JP2731554B2 - Stepping motor control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a stepping motor capable of stopping with high accuracy, maintaining positioning accuracy, and saving energy.

[Prior Art] A stepping motor is used as a drive source of a device that requires precise control because it can perform accurate rotation angle control. The driving method of the stepping motor is distinguished by the way of exciting the coil, but in the case of a four-set motor as an example, the four-phase motor is, as shown in FIG. A rotor RT is provided, and the rotor RT is magnetized in a half area around the rotor, one of which is magnetized to the north pole of the permanent magnet and the other is magnetized to the south pole. The stator ST is formed with teeth in order to form magnetic poles of the stator at different positions by 90 degrees, and a coil is wound around the teeth. The coil is wound so that the opposite magnetic poles of the stator have different polarities.

The method of driving, that is, the phase excitation, differs depending on how a current flows through the coil of the motor, and is roughly classified into unipolar driving and bipolar driving.

Here, the unipolar drive means that two coils of two systems are wound in opposite windings on opposite magnetic poles of the stator ST, respectively, and each of the coils has a common end on the other end side. Each coil is connected to a common, and one end of each coil is provided with a switching transistor, and the common side is connected to, for example, the positive side of the DC power supply V, and each transistor side is connected to the negative side. At the same time, the coils are excited by switching each transistor in sequence with the phase shifted, and the rotor RT is rotated. This method allows current to flow through each coil in only one direction, and is called unipolar drive (unipolar drive), and the control is simplest and the configuration of the drive circuit is simple.

In the bipolar drive, a single coil system is used to control the direction of current by changing the polarity of direct current applied to the coil. For example, a four-phase bipolar type will be described with reference to FIG. As described above, the coils L1 and L2 are wound around the opposing poles SP1 and SP3 and SP2 and SP4 of the stator ST by one winding each, and a current flows from the φ1 side (φ2 side) or from the φ3 side (φ4 side). This is a system in which the direction of the current is changed by flowing a current to excite. Therefore, as shown in FIG. 6, the driving circuit is constructed by connecting the transistors Q31 to Q34 and Q35 to Q38 by bridge connection, respectively.
A set of bridge connection circuits is formed, and the corresponding coils L1 and L2 are connected between the bridge midpoints. Then, these transistor bridges are connected to the DC power supply V. Each of the transistors Q31 to Q34 and Q35 to Q38 has a transistor protection diode D31 between its emitter and collector.
To D34 and D35 to D38. Then, among the transistors, Q31 in the diagonal position of the bridge
By turning on / off Q34, Q32 and Q33, Q35 and Q38, Q36 and Q37 according to the excitation sequence, the excitation control and the excitation direction of the coils L1 and L2 are performed.

The stepping motor can be driven by performing excitation by these driving methods, and this will be described below with reference to FIGS. 7 and 8, taking bipolar driving as an example.

That is, when Q31 and Q34 are turned on,
The current i1 flows to the side 3 and the upper and lower poles of the stator ST are excited in FIG. 5 to be in the state of FIG. 8 (a). When Q35 and Q38 are turned on, the current i2 flows from the terminal φ2 to the φ4 side from the terminal φ2. And the poles at the left and right positions in FIG. 5 are excited to be in the state of FIG. 8 (b). When Q33 and Q32 are turned on, the terminal φ3
Current i3 flows from the φ1 side to the φ1 side, and the upper and lower poles of the stator ST of FIG. 5 are excited to be in the state of FIG.
7, When Q36 is turned on, a current i4 flows from the terminal φ4 side to the φ2 side, and the poles at the left and right positions in FIG. 5 are excited to be in the state of FIG. 8D, and so on. By turning on / off the transistors one by one while changing the phase sequentially, the transistors can be driven to rotate.

The above is an example of one-phase excitation.
There is a sequence called -two-phase excitation or the like.

