JP2011139583A - Motor drive circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To continuously detect induced voltage at low cost and prevent a motor from stepping out. <P>SOLUTION: A coil current detection unit 30 detects a current component flowing through a coil. A scaling unit 38 scales a drive signal. An induced voltage component extraction unit 42 extracts an induced voltage component by removing the drive signal, scaled by the scaling unit 38, from the coil current component detected by the coil current detection unit 30. A phase difference detection unit 74 detects a phase difference between the phase of the drive signal and that of the induced voltage component. A step-out prediction/determination unit 80 compares the differential value of the phase difference detected by the phase difference detection unit 74 with a detection threshold value for step-out prediction to predict step-out. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a motor drive circuit for driving a synchronous motor.

  There are various types of synchronous motors, for example, SPMSM (Surface Permanent Magnet Synchronous Motor), PM (Permanent Magnet) type stepping motor, VR (Variable Reluctance) type stepping motor, HB (Hybrid) type stepping motor, BLDCM (Brushless) DC Motor) is known. As a method for detecting the rotational position of these synchronous motors, there are a detection method using a sensor and a detection method without a sensor.

  As a sensorless detection method, there is a method using an induced electric power (hereinafter also referred to as a speed electromotive force as appropriate) induced by a stator and a rotor. This method using speed electromotive force includes a method for estimating the position by performing vector calculation from the motor stator voltage / current and the motor model equation, or setting the motor drive line in a high impedance state for a specific period to directly There is a method to detect. With the former method, it is possible to estimate the position of the rotor during the entire drive period. In the latter method, the position of the rotor can be estimated at the zero cross timing of the detected speed electromotive voltage component.

JP 2007-274760 A

  In the former method, the circuit scale increases and the cost increases. In the latter method, it is necessary to stop energization of the motor during the period in which the speed electromotive voltage is detected, and the continuity of current is impaired. In addition, the sampling point for estimating the rotor position is limited to the zero-cross timing of the speed electromotive force. In particular, in a two-phase motor, even if the non-energization periods of each phase are added up, the rotor is only in every 1/4 electrical angle cycle. The state of cannot be detected.

  The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a technique for continuously detecting an induced voltage and avoiding motor step-out based on the detected induced voltage at a low cost.

  A motor drive circuit according to an aspect of the present invention includes a drive unit that supplies a current to a coil of a synchronous motor, a coil current detection unit that detects a current component flowing in the coil, and a scaling that scales the drive signal according to a drive signal. And an induced voltage component extraction unit that extracts the induced voltage component by removing the drive signal scaled by the scaling unit from the coil current component detected by the coil current detection unit, the phase of the drive signal, and the induced voltage A phase difference detection unit that detects a phase difference from the phase of the component, a differential value of the phase difference detected by the phase difference detection unit, and a detection threshold value for step-out prediction, and a step-out occurrence prediction that predicts step-out occurrence. A key prediction determination unit.

  According to the present invention, it is possible to detect an induced voltage continuously at low cost and to avoid motor step-out based on the detected induced voltage.

It is a figure for demonstrating the relationship between the stator and rotor of two-phase PMSM (Permanent Magnet Synchronous Motor). It is a figure which shows the structure of the motor drive circuit which concerns on embodiment of this invention. It is a figure which shows the structure of the motor drive circuit which concerns on the modification 1 of embodiment of this invention. It is a figure which shows the structure of the motor drive circuit which concerns on the modification 2 of embodiment of this invention. It is a figure which shows the structure of the motor drive circuit which concerns on the modification 3 of embodiment of this invention. It is a timing chart which shows the operation example of a phase difference detection part. It is a figure which shows the structure of a loss-of-synchronization detection part. It is a timing chart which shows the operation example of a continuous determination part. It is a figure which shows the structure of a rotational speed detection part. It is a timing chart which shows the operation example of a rotational speed detection part. It is a figure which shows the structure of the motor drive circuit which added the feedback loop to the motor drive circuit shown in FIG. It is a figure which shows the modification of the motor drive circuit shown in FIG. It is a figure which shows the structure of a step-out prediction determination part. It is a timing chart which shows the operation example of a phase determination part.

Prior to describing the embodiments of the present invention, knowledge to be used in the embodiments of the present invention will be described. This knowledge defines the relationship between the stator and the rotor included in the motor.
FIG. 1 is a view for explaining the relationship between the stator and rotor of the two-phase PMSM. As a premise, each symbol in FIG. 1 is defined.
L = inductance ia of each phase, Ib = current of each phase R = DC resistance DCR of each stator
Va, Vb = Voltage of each phase θ = An angle ω between the rotor axis and the A-phase axis = Rotor angular velocity (dθ / dt)

Although the rotor is a permanent magnet, if the maximum value of the linkage flux generated in each phase by the speed electromotive force is Φ, the A-phase axis component Φa is defined as the following equation (1).
Φa = Φcos θ (1)

Therefore, the speed electromotive force Ea induced in the A-phase stator is obtained by time differentiation of the A-phase axis component Φa as shown in the following formula (2).
Ea = −ωΦsinθ (2)

Therefore, the voltage equation of the A phase is defined as the following formula (3).
Va = (R + pL) Ia + (− ωΦsinθ) (3)
Here, p = d / dt.

