Substrate Transfer Robot Joint Control for Backlash-Free Alignment
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Solution Overview
Problem
Existing substrate transfer systems face challenges in maintaining positional accuracy due to backlash in gear transmission mechanisms, especially when the direction of rotation is switched during substrate handling, leading to incomplete center alignment correction.
Innovation Solution
A controller for a substrate transfer robot that drives the joint motor in a consistent direction to correct the hand's position by passing through a relay position before reaching the corrected position, thereby avoiding the adverse effects of backlash and ensuring stable and accurate alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the joint motor switches rotation direction during substrate transfer to correct positional misalignment, then the hand can reach the corrected position, but positional accuracy decreases due to backlash in the gear train
Solution Approach 1:
The hand is controlled to pass through a relay position before reaching the corrected position. This preliminary movement in a consistent rotation direction prepares the gear train by eliminating backlash beforehand, ensuring that the subsequent movement to the final corrected position maintains high positional accuracy without being affected by gear backlash.
2Productivity
If the hand moves directly to the corrected position without passing through a relay position, then the transfer process is faster, but backlash causes inaccurate center alignment correction
Solution Approach 1:
The relay position serves as an intermediate stopping point that allows the gear train to be pre-positioned without backlash. By making the hand pass through this relay position first, the system eliminates gear backlash before the final movement to the corrected position, ensuring accurate center alignment while minimizing the impact on overall transfer speed.
3Manufacturing precision
If a relay position is introduced in the hand movement path, then positional accuracy improves by avoiding backlash, but the transfer process time increases
Solution Approach 1:
The relay position is strategically positioned to allow the hand to first move in one direction to eliminate backlash, then reverse to reach the corrected position. This preliminary action of moving to the relay position ensures that the gear train is properly engaged without backlash, and the subsequent movement to the final position is smooth and accurate, optimizing the balance between time and precision.
Data Source
AI summary
A controller controls a substrate transfer robot whose joint axis is oriented in a vertical direction. The joint motor that drives the joint is switchable in a direction of rotation. The controller corrects a position of a hand in at least one of the cases of picking a substrate and placing a substrate based on positional misalignment information. The controller controls the hand to pass through a relay position before the hand reaches a corrected position that is the position of the hand after correction. The controller controls the hand to reach the relay position by driving the joint in one direction by the joint motor, and the hand to reach the corrected position from the relay position by driving the joint in the same one direction only by the joint motor.