JP3338143B2 - 3D position control system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position control system for a motion machine having a three-dimensional spatial mechanism, and more particularly to a three-dimensional position control system having a spatial error correction function using a software servo.

[0002]

2. Description of the Related Art In a motion machine having a three-dimensional space mechanism such as a three-dimensional coordinate measuring machine (CMM), a machine tool, and a robot, a motion space is commanded by a processing error of a mechanical part, deformation or distortion due to temperature, or the like. A problem arises that the space does not match. For this reason, a technique for correcting this spatial error by an appropriate calculation algorithm has been constructed. In particular, many coordinate measuring machines have been put into practical use, and basic technology has been developed in various fields.

A general three-dimensional position control system is composed of a command generator for outputting a position in a command coordinate system defining a motion as a command value, and a servo system which operates using the command value as an input. The servo system includes a feedback adder, a position controller equipped with a motor and a drive mechanism (such as a screw or a belt), and a position detector (such as a linear scale) that detects the position of the motion result of the position controller. Has,
These constitute a feedback control loop.

In such a position control system, if there is no error in any of the three axes between the command space and the motion space, the input coordinate system (ie, the command coordinate system) and the output coordinate system (ie, the motion coordinate system) of the servo system. Matches exactly. However, it is common for spatial mechanisms to have errors in straightness and squareness, and these errors change due to temperature. Therefore, in general, it is inevitable that the motion coordinate system has a spatial distortion (spatial error) with respect to the command coordinate system. Also, CMM
Then, the actual measurement value has a measurement error caused by a spatial error.

In order to correct the measurement error caused by such a spatial error, to output true measurement data, and to perform correct position control and trajectory control, a position detector and an adder in a control loop are required. Between them, an F converter for correcting a spatial error by a predetermined function F is provided. The value of the value on the motion coordinate system in the command coordinate system can be known using, for example, a laser interferometer, and the error correction function F is determined.

However, there are cases where the spatial error correction function F is complicated and its arithmetic processing takes a long time, and the F conversion processing cannot be performed in the control loop. This situation will be specifically described with reference to FIG. In the position control system, there is an appropriate control cycle S [msec] of the control loop for achieving the maximum gain in relation to the natural frequency and the damping rate of the control target. In response to the control cycle S, when performing sampling control of the control loop by software, that is, control for calculating and outputting a control command value for each time S, a calculation processing time including a spatial error correction operation per sampling. T
Needs to be within the range of the control cycle S as shown in FIG. However, when the spatial error correction function F is complicated and the processing capacity of the CPU is insufficient as described above, it becomes difficult to satisfy this condition.

[0007]

As described above, in a three-dimensional position control system using software servo, when a spatial error correction process is performed in a control loop, if the spatial error correction function is complicated, the error correction process is controlled. There was a problem that it could not be done within the cycle. If the control cycle is extended, the error correction can be calculated within the control cycle.
The control cycle is optimally set according to the control target as described above. If the control cycle is extended, the response of the control loop becomes slow and the control characteristics deteriorate. In addition, in order to perform trajectory control based on a position command, it is essential that spatial error correction be performed in a control loop, and this cannot be performed outside the control loop.

An object of the present invention is to provide a three-dimensional position control system capable of correcting a spatial error in a control loop without deteriorating control characteristics.

[0009]

SUMMARY OF THE INVENTION The present invention provides a position control means for controlling an operation position in a movement space in accordance with a target value inputted from the outside, and an operation position in the movement space by the position control means. And a position control loop having feedback means for performing feedback control of the position control means by an output of the position detection means so as to match the operating position with the target value. A spatial error correction means for calculating a spatial error between a command space and a motion space with respect to an output value of the position detection means and outputting a feedback correction value. Divides the spatial error over a plurality of control cycles set according to the control target of the control loop, and calculates a new correction value.
In each control cycle until the
It is characterized by performing control .

[0010]

According to the present invention, the arithmetic processing for spatial error correction, which should be processed within one sampling cycle, is divided and performed over a plurality of control cycles. Therefore, even when the spatial error correction function is complicated, a predetermined spatial error correction function can be mounted in the control loop without deteriorating the control characteristics of the control loop. In the original position control system, control is performed such that the current value is corrected in each control cycle, and the next command value is calculated and output based on the corrected current value. The correction calculation for the target value and the current value for which the sampling period spanning the cycle has elapsed ends. Therefore, in the plurality of sampling periods, a spatial error correction operation using the correction value calculated immediately before is performed. In order to actually perform spatial error correction by the divisional operation under such conditions, it is necessary that the error correction change in a small range where the error correction changes in the required moving distance and time range by the position control means. It is.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of a position control system according to an embodiment. The control loop basically includes a position controller 1 including a motor and its driving system, a position detector 2 such as a scale counter, and an adder 3 for forming a feedback circuit for feeding back a position detection output. The adder 3 receives a target value xt and a correction value xc based on coordinate values in the command space, and Δx =
A command value xt-xc is input to the position controller 1. The position detector 2 calculates a coordinate value xm = (Xm, Ym) in the motion space.
, Zm). In order to correct the error and to feed back the detection result to obtain a command value ΔX, a linear correction circuit 4 for performing linear correction and a spatial error correction circuit 5 are provided between the position detector 2 and the adder 3 as shown in the figure. And an adder 6 are inserted.