The B phase can be calculated in the same manner. When the voltage equations of the A phase and the B phase of the two-phase PMSM shown in FIG. 1 are collectively described, the following equation (4) is defined.

When the above equation (4) is modified, the following equation (5) is derived.

The first term on the right side of the above equation (5) indicates the current flowing through the stator coil when the speed electromotive force is zero. Here, in a motor having a relatively small inductance, such as a small stepping motor, there is no problem in practical use even if the pL component is ignored. Further, in the relationship with the electrical angle period for exciting the stator coil, there is no problem in practical use even when the influence of the pL component is relatively small and the pL component is ignored. Based on this, the above formula (5) can be approximated to the following formula (6).

When the motor is stopped and the stator coil is in a steady state by direct current excitation, the speed electromotive force is zero, and the above equation (6) is expressed as the following equation (7).

  The above equation (7) indicates that the scaling factor for matching the voltage value applied to the stator and the current value detected from the stator under the above conditions is expressed by the DC resistance DCR of the stator. ing.

The second term on the right side of the above equation (6) represents the speed electromotive voltage. Therefore, as shown in the following formula (8), the speed electromotive force Ev is obtained by multiplying the current value Is detected from the stator during motor rotation by multiplying the stator drive voltage value S0 during motor rotation by the scaling factor As. It is detected by subtracting the scaled drive signal Ss. Here, the scaling factor As is a factor for scaling the current value Idc detected from the stator in the DC excitation state and the voltage value Vdc applied to the stator in the DC excitation state.
Ev = Is-As * S0 = Is-Ss (8)
Here, the scales of Vdc and S0 are the same. That is, Vdc: S0 = 1: 1.

  FIG. 2 is a diagram showing a configuration of the motor drive circuit 100 according to the embodiment of the present invention. The motor drive circuit 100 is a circuit that drives a synchronous motor. In the present embodiment, a two-phase stepping motor 20 (hereinafter simply referred to as “stepping motor 20”) is driven. The stepping motor 20 includes two stator coils (hereinafter referred to as a first coil 22 and a second coil 24, respectively) and a rotor 26. Stator resistance Rs indicates a DC resistance component of the stator. In FIG. 2, the drive system of the first coil 22 is illustrated, and the drive system of the second coil 24 is omitted.

  The first coil 22 and the second coil 24 are arranged with an electrical angle of 90 ° shifted from each other.

  The rotor 26 includes a magnetic material (for example, a permanent magnet), and a stable position is determined according to the magnetic fields from the first coil 22 and the second coil 24. The motor drive circuit 100 can rotate the rotor 26 by providing the first coil 22 and the second coil 24 with alternating currents having phases different from each other by 90.degree.

  Moreover, the motor drive circuit 100 can stop the rotor 26 at a specific position corresponding to the current phase at the timing by stopping the change in the current phase at a specific timing. With these processes, the rotation of the stepping motor 200 can be controlled.

  The motor drive circuit 100 includes an excitation timing generation unit 10, an excitation amplitude generation unit 12, a signal adjustment unit 14, a PWM (Pulse Width Modulation) signal generation unit 16, an H bridge drive unit 18, a coil current detection unit 30, and a sign determination unit 36. , Scaling unit 38, comparison adjustment unit 40, induced voltage component extraction unit 42, amplifier 44, digital low-pass filter 46, differentiator 48, out-of-synchronization detection unit 50, rotation speed detection unit 60, first zero cross detection unit 70, second A zero cross detector 72 and a phase difference detector 74 are provided.

  The excitation timing generation unit 10 receives a scaling command or a normal excitation command from a host controller (not shown) and generates an excitation timing according to the command. The scaling command is a command for selecting a scaling detection mode for detecting the scaling factor As, and the normal excitation command is a command for selecting a normal drive mode.

  The scaling factor As includes a drive signal (more specifically, a voltage value applied to the stator in a DC excitation state) in a state where the induced voltage generated in the first coil 22 is zero, and a coil current component (more specifically, Defines the relationship with the current value detected from the stator in the DC excitation state.

  The scaling command is issued when the system is started. In addition, the scaling command is issued at an arbitrary timing while the stepping motor 20 is stopped and DC excitation is performed.

  In the normal drive mode, the excitation timing generator 10 and the excitation amplitude generator 12 generate an excitation signal having a predetermined excitation angle. As the excitation method, for example, sine wave excitation, microstep excitation, 1-2 phase excitation, 2 phase excitation, 1 phase excitation, etc. can be employed.

  The excitation amplitude generator 12 generates a drive signal or a scaling detection signal having an excitation amplitude corresponding to the excitation timing supplied from the excitation timing generator 10. The signal adjustment unit 14 adjusts the drive signal or scaling detection signal supplied from the excitation amplitude generation unit 12. More precisely, the amplitude of the signal is adjusted. Details of the amplitude adjustment will be described later.

  The PWM signal generation unit 16 converts the drive voltage value S0 supplied from the signal adjustment unit 14 into a PWM signal. The scaling detection voltage value Vdc is output as a DC signal. The H bridge drive unit 18 supplies a current to the stepping motor 20 in accordance with the supplied signal. The H bridge drive unit 18 includes four transistors around the first coil 22. A drive voltage value S0 in the PWM signal format supplied from the PWM signal generation unit 16 or a scaling detection voltage value Vdc in the DC signal format is input to the gate terminals of these transistors. When the drive voltage value S0 in the PWM signal format is input, the H bridge drive unit 18 supplies the first coil 22 with a current corresponding to the duty ratio of the PWM signal. At that time, the direction and amount of the current to be passed through the first coil 22 are determined by the PWM signal.

