Strecon has developed a new machine system for surface polishing of industrial tools and machine components. The technology is based on an industrial robot and known as RAP (Robot Assisted Polishing). The RAP machine consists of a part-holding spindle and a polishing module with controlled contact force held by an industrial robot, providing for spatial movements in the machine workspace. The spindle, driven by a direct–drive servomotor, provides either for rotation of an axisymmetric part or indexing of a stationary part. The polishing module with air–pressure controlled contact force provides either an oscillating (reciprocating) linear tool movement or a rotating tool movement . In the RAP, a generic part is polished in a number of process steps using increasingly finer abrasives. The determination of the optimal time for change of the abrasive media between the polishing steps (process End Point Detection — EPD) is a key and time consuming issue. The objective of the Strecon’s demonstrator is to apply the technologies required to fully automate the polishing process. The IFaCOM system customised on the Strecon’s application case foresees • A short-term control loop for process state monitoring Through the application of several sensors (force, acoustic emission, power), relevant process parameters are acquired and process state is quickly assessed; the control loop is based on simple algorithms for the detection of abnormal variations of some features of the acquired signals, symptoms of process anomalies and malfunctions. This approach allows minimizing defects due to sudden phenomena like tool breakage. • Medium and long-term control loop This control loop relies both on the data provided by the sensors mentioned above and on the application of an in-line Quality Control system for surface characterization (roughness, gloss) and local defects identification. The determination of the right moment for changing to finer abrasive between polishing steps relies on the correlation between part quality characteristics (surface roughness) and sensor signal features. The correlation has been studied and several algorithms have been developed and tested within the project. The software applied in the Strecon’s case is based on the existing control software of the robot, enriched with the IFaCOM algorithms and user interface .
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