阅读说明：本技术 步进马达的驱动电路及其驱动方法、以及使用该步进马达的驱动电路的电子设备 (Stepping motor drive circuit, stepping motor drive method, and electronic device using stepping motor drive circuit ) 是由 土桥正典 桥本浩树 冈田光央 于 2020-02-25 设计创作，主要内容包括：本发明的课题在于提供一种能够将对系统的设计或控制有用的信息输出到外部的驱动电路。本发明涉及一种步进马达的驱动电路及其驱动方法、以及使用该步进马达的驱动电路的电子设备。反电动势检测电路(230)检测线圈(L1)中产生的反电动势(VBEMF)。转数检测电路(232)获取步进马达(102)的转数(ω)。负载角推定部(222)基于反电动势(VBEMF)及转数(ω)算出负载角。接口电路(280)构成为能够将与负载角相关的角度信息输出到外部,或者能够从外部访问角度信息。(The invention provides a drive circuit capable of outputting information useful for system design or control to the outside. The present invention relates to a drive circuit for a stepping motor, a method of driving the same, and an electronic apparatus using the drive circuit for the stepping motor. A back electromotive force detection circuit (230) detects the back electromotive force (VBEMF) generated in the coil (L1). A rotation number detection circuit (232) acquires the rotation number (omega) of a stepping motor (102). A load angle estimation unit (222) calculates a load angle based on the back electromotive force (VBEMF) and the number of revolutions (omega). The interface circuit (280) is configured to be capable of outputting angle information relating to the load angle to the outside, or capable of accessing the angle information from the outside.)

1. A drive circuit, characterized by: the drive circuit is a drive circuit for a stepping motor, and includes:

a counter electromotive force detection circuit that detects a counter electromotive force generated in the coil;

a revolution detecting circuit that acquires a number of revolutions of the stepping motor; and

a load angle estimating unit that calculates a load angle based on the counter electromotive force and the number of rotations; and is

The drive circuit is configured to be able to output angle information related to the load angle to the outside, or to be able to access the angle information from the outside.

2. The drive circuit according to claim 1, wherein: the angle sensor further includes an interface circuit for outputting the angle information to the outside in the form of a digital signal.

3. The driving circuit according to claim 1, further comprising: a D/A converter converting the angle information into an analog signal; and

and a buffer circuit for outputting the analog signal to the outside.

4. The drive circuit according to any one of claims 1 to 3, characterized in that: the angle information is a margin before step loss.

5. The drive circuit according to any one of claims 1 to 3, characterized in that: the angle information is the load angle itself.

6. The drive circuit according to any one of claims 1 to 3, further comprising: a current value setting circuit for generating a current setting value;

a constant current chopper circuit that generates a pulse modulation signal that is pulse-modulated such that a detected value of a coil current flowing through the coil approaches a target value based on the current setting value; and

and the logic circuit controls the bridge circuit connected to the coil according to the pulse modulation signal.

7. The drive circuit according to claim 6, wherein: the current value setting circuit generates the current setting value based on the counter electromotive force.

8. The drive circuit according to claim 6, wherein: the current value setting circuit includes a feedback controller that generates the current setting value in such a manner that the load angle approaches its target value.

9. The drive circuit according to claim 6, wherein the constant-current chopper circuit includes: a comparator that compares a detected value of the coil current with a threshold value based on the current setting value;

an oscillator that oscillates at a prescribed frequency; and

and the trigger outputs the pulse modulation signal, and the pulse modulation signal is converted into an off level according to the output of the comparator and is converted into an on level according to the output of the oscillator.

10. The drive circuit according to any one of claims 1 to 3, characterized in that: integrated on a semiconductor substrate.

11. An electronic device, characterized in that: has a stepping motor and

the drive circuit according to any one of claims 1 to 10 that drives the stepping motor.

12. A driving method characterized by: the method for driving a stepping motor includes the steps of:

generating a current set value;

generating a pulse modulation signal that is pulse-modulated in such a manner that a detection value of a coil current flowing through the coil approaches a target amount based on the current setting value;

controlling a bridge circuit connected to the coil according to the pulse modulation signal;

detecting a back electromotive force generated in the coil;

acquiring the revolution number of the stepping motor;

calculating a load angle based on the back electromotive force and the number of rotations; and

supplying angle information related to the load angle to a host controller.

Technical Field

The present invention relates to a driving technique of a stepping motor.

