Position error correction equipment

Details Position error correction equipment Position error correction equipment

1982-06-29

1985-02-26

Ruggiero, Joseph F.

Boots, shoes, and leggings

318630, 318632, 364175, 364474, G06F 1546, G05B 1918

Patent

active

045021082

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to an improvement of position error correction equipment which corrects an error in the position of movement relative to a commanded position in a numerical control machine tool through using error correction data prestored in an error storage circuit.
In a numerical control machine tool in which commanded position information is compared with detected position information from a position detector mounted on a servomotor shaft or ball screw for moving a movable machine part and in which position control is carried out by driving a servomotor, so that an error between the commanded and detected position information may be reduced to zero, the position control accuracy is dependent substantially on the accuracy of the ball screw and other gear mechanisms. When requiring highly accurate position control, there have heretofore been adopted various position error correcting methods, such as a backlash correction, pitch error correction or the like in a mechanical system; in the past, however, since the correction has been effected based on only fixed error correction data, that is, correction data predetermined for one state of the machine tool, for example, a constant temperature of a ball screw and a constant weight of a movable part, accurate correction has not always been carried out. The reason is that, for instance, a pitch error of the ball screw may cometimes undergo a large variation due to a temperature change or the like of the ball screw, and the quantity of backlash in the mechanical system may greatly change with the change in the weight of different workpieces.


SUMMARY OF THE INVENTION

The present invention has for an object to permit more accurate position error correction by preparing error correction data corresponding to respective states of a numerical control machine tool and selectively using the error correction data in accordance with a particular state of the numerical control machine tool.
To achieve this object, the present invention is provided with an error storage circuit in which error correction data groups predetermined by measurement in respective states of the numerical control machine tool are stored corresponding to the respective states, an error correction data selecting circuit for selecting an error correction data group corresponding to a particular state of the numerical control machine tool from the error correction data groups stored in the error storage circuit, and a position correcting circuit for correcting an error in the position by adding a correction pulse to a command pulse or feedback pulse from a position detector through utilization of the error correction data group selected by the error correction data selecting circuit.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the equipment of the present invention;
FIG. 2 is a schematic diagram of an example of a pitch error characteristic;
FIG. 3 is a diagram of the contents of pitch error correction data groups;
FIG. 4 is a diagram showing variations in the quantity of backlash in the direction of movement; and
FIGS. 5 and 6 are diagrams of the contents of backlash error correction data groups.


DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram illustrating the principal part of an embodiment of the device of the present invention. Reference character MEM indicates an error storage circuit, PD.sub.1 to PD.sub.n pitch error correction data groups, BD.sub.1 to BD.sub.n backlash correction data groups, MPX a correction data selecting circuit, cd.sub.1 and cd.sub.2 status signals indicating the status of a numerical control machine tool, CPG a position correcting circuit, PT a command tape, DDC a direction reversal decision circuit, CONT a position counter, INT an interpolator, OG.sub.1 and OG.sub.2 OR gates, GAT a gate circuit, ERR an error register, SA a drive circuit, SM a servomotor, DS a ball screw, MP a movable machine part, DET a detector, such as a position coder or the like, and DDM a direction deciding cir

REFERENCES:
patent: 3555254 (1971-01-01), Gerber
patent: 3705400 (1972-12-01), Cordes, Jr.
patent: 3794902 (1974-02-01), Nishimura et al.
patent: 3852719 (1974-12-01), Nishimura et al.
patent: 4099113 (1978-07-01), Hayashi
patent: 4251761 (1981-02-01), Inoue

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