Parallel Platform Tracking Control Using Visual Feedback
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Solution Overview
Problem
Traditional planar parallel platforms lack a suitable sensor for precise measurement of 3 degree-of-freedom (2 translations and 1 rotation) errors, leading to semi-closed loop positioning and limitations in achieving high precision and large stroke, especially in size-constrained environments like scanning electron microscope cavities.
Innovation Solution
A CCD camera-based visual measurement system, combined with a position tracking feedback control apparatus, enables full closed-loop control by detecting termination position and gesture angle errors using image processing, allowing for high precision and compact integration without adding weight or altering the platform's structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If three single degree-of-freedom sensors (e.g., laser displacement sensors) are used to measure plane 3 degree-of-freedom errors, then measurement precision is improved, but device complexity and volume increase significantly
Solution Approach 1:
The patent merges multiple measurement functions into a single CCD camera sensor. The camera captures images of feature points on the platform and simultaneously provides information for measuring both position (x, y coordinates) and gesture angle (rotation θ) in one integrated system, eliminating the need for multiple separate sensors
Solution Approach 2:
The CCD camera serves multiple measurement functions simultaneously - it measures horizontal position, vertical position, and rotation angle all through a single device. This multi-functional approach reduces system complexity while maintaining comprehensive measurement capabilities for the planar parallel platform's 3 degree-of-freedom errors
2Device complexity
If traditional semi-closed loop positioning is used, then device complexity is reduced, but manufacturing error, assembling error, joint gap, friction, and elastic deformation cannot be compensated, worsening positioning precision
Solution Approach 1:
The patent implements a closed-loop control system where the CCD camera continuously measures the actual position and gesture angle of the moving platform, and this measurement information is fed back to the control system. The controller compares the actual state with the target state and adjusts the ultrasonic linear motors to compensate for errors caused by manufacturing tolerances, assembly errors, joint gaps, friction, and elastic deformation
Solution Approach 2:
The patent replaces traditional mechanical position feedback mechanisms with a visual measurement system using CCD camera and image processing. This substitution allows for non-contact, high-precision measurement of the platform's position and orientation, enabling accurate error detection and compensation without adding mechanical complexity to the feedback path
3Length of moving object
If macro-and-micro-combined method is used to achieve great stroke, then stroke is improved, but positioning precision requirement for macro-moving platform increases, worsening the challenge of achieving high precision
Solution Approach 1:
The patent introduces a CCD camera-based visual measurement system as an intermediary that directly measures the position and orientation of the moving platform. This measurement intermediary provides accurate feedback about the platform's actual state, enabling the control system to compensate for errors in the macro-moving platform, thereby achieving high precision even with large stroke capabilities
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 solution achieves submicron-class positioning precision with millimeter-class stroke, providing non-contact, high-precision, high-frequency feedback suitable for small-sized applications, including scanning electron microscope cavities, by using a simple and compact mechanism with quick dynamic response.
Implementation Method 1
perform image processing to obtain coordinate information of photographed first and second feature points on the moving platform
Data Source
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AI summary
A parallel platform tracking control apparatus and method using a visual device as a sensor are disclosed. The apparatus comprises a parallel platform body, a CCD camera (11), a lens (6), a camera light source (9), a computer (11), a Dspace semi-physical simulation controller, an ultrasonic motor driver and the like. The parallel platform comprises an ultrasonic linear motor (1), a linear grating encoder (5), a driven rod (2), a moving platform (3), a stationary platform (4) and the like. The CCD camera photographs the moving platform in a perpendicular and opposite manner, and the photographed images are subjected to an image processing algorithm to measure the position of the corresponding marker on the moving platform, which is not only applicable to measurement, but also implements real-time feedback of the termination position of the moving platform, such that a full closed-loop system is constituted. In this way, the parallel platform is precisely positioned.