JP2016073168A - Current detection gain switching method and apparatus for stepping motor driver circuit - Google Patents

Abstract

PURPOSE: To avoid degradation in an S/N ratio at a normal operation even after a motor current increases during an excitation detection operation.CONSTITUTION: The stepping motor driver circuit (20), including current detection circuits (23) (24) of motor currents and controlling so that an electric current corresponding to a command value runs through by feeding back a detection current, is configured to switch a gain of the current detection circuit and to switch so that the gain is decreased according to an increase in a motor current during an excitation detection operation. By switching connections of resistors R,R,R,Rof the current detection circuits, the gain is switched.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method and apparatus for switching the gain of a motor current detection circuit included in a drive circuit for a stepping motor.

  In the closed loop control of the stepping motor using the angle detection signal from the absolute encoder, the phase relationship between the rotor and the stator of the stepping motor can always be grasped. It is easy to determine the phase. However, since an absolute encoder is expensive, an incremental encoder is often used in closed-loop control. Incremental encoders do not know the absolute value of the rotation angle, but can only detect the change in rotation angle. Therefore, the excitation detection operation (magnetic pole determination operation or excitation phase signal detection) is performed when the stepping motor is energized for the first time (when the power is turned on). Operation) is required.

  The excitation detection operation is performed at the first energization in order to grasp the phase relationship between the rotor and the stator of the stepping motor (to ensure electrical angle consistency and to determine the magnetic pole position). An example is described in Patent Document 1, and a further improved control method is described in Patent Document 2.

Japanese Patent No. 4416541 JP 2014-57461 A

  In the excitation detection operation, the rotor is forcibly rotated to a position (excitation stable point) where the rotor magnetic pole faces the stator magnetic pole. Therefore, it is preferable to increase the output torque. This point is not described in the above Patent Documents 1 and 2.

  In order to increase the output torque, it is conceivable to increase the energization current to the motor. A stepping motor drive circuit is provided with a current detection circuit for current feedback control. When the motor current is increased in the excitation detection operation, the maximum value of the dynamic range of the current detection circuit must be set to a range where the increased motor current can be detected. Assuming that the motor current is set to twice that in normal operation in the excitation detection operation, the current detection circuit operates only within a range of half of the set full scale when shifting to normal operation. If it does so, S / N ratio will fall and noise resistance will worsen, and generation | occurrence | production of a vibration etc. is anxious about especially a low current region.

  The present invention makes it possible to expand the actual specification range without reducing the S / N ratio.

  In other words, an object of the present invention is to maintain a high S / N ratio during normal operation (operation other than the excitation detection operation) even if the motor current is increased during the excitation detection operation.

  Furthermore, the present invention provides a configuration in which the gain of the current detection circuit can be switched so that it can be shared by a plurality of types of stepping motors with different specifications (rated current, etc.), and the gain switching circuit can be used to detect the excitation of a stepping motor of a specific specification. It is intended to be used sometimes.

  A stepping motor drive circuit current detection gain switching method according to the present invention includes a motor current detection circuit, wherein the current detection circuit feeds back the detection current and controls the current to flow according to a command value. The gain of the detection circuit can be switched, and the gain is switched to decrease as the motor current increases during the excitation detection operation.

  A current gain switching device for a stepping motor drive circuit according to the present invention is a stepping motor drive circuit that feeds back a detected motor current and controls a current according to a command value to flow. , And switching means for switching so as to reduce the gain of the current detection circuit in accordance with an increase in the motor current during the excitation detection operation.

  When the motor current is increased to increase the torque in the excitation detection operation, the gain of the current detection circuit is reduced by the amount corresponding to the increased motor current, and the maximum level of the output voltage of the motor current detection circuit is Both the excitation detection operation and the normal operation are set to approximately the same level. Therefore, the dynamic range of the current detection circuit (the range in which the current detection signal changes) is maintained at almost the same level at any time, and the S / N ratio can be maintained at the same level at any time. The range of actual specifications can be expanded without reducing the S / N ratio.

  In one embodiment, the current detection circuit includes a plurality of resistors that determine its gain. The switching of the current detection gain is realized by switching the connection of these resistors.

  The present invention is more effective when applied to a stepping motor drive circuit having a current detection circuit capable of switching the gain according to the type of the stepping motor so that it can be shared by a plurality of types of stepping motors having different specifications.

  In other words, the motor current can be switched in the excitation detection operation of at least one type of stepping motor by switching to the gain of the stepping motor of another type during the excitation detection operation of at least one type of stepping motor. Can be dealt with.

