Meaning
Calibrated mechanical sensors mounted on coordinate measuring machines capture discrete spatial coordinates upon contact with component surfaces. A touch-trigger probe records position coordinates by generating an electrical trigger signal when its stylus deflects against a physical workpiece. The device enables automated dimensional verification of machined parts against CAD model specifications.
It provides discrete point measurement across prismatic shapes, bore diameters and surface boundaries. Metrology applications rely on these sensors for high-accuracy point collection in shop floor and laboratory inspection routines.
Deflection Mechanism
Internal kinematic seating mechanisms open electrical contacts when external force deflects the stylus tip. Within a touch-trigger probe, three equally spaced spring-loaded rods rest inside precision V-grooves to maintain a stable electrical circuit. Physical contact with a part surface lifts one or more rods out of their seat, interrupting current flow and sending an instantaneous latch signal to the CMM controller.
The machine controller records the exact encoder positions at that precise microsecond, storing the spatial coordinate in memory. Releasing contact allows internal springs to reset the stylus into its kinematic seat.
Measurement Error
Pre-travel variation introduces small directional errors that require mathematical calibration adjustments. Because a touch-trigger probe requires a finite physical force to unseat internal contacts, the stylus bends slightly before the trigger signal fires. The distance traveled between physical surface contact and signal generation varies depending on contact angle and stylus length.
Calibration procedures using precision reference spheres map this pre-travel variation to compensate for directional switching delays during measurement routines.
Application Limit
High-density point cloud requirements render discrete contact probing inefficient compared to continuous optical or scanning sensors. Measuring complex freeform surfaces with a touch-trigger probe requires extensive cycle times due to discrete point-by-point positioning requirements. Continuous scanning probes or laser sensors replace touch probes when inspecting complex aerodynamic profiles or soft pliable materials.
