JP7256043B2 - Driving circuit for stepping motor, control method thereof, and electronic device using the same - Google Patents

Description

The present invention relates to technology for driving a stepping motor.

Stepping motors are widely used in electronic equipment, industrial machinery, and robots. A stepping motor is a synchronous motor that rotates in synchronization with an input clock generated by a host controller, and has excellent controllability in starting, stopping, and positioning. Furthermore, the stepping motor has the characteristics of being capable of open-loop position control and being suitable for digital signal processing.

FIG. 1 is a block diagram of a motor system including a conventional stepping motor and its drive circuit. The host controller 2 supplies an input clock CLK to the drive circuit 4 . The drive circuit 4 changes the excitation position in synchronization with the input clock CLK.

FIG. 2 is a diagram for explaining excitation positions. The excitation position is grasped as a combination of coil currents (drive currents) I _OUT1 and I _OUT2 flowing through the two coils L1 and L2 of the stepping motor 6 . Eight excitation positions 1 to 8 are shown in FIG. In the one-phase excitation, current alternately flows through the first coil L1 and the second coil L2, and the excitation positions 2, 4, 6, and 8 are transited. In two-phase excitation, current flows through both the first coil L1 and the second coil L2, and the excitation positions 1, 3, 5, and 7 are transited. 1-2 phase excitation is a combination of 1-phase excitation and 2-phase excitation, and transitions between excitation positions 1-8. In microstep driving, the excitation position is further finely controlled.

In a normal state, the rotor of the stepping motor rotates synchronously by a step angle proportional to the number of pulses of the input clock CLK. However, synchronization is lost when sudden load fluctuations or speed changes occur. This is called step-out. Once stepping out occurs, special processing is required to drive the stepping motor normally, so it is desirable to prevent stepping out.

Therefore, during acceleration and deceleration, when the possibility of step-out is high, the target value I _REF of the drive current is set to a fixed value so as to obtain a sufficiently large output torque to the extent that step-out does not occur with respect to speed changes. set to a reasonable value I _FULL (high torque mode).

Patent Document 5 proposes a technique of reducing power consumption and improving efficiency by feedbacking and optimizing the output torque (that is, the amount of current) while preventing step-out.

JP-A-9-103096 JP 2004-120957 A JP-A-2000-184789 JP 2004-180354 A Japanese Patent No. 6258004

In the technique described in Patent Document 5, the amplitude I _REF of the coil currents (also referred to as drive currents) I _OUT1 and I _OUT2 is optimized by feedback control and reduced within a range that does not cause step-out, thereby reducing power consumption. there is More specifically, the load angle φ is estimated based on the back electromotive force, and the target value _IREF of the drive current is feedback-controlled so that the estimated load angle φ approaches a predetermined target value.

A relational expression between the load angle φ and the back electromotive force V _BEMF is given by equation (1).
V _BEMF = cos φ·ω·K _E (1)
_KE is the back electromotive force constant, and ω is the angular velocity (rotation speed, rotation frequency). The back electromotive force constant _KE is a constant unique to the motor, and must be measured in advance and stored in the memory of the drive circuit.

However, it is not easy to measure in advance the back electromotive force constant _KE for each type of stepping motor or for each solid body. Also, if the back electromotive force constant _KE changes due to aging, the load angle φ will be erroneously estimated.

The present invention has been made in view of such problems, and one exemplary object of some aspects thereof is to provide a driving circuit capable of measuring the back electromotive force constant _KE .

One aspect of the present invention relates to a drive circuit for a stepping motor. The drive circuit includes a back electromotive force detection circuit that detects the back electromotive force generated in the coil of the stepping motor, a rotation speed detection circuit that obtains the rotation speed of the stepping motor, and when it detects that the rotation speed has stabilized, and a calculation unit for calculating a back electromotive force constant _KE based on the rotation speed and the back electromotive force.

According to this aspect, the back electromotive force constant _KE can be calculated in the drive circuit, eliminating the need to measure it in advance. Also, even if the back electromotive force constant _KE changes due to aging, the value after the change can be obtained.

