Magnetic Actuator Feedforward Control for Thermal Motor Constant Drift
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Solution Overview
Problem
Existing control systems for magnetic actuators in optical systems, particularly in microlithography, fail to accurately compensate for the temperature-dependent reduction in motor constant due to self-heating, leading to positioning inaccuracies and requiring complex temperature measurements and calculations.
Innovation Solution
A method involving a mathematical model that predicts the change in motor constant based on electrical control power, allowing for feedforward correction without explicit temperature measurement, using a model calibrated under operational conditions to adjust the control power accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If temperature sensors and complex calculation systems are installed to compensate for motor constant changes, then positioning accuracy is improved, but device complexity increases and installation space requirements increase
Solution Approach 1:
The patent replaces the mechanical/physical measurement system (temperature sensors, infrared cameras) with a mathematical model-based computational approach. The motor constant change is calculated using a pre-determined mathematical relationship between drive power and motor constant, eliminating the need for physical temperature measurement devices and complex real-time temperature calculations.
Solution Approach 2:
The patent creates a virtual model (mathematical model) that replicates the thermal behavior and motor constant characteristics of the actual actuator. This model is calibrated beforehand to copy the relationship between drive power, temperature rise, and motor constant degradation, allowing accurate prediction without physical sensors.
2Manufacturing precision
If temperature measurements and corrections are implemented, then motor constant compensation is improved, but time delays occur due to slow temperature measurement and calculation processes
Solution Approach 1:
The patent performs preliminary calibration to establish the mathematical model relating drive power to motor constant before actual operation. During operation, the correction is calculated immediately using this pre-established relationship, avoiding the time delay associated with real-time temperature measurement and gradual thermal equilibrium calculations.
Solution Approach 2:
The patent replaces slow thermal measurement processes with instantaneous mathematical calculations. The mathematical model directly computes motor constant changes from drive power inputs without waiting for thermal sensors to detect temperature changes or for thermal equilibrium to be reached.
3Device complexity
If the actuator is controlled without considering motor constant changes, then device complexity is reduced, but positioning accuracy deteriorates due to self-heating effects
Solution Approach 1:
The patent uses a mathematical model that copies the thermal and magnetic characteristics of the actuator to predict motor constant degradation. This model is calibrated to replicate the actual physical behavior, enabling accurate compensation while maintaining simple control implementation.
Solution Approach 2:
The patent changes the control approach from using a constant motor constant to using a variable motor constant that is dynamically adjusted based on drive power levels. The mathematical model provides correction factors that modify the motor constant parameter according to the actual operating conditions, improving accuracy without complex hardware.
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
This approach enables precise actuator control by anticipating motor constant changes, reducing time delays and simplifying the control system design, thereby improving positioning accuracy and reducing the need for temperature sensors.
Implementation Method 1
When a current flows through the electrical conductor arrangement, a magnetic field is induced, which interacts with the magnetic field of the permanent magnet. This interaction manifests itself, for example, in a mechanical force acting between the electrical conductor arrangement and the permanent magnet.
Implementation Method 2
The magnitude of the force depends primarily on geometric factors and the strength of the respective magnetic fields. This interaction causes the permanent magnet to heat up.
Implementation Method 3
The higher the current, the greater the heating. Due to the heating, the magnetization and thus the magnetic field strength of the permanent magnet decreases, which leads to a reduction in the effective force.
Data Source
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AI summary
The invention relates to a method for operating a magnetic actuator (200), in particular for actuating an optical element (510) in an optical system (500), which is designed to provide a mechanical force (A) as a function of an electrical actuating power (PS), wherein the method comprises: A) determining (S1) a mathematical model of the actuator (200) which describes a change in a motor constant (k) of the actuator (200) as a function of the electrical actuating power (PS) supplied, B) actuating (S2) the actuator (200) with a first electrical actuating power (PS) as a function of to a predetermined target force (FS), C) determining (S3) the change in the motor constant (k) of the actuator (200) on the basis of the actuation of the actuator (200) with the first electrical actuating power (PS) by means of the mathematical model, D) determining (S4) a correction value for the first electrical actuating power (PS) according to the change in the motor constant (k) determined, and E) actuating the actuator (200) with a second electrical actuating power (PS) as a function of the first electrical actuating power (PS) and the correction value determined.