Background

Stepping motors are widely used in electronic devices, industrial machines, and robots. The stepping motor is a synchronous motor that rotates in synchronization with an input clock generated by a host controller, and has excellent controllability for starting, stopping, and positioning. Further, the stepping motor has the following characteristics: the position control in the open loop is enabled, and the method is suitable for digital signal processing.

In a normal state, the rotor of the stepping motor is synchronously rotated in units of a stepping angle proportional to the number of input clocks. However, if sudden load fluctuations or speed changes occur, synchronization is lost. This is referred to as loss of mains. Once step-out occurs, special processing is thereafter required to normally drive the stepping motor, and therefore it is desirable to prevent step-out.

Therefore, at the time of acceleration and deceleration when the possibility of step-out is high, the target value of the drive current is set to a fixed value so as to obtain an output torque sufficiently large enough not to cause step-out with respect to the speed change.

Patent document 5 proposes the following technique: by preventing step-out and optimizing the output torque (i.e., the amount of current) using feedback, power consumption is reduced and efficiency is improved. Fig. 1 is a block diagram of a motor system including a conventional stepping motor and a drive circuit thereof.

The host controller 2 supplies the 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 illustrating an excitation position. The excitation position can be understood as a combination of coil currents (drive currents) IOUT1 and IOUT2 flowing through the two coils L1 and L2 of the stepping motor 6. Fig. 2 shows 8 excitation positions 1 to 8. In the 1-phase excitation, the current alternately flows through the 1 st coil L1 and the 2 nd coil L2, and is switched among the excitation positions 2, 4, 6, and 8. In 2-phase excitation, current flows through both the 1 st coil L1 and the 2 nd coil L2, and is switched among the excitation positions 1, 3, 5, and 7. Regarding the 1-2 phase excitation, the combination of the 1-phase excitation and the 2-phase excitation is adopted, so that the transition is carried out between the excitation positions 1-8. In the micro-step drive, the excitation position is more finely controlled.

Fig. 3 is a diagram illustrating a driving sequence of the stepping motor. At the time of start-up, the frequency fIN of the input clock CLK rises with time, so that the stepping motor accelerates. Next, if the frequency fIN reaches a certain target value, it is kept fixed, and the stepping motor rotates at a constant speed. Thereafter, when the stepping motor is stopped, the frequency of the input clock CLK is lowered to decelerate the stepping motor. The control of fig. 3 is also referred to as trapezoidal wave drive.

In a normal state, the rotor of the stepping motor is synchronously rotated in units of a stepping angle proportional to the number of input clocks. However, if sudden load fluctuations or speed changes occur, synchronization is lost. This is referred to as loss of mains. Once step-out occurs, special processing is thereafter required to normally drive the stepping motor, and therefore it is desirable to prevent step-out.

Therefore, at the time of acceleration and deceleration when the possibility of step-out is high, the target value IREF of the drive current is set to the fixed value ifill (high torque mode) so as to obtain a sufficiently large fixed output torque in consideration of the step-out margin.

In a situation where the rotation number is stable and the possibility of step-out is low, the target value IREF of the drive current is reduced to improve the efficiency (high efficiency mode). Patent document 5 proposes the following technique: by preventing step-out and optimizing the output torque (i.e., the amount of current) using feedback, power consumption is reduced and efficiency is improved. Specifically, the load angle Φ is estimated based on the back electromotive force VBEMF, and the target value IREF of the drive current (coil current) is feedback-controlled in such a manner that the load angle Φ approaches the target value (referred to as target angle) Φ REF. The back electromotive force VBEMF is expressed by equation (1).

VBEMF＝KE×ω×cosφ…(1)

ω is an angular velocity (hereinafter referred to as a number of revolutions or frequency) of the stepping motor, and KE is a back electromotive force constant and is a parameter inherent to the motor.

In the technique described in patent document 5, the coil currents IOUT1 and IOUT2 in the high-efficiency mode are optimized by forming a feedback loop so that the detected value cos Φ corresponding to the load angle approaches the target value cos (Φ REF).

[ Prior art documents ]

[ patent document ]

[ patent document 1] Japanese patent laid-open No. Hei 9-103096

[ patent document 2] Japanese patent laid-open publication No. 2004-120957

[ patent document 3] Japanese patent laid-open No. 2000-184789

[ patent document 4] Japanese patent laid-open No. 2004-180354

[ patent document 5] Japanese patent No. 6258004

Disclosure of Invention

[ problems to be solved by the invention ]

As described in patent document 5, when feedback control based on the current target value IREF of the load angle is incorporated, the load angle is stabilized to the target value in a steady state, but if load fluctuation occurs, the load angle Φ deviates from the target angle Φ REF.

