JP2745606B2 - Stepping motor drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A. Industrial application fields B. Summary of the invention C. Conventional technology D. Problems to be solved by the invention E. Means to solve the problems F. Function G. Example G ₁ . Configuration of Embodiment (FIGS. 1 to 4) G ₂ . Operation of Embodiment (FIGS. 5 (a) and (b) to FIG. 8) H. Effects of the Invention A. Industrial Application Field The present invention relates to a drive circuit for rotating a stepping motor smoothly at high speed. Things.

B. Summary of the Invention The present invention relates to a stepping motor drive circuit that reads a voltage waveform stored in a memory corresponding to a rotation position of a rotor and applies the voltage waveform to a motor coil, detects a rotation speed of the rotor, and responds to the rotation speed. By increasing the phase of the voltage waveform applied to the motor coil and correcting the phase delay of the drive current during high-speed rotation and driving with the optimal phase relationship, high-speed rotation is possible and efficiency is improved. .

C. Conventional technology In recent years, not only positioning control of stepping motors, but also applications similar to ordinary brushless motors such as VT
There is a demand for use in applications such as capstan motors for R (video tape recorders). This is mainly because stepping motors are more cost-effective than other motors, and because they are open rooms and digital technology can be used. By the way, a stepping motor has noise, coking, and torque ripple in a normal pulse drive, and causes a problem such as a jitter in a VTR. Therefore, a smooth rotation is realized by a sine wave drive.

D. Problems to be Solved by the Invention However, in the sine wave drive of the stepping motor in the above-described conventional technology, when performing a high-speed rotation sine wave drive in an open room, the motor coil of the multi-pole structure and the iron core structure is used. The effect of inductance is large,
As shown in the relationship diagram between the applied voltage of the motor coil and the motor coil current in the conventional example shown in FIG. 10, the phase delay of the motor coil current I with respect to the sine wave applied voltage V was large. For this reason, there is a problem that not only the rotation speed of the stepping motor cannot be increased due to the generation of reverse torque but also the efficiency is deteriorated.

In order to solve this, a method of applying current feedback to apply servo is conceivable. FIG. 11 is an explanatory view of this, in which a voltage waveform signal applied to a motor coil of a stepping motor (not shown) is output from a waveform shaping unit 101 to an output stage 102 based on a control signal. it is intended to apply a current feedback to the waveform shaping section 101 detects the phase of the driving current I _s flowing from the voltage source V _s. However, in this solution, it is necessary to always apply the drive voltage V _s to the output stage 102, so that the drive power W _s
Is W _s = V _s × I _{s and the} PWM by the switching power supply is
(Pulse modulation) control cannot be performed, and power saving cannot be achieved.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a driving circuit for a stepping motor that enables high-speed rotation and increases efficiency at high-speed rotation.

E. Means for Solving the Problems In order to achieve the above object, a configuration of a drive circuit of a stepping motor according to the present invention stores a voltage waveform to be applied to a motor coil by associating an address with a rotational position of a rotor. A memory, means for detecting the rotation speed of the rotor, and an address for reading the memory, which is advanced to an address ahead of an address corresponding to the rotation position of the rotor, to be applied to the motor coil in accordance with the rotation speed. Means for reading the memory by advancing the phase of the voltage waveform.

F. Action The present invention advances the phase of the voltage waveform of the drive voltage applied to the motor coil according to the rotation speed of the rotor, corrects the phase lag of the drive current during high-speed rotation, and drives the motor with an optimal phase relationship. This enables high-speed rotation of the rotor and increases efficiency.

G. Examples Hereinafter, examples of the present invention will be described in detail with reference to the drawings.

G ₁ . Embodiment 1 (FIGS. 1 to 4) FIG. 1 is a block diagram of a drive circuit of a stepping motor motor showing an embodiment of the present invention. 1 is a stepping motor, 2 is a position detector for detecting a clock signal for detecting the rotational position and rotational speed of the rotor, and 3 is a drive for identifying the rotational position and rotational speed of the rotor from the clock signal and applying it to the motor coil. A microcomputer for calculating a lead angle of a voltage waveform, that is, a phase shift amount to determine a drive voltage waveform, 4 is a subtraction timer for measuring the interval of the clock signal and detecting the rotation speed of the rotor, and 5 is a case where the phase is not shifted. A memory for storing a drive voltage waveform as a digital value corresponding to the rotational position of the rotor; and 6, a drive voltage applied to the motor coil of the stepping motor 1 by power amplification or PWM control based on the drive voltage waveform determined by the microcomputer 3. Is an output stage for applying the voltage. The microcomputer 3 is a reading means of the memory 5, and shifts the memory address based on the phase shift amount calculated from the rotation speed with reference to the rotation position of the roller, so that the advance angle corresponding to the rotation speed is shifted from the reference. Also, the voltage waveform whose phase is advanced is read from the memory 5 to determine the drive voltage waveform.

