Cartesian Parallel Force Limiter for Robotic Collision Safety
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Solution Overview
Problem
Existing robotic systems face challenges in effectively limiting collision forces between moving devices and objects, particularly in unfenced environments, as current methods rely on electronic components that can fail and compromise precision and stiffness, with moment-limiting designs being overly sensitive and prone to false triggering.
Innovation Solution
A force limiting device using a parallel mechanism with torque limiters that provides a rigid connection during normal operation, becoming compliant only when excessive forces are applied, thereby reducing contact forces and preventing damage, with configurations for one, two, and three degrees of freedom to accommodate various robotic applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a flexible flange with breakaway function is used to limit contact force, then the maximum moment is limited, but the system becomes overly sensitive and prone to false triggering in high inertia non-collision situations
Solution Approach 1:
The patent introduces a Cartesian parallel mechanism as an intermediary device between the robot and end-effector. This mechanism includes torque limiters that act as mediators to transmit forces while preventing excessive moments from reaching the end-effector. The torque limiters are configured with specific torque thresholds that distinguish between normal operational forces and collision forces, thereby preventing false triggering while maintaining reliable contact force limitation.
Solution Approach 2:
The patent changes the parameter being limited from moment (torque) to force by using a Cartesian parallel mechanism. The torque limiters in the mechanism are configured with torque thresholds that correspond to maximum allowable contact forces. By transforming the limitation parameter from moment-dependent to force-dependent, the system avoids false triggering in high inertia situations where large moments may occur without actual collisions.
2Object-affected harmful factors
If compliance is added to reduce peak contact force during collision, then damage control is improved, but precision and stiffness of the robot are compromised
Solution Approach 1:
The patent applies dynamics by making the connection between the robot and end-effector conditionally rigid or compliant. During normal operation, the Cartesian parallel mechanism maintains a rigid connection for high precision. During collision, when forces exceed torque limiter thresholds, the mechanism dynamically becomes compliant to reduce peak contact forces. This dynamic switching resolves the contradiction between precision and damage control.
Solution Approach 2:
The patent segments the robot system into three distinct parts: the robot manipulator, the Cartesian parallel mechanism with torque limiters, and the end-effector. This segmentation allows the middle mechanism to serve as a protective interface that maintains precision during normal operation while providing compliance during collisions, thus resolving the contradiction between stiffness and damage control.
3Object-affected harmful factors
If torque limiters are placed in series with each joint actuator, then the force threshold depends on manipulator configuration, but this creates sub-optimized design for worst case moment arm
Solution Approach 1:
The patent replaces the traditional series torque limiter configuration at each joint with a Cartesian parallel mechanism containing torque limiters. This substitution transforms the mechanical system from a joint-based architecture to a Cartesian-based architecture, where the torque limiters are configured to limit forces in the Cartesian directions (x, y, z). This eliminates the dependency on manipulator configuration and moment arms, simplifying the optimization process.
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 solution allows for stiff and accurate robotic operation under normal conditions while ensuring compliance during collisions, reducing the severity of impacts and improving damage control by decoupling the end-effector from the robot, thus enhancing the reliability and safety of robotic interactions with objects.
Implementation Method 1
one of the revolute joints is replaced with a torque limiter that limits the torque that can be transmitted to the parallelogram linkage
Data Source
AI summary
The present invention relates to a method and apparatus for limiting the contact force between a moving device and another object, using a parallel mechanism and torque limiters where the threshold force to activate the force limiting mechanism is not related to the configuration of the moving device or the location of the contact force relative to the activation point of the force limiting mechanism, and where the mechanism may be configured for one, two or three degrees of freedom. A counterbalance mechanism is also provided to counteract gravity load when the force limiting mechanism is configured for three degrees of freedom and responsive to contact forces including a vertical element. In particular, the invention relates to a method and apparatus for limiting the contact force between a moving robotic device and a contactable object.