Rotary Stage Angular Orientation via Optical Reference Patterns
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Solution Overview
Problem
Existing rotary stages for payloads lack cost-effective solutions for precise angular orientation and tilt measurement, relying on expensive high-accuracy drives that often oscillate and fail to achieve high precision, especially for applications like template laser projection and large object inspection.
Innovation Solution
A rotary stage assembly with a low-cost rotary drive and an imaging assembly that uses reference patterns on a cylindrical wall to determine angular orientation and tilt, allowing the platform to be moved to a proximate position, then using cameras and a controller to calculate precise orientation and adjust for high accuracy without the need for expensive encoders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If expensive high-accuracy rotary drives with encoders are used, then angular orientation precision is improved, but device cost and complexity increase significantly
Solution Approach 1:
The patent replaces complex mechanical encoder systems with an optical imaging system. Instead of using expensive encoders mounted on the rotary drive, the invention uses a camera to capture images of reference patterns on the cylindrical wall, then processes these images to determine angular orientation. This substitutes a mechanical measurement system with an optical one, achieving high precision without the complexity and cost of precision rotary drives with encoders.
Solution Approach 2:
The invention creates a visual copy of the angular position information through reference patterns on the cylindrical wall. These patterns serve as optical encodings of angular position that can be read by the imaging system. The reference patterns are essentially visual copies of position information that replace the need for physical encoder disks and read heads.
2Ease of manufacture
If low-cost rotary drives are used, then device cost is reduced, but angular orientation accuracy deteriorates due to oscillation and inability to achieve precise positioning
Solution Approach 1:
The patent implements a feedback mechanism where the imaging system continuously monitors the actual angular position by capturing images of the reference patterns. The controller compares the measured position with the desired position and adjusts the rotary drive accordingly. This closed-loop feedback allows inexpensive open-loop drives to achieve precise positioning by correcting for their inherent inaccuracies and oscillations through active control.
Solution Approach 2:
The system performs preliminary positioning using the low-cost rotary drive to bring the platform close to the desired angular orientation, then uses the high-precision optical measurement system to determine the exact position and make fine adjustments. This two-stage approach combines the speed and cost advantages of inexpensive drives with the precision of optical measurement.
3Adaptability or versatility
If tilt measurement provisions are added to rotary stages, then tilt detection capability is improved, but device complexity and cost increase
Solution Approach 1:
The imaging system serves multiple functions: it measures both angular orientation around the vertical axis and tilt angles relative to the vertical axis. By using the same camera and reference pattern system for both measurements, the invention achieves multi-functionality without adding separate tilt sensors or complex mechanical tilt measurement mechanisms. The reference patterns on the cylindrical wall provide information for both types of measurements.
Data Source
AI summary
A rotary stage assembly includes a platform and a rotary drive defining an axis of rotation. The platform is mounted on a spindle for receiving rotary movement from the rotary drive. A cylindrical wall is attached to the platform receiving rotary movement from the rotary drive and is coaxial with the axis of rotation defined by the rotary drive. The cylindrical wall defines an inner surface including reference patterns. An imaging assembly images the reference patterns on the inner surface of the cylindrical wall. The imaging assembly detects angular orientation and tilt of the platform from an axis of rotation of the platform from imaging the reference patterns on the inner surface of the cylindrical wall. A controller calculates angular orientation and tilt of the platform from the location of said reference patterns signaled from the imaging assembly.