When obtaining the back electromotive force for calculating the back electromotive force constant, the stepping motor may be driven with a first predetermined amount of drive current. As a result, the stepping motor can be driven at a constant torque, the back electromotive force and the rotation speed can be stabilized, and the detection accuracy of the back electromotive force constant _KE can be improved.

The first predetermined amount may be 0.4 to 0.6 times the second predetermined amount supplied to the stepping motor at start-up. By setting the first predetermined amount to a value such that the load angle φ becomes a predetermined value, the back electromotive force constant _KE can be accurately measured. The second predetermined amount at startup may be a current amount corresponding to full torque, in which case the first predetermined amount is about 0.4 to 0.6 times the full torque current.

The first predetermined amount is preferably defined so that cos φ=1. φ is the load angle. This simplifies the calculation process of the back electromotive force constant _KE , and simplifies the hardware configuration.

The driving circuit includes a current value setting circuit that generates a current setting value indicating a target amount of coil current flowing through the coil, and a detected value of the coil current flowing through the coil that is pulse-modulated so as to approach the target amount based on the current setting value. A constant-current chopper circuit that generates a pulse-modulated signal and a logic circuit that controls a bridge circuit connected to the coil according to the pulse-modulated signal may be further provided.

The current value setting circuit may generate the current setting value by feedback based on the back electromotive force and the back electromotive force constant _KE when driving the stepping motor in the high efficiency mode.

The current value setting circuit includes a load angle estimator that estimates the load angle based on the back electromotive force and the back electromotive force constant _KE , and generates a current set value so that the estimated load angle approaches a predetermined target angle. and a feedback controller.

The back electromotive force constant _KE may be calculated each time the drive circuit is powered on.

The constant current chopper circuit consists of a comparator that compares the detected value of the coil current with a threshold value based on the current setting value, an oscillator that oscillates at a predetermined frequency, and a transition to the off level according to the output of the comparator. and a flip-flop that outputs a pulse-modulated signal that transitions to an on-level according to the output.

The drive circuit may be monolithically integrated on one semiconductor substrate. "Integrated integration" includes the case where all circuit components are formed on a semiconductor substrate, and the case where the main components of a circuit are integrated. A resistor, capacitor, or the like may be provided outside the semiconductor substrate. By integrating the circuits on one chip, the circuit area can be reduced and the characteristics of the circuit elements can be kept uniform.

It should be noted that arbitrary combinations of the above-described constituent elements and mutually replacing the constituent elements and expressions of the present invention in methods, devices, systems, etc. are also effective as aspects of the present invention.

According to one aspect of the present invention, the back electromotive force constant _KE can be obtained by the drive circuit.

1 is a block diagram of a motor system including a conventional stepping motor and its drive circuit; FIG. It is a figure explaining an excitation position. 1 is a block diagram of a motor system including a drive circuit according to an embodiment; FIG. 4 is an operation waveform diagram of the drive circuit of FIG. 3; FIG. 3 is a circuit diagram showing a configuration example of a drive circuit; FIG. FIG. 5 is a diagram showing another configuration example of the current value setting circuit; FIGS. 7A to 7C are perspective views showing examples of electronic devices having drive circuits.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent constituent elements, members, and processes shown in each drawing are denoted by the same reference numerals, and duplication of description will be omitted as appropriate. Moreover, the embodiments are illustrative rather than limiting the invention, and not all features and combinations thereof described in the embodiments are necessarily essential to the invention.

In this specification, "a state in which member A is connected to member B" refers to a case in which member A and member B are physically directly connected, as well as a case in which member A and member B are electrically connected to each other. It also includes the case of being indirectly connected through other members that do not substantially affect the physical connection state or impair the functions and effects achieved by their combination.

Similarly, "the state in which member C is provided between member A and member B" refers to the case where member A and member C or member B and member C are directly connected, as well as the case where they are electrically connected. It also includes the case of being indirectly connected through other members that do not substantially affect the physical connection state or impair the functions and effects achieved by their combination.