It is a functional block diagram which shows the drive system containing the drive circuit of a stepping motor. It is a circuit diagram which shows the specific structural example mainly of a current detection circuit. It is a flowchart which shows the process sequence of gain switching control. The electrical angle of a rotor and a stator is shown. Indicates the output signal pulse of the encoder.

  FIG. 1 is a functional block diagram of a drive system including a stepping motor drive circuit.

  The two-phase stepping motor 10 has an A phase (and an inverted phase of A, A bar. This is referred to as A_phase in the specification) and a B phase (and an inverted phase of B, B bar. It is driven by a drive current (motor current). An incremental encoder 11 is attached to the stepping motor 10, and encoder pulses representing the rotation speed of the motor 10 are output from the encoder 11, and the control device 30, the drive signal generation unit (circuit) 31, and the excitation detection control unit (circuit) Feedback to 32.

  When the stepping motor 10 is energized for the first time (when the power is turned on), an excitation detection operation is performed. Once the magnetic pole is determined by this excitation detection operation (when the rotor magnetic pole faces the stator magnetic pole and reaches a stable point), the stepping motor 10 is locked as it is or is operated in normal operation. An example of the excitation detection operation will be described later (also described in the aforementioned Patent Documents 1 and 2). The normal operation is driven by, for example, a microstep method. The normal operation is controlled by the drive signal generation unit 31, and the excitation detection operation is controlled by the excitation detection control unit 32. The drive signal generation unit 31 and the excitation detection control unit 32 can be realized as a part of the control device 30 incorporating software (computer program), or can be realized by a hardware circuit.

  The control device 30 is composed of a computer (CPU) and controls the above-described excitation detection operation and normal operation. In normal operation, the control device 30 activates the drive signal generation unit 31 (normal operation mode), generates a position command with a short cycle as an example, and provides the drive signal generation unit 31 with the rotation control of the stepping motor. It is done. As an example, the drive signal generation unit 31 includes a position control unit and a speed control unit. The (angle) position control unit generates a speed command based on the difference between the position command given from the control device 30 and the position detection signal (detection (angle) position) (position response) generated based on the encoder pulse. To do. The speed control unit generates a current command based on a difference between the speed command and a speed detection signal (detection speed) (speed response) created based on the encoder pulse. This current command includes A-phase and B-phase phase current commands. The operation of the speed control unit may be performed at a cycle shorter than the generation cycle of the position command.

  The motor drive circuit 20 includes current control circuits 21 and 22, an inverter 25 (shown as one block), and current detection circuits 23 and 24 for each of the A phase and the B phase. The current detection circuits 23 and 24 detect the motor currents of the A phase and the B phase, respectively, and a specific configuration example will be described later. The currents detected by these current detection circuits 23 and 24 are fed back to the current control circuits 21 and 22. Each of the current control circuits 21 and 22 generates a voltage signal to be applied to the inverter 25 by, for example, PID control based on the difference between the current command given from the drive signal generation unit 31 and the detected current of the current detection circuits 23 and 24. . The inverter 25 generates a control signal having a frequency corresponding to the input voltage signal for each of the A phase and the B phase, and turns on and off the switching elements (see symbols 28 and 29 in FIG. 2) provided in the motor current circuit. Control. Instead of the inverter 25, a PWM (Pulse Width Modulation) circuit may be used. Gain switching in the current detection circuits 23 and 24 is controlled by the control device 30.

FIG. 2 shows a specific configuration example of the current detection circuit 23 mainly for the A phase. As for the inverter, the portion related to the A phase is indicated by reference numeral 25A. The inverter 25A controls on / off of switching elements (FETs) 28, 29 of A phase and A_phase provided in the motor current circuit (stator coil wiring) of the stepping motor 10. The motor current circuit is connected to a current detection resistor R _S (in principle, both are indicated by R _S ) for detecting the A-phase and A_phase currents. The current detection circuit 23 generates a drop voltage V ₂ and V ₁ generated by a motor current (A_phase current is represented by i _A _ and A phase current is represented by i _A ) through these current detection resistors R _S. The voltage _Vout corresponding to the difference is detected.

The current detection circuit 23 is constituted by a differential amplifier circuit including an operational amplifier (OP amplifier) 26. The drop voltages V ₁ and V ₂ are connected to the inverting input terminal (inverting input side) and the non-inverting input terminal (inverted input side) of the operational amplifier 26 via resistors R ₁ (both are indicated by R ₁ since they have the same resistance value in principle). Input to non-inverting input side. Between the inverting input terminal and the output terminal (output side) of the operational amplifier 26, resistors R ₂₁ , R ₂₂ , R ₂₃ , R ₂₄ are connected via switches (for example, semiconductor switching elements) 41, 42, 43, 44, respectively. Are connected in parallel. Similarly, between the non-inverting input terminal and the output terminal of the operational amplifier 26, switches (for example, semiconductor switching elements) 41, 42, 43, 44 (on / off control is performed simultaneously with the non-inverting switch). Having the same resistance value as the resistors R ₂₁ , R ₂₂ , R ₂₃ , R ₂₄ connected to the inversion side through the resistors R ₂₁ , R ₂₂ , R ₂₃ , R ₂₄ Are shown in parallel with each other).

