JP2018107972A - Motor driving apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress breakdown of balance between positive current and negative current flowing into a coil of a stepping motor.SOLUTION: A motor driving apparatus includes: a coil drive unit for switching an energization direction of a coil of a stepping motor by a period of a PWM signal generated by a PWM signal generation unit; a current detection unit for detecting a coil current flowing into the coil; a peak hold unit for holing a peak value of the detection value of the coil current detected by the current detection unit; a delay unit for outputting a delay output value which is a value obtained by holding the peak value held by the peak hold unit for one switching of the energization direction; a comparison unit for comparing a partial pressure value of the detection value with the delay output value; and a control unit for controlling the coil drive unit so that the coil current is limited on the basis of a comparison result of the comparison unit.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a motor drive device.

  When driving a stepping motor, it is often driven by open loop control with a simple configuration. However, in recent years, the number of cases where the stepping motor is driven by closed control is increasing due to the demand for higher speed and lower power consumption. As a prior art document for driving a stepping motor by closed control, for example, Patent Document 1 is cited.

Japanese Patent Laid-Open No. 1-110085

  However, when a relatively large load of inertia is rotated by a stepping motor having a relatively large inductance, the positive / negative balance of the current flowing through the coil of the stepping motor may be lost. When the positive / negative balance of the current flowing through the coil is lost, for example, resonance may occur in a specific load or a specific rotation region, and the vibration of the motor may increase or the torque generated by the motor may decrease.

  In view of the above, an object of one embodiment of the present disclosure is to provide a motor driving device that can prevent the balance between the positive and negative currents flowing in the coils of the stepping motor from being lost.

In order to achieve the above object, according to one aspect of the present disclosure,
A PWM signal generator for generating a PWM signal;
A coil drive unit that switches the energization direction of the coil of the stepping motor at a cycle of the PWM signal generated by the PWM signal generation unit;
A current detector for detecting a coil current flowing in the coil;
A peak hold unit for holding a peak value of the detected value of the coil current detected by the current detection unit;
A delay unit for outputting a delay output value which is a value obtained by holding the peak value held by the peak hold unit for one switching of the energization direction;
A comparison unit that compares the divided voltage value of the detected value with the delayed output value;
A motor drive device is provided, comprising: a control unit that controls the coil drive unit such that the coil current is limited based on a comparison result by the comparison unit.

  According to one aspect of the present disclosure, it is possible to suppress the balance between the positive and negative currents flowing through the coils of the stepping motor from being lost.

It is a figure which shows an example of a structure of the motor control system which drives a stepping motor by closed control. It is a figure which shows an example of the signal waveform of each part at the time of carrying out 2 phase electricity supply by closed loop control of a 2 phase stepping motor. It is a figure which shows an example in the state where the positive / negative balance of the U-phase current collapsed from the state of FIG. It is a figure which shows an example of the state which resonance generate | occur | produced in the motor. It is a figure which shows an example of a structure of the motor control system provided with the motor drive device which concerns on this embodiment. It is a figure which shows an example of the signal waveform of each part of the motor control system which concerns on this embodiment. It is a figure which shows an example of the waveform of a U-phase detection voltage. It is a figure which shows an example of the signal waveform of each part of the motor control system which concerns on this embodiment. It is a figure which shows an example of the analog hardware circuit which implement | achieves a peak hold part and a delay part.

  FIG. 1 is a diagram illustrating an example of a configuration of a motor control system that drives a stepping motor by closed control. The motor control system 100 in FIG. 1 generates a drive control signal by combining an encoder 120 that detects the rotational phase of the stepping motor 110 and a phase signal that represents the rotational phase detected by the encoder 120 with a control signal. Circuit 130. The logic synthesis circuit 130 drives the output stage 140 that supplies current to the coils 111 and 112 for two phases so that the torque in the direction in which the stepping motor 110 is to be rotated is generated in any phase of the rotor of the stepping motor 110. Control by control signal.

  With such a configuration, occurrence of a step-out phenomenon can be prevented as in open loop control. The output stage controller that controls the output stage 140 is not limited to the logic synthesis circuit 130. For example, the waveform of the voltage or current applied to each coil of the motor is previously stored in the memory as information corresponding to the motor phase, and the information is read from the memory according to the phase of the motor obtained by the encoder, and the output stage 140 There are also ways to control this.

  However, in the case of closed-loop control, vibrations due to resonance and torque reduction due to resonance may occur due to the relationship between the motor inductance and the load or rotation speed. An example of the mechanism of occurrence of this phenomenon will be described below with reference to FIGS.

