JPH09313000A - Method of driving stepping motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen current ripple by performing microstep drive in the low frequency acceleration.deceleration range at low speed revolution and high speed revolution of a motor, and driving it by usual excitation method in the high frequency acceleration.deceleration range at high speed revolution. SOLUTION: In the case where a motor is at low speed revolution in one step of performing the switching of each phase 2, 3, 4, and 5 by bipolar drive, microstep drive is performed from an acceleration range to the whole sphere of a low-speed sphere and a deceleration range. On the other hand, in the case where the motor 1 is at high speed revolution, microstep drive is performed only in the range where the drive pulse width per step is from three times the self starting frequency of the motor 1 to 10 millisec, out of the range of accelerating it up to a desired fixed velocity and the range of decelerating it from a desired fixed velocity to its stoppage, and it is driven by usual excitation method in other high frequency acceleration.deceleration range and fixed velocity range. Hereby, the current ripple can be made small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a stepping motor, and more particularly to a method for driving a stepping motor used as a driving source for a carriage driving mechanism or a paper feeding mechanism of a printer.

[0002]

2. Description of the Related Art One line of printing is performed while a carriage on which a print head is mounted is moved along a platen. After this one line of printing is performed, a recording sheet is conveyed by one line and the next line is printed. Serial printers that perform predetermined printing by repeating printing are often used as output devices such as word processors.

A stepping motor is generally used to drive and control the carriage driving mechanism or the paper feeding mechanism of such a serial printer. This stepping motor is used for the following reasons.

1. The rotation angle of the motor is proportional to the number of input pulses, and no accumulated error occurs.

[0005] 2. The rotation speed of the motor is proportional to the input pulse speed, precise synchronous operation is possible, and the control range is wide.

[0006] 3. The start / stop characteristics are extremely good, and operation at a constant frequency is possible below the self-start frequency.

[0007] 4. High response and high output.

[0008] 5. The position can be controlled only by generating the input pulse according to the target position.

6. Can be controlled digitally.

As shown in principle in FIG. 4, the structure of the stepping motor is, for example, first (A), second (B), third (C) and fourth (D) arranged at 90 degree intervals. ) Is provided with a stator 6 having magnetic poles (phases) 2, 3, 4, 5 and a rotor 7 composed of a rotatable permanent magnet having an N pole and an S pole at intervals of 180 degrees. An output shaft (not shown) is connected to the child 7. A first coil 8 is wound around the first (A) and third (C) magnetic poles 2 and 4,
A second coil 9 is wound around the second (B) and fourth (D) magnetic poles 3 and 5.

When an exciting current (phase current) is passed through the coils 8 and 9 of each phase of the stator 6 in order to drive the stepping motor 1 to rotate, a magnetic field is generated by this current.
An electromagnetic force that is attracted or repelled is generated between the stator 6 and the rotor 7. By sequentially switching this phase current,
The electromagnetic force between the stator 6 and the rotor 7 is switched, and becomes a torque for moving the rotor.

FIG. 5 is a block diagram of a driver for driving a general stepping motor. As shown in FIG. 1, the driver 10 includes a control circuit 11, a drive circuit 12, and a power supply 13. The control circuit 11 has a function for controlling input voltage, variable input voltage, overall rotation speed, direction, distance and angle, in addition to an input interface. The control circuit 11 controls pulse timing supplied to the stepping motor 1. It has become. The drive circuit 12 is a circuit for distributing and amplifying the pulse signal from the control circuit 11 to each phase and exciting each phase of the stepping motor 1 in a certain order. The power source 13 needs two types, one for driving a stepping motor and the other for an IC circuit.

The driving method of the stepping motor 1 includes a unipolar drive and a bipolar drive.

In the unipolar drive, as shown in an example in FIG. 6, one transistor 21 is provided for each coil,
By connecting 22, 23, and 24 and turning on the respective transistors, a current in only one direction is passed through each coil. On the other hand, in the bipolar drive, as shown in FIG. 7, a plurality of transistors 25, 26, 2 are provided in each coil.
7 and 28 are connected and only the phase A will be described. In operation, a current in the direction A flows by turning on the first transistor 25 and the fourth transistor 28,
The second transistor 26 and the third transistor 27 are
By setting N, a current in the opposite direction B flows. The unipolar drive has a simpler circuit configuration because the number of transistors is 比 べ compared to the bipolar drive, while the bipolar drive has an advantage that the motor torque can be larger than the unipolar drive when the input power is the same. The driving method of the stepping motor 1 in the present invention described later is based on bipolar driving.