  The coil current detection unit 30 detects a current component flowing through the first coil 22. The coil current detection unit 30 detects the current component by detecting the voltage across the stator resistance Rs. When detecting the current component, a current detection resistor may be provided separately from the stator resistor Rs, and the voltage across the resistor may be detected. The coil current detection unit 30 includes a differential amplifier 31, an offset adjustment unit 32, and an analog / digital converter 33.

  The differential amplifier 31 amplifies the voltage across the stator resistor Rs with a predetermined amplification factor and outputs the amplified voltage to the analog-digital converter 33. A low-pass filter is connected to the output terminal of the differential amplifier 31, and noise included in the output signal of the differential amplifier 31 is removed by the low-pass filter, and then the output signal is input to the analog-digital converter 33. Is done.

  The offset adjustment unit 32 adjusts an offset generated in the differential amplifier 31. For example, the offset adjustment unit 32 detects the output signal of the differential amplifier 31 when the drive current is zero (that is, the current flowing through the stator resistor Rs is zero), and stores it as an offset value. This offset value is added to the input terminal of the differential amplifier 31 to cancel the offset generated in the differential amplifier 31. The offset value detection process by the offset adjustment unit 32 is executed based on an offset adjustment command from the control device (not shown).

  The analog-digital converter 33 converts the analog signal output from the differential amplifier 31 into a digital signal. This digital signal is a signal indicating the driving coil current component Is or the scaling detection coil current component Idc detected by the coil current detector 30. The sign determination unit 36 determines whether the signal input from the analog-digital converter 33 is positive or negative and supplies it to the scaling unit 38. By this sign determination, the direction of the current flowing through the stator resistor Rs is detected.

  The scaling unit 38 stores the scaling factor As. In the normal drive mode, the scaling unit 38 scales the drive voltage value S0 output from the signal adjustment unit 14 (hereinafter referred to as drive signal S0) using the scaling factor As. More specifically, the drive signal S0 is multiplied by the scaling factor As to generate a scaled drive signal Ss, which is supplied to the induced voltage component extraction unit 42.

  In the scaling detection mode, the scaling unit 38 supplies the comparison adjustment unit 40 with a value (Vdc · As) obtained by multiplying the scaling detection voltage value Vdc output from the signal adjustment unit 14 by the scaling factor As. The comparison adjustment unit 40 compares the value (Vdc · As) supplied from the scaling unit 38 with the coil current component Idc at the time of scaling detection supplied from the coil current detection unit 30 in the scaling detection mode, and compares them. A scaling factor As for matching is calculated and set in the scaling unit 38. This scaling factor As is individually adjusted according to the direction of the current flowing through the first coil 22. That is, two types of positive and negative scaling factors As are set. This is to eliminate the difference in DC characteristics of the motor drive circuit 100.

  The induced voltage component extraction unit 42 removes the scaled drive signal Ss from the driving coil current component Is detected by the coil current detection unit 30 and extracts the induced voltage component. Here, the induced voltage component is extracted as the speed electromotive voltage component Ev. That is, since the scaled drive signal Ss indicates a current component detected from the first coil 22 in a state where no induced current is generated, the scaled drive signal is detected from the actually detected coil current component. The induced current component can be calculated by subtracting the signal Ss.

  Thus, in the normal drive mode, the speed electromotive force component Ev is continuously obtained by calculating the difference between the drive signal Ss generated by multiplying the drive signal S0 and the scaling factor As and the driving coil current component Is. Can be detected automatically.

  The amplifier 44 amplifies the speed electromotive voltage component Ev output from the induced voltage component extraction unit 42 with a predetermined amplification factor. The digital low-pass filter 46 removes high frequency noise from the speed electromotive voltage component Ev amplified by the amplifier 44. The digital low-pass filter 46 is supplied with a sampling clock Smpclk from the excitation timing generator 10. The digital low-pass filter 46 can adjust the cutoff frequency based on the sampling clock Smpclk. The excitation timing generation unit 10 determines an excitation speed based on the rotation speed information included in the normal excitation command, and generates a sampling clock Smpclk corresponding to the excitation speed. Therefore, the digital low-pass filter 46 can set the cutoff frequency to an optimum value according to the excitation speed by receiving the sampling clock Smpclk.

  The speed electromotive force component Vb output from the digital low-pass filter 46 (hereinafter, the speed electromotive voltage component Ev that has passed through the amplifier 44 is expressed as a speed electromotive voltage component Vb) includes a differentiator 48, a second zero cross detector 72, and a rotational speed. Input to the detection unit 60.

  The differentiator 48 differentiates the input speed electromotive voltage component Vb and outputs a speed electromotive voltage component differential value Vb '. By this differentiation, the phase of the speed electromotive voltage component Vb advances by 90 °. The speed electromotive force component differential value Vb ′ generated by the differentiator 48 is input to the out-of-synchronization detector 50 and the first zero-cross detector 70.

  The out-of-synchronization detection unit 50 detects out-of-synchronization of the stepping motor 20 based on the excitation speed information supplied from the excitation timing generation unit 10 and the speed electromotive force component differential value Vb ′ supplied from the differentiator 48, The out-of-synchronization detection signal Se is output. Details of this detection process will be described later.

