JPS6344000B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a closed loop drive system for a stepping motor.

The object of the invention is to provide a wide power supply voltage range and
An object of the present invention is to realize a stepping motor drive system that eliminates motor vibration during acceleration and deceleration of the stepping motor in response to load fluctuations, and performs good constant speed control during constant speed rotation.

Another object of the present invention is to improve the maximum response frequency of the stepping motor in both forward and reverse rotational directions, and to improve the stability of constant speed control in both of the rotational directions.

Conventionally, it has been known that the vibration characteristics and response frequency of a stepping motor can be improved by attaching a phase switching position detector to the stepping motor and performing closed-loop control. Figure 1 shows a conventional example of this. This figure shows the dot head carrier drive mechanism of a dot printer, which is an application example of the dot printer.

In Fig. 1, 1 is a stepping motor, and 2 is a timing disk having the same number of slits as the number of steps required for one rotation of the stepping motor 1.
It is divided equally into the number of steps required for rotation.

3 is an optical timing detector, and 4 is a timing detector fixing board that can be moved in the direction of the arrow for adjustment. 5 is a reduction gear, 6 is a timing belt, and 7 is a dot head carrier fixed to the timing belt 6. 8 is the dot head. By switching the phase of the stepping motor when the timing pulse outputted by the optical timing detector 3 is detected, the stepping motor can be ideally started.

However, in cases where the stepping motor must be rotated in both forward and reverse directions to move the carrier left and right, such as in the dot head carrier drive mechanism of a dot printer, positioning accuracy is poor due to the difference in the rotation direction of the stepping motor.
Due to the time delay from detection of the position detector and phase switching position to phase switching, the optimum position of the phase switching detector differs depending on the rotational direction as shown in FIG.
This deviation does not become a problem when the output torque of the stepping motor is low and in the case of Fig. 2 E, but
As shown in FIG. 2F, the higher the output torque, the greater the effect, and the drawback is that the characteristics of the stepping motor cannot be fully exploited.

Here, FIG. 2 will be further explained. Second
The figure shows the position of the detector and the output torque of the step motor obtained when the phase is switched based on the output signal from the detector at the position.

In the case of having only one conventional detector, A
Position I corresponding to the intersection point P of the curve in direction and B direction
A detector was installed at However, in this case, as is clear from the figure, an output torque greater than H cannot be obtained in either direction A or B. In other words, you can't get enough speed.

The present invention focuses on this point, and in order to optimally drive the stepping motor, the phase of the stepping motor is switched in the rotational direction of direction A in FIG. 5 by the signal from the detector installed at position C. In the rotational direction B, the phase of the stepping motor is switched by a signal from a detector installed at position D.

FIG. 3 shows a dot head carrier drive mechanism of a dot printer which is a specific example of the stepping motor drive system according to the present invention.

In Figure 3, 10 is a stepping motor, 1
1 is a timing disk having the same number of slits as the number of steps required for one rotation of the stepping motor 10, and the slit interval is equally divided into the number of steps required for one rotation of the stepping motor 10.

12 is an A-direction optical timing detector, 13 is a B-direction optical timing detector, and 14 is a timing detector fixing board which can be moved in the direction of the arrow for adjustment. 15 is a reduction gear, 16 is a timing belt, and 17 is a dot head carrier fixed to the timing belt 16. 18 is the dot head.

FIG. 4 shows a drive timing chart of the dot head carrier drive mechanism. In the figure, g indicates a timing pulse, and h indicates an arrow indicating the phase switching timing of the stepping motor 1 obtained from the relationship between the timing pulse g and the set time Tc.

The period 20 indicates the stopping state of the stepping motor 10, and the period 21 indicates the stopping state of the stepping motor 10.
This is the driving start timing, and the first phase switching is performed at this position. 22 is a slow-up period of the stepping motor 10, 23 is a constant speed control period, and 24 is a slow-down period of the stepping motor 10.

Next, the driving method of the dot head carrier drive mechanism of this dot printer will be explained with reference to the timing chart shown in FIG. stepping motor 10
is excited to a certain phase in the stopped state 20, but when driving the motor in the A direction, as shown by the arrow at the phase switching timing h of the stepping motor 10 at the start of driving (drive start timing 21) When the phase of the stepping motor 10 is switched, the motor starts rotating. At the same time as the phase switching is performed, a timer is started whose set time is the timing pulse period tc output from the A-direction optical timing pulse detector 12 during the constant speed control period 23 of the motor. If the timing pulse T ₁ is not output before the timer ends after the time tc has elapsed since the start of driving, phase switching is performed when the timing pulse T ₁ is output. At this point, a timer with tc as the set time is started again, and if timing pulse _T2 is not output before the timer ends, phase switching is performed when timing pulse _T2 is output. At this point, the timer is started again with Tc as the set time. If the above operation is repeated and the timing pulse Tn is output before the timer ends with Tc as the set time, the phase switching of the motor is performed at the end of the timer and not at the time the timing pulse is output.

