JPH02145239A - Positioning method for moving body of machine tool - Google Patents

Abstract

PURPOSE:To correctly position a moving body by performing the correction corresponding to the backlash amt. existed in a feed driving system at multiple points in the optional position on the way of the whole process of the moving body in a machine tool. CONSTITUTION:Wear is small at (a) part and large at (b) part. So the backlash amt. of a feeding screw 3 and nut is not constant and this backlash amt. is stored in an NC (numerical control unit) 7 by dividing and setting it as shown by a broken line by dividing into l1 - lm..., etc., from a reference point A. At the time when a moving body 4 performs a change-direction, the optimum backlash at the point thereof is commanded from the NC 7 and the moving body 4 is correctly positioned.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is aimed at reducing the play (
The present invention relates to a backlash correction method for accurately positioning a moving object by eliminating backlash.

[Conventional technology]

tUWe is a numerical control device widely used in machine tools.
One of these is a backlash correction function.

This is intended to eliminate play (backlash) in the feed drive system and accurately position the moving body. However, among conventional products, there is no control system that compensates for irregular wear of the feed screw or the like, or compensates for the rigidity of the feed screw to compensate for backlash in various parts of the feed screw.

An example of a conventional backlash correction means for a feed drive system is shown in FIG. The figure shows the amount of backlash applied to the entire stroke of the feed drive system of a moving object in a machine tool.As shown in the figure, the conventional backlash correction amount is a constant value throughout the entire stroke, and It is normal to set the total amount of backlash up to the nut. For this reason, conventional closed-loop control methods such as expensive inductosin feedback have been used as accurate position control methods for moving objects.

[Problem to be solved by the invention]

By the way, according to the above-mentioned conventional backlash correction method, for example, in the case of a feed screw with poor machining accuracy or a feed screw with extremely worn parts after long-term use, the amount of backlash correction is changed depending on the position of the feed screw. There is a problem where it cannot be done. In the case of a feed screw with a wide support interval as shown in FIG. 3, the axial rigidity of the feed screw is weaker at the center of the screw than at the shaft ends as shown in FIG. 4. For this reason, even if an attempt is made to move the movable body in the forward and backward direction by a minute amount at the central portion of the feed screw, the displacement of the feed screw is absorbed and the movable body does not move according to the command value of the servo motor. However, when the movable body is located at the end of the shaft of the screw, the rigidity of the screw is also high, so the movable body moves according to the command value of the servo motor.

For this reason, for backlash correction in the feed system, it is insufficient to simply set a constant value as in the conventional method, and it is better to use a method that allows correction values to be set at multiple points throughout the entire stroke of the moving body.

The present invention aims to solve the above-mentioned problems and provide a new method for positioning a moving body in a machine tool, in which sufficiently satisfactory positioning accuracy can be obtained even with a resolver feedback semi-closed loop method.

[Means to solve the problem]

Therefore, the method for positioning a moving body of a machine tool according to the present invention is as follows:
Accurate positioning of the moving object is made possible by performing multi-point correction commensurate with the amount of backlash that exists in the feed drive system at any position during the entire process of the moving object in the machine tool. It is characterized by

[Effect]

In order to accurately position a moving body in a machine tool, it is necessary to eliminate error factors included in the feed drive unit.

The present invention is a method for eliminating backlash (play) between the feed screw (rack in the case of rack-pinion feed) and the nut, which is one of the causes of this error. To explain the operation, the feed screw 3 has the first. As shown in FIG. 2, the clearance with the nut is not constant over the entire length of the screw. Particularly for those that have been used for a long time, the screws are often worn out (c).
The part force is 1 mm small, and the 0 part is worn 9 degrees. Therefore, this backlash is 2 degrees from the reference point ■! □, etc., and set the division as shown by the broken line in Fig. 2, and place the dead weight in the NC (numerical control device). When the moving body 4 changes direction, the optimum backlash at that point is commanded, so that the moving body can be accurately positioned.

When a feed screw is fixedly supported at both ends, the axial direction l1 of the screw
As shown in the fourth factor, the stiffness is the lowest at the center of the screw. If the amount of backlash correction can be set arbitrarily for each part,
The moving object can be accurately positioned.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.
1 to 4 are diagrams for explaining the backlash removal method according to the present invention. In these figures, Figs. 1 and 3 are schematic diagrams of the movable body drive system of the machine tool, Fig. 2 is an explanatory diagram showing the amount of play between the screw and nut during the stroke of the movable body, and Fig. 4 is a schematic diagram of the moving body drive system of the machine tool. FIG. 6 is an explanatory diagram showing the failure property of the screw shaft during the same process.

Conventionally, there is no technology that incorporates a multi-point memory-type backlash correction function within a numerical control unit. As an alternative to this, the present invention provides a backlash that is adapted to the feed bag of the movable body in order to compensate for changes in the stiffness of the feed screw.
The feature is that the moving body is correctly positioned by adding a correction on the program that commands the feed movement amount including slippage.

Fig. 1 shows a case where the feed screw 3 has extreme wear. The movable body 4 slides on the movable body base 5 in the direction of the arrow shown in the figure by rotating the feed screw 30 times. 6 is a servo motor detector such as a resolver, and 7 is a numerical control device* (NC). In the case of FIG. 1, in which the feed screw 3 has worn out locally due to long-term use, portions a have less wear and portions b have more wear. For this reason, the amount of backlash between the feed screw 3 and the nut is not constant, so
From the reference point ■, -Am...
Divide into equal parts and set the division as shown by the broken line in Figure 2.
C (numerical control device) 7. When the moving body 4 changes direction, the optimum backlash at that point is commanded by the NC 7, so that the moving body 4 can be accurately positioned.

Fig. 3 shows the case where the axial rigidity of the feed screw is weak, and when the feed screw 3' is fixedly supported at both ends, the screw 3'
As shown in FIG. 4, the axial rigidity is lowest at the center of the feed screw 3'. (C part is team]
Even in this case, if the amount of backlash correction commensurate with the PLIJ characteristics of the center and ends of the screw 3/ can be arbitrarily set at each part during the stroke, the moving body 4 can be Accurate positioning is possible.

As shown in FIGS. 2 and 4, at point Jn of the stroke, δ. ,・Fist・−ra point is width, ノ. δn/... at one point δm'
The backlash correction amount is set at multiple points as shown in FIG. 4. In addition, Φ' in FIG. 4 is a reference point.

[Brief explanation of the drawing]

Figures 1 to 4 show one embodiment of the present invention.
Figures 2 and 3 are schematic diagrams of the drive system of the moving body of the machine tool.
The figure is an explanatory diagram showing the amount of play between the screw and the nut during the movement of the moving body, and Figure 4 is an illustration showing the amount of play between the screw and nut during the movement of the moving body.
□It is an explanatory diagram showing the nature. FIG. 5 shows an explanatory diagram of a conventional backlash correction means. 1... Feed servo motor 2... Screw drive gear 3.3'... Feed screw 5... Moving body base 7... Numerical control device. 4... Moving object 6... Servo motor detector

Claims (1)

[Claims] (1) By performing multi-point correction commensurate with the amount of play (backlash) that exists in the feed drive system at arbitrary positions during the entire stroke of the moving body in the machine tool, the moving body A method for positioning moving objects in machine tools that enables accurate positioning.