Vibration Isolation System With Intermediate Mass Feedback and Feedforward Control
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Solution Overview
Problem
Precision instruments face challenges in isolating unwanted motion caused by both external and internal dynamic forces, with existing active vibration isolation systems often failing to rapidly suppress internal sources of vibration to sub-micron or sub-100-nm levels, which can impair the accuracy of instruments like optical steppers and microscopes.
Innovation Solution
A vibration isolation system employing an intermediate mass with both electromechanical feedback and feedforward circuits, where the feedback circuit suppresses unwanted motion from external sources and the feedforward circuit rapidly addresses internal sources, using a soft spring coupling to decouple these systems and allow independent operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a single feedback control system is used to suppress unwanted motion, then the system structure remains simple, but the settling time is too long to achieve sub-micron or sub-100-nm levels rapidly
Solution Approach 1:
The control system is segmented into two independent subsystems: a feedback control system that handles external vibrations and a feedforward control system that handles internal vibrations. Each subsystem operates independently with its own controller, allowing parallel suppression of different vibration sources and significantly reducing the overall settling time without creating an overly complex integrated system.
Solution Approach 2:
The feedforward control system performs preliminary action by predicting and counteracting internal vibrations before they affect the payload. By using vibration sensors to detect internal vibrations and the feedforward controller to generate compensating signals, the system addresses internal disturbance sources proactively, reducing the time required to achieve stable sub-micron positioning.
2Measurement precision
If feedback and feedforward circuits are used together to rapidly suppress both external and internal vibration sources, then the settling time is reduced to sub-micron or sub-100-nm levels, but the device complexity increases
Solution Approach 1:
The control system is divided into separate feedback and feedforward circuits, each with dedicated sensors and controllers. The feedback circuit uses vibration sensors and a feedback controller to suppress external vibrations, while the feedforward circuit uses separate vibration sensors and a feedforward controller to suppress internal vibrations. This segmentation allows each circuit to be optimized for its specific function while maintaining overall system precision.
Solution Approach 2:
Vibration sensors serve as intermediaries that detect both external and internal vibration sources. These sensors provide input signals to both the feedback and feedforward controllers, enabling the system to rapidly identify and counteract different vibration sources. The intermediary sensors bridge the gap between disturbance sources and control actions, achieving sub-micron positioning accuracy through coordinated control.
3Adaptability or versatility
If the feedback and feedforward systems are coupled tightly, then the system operates as a unified control mechanism, but the systems cannot operate independently to address different vibration sources effectively
Solution Approach 1:
The control architecture is segmented into independently operable feedback and feedforward circuits. Each circuit has its own sensors, controllers, and actuation paths, allowing them to function independently when needed. The feedback circuit can suppress external vibrations while the feedforward circuit simultaneously suppresses internal vibrations, providing versatile adaptation to different operating conditions and maintaining reliable vibration suppression.
Solution Approach 2:
The system dynamically adapts its control strategy based on the operating conditions. When internal vibrations are present, the feedforward circuit becomes active; when external vibrations dominate, the feedback circuit takes primary responsibility. This dynamic operation allows the system to maintain high reliability across varying conditions while preserving the capability for independent circuit operation.
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 system effectively reduces unwanted motion to micrometer-scale or sub-micrometer-scale distances in less than one second, significantly improving the settling time of precision equipment by combining feedback and feedforward control, enhancing the stability and accuracy of instruments.
Implementation Method 1
An electromechanical feedback circuit may be included to suppress unwanted motion of the intermediate mass
Implementation Method 2
An electromechanical feedforward circuit may be included to suppress unwanted motion of the payload
Implementation Method 3
using a soft spring coupling to decouple these systems and allow independent operation
Data Source
AI summary
Apparatus and methods to reduce unwanted motion in a payload of a precision instrument are described. The payload may be supported by an intermediate mass. A feedback signal based upon sensed motion of the intermediate mass may be applied to an intermediate-mass actuator arranged to drive the intermediate mass. Additionally, a feedforward signal may be applied to a payload actuator arranged to drive the payload and used to suppress unwanted motion of the payload. The feedforward signal may be derived from a source within the apparatus or external to the apparatus that would otherwise cause unwanted motion of the payload.