The vertical and horizontal axes of the waveform diagrams and time charts referred to in this specification are enlarged or reduced as appropriate for ease of understanding, and each waveform shown is also simplified for ease of understanding. or exaggerated or emphasized.

(Embodiment)
FIG. 3 is a block diagram of motor system 100 including drive circuit 200 according to the embodiment. The drive circuit 200 constitutes the motor system 100 together with the stepping motor 102 and the host controller 2 . The stepping motor 102 may be of PM (Permanent Magnet) type, VR (Variable Reluctance) type, or HB (Hybrid) type.

An input clock CLK is input from the host controller 2 to the input pin IN of the drive circuit 200 . A direction indicating signal DIR for indicating clockwise (CW) or counterclockwise (CCW) is input to the direction indicating pin DIR of the drive circuit 200 .

The drive circuit 200 rotates the rotor of the stepping motor 102 by a predetermined angle in the direction according to the direction instruction signal DIR each time the input clock CLK is input.

The drive circuit 200 includes bridge circuits 202_1 and 202_2, a current value setting circuit 210, a back electromotive force detection circuit 230, a rotational speed detection circuit 232, constant current chopper circuits 250_1 and 250_2, a logic circuit 270, and an arithmetic unit 290. It is monolithically integrated on a semiconductor substrate.

In this embodiment, the stepping motor 102 is a two-phase motor and includes a first coil L1 and a second coil L2. The drive method of the drive circuit 200 is not particularly limited, and may be any of 1-phase excitation, 2-phase excitation, 1-2 phase excitation, or microstep drive (W1-2 phase drive, 2W1-2 phase drive, etc.). good.

The bridge circuit 202_1 of the first channel CH1 is connected to the first coil L1. Bridge circuit 202_2 of second channel CH2 is connected to second coil L2 of stepping motor 102 .

Each of the bridge circuits 202_1 and 202_2 is an H bridge circuit including four transistors M1-M4. The transistors M1 to M4 of the bridge circuit 202_1 are switched based on the control signal CNT1 from the logic circuit 270, thereby switching the voltage of the first coil L1 (also referred to as the first coil voltage) _VOUT1 .

The bridge circuit 202_2 is configured similarly to the bridge circuit 202_1, and its transistors M1 to M4 are switched based on the control signal CNT2 from the logic circuit 270, thereby increasing the voltage of the second coil L2 (also called the second coil voltage). ) V _OUT2 is switched.

A current value setting circuit 210 generates a current setting value _IREF . Immediately after the stepping motor 102 is started, the current set value I _REF is fixed at a certain predetermined value (referred to as a full torque set value) I _FULL . The predetermined value I _FULL may be the maximum value of the range that the current set value I _REF can take, in which case the stepping motor 102 is driven with full torque. This state is called a full torque mode.

When the stepping motor 102 starts to rotate stably, in other words, when the possibility of stepping out decreases, the mode is changed to the high efficiency mode. In the high efficiency mode, the current value setting circuit 210 adjusts the current setting value _IREF by feedback control, thereby reducing power consumption.

Back electromotive force detection circuit 230 detects back electromotive force V _BEMF1 (V _BEMF2 ) generated in coil L1 (L2) of stepping motor 102 . A method for detecting the back electromotive force is not particularly limited, and a known technique may be used. In general, the back electromotive force can be obtained by setting a certain detection window (detection interval), making both ends of the coil high impedance, and sampling the voltage of the coil at that time. For example, in 1-phase excitation and 1-2 phase excitation, the counter electromotive force V _BEMF1 (V _BEMF2 ) is set to the excitation position (2, 4, 6, 8), ie for each predetermined excitation position.

