JPS6042483B2 - numerical control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a numerical control (hereinafter referred to as NC) device equipped with a computer.

Recent NC devices are shifting to CNCs equipped with computers, and digital servos have also begun to be used instead of conventional analog servos.

This digital servo uses a computer to perform much of the processing necessary for a servo, and outputs the processed information to a servo motor to control it. In this case, the processing time of the computer differs depending on the contents of the command data, so if the information processed by the computer is directly output to the servo motor, there is a drawback that the servo characteristics will not be linear. SUMMARY OF THE INVENTION An object of the present invention is to provide a numerical control device that does not have the above drawbacks and can output computer processing information to a servo motor under certain time conditions.

The present invention will be described below based on an embodiment shown in the drawings.

FIG. 1 is a block diagram showing the configuration of the present invention, and numeral 11 indicates a computer, such as a minicomputer T-40N made by our company.
etc. are used. 12 is a buffer circuit for temporarily storing the output of the computer 12 which is output in synchronization with the sampling signal a, and 13 is a buffer circuit until the next command comes.
This is a hold register for holding commands.

14 is a digital-to-analog converter that converts the digital quantity command value held in this register 13 into a required pulse width, and the servo motor 15 is driven by this analog output.

A position detector 16 detects the actual position of the servo motor 15, and is composed of a combination of a pulse encoder and a reversible counter.

Further, 17 and 18 represent transfer circuits that transfer input data in synchronization with the sampling signals b and c. Next, the action will be explained.

FIG. 2 is a diagram showing the operation timing of the above configuration. In the same figure, C indicates the timing of the sampling signal c, and the current position of the servo motor 15 or a machine not shown is detected by the position detector 16 from the computer 1 at the sampling period of TC.
1 is input. When the computer 11 receives the detected current position, it performs the necessary processing for the servo shown in FIG. In other words, the position command value is E(N), and the detector 1 is
Letting the feedback signal output from 6 be H(N), the output 1(N) can be obtained from the following equation. Here, N represents a suffix indicating the Nth sampling.

When the above calculation is completed, the command value for the servo motor 15 is immediately output to the buffer circuit 12.

d in FIG. 2 indicates the processing time of the computer 11, and since this value varies depending on the command value, the timing of the output is not constant. Next, the contents of the buffer circuit 12 are transferred to the hold register 13 at the timing shown in FIG. This register 1
The digital value outputted from 3 is converted by the digital-to-analog converter 14 into an analog value with a pulse width proportional to the digital value to drive the servo motor. As mentioned above, the processing time d of the computer 16 is not constant depending on the command value.

Therefore from the computer 11 - directly the hold register 13
When output to , this content is updated at the timing of sampling signal a. As described above, since the timing of the sampling signal a is not constant, the output to the servo motor 15 lacks linearity and the control becomes unstable. So here comes the main idea. In the present invention, if the timing of the sampling signal b is kept constant and the contents of the buffer circuit 12 are sent out, the update of the contents of the hold register 13 becomes constant. In this case, the sum of sampling periods is TD>maximum processing time of computer 11+time required to output to buffer register 512.
...It must be (2). TD is a dead time in control, so that it does not have a negative effect on servo characteristics.
It is necessary to keep it as short as possible. Although the above description was about a single-axis servo, since the NC moves multiple axes at the same time, one or more servo motors are required for each axis.

In this case, the configuration is exactly the same as the one-axis case, and by making the timing of the sampling signal b of each servo motor 15 the same, it is possible to synchronize each servo.
Further, if the sum of the sampling periods TD and TC is set to TC, the buffer circuit 12 and the transfer circuit 17 become unnecessary. To do this, the sampling signal A is
, c and the processing time d of the computer 11 are determined. However, the data output at sampling time a(n) is a value processed by the computer 11 in processing time d(n-1). In this case, although the circuit is simpler, the dead time becomes longer, so the servo characteristics become a little longer than in the previous embodiment. In this way, according to the present invention, it is possible to provide an effective numerical control device that can stably operate the servo motor by keeping the timing of output to the servo motor constant.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a diagram showing the operation timing of the device of the present invention, FIG. 3 is a block diagram showing internal processing of a computer, and FIG. 4 is another embodiment. This figure shows the operation timing adapted to the following. 11... Computer, 12... Buffer circuit, 13... Hold register, 14...
Digital ●Analog converter, 15... Servo motor, 16... Position detector, 17, 18...
... Transfer circuit, A, b, c... Sampling signal.

Claims (1)

[Claims] 1. A computer that outputs a command value, a hold register that inputs the command value via a buffer circuit and stores it as a digital quantity, a digital-analog converter that converts the contents of this hold register into an analog quantity, and a digital-to-analog converter that converts the contents of this hold register into an analog quantity. Controls data transfer between a servo motor that inputs the output of an analog converter and drives the machine via a servo motor, a position detector that detects the position of this servo motor or the machine, and the buffer circuit and hold register. a first transfer circuit that transfers the contents of the position detector to the computer, and a second transfer circuit that transfers the contents of the position detector to the computer; The servo motor is sampled by keeping the sampling period of the sampling signal output to the first transfer circuit constant and updating the contents of the hold register at a constant value that is slower than the maximum processing time of the computer. A numerical control device characterized by controlling.