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Motion Control: Generating Intelligent Comands for Mechatronic Devices. Kelvin Peng Feburary 7 th 2012. Getting the System to do What you Want. What is Control?. How to Control? Add a Feedback Loop. Pros: Eliminates errors Disturbance rejection. Cons: Stability? Sensors.
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Motion Control: Generating Intelligent Comands for Mechatronic Devices Kelvin Peng Feburary 7th 2012
Getting the System to do What you Want What is Control?
How to Control? Add a Feedback Loop • Pros: • Eliminates errors • Disturbance rejection • Cons: • Stability? • Sensors
Let’s go back to simple control • Pros: • Simple, no sensors • Stable (if plant is stable) • Accurate model not needed • Cons: • No disturbance rejection • Increase rise time Today’s topic: How to design the command generator
Before we go on… A General Control System
Bridge Crane Vibration Problem (and solution)
Normalization Positive Impulses Time Optimality Derivation for a Simple Case Constraints Vibration Amplitude (At the end of n impulses)
Simple Derivation (V=0, 2 impulses) 3 equations, 3 unknowns
Input Shaping Arbitrary Commands From previous example: Zero-Vibration (ZV) shaper • Slight increase in rise time • ΣAi = 1 so that shaped and initial commands have same steady state
Implementing a Digital Input Shaper Unshaped Command Shaped Command
Shaper Robustness Insensitivity – the width of a sensitivity curve where vibration remains under Vtol , the tolerable level of vibration
Increasing Shaper Robustness Insensitivity – the width of a sensitivity curve where vibration remains under Vtol , the tolerable level of vibration
Increasing Shaper Robustness Extra Insensitive (EI) Shaper Insensitivity – the width of a sensitivity curve where vibration remains under Vtol , the tolerable level of vibration
Increasing Shaper Robustness Like a Boss Tradeoff: More impulses are needed, and therefore slower rise time.
Multi-Mode Input Shaping Design a shaper for each mode, then convolve to get a shaper that eliminates both modes
ZV Shaper for 1 Hz and 2 Hz ZV Shaper for 1 Hz X ZV Shaper for 2 Hz
Shapers with Negative Impulses • Negative shapers: • Faster • But less robust • May excite un-modeled higher modes Unity Magnitude UMZV shaper
Special Case: Negative Shapers for On-Off Actuators UMZV Shaper: On-Off Not On/Off
On-Off Thrusters: Flexible Satellites (Tokyo Institute of Technology)
On-Off Thrusters: Flexible Satellites (Tokyo Institute of Technology)
Input Shaping With Feedback Control Collapse the feedback loop Input Shaper * Cascaded set of 2nd order systems
Disturbance During Motion Input Shaping and Feedback Control: Experimental Data Disturbance at End
Input Shaping Inside the Feedback Loop: Hand-Motion Crane Control
Human Operator Learning Unshaped Shaped
Portable Tower Crane • 2mx2mx340o • Interfaces: Pendent, GUI, Internet GUI • Overhead Camera • Used by Researchers and Students in Atlanta, Japan, Korea
Screen Interface Tower Crane: System Overview
Other Applications • Many types of cranes • Milling machines • Coordinate measuring machines • Disk drives • Long reach robots • Spacecraft
Application of Command Shaping to Micro Mills • Scale of Micro Meters (10-6m) • High Spindle Speeds (120 kRPM)
Part Surface Experimental Results Stage Tracking Error
Conclusions • Every control method has strengths and weaknesses (Feedback is not a magic cure-all) • The command issued to a system has a significant influence on its response • Input shaping • Can dramatically reduce system vibration • Is easy to implement