  FIG. 2 is a diagram illustrating an example of a waveform of each part when a two-phase stepping motor is energized in two phases by closed loop control. Regarding the U-phase coil 111 shown in FIG. 1, the current flowing through the U-phase coil 111 (U-phase current) and the zero cross position of dΦ / dθ (back electromotive force constant) of the U-phase coil 111 coincide. In addition, regarding the V-phase coil 112 shown in FIG. 1, the zero crossing position of the current flowing in the V-phase coil 112 (V-phase current) and dΦ / dθ (back electromotive force constant) of the V-phase coil 112 coincides. That is, FIG. 2 shows a state in which positive and negative currents flowing through the coils 111 and 112 are balanced.

  FIG. 3 is a diagram showing an example of a state in which the positive / negative balance of the U-phase current is lost from the state of FIG. When the positive-side U-phase current increases, the time constant determined by the inductance and resistance of the U-phase coil 111 even after the voltage applied to the U-phase coil 111 (U-phase voltage) is switched in the reverse direction. The U-phase current changes. Therefore, the U-phase current cannot reach a sufficient negative current value while the U-phase voltage is applied in the reverse direction (for example, during an angle from 180 ° to 360 (0 °)). On the other hand, since the absolute value of the current value of the negative current becomes small, after the U-phase voltage is further switched in the reverse direction, a large positive current flows through the U-phase coil 111 and an unbalanced state continues.

  This current imbalance causes a torque difference when the positive and negative currents are flowing. In addition, when the zero cross position of the current and dΦ / dθ (counterelectromotive force constant) is shifted, the polarity of the current and dΦ / dθ (counterelectromotive force constant) is reversed, and the period in which the reverse torque is generated (in FIG. 3). A shaded area appears.

  However, even if the torque pulsates in this way, if the motor rotation does not pulsate, the voltage applied to the coil will be positive and negative due to the back electromotive voltage and the voltage drop caused by the current flow. Occurs to balance. Therefore, the state of FIG. 3 automatically returns to the state of FIG.

  However, when the torque fluctuation period matches the mechanical time constant of the motor, resonance as shown in FIG. 4 occurs and the rotation of the motor pulsates. In FIG. 4, the reason why the scale of the rotor phase is not equally spaced is that the change in the rotor phase with respect to the time axis is not constant due to the change in the rotational speed of the motor. Since the logic synthesis circuit 130 detects the phase of the rotor that does not change uniformly in this way by the encoder 120 and determines the voltage application timing to the coils 111 and 112 of each phase, the following resonance operation is performed. Arise.

  When the rotational speed of the rotor becomes slow, the period of the energization pattern that flows through one coil becomes long. As a result, the current flowing through the coil increases with a delay due to the electrical time constant, and the rotation of the rotor is accelerated. Next, when the rotor accelerates and the rotor rotation speed increases, the rotor phase rotates before the polarity of the current switches due to the electrical time constant, generating torque in the reverse direction and slowing down the rotor rotation. To do. When these acceleration / deceleration timings coincide with the mechanical time constant, resonance occurs in the motor, causing vibration and torque reduction.

  In order not to fall into such a resonance phenomenon, the positive / negative balance of the current flowing in the coil should not be greatly broken. In the present embodiment, the occurrence of vibration and torque reduction due to resonance is avoided by maintaining the current balance by the following means.

  FIG. 5 is a diagram illustrating an example of a configuration of a motor control system including the motor driving device according to the present embodiment. FIG. 6 is a timing chart showing an example of the waveform of each part of the motor control system according to the present embodiment.

  A motor control system 101 shown in FIG. 5 is an example of a system that controls the rotation operation of the stepping motor 10. The motor control system 101 includes a stepping motor 10, an encoder 20, and a motor driving device 1.

  The stepping motor 10 has a plurality of coils. The stepping motor 10 is an example of a two-phase stepping motor having a U-phase coil 11 and a V-phase coil 12. The coils 11 and 12 are respectively applied with a U-phase voltage Vu and a V-phase voltage Vv whose phases are 90 ° different from each other. Further, the U-phase coil current Iu and the V-phase coil current Iv having phases different from each other by 90 ° flow through the coils 11 and 12, respectively.

  The motor driving device 1 drives the stepping motor 10. The motor drive device 1 includes a PWM signal generation unit 200, a coil drive unit 146, a current detection unit 150, a peak hold unit 160, a delay unit 170, a comparison unit 180, and a control unit 190. For example, the control unit 190 includes a flip-flop 191 and a drive control unit 210. The drive control unit 210 includes, for example, an AND operation unit 211 and a logic synthesis circuit 30. A part or all of the PWM signal generation unit 200, the coil drive unit 146, the current detection unit 150, the peak hold unit 160, the delay unit 170, the comparison unit 180, and the control unit 190 are realized by a hardware circuit. Alternatively, some or all of the processing functions may be realized by the CPU executing a program stored in the ROM.

