NL9202068A - Printing device designed for being fitted in electronic equipment - Google Patents

Abstract

The invention comprises a compact printing device consisting of a little wheel, an ink-jet printer head (printhead) and the associated electronics. Moving the printing device over a surface by means of the wheel causes the electronics to activate the ink-jet printer head to produce an printout of a section of text or a graphic representation. The invention is highly suitable for use in various types of portable electronic equipment.

Description

short description: printing device intended for installation in electronic equipment.

The invention includes a printing device which, due to its shape, is suitable for use in portable electronic equipment. Figure 1 shows an example of the printing device added to a calculator. The printing device consists of a wheel 3 and an inkjet printer head 4. When the print button 5 is held down and the instrument is moved with the wheel against a surface from left to right, the inkjet printer head 4 prints the data as it is for example, can be seen in the display 1. Figure 1 may also be the appearance of an electronic stamp. Use keys 2 to set the desired text which can be checked on display 1. One or more prints of this text can then be made with the aid of the printing device.

When a second wheel is placed exactly in front of or behind the wheel, printing is done in a straight line.

The printing device described in this patent can be used in a wide variety of portable instruments such as calculators, electronic clocks, electronic calendars, laptops, notebook computers, digital thermometers and digital voltmeters. In addition, one electronic stamp can replace a large number of rubber stamps. Due to the application of the inkjet principle, a print can easily be made on a non-flat surface. This makes it also suitable for applying the price and / or other information to all kinds of products. When connected to a computer via a data connection, it can be used as a manual printer for printing addresses on envelopes or packages. In addition to text, this printing principle also allows printing graphics or barcodes.

The principle of a manual printing unit applied here is not entirely new. As early as August 1979, a similar device was described in an IBM technical disclosure bulletin. Also, a similar mechanism is described in U.S. Patent No. 4168533 as part of a postage meter.

In these and other descriptions, a printing mechanism has always been assumed in which the printing unit must come into contact with the surface on which the print must come. By applying the inkjet principle, a product is created which is much more flexible in use. By using a thermal inkjet printer head, an extremely compact printing mechanism is obtained.

Earlier publications have not yet discussed the application of this printing principle as part of a pre-existing device such as a calculator.

Figure 1 shows how the printing unit can be used. Figures 2, 3 and 4 show the mechanical construction of an embodiment of the printing mechanism. Figure 2 is a side view. Figure 3 is a rear view and Figure 4 is a bottom view.

Figure 5 gives an overview of the electronic part of the embodiment.

Figure 6 is the flow chart of the main program of the microcontroller used.

Figures 7 and 8 are the flow charts of two interrupt routines in the microcontroller.

To prevent the inkjet printer head from drying out, inkjet openings should be closed when the mechanism is not in use. For the device shown in Figure 1, a closure mechanism may consist of a cover that can be slid over the printer portion. At the bottom of this hood there is a piece of foam rubber. Opposite the print head nozzles, a recess should be made in the foam to prevent ink from being sucked out of the inkjet print head through the foam.

In the embodiment shown in Figure 2 and further, an inkjet cartridge of the brand Hewlett Packard type 61608A (14 in the figures) has been used. At the bottom of this cartridge there are 50 inkjet nozzles grouped in two rows of 25 which run from left to right in the orientation of Figure 2. An ink droplet can be released from each of these openings by applying an electric pulse.

The cartridge is clamped with two bent metal strips 15 against a support plate 16. This is located at some distance parallel to a printed circuit board 17. The electronics 18 is located on this printed circuit board. The electrical connections to the inkjet cartridge consist of contact pads on the cartridge under the support plate. There is a hole in the support plate opposite each contact surface. The conductive wires 19 of resilient material connect the electronics to the cartridge through the holes. For the sake of clarity, only two of these wires are shown in the figure.

Figure 3 shows the operation of a closing mechanism. A piece of rubber-like material 21 on the valve 20 is pressed against the bottom of the cartridge. Opposite the ink nozzles there is a hole in the material (not shown) so that the openings do not come into contact with the rubber-like material but are closed off from the ambient air.

The valve is rotatably mounted about the pivot point 22 on the printed circuit board. A spring 23 about the pivot ensures that the valve remains in the closed position. When the user wants to make a print, he presses point 24 against the valve to expose the openings of the inkjet cartridge. When the valve is opened further, the valve hits the pressure switch 25.

The electronics are switched on via this switch.

The wheel 13 is provided with spokes. Figure 4 shows how a light-emitting diode 26 is placed opposite a phototransistor 27. Both are attached to the PCB with their connecting wires. When the wheel is rotating, the spokes of the wheel will always interrupt the light connection. From the impulses that are measured at the phototransistor, it is therefore possible to measure how much the wheel turns and thus how far the displacement of the printing mechanism has moved across the printing surface.