  The rotational speed detector 60 detects the rotational speed of the stepping motor 20 based on the speed electromotive voltage component Vb supplied from the digital low-pass filter 46 and the speed electromotive voltage component differential value Vb ′ supplied from the differentiator 48. The rotation speed signal FG is output. Details of this detection process will be described later.

  The first zero cross detection unit 70 detects the zero cross point of the speed electromotive force component differential value Vb ′ supplied from the differentiator 48, and outputs the first zero cross signal Tp to the phase difference detection unit 74. The second zero cross detector 72 detects the zero cross point of the speed electromotive voltage component Vb supplied from the digital low pass filter 46 and outputs the second zero cross signal Tz to the phase difference detector 74.

  The phase difference detection unit 74 detects a phase difference between the phase of the drive signal and the phase of the speed electromotive voltage component, and outputs a first phase difference signal Pp and a second phase difference signal Pz. In addition to the first zero cross signal Tp and the second zero cross signal Tz described above, the phase difference detection unit 74 is supplied with the first flag signal Tp0, the second flag signal Tz0, and the count clock Cntclk. The first flag signal Tp0 and the second flag signal Tz0 are signals indicating two types of excitation timings that are 90 ° out of phase with each other, and are supplied from the excitation timing generation unit 10.

  For example, the first flag signal Tp0 is a signal indicating the timing when the excitation angle is 90 °, 270 °, and the second flag signal Tz0 is a signal indicating the timing when the excitation angle is 0 °, 180 °, 360 °. May be. In this case, the phase difference detection unit 74 measures the time difference between the timing at the 90 ° and 270 ° timings indicated by the first flag signal Tp0 and the zero cross timing indicated by the first zero cross signal Tp at each timing, The phase difference at the excitation angle is detected. This detection result is output as the first phase difference signal Pp. Similarly, the phase difference detection unit 74 measures the time difference between the timings of 0 °, 180 °, and 360 ° indicated by the second flag signal Tz0 and the zero cross timing indicated by the second zero cross signal Tz at each time point. Then, the phase difference at each excitation angle is detected. This detection result is output as the second phase difference signal Pz.

  If the stepping motor 20 is rotating ideally, the speed electromotive voltage component Ev is detected as a sine wave. Due to the characteristics of the stepping motor, the phase of the driving voltage and the phase of the driving current can be regarded as substantially the same at the electrical angular frequency. Using this characteristic, the state of the rotor 26 can be detected by observing the speed electromotive force component Ev with the scaled drive signal Ss as a reference. Since the drive signal S0 before scaling and the drive signal Ss after scaling are signals generated in the motor drive circuit 100, the timing when the excitation angle is 0 °, 90 °, 180 °, 270 °, 360 ° It is easy to generate a flag signal indicating It is also easy to grasp the excitation cycle.

  FIG. 3 is a diagram showing a configuration of the motor drive circuit 100 according to the first modification of the embodiment of the present invention. In the first modification, the drive signal S0 is detected as an analog value, and the subtraction process between the drive coil current component Is and the scaled drive signal Ss is performed in the analog domain. Note that the setting process of the scaling factor As by the comparison adjustment unit 40 is also performed in the analog domain. On the other hand, the motor drive circuit 100 shown in FIG. 2 performs these processes in the digital domain.

  In the first modification, a differential amplifier 34 is added. The differential amplifier 34 amplifies the voltage applied to both ends of the first coil 22 from the H bridge drive unit 18 with a predetermined amplification factor, and outputs the amplified voltage to the scaling unit 38. A low-pass filter is connected to the output terminal of the differential amplifier 34. After the noise contained in the output signal of the differential amplifier 34 is removed by this low-pass filter, the output signal is supplied to the scaling unit 38. .

  In Modification 1, the output signal of the differential amplifier 31 is supplied to the sign determination unit 36, the comparison adjustment unit 40, and the induced voltage component extraction unit 42 without going through the analog-digital converter 33. The output signals of the differential amplifier 31 and the differential amplifier 34 can be directly output to the analog-digital converter 33. The analog-digital converter 33 can output the output signal to the offset adjustment unit 32. The offset adjustment unit 32 can detect the offset values of the differential amplifier 31 and the differential amplifier 34 through this path.

  The induced voltage component extraction unit 42 outputs a speed electromotive voltage component Ev in the form of an analog signal. The speed electromotive voltage component Ev is amplified by the amplifier 44, and the speed electromotive force component Vb in the form of a digital signal is produced by the analog / digital converter 33. Is converted to

  FIG. 4 is a diagram showing a configuration of a motor drive circuit 100 according to the second modification of the embodiment of the present invention. In the second modification, a switched capacitor type low-pass filter 35 is connected to the output terminal of the differential amplifier 31 and the digital low-pass filter 46 is removed.

  The switched capacitor type low-pass filter 35 can change the cut-off frequency according to its operation clock. Therefore, the cut-off frequency can always be controlled to an optimum value according to the driving frequency of the stepping motor 20. In the second modification, the high frequency noise removal by the digital low pass filter 46 of FIG. 2 is performed by the switched capacitor type low pass filter 35. The switched capacitor type low-pass filter 35 adjusts the operation clock according to the operation clock Opclk supplied from the excitation timing generation unit 10 and adjusts the cutoff frequency to an optimum value.

