Variable-Stiffness Elastic Joint With Nonlinear Torque Control
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Solution Overview
Problem
Existing robot joint systems lack adjustable stiffness, limiting their versatility and safety in human-robot interaction and assembly tasks.
Innovation Solution
A nonlinear elastic joint with variable stiffness, utilizing a control disk, rollers, double-sided levers, and a compression spring, where the stiffness is adjusted by an adjustment mechanism connected to the pivots of the levers, allowing for a progressive, nonlinear torque curve.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a robot joint system uses multiple drive motors and energy storage devices to enable energy transfer between joints, then the system achieves enhanced functionality and versatility, but the device complexity and manufacturing effort increase considerably
Solution Approach 1:
The patent combines the functions of multiple drive motors and energy storage devices into a single integrated elastic mechanism. The elastic element serves both as a spring for energy storage and as a cam for motion transmission, eliminating the need for separate components and reducing overall system complexity while maintaining energy transfer capability between joints.
Solution Approach 2:
The elastic mechanism performs multiple functions simultaneously: it stores energy like a spring, transmits motion like a cam, and provides stiffness control. This multi-functional design replaces what would traditionally require separate dedicated components for each function, thereby reducing device complexity while preserving versatility.
2Ease of operation
If an antagonistic pivoting device uses two drive units with power transmission devices, then the device achieves bidirectional motion control, but the device complexity and number of components increase
Solution Approach 1:
The patent merges two separate power transmission devices into a single elastic mechanism with an asymmetric cam profile. The cam's asymmetric geometry inherently provides different mechanical advantages for clockwise and counter-clockwise rotation, enabling bidirectional motion control without requiring separate transmission paths or additional components.
Solution Approach 2:
The cam profile has different geometric properties at different locations - the asymmetric design creates locally optimized contact surfaces for different rotation directions. This local differentiation in geometry provides direction-dependent mechanical characteristics without adding overall system complexity.
3Adaptability or versatility
If a robot joint uses a fixed stiffness elastic mechanism, then the structure is simple, but the adaptability for different tasks and safety requirements is limited
Solution Approach 1:
The patent transforms the static, fixed stiffness elastic mechanism into a dynamic system where stiffness can be adjusted in real-time. By making the cam profile adjustable, the mechanical advantage and resulting joint stiffness can be dynamically changed to match different task requirements and safety needs, enhancing adaptability.
Solution Approach 2:
The invention enables change in the stiffness parameter of the elastic mechanism by adjusting the cam profile position or geometry. This parameter adjustment allows the same physical mechanism to provide different stiffness characteristics without requiring fundamentally different structural designs.
4Power
If a cam and lever mechanism is used to achieve nonlinear torque characteristics, then the torque curve can be optimized, but the transmissible torque is limited by spring force
Solution Approach 1:
The patent employs a dynamically adjustable cam profile that can change its geometric characteristics during operation or between operations. This dynamic adjustment allows optimization of the torque curve for different operating conditions while the adjustable nature enables scaling of the spring force to increase transmissible torque capacity.
Solution Approach 2:
By adjusting parameters of the cam profile and spring system, the invention simultaneously optimizes both the torque curve shape and the maximum transmissible torque. The adjustable parameters allow tuning of both the nonlinear characteristics and the force capacity without the trade-off present in fixed designs.
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
Enables safe human-robot interaction and performance of physically demanding tasks by providing controllable stiffness, ensuring high contact forces while maintaining safety and versatility.
Implementation Method 1
a compression spring (6), wherein the second end of the compression spring (6) is connected to the rollers (3)
Implementation Method 2
The control disk (1), as the first component of the elastic mechanism, is connected to the first drive (18)
Implementation Method 3
double-sided levers (4), wherein the rollers (3) are pivotally connected to the first lever arms (9) of the double-sided levers (4)
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The invention relates to nonlinear elastic joints with an elastic mechanism and drives, said joints being distinguished in particular by a variable rigidity. To this end, a control plate connected to a first drive has indentations or elevations arranged distanced from one another on at least one circular path, the indentations or the elevations each being paths of a roller. The rollers are connected articulatedly to first lever arms of double-ended levers. The second lever arms of the double-ended levers are connected articulatedly via a connection part to a first end of a compression spring. The second end of the compression spring is connected to the rollers and the first lever arms. Furthermore, pivots of the double-ended levers are coupled at an adjustment mechanism to a second drive to change the position of the pivots parallel to the control plate, and thus to change the rigidity.