The linear correction circuit 4 corrects a linear function x with respect to the position detector output x 'in order to correct environmental changes such as temperature, reproducibility of assembly, and subtle linear errors occurring with time. = Ax 'to perform straight line correction.
The spatial error correction circuit 5 calculates a coordinate value xm = (X
m, Ym, Zm) for the spatial error correction δx = f
(Xm) = (δX, δY, δZ).
The adder 6 adds the output value x of the linear correction circuit 4 and the correction δx calculated by the operation of the spatial error correction circuit 5 to obtain a correction value xc as a feedback control value.

In practice, the linear correction circuit 4, the spatial error correction circuit 5, and the adders 3 and 6 are constituted by computer software. In this embodiment, the calculation processing for obtaining the correction amount δx by the spatial error correction circuit 5 is performed over N sampling periods. That is, assuming that one control cycle is S [msec], the loop control using the old uncorrected correction δxOLD is performed during the N × S period, and the calculation for obtaining the new correction δxNEW is performed in the meantime.

FIG. 2 shows a control flow of this embodiment for performing such a division operation. First, a straight line correction of x = ax 'is performed on the position detection output x' by the position detector 2 (S1). Next, C value corresponding processing for dividing the calculation for the spatial error correction is performed (S2). That is, while counting the number of sampling cycles, a new error correction amount δx is calculated by a plurality of processes ΔCi until the count value C reaches the predetermined number N of cycles. FIG. 3 shows the flow of the C value handling process. C1, C2,..., CN are calculation processes for obtaining an error correction amount divided into each sampling period. Then, the count value C is stepped up at each sampling period (S3), and it is determined whether or not the count value has exceeded N (S4). An operation for obtaining xc = x + δx is performed (S7), and an operation for obtaining a command value Δx = xt−xc from the target value xt is performed as usual using the correction value xc (S8). When the count value C exceeds N, the new error correction value .delta.xNEW obtained during that time is adopted, and at the same time, the count value C is reset (S5), and the same operation is repeated thereafter.

FIG. 4 shows a temporal flow of the position control calculation processing according to this embodiment in correspondence with FIG. FIG.
Is within the range of the control cycle S, and this processing time T 'is the time T for performing the same calculation processing as before, and the steps S2 to S for spatial error correction.
7 requires a processing time U. Division operation processing time U
It is necessary to satisfy the condition of T + Umax <S, where Umax is the maximum calculation time of.

As described above, in this embodiment, the loop control is performed using the old error correction amount δx OLD during the time of N × S during which the new error correction amount δx NEW is calculated. Specifically, for example, when accurate trajectory control is required while moving at the maximum moving speed V, the distance L = N ×
During S × V, the old error correction δxOLD is used. Therefore, during this time, the amount of change of the error correction amount δx needs to be within a certain minute range.

[0017]

As described above, according to the present invention, the arithmetic processing for spatial error correction is divided into a plurality of control cycles so that the control cycle is not lengthened, and thus the control characteristics are improved. A three-dimensional position control system capable of correcting a spatial error in a control loop based on a complicated correction function without deterioration can be obtained.

[Brief description of the drawings]

FIG. 1 shows a configuration of a position control system according to an embodiment of the present invention.

FIG. 2 shows a control flow of the embodiment.

FIG. 3 shows a flow of a division operation process of the embodiment.

FIG. 4 is a control timing of the embodiment.

FIG. 5 is a control timing chart of a conventional position control system.

[Explanation of symbols]

1: Position controller, 2: Position detector, 3, 6: Adder, 4
... a linear correction circuit, 5 ... a spatial error correction circuit.

Continuation of front page (56) References JP-A-5-248852 (JP, A) JP-A-5-233005 (JP, A) JP-A-5-204461 (JP, A) (58) Fields investigated (Int) .Cl ^7, DB name) G05D 3/00 -. 3/20 G05B 11/00 - 13/04 G05B 19/18 - 19/46 G05B 21/00 - 21/02

Claims (1)

(57) [Claims] 1. A position control means for controlling an operation position in a movement space according to a target value inputted from the outside, a position detection means for detecting an operation position in the movement space by the position control means, and A position control loop having feedback means for performing feedback control of the position control means by an output of the position detection means so as to make the operating position coincide with the target value; an output of the position detection means provided in the control loop; A three-dimensional position control system having a spatial error correction means for calculating a spatial error between the command space and the motion space for the value and outputting a correction value for feedback, wherein the spatial error correction means is controlled by the control loop. Until a new correction value is obtained by dividing the spatial error over a plurality of control cycles set according to
A loop control based on the immediately preceding correction value in each control cycle .