The constant-current chopper circuit 250_1 is pulse-modulated so that the detected value _INF1 of the coil current _IL1 flowing through the first coil L1 approaches the target amount based on the current setting value _IREF while the first coil L1 is energized. A modulated signal S _PWM1 is generated. The constant-current chopper circuit 250_2 generates a pulse-modulated signal S _PWM2 that is pulse-modulated so that the detected value I _NF2 of the coil current I _L2 flowing through the second coil L2 approaches the current set value I _REF while the second coil L2 is energized. to generate

Each of the bridge circuits 202_1 and 202_2 includes a current detection resistor _RNF , and the voltage drop across the current detection resistor _RNF is the detected value of the coil current _IL . The position of the current detection resistor _RNF is not limited, and it may be provided on the power supply side, or may be provided in series with the coil between the two outputs of the bridge circuit.

The logic circuit 270 controls the bridge circuit 202_1 connected to the first coil L1 according to the pulse modulated signal _SPWM1 . The logic circuit 270 also controls the bridge circuit 202_2 connected to the second coil L2 according to the pulse modulated signal S _PWM2 .

The logic circuit 270 changes the excitation position and switches the coil (or the pair of coils) to which the current is supplied each time the input clock CLK is input. The excitation position is grasped as a combination of the magnitude and direction of the coil current of the first coil L1 and the coil current of the second coil L2. The excitation position may make a transition only according to the positive edge of the input clock CLK, may make a transition only according to the negative edge, or may make a transition according to both of them.

The current value setting circuit 210 fixes the current setting value _IREF , which defines the amplitude of the coil current, to a large value corresponding to full torque immediately after the motor is started, and when the motor starts to rotate stably, in other words, it is stopped. When the risk of overheating decreases, the system then transitions to the high efficiency mode and adjusts the current set value _{I_REF} by feedback control.

Back electromotive force detection circuit 230 detects back electromotive force V _BEMF1 (V _BEMF2 ) generated in coil L1 (L2) of stepping motor 102 .

A rotation speed detection circuit 232 acquires the rotation speed (ω) of the stepping motor 102 and generates a detection signal indicating the rotation speed ω. For example, the rotational speed detection circuit 232 may measure a period T (=2π/ω) proportional to the reciprocal of the rotational speed ω and output the period T as a detection signal. When no step-out occurs, the frequency (cycle) of the input clock CLK is proportional to the number of revolutions (cycle) of the stepping motor 102 . Therefore, the rotation speed detection circuit 232 may measure the period of the input clock CLK or the internal signal generated based on it, and use it as a detection signal.

When the calculation unit 290 detects that the rotational speed ω (cycle T) has stabilized, it calculates the counter electromotive force constant _KE based on the rotational speed ω and the counter electromotive force V _BEMF at that time. By transforming the formula (1), the formula (2) is obtained.
K _E =V _BEMF ·ω ⁻¹ ·(cos φ) ⁻¹
=V _BEMF ·T/2π·(cosφ) ⁻¹ (2)
The quantities V _BEMF and T required to calculate the back electromotive force constant _KE are preferably measured under conditions where the load angle φ is a predetermined value. By using the period T, division can be replaced with multiplication, and the circuit can be simplified.

Preferably, the back electromotive force constant _KE is calculated under the condition of load angle φ=0°, that is, cos φ=1. In this case, equation (2) simplifies to equation (3).
K _E =V _BEMF ·T/2π (3)

In order to set the load angle φ=0°, the stepping motor 102 should be driven with a relatively large torque. For this reason, the constant current chopper circuits 250_1 and 250_2 change the current set value _IREF to the second value for acquiring the back electromotive force constant _KE during the period for acquiring the back electromotive force constant _KE (referred to as a parameter measurement mode). One predetermined amount (called a set value for detection) should be set to I _MEAS . This value I _MEAS may be set smaller than the second predetermined amount (referred to as the full torque set value) I _FULL used at the time of starting. For example, I _MEAS can be 0.4-0.6 times I _FULL , or I _MEAS =0.5×I _FULL .

