Development of a Pneumatic Clamping System with Position and Force Control Machining

Precision machining plays a vital role in modern, efficient, and sustainable manufacturing. Monitoring and controlling the clamping forces can influence positioning accuracy, workpiece deformation, thus improving the production outcome. The clamping force must be adapted to the cutting forces, workpiece geometry, and material properties to improve accuracy and control workpiece deformation during machining. The best devices available have a repeatability of ±1 µm, however, with limited precision and repeatability when re-clamping the workpiece. This paper presents the newly developed high-precision adaptable clamping system for controlled high-precision positioning and repositioning of a workpiece in the x-y plane with visual pattern recognition, adjustment, and controlled clamping forces. The clamping system is based on a pneumatic clamping chuck with controlled air pressure on a very accurate CNC machine. FEA calculations of thin-walled workpieces are used for designing associated jaws to ensure workpiece holding, limited forces and limited deformations. Once the workpiece has been removed and re-clamped with the defined forces, the vision device identifies the new workpiece position. Force and position data are collected and analyzed for calculating the repositioning movement in the x, y, and theta axes. The difference between the measured position after re-clamping and the reference position is calculated using a specially developed algorithm, yielding the motion commands to the x, y and theta axis. Using the vision system made it possible to identify an accuracy of ±1 µm and a repeatability of ±0.5 µm.