The switches 41, 42, 43, and 44 are controlled by a gain switching signal from the control device 30. For example, when the switch 41 is turned on, the other switches 42, 43 and 44 is off, the inverting side and the non-inverting side of the two feedback resistors R ₂₁ is inverted, is connected by between the non-inverting input and output sides . The other resistors R ₂₂ , R ₂₃ , and R ₂₄ are also connected between the inverting and non-inverting input sides and the output side when the switches 42, 43, and 44 are turned on, respectively. Only one of the switches 41, 42, 43, and 44 is controlled to be turned on, and the others are controlled to be turned off. However, it is also possible to change the resistance value by simultaneously turning on two or more switches and connecting two or more feedback resistors in parallel. A voltage of V _P / 2 is applied to the terminal opposite to the non-inverting input terminal of the resistors R ₂₁ , R ₂₂ , R ₂₃ and R ₂₄ connected to the non-inverting input side with the power supply voltage as V _P. .

The output voltage V _out of the current detection circuit 23 is given by the following equation, where the feedback resistor connected by any of the switches 41, 42, 43, 44 is represented by R _2i .

V _out = (V _P / 2) + (R _2i / R ₁ ) (V ₂ −V ₁ ) Equation (1)
V ₁ = i _A _ · R _S (2)
V ₂ = i _A · R _S (3)

The motor currents i _A and i _A _ are currents of opposite phases. (R _2i / R ₁ ) represents the current detection gain.

Since four types of feedback resistors R ₂₁ , R ₂₂ , R ₂₃ , and R ₂₄ having different resistance values are connected to the current detection circuit 23, the gain of the current detection circuit 23 can be switched in four stages.

  The main reason why four types of resistors are provided in the current detection circuit 23 and the gain is switched in four stages is as follows.

  That is, the stepping motor drive system shown in FIG. 1 including the motor drive circuit 20 including the current detection circuits 23 and 24 can be shared for driving a plurality of types (four types) of stepping motors. The four types of specifications are specifications 1, 2, 3, and 4, and the ratio of the rated current values is 1: 2: 3: 4 for simplicity. The rated current of the stepping motor of specification 1 is the smallest. The rated current of the stepping motor of specification 4 is the largest and is four times the rated current of the stepping motor of specification 1.

In equation (1), since the resistance R ₁ on the input side of the operational amplifier 26 is fixed, the current detection gain is determined by the value of the feedback resistance R _2i . The value of the feedback resistor R _2i is expressed as a ratio thereof, and R ₂₁ : R ₂₂ : R ₂₃ : R ₂₄ is set to 4: 3: 2: 1 (specific resistance of the resistor R _2i The value may be determined appropriately according to the value of other resistor R ₁ and other conditions). When driving the stepping motor of the specification 1, the switch 41 is turned on, the other switches 42 to 44 are turned off, and only the resistor R ₂₁ is connected between the input side and the output side of the operational amplifier 26. When this drive system is used to drive stepping motors of other specifications 2, 3, and 4, the switches 41 to 41 are connected so that the resistors R ₂₂ , R ₂₃ , and R ₂₄ are connected and the other resistors are disconnected. Control 44. According to such an operation method, the ratio of the current detection gain when the stepping motors of specifications 1, 2, 3, and 4 are operated (during normal operation) is 4 to 3 to 2 to 1. (Assuming that the DC component V _P / 2 is excluded. It is possible to remove this by setting an offset appropriately.)

  Thus, by reducing the current detection gain as the rated current is larger, the dynamic range of the output of the current detection circuit can always be kept within substantially the same range.

