOP represents a driving voltage, P1 represents the pulse width of the first pulse (hereinafter referred to as preheating pulse) of a plurality of divided heating pulses, P2 represents the time interval, and P3 represents the pulse width of the second pulse (hereinafter referred to as main heating pulse). T1, T2, and T3 represent times for determining PT, P2, and P3. The driving voltage VOP corresponds to a kind of electric energy required to cause an electrothermal converting element to be supplied with this voltage to generate a heat energy in an ink in an ink channel formed by the heater board of the upper plate. The value of the driving voltage VOP is determined by the area, resistivity, and film structure of the electrothermal converting element and the channel structure for the recording head. In the split pulse width modulation driving method, pulses are applied sequentially to have widths P1, P2 and P3. The preheat pulse is a pulse mainly for controlling the ink temperature in the ink channel and plays an important role in Ejection amount control according to the present invention. The preheat pulse width is set to a value that does not cause a bubbling phenomenon in an ink by heat energy generated by the electrothermal converting element upon application of the preheat pulse.

The interval time is set to form a predetermined time interval so that the preheat pulse and the main heat pulse do not interfere with each other and to achieve a uniform temperature distribution of the ink in the ink channel. The main heat pulse forms a bubble in an ink in the ink channel to eject the ink from the ejection port. The pulse width P3 of the main heat pulse is determined by the area, resistivity and film structure of the electrothermal conversion element and the ink channel structure of the recording head.

The function of the preheat pulse in a recording head having the structure shown in, for example, Figs. 8A and 8B is explained below. Figs. 8A and 8B are a schematic longitudinal cross-sectional view and a schematic front view, respectively, showing an arrangement along an ink channel of a recording head to which the present invention can be applied. In Figs. 8A and 8B, each of the electrothermal converting elements (ejection heater) 21 generates heat upon application of the above-described divided pulses. The electrothermal converting element 21 is arranged together with an electrode wiring line on the heater board and the like for applying the divided pulses to the converter. The heater board is formed of a silicon layer 29 and is supported by an aluminum plate 31 which forms the board of the recording head. A groove 35 which forms, for example, an ink channel 23 is formed on the upper plate (orifice plate) 32. When the upper plate 32 and the heater board (aluminum plate 31) are connected to each other, the ink channel 23 and a common ink chamber 25 for supplying ink to the channel are defined. Ejection ports 27 (ports with a hole area corresponding to a hole diameter of 20 u are shown in Fig. 8B) are formed in the upper plate 32 and communicate with the ink channel 23.

In the recording head shown in Figs. 8A and 8B, when the drive voltage VOP = 18.0 V and the main heat pulse width P3 = 4,114 usec is set and the preheat pulse width P1 can be changed within a range of 0 and 3,000 usec, the relationship between the ejection amount Vd [ng/dot] and the preheat pulse width P1 [usec] as shown in Fig. 9 is obtained.

Fig. 9 is a graph showing the preheat pulse dependence on the ejection amount. In Fig. 9, VO represents the ejection amount when P1 = 0 usec. This value is determined by the head structure shown in Figs. 8A and 8B. In this connection, V0 in this embodiment was = 18.0 ng/dot at an ambient temperature TR = 25º G. As shown by a curve a in Fig. 9, the ejection amount Vd is increased with the pulse width P1 of the preheat pulse to be linear when the pulse width P1 falls within a range of 0 and P1LMT, and its change loses linearity when the pulse width P1 exceeds P1LMT. The ejection amount Vd is saturated and becomes maximum at a pulse width P1MAX.

The range up to the pulse width P1LMT in which the change in the ejection amount Vd thus shows linearity with respect to the change in the pulse width P1 is effective as a range in which ejection amount control is easily carried out by changing the pulse width P1. In this embodiment, in this connection, P1LMT = 1.87 µs, and the ejection amount at that time was VLMT = 24.0 ng/dot. Moreover, the pulse width P1MAX according to the saturation state of the ejection amount Vd was P1MAX = 2.1 µs, and the ejection amount at that time was VMAX = 25.5 ng/dot.

If the pulse width is larger than P1MAX, the discharge amount Vd becomes smaller than VMAX. This phenomenon occurs for the following reason. That is, if the preheat pulse is pulse width within the aforementioned range, a very small bubble (in a state immediately before film boiling) is formed on the electrothermal conversion element, and the next main heating pulse is applied before this bubble disappears, and the very small bubble interferes with the bubble formation by the main heating pulse, thus reducing the ejection amount. This zone is hereinafter referred to as a pre-bubble zone, and it is difficult to carry out the ejection amount control using the pre-heating pulse in this zone.

If the inclination of a straight line representing the relationship between the ejection amount and the pulse width within the range of P1 (0 to P1LMT [jxs]) shown in Fig. 9 is set as a dependency coefficient of the preheat pulse, the dependency coefficient of the preheat pulse can be given as follows:

KP = ΔVdP / ΔP1 [ng/usec dot]

This coefficient KP is determined by the head structure, driving conditions, physical ink properties and the like, regardless of the temperature. More specifically, the curves b and c in Fig. 9 represent other recording heads. As can be seen from these curves, different recording heads have different ejection properties. In this way, since the different recording heads have different upper limit values P1LMT of the preheat pulse P1, the ejection amount control is carried out by determining the upper limit value P1LMT for each recording head, as will be described later. Note that KP = 3.209 ng/usec dot in a recording head and an ink is represented by the curve a of this embodiment.

Another factor for determining the ejection amount of the inkjet recording head is the temperature of the recording head (ink temperature).

Fig. 10 is a graph showing the temperature dependency of the ejection amount. As shown by a curve a in Fig. 10, the ejection amount Vd increases linearly with respect to the increase in the ambient temperature TR (= head temperature TH) of the recording head. When the inclination of the straight line is set as a temperature dependency coefficient, the temperature dependency coefficient can be given as:

KT = ΔVdT / ΔTH [ng/ºC dot]

This coefficient KT is determined by the head structure, the physical properties of ink and the like, regardless of driving conditions. Fig. 10 also shows curves b and c representing other recording heads. Note that KT = 0.3 ng/°C dot in the recording head of this embodiment.

As described above, the ejection amount control according to the present invention can be carried out using the relationship shown in Figs. 9 and 10.

(Temperature Presumption Control)

An operation when a recording operation is carried out using the recording apparatus having the above arrangement will be described below with reference to flow charts shown in Figs. 11 to 13.

When a power supply is turned on in step S100, a temperature correction timer is reset and set (S110). Then, the temperature is read from a temperature sensor (hereinafter referred to as a reference thermistor) on a main circuit board (hereinafter referred to as a PCB) (S120), thereby detecting the ambient temperature. However, since the reference thermistor is present on the PCB, it cannot often detect an accurate ambient temperature of the head under the influence of a heat generating member (i.e., a driver) on the PCB. Thus, the detection value is determined according to a elapsed time from the power-on operation of the main unit power supply is corrected so as to obtain an ambient temperature. More specifically, an elapsed time from the power-on operation is read from the temperature correction timer (S130) to refer to a temperature correction table (Table 1), thereby obtaining an accurate ambient temperature from which the influence of the heat generating element is eliminated (S140). Table 1

In step S150, a current head chip temperature (β) is assumed by referring to a temperature guess table (Fig. 14), and the controller waits for the input of a pressure signal. The guess of the current head chip temperature (β) is carried out by adding to the ambient temperature obtained in step S140 a value obtained from a matrix of temperature differences between the head temperature and the ambient temperature with respect to the input energy (power ratio) for the head, thereby updating the ambient temperature. Since no pressure signal is input immediately after a power-on operation (input energy = 0) and the temperature difference between the head temperature and the ambient temperature is also 0, a matrix value 0 (thermal equilibrium) is added. If no pressure signal is input, the flow returns to step 120, and the processing is repeated from a reading operation of the temperature from the reference thermistor. In this embodiment, the head chip temperature guessing cycle was set to 0.1 sec.

The temperature presumption table shown in Fig. 14 is a matrix table showing temperature rise characteristics per unit time determined by the thermal constant of the head and the energy supplied to the head. When the power ratio is large, the matrix value becomes large, while when the temperature difference between the head temperature and the ambient temperature becomes large, the matrix value is reduced because a thermal equilibrium state is easily established. The thermal equilibrium state is established when the energy supplied is equal to the radiation energy. In the table shown in Fig. 14, "power ratio = 500%" means that the energy supplied is obtained after energy is supplied to the sub-heater, converted into a power ratio.

