OHT Load Port Alignment Using Vision and Inertial Feedback
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Solution Overview
Problem
Manual alignment of overhead hoist transport vehicles with load ports in semiconductor fabrication facilities is labor-intensive, time-consuming, and costly, leading to misalignment issues that can cause operational delays and damage, requiring frequent realignment without interrupting production.
Innovation Solution
An automated wafer carrying pod alignment system using a digital image capture device and inertial measurement device to determine positioning errors and adjust the OHT vehicle's set points for precise alignment, enabling fast initial alignment during installation and continuous realignment during operation without halting production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If manual alignment of OHT vehicles with load ports is performed, then alignment can be achieved, but it is labor-intensive, time-consuming, and costly
Solution Approach 1:
The patent replaces manual mechanical alignment operations with an automated vision-based system. A camera captures images of alignment features on the OHT vehicle and load port, and a computer processing system automatically calculates positioning errors and adjusts set points, eliminating the need for manual measurement and alignment operations.
Solution Approach 2:
The system enables the OHT vehicle to perform self-alignment by automatically detecting its own position relative to the load port using vision sensors, calculating positioning errors, and adjusting its set points without external intervention. This self-service capability continuously maintains alignment during operation.
2Measurement precision
If manual alignment is performed frequently to maintain accuracy, then alignment precision is maintained, but production is interrupted
Solution Approach 1:
The automated vision-based alignment system operates continuously during OHT vehicle operation, constantly monitoring alignment through image capture and processing. The system maintains alignment precision without interruption to production by performing alignment checks and adjustments as part of normal operational flow.
Solution Approach 2:
The system continuously captures images of alignment features, processes the image data to determine positioning errors, and feeds back adjusted set points to the OHT vehicle control system. This closed-loop feedback mechanism maintains alignment precision automatically during continuous production operation.
3Loss of time
If automated alignment system is implemented, then alignment time is reduced, but device complexity increases
Solution Approach 1:
The vision-based alignment system serves multiple functions: it captures images for alignment measurement, processes images to calculate positioning errors, communicates errors to the OHT vehicle, and adjusts set points for correction. This multi-functional system replaces multiple separate alignment devices and manual procedures with a single integrated solution.
Data Source
AI summary
Methods and systems for automatically aligning an overhead hoist transport (OHT) vehicle with a load port of a wafer fabrication tool during operation and at the installation phase of the equipment in a semiconductor fabrication facility are described herein. In one aspect, an alignment frame including a digital image capture device is mounted to a wafer-in-progress (WIP) carrying pod. An image captured by the image capture device is analyzed to determine a positioning error of the OHT vehicle relative to the alignment frame based on the location of the OHT vehicle within the image. In another aspect, an inertial measurement device is coupled to a gripper assembly of an OHT vehicle. Inertial measurement signals are collected when the gripper assembly docks with a WIP carrying pod. The inertial measurement signals are analyzed to determine an initial positioning error of the gripper assembly with respect to the WIP carrying pod.