In the motor system using the drive circuit described in patent document 5, a detection value cos Φ corresponding to the load angle Φ is generated inside the drive circuit. The load angle phi contains information useful for the design or control of the system, but it is not known from the outside of the drive circuit how large the load angle is currently driving the stepper motor 6.

The present invention has been made in view of the above problems, and an exemplary object of one aspect of the present invention is to provide a driver circuit capable of outputting information useful for system design or control to the outside.

[ means for solving problems ]

An aspect of the present invention relates to a drive circuit for a stepping motor. The drive circuit includes: a counter electromotive force detection circuit that detects a counter electromotive force generated in the coil; a rotation number detection circuit for detecting the rotation number of the stepping motor; and a load angle estimating unit that calculates a load angle based on the counter electromotive force and the number of rotations. The drive circuit is configured to be able to output angle information related to the load angle to the outside or access the angle information from the outside.

The load angle phi can be understood as the delay of the mechanical angle relative to the electrical angle. Since the load angle Φ is related to a margin before step-out or a sudden load change, it can be effectively used for estimation of the state of the stepping motor, optimization of a control parameter, and the like by outputting information related to the load angle to the outside. The term "calculating the load angle" includes generating a detection value cos Φ related to the load angle Φ, in addition to calculating the load angle Φ itself.

The drive circuit may further include an interface circuit for outputting the angle information to the outside in the form of a digital signal.

The drive circuit may further include a Digital/analog (D/a) converter for converting the angle information into an analog signal, and a buffer circuit for outputting the analog signal to the outside.

The angle information may also be a margin to before the step loss. For example, the margin may be a difference between pi/2 of ideal step-out and the load angle phi, or may be a difference between an actual step-out limit set from the outside and the load angle phi.

The angle information may also be the load angle itself.

The drive circuit may further include: a current value setting circuit for generating a current setting value; a constant current chopper circuit that generates a pulse modulation signal that is pulse-modulated in such a manner that a detection value of a coil current flowing through the coil approaches a target amount based on a current setting value; and a logic circuit for controlling the bridge circuit connected to the coil according to the pulse modulation signal.

The current value setting circuit may generate the current setting value based on the counter electromotive force.

The current value setting circuit may also include a feedback controller that generates the current setting in such a way that the load angle phi approaches its target value phi REF. The feedback controller can also generate the current set-point in such a way that the detected value cos phi corresponding to the load angle phi approaches its target value cos (phi REF).

The constant-current chopper circuit may include: a comparator that compares a detected value of the coil current with a threshold value based on a current set value; an oscillator that oscillates at a prescribed frequency; and a flip-flop outputting a pulse modulation signal which is converted into an off level according to an output of the comparator and is converted into an on level according to an output of the oscillator.

The driver circuit may be integrated with one semiconductor substrate. The term "integrated" includes a case where all the components of the circuit are formed on the semiconductor substrate, or a case where the main components of the circuit are integrated, and some of the resistors, capacitors, and the like may be provided outside the semiconductor substrate in order to adjust the circuit constant. By integrating the circuit on 1 chip, the circuit area can be reduced and the characteristics of the circuit elements can be uniformly maintained.

In addition, any combination of the above-described constituent elements or mutual substitution of the constituent elements or expressions of the present invention between methods, apparatuses, systems, and the like is also effective as an aspect of the present invention.

[ Effect of the invention ]

According to an aspect of the present invention, information useful for designing or controlling a system can be provided to the outside.

Drawings

Fig. 1 is a block diagram of a motor system including a conventional stepping motor and a drive circuit thereof.

Fig. 2 is a diagram illustrating an excitation position.

Fig. 3 is a diagram illustrating a driving sequence of the stepping motor.

Fig. 4 is a block diagram of a motor system including the drive circuit of the embodiment.

Fig. 5(a) to (c) are diagrams showing configuration examples of the interface circuit.

Fig. 6 is a circuit diagram showing an example of the configuration of the drive circuit.

Fig. 7 is a diagram showing another configuration example of the current value setting circuit.

Fig. 8 is a voltage and current waveform diagram of the stepping motor.