If the matrix value per unit time is accumulated based on this table, the temperature of the head at that time can be assumed.

When a print signal is input, a print target temperature (α) of the head chip that enables an optimal drive operation of the current ambient temperature is obtained by referring to a target temperature table (drive temperature table) (Table 2) (S170). In Table 2 below, the reason why the target temperature varies depending on the ambient temperature is that even if the temperature on the silicon heater board of the head is controlled to a predetermined temperature, since the temperature of an ink flowing into the head is low and the thermal time constant is large, the temperature of the system around the head chip consequently becomes low when this temperature is regarded as an average temperature. For this reason, as the ambient temperature becomes lower, the target temperature of the silicon heater board of the head must be increased.

Table 2 Ambient temperature (ºC) Target temperature (ºC)

under 12 35

12 to 15 33

15 to 16 31

16 to 17 29

17 to 19 27

19 to 21 25

over 21 23

In step S180, a difference γ (= α - β) between the printing target temperature (α) and the current head temperature (β) is calculated. In step S190, an on-time (t) of the sub-heater before the printing operation for the purpose of lowering the difference (γ) is obtained by referring to a sub-heater control table (Table 3), and the sub-heater is turned on (S300). This is a function of raising the temperature of the entire head chip by the sub-heater when the assumed temperature of the head and the target temperature have a difference between each other at the start of the printing operation. Thus, the temperature of the entire head chip can be set as close to the target temperature as possible.

Table 3 Difference γ (ºC) Underheating element Switch-on time (sec)

under -15 6

- 15 to -12 5

- 152 to -9 4

- 9 to -5 3

- 6 to -5 2

- 5 to -4 1

Continuation of Table 3 Difference γ (ºC) Underheating element Switch-on time (sec)

- 4 to -3 0.5

- 3 to -2 0.2

over 20

After the sub-heater is turned on for the above set time, the sub-heater is turned off, and the current chip temperature (β) is determined by referring to the current temperature assumption table (Fig. 14). Then, a difference (γ) between the print target temperature (α) and the head chip temperature (β) is calculated (S320), and a PWM value at the start of the print operation is obtained from a PWM value determination table (Table 4) according to the difference (γ) (S330). It is difficult to make the chip temperature approach the target temperature exactly even by using the sub-heater, and further, it is very difficult to carry out the temperature correction in one line by the sub-heater. Thus, in this embodiment, the ejection amount is corrected by the PWM method according to the remaining difference from the target value. In this embodiment, in particular, the aforementioned value P1 is increased to also increase the ejection amount. Table 4

In this embodiment, the PWM value is optimized each time a predetermined area is printed in a one-line printing operation. In this case, one line is divided into 10 areas, and an optimal PWM value is set for each area. More specifically, this operation is carried out in the following manner.

A variable n is reset (n = 0) and n is incremented (n = n + 1) (S340, S350). Note that n represents each area. The printing operation of an n-th area is carried out (S360), and after completion of the printing operation of the 10th area, the flow returns to step S310 to read the temperature of the reference thermistor. If n < 10, the flow advances to step S380 and areas to be printed remain in one line (S370) to obtain a change in the temperature of the head caused by the printing operation of the immediately preceding area. More specifically, a head chip temperature (β) after completion of the printing operation of the n-th area (immediately before the printing operation of an (n+1)-th area) is obtained by referring to the current temperature assumption table (Fig. 14). (S380). A difference (γ) between the print target temperature (α) and the head chip temperature (β) is calculated, and a PWM value after printing the (n + 1)-th area is set according to the difference (γ) by referring to the PWM value determination table (Table 4) (S390, S400, S410). Thereafter, the flow returns to step S350. Thus, n is incremented (n = n + 1), and the above-described control is repeated until n = 10.

Under the control described above, the chip temperature (β) can be gradually approached to the print target temperature (α). Even when there is a large temperature difference between the head chip temperature (β) and the print target temperature (α) as in an earlier period after power-on, an actual ejection amount can be controlled as the print target temperature because PWM control is carried out within one line, and high quality can be realized. The reason why this embodiment does not simply use the number of dots (print ratio) is that the power to be supplied to the head chip varies depending on different PWM values even if the number of dots remains the same. Since the concept of "power ratio" is used, the same table can be used even when the maintenance element is turned on.

The ejection amount control will be described again. Stabilization control of the ejection operation/operation amount of the head is achieved by controlling from two aspects.

1. A target temperature (stable discharge head temperature) at which the discharge is most stabilized is obtained, and control is performed so that the head temperature reaches the target temperature. The target temperature is obtained from a "target temperature table". The target temperature (stable discharge head temperature) depends on the ambient temperature. At this time, the head temperature control is carried out within a wide range is carried out using the sub-heater (with a large amount of heat generation). Head temperature control within a narrow range is achieved by self-temperature increase/self-heat radiation of the head. Note that PWM control which anticipates a temperature drop is feasible.

2. An ejection amount obtained when an ink is normally ejected at the target temperature is determined as a target ejection amount, and even if the head temperature shifts from the target temperature, control is performed so that the ejection amount becomes equal to the target ejection amount. A shift (difference) between the target temperature and the current head temperature is assumed. At this time, an applied ejection energy that can compensate for the difference can be applied by the PWM control.

A recording signal sent through an external interface is stored in a receiving buffer 78a of the gate array 78. The data stored in the receiving buffer 78a is expanded to a binary signal (0, 1) indicating "ejection/no-ejection" and the binary signal is transferred to a print buffer 78b. The CPU 60 can refer to the recording signal from the print buffer 78b as necessary.

In the gate array 78, two line ratio buffers 78c are prepared. A line after recording is divided into equal intervals (into, for example, 10 areas), and the print ratio of each area is calculated and stored in ratio memories. The "line ratio buffer 78c1" stores print ratio data in units of areas of the current print line. The "line ratio buffer 78c2" stores print ratio data in units of areas of a line adjacent to the current print line. The CPU 60 can refer to print ratio data in units of areas of the current print line and, if necessary, the next line at any time.

The CPU 60 refers to the line ratio buffers 78c during the temperature prediction control described above to obtain the pressure ratios of the regions. A computational load on the CPU 60 can therefore be reduced.

The temperature prediction control is described in detail below with reference to explanatory views shown in Figs. 15A to 16E. First, a difference between the ambient temperature and the head temperature is calculated to check whether the heating operation of the sub-heater immediately before printing is required. In Fig. 15B, since the head temperature is not far shifted from the target temperature, the heating operation of the sub-heater is not carried out (Fig. 15D). The head temperature (Fig. 15B) immediately before printing of an area A1 is assumed, and the printing operation is carried out using a PWM value (Fig. 15C) for the area A1 according to the difference. In this case, since it can be determined based on the PWM value of the area A1 that the area A1 has been printed at a ratio of 100%, the temperature immediately before printing of the next area A2 is assumed.

Since the ratio of area A1 is high, it can be assumed that the temperature immediately before printing area A2 is high, and a low PWM value is set. Since area A2 has a low ratio (0%) and a low PWM value, it can be assumed that the temperature immediately before printing area A3 has dropped.

Consequently, a large PWM value is set immediately before printing an area A4 to perform the printing operation. Since in areas A4, A5, A6 and A7, actual printing conditions are high, it can be assumed that the head temperature is gradually increasing, and the printing operations are performed while gradually decreasing the PWM values. Since after an area A8, actual printing conditions are low, it can be assumed that the head temperature is gradually decreasing, and the printing operations are carried out while gradually increasing the PWM values (since the printing ratio is 0, no printing operation is currently carried out). As described previously, the printing operation is carried out while adjusting the PWM value after printing each area based on the presence/absence of use and the performance of the sub-heater before printing, the value of the head temperature is assumed immediately before printing each area. Since the head temperature (Fig. 15B) is not expected to be greatly shifted from the reference temperature in the one-line printing operation, the sub-heater is not turned on immediately before printing the next line.

