Unequal Link SCARA Arm Resolving Reach Footprint Trade-off
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Solution Overview
Problem
Conventional SCARA arm robots with equal length links have a limited containment to extension ratio, resulting in a larger footprint and reduced reach, and the end effector is not orthogonal to the substrate holding area, limiting their effectiveness in substrate transport applications.
Innovation Solution
A substrate transport apparatus with an articulated arm featuring unequal lengths for the upper arm and forearm, along with an independently rotatable substrate holder, allowing for greater reach and maintaining a consistent swing diameter, enabling efficient transport between multiple substrate holding areas while keeping the drive section fixed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the upper arm and forearm are made equal in length, then the structure is simpler and more symmetric, but the reach-to-containment ratio is limited and the footprint increases
Solution Approach 1:
The patent applies asymmetry by making the upper arm and forearm of unequal lengths. Specifically, the upper arm has a first length and the forearm has a second length that is different from the first length. This asymmetric configuration allows the robot arm to achieve a greater reach-to-containment ratio while maintaining a compact footprint, resolving the contradiction between maximizing reach and minimizing footprint.
2Length of moving object
If the upper arm and forearm length are increased to enable greater extension, then the reach is improved, but the swing diameter (footprint) also increases
Solution Approach 1:
The patent resolves this contradiction by using asymmetric link lengths where the upper arm and forearm have different lengths. This allows the arm to achieve greater extension capability without proportionally increasing the swing diameter. The unequal length configuration optimizes the extension-to-footprint ratio, enabling greater reach while maintaining a compact base area.
3Ease of operation
If the end effector rotation tracks with the upper arm rotation, then the control is simpler, but the end effector is not orthogonal to the substrate holding area
Solution Approach 1:
The patent applies dynamics by making the end effector independently rotatable rather than passively tracking the upper arm rotation. The end effector has an independent rotation degree of freedom that allows it to be dynamically adjusted to maintain orthogonality with the substrate holding area during movement. This dynamic independence resolves the contradiction between simple control and adaptability by allowing programmable control of the independent rotation.
Data Source
AI summary
A substrate transport apparatus comprising a drive section, a controller, an upper arm, forearm and substrate holder. A proximate end of the upper arm being rotatably mounted to the drive section at a shoulder joint. A proximate end of the forearm being rotatably mounted to a distal end of the upper arm at an elbow joint. The substrate holder being rotatably mounted to a distal end of the forearm at a wrist joint. The upper arm and the forearm being unequal in length from joint center to joint center. The substrate transport arm is adapted to transport substrate to and from at least two substrate holding areas with the drive section of the transport apparatus remaining in a fixed position relative to the holding areas. Each of the upper arm, forearm and substrate holder being independently rotatable with respect to each other.