By the way, in such a stepping motor,
Assuming that a certain pole of the stator ST is excited, the rotor RT rotates with its opposite polarity attracted to the excited pole. Assuming that the excitation pole of the rotor RT is fixed in this state, as shown in FIG. 10 (a), the rotor RT tends to go further from the stable point B in the rotation direction due to its inertia force (point A → point B → C
Point), if it goes too far, a pull-back torque is generated, and a force for pulling back to a stable point acts (point C → point D → point E). By repeating such an operation, the vibration of the rotor in the rotation direction is generated. However, the magnetic flux Φ is generated from the exciting magnetic pole of the stator with the maximum point at the stable point B or D. (Fig. 10 (b))
Assuming that the above-described vibration of the rotor causes a change in magnetic flux Φ according to the amount of deviation of the rotor from a stable point as shown in FIG. 10 (c), a counter electromotive voltage as shown in FIG. 10 (d) is generated. Will be. This generates an oscillating current by affecting the exciting current. That is, the exciting current has a magnitude obtained by dividing the sum of the power supply voltage V and the oscillating voltage by the resistance of the coil. The vibration of the rotor affects the stop position accuracy due to the relationship between the stiffness characteristic of the stepping motor and the frictional resistance of the motor and the pulling drive system.

Here, the stiffness characteristic (Stiffness) of the stepping motor is a characteristic indicating the relationship between the displacement of the rotor with respect to the excitation pole of the stator and the return to a stable point, for example, as shown in FIG. Referring to FIG. 9, when the position of the rotor deviates from the stable point in the excited state, a reverse torque is generated in the rotor. This torque is the hold torque of I. Further, even when the excitation of the excitation pole is released, if the excitation pole is shifted from the stable point, a torque to be attracted to the magnetic pole is generated, which is a force to pull back the rotor. This torque is the detent torque of II.

Here, if the friction resistance Tf exists, this friction resistance
Since the rotor cannot be rotated without torque enough to overcome Tf, the rotor has a dead zone corresponding to the rotation angle ± θ due to the frictional resistance Tf, and a stationary angle error corresponding to the dead zone is generated.
This corresponds to θ1 for the hold torque I and θ2 for the detent torque II, and it can be seen that the stationary angle error when trying to hold only the detent torque II having a small torque is larger. On the other hand, to save energy, the hold torque stable point and the detent
By using a motor having the same torque stable point, a control method is used in which after the driving is completed, the energization is stopped and the rotor is held by the detent torque. In this case, since the detent torque is much smaller than the hold torque, the angle shift corresponding to θ described above becomes very large. Therefore, when the above-described stepping motor control method is adopted, it is necessary to sufficiently attenuate the vibration of the rotor by the hold torque during energization, then stop the energization, and hold the rotor by detent torque.

[Problems to be Solved by the Invention] As described above, in a stepping motor, a pair of stator coils having a pair of poles are wound around the same wire, and are wound so as to have opposite polarities. In addition, the unipolar type has a two-system coil winding configuration in which another winding is wound in the opposite polarity, and the winding of each coil has a common terminal at one end and a positive electrode at the other end according to a predetermined excitation sequence. By applying the voltage on the side, the rotor is rotated.

On the other hand, the rotor is rotated by such excitation to drive and drive the object to be driven. However, in precision equipment, it is necessary to accurately stop the rotor at a desired rotation angle in order to perform precise drive control. For this reason, the magnetic pole corresponding to the rotation angle to be stopped in the stator is excited, the rotor is attracted here, the excitation is released when the rotor is stopped, and control is performed so that the position of the rotor is maintained only by the detent torque. Due to the inertial force of the rotor, repeated vibrations in the direction of rotation of the rotor are inevitable until the rotor completely stops. Therefore,
After sufficiently attenuating the vibration with the hold torque, the rotor is held with the detent torque.In this case, under normal operating conditions, the vibration is sufficiently reduced, and there is a danger that the rotor will lose synchronism and lose synchronization. In order to avoid this, hold, that is, energization must be performed with sufficient time.
Therefore, the amount of energization increases and the control time also increases. Also, when used in abnormal environments such as vibration, temperature, and humidity,
In particular, the vibration becomes large, and cannot be suppressed by a predetermined hold time set assuming a normal condition, and there is a problem that a step-out occurs. Therefore, if a method of controlling the vibration convergence time under such worst conditions and determining the vibration convergence time as the predetermined hold time is employed, the control time becomes too long and the control circuit consumes a large amount of power. That is inevitable. In particular, when a battery such as an electronic camera having an auto-focus mechanism is used as a power source and is used for a device that requires precise drive control, power saving and high-speed operation are required. It is hoped that a control device that can perform the functions will appear.

