Actuator Stiffness Compensation for Optical Element Actuation
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Solution Overview
Problem
In optical systems, particularly in microlithographic projection exposure apparatuses using EUV, there is a challenge in actuating facet mirrors with limited structural space and minimizing thermal loads, as conventional actuators struggle to overcome the stiffness of joints while maintaining precise control and reducing energy dissipation.
Innovation Solution
The design incorporates an actuator with negative stiffness that compensates for joint stiffness, using a force-distance characteristic that increases with deflection, allowing for precise actuation with reduced structural space requirements and minimized thermal loads by leveraging the joint stiffness in the actuator's design, particularly through the use of a heteropolar motor with magnets and a soft-iron core, and a parallel guide to translate forces effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional actuators are used to overcome joint stiffness, then actuation force is increased, but thermal load and energy dissipation increase
Solution Approach 1:
The actuator's force-distance characteristic is modified by introducing negative stiffness that compensates for joint stiffness. This changes the force parameter dynamically based on position, reducing the net force required from the actuator and thereby reducing energy dissipation and thermal load.
Solution Approach 2:
A parallel guide mechanism is introduced as an intermediary element that translates and transmits forces more effectively. This mediator optimizes the force transmission path, reducing the workload on the actuator and minimizing energy loss.
2Measurement precision
If actuator stiffness is increased to compensate for joint stiffness, then actuation precision is improved, but structural space requirements increase
Solution Approach 1:
Instead of increasing physical dimensions to achieve required stiffness, the patent changes the stiffness parameter through negative stiffness compensation. This allows achieving the same actuation precision with a more compact actuator design, reducing structural space requirements.
Solution Approach 2:
The patent replaces traditional mechanical stiffness (physical rigidity) with a controlled force-field approach using negative stiffness. This substitution allows achieving equivalent mechanical performance with reduced physical dimensions.
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 efficient actuation of optical elements with reduced structural space usage and minimized thermal loads, as the actuator's force compensates for joint stiffness, reducing the need for high electric current and subsequent heat dissipation, thereby optimizing performance in densely packed optical systems.
Implementation Method 1
the use of a heteropolar motor with magnets and a soft-iron core
Data Source
AI summary
The invention relates to an arrangement for actuating an element in an optical system, in particular an optical system of a projection exposure apparatus, wherein the optical element is tiltable about at least one tilting axis via at least one joint having a joint stiffness, comprising at least one actuator for exerting a force on the optical element, wherein the actuator has an actuator stiffness which at least partly compensates for the joint stiffness.