In Figs. 16A to 16E, a difference between the ambient temperature and the head temperature is calculated to check whether the heating operation of the sub-heater is required immediately before printing. In this case, since the head temperature is largely shifted from the target temperature, it is determined that the heating operation of the sub-heater is required and the heating operation of the sub-heater is carried out (Fig. 16D). Then, a head temperature after completion of the heating operation of the sub-heater and immediately before printing of an area A1 (Fig. 16B) is assumed. Since the head temperature is assumed to exceed the target temperature, a minimum value is assigned to the PWM value (Fig. 16C) after printing of the area A1. Although the heating operation of the sub-heater may raise the temperature in an early period of the heating operation, it is easy to assume that the head temperature has dropped below the reference temperature after completion of printing because the difference between the head temperature and the target temperature is large. The head temperature immediately after the sub-heater is turned on is therefore intentionally set to exceed the target temperature.

The minimum value is assigned to the PWM value of area A1 to perform the printing operation. However, since the ratio (100%) of area A1 is high, it is assumed that the temperature immediately before printing of an area A2 has not dropped below the target temperature, and a minimum PWM value is set for the area A2. Since actual printing ratios are small in areas A2 and A3, the head temperature is gradually lowered to a temperature below the target temperature, and optimum PWM values are set to perform the printing operations (since the printing ratios are 0 in this case, no actual printing operations are performed). Thereafter, the printing operation of the sub-heater and the actual printing operations are performed while setting the PWM values of the areas in the same manner as in Figs. 15A to 15E.

A difference between the cases of Figs. 15A to 15E and Figs. 16A to 16E is that the discharge amount does not exceed the discharge amount (Fig. 15E) at the target temperature in the former case, while the discharge amount sometimes exceeds the discharge amount (Fig. 16E) at the target temperature in the latter case. This is because no negative PWM value is set for lowering the discharge amount in this embodiment. In practical application, a negative PWM value may be provided.

In this embodiment, double-pulse PWM control is performed to control the ejection amount. However, single-pulse PWM or PWM using three pulses or more may be used.

When the head chip temperature (β) is higher than the print target temperature (α), and the head temperature cannot be lowered even if the head is driven with a small power PWM value, the scanning speed of the carriage can be controlled, or the scanning time of the carriage can be controlled.

The number of divided areas (10 areas) in one line and constants such as the temperature prediction cycle (0.1 sec) and the like used in this embodiment are merely examples, and the present invention is not limited to them.

(Second embodiment)

Another embodiment for further stabilizing the ejection amount will be described below with reference to Fig. 21. In the first embodiment, a PWM value is optimized every time a certain area is printed in a one-line printing operation. For this reason, even if a large change in the printing ratio occurs in one line, the density unevenness does not occur often in one line. However, since the PWM values are optimized during printing, the load on the CPU is undesirably increased. In the second embodiment, therefore, the control for carrying out a one-line printing operation is made using a PWM value at the start of the printing operation in order to reduce the load on the CPU.

Since the same control as in the first embodiment up to step S190

S190 (Fig. 11), a description of this is omitted here.

In step S190, an on-time (t) of the sub-heater before printing for the purpose of decreasing the difference (γ) is obtained by referring to a sub-heater control table (Table 3). Thereafter, the sub-heater is turned on as shown in Fig. 21 (S200). After the sub-heater is turned on for the set time, the sub-heater is turned off, a current chip temperature (β) (chip temperature immediately before printing) is assumed by referring to a current temperature assumption table (Fig. 14) (S210).

A difference (β) between the print target temperature (α) and the current head chip temperature (β) is calculated, and a PWM value is obtained by referring to a PWM Value determination table (Table 4) (S220, S230). A one-line printing operation is carried out according to the obtained PWM value (S240), and after the printing operation, the flow returns to step S120 to read the temperature of a reference thermistor.

Under the control described above, the head chip temperature (β) gradually reaches the print target temperature (α). Even when there is a large temperature difference between the head chip temperature (β) and the print target temperature (α), as in an early period after power-on, an actual ejection amount can be controlled by approaching that at the print target temperature because the PWM control is carried out in units of lines, and high quality can be realized.

In this embodiment, double-pulse PWM control is used to control the ejection amount. However, single-pulse PWM or PWM using three pulses or more may be applied. When the head chip temperature (β) is higher than the print target temperature (α), the head chip temperature cannot be lowered even if the head is driven with a small PWM power value, the scanning speed of the carriage may be controlled, or the scanning start time of the carriage may be controlled.

(Third embodiment)

Explained below is a method of assuming the current temperature in an ink jet recording apparatus based on the pressure ratio (hereinafter referred to as pressure ratio) and controlling a recovery sequence to stabilize the ejection. When the PWM control described above is not carried out, the pressure ratio becomes equal to a duty ratio.

In this embodiment, the current head temperature is assumed from the pressure ratio as in the first embodiment, and a suction condition of a suction means is changed according to the assumed temperature of the head. Control of the suction state is performed based on the suction pressure (piston initial position) and the suction amount (a change in volume or a vacuum holding time). Fig. 17 shows head temperature dependence on the vacuum holding time and the suction amount. Although the suction amount can be controlled by the vacuum holding time during a given period, the suction amount does not depend on the vacuum holding time outside the given period. Since the suction amount is affected by the head temperature assumed from the pressure ratio, the vacuum holding time is changed according to the assumed head temperature. In this way, even if the head temperature changes, the discharge amount can be maintained at a constant value (an optimum amount), thus stabilizing the discharge.

When a plurality of heads are used, heat radiation correction is performed according to the arrangement of the heads to more accurately estimate the head temperature. At the end portion of a carriage, heat radiation occurs easily compared with the center position, and the temperature distribution varies. For this reason, the discharge is largely influenced by the temperature and varies. The correction is performed while assuming heat radiation at the end portion = 100% and the center position = 95%. With this correction, thermal variation can be avoided and stable discharge can be achieved. Furthermore, the suction condition can be changed in units of heads according to the characteristics or conditions of the heads.

In this embodiment, a drop in the head temperature after a suction operation is further assumed. When the ambient temperature and the head temperature are different from each other, an ink at a high temperature is discharged by suction, and a new ink at a low temperature is supplied from the ink tank. The head at a high temperature is cooled by the supplied ink. Table 5 below shows differences between the ambient temperature and the head temperature. assumed head temperature, and post-suction temperature drop correction values. If the head temperature is assumed from the pressure ratio, a post-suction temperature drop can be corrected based on a difference between the ambient temperature and a post-suction head temperature that can be predicted simultaneously.

Table 5 Difference between ambient temperature and assumed head temperature (ºC) ΔT during suction (ºC)

0 to 10 -1.2

10 to 20 -3.6

20 to 30 -6.0

In the case of a replaceable head, the temperature of the ink tank must be assumed. Since the ink tank is in contact with the head, a temperature increase caused by ejection affects the ink tank. An ink tank temperature is therefore assumed from an average value of the temperatures for at least 10 minutes. In this way, the ink tank temperature can be fed back in the event of a temperature drop after a suction operation.

In the case of a permanent head, since the head and the ink tank are separated, the temperature of the supplied ink is equal to the ambient temperature and the temperature of the ink tank does not need to be predicted.

Since in an ink tank system shown in Fig. 18, the suction amount is further increased when a suction operation is carried out in a high temperature state of an ink, an ink level pull-up effect cannot be expected, and this may cause an ink supply failure. Thus, when the head temperature predicted to be high from the pressure ratio, the number of suction operations is increased to achieve a sufficient ink level pulling up effect. Table 6 below shows the relationship between the difference between the ambient temperature and the assumed head temperature, and the number of suction operations. As the difference between the ambient temperature and the assumed head temperature becomes larger, the number of suction operations is increased. Thus, the ink level pulling up effect can be prevented from deteriorating. In Fig. 18, a main tank 41 is housed in a device main body. A sub-tank 43 is mounted on a carriage, for example. A head chip 45 is covered by a cap 47. A pump 49 provides suction power to the cap 47.

Table 6

Difference between ambient temperature and assumed head temperature (ºC) ΔT during suction (ºC)

0 to 10 8

10 to 20 10

20 to 30 12

(Fourth embodiment)

As in the third embodiment, the current head temperature is assumed from the pressure ratio. In this embodiment, a pre-discharge condition is changed according to the assumed head temperature.

When the head temperature is high, the ejection amount is increased and wasteful pre-ejection may be carried out. In this case, control may be made to reduce the pre-ejection pulse width. Table 7 below shows the relationship between the assumed head temperature and the pulse width. Since the ejection amount increases when the temperature increases, the output quantity is controlled by decreasing the pulse width.