The back electromotive voltage constant _KE calculated by the calculation unit 290 may be used as a parameter when driving the stepping motor 102 in the high efficiency mode. Further, the drive circuit 200 may be capable of outputting the back electromotive voltage constant _KE to the host controller 2 or other circuits.

The above is the configuration of the drive circuit 200 . Next, the operation will be explained. FIG. 4 is an operation waveform diagram of the driving circuit 200 of FIG. The drive circuit 200 may measure the back electromotive force constant _KE each time the power is turned on. Alternatively, it may shift to a mode for measuring the back electromotive force constant _KE according to an instruction from the host controller.

An input clock CLK is supplied from the host controller 2 at time _t0 . The frequency of the input clock CLK increases from 0 toward a value corresponding to the target rotation speed of the stepping motor 102 (this is also called trapezoidal wave driving).

Immediately after the stepping motor 102 is started, the full torque mode is selected, and the current setting circuit 210 sets the current setting value I _REF to the full torque setting value I _FULL . As a result, the stepping motor 102 is driven with full torque, and the number of rotations of the stepping motor 102 increases as the frequency f of the input clock CLK increases.

After time _t1 , the frequency f of the input clock CLK becomes constant. The calculation unit 290 determines whether or not the period T (rotational speed) detected by the rotational speed detection circuit 232 is constant. For example, when a plurality of N period T errors that are continuously measured are included in a predetermined range, the period T is determined to be constant, and the capture signal CAPTURE is asserted (high). At time _t2 , when it is determined that the period T is constant, the current value setting circuit 210 switches the current setting value _{I_REF} to the detection setting value _{I_MEAS} . This keeps cos φ close to 1.

The calculation unit 290 captures the period T (rotational speed ω) and the back electromotive force V _BEMF at this time, and calculates the back electromotive force constant _KE based on equation (3). The calculator 290 may calculate the back electromotive force constant _KE using an average value of a plurality of continuously measured back electromotive forces V _BEMF .

The above is the operation of the drive circuit 200 . According to this drive circuit 200, the back electromotive force constant _KE can be calculated with high accuracy, and the need for pre-measurement is eliminated. This means that the burden on the designer of motor system 100 is reduced.

Also, even if the back electromotive force constant _KE changes due to aging, the value after the change can be obtained. This advantage is particularly important in a drive circuit that estimates the load angle φ by using the back electromotive force constant _KE as will be described later.

FIG. 5 is a circuit diagram showing a configuration example of the drive circuit 200. As shown in FIG. Only the part related to the first coil L1 is shown in FIG.

The logic circuit 270 changes the excitation position in synchronization with the input clock CLK. In logic circuit 270 several intermediate signals are generated. Among them, the timing signals PHASE_A and PHASE_B can be used as signals indicating the period or timing when the output OUT1A becomes high impedance and the period or timing when the output OUT1B becomes high impedance.

Back electromotive force detection circuit 230 measures back electromotive force V _BEMF1 in response to timing signals PHASE_A and PHASE_B.

The rotation speed detection circuit 232 includes a counter 234 . Counter 234 measures the period T of at least one of timing signals PHASE_A and PHASE_B. The period T of the timing signals PHASE_A and PHASE_B is inversely proportional to the number of revolutions of the stepping motor 102 .

The calculation section 290 includes a determination section 291 , a memory 293 , an average circuit 295 and a calculator 297 . The determination unit 291 monitors the detection value T detected by the rotational speed detection circuit 232, determines whether or not it has stabilized to a constant value, and asserts the determination signal DET when detecting the stabilization of the detection value T. The determination signal DET is supplied to the current value setting circuit 210 . The current value setting circuit 210 uses the assertion of the determination signal DET as a trigger to switch the current setting value I _REF from I _FULL to I _MEAS . Further, the detected value T when stabilized is output as the detected value Ts.