Most of the inkjet cartridge used here consists of an ink reservoir. By reducing the size of the reservoir and / or changing its shape, a printing unit which is more convenient for this application is obtained.

Figure 5 shows an example of an electrical diagram of the invention. This scheme assumes the addition of the printing mechanism to a product that is already equipped with a lyquid crystal display. The electrical connections to the display are used by this circuit to determine what to print. There are segment and common connections on an LCD. A certain square on the LCD will darken if the effective AC voltage between a certain common and a certain segment connection exceeds a certain value. Both the common and the segment connections switch between a number of discrete voltage levels with a frequency below 1000Hz. With most LCD controls, when the common connection of a square is at the lowest level, and the segment connection at the same time at the highest voltage level, this square should be dark.

In the figure, it can be seen that when the pressure switch 25 is pressed, the printing unit receives power supply from the 12V battery 30. The microcontroller 32 also receives a supply voltage via the voltage regulator 31. The capacitor 33 ensures that the microcontroller receives a reset pulse so that the internal program is started properly.

The program starts reading the LCD. The common terminals of the LCD are connected to a multiplexer 34. Via the control inputs 35, the microcontroller can ensure that one of the common signals is switched through to the output 36. Resistors 37, 38 and 39 are selected so that the plus input of comparator 40, a voltage will be slightly above the lowest common voltage. The segraent terminals are connected to the multiplexer 41. Via the control inputs 42 it is possible to select which segment terminal at the comparator 43 is compared to the voltage at the minus input of the comparator. This input carries a voltage slightly lower than the highest segment voltage. The controller waits for each common connection until it is at the lowest voltage level and then determines which segment connections are at the highest voltage level. From these measurements, the controller makes a copy of the display structure in the internal memory.

The LED 26 is powered via a resistor 45. Depending on the position of the wheel, the phototransistor 27 may or may not receive light. The change in wheel position can be monitored via input 59 of the controller.

The controller first waits until a certain number of signal transitions have passed at input 59. In addition, an internal timer measures the time between successive signal transitions. When printing, a vertical row of dot is always sprayed on the print medium. Which dots of such a row do not and which do need to be applied depends on the display structure as recorded in the internal memory. A specific point is made by generating a pulse of approximately 10 microseconds on one of the outputs 47. This pulse causes a current pulse through the inkjet cartridge 14 via one of the darlington transistor pairs 46. A droplet of ink is launched through this current pulse in one of the ink channels of the cartridge. The dots of a certain row are applied by generating a pimple for each dot to be applied one by one on one of the outputs 47. After applying a row of dots, the next row is applied after a waiting time. This waiting time is calculated from the measured time between signal transitions at input 59. By ensuring that there is a fixed ratio between the measured time and the waiting time, the print remains the same regardless of the speed of the print unit moving across the surface. When all data from the memory has been printed, the time between signal transitions on input 59 is greater than a certain value. The wheel is then almost stationary. The program will then be restarted.

In addition to printing display data, data from another data processing device can also be printed. This device can be connected to the rs232 connection 50. Data can be sent to and from the microcontroller's serial connection via the RS232 transmitter 51 and receiver 52. These data can then be stored in internal memory so that this data can be printed.

The microcontroller 32 must have 2 internal timers and sufficient I / O lines. The type 87C451 of the manufacturer Philips meets these requirements. One of the timers (the wheel pulse timer) is used to measure the time between successive positive edges on input 59. The other timer (print timer) is used to generate an interrupt after an adjustable interval.

Figures 6,7 and 8 show a flow chart of the program as used in the microcontroller. Figure 6 is a flow chart of the main program. Figure 7 is the interrupt routine called at a positive edge on input 59. Figure 8 is the flow chart of the inter-routine routine called when the print timer reaches 0.

In step 101 of the main program, a wheel pulse counter is reset to zero. In step 102 it is tested whether something is connected to the RS232 port, if not then step 104 follows. In step 103 data is read from the rs232 port. This is converted into a graphical representation in the ram memory, which consists of a number of rows of dots that must be printed later. In step 104, the command counter is reset to zero. In step 105, the common multiplexer 34 is set to the value indicating the command counter. In step 106, the program waits until the output of comparator 34 is high. In step 107, the segment counter is reset to zero. In step 108, the multiplexer 41 is set to the value indicating the segment counter. In step 109, a bit from comparator 43 is transferred to a bit at a suitable location in the ram. In step 110, the segment counter is incremented by one. Step 111 skips back if the segment counter is not yet equal to the number of segment connections. In step 112 the command counter is incremented by one, in step 113 it is jumped back if the command counter is not yet equal to the number of common connections present. In step 114, the bit pattern in the ram is converted into a pattern consisting of a number of rows of dots. In step 115, the row number is reset to zero. In step 116, the print flag is set. In step 117, it is waited for the print flag to return to zero. In step 118, it is waited for the wheel pulse timer to indicate a time greater than a quarter of a second. This step makes it possible to make a new print only after the wheel has stopped moving.