  FIG. 5 is a diagram showing a configuration of a motor drive circuit 100 according to the third modification of the embodiment of the present invention. Modification 3 is a combination of Modification 1 and Modification 2. That is, a differential amplifier 34 is added, a switched capacitor type low-pass filter 35a is connected to the output terminal of the differential amplifier 31, and a switched capacitor type low-pass filter 35b is connected to the output terminal of the differential amplifier 34. In this configuration, the filter 46 is removed.

  The differential amplifier 34 amplifies the voltage applied to both ends of the first coil 22 from the H-bridge driving unit 18 with a predetermined amplification factor, and outputs the amplified voltage to the scaling unit 38 via the switched capacitor type low-pass filter 35b. The switched capacitor type low pass filter 35b removes high frequency noise contained in the output signal of the differential amplifier 34. The switched-capacitor-type low-pass filter 35a and the switched-capacitor-type low-pass filter 35b adjust the operation clock according to the operation clock Opclk supplied from the excitation timing generation unit 10 and adjust the cutoff frequency to an optimum value.

  Similarly to the first modification, the third modification also has a configuration in which the drive signal S0 is detected as an analog value, and the subtraction process between the drive coil current component Is and the scaled drive signal Ss is performed in the analog domain. Note that the setting process of the scaling factor As by the comparison adjustment unit 40 is also performed in the analog domain.

  FIG. 6 is a timing chart illustrating an operation example of the phase difference detection unit 74. In order to supply the first coil 22 and the second coil 24 included in the stepping motor 20 with drive signals having phases different from each other by 90 °, the excitation timing generation unit 10 generates two types of excitation timing. A first flag signal Tp0 and a second flag signal Tz0 are generated based on these two types of excitation timings. The first flag signal Tp0 and the second flag signal Tz0 are signals having a frequency twice that of the drive signal, and are signals having the same frequency as the rotational speed signal FG.

  The phase difference detection unit 74 has two counters and a subtracter (not shown). The first counter counts a period from the falling edge of the first flag signal Tp0 to the falling edge of the first zero cross signal Tp in synchronization with the clock CLK. Then, the first count value C1 in the first counter at the time of falling of the first zero cross signal Tp is output as the first output count value Cout1. Similarly, the second counter counts a period from the falling edge of the second flag signal Tz0 to the falling edge of the second zero cross signal Tz in synchronization with the clock CLK. Then, the second count value C0 in the second counter at the time of falling of the second zero cross signal Tz is output as the second output count value Cout0.

  In order to compensate for the offset component by the phase difference detection unit 74, the subtracter subtracts a predetermined constant Pc from the first output count value Cout1 supplied from the first count to generate the first phase difference signal Pp. . Similarly, a predetermined constant Pc is subtracted from the second output count value Cout0 supplied from the second count to generate a second phase difference signal Pz.

  FIG. 7 is a diagram illustrating a configuration of the out-of-synchronization detection unit 50. The out-of-synchronization detection unit 50 detects out-of-synchronization using the principle that the stepping motor 200 cannot rotate when the rotation synchronization of the stepping motor 20 is lost, and the speed electromotive force is lost. The out-of-synchronization detection unit 50 includes a variable threshold value setting unit 52 and a continuity determination unit 54. Excitation speed information is supplied from the excitation timing generation unit 10 to the variable threshold setting unit 52. The variable threshold setting unit 52 determines the determination continuous time and the determination threshold based on the excitation speed information, and sets the determination continuous time and the determination threshold in the continuous determination unit 54. The continuation determination unit 54 detects loss of synchronization by determining whether or not the speed electromotive force component differential value Vb ′ supplied from the differentiator 48 stays within a predetermined range for a predetermined time or more.

  FIG. 8 is a timing chart illustrating an operation example of the continuity determination unit 54. As shown in FIG. 8, when the speed electromotive force component differential value Vb ′ falls within a range defined by a positive threshold value + and a negative threshold value − that are symmetrically located with reference to zero, the continuous determination unit 54. Sets the threshold determination signal to a high level. When the speed electromotive force component differential value Vb ′ remains within the range even after the set continuous time has elapsed (that is, when the threshold determination signal remains at the high level), the continuous determination unit 54 is synchronized. It is determined that a loss has occurred, and the synchronization loss detection signal Se is set to a high level.

  Since the speed electromotive force component differential value Vb ′ is a differential value of the speed electromotive voltage component Vb, the amplitude component is proportional to the rotational speed of the stepping motor 20. Further, the frequency of the speed electromotive force component differential value Vb ′ matches the rotational speed of the stepping motor 20. Therefore, the variable threshold value setting unit 52 can set the determination continuous time and the determination threshold value to optimum values by acquiring excitation speed information from the excitation timing generation unit 10 in real time. Thereby, it is possible to accurately detect the loss of synchronization in various states from low speed rotation to high speed rotation.

  FIG. 9 is a diagram illustrating a configuration of the rotation speed detection unit 60. The rotation speed detection unit 60 includes a first hysteresis comparator 62, a second hysteresis comparator 64, and an exclusive OR circuit 66. The speed hysteresis voltage component Vb is input to the first hysteresis comparator 62. The second hysteresis comparator 64 receives the speed electromotive force component differential value Vb ′.

