DE3416091A1 - Device for scale correction in a numerically controlled machine tool - Google Patents

Abstract

The invention relates to the correction of an incremental scale (2) used in numerically controlled machine tools for angular measurements on rotary tables (1). The pulse number detected is corrected electronically depending on the deviation between the desired and actual graduations. <IMAGE>

Description

Facility for scaling correction for a numerical

controlled machine tool The invention relates to a device for scaling correction on a numerically controlled machine tool in which On the circumference of a rotary table, an incremental pulse scale serving to measure angles with an actual division that deviates from the number of target divisions and the The actual division can be recorded with a measuring head.

For distance or angle measurement on numerically controlled machine tools a large number of different analog or digital encoders are known. A special position encoder is the so-called incremental encoder, in which per position or angle unit a counting pulse is delivered (see e.g. DE-PS 12 14 307 or Siemens-Zeitschrift 1970, supplement Numerical Controls, p. 16).

The numerically controlled rotary tables are used for angle measurement a pliable, flexible digital incremental loop scale is increasingly being used. This is on a circular circumference that is centric to the center of rotation of the rotary table attached to the rotary table.

The circumference for recording the length scale is dimensioned in such a way that that the use of a normal metric scale with the resolution with e.g.

1 t is possible and that the number of pulses generated - related on the circumference is 360 x the resolution. At the joint of the length rule will this scale cut off and pushed so that an angle measurement over the joint away becomes possible.

Despite the precisely calculated circumference, the application of the Scale, related to the length, subject to tolerances.

As a result, the actual number of generated pulses differs from the Target number, based on the scope.

This leads to a positioning error, which is reflected in an angle measurement added over several revolutions.

The object of the present invention is to provide by the to compensate for errors that deviate from the target division, that the highest possible positioning accuracy is achieved.

This object is achieved according to the invention in that the scope of the pulse scale electronically in a series of determined by pulse counting Areas is subdivided and that when each area limit is exceeded one Corresponding correction of the from Sensing head detected pulses is made.

In this way, during the positioning of the rotary table, correct distributed over the scope, by adding or eliminating pulses a corresponding one Correction made. The number of correction units, based on the circumference, can be set easily.

Based on an embodiment shown in the drawing the invention explained in more detail: The one to be positioned numerically Rotary table 1 of a machine tool not shown has a cylindrical one Scale carrier 2, on the circumference of which an incremental pulse scale 3 is arranged is. This pulse scale 3 can be used, for example, with one complete revolution of the rotary table 1 cause a delivery of 360,000 pulses.

In spite of the most exact adjustment possible and a new push of the yardstick at the joint 4 it is generally not absent that the actual scale not the specified nominal division of 360,000 pulses, but an actual division, for example of 359 900 pulses per revolution. Such a deviation from the actual value the setpoint is relatively uncritical for a simple angle measurement; more uncomfortable However, it will affect the measuring accuracy if several revolutions in the same direction executed so that the error is added.

The individual pulses on the circumference of the pulse scale 2 are over a measuring head 5, e.g., magnetically or optically, depending on the type of scale and fed to a counter 6. starting from a certain zero point the status of this counter is then a measure for the respective angular position of the rotary table 1. The status of this counter 6 is in turn in periodic Intervals picked up by a known computer control 7 and used in conjunction with a predetermined setpoint for controlling the motor 8 for the movement of the Rotary table 1.

For example, if - as stated above - there is an actual division that If the target division deviates by 100 pulses, such a correction is necessary, for example possible that the scope of the pulse scale 2 is electronically divided into 100 equal parts is divided, i.e. into areas 10 of 3.60 each and that each 1 pulse is added to the counting result or 1 pulse is subtracted at the range limits. Addition or subtraction are dependent on the direction of rotation. This can be In terms of circuitry, this can be achieved relatively easily by having each of the count values of the counting device 6, which correspond to these aforementioned angle values, by means of of the memory device 9, in which 1 pulse is stored, this value is either additive or added subtractively to the reading of the counter 6. In this way an error in the scale division can be compensated relatively easily so that a high level of accuracy is achieved.

1 claim 1 figure - L e r s e i t e -

Claims (1)

Claim facility for scale correction in a numerical controlled machine tool, with an angle measurement on the circumference of a rotary table Serving incremental pulse scale with different from the number of nominal divisions The actual graduation is present and the actual graduation can be detected with a measuring head, d a it is indicated that the scope of the pulse scale (3) is electronic is subdivided into a number of areas (10) which can be determined by pulse counting and that when each range limit is exceeded, one of the deviation and the Corresponding correction of the actual pulses recorded by the measuring head (5) depending on the number of areas is made.