Balance-Mass Positioning with Gravity Compensation for Longer Stroke
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Solution Overview
Problem
Existing positioning devices in e-beam apparatuses face challenges with high effective stiffness in the direction of movement, leading to increased stress and potential fatigue in leaf springs, which limits stroke and performance.
Innovation Solution
The introduction of a gravity compensator and a stiffness reduction device, such as magnetic gravity compensators and negative stiffness mechanisms, to reduce the vertical support requirements of leaf springs, thereby lowering horizontal stiffness and minimizing reaction force transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If leaf springs are designed with relatively low stiffness in the horizontal direction to reduce disturbance effect, then the disturbance effect is reduced, but the achievable stroke is limited due to stress and fatigue of the material
Solution Approach 1:
A balance mass is arranged between the actuator and the reference, moving in the opposite direction to the stage movement. This counterbalances the reaction forces from the actuator, reducing the disturbance effect on the reference while allowing larger strokes without increasing stress on the leaf springs.
Solution Approach 2:
The stiffness of the leaf springs in the horizontal direction is optimized to a specific low value that minimizes disturbance effect while maintaining sufficient stress margins. This parameter optimization allows the system to achieve larger strokes before reaching material fatigue limits.
2Stress or pressure
If the weight of the balance mass is reduced to reduce stress and fatigue, then stress and fatigue are reduced, but a larger stroke is required for the balance mass to follow movements of the stage
Solution Approach 1:
The balance mass is designed with an optimal weight that provides sufficient counterbalancing effect to reduce reaction forces while maintaining a compact stroke. The balance mass weight is typically higher than the stage weight (e.g., 5:1 ratio), creating a mechanical advantage that reduces both stress and required stroke simultaneously.
3Strength
If leaf springs are designed with sufficient stiffness in the vertical direction to support the balance mass, then gravitational support is provided, but this creates a relatively low stiffness in the horizontal direction which limits performance
Solution Approach 1:
The leaf springs are designed with different stiffness characteristics in different directions: high vertical stiffness to support the balance mass against gravity, and low horizontal stiffness to minimize disturbance effect. This anisotropic stiffness design allows the same component to fulfill multiple conflicting requirements.
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 reduces the disturbance effect of leaf springs, allows for larger displacements without increasing stress, and lowers the actuation force required, thereby enhancing the positioning device's performance and reducing the risk of fatigue.
Implementation Method 1
a gravity compensator acting between the reference and the balance mass to exert a lifting force on the balance mass
Implementation Method 2
a stiffness reduction device acting between the reference and the balance mass, the stiffness reduction device providing a second stiffness in the direction of movement, wherein the second stiffness is a negative stiffness that counteracts the first stiffness at least partly
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
The present invention provides a positioning device configured to displace an object, comprising: a stage to support the object, an actuator to move the stage with respect to a reference in a direction of movement, a balance mass arranged between the actuator and the reference to reduce transfer of reaction forces from the actuator to the reference, a support device arranged between the reference and the balance mass to support the balance mass, and a gravity compensator acting between the reference and the balance mass to exert a lifting force on the balance mass to reduce a gravitational support force to be provided by the support device to support the balance mass.