  In FIG. 5, the PWM signal generation unit 200, the coil drive unit 146, the current detection unit 150, the peak hold unit 160, the delay unit 170, the comparison unit 180, and the control unit 190 control the current flowing through the U-phase coil 11. It is the structure for. The illustration of the configuration for controlling the current flowing through the V-phase coil 12 is omitted. The motor drive device 1 has a configuration for controlling the current flowing in the V-phase coil 12 and a configuration for controlling the current flowing in the U-phase coil 11, and both configurations have the same configuration and function. . Therefore, for the description of the configuration for controlling the current flowing through the V-phase coil 12, the description of the configuration for controlling the current flowing through the U-phase coil 11 is cited.

  The PWM signal generation unit 200 generates a PWM (pulse width modulation) signal according to the control signal. The control signal is a signal for controlling the voltage applied to the U-phase coil 11.

  The coil drive unit 146 switches the energization direction of the U-phase coil 11 of the stepping motor 10 at the cycle of the PWM signal generated by the PWM signal generation unit 200. The coil driver 146 is an H bridge circuit in which the transistors 141 to 144 have an H bridge configuration. The coil drive unit 146 can flow current in both directions through the U-phase coil 11 by the configuration of the H bridge.

  Current detector 150 detects a current (U-phase coil current Iu) flowing through U-phase coil 11. The current detection unit 150 includes, for example, a resistor 151 and an amplifier 152. A resistor 151 is provided between the coil driving unit 146 and the ground. The current detection unit 150 can quantify the U-phase coil current Iu by measuring the voltage generated across the resistor 151. Note that the resistance value of the resistor 151 is set to be relatively low in order to reduce the power loss in the resistor 151 as much as possible. For this reason, since the voltage generated at both ends of the resistor 151 is very small, the voltage is amplified by the amplifier 152.

  The peak hold unit 160 holds the detected value of the U-phase coil current Iu detected by the current detection unit 150 (specifically, the output value of the amplifier 152) at each peak switching of the energization direction of the U-phase coil 11. The detected value of the U-phase coil current Iu detected by the current detection unit 150 is represented by the U-phase detection voltage Vau. Peak hold unit 160 holds peak value Vpu of U-phase detection voltage Vau.

  Delay unit 170 is a delay output value Vdu that is a value obtained by holding the value peak-held by peak hold unit 160 (in this case, peak value Vpu of U-phase detection voltage Vau) for one switching of the energization direction of U-phase coil 11. Is output.

  The comparison unit 180 divides the delay output value Vdu and the current detection value (specifically, the U-phase detection voltage Vau) detected by the current detection unit 150 by a predetermined voltage ratio r (reference voltage). Vr) is compared. The ratio r is determined by the resistance values of the resistor 181 and the resistor 182.

  Based on the comparison result by comparison unit 180, control unit 190 controls coil drive unit 146 such that U-phase coil current Iu is limited.

  With this configuration, when the comparison unit 180 determines that the current value corresponding to the reference voltage Vr determined by the ratio r has exceeded the peak current value one time before switching the energization direction of the U-phase coil 11, the comparator 183 Outputs a low level signal Vc. The peak current value one time before switching the energization direction of the U-phase coil 11 is a current value corresponding to the delayed output value Vdu. The signal Vc is a signal representing a comparison result by the comparison unit 180.

  Since the D-type flip-flop 191 of the control unit 190 is reset by the low-level signal Vc, the Q output signal of the flip-flop 191 becomes low level. The Q output signal of the flip-flop 191 and the PWM signal output from the PWM signal generation unit 200 are input to the logical product calculation unit 211 of the drive control unit 210.

  The drive control unit 210 controls the coil drive unit 146 based on the result of the logical product operation unit 211 calculating the logical product of the Q output signal from the flip-flop 191 and the PWM signal from the PWM signal generation unit 200. It has a logic synthesis circuit 30 that outputs a drive control signal. The logic synthesis circuit 30 synthesizes a phase signal representing the rotational phase detected by the encoder 20 with a logical product signal representing a computation result by the logical product computation unit 211, thereby driving control for controlling the coil drive unit 146. Generate a signal. The logic synthesis circuit 30 includes a coil driving unit 146 that supplies current to the coils 11 and 12 for two phases so that the torque in the direction in which the stepping motor 10 is desired to rotate is generated in any phase of the rotor of the stepping motor 10. It is controlled by a drive control signal.