Table 7 Assumed head temperature (ºC) Pulse width (usec)

0 to 10 7.0

10 to 20 6.5

20 to 30 6.0

over 50 5.5

Since a temperature variation among nozzles is increased as the temperature rises, the distribution of the number of pre-firings must be optimized. Table 8 below shows the relationship between the assumed head temperature and the number of pulses in pre-firing. Even at normal temperature, the number of pre-firings from nozzles at the end portion is set to be different from that at the center portion, thus suppressing the influence due to the temperature variation. When the head temperature rises, because a temperature difference between the end portion and the center portion becomes larger, the difference in the number of pre-firings is also increased. Thus, a variation in the temperature distribution among nozzles can be suppressed and can be carried out efficiently (at least minimally) before ejection, thus enabling stable ejection. Table 8

When a plurality of heads are used, different pre-jet temperature tables in units of ink colors may be used. Table 9 below shows an example of a temperature table. When the head temperature is high, Bk (black) having a larger number of hues than Y (yellow), M (magenta) and C (cyan) tends to increase in viscosity. For this reason, the number of pre-jets for Bk must be set to a larger value than Y, M and C. In addition, since the ejection amount is increased as the temperature rises, the number of pre-jets is suppressed. Table 9

As the number of nozzles increases, a method of assuming the head temperature is also available while dividing nozzles 49 into two zones as shown in Fig. 19A showing the head temperature. As shown in the block diagram of Fig. 19B, counters 51 and 52 for independently obtaining pressure ratios are arranged in units of nozzle zones, and the head temperature is assumed for the independently obtained pressure ratio for independently setting a pre-discharge condition. A head temperature prediction error due to the pressure ratio can thus be eliminated, and more stable discharge can be expected. In Fig. 19B, a main computer 50 is connected to the computers 51 and 52. The same reference numerals in Fig. 19B denote the same parts as in Fig. 5.

(Fifth embodiment)

In this embodiment, an average temperature during a certain elapsed period is assumed from a reference temperature sensor provided in the main body and the printing ratio, and a predetermined recovery means is operated at optimally set intervals according to the average head temperature. In this embodiment, the recovery means controlled according to the average head temperature includes pre-discharge and wiping means which are applied at certain time intervals during printing (in a cap open state) so as to stabilize the discharge. As is generally known in the ink jet art, the pre-discharge is carried out for the purpose of preventing a non-discharge state or a change in density caused by evaporation of the ink from nozzle locations. Attention should be paid to the fact that the ink evaporation amount varies depending on the head temperature, this embodiment employs an optimum pre-discharge interval and an optimum number of pre-discharges according to the average head temperature in order to thus efficiently carrying out the pre-ejection in terms of time and ink consumption.

In the open loop control as the principle constituting the element of this embodiment, that is, a method of calculating and assuming a temperature at that time based on the temperature detected by a reference temperature sensor provided in the main body and the past printing conditions, an average head temperature during a predetermined past period required in this embodiment can be easily obtained. This embodiment pays attention to the fact that the ink evaporation amount is associated with the head temperatures at respective times, and a total ink evaporation amount during a predetermined period has a strict correlation with an average head temperature during that period. In a method of directly detecting the head temperature, on the other hand, it is relatively easy to perform the real-time control according to the head temperatures at respective times. However, a special memory/calculation circuit is required to obtain the past average head temperature required for control of this embodiment.

Meanwhile, as another ejection stabilizing means to be controlled by this embodiment, it is carried out for the purpose of removing an unnecessary liquid such as an ink or water vapor, or a solid foreign matter such as powder paper, dust or the like adhering to an orifice forming surface. This embodiment pays attention to the fact that the wet amount due to an ink varies depending on the head temperature, and the evaporation of a wet component which makes it difficult to remove ink or a foreign matter is associated with the head temperature (the temperature of the orifice forming surface). An optimum wiping interval is thus set according to the past average head temperature, thus efficiently the wiping is carried out. The moisture amount or the evaporation of the moisture component associated with the wiping has a strict correlation with the past average head temperature rather than with the head temperature at the time when the wiping is carried out. Therefore, a head temperature detecting means of this embodiment is suitable.

Fig. 20 is a flow chart showing a schematic print sequence of an ink jet recording apparatus according to this embodiment. When a print signal is input, the print sequence is executed. A pre-discharge timer is set according to an average head temperature at that time and started. A wiping timer is similarly set according to the average head temperature at that time and started. When no sheet of paper is detected, a sheet of paper is fed and a carriage scan (print scan operation) is carried out to print one line after completion of a data input operation.

When the printing operation is finished, the sheet of paper is ejected and a standby mode is set. When the printing operation is continued, the sheet of paper is fed by a certain amount and then it is checked whether the end part of the sheet is detected. The wiping timer and the pre-discharge timer set according to the average head temperature are checked and reset. Wiping or pre-discharge is carried out if necessary and the timers are then restarted. At this time, an average head temperature is calculated regardless of the presence/absence of an operation and the wiping timer and the pre-discharge timer are reset according to the calculated average head temperature.

In this embodiment, the wiping and pre-jetting timing is finally adjusted according to a change in the average head temperature in units of print lines reset so that optimum wiping and pre-discharge are carried out according to the ink evaporation and humidity situations. The controller waits for the completion of the data input operation after the predetermined recovery operation, and the above-described steps are repeated to again carry out the print scanning operation.

Table 10 below is a correspondence table of the pre-discharge interval and the number of pre-discharges according to an average head temperature for at least 12 sec, and also a correspondence table of the wiping interval according to an average head temperature for the last 48 sec. In this embodiment, when the average head temperature rises, the pre-discharge interval is shortened to decrease the number of pre-discharges. In contrast, when the average temperature falls, the pre-discharge interval is lengthened to increase the number of pre-discharges. Such an adjustment operation can be carried out accurately in view of the properties such as the ejection properties according to the evaporation/viscosity increase properties of an ink and a density change. In the case of an ink containing a large amount of non-volatile solvent, for example, it is considered to suffer from a decrease in viscosity due to a rise in temperature more than an increase in viscosity due to evaporation, the pre-discharge interval can be lengthened at a higher temperature. Table 10

Regarding wiping, a normal liquid ink tends to increase the moisture amount and the difficulty of removal as the temperature becomes higher. In this embodiment, the wiping is carried out at high temperature. This embodiment represents a case of a recording head. In the apparatus realizing the color printing operation or the high-speed operation using a plurality of heads, a recovery condition may be controlled according to an average head temperature in units of recording heads, or the plurality of heads may be simultaneously driven according to a recording head with the shortest interval.

(Sixth embodiment)

This embodiment provides suction recovery means according to an assumed value of a past average head temperature for a relatively long period of time, as another example of recovery control based on the assumption of an average head temperature as in the fifth embodiment. A recording head of a Ink jet recording apparatus is often provided to provide a negative head at nozzle locations for the purpose of stabilizing a meniscus shape at the nozzle locations. An unexpected bubble in an ink channel causes various problems in ink jet recording apparatus, and is particularly a problem in a system operating with a negative head.

More specifically, when the apparatus is left without performing a recording operation, a bubble which disturbs normal ejection grows in the ink channel due to dissociation of a dissolved gas in an ink or gas exchange through channel forming members, thus raising new problems. The suction recovery agent is prepared for the purpose of eliminating such a bubble in the ink channel and an ink whose viscosity is increased due to evaporation in the end portion of a nozzle part. The ink evaporation amount changes depending on the head temperature as described above. The growth of a bubble in the ink channel is further easily influenced by the head temperature, and a bubble tends to be formed more readily as the temperature rises. In this embodiment, as shown in Table 10, a suction recovery interval is set according to the average head temperature for the past 12 hours, and suction recovery is performed more frequently as the average head temperature has increased. The average temperature can be reset for each side.

When the past average head temperature is assumed over a relatively long period of time using a plurality of heads, as shown in Fig. 4, the plurality of heads are thermally coupled and then the average head temperature is assumed based on the average ratio of the plurality of heads and the temperature detected by a reference temperature sensor in the base unit, so as to achieve a simple Control is to be carried out on the assumption that the plurality of heads are almost equal to each other. The thermal coupling of the heads in Fig. 4 is realized by directly mounting the base portions having a thermal conductivity of the recording heads on a carriage which is partially (including a common support portion of the heads) or entirely made of a material having a high thermal conductivity, such as aluminum.