The phase current supply pattern includes one-phase excitation, one-two phase excitation, two-two phase excitation and the like.

Stepping motor 1 by one-phase excitation
Is the most basic driving method in which each phase is sequentially excited one by one and rotated at a basic step angle, and although the angular accuracy is good, the driving torque is small and the power efficiency is not good. Due to the drawback, it is not widely used. In particular, one step angle when driven by one-phase excitation is referred to as a basic step angle.

The method of driving the stepping motor 1 by the 2-2 phase excitation is a method in which two phases adjacent to each other are always excited at the same time, and the excitation of one phase is switched at a time.
Since two phases are always excited, the power utilization efficiency is higher than that of one-phase excitation, and a higher output can be obtained for the same motor power supply voltage. Therefore, it is often used as a driving method of the stepping motor 1 because it works advantageously.

Further, the method of driving the stepping motor 1 by the 1-2-phase excitation is a method of alternately repeating the one-phase excitation and the 2-2-phase excitation. Since the stop position by the two-phase excitation deviates by 停止 of the basic step angle, the two excitation states are alternately repeated to perform the one-phase excitation and the two-phase excitation.
An output is obtained at a step angle of 1/2 of the step angle of the two-phase excitation drive. For this reason, the resolution is doubled as compared with other driving methods, and fine step feed can be performed.Also, it is possible to drive with low noise, and to obtain a precise rotation amount for stable driving at high speed. Is used when necessary.

However, in such a method of driving the stepping motor 1, if the input power is increased in order to secure the torque at the time of high-speed operation, excessive torque is generated in a low-speed region, causing vibration and noise. .

In order to solve such a problem, the step angle mechanically determined by the structure of the stepping motor 1 is further finely divided by an electronic circuit so as to smoothly drive the rotation of the rotor of the stepping motor 1. A driving method called microstep driving by a chopper method is performed. Here, a case in which micro-step driving is performed by bipolar driving with 2-2 phase excitation will be described.

FIG. 8 shows how the winding current changes during full-step driving and during micro-step driving.
If the torque angle characteristic of the stepping motor 1 has a sine wave shape, smooth rotation with less torque fluctuation can be achieved by passing a sine wave winding current as shown in FIG. This sinusoidal winding current is formed by dividing one cycle into a plurality by the control circuit. FIG. 8 shows an example in which one cycle is divided into 40, but since the basic step angle is divided into 10, the resolution is 10 times. The number of divisions can be set arbitrarily.

[0022]

By the way, in the conventional constant current chopper method in the micro step drive, a constant current is obtained by using one of the methods described below. Here, the constant current chopper driver used is provided with a current OFF state for a predetermined time when the supply current value reaches a set value as shown in the current waveform in FIG. It is configured such that a constant current is maintained by setting the ON state so as to become.

A first method for obtaining this constant current is to turn on the power supply in the drive circuit shown in FIG.
The first transistor 25 and the fourth transistor 28 are turned on, and when the supply current value reaches a set value, the first transistor 25 is turned off while the fourth transistor 28 is kept on. Then, the coil current gradually decreases, but after a lapse of a predetermined time, the operation of turning on the first transistor 25 again, increasing the current to the set value, and turning off the first transistor 25 again is repeated. It is a thing. The second method is shown in FIG.
In the drive circuit shown in FIG. 7, the first transistor 25 and the fourth transistor 28 are turned on, and when the supply current value reaches the set value, the first transistor 25 is turned off and the fourth transistor 28 is also turned off. , The current value is rapidly decreased, and after a predetermined time has elapsed, the first transistor 25 and the fourth transistor 28 are turned on.
The current is increased to the set value, and the operation of turning off the first transistor 25 and the fourth transistor 28 again is repeated.

In the above description, only the A-phase coil current is described, but the same control is performed for the coils of other phases by shifting the excitation time.

According to the first method, the current ripple can be reduced as shown in FIG. 10, but the coil current is distorted and the heat generation of the stepping motor increases.

In the second method, as shown in FIG. 11, there is a problem that the current ripple increases, the loss of the motor increases, and the torque decreases.

