Trim-Motor Force Limiter for Counter-Mass Stability
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Solution Overview
Problem
In precision systems, such as microlithography, counter-mass trim-motors often experience saturation due to excessive power, leading to instability and vibration transmission, which conventional systems fail to adequately address without compromising system performance or requiring additional components.
Innovation Solution
A control system with a PI feedback controller and phase lead filter is implemented to regulate the counter-mass motion by distributing center-of-gravity force commands to trim-motors using a force-distribution matrix, coupled with a trim-motor force limiter to limit applied forces, ensuring stable operation without additional components or reduced throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If counter-mass trim-motors are used to control counter-mass position and absorb reaction forces, then system stability is improved, but the trim-motors experience saturation due to excessive power requirements, leading to vibration transmission and instability
Solution Approach 1:
The control system segments the trim-motor control into multiple independent control loops, each managing specific degrees of freedom (x-position, y-position, z-position, and rotational orientations). This segmentation allows each control loop to operate independently within its power limits, preventing saturation while maintaining overall system stability.
Solution Approach 2:
The system dynamically adjusts the control strategy based on real-time operating conditions. The controller monitors trim-motor commands and adapts the control algorithm to distribute forces optimally across available motors, ensuring dynamic operation within power constraints while maintaining stability during varying operational phases.
2Reliability
If trim-motor force capacity is increased to prevent saturation, then system stability is maintained, but vibration transmission to the base structure and ground increases
Solution Approach 1:
The control system implements feedback mechanisms that monitor trim-motor performance and system response in real-time. This feedback allows the controller to optimize force distribution, maintaining stability while minimizing excessive force application that would generate harmful vibrations in the base structure and ground.
Solution Approach 2:
The system changes control parameters dynamically to optimize performance. By adjusting control gains, force distribution ratios, and operational parameters based on real-time conditions, the system maintains stability without requiring excessive force capacity that would transmit harmful vibrations to the supporting structure.
3Reliability
If additional components are added to prevent trim-motor saturation, then system stability is improved, but device complexity increases
Solution Approach 1:
The control system is designed to perform multiple functions using the existing trim-motor infrastructure. The same control algorithm manages position control, force distribution, saturation prevention, and vibration minimization across all trim-motors, eliminating the need for additional specialized components while maintaining system stability.
4Object-generated harmful factors
If trim-motor force capacity is limited to reduce vibration transmission, then harmful factor transmission is reduced, but system stability deteriorates due to motor saturation
Solution Approach 1:
The control system applies partial action by distributing forces across multiple trim-motors rather than relying on any single motor for full force capacity. This distributed approach allows each motor to operate within its force limits, reducing vibration transmission while collectively maintaining sufficient total force to prevent saturation and ensure system stability.
Data Source
AI summary
An exemplary stage assembly has movable stage mass and counter-mass. A stage motor is coupled to the stage mass and counter-mass such that stage-mass motion imparted by the stage motor causes a reactive motion of the counter-mass counter to the motion of the stage mass. At least one trim-motor is coupled to the counter-mass. A control system commands the trim-motor to regulate movement of the counter-mass in reaction to stage-mass motion. A PI feedback controller receives the following-error of the counter-mass and generates corresponding center-of-gravity (CG) force commands and trim-motor force commands to the trim-motor(s) to produce corrective counter-mass motion. A trim-motor force limiter receives trim-motor force commands and produces corresponding limited trim-motor force commands that are fed back as actual CG force commands to the feedback controller to modify integral terms of the feedback controller according to the limited trim-motor force commands.