  FIG. 10 is a timing chart illustrating an operation example of the rotation speed detection unit 60. Each of the first hysteresis comparator 62 and the second hysteresis comparator 64 is input with a positive threshold value + and a negative threshold value − which are symmetrically positioned with respect to zero as shown in FIG. The first hysteresis comparator 62 sets the determination signal A to the high level when the speed electromotive voltage component Vb exceeds the positive threshold value +, and sets it to the low level when it falls below the negative threshold value −. Within the range between the positive threshold + and the negative threshold −, the level of the determination signal A is maintained as it is. Similarly, the second hysteresis comparator 64 sets the determination signal B to a high level when the speed electromotive force component differential value Vb ′ exceeds the positive threshold value +, and sets it to a low level when it falls below the negative threshold value −. Within the range between the positive threshold value + and the negative threshold value −, the level of the determination signal B is maintained as it is.

  From the first hysteresis comparator 62 and the second hysteresis comparator 64, a determination signal A and a determination signal B that are 90 ° out of phase with each other are output and input to the exclusive OR circuit 66. The exclusive OR circuit 66 calculates the exclusive OR of the determination signal A and the determination signal B and outputs the calculation result as the rotation speed signal FG. In this way, a rotational speed signal FG having a frequency twice as high as the speed electromotive voltage component Vb and the speed electromotive voltage component differential value Vb ′ is obtained. By measuring the period of the rotational speed signal FG, it is possible to grasp the speed change for each half period of the speed electromotive voltage component Vb. Further, the rotational direction of the stepping motor 20 can also be detected by determining the phase relationship of the rotational speed signal FG generated in each phase of the stepping motor 20. The positive threshold value + and the negative threshold value − may be diverted from those used in the out-of-synchronization detection unit 50.

  FIG. 11 is a diagram showing a configuration of the motor drive circuit 100 in which a feedback loop is added to the motor drive circuit 100 shown in FIG. In order to simplify the drawing, the amplifier 44, the digital low-pass filter 46, the differentiator 48, the out-of-synchronization detection unit 50, the rotation speed detection unit 60, the first zero cross detection unit 70, and the second zero cross detection unit 72 are omitted. I'm drawing.

  The motor drive circuit 100 shown in FIG. 11 has a selector 76, a subtracter 90, a compensation filter 92, a selector 94, an adder 96, a selector 98, and a step-out prediction determination unit 80 added to the motor drive circuit 100 shown in FIG. It is the structure which was made.

  The selector 76 alternately selects and outputs the first phase difference signal Pp and the second phase difference signal Pz output from the phase difference detector 74. Thereby, the phase difference signals are combined into one system. The subtractor 90 generates a deviation signal by subtracting the phase difference signal input from the selector 76 from a predetermined target phase difference Tp.

  The compensation filter 92 filters the deviation signal input from the subtracter 90 to generate a control signal. For example, when the compensation filter 92 is configured by a PI compensator, the PI compensator multiplies the deviation signal by a proportional gain Kp and an integral gain Ki / s, adds both calculation results, and outputs a control signal. Generate. The PI compensator basically keeps the previous value while the stepping motor 20 is stopped, and operates by clearing the previous value at a specific time. The specific period is immediately after a system reset or at the time of restart after a step-out. During operation of the stepping motor 20, it continues to operate.

  The signal adjustment unit 14 calculates the phase difference detected by the phase difference detection unit 74 based on the control signal F0 generated by the compensation filter 92 or the control signal F0 after the offset value is added by the adder 96. The drive signal S0 is adjusted so as to approach the target phase difference Tp. More specifically, the amplitude of the drive signal S0 is adjusted. When the phase of the speed electromotive force component Ev is delayed, the amplitude of the drive signal S0 is attenuated, and when the phase of the speed electromotive voltage component Ev is advanced, the amplitude of the drive signal S0 is increased.

  Here, the controlled object is a phase difference. Since this phase difference changes depending on the drive current, the feedback loop is a current loop. The phase difference is a phase difference between the scaled drive signal Ss and the speed electromotive voltage component Ev. In the case of the stepping motor 20, as described above from the operation condition, the phase difference between the drive voltage and the drive current is obtained. The phase difference can be ignored. This is because the stepping motor 20 is basically operated so that the stator current reaches a steady state for each step.

  The target phase difference Tp is set within the range of the phase of the speed voltage component Ev by 90 ° to 0 ° with respect to the phase of the scaled drive signal Ss. The target phase difference Tp is determined in accordance with the system to be applied within the range. In practice, the angle is often set to 0 ° with a predetermined margin.

  As the phase difference is smaller, the drive current is reduced and the power consumption can be reduced. However, the stop position accuracy for each step of the stepping motor 20 is lowered. That is, power consumption and stop position accuracy are in a trade-off relationship. The maximum efficiency point of the stepping motor 20 is at a position where the phase of the current is advanced by 90 ° with respect to the rotor 26. However, in this embodiment, the operation is performed at the minimum point of the total power consumption even if the efficiency is reduced. Therefore, the target phase difference is set between + 90 ° and 0 °.