FIG. 2 is a sectional view showing a structural example of a stepping motor used in the above embodiment. This example shows an example of a PM (permanent magnet rotor) type stepping motor having an outer rotor structure. 11 is a stator and 12 is a rotor. The rotor 12 is fixed to the pulley 13 and the pulley 13 is
Stick to The shaft 14 is rotatably attached to the stator 11 by a bearing 15. On the stator 11 side, two-phase motor coils 16 and 17 are arranged side by side in the axial direction of the shaft 14, and magnetic pole plates 18 and 19 that form pole teeth in the circumferential direction so as to cover the motor coils 16 and 17 are provided. Provide. The pole teeth of each of the magnetic pole plates 18 and 19 alternately form opposite magnetic poles by a current flowing by a drive voltage applied to the motor coils 16 and 17, and the pitch of the magnetic poles is
They are arranged so as to be shifted by a predetermined pitch (1/2 pitch for two phases) between 18 and 19. On the other hand, the rotor 12 is formed in a cylindrical shape, and a main magnet 20 in which opposite magnetic poles are alternately magnetized in the circumferential direction is arranged inside the magnetic pole plates 18 and 19 facing the pole teeth. Thus, a normal stepping motor is configured.

In addition to the above, the stepping motor used in this embodiment includes an FG (frequency generator) magnet 21 for detecting the rotation position and the rotation speed of the rotor 12,
An MR (magnetoresistive) element 22 for detecting the magnetic pole of the FG magnet 21 is provided. The FG magnet 21 is connected to the rotor 12
The pitch is finer than the main magnet 20 (for example, 480 poles for 24 poles of the main magnet)
To alternately magnetize opposite magnetic poles in the circumferential direction. MR element 22,
The rotation detector 2 shown in FIG.
On the 11 side, face the magnetized surface of the FG magnet 21 and
By detecting the magnetic pole of the FG magnet 21, a clock signal for detecting the rotational position and rotational speed of the rotor 2 is created.

FIG. 3 is a flowchart showing an operation example of the embodiment configured as described above. When the operation is started, the microcomputer 3 first counts the number of input clock signals of the rotation detector 2 using a counter at the first stage, and specifies the rotational position (rotor phase) of the rotor of the stepping motor 1 at a certain point in time. I do. Subsequently, in the first to third stages, the rotational speed is detected, and the lead angle of the voltage waveform to be applied to the motor coil, that is, the phase shift amount is calculated from the rotational speed. In this example, the relationship between the rotational speed and the lead angle is calculated. Is approximated by a straight line, and the phase shift amount is obtained by subtracting an amount corresponding to the rotation speed from a constant value. That is, the rising of the clock signal of the rotation detector 2 is detected and the subtraction timer 4
To ON. The subtraction timer 4 sets a predetermined value in advance and counts down from that value in accordance with the internal clock signal. This down-counting is performed until the cycle until the next clock signal rises after the clock signal is detected and the subtraction timer 4 is controlled to be OFF. The cycle of the internal clock signal of the subtraction timer 4 is set so that the remaining value of the subtraction after the OFF becomes the phase shift amount. After the subtraction timer 4 turns off,
The memory address of the memory 5 for storing the voltage waveform data is determined in the first stage, and the voltage waveform data is read out in the first stage. The memory 5 stores voltage waveform data when the angle of advance to the memory address corresponding to each rotor phase is 0. In the first stage, an address (counter value) corresponding to the rotor phase obtained in the first stage is stored. , The phase of the voltage waveform read from the memory 5 is advanced according to the rotation speed. Next, in the first stage, the microcomputer 3 or the output stage 6 performs A / D
After conversion and, if necessary, filtering, the output stage 6 drives the motor in the first stage. In the above, when the output stage 6 drives the motor by PWM control, A / D conversion is not performed, and the microcomputer 3 outputs a PWM waveform.

