Robot Joint Linkage With Variable Torque at High Bending Angles
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Solution Overview
Problem
Existing joint structures in walking humanoid robots face challenges in securing required torque as the bending angle increases, often requiring larger motors and compromising the robot's size and mobility.
Innovation Solution
A joint structure featuring intersecting link members and a linear-movement actuator, where the actuator's tip-end is rotatably connected to a movable link, allowing the second link member to pivot relative to the first, thereby securing torque without increasing the motor size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a bending angle of a knee joint increases, then a knee torque which acts on the knee joint as a load increases, but a motor size must be increased to secure the required torque
Solution Approach 1:
The patent changes the mechanical parameters of the linkage mechanism by introducing a variable reduction ratio system. As the knee joint bending angle increases, the reduction ratio automatically increases, allowing the motor to maintain constant size while delivering higher torque through mechanical advantage rather than motor power increase.
Solution Approach 2:
The patent implements a dynamic reduction ratio that varies with the joint angle. The linkage mechanism transitions from a fixed reduction ratio to a variable one, where the reduction ratio increases as the knee bends, enabling the motor to operate at constant power while providing variable torque output matching the load requirements.
2Volume of moving object
If a reduction ratio increases to secure required torque, then a motor size can be reduced, but a movable range (rotating angle) of the joint decreases
Solution Approach 1:
The patent employs a dynamic reduction ratio mechanism that adapts to the joint angle. At small bending angles, the reduction ratio remains low to preserve movable range. As the joint bends further, the reduction ratio increases automatically, allowing the system to achieve high torque only when needed while maintaining full range of motion capability.
Solution Approach 2:
The linkage geometry is designed to change parameters dynamically - specifically, the effective lever arms and transmission angles vary with joint position. This causes the reduction ratio to be a function of the joint angle, enabling the system to optimize between range of motion and torque output at different positions in the movement cycle.
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
This configuration ensures the required torque is maintained as the bending angle increases, enabling robot downsizing without enlarging the motor, thus enhancing mobility and compactness.
Implementation Method 1
a first movable link and a second movable link, disposed so as to intersect with each other and configured to rotatably couple the first link member to the second link member through the first to fourth shaft members
Data Source
AI summary
A joint structure of a robot according to an embodiment may include first link member, a second link member, a first movable link and a second movable link, disposed so as to intersect with each other and configured to rotatably couple the first link member to the second link member, and a linear-movement actuator connected at a base-end part thereof to the first link member, and connected at a tip-end part thereof to the first movable link. The second link member relatively pivots to the first link member by the linear-movement actuator advancing and retreating.