Triggered by the assertion of the determination signal DET, the back electromotive force detection signal V _BEMF1 is taken into the memory 293 for a predetermined number of times. The memory 293 may hold the detection signal V _BEMF1 for three times, for example. Averaging circuit 295 calculates an average value V _{BEMF1 (AVE)} of three detection signals V _BEMF1 stored in memory 293 . The arithmetic unit 297 calculates the back electromotive force constant _KE based on the average value V _{BEMF1 (AVE)} of the detection signal V BEMF1 and the period Ts obtained by the determination unit 291 .
_KE =A×V _BEMF(AVE) ·Ts (3)
A is a constant for proper scaling.

Current value setting circuit 210 includes feedback controller 220 , feedforward controller 240 and multiplexer 212 . The feedforward controller 240 outputs a fixed current set value Ix (=I _FULL or I _MEAS ) that is used in the full torque mode immediately after starting or in the parameter measurement mode. The feedforward controller 240 switches the value of the output Ix from I _FULL to I _MEAS according to the determination signal DET from the determination section 291 .

The feedback controller 220 is active in high efficiency mode and outputs a current setpoint Iy that is feedback controlled based on the back electromotive force V _BEMF . In the drive circuit 200 of FIG. 5, the back EMF constant _KE is used to generate the current setpoint _IREF in the high efficiency mode.

A multiplexer 216 selects one of the two signals Ix and Iy according to the operation mode of the drive circuit 200 and outputs it as the current set value _Iref .

Feedback controller 220 includes load angle estimator 222 , subtractor 224 , and PI controller 226 .

A load angle estimator 222 estimates a load angle φ based on the back electromotive force V _BEMF1 . The load angle φ corresponds to the difference between the current vector (that is, the position command) determined by the driving current flowing through the first coil L1 and the position of the rotor (moving element). As mentioned above, the back electromotive force V _BEMF1 is given by the following equation.
V _BEMF1 =K _E ·ω·cosφ
_KE is the back electromotive force constant and ω is the rotation speed. Therefore, by measuring the back electromotive force V _BEMF , it is possible to generate a detected value having a correlation with the load angle φ. For example, cos φ may be used as the detected value, and in this case the detected value is represented by Equation (4).
cos φ=V _BEMF1 ·ω ⁻¹ /K _E
=V _BEMF1 ·(T/2π)·K _E ⁻¹ (4)

Feedback controller 220 generates current setpoint Iy such that estimated load angle φ approaches a predetermined target angle φ _REF . Specifically, the subtractor 224 generates an error ERR between the detected value cos φ based on the load angle φ and its target value cos (φ _REF ). A PI (proportional-integral) controller 236 performs a PI control operation so that the error ERR becomes zero, and generates a current set value Iy. Instead of the PI controller, a P controller that performs P (proportional) control calculation or a PID controller that performs PID (proportional, integral, differential) control calculation may be used. Alternatively, the processing of the feedback controller 220 can be implemented with an analog circuit using an error amplifier.

The constant current chopper circuit 250_1 includes a D/A converter 252, a PWM comparator 254, an oscillator 256 and a flip-flop 258. A D/A converter 252 converts the current setpoint I _REF to an analog voltage V _REF . The PWM comparator 254 compares the feedback signal I _NF1 with the reference voltage V _REF and asserts (high) the off signal S _OFF when I _NF1 >V _REF . Oscillator 256 produces a periodic _ON signal SON that defines the chopping frequency. The flip-flop 258 outputs a PWM signal S _PWM1 that transitions to an on level (eg, high) in response to the on signal S _ON and transitions to an off level (eg, low) in response to the off signal S _OFF .

The above is the configuration of the drive circuit 200 in FIG. If the same value of back electromotive force constant _KE is used regardless of aging, the load angle φ will be calculated incorrectly, resulting in step-out due to insufficient torque or excessive torque, resulting in increased power consumption. may increase and reduce efficiency. On the other hand, according to the drive circuit 200 of FIG. 5, the actually measured back electromotive force constant _KE is used as a parameter to generate the current set value _IREF in the high efficiency mode. can be suppressed.

