Negative Stiffness Gravity Compensation for Micropositioner
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Solution Overview
Problem
In lithography machines, the heat generated by drive motors affects the precision of workpiece positioning due to increased motor load, and existing non-contact gravity compensating structures face challenges in achieving both low stiffness and high bearing capacity, especially with the influence of magnetic fields from Halbach magnetic steel arrays in maglev systems.
Innovation Solution
A negative stiffness system for gravity compensation using quasi-zero stiffness units composed of pairs of negative and positive stiffness springs, arranged in triangular or rectangular configurations, which reduces the overall stiffness while maintaining a large bearing capacity and simplifies processing and maintenance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a drive motor is used to directly provide support for multiple-degree-of-freedom motion and precise positioning, then the positioning precision is improved, but the motor load and heating are increased
Solution Approach 1:
The patent employs a gravity compensating structure using permanent magnets arranged in a Halbach array configuration. The magnetic field generated by these magnets creates a lifting force that counteracts the gravitational force on the workpiece table, effectively reducing the motor load to only what is needed for positioning rather than supporting the full weight. This allows precise positioning with minimal motor heating.
2Device complexity
If a non-contact type gravity compensating structure of permanent magnet is used, then the structure is simplified and processing requirements are reduced, but the stiffness in the axis direction between fixing part and supporting part is small
Solution Approach 1:
The patent combines permanent magnets with a specific mechanical structure featuring pre-compressed springs. The permanent magnets provide non-contact gravity compensation while the pre-compressed springs provide mechanical support and stiffness. This composite approach integrates both magnetic and mechanical elements to achieve both simplicity and sufficient bearing capacity.
Solution Approach 2:
The patent introduces a vertical dimension element with pre-compressed springs that work in conjunction with the horizontal magnetic field. The springs are arranged vertically between the fixing plate and supporting plate, providing stiffness in the axis direction while the magnetic field handles gravity compensation, thus solving the stiffness problem without compromising the non-contact advantage.
3Force
If a large array of halbach magnetic steel is used to generate a strong magnetic field for magslev workpiece table, then the magnetic field strength is improved, but the influence on gravity balancing of the rotor of micropositioner is increased
Solution Approach 1:
The patent introduces magnetic shielding plates made of high-permeability magnetic material as intermediaries between the Halbach array and the micropositioner rotor. These shielding plates redirect and contain the magnetic field lines, allowing the strong magnetic field to effectively lift the workpiece table while preventing excessive magnetic field penetration to the micropositioner rotor, thus reducing interference with gravity balancing.
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 design enhances the precision of motion by minimizing the impact of magnetic fields and improving vibration isolation, allowing for thinner micropositioner designs and reduced motor heating, thus improving the accuracy and capacity of the micropositioner's motion.
Implementation Method 1
a pair of negative stiffness springs and a positive stiffness spring... upper ends of the negative stiffness springs and the positive stiffness spring are connected together and fixed to the bottom surface of a rotor
Implementation Method 2
the stiffness of the gravity support in the direction of the axis between the stator and the rotor is near to zero
Implementation Method 3
a large array of halbach magnetic steel to generate a strong magnetic field
Implementation Method 4
non-contact type gravity compensating structure of permanent magnet
Implementation Method 5
the magnetic field of the Lorentz motor of the six-degree-of-freedom micropositioner
Data Source
AI summary
A negative stiffness system for gravity compensation of a micropositioner of wafer table in lithography machine, characterized in that, the negative stiffness system includes at least three sets of quasi-zero stiffness units, each of the sets of quasi-zero stiffness units comprises a pair of negative stiffness springs and a positive stiffness spring, the positive stiffness spring is vertically positioned, the pair of negative stiffness springs are obliquely and symmetrically positioned at two sides of the positive stiffness spring, upper ends of the negative stiffness springs and the positive stiffness spring are connected together and fixed to the bottom surface of a rotor of the micropositioner, and lower ends of the negative stiffness springs and the positive stiffness spring are connected to a base, respectively. The system reduces the stiffness in vertical direction and prevents the influence of permanent magnet on its surroundings, while improving the bearing capacity.