JPH03198112A - Safety device for servo control mechanism - Google Patents

Abstract

PURPOSE:To improve the stability of a servo control mechanism by inhibiting the start of the servo control mechanism when the difference of counter values of an absolute position type ABS encoder is larger than a prescribed level at the time of turning on/off a power supply. CONSTITUTION:The counter value 5a of an ABS encoder 5 is stored at the time of turning on/off a power supply, respectively. Then the values 5a set at both states are compared with each other. If the difference between both values 5a is larger than a prescribed level, the start of a servo control mechanism is inhibited. Thus the servo control mechanism is not started as long as the difference of values 5a of the encoder 5 at the time of preceding turning off and present turning on of the the power supply is larger than a prescribed level. Thus it is possible to obtain a safety device of the servo control mechanism that secures the safety even if an error is produced to the encoder 5 at the time of turning on the power supply.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a safety device for a servo control mechanism using an absolute position (hereinafter referred to as ABS) encoder.

[Prior Art] FIG. 2 is a block circuit diagram of the main parts of a conventional servo control mechanism.

In the figure, (1) is a position command signal, (2) is an adder, and (3)
is a servo amplifier connected to the adder (2), (4) is a motor connected to the servo amplifier (3), and (5) is an ABS encoder coupled to the motor (4) and outputs a position signal (5a). be.

The conventional servo control mechanism is configured as described above, and the position command signal (1) and the position signal (5a) negative feedback from the ABS encoder (5) are collated in the adder (2), and the deviation ( The movement command value) is sent to the servo amplifier (3). The output of the servo amplifier (3) is given to the motor (4), and the motor (4) is controlled so that its rotational position follows the position command signal (1).

[Problems to be Solved by the Invention] In the conventional servo control mechanism as described above, the counter value of the ABS encoder (5) is controlled by negative feedback. If an error occurs in the counter value in 5), an abnormal movement command value will be given, and there is a problem that there is a risk of movement to an unexpected position.

This invention was made to solve the above problems, and its purpose is to provide a safety device for a servo control mechanism that can ensure safety even if an error occurs in the ABS encoder when the power is turned on. do.

[Means for Solving the Problems] A safety device for a servo control mechanism according to the present invention stores counter values of an ABS encoder when the power is turned off and when the power is turned on, and compares them to determine whether the difference is greater than a predetermined value. when,
This prevents the servo control mechanism from starting.

[Operation] In the present invention, if the difference between the ABS encoder counter value at the time of the previous power-off and the current power-on is equal to or greater than a predetermined value, the servo control mechanism is not activated.

[Embodiment] FIG. 1 is a block circuit diagram showing an embodiment of the present invention, and parts similar to those of the conventional device are designated by the same reference numerals.

In the figure, (11) is a safety device, (12) is a switch that is connected to the ABS encoder (5) and closes when the servo power is turned off, (13) is a switch that is closed when the main power or servo power is turned on, and (14) (15) are the switches (1
2) The buffer connected to (13), (16) is a comparator that compares the outputs of buffers (14) and (15) and issues an abnormal signal (16a) when the difference exceeds a predetermined value, (17)
) is a switch that opens when an abnormality signal (16a) is output.

Next, the operation of this embodiment will be explained.

When the servo power is cut off, the switch (12) is closed and the counter value of the ABS encoder (5) at that time, ie, the position signal (5a), is stored in the buffer (14). Next, when the main power or servo power is turned on, the switch (13) is closed and the current position signal (5a) is sent to the buffer (15).
is memorized. Then, the two values are compared by a comparator (16), and if the difference is greater than a predetermined value, an abnormality signal (16) is detected.
a) is output and the switch (17) is opened, so the servo control system is not activated. Therefore, the position signal (5a
), the risk of unexpected behavior is eliminated.

Furthermore, when the power is turned on for the first time and when the ABS encoder (5) is reset, the counter value of the ABS encoder (5) at that time is stored in the buffer (1) of the counter value when the power is turned off.
4).

[Effects of the Invention] As explained above, in this invention, if the difference between the ABS encoder counter values at power-off and power-on is greater than or equal to a predetermined value, the servo control mechanism is not activated. Therefore, the validity of the counter value of the ABS encoder can be confirmed, and the safety of the servo control mechanism can be improved.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram showing an embodiment of a safety device for a servo control mechanism according to the present invention, and FIG. 2 is a block circuit diagram of essential parts of a conventional servo control mechanism. In the figure, (4) is a motor, (5) is an absolute position encoder, (5a) is a position signal, (14) is a first storage means (buffer), and (15) is a second storage means (buffer). ,
(16) is a comparator. Note that the same reference numerals in the figures indicate the same parts. Agent Masuo Oiwa

Claims (1)

[Claims] In a servo control mechanism that detects a position based on a counter value of an absolute position encoder, a first storage means stores a counter value of the encoder when the power is turned off, and a second storage means stores a counter value of the encoder when the power is turned on. and a comparator that compares the outputs of the first and second storage means and issues a signal to prevent activation of the servo control mechanism when the difference is greater than a predetermined value. Safety device for servo control mechanism.