In step 120 of the wheel pulse interrupt routine, the pulse counter is incremented by one. Step 121 skips to step 125 if the pulse counter is less than 5. Step 122 skips to step 125 if the print flag is still zero. In step 123, the print timer is set to 1/6 of the wheel pulse timer. The printing interrupt is then turned on in step 124. In step 125, the wheel pulse timer is reset to zero. In step 126, the interrupt routine is exited.

In step 130 of the print interrupt, a dot number is reset to zero. Step 131 skips to step 135 if the memory bit associated with row number and dot number is zero. In step 132, one of the terminals 47 associated with the dot number is made high. In step 133, 10 microseconds are waited. In step 134 the connection is made low again. In step 135, the dot number is increased by one. Step 136 skips back if the dot number is less than the number of dots used. In step 137, the row number is increased by one. Step 138 skips if the row number is less than the number of available rows of print information. In step 139, the print flag is made zero and the print interrupt is turned off. In step 140, the interrupt routine is exited. If the wheel, the LED and the phototransistor are omitted, the simplest form of the printing mechanism described here is created. The wheel pulse interrupt is then canceled in the software. In step 114, the print timer is then set to a fixed value, the print interrupt is turned on and the print flag is set. Step 121 is canceled in this case. The resulting printing mechanism must be engaged while moving at a fixed speed over a surface to make an impression.

To determine the speed at which the mechanism moves along the surface, an accelerometer could also be used. When the accelerometer is coupled to an integrator circuit, the integrator output voltage is proportional to the speed. This integrator voltage can again be coupled to a voltage to frequency converter. With the correct dimensioning, this frequency can be applied to input 59 of the microcontroller. This system only works properly if the print mechanism is kept still when the machine is switched on.

One can force the movement at a constant speed along the surface by driving the wheel at a constant speed with an electric motor.

In the embodiments described here, a proprietary processor for the printing mechanism is assumed. The printing mechanism can also be controlled by the processor, which is already present in the electronic device.

Consideration may also be given to combining the printing unit with a barcode reader. The text to be printed may then depend on the barcode read. After reading barcode on an item, the printing unit prints the corresponding price, which is stored in the memory. The printing mechanism described here can also be combined with an optical scanner. One can then make a copier with which one can copy text line by line.

By adding a second phototransistor to the wheel, the direction of rotation of the wheel can be determined by the processor. When the mechanism is moved from right to left over the paper, it can be ensured that the print appears correctly on the paper, instead of in mirror image. One can also ensure that the text is different when moving from right to left. For example, a stamp that prints the date and to the right the time when moving to the left.

Time and date stamps can become an important application for this printing mechanism. When a clock with a time code receiver is used as a timer, one gets a stamp that one cannot or does not have to set. As a result, some evidential value can be derived from an imprint of this stamp.

It will be clear to a person skilled in the art that it is possible to change the illustrated embodiments of the device without leaving the inventive idea or the scope of protection.

Claims (12)

1 Institution, which at least consists of an inkjet printer head and control electronics, characterized in that an imprint can be made on a surface by moving the printing unit along the surface. The device according to claim 1, characterized in that provision is made for closing the nozzles of the inkjet printer head. An adjustment according to any one of the preceding claims, characterized in that the electronics are coupled to a displacement sensor. Institution according to claim 3, wherein the displacement sensor consists of a wheel which has to be rolled against the surface. An adjustment according to claim 4, characterized in that the rotation of the wheel is electronically determined without the intervention of mechanical transmissions. An institution according to claim 4 or 5, characterized in that the direction of rotation of the wheel partly determines what is printed. Institution according to claim 4, 5 or 6, wherein a second wheel is added in the same plane as of the first wheel. An adjustment according to claim 1 or 2, characterized in that the degree of displacement along the surface by the electronics is derived from a built-in accelerometer. An adjustment according to claim 1 or 2, characterized in that the displacement is forced by a motor-driven wheel. An apparatus according to any one of the preceding claims, built into a portable electronic device, so that data can be printed from the device by moving the entire device over a surface. Institution according to any one of the preceding claims, characterized in that a communication connection can be made to the institution, so that data originating from another institution can be printed. An institution according to any one of claims 1 to 9, added to an electronic timepiece with a built-in time code receiver enabling the time and / or date to be printed.