Machine tool dynamic accuracy checks made independent of machining influence
Machine tool dynamic accuracy checks made independent of machining influence
Keywords Grids,Heidenhain, Machine tools, Software, Tests
We are informed that a new development using grid encoder technology from Heidenhain allows dynamic tests of the contouring accuracy of computer controlled machine tools to be performed on very small radii and curved axis trajectory paths at high speed in order to determine the condition, positional and contouring performance of the machine.
Now available from Heidenhain (GB) of Burgess Hill in West Sussex, the KGM 182 grid encoder operates independent of any machining influences and a system accuracy within± two microns (Plate 9). The unit comprises a glass grid plate with a waffle-type graduation embedded in the base and a non-contact scanning head.
The base is simply mounted to the machine tool table and aligned. The scanning head is locked in the spindle and a feeler gauge is used to set the scanning gap at 0.5 ± 0.05mm. The scanning head is then set for an optimised signal display.
For each of the two perpendicular axis directions, the unit outputs two 90º phase shifted signals with a signal period of four microns. These data are sent to a PC for final processing via Heidenhain's ACCOM software. The software requests the appropriate parameter information and will then generate the corresponding NC program for loading into the CNC control of the machine.
Plate 9 The KGM 182 grid encoder
KGM 182 reportedly can carry out circular interpolation tests with radii ranging from just one micron to 115mm at high feed rates up to 80m/min.
By measuring dynamically,and especially at high traverse speeds, conclusions can be drawn on both the condition of the machine tool and the parameter settings of the control loop. This can also include the CNC control, drives and positional feed back systems. While the ACCOM software evaluation program will determine deviations from the ideal circular path, as a motion error trace, it will also calculate numerical values such as circular deviation, circular hysteresis and radial deviation.
In addition, the static positioning accuracy and repeatability of the machine can be measured. It is believed that this capability will allow any guideway error up to 230 mm in a direction perpendicular to the traverse direction of the machine tool slide to be determined.
Further details are available from Heidenhain (GB) Ltd. Tel: +44 (0) 1444 247711.