  Therefore, when the Q output signal of the flip-flop 191 input to the AND operation unit 211 becomes low level, the drive control signal input to the coil drive unit 146 is turned off by the logic synthesis circuit 30. When the drive control signal input to the coil drive unit 146 is turned off, the transistors 141 to 144 in the coil drive unit 146 are turned off.

  On the other hand, the control signal input to the PWM signal generation unit 200 is subjected to pulse width modulation by the PWM signal generation unit 200 and then input to the AND operation unit 211. The logic synthesis circuit 30 of the drive control unit 210 turns on or off the transistors 141 to 144 in the coil drive unit 146 according to the logical product signal of the control signal (PWM signal) after pulse width modulation and the Q output signal of the flip-flop 191. Control off. The energization direction of the coil current Iu flowing through the U-phase coil 11 is controlled by the on / off control of the transistors 141 to 144. The PWM signal becomes a trigger signal for setting the flip-flop 191. At the same time as the PWM signal becomes high level, the Q output signal of the high bell voltage input to the D terminal of the flip-flop 191 is output from the Q output terminal. . The coil drive unit 146 is controlled by the logic synthesis circuit 30 in accordance with a logical product signal of the Q output signal and the PWM signal. As a result, for each PWM signal cycle, the U-phase coil current Iu is limited based on the ratio r with respect to the peak current value of the current one time before the energization direction switches (that is, the current in the opposite direction). Can call

  In FIG. 6, a high-level U-phase voltage Vu indicates a state in which both the transistors 141 and 143 are turned on and the transistors 142 and 144 are both turned off. The low-level U-phase voltage Vu indicates a state where both the transistors 142 and 144 are turned on and both the transistors 141 and 143 are turned off. However, FIG. 6 shows an ON state or an OFF state of each transistor when the PWM-modulated control signal (PWM signal) is at a low level or when the Q output signal output from the flip-flop 191 is at a low level. This is not the case.

  In FIG. 6, the U-phase voltage Vu is as described above. In the U-phase coil current Iu, the direction of current flowing in the order of the transistor 141, the U-phase coil 11, and the transistor 143 is a positive direction. By setting the U-phase voltage Vu to a high level state, the current value of the U-phase coil current Iu increases in a positive direction from a predetermined state according to the LR time constant of the U-phase coil 11. The voltage output from the amplifier 152 when the U-phase coil current Iu flows through the resistor 151 corresponds to the U-phase detection voltage Vau. When synchronous rectification is performed by the coil drive unit 146 every time the PWM signal is in the OFF state, the U-phase detection voltage Vau has a waveform as shown in FIG.

  Next, as shown in FIG. 6, the peak value Vpu held by the peak hold unit 160 is reset to zero at every switching timing of the energization direction of the U-phase coil 11. Thereafter, the peak hold unit 160 samples and holds the peak value of the U-phase detection voltage Vau until the next energization direction switching timing is reached. Delay unit 170 samples peak value Vpu at every switching timing of the energization direction of U-phase coil 11, and then holds the sampled peak value Vpu until the next switching timing of the energization direction.

  Reference voltage Vr represents a voltage obtained by resistance-dividing U-phase detection voltage Vau. In FIG. 6, the reference voltage Vr is set to a value obtained by dividing the U-phase detection voltage Vau by a ratio r of 0.4.

  The signal Vc represents the result of the comparator 183 comparing the delayed output value Vdu, which is a value obtained by holding the peak value Vpu, with the reference voltage Vr, which is a divided value of the U-phase detection voltage Vau. In this example, since the delay output value Vdu always exceeds the reference voltage Vr, the signal Vc is fixed at a high level.

  In FIG. 6, the reference voltage Vr is set to 0.4 times the U-phase detection voltage Vau. When a coil current Iu that is 2.5 times (1 / 0.4) the peak current value before the energization direction is switched flows, the flow of the coil current Iu is limited by the coil drive unit 146 being turned off. .

  On the other hand, in FIG. 8, the reference voltage Vr is set to 0.8 times the U-phase detection voltage Vau. When the coil current Iu that is 1.25 times (1 / 0.8) the peak current value one time before the energization direction is switched flows, the flow of the coil current Iu is limited by the coil drive unit 146 being turned off. . That is, in FIG. 8, when the current value corresponding to the reference voltage Vr reaches the peak current value one time before the energization direction is switched, the signal Vc becomes low level, and thus the U-phase coil current Iu is limited. The FIG. 8 shows that the positive-side peak current value and the negative-side peak current value of the U-phase coil current Iu are limited while the signal Vc is at a low level.