FIG. 4 is a flowchart showing a detailed processing procedure of the microcomputer 3. In the present embodiment, in order to detect the rotation direction of the stepping motor 1 and determine the reading direction of the memory 5, two MR elements of the rotation detector 2 are arranged to detect the A and B two-phase clock signals. . First, after the start, the phase of the rotor is adjusted for initialization. The phase matching is to lock a rotational position (rotor phase) of a rotor by supplying a current to a certain phase of a motor coil for a certain period of time. In this locked state, a counter or a subtraction timer (hereinafter, referred to as a timer) for specifying the rotor phase is used. Each value of a memory address C of a register that specifies reading of the memory 4 and the memory 5 is initialized to 0. Here, the timer 4 is configured to generate an interrupt with a timer value 0 and hold the value 0 until the timer starts. Subsequently, the operation shifts to a rotation operation, but it is determined whether or not the B-phase clock signal is at H (high level). If not (N), the process waits until the B-phase clock signal becomes H (rising), which becomes H. At this time, it is determined whether or not the A-phase clock signal is H, and if it is H (Y), it is determined that the motor is rotating forward, and it is confirmed that the counter is not the maximum value (for example, 127), and the counter is advanced by +1. In the above, when the first B-phase clock signal is H (Y) in the determination as to whether or not, and the A-phase clock signal is N (N) in the determination whether the H is not, this time. Wait until the B-phase clock signal is no longer H (falling), and when it is no longer H, determine whether the A-phase clock signal is H, and if H (Y), determine reverse rotation. The counter is decremented by 1 after confirming that the counter value is not the lowest value (for example, 0). If the A-phase clock signal is not H (N) in the above, the processing is executed from the determination of the rise of the B-phase clock signal in the above-described normal rotation example.

In the process on the positive rotation side, before performing the operation of incrementing the counter by 1, it is determined whether the counter value is the maximum value (127) or not.
If it is 27, the operation of subtracting 127 from the counter value and increasing +1 is not performed. After the operation of incrementing the counter by 1 or the operation of subtracting 127 from the counter, the previous value of the timer 4 is read on the forward rotation side, and the timer 4 is started using the counter value + timer remaining value as the memory address C of the memory 5. The start of the timer indicates that the operations from the first stage to the second stage in FIG. 3 are performed.

Before performing the operation of decrementing the counter by −1 in the process on the reverse rotation side, it is determined whether or not the counter value is the minimum value (0) and 0 is determined.
In the case of, 127 is added to the counter value, and the operation of -1 is not performed. After the operation of decrementing the counter or the operation of adding 126 to the counter, the reverse rotation side reads the previous residual value of the timer 4 and sets the timer 4 as the memory address C of the counter value-timer residual value as described above. To start.

In both the normal rotation side processing and the reverse rotation side processing, after the timer is started, the memory 5 is read out based on the memory address C and output to the output stage 6 as shown in FIG. The voltage waveform read out here is advanced by a predetermined advance angle corresponding to the rotation speed by shifting the address in both the forward rotation side processing and the reverse rotation side processing. Thereafter, the procedure of determining the direction of rotation is periodically repeated again, the phase of the voltage waveform is corrected for each rotation position of the rotor, and output to the output stage 6.

G ₂ . Operation of Embodiment (FIGS. 5 (a) and (b) to FIG. 8) The operation of the embodiment configured as described above will be described. 5 (a) and 5 (b) are waveform diagrams of the drive voltage and drive current of the motor coil for explaining the operation, FIG. 6 is a diagram showing the relationship between the phase delay of the drive current and the rotation speed, and FIG. 7 (a). And (b) is a diagram showing the relationship between the clock signal and the voltage waveform for explaining the operation. In the present embodiment, a memory address of the memory 5 corresponding to the rotor phase is created based on the clock signal of the position detector 2, and the drive voltage waveform stored in the memory 5 is read to drive the motor coil. And However, in this state, since the phase relation between the counter electromotive voltage Vr of the drive voltage V _s and the motor coil as shown in FIG. 5 (a) is fixed, the actual torque as shown in FIG. 5 (b) contributes driving current I _s to the results of the delayed electrical angle θ due to the influence of the inductance of the motor coil. The delay amount θ is, as shown in FIG. 6, the rotational speed of the stepping motor (rp
m). Therefore, in this embodiment, in order to cancel this delay, a method of measuring the interval of the clock signal from the position detector 2 and advancing the phase of the drive voltage waveform according to the value is used. Here, the sixth
In the function shown in the figure, the range of rotation speed to be used (for example,
(1800 rpm is the center), a straight line approximation is performed, and a simple subtraction by a calculation timer is performed from the measured clock signal interval without performing a complicated calculation based on the function. As a result, the present embodiment can be realized even with the performance of a microcomputer.

