Gravity-Counterbalanced Robot Arm With Remote Differential
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Solution Overview
Problem
Existing robot arm designs for humanoid robots face challenges in achieving a balance between safety, range-of-motion, and counterbalancing, as traditional counterbalancing methods either add bulk, restrict motion, or fail to address shoulder singularities effectively.
Innovation Solution
A robot arm design utilizing a differential mechanism with counterweights or counterbalance springs positioned remotely from the arm and shoulder, allowing for gravity counterbalancing while maintaining a large range-of-motion and avoiding shoulder singularities, with motors grounded to facilitate better mass distribution and backdrivability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If counterweights are positioned on or in the arm to provide gravity counterbalancing, then the counterbalancing function is achieved, but the arm mass increases significantly
Solution Approach 1:
The counterweight is extracted from the arm and relocated to a separate position (such as the base or external mounting). The arm assembly includes a drive assembly with motor mounted at a first position and a counterweight mounted at a second position, connected through a linkage mechanism. This separation removes the counterbalancing mass from the moving arm, achieving gravity counterbalancing without significantly increasing arm mass.
2Reliability
If the counterweight is positioned on an extension element extending from the upper arm, then gravity counterbalancing is provided, but the range-of-motion is limited and human form factor is exceeded
Solution Approach 1:
The counterweight system is extracted from the arm structure and repositioned externally or at the base. The linkage mechanism connects the drive assembly at the shoulder to the counterweight at a remote position, allowing the arm to achieve full human-like range of motion without the counterweight interfering with movement or exceeding human form factors.
Solution Approach 2:
A linkage mechanism serves as an intermediary between the drive assembly and the counterweight. This intermediary transmission system allows the counterweight to be positioned remotely while still providing effective gravity counterbalancing at the arm, enabling both full range of motion and proper counterbalancing function.
3Reliability
If spring-based counterbalance systems are used with components positioned within or on the arm, then gravity counterbalancing is achieved, but the mechanical complexity increases and mass reduction is limited
Solution Approach 1:
The counterbalancing components (motor and counterweight) are extracted from the arm and positioned externally or at the base. The drive assembly includes a motor mounted at a first position and a counterweight mounted at a second position, connected through a linkage, simplifying the arm's mechanical structure while maintaining effective gravity counterbalancing.
4Ease of operation
If motors are positioned close to the arm and shoulder for direct actuation, then actuation effectiveness is improved, but mass distribution and packaging are compromised
Solution Approach 1:
A linkage mechanism acts as an intermediary transmission system between the motor (mounted at a remote first position) and the arm (at a second position). This allows the motor to be positioned away from the arm for better packaging and mass distribution while still providing effective actuation through the linkage transmission.
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
The design achieves a balanced and backdrivable robot arm with an unrestricted range-of-motion, effectively counterbalancing the arm's weight, ensuring safety and expressive movement, and allowing for the placement of motors within the torso, reducing overall mass and interference.
Implementation Method 1
a counterweight providing the gravity counterbalancing for the predefined mass of the arm link
Data Source
AI summary
An arm assembly for use in a robot to provide gravity counterbalancing of the robot arms. The arm assembly includes an arm and a drive assembly. The arm assembly includes a differential interconnecting the drive assembly with the arm link. The differential is attached to a torso-side or upper end of the arm link, and the differential is adapted to provide gravity counterbalancing for the predefined mass of the arm link. A pair of half counterweights are provided and arranged to each move in one degree of freedom and to provide two equal counterweights to the differential's two inputs such as input gears, pulleys, or the like. The drive assembly includes two motors that are grounded. In some embodiments, both the motors and the counterweights are spaced apart from the robot's shoulder, i.e., spaced apart from the differential near the robot's pelvis or low in the torso.