Servo Tuning for Path Applications

Introduction The purpose of this power point to show the effects of servo gains when performing path motions. The desired path is the result of multiple axes. There are two requirements that must be met to be successful. The System bandwidths of the individual axes must be meet the performance requirements of the process. The two primary requirement being velocity regulation and position loop performance . Process parameters such cut feedrate on plasma cutter will determine velocity regulation requirements. The position loop performance will be determined by the actual path to generated and system throughput. System bandwidths must be matched to minimize error of actual path and Desired path Simulated Test System Simple Axis model using ; Kp position proportional gain Ki velocity loop Integrator Kv velocity loop proportional gain Mechanical Plant (including current loop) assumed to be ideal Path motion 20 mm 45 degree angle in X and Y, Motion time 100 ms; In this presentation term gain matching will be used, this really means the bandwidths corresponding to the respective gains are the same. Due to the simple models used the gain Kp directly controls position loop bandwidth, and Kv and Kvfff directly effect velocity bandwidth. In an actual system the gain values may not be identical due to different loads and drives used in the system. Two systems with matched or equal bandwidth will have the same open crossover frequency on the bode plot, or will have the identical error signal when given the same input.

X and Y Axis Model

Test Simulation Diagram

Matched Kp,Kvff,Kiv Nominal Gains

Matched Kp,Kvff,Kiv Nominal Gains Summary Nominal Gains All gains set to nominal. The gains Kp, Kiv, and Kvff are matched between the to systems. Slight mismatch in Kv to simulate Y and X mechanical difference; Path Motion , Figure(50) Excellent Path Error Figure(69) Axis Error Figure(34) X and Y Axis signatures match Axis motion Figure(40) X and Y complete motion in require time (100 ms) Conclusion Path Motion Acceptable Axis Motion Acceptable

Matched Kp,Kvff,Kiv Kp extremely low

Matched Kp,Kvff,Kiv Kp extremely low Summary Nominal Gains The gains between Kp, Kiv, and Kvff are matched between the to systems. Kp gains are set way below nominal Slight mismatch in Kv to simulate Y and X mechanical difference; Path Motion , Figure(50) Acceptable Path Error Figure(69) Not as good as with Nominal Kp could be acceptable depending on process Axis Error Figure(34) X and Y Axis shapes match sligh variation in amplitude Axis motion Figure(40) X and Y complete motion in require time (100 ms) Conclusion Path Motion Acceptable Axis Motion Acceptable

Matched Kp, Kvff=0 Kp Extremely Low

Matched Kp, Kvff=0 Kp Extremely Low Summary Nominal Gains The gains between Kp, Kiv, and Kvff are matched between the to systems. Kp gains are set way below nominal. Kvff=0 Slight mismatch in Kv to simulate Y and X mechanical difference; Path Motion , Figure(50) Excellent Path Error Figure(69) Axis Error Figure(34) X and Y Axis error signatures match Axis motion Figure(40) X and Y do not complete motion in require time (100 ms) Conclusion Path Motion Acceptable Axis Motion Unacceptable

Matched Kp Kvff=0 Kp set below Nominal

Matched Kp Kvff=0 Kp set below Nominal Summary Nominal Gains The gains between Kp, Kiv, and Kvff are matched between the to systems. Kp gains are set below nominal. Kvff=0 Slight mismatch in Kv to simulate Y and X mechanical difference; Path Motion , Figure(50) Excellent Path Error Figure(69) Axis Error Figure(34) X and Y Axis error signatures match Axis motion Figure(40) X and Y do not complete motion in require time (100 ms) Conclusion Path Motion Acceptable Axis Motion Unacceptable

Mismatched Kp Kvff=0 Kp lower than Nominal

Mismatched Kp Kvff=0 Kp lower than Nominal Summary Nominal Gains The gains between Kiv, and Kvff are matched between the to systems. Kp gains are set below nominal and do not match. Kvff=0 Slight mismatch in Kv to simulate Y and X mechanical difference; Path Motion , Figure(50) Failed Path Error Figure(69) poor Axis Error Figure(34) X and Y Axis error shape match but not amplitude does not. Axis motion Figure(40) X and Y do not complete motion in required time (100 ms) Conclusion Path Motion Unacceptable Axis Motion Unacceptable

Mismatched Kp, Kvff=1 Kp Lower than Nominal

Mismatched Kp, Kvff=1 Kp Lower than Nominal Summary Nominal Gains Kiv, and Kvff are matched between the to systems. Kp gains are set way below nominal and mismatched. Kvff=1 this compensates for low Kp Slight mismatch in Kv to simulate Y and X mechanical difference; Path Motion , Figure(50) Excellent , Not as good as nominal Path Error Figure(69) Excellent, Not as good as nominal Axis Error Figure(34) X and Y Axis signatures match Axis motion Figure(40) X and Y complete motion in require time (100 ms) Conclusion Path Motion Acceptable Axis Motion Acceptable

Mismatched Kp Kvfff Kp lower than nominal

Mismatched Kp Kvfff Kp lower than nominal Summary Nominal Gains Mismatched Kp and Kvff Kp gains are set way below nominal. Slight mismatch in Kv to simulate Y and X mechanical difference; Path Motion , Figure(50) Fail Path Error Figure(69) Excellent Axis Error Figure(34) X and Y Error Axis signatures do not match Axis motion Figure(40) X complete motion in require time (100 ms) Y does not complete motion in require time (100 ms); Conclusion Path Motion Not Acceptable Axis Motion Not Acceptable

Matched Kp Kvff=0 Kp set to nominal

Matched Kp Kvff=0 Kp set to nominal Summary Nominal Gains Matched Kp and Kvff Kp gains are nominal. Kvff=0 Slight mismatch in Kv to simulate Y and X mechanical difference; Path Motion , Figure(50) Excellent not as as good as nominal Path Error Figure(69) Axis Error Figure(34) X and Y Error Axis signatures match Axis motion Figure(40) X and Y complete motion in require time (100 ms) Conclusion Path Motion Acceptable Axis Motion Acceptable

Mismatched Kp Kvff=0 Kp at nominal

Matched Kp, Kvff, Kiv Nominal Gains Summary Nominal Gains MisMatched Kp Kp gains are nominal. Kvff=0 Slight mismatch in Kv to simulate Y and X mechanical difference; Path Motion , Figure(50) Good, not as as good as nominal, acceptance based on process requirements Path Error Figure(69) Axis Error Figure(34) X and Y Error shape match, Amplitude does not. Axis motion Figure(40) X and Y complete motion in require time (100 ms) Conclusion Path Motion Acceptable subject to process requirements Axis Motion Acceptable subject to process requirements