FIG. 6 is a diagram showing another configuration example of the current value setting circuit 210. As shown in FIG. Feedback controller 220 is active in high efficiency mode and produces a current correction value ΔI whose value is adjusted so that load angle φ approaches target value φ _REF . The current correction value ΔI is zero in full torque mode and parameter measurement mode.

Feedforward controller 240 outputs a predetermined high efficiency setpoint I _LOW in high efficiency mode. A relationship of I _FULL >I _MEAS >I _LOW may be established. Current value setting circuit 210 includes an adder 214 in place of multiplexer 212 in _FIG . As a result, the current set value I _REF =I _LOW +ΔI is adjusted so that the load angle φ approaches the target value φ _REF .

Finally, the application of the drive circuit 200 will be explained. The drive circuit 200 is used in various electronic devices. 7A to 7C are perspective views showing examples of electronic equipment including the drive circuit 200. FIG.

The electronic device in FIG. 7A is an optical disk device 500 . The optical disc device 500 includes an optical disc 502 and a pickup 504 . A pickup 504 is provided for writing data to and reading data from the optical disc 502 . The pickup 504 is movable on the recording surface of the optical disc 502 in the radial direction of the optical disc (tracking). Also, the distance between the pickup 504 and the optical disk is variable (focusing). The pickup 504 is positioned by a stepping motor (not shown). A drive circuit 200 controls a stepping motor. According to this configuration, the pickup 504 can be positioned with high efficiency and high accuracy while preventing step-out.

The electronic equipment in FIG. 7B is a device 600 with an imaging function such as a digital still camera, a digital video camera, or a mobile phone terminal. A device 600 includes an imaging element 602 and an autofocus lens 604 . A stepping motor 102 positions the autofocus lens 604 . According to this configuration in which the drive circuit 200 drives the stepping motor 102, the autofocus lens 604 can be positioned with high efficiency and high accuracy while preventing stepping out. The drive circuit 200 may be used to drive a camera shake correction lens in addition to the autofocus lens. Alternatively, the drive circuit 200 may be used for aperture control.

The electronic device in FIG. 7C is a printer 700 . A printer 700 includes a head 702 and guide rails 704 . Head 702 is supported along guide rail 704 so as to be positioned. A stepping motor 102 controls the position of the head 702 . A drive circuit 200 controls a stepping motor 102 . According to this configuration, the head 702 can be positioned with high efficiency and high accuracy while preventing step-out. In addition to driving the head, the drive circuit 200 may be used to drive the motor for the paper feeding mechanism.

The present invention has been described above based on the embodiments. It should be understood by those skilled in the art that this embodiment is merely an example, and that various modifications can be made to the combination of each component and each treatment process, and that such modifications are within the scope of the present invention. be. Such modifications will be described below.

(Modification 1)
Instead of or in combination with adjusting the duty ratio of pulse modulated signal S2, logic circuit 270 adjusts power supply voltage V _DD supplied to bridge circuit 202 so that load angle φ approaches target angle φ _REF . may be adjusted. By changing the power supply voltage _VDD , the power supplied to the coils L1 and L2 of the stepping motor 102 can be changed.

(Modification 2)
Although the case where the bridge circuit 202 is composed of a full bridge circuit (H bridge) has been described in the embodiment, it is not limited thereto, and may be composed of a half bridge circuit. Also, the bridge circuit 202 may be a separate chip from the drive circuit 200, or may be a discrete component.

(Modification 3)
The method of generating the current set value I _REF (Iy) in the high efficiency mode is not limited to that described in the embodiment. For example, a target value V _{BEMF (REF)} of back electromotive force V _{BEMF1 may be determined, and a feedback loop may be configured so that back electromotive force V BEMF1} approaches target value V _BEMF(REF) .

(Modification 4)
In FIG. ₂ , the currents I _OUT1 and I _OUT2 of the two coils are constant regardless _of the excitation position. good. For example, in 1-2 phase excitation, the amount of current I _OUT1 , I _OUT2 at excitation positions 2, 4, 6, 8 may be √2 times the amount of current at excitation positions 1, 3, 5, 7 .

