1. Servo Tuning for Path Applications

2. 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.

3. X and Y Axis Model

4. Test Simulation Diagram

5. Matched Kp,Kvff,Kiv Nominal Gains

6. 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

7. Matched Kp,Kvff,Kiv Kp extremely low

8. 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

9. Matched Kp, Kvff=0 Kp Extremely Low

10. 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

11. Matched Kp Kvff=0 Kp set below Nominal

12. 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

13. Mismatched Kp Kvff=0 Kp lower than Nominal

14. 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

15. Mismatched Kp, Kvff=1 Kp Lower than Nominal

16. 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

17. Mismatched Kp Kvfff Kp lower than nominal

18. 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

19. Matched Kp Kvff=0 Kp set to nominal

20. 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

21. Mismatched Kp Kvff=0 Kp at nominal

22. 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