  If the target phase difference is less than + 90 °, the basic operating condition of the stepping motor 20 that the stator current reaches the steady state for each step cannot be strictly met. Therefore, when the rotor 26 included in the stepping motor 20 moves from a certain stop position (point A) to the next stop position (point B), the signal adjustment unit 14 changes the phase difference to the target phase difference. The adjustment of the drive signal for approaching is executed, and when the rotor 26 is stopped at the stop position, the adjustment of the drive signal is stopped. That is, driving with low power consumption is limited to a period from the start of movement in the movement from point A to point B until just before point B is reached.

  The selector 98 selects and outputs the feedback control signal F0 when the rotor 26 is moving from one stop position (point A) to the next stop position (point B). When the rotor 26 is stopped, the set value Cs at the time of stop is selected and output. The stop-time set value Cs is a value set in advance to ensure sufficient stop position accuracy. It may be a fixed value or a fluctuation value corresponding to the excitation speed. Note that the switching control of the selector 98 is performed by a host control device (not shown).

  The selector 94 selects the first offset value Kf and the second offset value Cf and outputs them to the adder 96. The first offset value Kf is a value that varies according to excitation speed information so that stable operation is possible even when the rotation speed of the stepping motor 20 is switched. The first offset value Kf is controlled to increase when the excitation speed is high and to decrease when the excitation speed is low. This is because if the load is the same, a large torque is required when the speed is high, and a small torque is sufficient when the speed is low.

  The second offset value Cf can be set to an arbitrary value, and is selected when it is desired to start operation from an arbitrary drive amount when the operation of the stepping motor 20 is started. Thereby, after the operation is started, the phase difference can be converged earlier than the target phase difference. The switching control of the selector 94 is also performed by a host controller (not shown).

  The adder 96 adds the offset value input from the selector 94 to the control signal input from the compensation filter 92 and outputs the result to the selector 98.

  The step-out prediction determination unit 80 compares the differential value of the phase difference detected by the phase difference detection unit 74 with a detection threshold for step-out prediction, and predicts the occurrence of step-out. The detailed configuration of the step-out prediction determination unit 80 will be described later.

  The motor drive circuit 100 detects the phase difference of the first coil 22 and adjusts the drive signal S0 of the first coil 22 so that the phase difference approaches the target phase difference Tp. In the embodiment, the drive signal of the second coil 24) is adjusted. That is, the control signal F0 is also supplied to the other-phase signal adjustment unit (ATT) via the selector 98. Thereby, the current ratio between the first coil 22 and the second coil 24 can be maintained. The signal adjustment unit 14 may adjust both the drive signal for the first coil 22 and the drive signal for the second coil 24.

  FIG. 12 is a view showing a modification of the motor drive circuit 100 shown in FIG. The motor drive circuit 100 shown in FIG. 12 has a configuration in which an averaging unit 78 is added to the motor drive circuit 100 shown in FIG. The averaging unit 78 is inserted between the selector 76 and the subtracter 90. In the present modification, the phase difference of the other-phase coil (second coil 24 in the present embodiment) is also detected. Although omitted in FIG. 12, the same circuit element as the circuit element for detecting the phase difference of the first coil 22 is separately provided for the second coil 24.

  The motor drive circuit 100 shown in FIG. 12 detects the phase difference of the first coil 22 and the phase difference of the other-phase coil (second coil 24 in the present embodiment), and averages the phase differences. The drive signal S0 of the first coil 22 and the drive signal of the other-phase coil (second coil 24 in the present embodiment) are adjusted so as to approach the target phase difference Tp. The phase difference of the first coil 22 and the phase difference of the second coil 24 are averaged by the averaging unit 78.

  When the phase difference of the first coil 22 and the phase difference of the second coil 24 are detected and the drive signals are adjusted independently, the current ratio between the first coil 22 and the second coil 24 is destroyed. In the two-phase motor as in the present embodiment, the phase difference detection timing is substantially the same for each phase. Therefore, a window for capturing the phase difference of the other phase is provided in the averaging unit 78, and after averaging the phase difference of the first coil 22 and the phase difference of the second coil 24, a common feedback system is obtained. The common control signal F0 is supplied to the signal adjustment units of the first coil 22 and the second coil 24. Thereby, the feedback control which considered the response of the mutual phase is attained, without destroying the current ratio of the 1st coil 22 and the 2nd coil 24.

  FIG. 13 is a diagram illustrating a configuration of the step-out prediction determination unit 80. The step-out prediction determination unit 80 includes a differentiator 82 and a phase determination unit 84. The differentiator 82 and the phase determination unit 84 are each input with the phase difference from the phase difference detection unit 74 via the selector 76. The differentiator 82 differentiates the input phase difference to generate a phase difference differential value Pd and outputs it to the phase determination unit 84.

  FIG. 14 is a timing chart illustrating an operation example of the phase determination unit 84. The phase determination unit 84 compares the phase difference differential value Pd supplied from the differentiator 82 with a detection threshold value for step-out prediction, and when the phase difference differential value Pd exceeds the detection threshold value in the phase delay direction, The step-out prediction signal SOP is set to a high level. After that, the phase determination unit 84 compares the phase difference input from the phase difference detection unit 74 via the selector 76 with the return threshold value, and when the phase difference exceeds the return threshold value in the phase advance direction, The key prediction signal SOP is set to a low level.

  The period when the step-out prediction signal SOP is high indicates that the risk of step-out occurrence is high. The detection threshold and the return threshold can be set by the designer or the user according to the desired step-out prediction sensitivity.

