Pitch error compensating system

Details Pitch error compensating system Pitch error compensating system

1991-12-02

1994-05-03

Nguyen, Long T.

Boots, shoes, and leggings

36447428, G06F 1546

Patent

active

053093674

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a system for compensating for a pitch error of a ball screw in a numerically controlled machine tool, and more particularly to a pitch error compensating system suitable for precision machining.
2. Description of Related Art
Ball screws for controlling movable components of numerically controlled machine tools do not have accurately constant pitches. Pitch errors of such ball screws are compensated for by computerized numerical control apparatus to increase positioning accuracy. According to a general pitch error compensating system, the strokes of respective axes are divided into suitable periods, and pitch error corrective quantities are measured in the respective periods. The measured corrective quantities are then stored in a nonvolatile memory. Each time an axis moves, the pitch error corrective quantity that corresponds to the present value of the axis is read from the memory, and added to or subtracted from interpolated pulses, thereby compensating the pitch error.
FIG. 6 of the accompanying drawings shows, by way of example, pitch error corrective pulses in a conventional pitch error compensating system. In FIG. 6, a first period P.sub.0 -P.sub.1 has a pitch error corrective quantity .epsilon.1, a second period P.sub.1 -P.sub.2 a pitch error corrective quantity .epsilon.2, and a third period P.sub.2 -P.sub.3 has a pitch error corrective quantity .epsilon.3, each period being indicated as a pitch error correcting period l. The pitch error corrective quantity in each period is outputted as a pitch error corrective pulse at an intermediate point of the period, and added to interpolated pulses.
A pitch error corrective quantity is outputted at once as a pitch error corrective pulse. If the pitch error corrective quantity is large, then the corresponding error corrective pulse is also large. The large error corrective pulse that is outputted at once is not preferable from the standpoint of positioning accuracy. Such pitch error corrective pulse may lower the quality of the machined surface in precision machining.


SUMMARY OF THE INVENTION

In view of the aforesaid drawbacks of the conventional system, it is an object of the present invention to provide a pitch error compensating system which is capable of smoothing the movement of a machine.
To achieve the above object, there is provided a system for compensating for a pitch error of a ball screw of a numerically controlled machine tool, comprising a memory for storing pitch error corrective data, a present value register for integrating output pulses from interpolating means and storing a present value, pitch error calculating means for reading said present value and outputting pitch error corrective quantities at equal intervals in a period having said present value, and an adder for adding interpolated pulses from said interpolating means and said pitch error corrective quantities, and outputting sum pulses to an axis control circuit.
The pitch error calculating means reads a present value, reads pitch error corrective data, and outputs pitch error corrective quantities as pitch error corrective pulses at equal intervals in the period. The pitch error corrective pulses are added to interpolated pulses. Since the pitch error corrective quantities are not outputted all at once, the machine tool moves smoothly, and the quality of the machined surface of the workpiece is improved.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a pitch error compensating system according to the present invention;
FIG. 2 is a block diagram of the hardware arrangement of a computerized numerical control (CNC) apparatus for implementing the pitch error compensating system according to the present invention;
FIG. 3 is a diagram showing the manner in which pitch error corrective pulses are outputted;
FIG. 4 is a diagram illustrative of the manner in which a pitch error calculating means calculates pitch error corrective pulses;
FIG. 5 is flowchart of a processing sequenc

REFERENCES:
patent: 4864508 (1989-09-01), Iwagaya
patent: 5210478 (1993-05-01), Sasaki et al.

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