(Seventh embodiment)

In this embodiment, a recovery system is controlled according to the hysteresis of a temperature assumed from the temperature detected by a reference temperature sensor located in the base unit and the pressure ratio.

A foreign matter such as an ink is often deposited on an orifice forming surface to shift the ejection direction or cause an ejection failure. As a means for recovering deteriorations in ejection characteristics, a wiping means is provided. In some cases, a wiping member having a stronger scrubbing force may be prepared, or a wiping state is temporarily changed to increase the wiping effect. In this embodiment, the amount of entry (impact amount) of a wiping member formed of a rubber blade into the orifice forming surface is increased to temporarily improve a wiping effect (scrubbing mode).

It has been experimentally proved that the deposition of a foreign matter requires scrubbing corresponding to the wet ink amount, the unwiped amount after wiping and its evaporation and a correlation between the number of ejections and the temperature after ejection was strong. Therefore, in this embodiment, the scrubbing mode is controlled according to the number of ejections weighted by the head temperature. Table 11 shows weighting coefficients calculated with the number of ejections as basic data of a printing ratio. multiplied according to a head temperature assumed from the printing ratio. More specifically, at a higher temperature which easily causes a wet ink or non-wiped ink, the number of ejections which are considered as an index of application in the control is increased.

Table 11 Assumed head temperature (ºC) Weighting coefficient Pulse count

20 to 30 1.0

30 to 40 1.2

40 to 50 1.4

over 50 1.6

When the weighted number of ejections reaches five million, the scrubbing mode is operated. The scrubbing mode is effective for removing a deposit. However, since the scrubbing force is strong, the orifice-forming surface may be mechanically damaged, and therefore, execution of the scrubbing mode is preferably minimized. When the control is based on data directly correlated with the deposition of a foreign matter, as in this embodiment, the arrangement can be simple and high reliability is ensured. For example, in a system having a plurality of heads, the printing ratio is managed in units of colors, and the scrubbing mode can be controlled in units of ink colors having different deposition characteristics.

(Eighth embodiment)

This embodiment illustrates a suction recovery means as in the sixth embodiment. In this embodiment, the assumption of a bubble, formed after printing (print bubble) is performed in addition to the assumption of a bubble due to a non-printing state (non-print bubble), thus enabling accurate assumption of bubbles in an ink channel. As described above, the ink evaporation amount changes according to the head temperature. The growth of a bubble in the ink channel is further slightly affected by the head temperature, and the bubble tends to grow more easily as the temperature is higher. As can be seen from the above description, a non-print bubble can be assumed by counting a non-printing time weighted by the head temperature.

A print bubble tends to be formed when the temperature is higher and actually has a positive correlation with the number of ejections. The print bubble can also be assumed by counting the number of ejections weighted by the head temperature. In this embodiment, as shown in Table 12 below, the number of dots according to a non-printing time (non-print bubble) and the number of pica dots according to the number of ejections (print bubbles) are set, and when the total number of pica dots reaches 100 million, it is determined that the bubbles in the ink channel adversely affect the ejection, and a suction recovery operation is carried out to eliminate the bubbles. Table 12

The matching between the pica points of printing and non-printing bubbles was experimentally determined so that the same points were obtained when the ejection error is caused by each factor under the same temperature condition. Weighting coefficients according to temperature were also experimentally obtained, and the obtained values were implemented. As the bubble removing means, either the suction means of this embodiment or a compression means may be used. Alternatively, after an ink in the ink channel is removed by a certain method, the suction means may be put into operation.

In each of the third to eighth embodiments, the discharge amount control described in the first and second embodiments may or may not be performed together. If no discharge amount control is performed, the steps required for PWM control and sub-heater control may be omitted.

According to the present invention, the ejection amount can be controlled to a constant value as described above without providing a temperature sensor in a recording head, and the recovery processing can be accurately carried out. Consequently, a good recording image can be obtained regardless of the accuracy of the temperature sensor.

(Ninth embodiment)

In each of the above embodiments, a change in the temperature of a head is detected from the past to the present time by calculation processing, thereby assuming a head temperature.

(Temperature forecast summary)

In this embodiment, after performing a recording operation by ejecting an ink droplet from a recording head, an ambient temperature sensor for measuring the Ambient temperature is provided on the main body side, and a change in the head temperature from the past to the present time and also from the present time to the future is detected by calculation processing, so that optimum temperature control is possible without disposing a head temperature sensor having a correlation with the head temperature. In short, a change in the head temperature is predicted by evaluating using a matrix calculated in advance within a range of a thermal time constant of the head and an input power.

(Temperature prediction control)

The operation of this embodiment will be described below with reference to the flow charts shown in Fig. 11 previously and Figs. 22 and 23. Note that the description of steps S100 to S190 shown in Fig. 11 is omitted here. In the above embodiment, the table shown in Fig. 14 is referred to as "temperature assumption table". However, in this embodiment, this table is called "temperature prediction table".

When matrix values based on this table are accumulated every unit time, a head temperature at that time can be assumed, and future printing data or a power to be supplied to the head such as a sub-heater in the future is input, whereby a change in the head temperature in the future can be predicted.

In step S180 in Fig. 11, a difference γ (= α - β) between a print target temperature (α) and a current head temperature (β) is calculated. In step S190, a sub-heater control table (Table 3) is referred to, whereby an on-time (t) of the sub-heater before the printing operation is obtained for the purpose of decreasing the difference (γ). This is a function of increasing the temperature of the entire head chip by the sub-heater when the assumed temperature of the head and the target difference have a difference between each other at the start of the printing operation. The temperature of the entire head chip can thus be controlled as close to the target temperature as possible. Note that a heater turn-on operation step in step S300 in the first embodiment is not carried out for this present embodiment.

After the sub-heater on-time (t) has elapsed before printing is achieved, reference is made to the temperature prediction table (Fig. 14), whereby a (future) head chip temperature immediately before printing is predicted when the print heater is assumed to be on for the set time (S500). A difference (γ) between the print target temperature (α) and the predicted head chip temperature (β) is calculated (S510). Needless to say, it is desirable that the temperatures (α) and (β) be equal to each other. Even if these two temperatures are not equal to each other, a PWM value is set at the start of the printing operation according to the difference (γ) with reference to the PWM value determination table (Table 4) so that an ejection amount equal to that obtained in the printing operation at the printing target temperature (α) is obtained (S520, S530). It is difficult to cause the chip temperature to approach the target temperature precisely even when using the sub-heater, and further, it is very difficult to carry out temperature correction in one line by the sub-heater. In this embodiment, therefore, the ejection amount is corrected by the PWM method according to the remaining difference from the target value. The aforementioned value P1 in this embodiment is particularly increased to increase the ejection amount.

The chip temperature of the head changes according to the ejection ratio during a one-line printing operation. More specifically, since the difference (γ) sometimes changes even in one line, it is desirable to optimize a PWM value in one line according to the change of the difference. In In this embodiment, 1.0 sec is required to print one line. Since the temperature prediction cycle of the head chip is 0.1 sec, one line is divided into 10 areas in this embodiment. The previously set PWM value at the start of the printing operation corresponds to the one at the start of the first area.

A method for determining PWM values at the beginning of the second through the 10th ranges is described below. In step S540, n is set to 1, and n is incremented in step S550. Note that n indicates a range. Since there are 10 ranges, when n exceeds 10, control exits the following loop (S560).

In the first loop, the PWM value at the beginning of the second area is set. As a method, a power ratio of the first area is calculated based on the number of points and the PWM value of the first area (S570).

A head chip temperature after completion of the printing operation of the first area (that is, at the start of the printing operation of the second area) is predicted by substituting the duty ratio in (with reference to) the temperature prediction table (Fig. 14) (S580). In step S590, a difference (γ) between the printing target temperature (α) and the head chip temperature (β) is calculated again. A PWM value for printing the second area is obtained according to the difference (γ) with reference to the PWM value determination table (Table 4) and the PWM value for the second area is set in the memory (S600, S610).