  Returning to FIGS. 11 and 12, the selector 98 selects the step-out prediction time set value Ca and supplies it to the signal adjustment unit 14 while the step-out prediction signal SOP is at a high level. The step-out prediction setting value Ca is set to a value necessary and sufficient to cause the stepping motor 20 to generate a large torque. Therefore, the step-out prediction set value Ca is a value equal to or greater than the stop-time set value Cs.

  The signal adjustment unit 14 supplies the drive signal S0 so as to increase the current flowing through the first coil 22 during the period when the step-out prediction time set value Ca is supplied (that is, the period when the step-out prediction signal SOP is at a high level). adjust. More specifically, the amplitude of the drive signal S0 is increased.

  When the supply of the step-out prediction time set value Ca is completed (that is, when the step-out prediction signal SOP returns to the low level), the signal adjustment unit 14 ends the adjustment of the drive signal S0. The processing during the period in which the signal adjustment unit 14 is supplied with the control signal F0 or the set value Cs when stopped is as described above. Thus, the prediction determination process by the step-out prediction determination unit 80 can predict and avoid step-out when the load change is large with respect to the generated torque.

  As described above, according to the present embodiment, by performing feedback control so that the phase difference between the scaled drive signal Ss and the speed electromotive force component Ev approaches the target phase difference Tp, high motor efficiency is achieved. Driving can be realized at low cost. Compared with the method of estimating the rotor position using vector calculation, the circuit can be greatly simplified. In addition, by setting the feedback control target as the amplitude of the drive signal S0, it is possible to simplify the circuit elements of the feedback control system. Further, compared to a method of detecting the speed electromotive voltage only in the high impedance state, the speed voltage component can be detected without losing the continuity of the current, so that driving noise can be reduced.

  Moreover, power consumption can be reduced by setting the target phase difference Tp between + 90 ° and 0 °. Further, when the rotor 26 is stopped, the feedback control is stopped, and the drive signal S0 is controlled by another set value, so that the stop position accuracy of the rotor 26 can be ensured. Therefore, it is possible to satisfy both the demand for reducing power consumption and the demand for ensuring stop position accuracy.

  Further, step-out can be predicted by observing the differential value of the phase difference. In particular, a step-out due to a sudden change in load can be predicted. When the risk of step-out is predicted to be high, step-out can be avoided by adjusting the drive signal S0 so as to increase the torque. At this time, the circuit element of the step-out avoidance system can be simplified by adjusting the amplitude of the drive signal S0 to increase the torque. Many of the circuit elements can be shared with the circuit elements of the feedback control system.

  The present invention has been described based on some embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  DESCRIPTION OF SYMBOLS 10 Excitation timing production | generation part, 12 Excitation amplitude production | generation part, 14 Signal adjustment part, 16 PWM signal production | generation part, 18 H bridge drive part, 20 Stepping motor, 22 1st coil, 24 2nd coil, 26 Rotor, Rs stator resistance, 30 coil current detection unit, 31 differential amplifier, 32 offset adjustment unit, 33 analog-digital converter, 34 differential amplifier, 35 low-pass filter, 36 sign determination unit, 38 scaling unit, 40 comparison adjustment unit, 42 induced voltage component extraction Unit, 44 amplifier, 46 digital low-pass filter, 48 differentiator, 50 out-of-synchronization detection unit, 52 variable threshold setting unit, 54 continuous determination unit, 60 rotation speed detection unit, 62 first hysteresis comparator, 64 second hysteresis comparator 66 exclusive OR circuit, 70 first zero cross detection unit, 72 second zero cross detection unit, 74 phase difference detection unit, 76 selector, 78 averaging unit, 80 step out prediction determination unit, 82 differentiator, 84 phase determination unit , 90 subtractor, 92 compensation filter, 94 selector, 96 adder, 98 selector, 100 motor drive circuit.

Claims (5)

A drive unit for supplying current to the coil of the synchronous motor according to the drive signal;
A coil current detector for detecting a current component flowing in the coil;
A scaling unit for scaling the drive signal;
An induced voltage component extracting unit that extracts the induced voltage component by removing the drive signal scaled by the scaling unit from the coil current component detected by the coil current detecting unit;
A phase difference detector that detects a phase difference between the phase of the drive signal and the phase of the induced voltage component;
A step-out prediction determination unit that compares the differential value of the phase difference detected by the phase difference detection unit with a detection threshold for step-out prediction and predicts out-of-step occurrence;
A motor drive circuit comprising:   The scaling unit scales the drive signal using a scaling factor that defines a relationship between the drive signal and a coil current component detected by the coil current detection unit when an induced voltage generated in the coil is zero. The motor drive circuit according to claim 1. A drive signal adjustment unit for adjusting the drive signal;
The drive signal adjustment unit adjusts the drive signal so as to increase a current flowing through the coil when a differential value of the phase difference exceeds the detection threshold in a phase delay direction. The motor drive circuit described.   The drive signal adjustment unit increases the current that flows through the coil when the differential value of the phase difference exceeds the detection threshold value in the phase delay direction and then the phase difference exceeds the return threshold value in the phase advance direction. The motor drive circuit according to claim 3, wherein the adjustment of the drive signal is terminated.   The motor drive circuit according to claim 3, wherein the drive signal adjustment unit adjusts an amplitude of the drive signal.

Images