SUMMARY OF THE INVENTION It is an object of the present invention to control a stepping motor in which the speed of stop control of a rotor can be increased, the rotor can be accurately held at a desired position, and power can be saved. It is to provide a device.

[Means for Solving the Problems] In order to achieve the above object, the present invention is configured as follows. That is, a detecting means for detecting the vibration state of the rotor in the stepping motor, and when energizing the winding to obtain a hold torque for suppressing the vibration of the rotor, the duration of the energization is controlled in accordance with the output of the detecting means. And control means for performing the control.

[Operation] In such a configuration, the detection means detects the vibration state of the rotor, and the detection output is input to the control means. The control means is for controlling the duration of the energization in accordance with the output of the detection means when the winding is energized to obtain a hold torque for suppressing the vibration of the rotor. The energization time of the winding is controlled so that the energization duration corresponds to the output of the means.

As described above, the present invention supports the detection output of the vibration state of the rotor in order to electrically detect the vibration of the stepping motor during the stop control of the stepping motor and to hold the vibration by energizing until the vibration amount becomes smaller than the predetermined amount. Excitation of the magnetic pole at the stop position for the specified duration
The excitation is discontinued, and switching to holding by detent torque is performed. With this, a minimum holding torque is given, and switching to holding by detent torque is performed when holding by detent torque becomes possible. Therefore, it is possible to obtain an efficient stepping motor control device capable of saving power and performing high-accuracy position control with a minimum control time.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. This device has a hold torque stable point and a detent
By using a stepping motor having the same stable point of torque, energization is stopped after driving is completed, and thereafter, a stop control system that holds the rotor with detent torque is intended. An example in which the control circuit is applied to a four-phase bipolar type will be described. First
The figure shows a control circuit according to the invention. In the figure, L1, L
Numeral 2 denotes a coil, φ1 and φ3 denote terminals of the coil L1, φ2 and φ4 denote terminals of the coil L2, which are wound around the same pair of stator poles. As shown in FIG. 5, the bipolar type has a counter pole SP in the stator ST.
1 and SP3, SP2 and SP4, each with one coil for coil L
1, L2 is wound, and current flows from φ1 side (φ2 side)
By flowing current from the φ3 side (φ4 side)
This is a method of exciting by changing the direction of current.

Therefore, the driving circuit is the same as in the case of FIG.
The transistors Q5 to Q8 and Q9 to Q12 are bridge-connected, and the corresponding coils L1 and L2 are connected between the bridge midpoints. Then, these transistor bridges are connected to a DC power supply (between Vcc and ground). In addition, each transistor Q5
Q8, Q9-Q12 are constructed by connecting diodes D1-D4, D5-D8 for transistor protection between their emitters and collectors. Then, in each transistor, Q5 and Q8, Q7 and Q6, Q9 and Q12, Q10 and Q11, which are in a diagonal relationship of the bridge, are turned on / off according to an excitation sequence as a pair, so that the excitation control of the coils L1 and L2 is performed. And the excitation direction is controlled.

The CPU is a microprocessor and plays a central role in control. P0 to P3 are output ports, and P4 is an input port. Output ports P0 to P3 are ports for controlling the excitation and current direction of the coils L1 and L2,
P0 is connected to the base of the transistor Q1 via the resistor R2. The transistor Q1 is for driving the transistor Q5 constituting the bridge, and has a collector
Connected to the base side of Q5, the emitter is grounded.
The output port P0 is connected to the base of the transistor Q8 via the resistor R4.

Output port P1 is connected to transistor Q6 via resistor R3.
And connected to the base of the transistor Q2 via the resistor R5. The transistor Q2 is for driving the transistor Q7 constituting the bridge, and has a collector connected to the base side of the transistor Q7 and an emitter grounded.