Further, the micro-step driving at the time of high-speed rotation requires further division of one step (pulse) by applying a driving pulse at a high frequency, so that the driving circuit and its control become complicated. Was.

The present invention overcomes the problems in the prior art, can reduce the current ripple without complicating the control circuit, can suppress the heat generation of the stepping motor, and can be used at low speed rotation and It is an object of the present invention to provide a driving method for a stepping motor that suppresses vibration in a low frequency acceleration / deceleration region during high speed rotation.

[0029]

A stepping motor driving method according to a first aspect of the present invention is characterized in that, in one step of switching phases by bipolar driving, a low speed rotation and a high speed rotation of the motor are performed. In the low frequency acceleration / deceleration region, the control is performed so as to perform the micro step drive.

The stepping motor driving method according to a second aspect of the present invention is characterized in that the low speed rotation is 1
The driving pulse width per step is 3 times the self-starting frequency of the motor to 10 ms for driving.

By driving the stepping motor in this way, the rotor core of the stepping motor smoothly rotates in the low frequency acceleration / deceleration region during low speed rotation and high speed rotation without complicating the control circuit. Vibration can be minimized.

The stepping motor driving method according to a third aspect of the present invention is characterized in that the low frequency acceleration / deceleration region during low-speed rotation and high-speed rotation of the motor is controlled by microstep drive, and the current value is changed. The point is to control the amount of attenuation.

As described above, by driving the stepping motor, the rotor core of the stepping motor smoothly rotates even during low-speed rotation, and vibration can be suppressed to a minimum, and at the time of high-speed rotation, a normal rotation occurs. By controlling by phase excitation, it is not necessary to complicate the control circuit, and it suffices to change the control method, and thus no special circuit is required.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for driving a stepping motor according to the present invention will be described below with reference to the drawings.

The method of driving a stepping motor according to the present invention is based on the premise that chopping is driven by the above-described bipolar drive circuit. In the present invention, microstep driving is performed in the low frequency acceleration / deceleration region during low speed rotation and high speed rotation of the stepping motor 1, and the normal step is performed in the high frequency acceleration / deceleration region and constant speed region during high speed rotation. It is driven by an excitation method. Here, at low speed rotation, the drive pulse width per step is three times the self-starting frequency of the motor (about 65
The driving time is from 0 microsecond) to 10 milliseconds. Also,
The low-frequency acceleration / deceleration region during high-speed rotation refers to a low-speed region equivalent to the above-described low-speed rotation in the acceleration region and the deceleration region, that is, the drive pulse width per step is the self-starting frequency of the stepping motor 1. 3 times (about 650
Microseconds) to 10 milliseconds.

This is shown in FIGS. 1 and 2. FIG. 1 (a)
Indicates the speed of the stepping motor 1 during low-speed rotation, and FIG. 1B shows the voltage applied to each phase at that time. FIG. 2A shows the speed of the stepping motor 1 during high-speed rotation, and FIG. 2B shows the voltage applied to each phase at that time. Figure 1 (b)
The portion indicated by the mountain-shaped line in FIG. 2B is a region driven by microstep driving.

As shown in FIG. 1, the stepping motor 1
In the case of low speed rotation, it is controlled to be driven by microstep drive from the acceleration region (t0 to t1 time) to the constant velocity region (t1 to t2 time) and deceleration region (t2 to t3 time). ing.

On the other hand, as shown in FIG. 2, when the stepping motor 1 is rotating at a high speed, one step is selected from the range of acceleration to a desired constant speed and the range of deceleration from the desired constant speed to a stop. Drive pulse width of 3 times the self-starting frequency of the stepping motor 1 (about 650 microseconds) to 10 milliseconds, that is, t0 to t
It is driven by microstep driving only for 1 hour and t4 to t5 hours, and the other high frequency acceleration / acceleration region and constant velocity region are controlled by the normal excitation method.

The current supplied in the micro-step drive is of the constant current chopper system, but at each division, when the current value reaches the set value in the drive circuit shown in FIG. Transistor 25 is OF
However, in this state, the fourth transistor 28
The ON state and the OFF state can be selected so that when the supply current value reaches the set value, the first transistor 25 and the fourth transistor 28 are OF
Change to F. Then, the coil current sharply decreases (fast decay). Then, when it decreases to a predetermined value (predetermined time), the fourth transistor 28 is turned on. Then, the coil current decreases slowly (slowly decays). When the current value decreases to the second set value (a predetermined time has elapsed),
The first transistor 25 is turned on again to increase the current value. When the current value increases to the set value, the above-described control is performed on the first transistor 25 and the fourth transistor 28. This control is repeated a plurality of times to control the chopping operation in one division.