Fig. 9(a) and (b) are diagrams illustrating measurement of back electromotive force.

Fig. 10 is a waveform diagram of the coil voltage at a fast revolution.

Fig. 11(a) to (c) are perspective views showing examples of electronic devices provided with drive circuits.

Detailed Description

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 the respective drawings are denoted by the same reference numerals, and redundant description thereof will be omitted as appropriate. The embodiments are illustrative and do not limit the invention, and all the features or combinations thereof described in the embodiments are not necessarily essential to the invention.

In the present specification, the term "state in which the member a and the member B are connected" includes not only a case in which the member a and the member B are physically and directly connected but also a case in which the member a and the member B are indirectly connected via another member which does not substantially affect the electrical connection state therebetween or impair the function or effect exerted by the connection therebetween.

Similarly, the phrase "the member C is disposed between the members a and B" includes not only the case where the members a and C are directly connected or the case where the members B and C are indirectly connected via another member which does not substantially affect the electrical connection state thereof or impair the function or effect exerted by the connection thereof.

The vertical axis and the horizontal axis of the waveform diagrams and the time charts referred to in the present specification are appropriately enlarged or reduced for easy understanding, and the respective waveforms shown are also simplified, exaggerated, or emphasized for easy understanding.

Fig. 4 is a block diagram of the motor system 100 including the drive circuit 200 according to the embodiment. The drive circuit 200, together with the stepping motor 102 and the host controller 2, constitute a motor system 100. The stepping motor 102 may be any one of a PM (Permanent Magnet) type, a VR (Variable Reluctance) type, and an HB (Hybrid) type.

The input clock CLK is input from the host controller 2 to an input pin IN of the drive circuit 200. Further, a direction indication signal DIR indicating Clockwise (CW) and counterclockwise (CCW) is input to the direction indication pin DIR of the driver circuit 200.

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

The driver circuit 200 includes bridge circuits 202_1 and 202_2, a current value setting circuit 210, a counter electromotive force detection circuit 230, a rotation number detection circuit 232, a load angle estimation unit 222, constant current chopper circuits 250_1 and 250_2, a logic circuit 270, and an interface circuit 280, and is integrated over one semiconductor substrate.

In the present embodiment, the stepping motor 102 is a 2-phase motor, and includes the 1 st coil L1 and the 2 nd coil L2. The driving method of the driving circuit 200 is not particularly limited, and may be any of 1-phase excitation, 2-phase excitation, 1-2-phase excitation, or micro-step driving (W1-2-phase driving, 2W 1-2-phase driving, etc.).

The bridge circuit 202_1 of the 1 st channel CH1 is connected to the 1 st coil L1. The bridge circuit 202_2 of the 2 nd channel CH2 is connected to the 2 nd coil L2.

The bridge circuits 202_1 and 202_2 are H bridge circuits including 4 transistors M1-M4, respectively. 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 1 st coil L1 (also referred to as the 1 st coil voltage) VOUT 1.

The bridge circuit 202_2 is configured similarly to the bridge circuit 202_1, and switches the voltage of the 2 nd coil L2 (also referred to as a 2 nd coil voltage) VOUT2 by switching the transistors M1 to M4 based on the control signal CNT2 from the logic circuit 270.

The current value setting circuit 210 generates a current setting value IREF. Immediately after the stepper motor 102 is started, the current set point IREF is fixed at some specified value (referred to as the full torque set point) ifill. The specified value ifill may be set to the maximum value of the range that can be obtained by the current set value IREF, in which case the stepping motor 102 is driven at full torque. This state is referred to as a high torque mode.

After the stepping motor 102 is stably rotated, in other words, when the fear of step loss is reduced, the transition is made 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.

The bridge circuits 202_1 and 202_2 each include a current detection resistor RNF, and a drop in voltage of the current detection resistor RNF is a detection value of the coil current IL. The position of the current detection resistor RNF is not limited, and may be provided on the power supply side, or may be provided between two outputs of the bridge circuit in series with the coil.

When the 1 st coil L1 is energized, the constant-current chopper circuit 250_1 generates a pulse modulation signal SPWM1, and the pulse modulation signal SPWM1 performs pulse modulation so that the detected value INF1 of the coil current IL1 flowing through the 1 st coil L1 approaches a target value based on the current set value IREF. When the 2 nd coil L2 is energized, the constant-current chopper circuit 250_2 generates a pulse modulation signal SPWM2, and the pulse modulation signal SPWM2 performs pulse modulation so that the detected value INF2 of the coil current IL2 flowing through the 2 nd coil L2 approaches the current set value IREF.