A current detection circuit having a plurality of switchable current detection gains can also be used for switching the current detection gain between the excitation detection operation and the normal operation of a stepping motor having a specific specification. Resistor R ₂₁ is selected during normal operation of most small Specifications 1 stepper motor rated current. When the resistance R ₂₂ is selected during the excitation detection operation of the stepping motor of this specification 1, the current detection gain becomes 1/2 of that during normal operation. That is, even if twice the motor current is passed through the stepping motor in order to increase the torque during the excitation detection operation, the dynamic range of the output voltage of the current detection circuit falls within substantially the same range as during normal operation. In other words, normal operation that keeps the output voltage range of the current detection circuit within the specified full scale even when twice the motor current is passed during excitation detection operation, and also halves the motor current during excitation detection operation. Even at times, the output voltage of the current detection circuit can be kept within the same full scale. Since a situation in which the change in the output voltage of the current detection circuit falls within a small range during normal operation can be avoided, the S / N ratio of the motor drive circuit is not lowered.

In the above example, the stepping motor of specification 2 can cope with flowing a motor current twice that in the normal operation during the excitation detection operation by switching the feedback resistors R ₂₂ and R ₂₄ .

  The numerical values such as the above two times or the resistance value ratio of 1: 2: 3: 4, etc. are for easy understanding and are not limited thereto.

The current detection circuit shown in FIG. 2 is designed so that the current detection gain can be switched in four stages in order to be shared by four types of stepping motors. If only the current detection gain is switched between the excitation detection operation and the normal operation, it is sufficient that at least two stages of current detection gain switching can be performed. For example, only resistors R ₂₁ and R ₂₂ are connected so as to be switchable for a stepping motor of a specific specification (other resistors R ₂₃ and R ₂₄ are not provided). The resistor R ₂₂ is connected at the time of excitation detection operation, the resistance R ₂₁ disconnected, during the normal operation by connecting a resistor R _21, detach so the switches 41 and 42 a resistor R ₂₂ ON may be off control.

  FIG. 3 shows a control processing procedure by the control device 30 when shifting from the excitation detection operation to the normal operation. The current detection gain during normal operation is G1, the current detection gain during excitation detection operation is G2, and the gain ratio in both of these states is n.

    n = G1 / G2 Equation (4)

When starting the excitation detection operation, the control device 30 activates the excitation detection control unit 32 (excitation detection operation mode) (at this time, the drive signal generation unit 31 is inactive). Further, the current detection gain of the current detection circuits 23 and 24 is set as a gain G2 in the excitation detection operation. This, for example, by turning on the switch 42 to connect the resistor R _22, turns off all the other switches are realized by disconnecting the other resistor. Further, the current command value (command current value) given to the excitation detection control unit 32 is set to n times the normal operation. The stepping motor is supplied with a motor current n times that of the normal operation, and the excitation detection operation is performed with a large torque (S1).

  When the magnetic pole is determined, the control device 30 reduces the command current value to 1 / n during the excitation detection operation, and keeps the gain of the current detection circuit at G2 (S2). Since the current detection gain is maintained at a value smaller than the gain G1 during normal operation, the output voltage of the current detection circuit decreases and the S / N ratio also decreases, but this is a very short time.

Since the magnetic pole has been determined, the control circuit 30 locks as all-phase excitation when holding (standby) as it is, and when starting the stepping motor, the excitation detection control unit 32 is deactivated and the drive signal generation unit 31 is activated to start. Give a command and switch to normal operation. Further, the gain of the current detection circuit is switched to G1 (S3). In the circuit of FIG. 2, this is realized by turning off the switch 42 to disconnect the resistor R ₂₂ and turning on the switch 41 to connect the resistor R ₂₁ . Since the current detection gain increases to G1, the current detection circuit operates again within the full scale range, and the S / N ratio is improved.

  Finally, an example of the excitation detection operation by the control device 30 and the excitation detection control unit 32 will be described.

It is assumed that the stepping motor 10 has a 50-pole electrical angle pair and the encoder 11 has a resolution of 800 per mechanical angle rotation. There are 50 electrical angles in one rotation of the mechanical angle (1 rotation). Therefore,
800 pulses / 50 laps = 16 pulses / lap ...... Formula (5)
Thus, one electrical angle (360 degrees) is 16 resolution.

  FIG. 4 represents a circle of one electrical angle. The inner circle is the rotor and the outer circle is the stator. In the stator, one electrical angle is divided into 16 and numbers 1 to 16 are assigned clockwise. An electrical angle of 0 degrees is a stator (angle) position 1. The stator positions 1 to 4 are the first quadrant, the stator positions 5 to 8 are the second quadrant, the stator positions 9 to 12 are the third quadrant, and the stator positions 13 to 16 are the fourth quadrant.

  FIG. 5 shows an output pulse signal of the encoder 11. There are two phases in the output of the encoder 11, which are referred to as pulse signals Sa and Sb. The signals Sa and Sb take H (high) level and L (low) level, respectively. A combination of the levels of the signals Sa and Sb is expressed as HH, LH, LL, and HL. The change in the combination is counted by a counter (not shown), and the value of the counter is incremented by 1 each time it changes. 16 counts per electrical angle.

