A joint trajectory generator for motion recovery

A joint trajectory generator for motion recovery" (2003). All Faculty Publications. Paper 509. SUMMARY This paper describes an adaptive S-curve used to recover a tool path upon a system crash in the Windows operating system (OS). For a mechanism such as a robot or machine tool, the joint values, being delivered as setpoints to the servo-controller, are dynamically recorded by the real-time operating system also residing on the computer. The real-time OS can control the abort and record pertinent motion data after Windows OS crash. Upon system recovery, the recovery trajectory generator examines the setpoints intervals to determine the current slow joint. At every trajectory step, and for the current slow joint, the S-curve velocity profile applies the joint entry state (position, speed, acceleration, and jerk) to interpolate the motion between the setpoints in a reverse direction. The other joints are proportionally interpolated (slowed) so that they pass through each setpoint simultaneously with the slow joint, but in a reverse direction. The trajectory algorithm is optimal since the slow joint always uses the maximum allowable jerk to change the profile speed and acceleration for each trajectory step. INTRODUCTION New open controllers may use a real-time operating system (OS) that resides concurrently with the Windows OS on a PC. This environment is more vulnerable to system crashes, but brings tremendous advantage to the integration of modern applications on the control platform. The direct machining research at Brigham Young University uses the process plan in a Computer Aided Manufacturing (CAM) application to control directly a machine tool, without post-processing into APT, CL, or M&G files. In an instance where the Windows OS crashes, it is important to first stop the machining process gracefully, and then recover the tool to an acceptable prior configuration where the process can be restarted. In a system crash a real-time OS such as VenturCom's RTX can continue processing until the tool can be stopped. Unfortunately, the CAM application running under Windows will lose contact with the mechanism's final joint values through the stop sequence. The tool, once stopped awaiting the Windows OS reboot, may be located relative to the part such that it cannot be safely jogged by the operator without damaging the part.