Q: How to implement position control for servo motors in robotics and CNC applications?
Answer
Servo position control architecture: trajectory generator -> position PID -> velocity PID -> current PI -> PWM. Trajectory generation: S-curve or trapezoidal velocity profile to avoid jerking. Trapezoidal: constant acceleration -> cruise -> constant deceleration. S-curve: smooth acceleration/deceleration with jerk limiting (critical for CNC). Position PID: u = Kp*e + Ki*integral(e) + Kd*derivative(e). Add feedforward terms for friction and inertia. For CNC: use G-code interpreter (LinuxCNC GRBL) to generate trajectories. Tuning procedure: (1) Zero all gains. (2) Increase P until sustained oscillation. (3) Reduce P by 50%. (4) Add D to damp oscillation. (5) Add I to eliminate steady-state error. Use backlash compensation: detect direction change measure dead zone and pre-load opposite direction. For multi-axis (XY table): implement coordinated motion with linear interpolation (G01) and circular interpolation (G02/G03). Safety: hardware overtravel limit switches and software soft-limits.
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