The output port P2 is connected to the base of the transistor Q3 via the resistor R6, and is connected to the transistor Q12 via the resistor R7.
Connected to the base. The transistor Q3 is for driving the transistor Q9 constituting the bridge, and has a collector connected to the base of the transistor Q9 and an emitter grounded. The output port P3 is connected to the base of the transistor Q10 via the resistor R8 and the resistor R9
Connected to the base of the transistor Q4. The transistor Q4 is a transistor Q1 constituting the bridge.
1 is for drive, the collector is connected to the base side of Q9, and the emitter is grounded.

The ground side of the transistor bridge is grounded via a resistor R1, and the transistor bridge connection side of the resistor R1 is connected to the input side of a differentiating circuit constituting a vibration detection circuit. The differentiating circuit is configured using an operational amplifier OP1.The inverting input terminal of the operational amplifier OP1 is connected to a series circuit including a resistor R12 and a capacitor C1, and a resistor R13 is provided between the input terminal and the output terminal. They are connected, and these are the differential elements. The non-inverting input terminal of the operational amplifier OP1 is connected to the DC positive line Vcc via a resistor R10, and the non-inverting input terminal of the operational amplifier OP1 is grounded via a resistor R11. The divided voltage of Vcc determined by the division ratio is input to the operational amplifier OP1 as a reference voltage, and the voltage corresponding to the current value appearing at the non-ground side point of the resistor R1 is differentiated by a differentiation element, and the current fluctuation is performed based on the reference value. The corresponding voltage is output. This output is connected to the opposite input terminal of an operational amplifier OP2 that constitutes a comparison circuit (comparator), and the non-inverting input terminal of the operational amplifier OP2 receives a voltage obtained by dividing the reference voltage by the voltage dividing resistors R14 and R15. Have been added. The voltage dividing resistor R14 is connected to the resistor R10 on the OP1 side, the resistor R15 is connected to the output terminal side of the OP2, and the output terminal of the OP2 is pulled up to Vcc via the resistor R16 and is connected to the input port P4 of the CPU. By connecting the reference voltage to the non-inverting input terminal of OP2 by dividing the reference voltage by the resistors R14 and R15, the comparison circuit can have a hysteresis characteristic. The configuration is such that the output of the comparison circuit does not change and a change of a certain width can be captured. The components formed by the above OP1 and OP2 form a vibration detection circuit.

The CPU controls the output ports P0 to P
Output transistor drive output while sequentially switching 3
When the motor reaches a predetermined stop position and stops the motor, the output of the OP, which is the detection output of the vibration detection circuit, is taken from the input port P4, and the vibration detection output does not change for a predetermined time, for example, 3 ms. In some cases, a program for controlling the excitation to end assuming that the vibration has subsided is provided.

The operation of this device having such a configuration will be described with reference to the timing chart of FIG.

When the motor is driven to rotate, (a) to (d) of FIG.
As shown in (2), in accordance with the excitation sequence of the stepping motor, the CPU sequentially generates transistor drive output pulses from its output ports P0 to P3 to excite the coils L1 and L2. That is, when a drive pulse is generated from P0, Q1 is turned on, thereby turning on Q5, and at the same time, a drive pulse from P0 is also turned on, thereby causing the coil L1 to have a current flowing in the direction from φ1 to φ2. Flows and is excited. Next, when a drive pulse is generated by switching from P0 to P2, Q3 is turned on, whereby Q9 is turned on, and Q12 is also turned on by the drive pulse from P2, whereby the coil L2 is moved in the direction from φ2 to φ4. A current flows and is excited. Next, a drive pulse is generated by switching from P2 to P1. Then, Q2 is turned on, whereby Q8 is turned on, and Q6 is also turned on by the drive pulse from P1, whereby a current flows in the coil L1 in the direction from φ3 to φ1 and is excited. Next, when switching from P1 to P3 to generate a drive pulse, Q4 is turned on, thereby turning on Q11 and, at the same time, the drive pulse from P3 is also turned on, thereby causing the coil L2 to have a current flowing in the direction from φ4 to φ2. Flows and is excited. The motor rotates by repeating such a sequence. The waveform of the current flowing through the resistor R1 by the excitation control of each coil is as shown in FIG. 2 (e), and the waveform oscillates every time the phase is switched.

