Solution for real time sensor guided programmable logic controller of galvanometer scanners

Abstract

This paper introduces PLC (programmable logic controller)-based real-time motion control of 2D galvanometer scanners under consideration of different sensor information. The Fraunhofer IWS developed ESL2-100 module works as a locally separated client of a higher-level machine control to drive the scanner. The EtherCAT field bus supports extensive and constant exchange of information between the control levels. An application example, therefore, is the spatially resolved surface structuring of large areas using a continuous wave laser. In this application, the scanner must move the laser beam to predefined positions, stop there during the processing time, and jump to the next position. Frequencies up to 2 kHz are applicable depending on the scanner performance. The working area of a scanner can be extended by moving the scanner head with Cartesian machine axes. In the presented solution, the scanner control records these movements via encoder signals and captures the geometrical boundaries of the workpiece, i.e., previous operated areas, via cameras. The obtained data are included in the real-time calculation of scanner position data and laser emission signals. These measures maintain precision in positioning the patterns for surface structuring and adapt them to existing contours. The processing of the control data, the 2D-on-the-fly correction, and the correction of the target positions are done on the PLC level. Then, within one control cycle, multiple position data are sent in blocks from the PLC to the ESL2-100 module within one control cycle. At the end, the ESL2-100 module converts the field bus data into the scanner control protocol (here SL2-100 protocol). The approach described enables the deterministic calculation of the scan movement and responds dynamically to changing conditions by linking all necessary sensor information on one control platform.