From the point in time when the timing pulse is output before the timer ends, the slow-up period 22 ends and a constant speed control period 23 begins. During the slow-up period, the time interval tm (where t ₁
In this case, the time from the drive start point 21 until _T1 is output) is sequentially stored in the memory from m=1 to m=n-1. During the constant speed control period 23, the timing pulse is normally set at Tc at the time of phase switching.
Since the signal is output before the timer with the set time ends, the motor phase switching is performed at the time the timer ends, and the timer is restarted at the same time.

However, if the motor speed decreases due to a sudden increase in motor load and the timing pulse is not output before the timer ends, the phase change and timer restart will be performed as soon as the timing pulse is output, as in the slow-up period. The timing pulse time interval tm at this time is not stored in the memory. The above operations are repeated to perform constant speed control of the stepping motor 10. If the number of steps from the driving time point 21 of the stepping motor 10 is the drive step amount specified in advance as l, then l-
(n-1), a slowdown period begins and slowdown control is started. Slowdown control starts a timer whose set time is the last timing pulse time interval tn-1 of the slowup period stored in memory at the time of the last phase change of constant speed control, and when this timer ends, the phase is stopped. At the same time as the switching is performed, a timer whose set time is tn-2 stored in the memory is started. In this way, when the timer ends, the phase is switched, and at the same time, the operation of starting the timer with the timing pulse time interval stored in the memory as the set time in the reverse order to that stored at the time of slow-up is repeated. , _t1 as the set time ends, the stepping motor 10 completes the slowdown by performing the final phase switching.

When the dot head carrier 17 moves in the B direction, similar control is performed using the B direction optical timing detector 13.

That is, as shown in FIG. 5, in the A direction, the phase is switched by the output signal from the detector placed at position C, and in the B direction, the phase is switched by the output signal from the detector placed at position D. By switching the phase with a signal, the maximum output torque on each curve can be obtained in any case.

The shape of the curve in Figure 5 shows that as the phase switching position moves away from a certain point, the output torque obtained gradually increases, but after a certain distance, it rapidly decreases. . Since the slit of the timing disk 11 has a certain width, different curves are drawn in the A direction and the B direction as shown in the figure.

In the present invention, detectors are installed at two different positions C and D corresponding to the maximum output torque reached by each curve, and the phase is switched by the output signal from each detector.

By performing the above-described operations from slow-up to slow-down, the dot head carrier 17 can be smoothly driven at high speed and without vibration even in response to fluctuations in the power supply voltage and load of the stepping motor 10. Furthermore, since the printing timing of the dot head is the rise of the timing pulse output and the timing that equally divides the timing pulse time interval, very good printing quality can be achieved.

Furthermore, since the stepping motor can achieve high-speed response, it is very advantageous to use the stepping motor in the head carrier drive mechanism of a high-speed printer, where DC servo motors have traditionally been the mainstream.

[Brief explanation of drawings]

FIG. 1 shows a dot head carrier drive mechanism of a dot printer which is an application example of the conventional stepping motor drive system. FIG. 2 shows the relationship between the timing detector position and the motor maximum response frequency in the dot head carrier drive mechanism of FIG. FIG. 3 shows a dot head carrier drive mechanism of a dot printer which is an application example of the stepping motor drive system according to the present invention. FIG. 4 is a drive timing chart of the dot head carrier drive mechanism of FIG. 3. Fifth
The figure is a diagram showing the relationship between the timing detector position and the output torque of the motor in the present invention.

Claims (1)

[Claims] 1. In a stepping motor drive system that has a position detector that detects the phase switching position of a stepping motor and drives the stepping motor by closed loop control, the forward and reverse rotations of the stepping motor are It has two phase switching position detectors corresponding to the directions, and during forward rotation, phase switching is performed based on the output signal from the first position detector of the two position detectors, and during reverse rotation. In some cases, a stepping motor drive system is characterized in that phase switching is performed based on an output signal from a second position detector.