On the other hand, to stop at the magnetic pole position of coil L2,
It is assumed that the motor stop control is performed at time t5 after exciting L1. The state at this time is such that the excitation pulse is continuously output as a hold signal from the port P2 in the example of FIG. Then, the magnetic flux of the coil L2 is cut off by the vibration of the rotor magnetized in the NS, so that a back electromotive force corresponding to the vibration is generated in the coil L2, and the oscillating current as shown in FIG. Flows to This vibration is a DC component and a vibration component.
This oscillating current is input to an operational amplifier OP1 that constitutes a differentiating circuit of the vibration detecting circuit, where it is differentiated, and a difference voltage around a reference voltage determined by voltage dividing resistors R10 and R11 for dividing Vcc is used as an oscillating component. Is output. This output is
Although input to OP2, the output terminal of OP2 is pulled up to VcC via R16 and connected to the input port P4 of the CPU.
The configuration is such that the output divided by R14 and R15 is input, and the comparison circuit has a hysteresis characteristic. By setting R14 and R15 appropriately, it is possible to capture a change of only a certain width. Therefore, a certain width (dead zone VT) of the vibration from OP2
H) A detection output of the above fluctuation can be obtained. The dead zone VTH is determined by R11 · Vcc / (R10 + R11), and is set to a value at which vibration does not matter.

Here, for example, the vibration frequency is determined if the target motor and the mechanism driven by the motor are determined, and only the vibration corresponding to the magnitude of the vibration changes.
(See (f) of FIG. 2). Therefore, the comparison circuit input (OP
2) Even if it fluctuates as shown in FIG. 2 (g), the output of the comparison circuit is R11 · V in FIG. 2 (h).
When there is an input outside the dead zone VTH defined by cc / (R10 + R11), the input changes to "H" and "L". The cycle of this change is determined by the system as described above. If the system had a period slightly smaller than 2 ms, the C
The PU has a 3ms timer to monitor whether there is a change in the output of the comparator circuit (output of OP2) before the timer expires. If the change stops within this time, the vibration will not be a problem. Judgment is made that the convergence has been completed, the hold is terminated, and control is performed so as to switch to holding by detent torque.

Therefore, the CPU is caused to execute a control program as shown in the flowchart of FIG. 3 at the time of motor drive stop control. To explain this in order, when the motor reaches a predetermined stop position and enters the motor stop control, first, the CPU checks the level of the input port P4 which takes in the output of the vibration detection circuit (S1), Next, the value of a counter c, which is a timer for measuring a pulse interval, is set to zero (S2). Then, after waiting for 0.1 ms next (S3), the counter c is incremented (S4), and it is checked whether the value of c has reached 30 (S5). As a result, when the value of c has not reached 30, the input of P4 is checked (S6), and it is determined whether or not the level has changed (S7). Then, when it is determined that "there is no level change", the process returns to S3, and the above operation is repeated again. When it is determined in S7 that "there is a level change", the process returns to S2, and the value of the counter c is set to zero. Then, after waiting for 0.1 ms next (S3), the counter c is incremented (S4), and it is checked whether the value of c has reached 30 (S5). As a result, the value of c has reached 30. If not, the input of P4 is checked (S6), and the operation of judging whether or not there is a level change (S7) is repeated. As a result, it is possible to detect a section in which the amplitude of the oscillating current oscillating at a cycle slightly shorter than the oscillation cycle of 3 ms is oscillating at a predetermined dead level or higher. If the amplitude of the oscillating current is attenuated below a predetermined dead level, P
Since the level change of 4 does not occur, c reaches 30. In S5, it is determined that c has reached 30 and the process proceeds to S8 to stop energizing the motor. As a result, the excitation of the motor is completed, and the rotor starts to be held by the detent torque. Therefore,
The hold torque can be turned off as soon as the vibration is within a level that does not cause a problem in maintaining the positional accuracy, and the stop control can be completed in the minimum time required. Thus, high-speed control, energy saving, and high positioning accuracy can be achieved.