After that, the duty ratio in each subsequent area is calculated based on the number of dots and the PWM value of the area, and a head chip temperature (β) after completion of the printing operation of the corresponding area is predicted. Then, a PWM value of the next area is calculated according to the difference between the printing target value (α) and the predicted head chip temperature (β) (S550 to S610).

After the PWM values in all 10 areas in one line are set, the flow advances from step S560 to step S620, and the heating operation of the sub-heater before printing is carried out. Thereafter, a one-line printing operation is carried out according to the set PWM values (S630). When the one-line printing operation is completed in step S630, the flow returns to step S120 to read the temperature of a reference thermistor, and the above-described control is sequentially repeated.

Under the above-mentioned control, the head chip temperature (β) gradually approaches the print target temperature (α). Even when there is a large difference between the head chip temperature (β) and the print target temperature (α) as in a previous period after power-on, an actual ejection amount can be controlled as in the print target temperature since PWM control is carried out within a line, and high quality can be realized. Note that the control operation of this embodiment is carried out by a CPU 60 shown in Fig. 5. The CPU 60 can control print ratios of the respective areas with reference to line ratio buffers 78c during temperature prediction control, as in the first embodiment. A computational load on the CPU 60 can thus be reduced.

Hereinafter, with reference to the explanatory views shown in Figs. 15A to 16E, as in the first embodiment, the temperature prediction control is explained in detail. First, a difference between the ambient temperature and the head temperature is calculated to check whether the heating operation of the sub-heater is required immediately before printing. In Fig. 15B, since the head temperature is not far shifted from the target temperature, the heating operation of the sub-heater is not carried out. (Fig. 15D). The head temperature (Fig. 15B) immediately before printing of an area A1 is predicted, and a PWM value (Fig. 15C) for the area A1 is set according to the difference. In this case, based on the PWM value of the area A1, it is determined that the area A1 is printed at a ratio of 100%, and the temperature immediately before printing of the next area A2 is predicted.

Since the ratio of area A1 is high, it can be predicted that the temperature immediately before printing area A2 is high, and a low PWM value is set. Since area A2 has a low ratio (0%) and a low PWM value, it can be predicted that the temperature has dropped immediately before printing area A3. A large PWM value immediately before printing area A4 is therefore set.

In areas A4, A5, A6 and A7, the head temperature can be predicted to rise gradually since the current printing conditions are high, and the PWM values are gradually lowered. After an area A8, since the current printing conditions are low, the head temperature can be predicted to fall gradually, and the PWM values are gradually lowered. As described previously, the PWM value after printing each area is set based on the presence/absence of use and the performance of the sub-heater before printing, and the head temperature predicted immediately before printing each area, and thereafter the printing operations are carried out. Since the head temperature (Fig. 15B) can be predicted to be not far from the reference temperature of the one-line printing operation, the sub-heater is not turned on immediately before printing the next line.

In Figs. 16A to 16E, a difference between the ambient temperature and the head temperature is calculated to check whether the heating operation of the sub-heater immediately before printing. In this case, since the head temperature is far shifted from the target temperature, it is predicted that the heating operation of the sub-heater is required, and the heating operation of the sub-heater is carried out (Fig. 16D). Then, after completion of the heating operation of the sub-heater and immediately before printing of the area A1 (Fig. 16B), a head temperature is predicted. Since the head temperature is predicted to exceed the target temperature, a minimum value is assigned to the PWM value (Fig. 16C) after printing of the area A1. Although the heating operation of the sub-heater may raise the temperature in an early period of the heating operation, since the difference between the head temperature and the target temperature is large, it can be easily predicted that the head temperature has dropped below the reference temperature after completion of printing. The head temperature immediately after turning on the sub-heater is therefore intentionally set to exceed the target temperature.

The minimum value is assigned to the PWM value of the area A1. However, since the ratio (100%) of the area A1 is high, it is predicted that the temperature immediately before printing the area A2 has not fallen below the target temperature, and a minimum PWM value is set for the area A2. Since actual printing ratios are small in areas A2 and A3, the head temperature is gradually lowered to a temperature below the target temperature, and optimal PWM values are set. Thereafter, the heating operation of the sub-heater and the actual printing operations are carried out while setting the PWM values of the areas in the same manner as in Figs. 15A to 15E.

A difference between the cases in Figs. 15A to 15E and Figs. 16A to 16E is that the discharge amount does not exceed the discharge amount (Fig. 15E) at the target temperature in the former case, while the discharge amount sometimes exceeds the discharge amount (Fig. 16E) at the target temperature in the latter case. This is because no negative PWM value can be set for lowering the output quantity in this embodiment. In practical application, a negative PWM value can be provided.

In this embodiment, since a future head temperature can be predicted without using a temperature sensor, various head control operations can be carried out before a current printing operation, and a more accurate recording operation can be achieved. Since it is possible to predict a temperature by referring to a temperature prediction table, the prediction control can be simplified.

The temperature prediction described in the ninth embodiment can be applied to any of the third to eighth embodiments described above. The head temperature is not limited to an assumed temperature at the present time, and a future head temperature can also be easily predicted. Consequently, the optimal pre-discharge interval and the optimal number of pre-discharges can be set taking into account a future discharge condition. Moreover, an optimal suction recovery control can be set. Furthermore, the "weighted number of discharges" taking into account a future discharge condition can be used in a calculation of the "weighted number of discharges" to the optimal control.

In addition, "ink evaporation characteristics" or "bubble growth in an ink channel" may take into account future ejection conditions, which are used in the assumption or prediction of the "ink evaporation characteristics" or "bubble growth in an ink channel" for setting the optimal control.

(Tenth embodiment)

The tenth embodiment of the present invention will be described below with reference to the accompanying drawings. In this embodiment, a temperature sensor is provided to a recording head, and a predicted (calculated) head temperature is corrected to improve the prediction accuracy.

In the arrangement of this embodiment, as shown in Fig. 24, a head 8b having a temperature sensor 8e and a head temperature detected by the temperature sensor 8e can be received by a CPU 60.

(Determining the recording head temperature)

Fig. 25 shows a heater board of a recording head which can be used in this embodiment. A temperature sensor, a temperature control heater and an ejection heater and the like are arranged on the heater board.

Fig. 25 is a schematic plan view of the heater board. In Fig. 25, the temperature sensors 8e are arranged on both the right and left sides of an array of a plurality of ejection heaters 8c on a Si substrate 853. These ejection heaters 8c and the temperature sensors 8e are patterned together with the temperature control heaters 8e, similarly on both the right and left sides of the heater board, and are simultaneously manufactured in a semiconductor process. In this embodiment, as the temperature detected by the temperature sensor 8e, an average value of the temperatures detected by the two temperature sensors 8e is used.

(Operational Procedure)

Described below with reference to the flow charts shown in Fig. 13 above and in Figs. 26 to 28 an operation when a recording operation is carried out using a recording device having the above arrangement.

When a power supply is turned on in step S100, a temperature correction timer is reset/remained (S110), and a temperature prediction table correction value "CAL" is initialized (CAL = 1) (S115). The temperature detected by the temperature sensor (hereinafter referred to as a reference thermistor) on a board of the main unit (hereinafter referred to as a PCB) for detecting the ambient temperature is read (S120), thus detecting the ambient temperature. An elapsed time from the power-on operation is read from the temperature correction timer (S130), and a precise ambient temperature from which the influence of the heat generating elements is corrected is obtained by referring to a temperature correction table (Table 1) (S140).

In step S150, a current head chip temperature (β) is predicted from a temperature prediction table (Fig. 14), and the controller waits for the input of a pressure signal. The current head chip temperature (β) is predicted as follows. That is, the ambient temperature obtained in step S140 is updated by adding a value determined from a matrix of a temperature difference between the head temperature and the ambient temperature with respect to an input energy (power ratio) from the head per unit time, and the updated ambient temperature is multiplied by the correction value "CAL" (β = β*CAL) (S155). Immediately after the power-on operation, no pressure signal is input (input energy = 0), a temperature difference between the head temperature and the ambient temperature is 0, and the correction value "CAL" is also 1. A matrix value 0 (thermal equilibrium) is thus added to the ambient temperature, and the sum is multiplied by 1. If no print signal is input, the flow returns to step S120 to read the temperature of the reference thermistor again. In this embodiment, the head chip temperature prediction cycle is set to 0.1 sec.

