Coordinate Measuring Machine Restraint Fixture Calibration for Thermoplastic Assemblies
Calibrate CMM restraint fixtures by matching datum locators to nominal CAD and regulating clamping forces to eliminate non-rigid part deflection.
Tactile Probe Deflection
Meaning
Measurement error source occurs when the physical tip of a coordinate measuring machine bends or moves during contact with a surface. Managing tactile probe deflection is necessary for maintaining high accuracy in precision metrology. The amount of movement depends on the length of the stylus and the force applied by the machine.
Geometric Deviation
Displacement of the probe tip results in a false reading of the part dimension. When tactile probe deflection is not accounted for, the reported position of a feature will be shifted in the direction of the contact force. This error is most pronounced when using long, thin styli to measure deep bores.
High quality metrology systems use software algorithms to compensate for this known mechanical behavior.
Calibration Necessity
Regular qualification of the probe setup involves measuring a master sphere of a known size. Because tactile probe deflection varies with the angle of contact, the machine must be calibrated at multiple points. This process determines the effective diameter of the stylus tip under actual operating conditions.
If the probe is changed or the stylus is bumped, a new calibration is required to maintain the integrity of the data. Consistent measurement force is essential for repeatable results. Operators must select the shortest and stiffest stylus possible for each task to minimize the inherent flex.
Data Accuracy
Precise control of the machine dynamics ensures that the contact force remains constant. Understanding tactile probe deflection allows metrologists to trust the results of complex inspections. Reliable measurements lead to better process control.