The logic circuit 270 switches one output of the full bridge circuit 202_1 connected to the 1 st coil L1 in accordance with the pulse modulation signal SPWM 1. The logic circuit 270 switches one output of the full bridge circuit 202_2 connected to the 2 nd coil L2 in accordance with the pulse modulation signal SPWM 2.

The logic circuit 270 changes the excitation position every time the input clock CLK is input, and switches the coil (or coil pair) to which current is supplied. The excitation position can be understood as a combination of the magnitude and the flow direction of each of the coil current of the 1 st coil L1 and the coil current of the 2 nd coil L2. The excitation position may transition only in accordance with the positive edge of the input clock CLK, may transition only in accordance with the negative edge, and may transition in accordance with both of them.

As described above, the current value setting circuit 210 is configured to be switchable between: (i) a high torque mode in which a current set value IREF for defining the amplitude of the coil current is fixed to a large value corresponding to the full torque; and (ii) a high efficiency mode, adjusting the current set point IREF by feedback control.

The back electromotive force detection circuit 230 detects a back electromotive force VBEMF1(VBEMF2) generated in the coil L1(L2) of the stepping motor 102. The method of detecting the back electromotive force is not particularly limited as long as a known technique is used. Generally, the counter electromotive force can be obtained by setting a certain detection window (detection interval) to make both ends of the coil high impedance and sampling the coil voltage at that time. For example, in the 1-phase excitation or the 1-2-phase excitation, the back electromotive force VBEMF1(VBEMF2) can be measured for each excitation position (2, 4, 6, 8 of fig. 2) at which one end of the coil to be monitored (output of the bridge circuit) becomes high impedance, that is, for each designated excitation position.

The rotation number detection circuit 232 acquires the rotation number (ω) of the stepping motor 102, and generates a detection signal indicating the rotation number ω. For example, the revolution number detection circuit 232 may measure a period T (2 pi/ω) proportional to the reciprocal of the revolution number ω and output the period T as a detection signal. IN a condition where no step-out is generated, the frequency (period) of the input pulse IN is proportional to the number of rotations (period) of the stepping motor 102. Therefore, the rotation number detection circuit 232 may measure the input pulse IN or the period of the internal signal generated based on the input pulse IN, and use them as the detection signal.

The load angle estimating unit 222 estimates the load angle Φ based on the back electromotive force VBEMF and the rotation speed ω. The load angle Φ corresponds to a difference between a current vector (i.e., a position command) determined by the drive current flowing through the 1 st coil L1 and the position of the rotor (movable element). As described above, the back electromotive force VBEMF1 is obtained by the following equation.

VBEMF＝KE·ω·cosφ

KE is the back emf constant and ω is the number of revolutions. Therefore, by measuring the back electromotive force VBEMF and the rotation speed ω, a detection value correlated with the load angle Φ can be generated. For example, cos Φ may be used as the detection value, and in this case, the detection value is expressed by equation (2).

cosφ＝VBEMF·ω^-1/KE

＝VBEMF·(T/2π)·KE^-1…(2)

The drive circuit 200 is configured to be able to output the angle information INFO on the load angle Φ obtained by the load angle estimating unit 222 to the outside, or to be able to access the angle information INFO from the outside. For this purpose, the interface circuit 280 is provided in the drive circuit 200. The angle information INFO may be supplied to the host controller, or may be supplied to other circuits.

The angle information INFO is not particularly limited, and any of the following may be used, for example.

(1) The angle information INFO may use cos phi. In this case, the calculation can be performed by the calculation of expression (2).

(2) As the angle information INFO, phi may also be used. In this case, the calculation can be performed by the calculation of expression (3). Phi may be in units of degrees or radians.

φ＝arccos(VBEMF·(T/2π)·KE^-1…(3)

(3) As the angle information INFO, a margin may be used. The margin is the difference phi LIM-phi between the out-of-step limit phi LIM and the load angle phi. The ideal value pi/2 (90 deg.) can also be used as the out-of-step limit phi LIM. Alternatively, a real value may be set from the outside as the out-of-synchronization limit Φ LIM by a register or the like.

(4) When the current setting value IREF is adjusted by feedback control using the load angle Φ as described below, the error ERR of the load angle Φ from the target value Φ REF may be used as the angle information INFO.