In FIG. 7, (a) shows a driving voltage waveform when the rotation of the rotor is slow, and (b) shows a driving voltage waveform when the rotor is rotating at high speed. In (a), since the cycle T of the clock signal of the rotation detector 2 indicating the rotation speed is long, the subtraction timer 4 is decremented by the timer start from the rise to the next rise until the remaining value becomes zero. Therefore, the memory address of the memory 5 is not shifted.
The voltage waveform read out from the terminal has no phase advance. In (b), the cycle T of the clock signal is short because of high-speed rotation, and the remaining value of the subtraction timer 4 that is decremented by the timer start is not decremented until it becomes 0. The higher the speed, the larger the value. Accordingly, the remaining value becomes the shift amount of the memory address, and a voltage waveform having a phase advanced by a predetermined advance angle θ according to the rotation speed can be read from the memory 5. As a result, even if the rotation speed of the stepping motor becomes high, the drive current can be supplied with an optimal phase so that the reverse torque is not generated. For this reason. The stepping motor can be rotated to a higher speed and the efficiency can be increased. In this embodiment, since no reverse torque is generated, the torque ripple is small, the range of rotation speed is widened, and a brushless motor or a VTR capstan motor having a standard speed, a triple speed, a picture search, etc. is used. It can be used in place of a servomotor or the like.

FIG. 8 is a static characteristic diagram of a stepping motor showing the effect of the present embodiment, and FIG. 9 is a static characteristic diagram of a conventional stepping motor used for comparison of the effect. Both are 40
Rotational speed [rpm], drive current [mA], efficiency [%] versus torque [g-c] in a PM type stepping motor of about mmφ
m]. As is apparent from this graph, the case where the phase correction of the drive voltage waveform was performed (the eighth
In the case of the conventional example (FIG. 9), the rotation speed is twice or more, the range of the variable speed is three times or more, and the efficiency can be improved to about twice as compared with the conventional example (FIG. 9). . Thus, it can be seen that even if the phase is corrected by the linear approximation calculation, a practically sufficient effect can be obtained.

It should be understood that the phase shift amount may be calculated from a function formula of the actual rotation speed versus the lead angle using a high-speed computer or a computing unit, and the microcomputer in the embodiment may be constituted by a digital logic circuit. Of course. As described above, the present invention can be variously applied according to the gist and can take various embodiments.

H. Effects of the Invention As is apparent from the above description, the following effects can be obtained by the drive circuit of the stepping motor of the present invention.

(1) Since the energization phase does not shift, the torque ripple does not increase due to the rotation speed peaking due to the generation of the reverse torque or the phase shift accompanying the rotation speed increase.

(2) Even if the rotation speed changes, an efficient state can be always maintained.

(3) Compared to applying current feedback,
Since a switching power supply can be used as the drive power supply, power saving can be achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a stepping motor drive circuit showing one embodiment of the present invention, FIG. 2 is a sectional view showing an example of the structure of a stepping motor used in the above embodiment, and FIG. 3 is an operation of the above embodiment. FIG. 4 is a flowchart showing an example, FIG. 4 is a flowchart showing a processing procedure of a microcomputer,
5 (a) and 5 (b) are waveform diagrams of the drive voltage and drive current of the motor coil for explaining the operation, FIG. 6 is a diagram showing the relationship between the phase delay of the drive current and the rotation speed, and FIGS. 7 (a) and 7 (b). FIG. 8B is a diagram showing the relationship between a clock signal and a drive voltage waveform for explaining the operation, FIG. 8 is a static characteristic diagram of a stepping motor showing the effect of this embodiment,
FIG. 9 is a diagram showing static characteristics of a conventional stepping motor, and FIG.
FIG. 11 is a diagram showing the relationship between the applied voltage of the motor coil and the motor coil current in the conventional stepping motor, and FIG. 11 is an explanatory diagram of the current feedback method. 1 ... stepping motor, 2 ... position detector, 3 ...
Microcomputer 4, subtraction timer 5, memory 6, output stage.

Claims (1)

(57) [Claims] 1. A memory for storing a voltage waveform to be applied to a motor coil in association with an address corresponding to a rotational position of a rotor, means for detecting a rotational speed of a rotor, and a memory for reading the memory according to the rotational speed. Means for advancing the phase of the voltage waveform to be applied to the motor coil by advancing the address of the rotor to the address corresponding to the rotational position of the rotor and reading the memory. circuit.