Although the present invention has been described using specific terms based on the embodiments, the embodiments merely show the principles and applications of the present invention, and the embodiments are defined in the scope of claims. Many modifications and arrangement changes are possible without departing from the spirit of the present invention.

L1 first coil L2 second coil 2 host controller 100 motor system 102 stepping motor 200 drive circuit 202 bridge circuit 210 current value setting circuit 212 multiplexer 214 adder R _NF detection resistor 220 feedback controller 222 load angle estimator 224 subtractor 226 control device 230 back electromotive force detection circuit 232 rotation speed detection circuit 234 counter 240 feedforward controller 250 constant current chopper circuit 252 D/A converter 254 PWM comparator 256 oscillator 258 flip-flop 270 logic circuit 280 interface circuit 288 D/A converter 290 arithmetic unit 291 decision unit 293 memory 295 average circuit 297 calculator

Claims (12)

A drive circuit for a stepping motor,
a back electromotive force detection circuit for detecting a back electromotive force generated in the coil of the stepping motor;
a rotation speed detection circuit that acquires the rotation speed of the stepping motor;
a calculation unit for calculating a back electromotive force constant _KE based on the rotation speed at that time and the counter electromotive force when it is detected that the rotation speed has stabilized;
with
A driving circuit according to claim 1, wherein said back electromotive force constant KE _is calculated each time said driving circuit is powered on . 2. The drive of claim 1, wherein the stepping motor is driven with a first predetermined amount of drive current when obtaining the back electromotive force for calculating the back electromotive force constant KE _. circuit. 3. The driving circuit according to claim 2, wherein the first predetermined amount is 0.4 to 0.6 times the second predetermined amount, which is a drive current for starting the stepping motor. a current value setting circuit that generates a current setting value indicating a target value of the coil current flowing through the coil;
a constant current chopper circuit that generates a pulse-modulated signal that is pulse-modulated so that the detected value of the coil current flowing through the coil approaches a target amount based on the current setting value;
a logic circuit that controls a bridge circuit connected to the coil according to the pulse modulated signal;
4. The drive circuit according to any one of claims 1 to 3, further comprising: The current value setting circuit generates the current setting value by feedback based on the counter electromotive force and the counter electromotive force constant _KE when driving the stepping motor in a high efficiency mode. 5. A drive circuit according to claim 4. The current value setting circuit
a load angle estimator for estimating a load angle based on the counter electromotive force and the counter electromotive force constant _KE ;
a feedback controller that generates the current setpoint so that the estimated load angle approaches a predetermined target angle;
6. The drive circuit of claim 5, comprising: The constant current chopper circuit is
a comparator that compares the detected value of the coil current with a threshold based on the current set value;
an oscillator that oscillates at a predetermined frequency;
a flip-flop that outputs the pulse modulated signal that transitions to an off level according to the output of the comparator and transitions to an on level according to the output of the oscillator;
7. The drive circuit according to any one of claims 4 to 6, comprising: 8. The drive circuit according to claim 1, wherein the drive circuit is monolithically integrated on one semiconductor substrate. a stepping motor;
a driving circuit according to any one of claims 1 to 8 for driving the stepping motor;
An electronic device comprising: A stepping motor control method comprising:
a step of detecting a state in which the rotation speed of the stepping motor is stable;
detecting a back electromotive force generated in the coil of the stepping motor in a state where the rotational speed is stable;
calculating a counter electromotive force constant _KE based on the stable rotation speed and the counter electromotive force each time a driving circuit for driving the stepping motor is powered on;
A control method comprising: 11. The control method according to claim 10 , further comprising calculating a load angle of the stepping motor using the back electromotive force constant _KE during normal driving of the stepping motor. generating a current set value so that the load angle approaches a predetermined target value when the stepping motor is normally driven;
stabilizing the coil current flowing through the coil to a target amount based on the current set value;
12. The control method of claim 11 , further comprising:

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