The angle information INFO is not limited to the above, and a value related to the load angle Φ may be used.

The interface circuit 280 may be switched between enable and disable, and the interface circuit 280 may be enabled only when the angle information is desired to be known.

Fig. 5(a) to (c) are diagrams showing a configuration example of the interface circuit 280. The interface circuit 280 in fig. 5(a) includes a register 282 and an I2C (Inter IC, integrated circuit bus) circuit 284. The angle information at the specified time is written into the register 282. Alternatively, the value of the register 282 may be constantly updated based on angle information that changes at any time. The I2C circuit 284 may output angle information to the outside when receiving an access to the register 282 from the outside. Instead of I2C, SPI (serial peripheral Interface) or other transmitter or transceiver may be used.

Alternatively, the interface circuit 280 may always output the angle information to the outside regardless of the presence or absence of a request from the outside. In fig. 5(b), the digital angle information is always output to the outside through the transmitter 286.

In fig. 5(c), the digital angle information is converted into an analog signal (voltage signal) by a D/a converter 288. Next, the buffer 289 outputs the analog signal to the outside.

Fig. 6 is a circuit diagram showing an example of the configuration of the drive circuit 200. In fig. 6, only a portion associated with the 1 st coil L1 is shown.

The current value setting circuit 210 will be explained. The current value setting circuit 210 includes a feedback controller 220, a feedforward controller 240, and a multiplexer 212. The feedforward controller 240 outputs the fixed current set value Ix (═ ifill) used in the high torque mode immediately after the start of the startup. The current set value Ix is set to a large value in order to prevent step loss.

The feedback controller 220 is activated in the high efficiency mode, and outputs a current set value Iy that is feedback-controlled based on the back electromotive force VBEMF.

The multiplexer 212 selects one of the two signals Ix, Iy in accordance with the MODE selection signal MODE and outputs it as a current set value Iref.

In fig. 6, the load angle estimating unit 222 is incorporated in the feedback controller 220. The feedback controller 220 includes a subtractor 224 and a PI (proportional integral) controller 226 in addition to the load angle estimating unit 222.

The feedback controller 220 generates the current set value Iy in such a manner that the estimated load angle Φ approaches the specified target angle Φ REF. Specifically, the subtractor 224 generates an error ERR of the detected value cos Φ corresponding to the load angle Φ and its target value cos (Φ REF). The PI controller 226 performs PI control operation so that the error ERR becomes zero, and generates a current set value Iy. The processing of the feedback controller 220 can also be implemented in an analog circuit using an error amplifier.

The constant current chopper circuit 250_1 includes a D/a converter 252, a PWM (pulse width modulation) comparator 254, an oscillator 256, and a flip-flop 258. The D/a converter 252 converts the current set value IREF into an analog voltage VREF. The PWM comparator 254 compares the feedback signal INF1 with a reference voltage VREF and asserts (sets high) the turn-off signal SOFF if INF1> VREF. The oscillator 256 generates a periodic turn-on signal SON that defines the chopping frequency. The flip-flop 258 outputs a PWM signal SPWM1, which SPWM1 transitions to an on level (e.g., high) according to an on signal SON and transitions to an off level (e.g., low) according to an off signal SOFF.

The interface circuit 280 is omitted in fig. 6. The interface circuit 280 can generate the angle information INFO based on the detection value cos Φ generated by the load angle estimating section 222.

The above is the configuration of the driving circuit 200. Next, the operation will be described.

(i) The interface circuit 280 can be effectively utilized during the design phase of the motor system 100. For example, in the design stage, while monitoring the angle information (load angle Φ), the control parameters of the motor (for example, the current value ifill in the high torque mode, the current value ILOW in the high efficiency mode described below, or the frequency waveform of the input clock CLK) can be optimized.

(ii) The interface circuit 280 can be effectively used even during the actual operation of the motor system 100. For example, in the high torque mode or the high efficiency mode, the change in the load of the motor, the risk of step-out, and the like can be determined by monitoring the angle information. In addition, angle information is monitored, and if the angle information deviates from the accurate range, it can be determined as an error.

Fig. 7 is a diagram showing another configuration example of the current value setting circuit 210. The feedback controller 220 is activated in the high efficiency mode and generates a current correction value Δ I whose value is adjusted in such a way that the load angle Φ approaches the target value Φ REF. The current correction value Δ I is zero in the high torque mode.

