Sensor technology

  Prototype of a relative displacement sensor unit for robot-based laser material processing Copyright: © Leon Gorissen, 2023. CC BY-SA 4.0. Prototype of a relative displacement sensor unit for robot-based laser material processing

Motivation

To enable robotic systems for Laser Materials Processing (LMP), it is necessary to minimize the trajectory deviations from the planned target trajectory. In addition to trajectory optimization, position control of the laser spot using acoustic optical deflectors (AOD) or scan optics is one way to increase the position accuracy of the systems. The basis for the position control of the laser spot during the process is a sufficiently accurate state determination of the robotic Tool Center Point (TCP). For this reason, Digital Photonic Production group is engaged in testing different industrial and experimental sensors for process-integrated state determination of the TCP during laser material processing. The usability of different sensors is analyzed, approaches for sensor data evaluation and sensor fusion are tested and the resulting overall concepts are evaluated with a view to industrial application.

Problem

For various robots such as six-axis industrial robots (IR), the physical principles of motion can be described by kinematics. The actual dynamic behavior follows from the additional consideration of the acting forces and masses. The acting forces are generated here by various actuators such as electric motors. The position of the motors is measured with the help of encoders and then serves as the basis for calculating the TCP position of the robot. However, the oscillations caused by the joint stiffnesses cannot be measured by the encoders because they occur in the kinematic chain after the motor position is measured, resulting in an error-prone position calculation.

These errors are difficult to model and, as long as they cannot be measured, can only be included in the position control to a limited extent.

Furthermore, process-dependent influences such as reflected laser radiation, welding fumes or additives pose additional challenges to sensor technology.

Research focus

  • Testing of different sensors for measuring the TCP position during laser material processing
  • Investigation and validation of approaches for sensor fusion
  • Evaluation of concepts for industrial application in the context of laser technology