  As described above, according to the present embodiment, the width of the increase or decrease in the current after the energization direction is switched is limited from the peak current value before the energization direction is switched, so that the current flows through the coil of the stepping motor. It is possible to prevent the current positive / negative balance from being lost. As a result, for example, the occurrence of resonance is suppressed. Moreover, vibration and torque reduction due to resonance can be suppressed.

  The setting of the resistance partial pressure ratio r may be adjusted to an optimal value while confirming the behavior of the stepping motor 10.

  Further, as shown in FIG. 9, the peak hold unit 160 and the delay unit 170 can be configured by analog circuits. FIG. 9 is a diagram illustrating an example of an analog hardware circuit that implements a peak hold unit and a delay unit.

  In FIG. 9, the energization voltage switching signal represents the switching timing of the energization direction of the coil detected by the encoder 20 (see FIG. 5).

  The analog switch 163 switches the input of the U-phase detection voltage Vau from the L terminal side to the H terminal side when the rising edge of the communication voltage switching signal is input to the buffer 162. Thereby, the U-phase detection voltage Vau input via the diode 161 is sampled by the capacitor 164. The analog switch 163 switches the input of the U-phase detection voltage Vau from the H terminal side to the L terminal side when the falling edge of the communication voltage switching signal is input to the buffer 162. As a result, the peak value Vpu at the falling edge timing of the communication voltage switching signal is held in the capacitor 164, and the U-phase detection voltage Vau input via the diode 161 is sampled in the capacitor 165.

  On the other hand, the analog switch 166 switches the output of the delayed output value Vdu from the H terminal side to the L terminal side when the rising edge of the communication voltage switching signal is input to the buffer 179. As a result, the peak value Vpu sampled in the capacitor 165 is output as the delayed output value Vdu. The analog switch 166 switches the output of the delayed output value Vdu from the L terminal side to the H terminal side when the falling edge of the communication voltage switching signal is input to the buffer 179. As a result, the peak value Vpu sampled in the capacitor 164 is output as the delayed output value Vdu.

  The value sampled in the capacitor 164 is reset by turning on the transistor 174 at the next falling edge timing of the communication voltage switching signal. The transistor 174 is turned on when the falling edge of the communication voltage switching signal is input to the differentiation circuit 172 via the buffer 171. The diode 173 has a clamp function of protecting the transistor 174 from an excessive negative voltage.

  Similarly, the value sampled in the capacitor 165 is reset by turning on the transistor 178 at the next rising edge timing of the communication voltage switching signal. The transistor 178 is turned on when the rising edge of the communication voltage switching signal is input to the differentiation circuit 176 via the buffer 175. The diode 177 has a clamping function to protect the transistor 178 from an excessive negative voltage.

  As mentioned above, although the motor drive device was demonstrated by embodiment, this invention is not limited to said embodiment. Various modifications and improvements such as combinations and substitutions with some or all of the other embodiments are possible within the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Motor drive device 10 Stepping motor 11 U phase coil 12 V phase coil 100, 101 Motor control system 146 Coil drive part 150 Current detection part 160 Peak hold part 170 Delay part 180 Comparison part 190 Control part 191 Flip-flop 200 PWM signal generation part 210 Drive control unit 211 AND operation unit

Claims (4)

A PWM signal generator for generating a PWM signal;
A coil drive unit that switches the energization direction of the coil of the stepping motor at a cycle of the PWM signal generated by the PWM signal generation unit;
A current detector for detecting a coil current flowing in the coil;
A peak hold unit for holding a peak value of the detected value of the coil current detected by the current detection unit;
A delay unit for outputting a delay output value which is a value obtained by holding the peak value held by the peak hold unit for one switching of the energization direction;
A comparison unit that compares the divided voltage value of the detected value with the delayed output value;
A motor drive device comprising: a control unit that controls the coil drive unit such that the coil current is limited based on a comparison result by the comparison unit.   The motor according to claim 1, wherein the control unit controls the coil driving unit so that the coil current is limited when the comparison unit determines that the divided voltage value exceeds the delay output value. Drive device. The controller is
A flip-flop set by the PWM signal and reset by a comparison result by the comparison unit;
The motor drive device according to claim 1, further comprising: a drive control unit that controls the coil drive unit based on an output signal of the flip-flop and the PWM signal.   The motor drive device according to claim 3, wherein the drive control unit controls the coil drive unit by calculating a logical product of the output signal of the flip-flop and the PWM signal.

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