In the high efficiency mode, the feedforward controller 240 outputs a specified high efficiency set point ILOW. The relationship IFULL > ILOW may also hold. The current value setting circuit 210 includes an adder 214 instead of the multiplexer 212 in fig. 5, and the adder 214 adds the current correction value Δ I to the high efficiency setting ILOW generated by the feedforward controller 240. Thus, the current setting value IREF is adjusted to ILOW + Δ I so that the load angle Φ approaches the target value Φ REF.

Next, detection of the back electromotive force VBEMF in the back electromotive force detection circuit 230 will be described. Fig. 8 is a voltage and current waveform diagram of the stepping motor 102. In fig. 8, the coil current ICOIL1, the voltage VOUT1 across the 1 st coil L1, the coil current ICOIL2, and the voltage VOUT2 across the 2 nd coil L2 are shown in this order from the top. Hi-z1 and Hi-z2 indicate that the outputs OUT1A and OUT1B of the bridge circuit 202_1 are in a high impedance state. Hi-z3 and Hi-z4 indicate that the outputs OUT2A and OUT2B of the bridge circuit 202_2 are in a high impedance state. The back electromotive force VBEMF is detected in a high impedance interval (referred to as an off interval).

Fig. 9(a) and (b) are diagrams illustrating measurement of back electromotive force. The back electromotive force detection circuit 230 measures the length of the off interval TOFF for each cycle. Next, the OFF interval TOFF (i-1) measured in the previous cycle (i-1) is divided into N portions (for example, N is 8, 16, or 32) to generate a sampling interval Δ Ti for the current cycle i.

ΔTi＝TOFF(i－1)/N

Next, sampling timings Ts1 to TsN are set for each Δ Ti, and a voltage VOUT1 between both ends of the coil L1 is sampled. As shown in fig. 9, immediately after the transition to the off period TOFFi, the coil current ICOIL1 (regenerative current) flows, so that the voltage VOUT1 jumps to VDD + VF, and if the coil current ICOIL1 becomes zero, the back electromotive force VBEMF1 occurs.

The back electromotive force detection circuit 230 removes a few samples (1 st to 3 rd samples) from the beginning and a few samples (8 th samples, for example) from the last of the N samples (8 samples, for example) and calculates the average value of the remaining samples (these samples are referred to as effective samples; 4 th to 7 th samples, for example). This reduces the influence of noise, and can obtain accurate back electromotive force VBEMF.

Fig. 9(b) is a diagram illustrating the sampling time Tsi of the back electromotive force. When the bridge circuit 202_1 is in the off period, another bridge circuit 202_2 is PWM-controlled by the constant-current chopper circuit 250_ 2. The back electromotive force VBEMF1 contains noise generated by switching of the bridge circuit 202_ 2. Therefore, the sampling timing Tsi (i is 1 to N) of the back electromotive force VBEMFi is preferably offset from the transition timing of the bridge circuit 202_ 2.

The minimum on time TMIN is set for the PWM signals SPWM1 and SPWM2 generated by the constant current chopper circuits 250_1 and 250_ 2. Next, by setting the sampling timing Tsi to a predetermined time τ (< TMIN) from the positive edge of the PWM signal, it is possible to ensure that the sampling timing Tsi does not coincide with the negative edge of the PWM signal, thereby reducing the influence of noise.

If the stepper motor 102 is made faster, the off-time TOFF is also made shorter. Fig. 10 is a waveform diagram of the coil voltage VOUT1 at a fast revolution. As described above, during the regeneration period TRGN immediately after the transition to the off period TOFF, the regeneration current flows, and the coil voltage VOUT1 is fixed to be high (VDD + VF). If the rotation number becomes high, the off time TOFF becomes short, and on the other hand, the length of the regeneration period TRGN is substantially fixed. As a result, the number of sampling times included in the reproduction period increases. In other words, the active sample is fixed at a high level. Therefore, the detection of the back electromotive force may be disabled when one or more of the plurality of valid samples contains a high voltage (VDD + VF).

Finally, the use of the driving circuit 200 will be explained. The driving circuit 200 is used in various electronic devices. Fig. 11(a) to (c) are perspective views showing examples of electronic devices provided with the drive circuit 200.