  When the motor current power line is energized only in phase A and the rotor is electromagnetically locked, the encoder is adjusted so that the combination of the output signals is HH. Similarly, it is assumed that the combination of encoder output signals is LH when the stator current vector faces the stator position 2, LL when the stator position 3 faces, and HL when the stator position 4 faces.

  This excitation detection operation is devised to complete excitation detection with as little rotor movement as possible, and comprises an excitation stage, a rotation stage, and an end (magnetic pole determination) stage. Under the command of the control device 30 (including the A-phase and B-phase current commands), the excitation detection control unit 32 controls the motor drive circuit 20 as follows.

  First, at the excitation stage, the encoder output signal level combination is sampled simultaneously with the start of the magnetic pole detection operation. Assuming that the position where the rotor and the stator face each other is in the first quadrant, the A phase and B phase currents (n times the above-mentioned current) are very small in the same phase as the combination of the sampled signals Sa and Sb. Energized by energizing for a period of time (A phase corresponds to signal Sa and B phase corresponds to signal Sb). If the count value (the number of changes in the combination of encoder output signals) is 0 or 1 after excitation energization, and that state continues for a predetermined time (much longer than the energization time), there is a possibility that the magnetic pole is in a fixed state. Since it is high, move to the rotary stage.

  If the count value is 2 or more, change the excitation energization position. For example, when energizing the stator position 15 starting from the stator position 1 and energizing the stator position 15, energizing energizing the stator position 5 starting from the stator position 3 and counting down 2 times.

  The above steps are repeated, and when the count reaches 0 or 1, this excitation stage ends. Normally, this excitation stage can be completed within an electrical angle of 90 degrees. However, if the excitation energization position is changed 10 times, a retry is made, and if the retry is made 10 times, an error is stopped.

  In the rotary stage, the stator current vector is smoothly rotated by one electrical angle or more so as to go from the final excitation energization position to the electrical angle of 0 °.

  In the final end (magnetic pole determination) stage, excitation energization to an electrical angle of 0 degrees is maintained for a predetermined time. Thereafter, the encoder signal level is sampled. If the combination of the encoder signal levels is HL, the current position of the rotor is normally terminated as an electrical angle 16, if it is HH, the electrical angle is 1 and if it is LH, it is normally terminated as an electrical angle 2. In the case of LL, it is judged as illegal and a retry is made.

10 Stepping motor
11 Encoder
20 Motor drive circuit
21, 22 Current control circuit
23, 24 Current detection circuit
25, 25A inverter
26 Operational amplifier
28, 29 Switching element (FET)
30 Control unit
31 Drive signal generator
32 Excitation detection control section
41, 42, 43, 44 switch (semiconductor switching element)
R _S current detection resistor R ₁ resistor connected to R ₁ input side R ₂₁ , R ₂₂ , R ₂₃ , R ₂₄ feedback resistor

Claims (6)

In a stepping motor drive circuit that has a current detection circuit for motor current and controls the current to be fed according to the command value by feeding back the detection current.
The gain of the current detection circuit can be switched,
Switch to decrease gain according to motor current increase during excitation detection operation.
Stepping motor drive circuit current detection gain switching method. A plurality of resistors for determining the gain of the current detection circuit;
The method for switching the current detection gain of the stepping motor drive circuit according to claim 1, wherein the connection of these resistors is switched. Equipped with a current detection circuit that can switch the gain according to the type of stepping motor so that it can be shared by multiple types of stepping motors with different specifications.
When the excitation detection operation of at least one type of stepping motor is performed, the gain is switched to the gain of another type of stepping motor.
The method for switching the current detection gain of the stepping motor drive circuit according to claim 1. In the stepping motor drive circuit that feeds back the detected motor current and controls the current according to the command value to flow.
A current detection circuit of a motor current capable of gain switching, and a switching means for switching to reduce the gain of the current detection circuit in accordance with an increase in motor current during excitation detection operation;
A current detection gain switching device for a stepping motor drive circuit comprising: A plurality of resistors for determining the gain of the current detection circuit;
5. The current detection gain switching device for a stepping motor drive circuit according to claim 4, wherein the switching means switches connection of these resistors. Provided with the current detection circuit that can switch the gain according to the type of stepping motor so that it can be shared by multiple types of stepping motors with different specifications,
The switching means is for switching so as to obtain a gain of a stepping motor of another type at the time of excitation detection operation of at least one type of stepping motor.
The current detection gain switching device for a stepping motor drive circuit according to claim 4.

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