The temperature prediction table shown in Fig. 14 is a matrix table showing temperature rise characteristics per unit time determined by the thermal time constant of the head and a power supplied to the head as described previously. More specifically, since the thermal time constant of the head varies depending on heads, the temperature rise characteristics may vary slightly. The correction value "CAL" for the temperature prediction table is a coefficient for correcting this variation.

When a pressure signal is input, control is carried out in the following manner.

Before executing the printing operation, it is checked whether a paper feed/eject operation of a recording medium is being executed (S162). If YES in step S162, the flow branches to a temperature prediction table correction routine (S164). In the temperature prediction table correction routine, a value in the temperature prediction table is corrected. More specifically, as shown in Fig. 28, the temperature of the head chip is measured by the head temperature sensor (S166), and a ratio of the measured temperature to the head chip temperature predicted in the temperature prediction table is obtained. The ratio is set in "CAL" (CAL = sensor value/predicted value "β") (S168). Since the thermal time constant of the head varies in units of the head in the strict sense, as already described, the acceleration (inclination) of a temperature rise with respect to the supplied energy varies in units of heads, and a small difference from the temperature prediction table is often generated. This difference, that is, the result of the acceleration of the The correction value of the temperature rise with respect to the supplied power is obtained as "CAL" (CAL = sensor value/predicted value "β"), thereby correcting the following predicted values of a head chip temperature. After the correction value is obtained, the flow returns to step S170 in the main routine (S169).

The reason why the temperature is read from the head temperature sensor during a paper feed/eject period is that a change in temperature is continuous since the head is not driven (heated), and the influence of the delay of a heat state is small.

In step S170, a print target temperature (α) of the head chip at which an optimal driving operation can be performed at the current ambient temperature can be obtained with reference to a target temperature table (driving temperature table) (Table 2).

In step S180, a difference γ (= α - β) between the printing target temperature (α) and the current head chip temperature (β) is calculated. In step S190, an on-time (t) of a sub-heater before printing for the purpose of decreasing the difference (γ) is obtained by referring to a sub-heater control table (Table 3).

After the on-time (t) of the sub-heater before printing is obtained, reference is made to the temperature prediction table (Fig. 14), whereby a (future) head chip temperature immediately before the start of printing is predicted on the assumption that the sub-heater is on during the setting time (S500). The predicted temperature is corrected by the correction value CAL (S505), thereby adjusting the chip temperature. A difference (γ) between the print target temperature (α) and the predicted head chip temperature (β) is calculated (S510). Needless to say, it is desirable that the temperatures (α) and (β) are equal to each other. Even if these two temperatures are not equal to each other, a PWM value at the start of the printing operation according to the difference (γ) with reference to a PWM value determination table (Table 4) so that an ejection amount equal to that obtained in the printing operation at the printing target temperature (α) is obtained (S520, S530).

The chip temperature of the head changes due to the ejection ratio during a one-line printing operation. More specifically, since the difference (γ) sometimes changes even in one line, it is desirable to optimize a PWM value in one line according to the change in the difference. In this embodiment, 1.0 sec is required to print one line. Since the temperature prediction cycle of the head chip is 0.1 sec, one line is divided into 10 areas in this embodiment. The previously set PWM value at the start of the printing operation corresponds to the one at the start of the first area.

A method for determining PWM values at the beginning of the second to tenth ranges is described below. In step S540, n = 1 is set, and n is incremented in step S550. Note that n indicates one range. Since there are not 10 ranges, control exits the following loop when n exceeds 10 (S560).

156 In the first loop, the PWM value at the beginning of the second area is set. As a process, a power ratio of the first area is calculated based on the number of points and the PWM value of the first area (S570).

A head chip temperature after completion of the printing operation from the first area (i.e., the start of the printing operation from the second area) is predicted by substituting the duty ratio into (with reference to) the temperature prediction table (Fig. 14) (S580). The predicted temperature is corrected by the correction value CAL (S585), thereby setting the head chip temperature β. In step S590, a difference (γ) between the printing target temperature (α) and the head chip temperature (β). In Fig. 13 presented previously, a PWM value for printing the second area is obtained according to the difference (γ) by referring to the PWM value determination table (Table 4), and the PWM value for the second area is given to a memory (S600, S610).

Thereafter, the duty ratio of the associated area is calculated based on the number of dots and the PWM value of the immediately preceding area, and a chip temperature (β) after completion of the printing operation of the associated area is predicted. The predicted temperature is corrected with the correction value CAL. Then, a PWM value of the next area is set according to the difference between the print target value (α) and the predicted head chip temperature (β) (S550 to S610). After the PWM values for all 10 areas in one line are set, the flow advances from step S560 to step S620, and the heating operation of the sub-heater before printing is carried out. Thereafter, a one-line printing operation is carried out according to the set PWM values (S630). When the one-line printing operation ends in step S120, the flow returns to step S120 to read the temperature of a reference thermistor, and the above-described control is sequentially repeated.

Under the control described above, the head chip temperature (β) gradually reaches the print target temperature (α). Even when there is a large temperature difference between the head chip temperature (β) and the print target temperature (α) as in an early period after power-on, an actual ejection amount can be controlled as that at the print target temperature because PWM control is carried out within one line, and high quality is realizable. Furthermore, since a predicted temperature is corrected with the correction value CAL indicating an error between a measured temperature and a predicted temperature in a steady state of the head temperature (S155, S505, S585), the head temperature can be accurately predicted.

Since the detailed arrangement of this embodiment is the same as that of the ninth embodiment, a description thereof is omitted here.

In this embodiment, the correction value CAL of the temperature prediction table is updated only during the paper feed/eject operation of a recording medium. This is because, in addition to the steady state of the head temperature described above, when the paper feed/eject operation of a recording medium requires a time of several seconds, the correction value CAL can be updated without affecting a recording time as long as the control can be performed within that time. More specifically, the temperature of the head chip is measured several times, thus avoiding a detection error due to noise. In this embodiment, the correction is carried out once per paper feed/eject operation. Alternatively, the correction (prediction → measurement → correction) can be repeated frequently during a single paper feed/eject operation, thereby improving the accuracy of the correction value CAL.

A method of repeatedly correcting until the correction value CAL converges with a predetermined value may be adopted. The correction time is not limited to being carried out during a paper feed/eject operation, but may be set before or during a print operation at each line.

In this embodiment, the correction value CAL disappears when the power supply is turned off. However, the correction value can be stored in, for example, a programmable non-volatile storage medium (i.e., an EEPROM). Alternatively, the temperature prediction table itself can be assigned to a non-volatile storage medium and can be rewritten with each correction.

The correction value "CAL" is calculated in this embodiment by (CAL = sensor value/predicted value "β"). However, the correction value can be calculated by other Calculation means. Similarly, the predicted temperature of the head chip is calculated by (β = β*CAL) in this embodiment, but may be calculated by other calculation means.

As described above, the recording apparatus according to this embodiment comprises head temperature measuring means that measures the temperature of a recording head, ambient temperature measuring means that measures the ambient temperature, temperature calculating means that calculates a variation in temperature in the recording head, and control means that controls the recording head based on the calculation result. Consequently, the following advantages can be provided:

1. The control can be carried out in real time without any response delay time when measuring the head temperature;

2. Accumulation of prediction error of head temperature can be prevented; and

3. Fuzzy control can be automatic and improve the prediction accuracy when the device is in use.

The temperature prediction described in the tenth embodiment can be applied to any of the third to eighth embodiments described above, as in the ninth embodiment.

(Eleventh embodiment)

In this embodiment, a temperature sensor is provided for a recording head, and a head temperature is predicted with reference to the temperature detected by the temperature sensor in view of a predicted variation in temperature. The arrangement of this embodiment is the same as that shown in Figs. 24 and 25 described in the tenth embodiment.

According to this embodiment, a future temperature can be predicted from a predicted printing ratio, thus avoiding trouble caused by a time delay in temperature detection. Since the response time characteristics in temperature control can be improved, the ink ejection can be stabilized.

The temperature prediction described in the eleventh embodiment can be applied to any of the third to eighth embodiments described above, as in the ninth embodiment.

When the recovery control is performed, the number of ejections, a wiping time and a pre-ejection time are set in advance, the control can be performed in accordance with the predicted head temperature, and the response characteristics can be further improved compared with the control performed while predicting a head temperature.