The electronic device of fig. 11(a) is an optical disc device 500. The optical disc apparatus 500 includes an optical disc 502 and a pickup 504. The reading head 504 is provided for writing and reading data to and from the optical disc 502. The pickup 504 is movable (tracking) in the radial direction of the optical disk on the recording surface of the optical disk 502. In addition, the distance of the read head 504 from the optical disc is also variable (focused). The read head 504 is positioned by a stepper motor, not shown. The driving circuit 200 controls the stepping motor. With this configuration, it is possible to efficiently and accurately position the head 504 while preventing step-out.

The electronic apparatus in fig. 11(b) is a device 600 with an imaging function, such as a digital still camera, a digital video camera, or a mobile phone terminal. The device 600 includes an image pickup device 602 and an autofocus lens 604. The stepping motor 102 positions the autofocus lens 604. With this configuration in which the drive circuit 200 drives the stepping motor 102, the autofocus lens 604 can be positioned efficiently and accurately while preventing step-out. The drive circuit 200 may be used for driving a lens for shake correction, in addition to the lens for auto focus. Alternatively, the driving circuit 200 may be used for aperture control.

The electronic device of fig. 11(c) is a printer 700. The printer 700 includes a head 702 and a guide 704. The handpiece 702 is supported so as to be positionable along a guide rail 704. The stepper motor 102 controls the position of the handpiece 702. The drive circuit 200 controls the stepping motor 102. With this configuration, the head 702 can be positioned efficiently and accurately while preventing step-out. The driving circuit 200 may be used to drive a motor for a sheet feeding mechanism, in addition to the head.

The drive circuit 200 can be used not only for consumer devices as shown in fig. 11(a) to (c), but also preferably for industrial devices or robots.

The present invention has been described above based on the embodiments. This embodiment is exemplary and one skilled in the art will appreciate that: various modifications may be made to the combination of the constituent elements and the processing steps, and these modifications are also within the scope of the present invention. Hereinafter, such a modification will be described.

(modification 1)

The logic circuit 270 may also be capable of adjusting the supply voltage VDD supplied to the bridge circuit 202 in place of adjusting the duty cycle of the pulse modulated signal S2, or in combination with adjusting the duty cycle of the pulse modulated signal S2, in such a manner that the load angle φ approaches the target angle φ REF. By changing the power supply voltage VDD, the power supplied to the coils L1, L2 of the stepping motor 102 can be changed.

(modification 2)

In the embodiment, the case where the bridge circuit 202 is configured by a full bridge circuit (H bridge) has been described, but the present invention is not limited thereto, and may be configured by a half bridge circuit. The bridge circuit 202 may be a chip different from the driver circuit 200(200B) or may be a discrete component.

(modification 3)

The method for generating the current set value Iy in the high efficiency mode is not limited to the method described in the embodiment. For example, a target value VBEMF (ref) of the back electromotive force VBEMF1 may be determined in advance, and the feedback loop may be configured such that the back electromotive force VBEMF1 approaches the target value VBEMF (ref).

(modification 4)

In an embodiment, electricity flows through both coilsThe currents IOUT1, IOUT2 are turned on and off according to the excitation position, but the amount of current is fixed regardless of the excitation position. In this case, the torque fluctuates when the 1-2 phases are excited. Instead of this control, the currents IOUT1, IOUT2 may be corrected so that the torque is fixed regardless of the excitation position. For example, in the 1-2 phase excitation, the amounts of the currents IOUT1 and IOUT2 at the excitation positions 2, 4, 6, and 8 may be set to the amounts of the currents at the excitation positions 1, 3, 5, and 7And (4) doubling.

(modification 5)

In the embodiment, the feedback controller 220 is configured by a PI controller, but the present invention is not limited thereto, and a PID (proportional integral derivative) controller or the like may be used.

The present invention has been described based on the embodiments using specific terms, but the embodiments merely show the principle and application of the present invention, and a plurality of modifications and changes in arrangement can be made to the embodiments without departing from the scope of the idea of the present invention defined in the claims.

[ description of symbols ]

L1 coil1

L2 coil2

2 host controller

100 motor system

102 stepping motor

200 driving circuit

202 bridge circuit

210 current value setting circuit

RNF detection resistance

212 multiplexer

214 adder

220 feedback controller

222 load angle estimating unit

224 subtracter

226 PI controller

230 counter electromotive force detection circuit

240 feedforward controller

250 constant current chopper circuit

252D/A converter

254 PWM comparator

256 oscillator

258 trigger

270 logic circuit

280 interface circuit

288D/A converter