Robot Motion Trajectory-Measurement with Linear Inertial Sensors

When referring to the term “industrial robot” in the following, we mean universal, programmable processing machines, which are usually incorporated in industrial manufacturing processes. Industrial robots are multi-functional handling automata which consist of a set of more or less rigid members, interconnected to a kinematic chain by rotational or prismatic joints. One end of this chain represents the base of the robot, the other end is equipped with a tool or a gripper to execute the desired production work. For the considerations presented here (which deal with dynamic trajectory accuracy), we think of both common programming methods, on-line and off-line. On-line programming usually is based on a teaching-process, where the startand endpoints of a trajectory are defined by moving the robot to the desired poses. An interconnecting trajectory for interpolated movement is then defined by choosing a connective geometry from a library (line, circle, spline-curve) and by specifying additional dynamic parameters as speed or time. Additional “pass-points” can be specified which are not actually a part of the end-effector trajectory but which are passed-by within a certain distance. In point-to-point movements the end-effector does not follow a user-determined path, but is rather defined by the motion of drives in axis-space. Off-line programming makes use of the known kinematic properties of the robot, the geometrical and structural conditions of the work task and a simulative environment to test the program before implementation on the actual shop-floor. The simulation environment can handle additional tasks like cycle time evaluation, robot cell layout optimization, reach determination, trajectory optimization, simulation and calibration. When a program is transferred from simulation to a real robot station, considerable disparities between simulated and real results can be observed. Deviations of several millimeters can ensue—sufficient to make manufactured parts unusable.