CMM touch trigger performance verification using a probe test apparatus

A probe test device has been developed to assess CMM touch trigger probe errors. A precise single axis translational table triggers the probe through the use of gauge blocks fixed to the table carriage. The position of the carriage is monitored by a laser interferometer. The gauge block surface is brought into contact with the probe ball tip until the probe is triggered at which point the coordinate position is displayed by the laser. The probe is rotated 360° using the motorized probe head in 7.5° intervals and the coordinate of each position is computed. Repeatability errors (i.e. the ability of the probe to trigger at the same point each time with a 95% confidence level) and pre-travel variation (i.e. the distance traveled by a probe between the actual touching of a surface and the trigger event) are then calculated. This paper reports the measurement strategy and the design of the prototype rig. Results are also provided to demonstrate the test apparatus performance