JPH05108164A - Position controller - Google Patents

Abstract

PURPOSE:To reduce a limit cycle phoenomenon by inputting the output of a positional deviation device and providing a deviation comparator generating a signal to the position controller at the moment when the positional deviation gets zero. CONSTITUTION:This controller is provided with a deviation comparator 10 inputting the output of a positional deviation device 2 and generating a signal to a position controller 3 at the moment when the positional deviation becomes zero. When the position controller 3 receives the signal, it changes a speed command to a speed controller 5 to zero. At this time, the deviation comparator 10 outputs a signal the moment when the positional deviation becomes zero during a sampling period, the output of the positional deviation device 3 becomes zero, a motor 7 stops approximately at an aimed position although it slightly passes away the aimed position. That is, the limit cycle phenomenon can be reduced by sampling time and thus can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position controller for controlling the position of a motor having a quantized position detector such as a pulse encoder in a discrete time system.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram of a conventional example of this type of position control device.

In a general operation, a command is generated by the position commander 1, a difference from the actual movement distance calculated by the position detector 9 is calculated by the position deviation device 2, and an appropriate calculation by the position controller 3 is performed. Is converted into a command for the speed controller 5. In the speed controller 5, appropriate calculation processing is performed based on the deviation between the command from the position controller 3 ′ calculated by the speed deviation device 4 and the actual speed detected by the speed detector 8, Is converted into a command to the power amplifier 6. The electric power of the power converter 6 is supplied to the electric motor 7 and the electric motor 7 moves to achieve position control.

When a quantized detector (for example, a pulse encoder) is used as the position detector 9 in such a position control device, the position controller 3 is inevitably a digital structure and is managed at regular intervals. It is a discrete time control.

[0005]

In the discrete time control, if the time interval for management (hereinafter referred to as sampling time) is very short, the characteristic value (eg, positioning accuracy) of the position control device is not adversely affected. Can be said. However, in a normal case, due to the configuration of the system, for example, when a microcomputer is used, an interval of a certain time or more, which is a necessary time for calculation or the like, is absolutely necessary.

In such an example, if the sampling time becomes particularly long, the control system will eventually become unstable. Therefore, the sampling time is required to be within a certain time required for the control system in order to maintain the stability of the control system.

A position command is first generated in the position control, the motor 7 moves based on the deviation between the command and the actual position, the deviation gradually decreases, and finally the command and the actual position are Will be equal. However, in the general case and in the case where the position controller 3 ′ and the speed controller 5 are composed of only proportional gains, the deviations remain steadily. In order to eliminate such a phenomenon, a method is adopted in which an integral element is added to the configuration of the position controller 3'or the speed controller 5 to eliminate the steady deviation.

When the integral element is inserted, the steady deviation is surely eliminated, but the phenomenon of limit cycle appears at the time of stop due to the influence of the integral element at the end of positioning.

The limit cycle is, as shown in FIG.
This is a phenomenon in which the actual position of the electric motor 7 moves back and forth around the target position in cycles. There are several possible factors that cause this phenomenon, but the sampling time of the position controller 3 ′ is also one of the major factors. The main reasons are considered as follows.

When a deviation occurs in the position controller 3 ', a calculation is added to the deviation to generate a command to the speed controller 5. This calculation is performed at every sampling timing shown in FIG. 5A, and the calculated value is kept constant during the sampling period as shown in FIG. 5B. On the other hand, in response to the command, the electric motor 7 starts moving through the speed controller 5 and the power amplifier 6. As a result of the calculation at time t ₁ , FIG.
As shown in (3), if a movement command in the positive direction is issued, for example, a constant positive movement command is held during the sampling period from time t ₁ , as shown in FIG. 5 (3). The command will be retained even after the target position has passed. Then at time t _2, is recognized current position, a time t ₂ thereafter becomes a negative command, the command value will be retained by one sampling time, similar phenomenon to occur continuously or less There is a limit cycle.

It is an object of the present invention to provide a position control device of the kind mentioned at the outset in which the phenomenon of limit cycles as described above is reduced.

[0012]

In order to achieve the above object, the position control device of the present invention is arranged such that when the deviation between the target position from the position commander and the current position of the electric motor reaches zero, the position is instantaneously changed. The position controller is characterized in that it has means for generating a signal to the controller, and the position controller sets the speed command to the speed controller to zero upon receiving the signal.

[0013]

Therefore, the phenomenon of limit cycle is reduced.

[0014]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram of a position control device according to one embodiment of the present invention, and FIG. 2 is a timing diagram for explaining the effect of this embodiment. 1, the same numbers as those in FIG. 3 indicate the same elements.

In this embodiment, a deviation comparator 10 is provided which inputs the output of the position deviation device 2 and generates a signal to the position controller 3 at the moment when the position deviation becomes zero. When the signal is received, the speed command for the speed controller 5 is set to zero.

Therefore, during the sampling period (see FIG.
Even in the case of (1)), the signal is output from the deviation comparator 10 at the moment when the position deviation becomes zero (FIG. 2 (3)), and the output of the position controller 3 becomes zero (FIG. 3 (4)). )), The electric motor 7
Although it goes too far from the target position, it stops almost at the target position (Fig. 2 (4)). That is, the phenomenon of limit cycle is improved by the sampling time.

[0017]

As described above, the present invention has the effect of reducing the phenomenon of limit cycle by detecting that the position deviation becomes zero and making the output of the position controller zero.

[Brief description of drawings]

FIG. 1 is a block diagram of a position control device according to an embodiment of the present invention.

FIG. 2 is a timing diagram illustrating effects of the embodiment of FIG.

FIG. 3 is a block diagram of a conventional example of a position control device.

FIG. 4 is a diagram showing a limit cycle phenomenon.

FIG. 5 is a timing diagram illustrating the reason why a limit cycle phenomenon occurs.

[Explanation of symbols]

 1 position command device 2 position deviation device 3 position controller 4 speed deviation device 5 speed controller 6 power amplifier 7 electric motor 8 speed detector 9 position detector 10 deviation comparator

Claims (1)

[Claims] 1. A position control device for position controlling a motor having a quantized position detector such as a pulse encoder in a discrete time system, wherein a deviation between a target position from a position commander and a current position of the motor is zero. A position control device comprising means for generating a signal to the position controller at that moment when the signal reaches the position controller, and the position controller sets the speed command to the speed controller to zero when receiving the signal.