FIG. 3 shows a current waveform obtained by controlling in this way. By repeating this control at each division, the coil current has a smooth waveform with no distortion or ripple, heat generation of the stepping motor 1 can be suppressed, and the power loss of the stepping motor 1 can be suppressed to be small. The torque is not reduced, and the rotation of the rotor of the stepping motor 1 is smooth without vibration. The control circuit 14 turns on / off the transistors 25 and 28.
Controlled by the CPU.

Therefore, according to an embodiment of the present invention,
The current ripple can be reduced without complicating the control circuit, heat generation of the motor can be suppressed, and vibration in the low frequency acceleration / deceleration region during low speed rotation and high speed rotation of the stepping motor 1 can be suppressed. .

In the above-described embodiment, the supplied coil current is described as a sine wave, but the present invention is not limited to this, and a linearly increasing or decreasing current (triangular wave), or Even if the current is an exponential curve, the current value at the middle point is 3 of the maximum current value.
It has been found that if it is 5 to 80%, the heat generation of the motor and the driver is suppressed, so that effects such as downsizing and cost reduction can be obtained.

Further, even in the case of high speed rotation, in the acceleration region, if the micro step drive is used by the constant current chopper method described above, it is very effective in preventing vibration.

[0044]

As described above, according to the present invention, the motor is driven by a normal excitation method when the motor rotates at a high speed, and the microstep driving is performed when the motor rotates at a low speed. Since the current is connected to each coil to control ON / OFF of each transistor so as to combine high-speed attenuation and low-speed attenuation, the current ripple can be reduced without complicating the control circuit. It is possible to suppress the heat generation of, and to suppress the vibration in the low frequency acceleration / deceleration region during low speed rotation and high speed rotation.

[Brief description of drawings]

FIG. 1A is a diagram showing a speed change of a stepping motor at a low speed rotation, FIG. 1B is a diagram showing a change of a voltage applied to each phase at a low speed rotation (a portion shown by a chevron is driven by a microstep drive). position)

FIG. 2A is a diagram showing a speed change of a stepping motor at a high speed rotation, and FIG. 2B is a diagram showing a voltage change applied to each phase at a high speed rotation. position)

FIG. 3 is a waveform diagram of a coil current according to an embodiment of a stepping motor driving method of the present invention.

FIG. 4 is a principle diagram for explaining the structure of a stepping motor.

FIG. 5 is a block diagram showing a driver of a stepping motor.

FIG. 6 is a drive circuit of a unipolar stepping motor.

FIG. 7: Driving circuit for bipolar stepping motor

FIG. 8 is an explanatory diagram for explaining changes in coil current during full-step driving and micro-step driving.

FIG. 9: Waveform diagram of coil current by constant current chopper method

FIG. 10 is a waveform diagram showing a coil current during slow decay which is a conventional driving method.

FIG. 11 is a waveform diagram showing a coil current during high-speed decay, which is a conventional driving method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Stepping motor 2,3,4,5 Magnetic pole (phase) 6 Stator 7 Rotor 8,9 Coil 10 Driver 11 Control circuit 12 Drive circuit 13 Power supply 21,22,23,24,25,26,27,28 Transistor

Claims (3)

[Claims] 1. A method of driving a stepping motor by bipolar drive of a constant current chopper method, wherein microstep drive is performed in a low frequency acceleration / deceleration region during low speed rotation and high speed rotation of the motor, and high speed rotation is performed. A method for driving a stepping motor, characterized in that the stepping motor is driven by a normal excitation method in a high frequency acceleration / deceleration area and a constant speed area. 2. The drive pulse width per step is 3 to 1 times the self-starting frequency of the motor during the low speed rotation.
The driving method of the stepping motor according to claim 1, wherein the driving is performed for 0 milliseconds. 3. The high-speed decay and the low-speed decay are combined to reduce the current at the time of OFF during the chopping operation for the constant current supplied during the micro-step drive. 2. The driving method of the stepping motor according to 2.