Although the present invention has been described with reference to the application example to the bipolar type, the present invention is also applicable to the unipolar type.

As described above, the present apparatus electrically detects the vibration of the stepping motor from the current or voltage of the driving system, holds the current by energizing until the vibration amount becomes smaller than a predetermined amount, and then performs the holding by the detent torque. By switching, the hold torque of the minimum required source is given, and when the holding by the detent torque is possible, it is switched to the holding by the detent torque, so that power saving and high-precision position control are possible. In addition, it is possible to obtain an efficient stepping motor control device capable of performing control with a minimum stop control time.

Therefore, the drive circuit of the present invention can be used for driving devices requiring high speed and high efficiency, for example, autofocus of a battery-driven camera, driving of an aperture mechanism, and the like.

Incidentally, if the oscillating current cannot be accommodated for some reason, hold-look will continue to be generated forever, and a program such as that shown in FIG. 4 may be considered as a method for preventing this. To explain this, an abnormality detection timer is provided, and in S0, after the timer is started, a routine after S1 is entered. The routine after S1 is the same as that shown in FIG. 3 up to S7, the vibration continues continuously and does not converge, and when this reaches the time-up time of the abnormality detection timer, an error is displayed (S11). Thereafter, the motor energization is stopped (S12). The abnormality detection timer time-up time is set to be slightly longer than the longest vibration convergence time under the worst conditions. If the level of the comparison circuit (OP2) changes and the abnormality detection timer has not timed out, the abnormality is detected. Clear the count value of the timer and restart from S2. In the case of an electronic camera, the error display uses a display unit in the main body or a display unit in a viewfinder to perform a character display, a symbol display, a light emission display using an LED, or the like so as to be clearly understood here.

The present invention is not limited to the embodiment described above and shown in the drawings, and can be appropriately modified and implemented within a scope that does not change the gist. For example, in the above-described embodiment, the vibration is detected by the vibration current. And used it for control.
Vibration may be detected by a coil as a vibration voltage and used for control, and control may be performed based on the output of this detection element using a detection element that detects the rotation angle of the shaft of the stepping motor. It may be performed.

[Effects of the Invention] As described above, the present invention electrically detects the vibration of the stepping motor during the stop control of the stepping motor and holds the current by energization until the vibration amount becomes smaller than a predetermined value. Excitation of the magnetic pole at the stop position is performed for a duration corresponding to the detection output, and then the excitation is discontinued and the mode is switched to holding by detent torque. Therefore, the minimum required holding torque is given, and when the holding by the detent torque becomes possible, the holding can be switched to the holding by the detent torque, so that power saving and high-precision position control are possible, and In addition, it is possible to obtain an efficient stepping motor control device capable of performing stop control with a minimum control time.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2 is a timing chart for explaining the operation of the present device in a four-phase bipolar type stepping motor, and FIG. FIG. 4 is a flowchart showing a modification of the CPU, FIG. 5 is a diagram for explaining a configuration of a four-phase bipolar type stepping motor, and FIG. 6 is a diagram showing a conventional four-phase bipolar type stepping. FIG. 7 is a diagram showing an excitation sequence and a current waveform in the circuit of FIG. 6, and FIG.
FIG. 9 is a diagram for explaining the operation of the phase stepping motor,
FIG. 10 is a diagram for explaining the stiffness characteristic of the stepping motor, and FIG. 10 is a diagram showing the relationship between the rotor vibration and the generated magnetic flux and the generated voltage in the stepping motor. L1, L2: coil, Q1-Q12: transistor, D1-D8:
... Diode, R1-R16 ... Resistance, RT ... Rotor, ST ...
... stator, OP1, OP2 ... operational amplifier, CPU ... microprocessor.

Claims (1)

(57) [Claims] 1. A detecting means for detecting a vibration state of a rotor in a stepping motor, and when energizing a winding to obtain a hold torque for suppressing the vibration of the rotor, a duration of the energizing is output to an output of the detecting means. A control device for a stepping motor, comprising: control means for controlling the stepping motor in response to the request.