Variable Gain Controller for Lithographic Positioning
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Solution Overview
Problem
Conventional lithographic apparatus positioning devices face challenges in handling low-frequency disturbances and time-varying disturbances, where increasing integrator control gain improves low-frequency disturbance rejection but deteriorates settling behavior at constant velocity, and require different control characteristics for varying disturbance spectra.
Innovation Solution
A positioning method and device with a controller that has a variable gain, selectively setting the gain higher for error signals within a predefined range to improve low-frequency disturbance rejection without affecting settling behavior, allowing for improved performance in one frequency range without compromising another.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the integrator control function gain is increased to improve low-frequency disturbance rejection, then low-frequency disturbance rejection is improved, but settling behavior at the start of constant velocity range deteriorates
Solution Approach 1:
The patent applies dynamics by making the controller gain variable rather than fixed. The gain adapts dynamically based on the operating phase: using higher gain during acceleration phases to reject low-frequency disturbances, and lower gain during constant velocity phases to maintain good settling behavior. This resolves the contradiction by allowing the system to optimize for different performance criteria at different times.
Solution Approach 2:
The patent changes the controller parameter (gain) based on the disturbance spectrum and operating conditions. By monitoring the error signal characteristics and adjusting the integrator gain accordingly, the system achieves improved low-frequency disturbance rejection when needed while maintaining acceptable settling behavior during constant velocity operation.
2Reliability
If the control characteristic is changed to handle disturbances with one spectrum better, then performance for that disturbance type is improved, but capability to handle disturbances of another kind is seriously affected
Solution Approach 1:
The controller dynamically adapts its characteristics based on the detected disturbance spectrum. By continuously monitoring error signals and adjusting gain parameters in real-time, the controller can optimize performance for the current disturbance type while maintaining capability to handle other disturbance types when they occur. This eliminates the need to choose a fixed control characteristic that compromises performance for any single disturbance type.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The variable gain controller achieves improved low-frequency disturbance rejection with minimal deterioration of settling behavior at constant velocity operations, enhancing overall positioning device performance.
Implementation Method 1
The controller receives a position signal from a position sensor detecting the position of the mover relative to the stator
Implementation Method 2
a second part, called a mover, which moves relative to the stator through the generation of electromagnetic forces between the stator and the mover
Data Source
AI summary
In a method for controlling a positioning device, the positioning device has a stator and mover, the mover being movable relative to the stator; a position sensor configured to generate a position signal indicative of a position of the mover relative to the stator; a controller configured to receive the position signal, compare it to a setpoint signal to obtain an error signal, and generate a mover control signal on the basis of a signal component of the position signal, the controller having a variable gain. The positioning device, including the position sensor and the controller, defines a control loop. For error signals having a magnitude in a predefined range, the gain is selectively set to a value higher than a value for error signals having a magnitude outside the range.