This embodiment is also applicable to a case where a sub-heater is controlled based on the printing ratio. When a future temperature predicted from the current head temperature and a future printing ratio is lower than an ink ejection standard temperature (23°C), the on-time of the sub-heater is controlled according to the difference between the two temperatures so as to always maintain a constant head temperature, thereby stabilizing the ejection. At this time, a time shown in Table 3 is used as the on-time for the sub-heater according to the difference between the predicted future temperature and the ink ejection standard temperature. Since the on-time of the sub-heater is controlled in advance, a control time delay at that time can be avoided, and the control with good response characteristics can be realized.

If the pressure ratio changes abruptly, even if the temperature is detected in real time to control the sub-heater, adequate control cannot be carried out due to the influence of a time lag which is considerable. However, when a future head temperature is predicted from the future pressure ratio, the turn-on time of the sub-heater is controlled in advance to be able to follow an abrupt change in the pressure ratio. Even if the pressure ratio changes abruptly, stable ejection can be ensured.

In each of the embodiments, the excitation time is used as an index of energy to be supplied to the head. However, the present invention is not limited to this. For example, when PWM control is not performed or when high-precision temperature prediction is not required, the number of printing dots can be simply used. Furthermore, when the printing ratio does not suffer from a large variation, the printing time and the non-printing time can be used.

The present invention brings about excellent effects, particularly in a recording head and a recording device of the ink jet system using thermal energy among the ink jet recording systems.

In terms of the representative structure and principle, for example, a practical use of the basic principle disclosed in, for example, U.S. Patent Nos. 4,723,129 and 4,740,796 is preferable. The above system is applicable to both the so-called demand type and the steady type. Particularly, in the case of the demand type, it is effective because, by applying at least one control signal giving a rapid temperature rise exceeding film boiling according to the recording information to electrothermal conversion elements arranged in the area corresponding to a sheet or liquid channels containing liquids (ink), a heating energy is generated by the electrothermal conversion elements to cause film boiling. on the heating effect surface of the recording head, and thus the bubbles can be formed within the liquid (ink) one by one according to the driving signals. By ejecting the liquid (ink) through an ejection port by growth and shrinkage of the bubble, at least one droplet is formed. By realizing the driving signals in pulse shapes, growth and shrinkage of the bubble can be promptly and adequately caused to effect favorable discharges of the liquid (ink) particularly excellently according to the characteristics. As the driving signals of such pulse shapes, the signals as disclosed in U.S. Patents 4,463,359 and 4,345,262 are suitable. Furthermore, excellent recording can be carried out by using the conditions of the invention disclosed in U.S. Patent 4,313,124 with respect to the temperature rise rate of the surface to be heated as described above.

As a structure of the recording head, in addition to the combined structure of a discharge opening, a liquid passage and an electrothermal conversion element (linear liquid passage or rectangular liquid passage) as disclosed in the above applications, the structure using U.S. Patents 4,558,333 and 4,459,600 disclosing the structure with the portion serving for heat supply arranged in the bent zone are also included in the invention. The present invention can be effectively constructed as disclosed in JP-A-59-123670 which discloses the structure using a slit common to a plurality of electrothermal converting elements as an ejection portion of the electrothermal converting element, or JP-A-59-138461 which discloses the structure having the opening for absorbing a pressure wave of heat energy according to the ejection portion.

As a full-line type recording head having a length corresponding to the maximum width of a recording medium, the can be recorded by the recording means, either the structure satisfying the length by a combination of a plurality of recording heads as disclosed in the above documents or the structure as a single recording head formed collectively may be adopted. The present invention can exhibit the effects as described above more efficiently.

Moreover, the invention is effective for a recording head and the free replacement chip type which enables the electrical connection to the main device or the supply of ink from the main device by being mounted on the main device, or for the case by using a cartridge type recording head which is integrally provided on the recording head itself.

It is also preferable to add a recovery means for the recording head, provisional additional means and the like provided as a structure of the recording device according to the invention because the effect of the invention can be further stabilized. Specific examples of these may include capping means, cleaning means, pressure or suction means for the recording head, and electrothermal converting elements or other heating elements or provisional heating elements according to a combination of these. It is also effective for carrying out stable recording to realize the provisional mode which carries out the ejection separately from the recording.

In a recording mode of the recording device, furthermore, the invention is extremely effective for not only the recording mode of only one primary color such as black or the like, but also a device having at least one of a plurality of different colors or a full color by color mixing depending on whether the recording head is either integrally constructed or combined in a plurality.

Claims (16)

1. Recording device, with: a recording head (S012) for ejecting ink from an ejection port (27) using bubbles generated in the ink by thermal energy by applying a drive signal to an electro-thermal conversion element; a control means for supplying the control signal; a control means (CPU60) for controlling the amount (Vd) of ink ejected from the ejection point by changing the control signal; a temperature measuring device (S024) for measuring the ambient temperature; and a computing means (CPU60) for calculating temperature changes of the recording head; characterized in that the calculation means are arranged to calculate a temperature change of the recording head according to the thermal time constant of the recording head and according to the energy supplied to the recording head during a predetermined unit time, and further comprising: means (CPU60) for predicting or estimating the temperature of the recording head according to the temperature change calculated by the calculating means and the ambient temperature measured by the measuring means, wherein the control means is arranged to change the drive signal for the recording head based on the predicted or estimated temperature so as to control the ink ejection amount, wherein the calculating means calculates a variation of the temperature on the basis of the drive signal changed by the control means. 2. Device according to claim 1, whose control signal comprises a preheating pulse (P1) which is separated from the main heating pulse (P3) by an interval (P2). 3. An apparatus according to claim 2, wherein said control means varies the pulse width of said preheat pulse based on said predicted or estimated temperature. 4. Device according to one of the preceding claims, comprising: a head temperature measuring means for measuring the temperature of the recording head; a detecting means for detecting the difference between the predicted temperature and the temperature measured by the head temperature measuring means; and with a correction means (CPU60) for correcting the calculations of the computing means according to the difference. 5. Apparatus according to any preceding claim, wherein the selection of temperature changes of the recording head to be calculated during operation is carried out from a table of temperature changes. 6. An apparatus according to any preceding claim, wherein the calculating means has a matrix table indicating temperature changes per unit time determined according to the thermal constant of the recording head and the level of the drive signal supplied to the recording head during the unit time. 7. An apparatus according to any preceding claim, wherein the control means is arranged to cause pre-ejection of the recording head in accordance with the predicted or estimated temperature. 8. An apparatus according to any preceding claim, wherein the control means is arranged to cause suction recovery of the recording head in accordance with the predicted or estimated temperature. 9. An apparatus according to any preceding claim, wherein the control means is arranged to cause the temperature control of the recording head in accordance with the predicted or estimated temperature. 10. Device according to one of the preceding claims, in combination with one of the following devices: facsimile device, copier or terminal device for a computer. 11. Recording procedure, with the following steps: Ejecting ink from an ejection port (27) in a recording head (S012) using bubbles generated in the ink by heat energy by applying a drive signal to an electro-thermal transducer member; Measuring (S024) the ambient temperature; and Calculating (CPU60) temperature changes of the recording head; characterized by the process steps: Calculating a temperature change of the recording head according to the thermal time constant of the recording head and the energy supplied to the recording head during a predetermined unit time, and predicting or estimating the temperature of the recording head according to the temperature change calculated in the step of calculating, and using a control means for changing the drive signal for the recording head based on the predicted or estimated temperature so as to control the amount of ink ejection, and calculating a temperature change of the recording head based on the drive signal changed by the control means. 12. The method according to claim 11, wherein the control signal comprises a preheating pulse (P1) which is separated from the main heating pulse (P3) by an interval (P2). 13. The method of claim 12, wherein the pulse width of the preheat pulse undergoes a change based on the predicted temperature. 14. A method according to any one of claims 11 to 13, comprising the further step of measuring the temperature of the recording head, determining the difference between the predicted and measured temperatures, and correcting the predicted temperature calculations according to the difference. 15. Method according to one of claims 11 to 14, in which the selection of temperature changes to be calculated is made from a temperature variation table. 16. A method according to any one of claims 11 to 15, wherein the calculation of the predicted temperature is carried out using a matrix table showing temperature changes per unit time determined according to the thermal time constant of the playback head and levels of the drive signal supplied to the recording head during the unit time.