Redundant Robot Force Monitoring With Null-Space Contact Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Kinematically redundant robots face inaccuracies in estimating external forces due to measurement and modeling errors, leading to inadequate safety reactions, especially when joint moments from contact forces at a distance from the TCP are incorrectly projected, resulting in insufficient safety responses.
Innovation Solution
A method that involves detecting joint forces using sensors and estimating externally induced joint forces, then mapping these forces to the working space using a pseudo-inverse Jacobian matrix, while introducing a further monitoring variable that accounts for forces at a distance from the robot-fixed reference, utilizing a zero-space projection operator to detect environmental contacts and model inaccuracies, triggering safety reactions when limit values are exceeded.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If joint forces are mapped to external effective force using pseudo-inverse of transposed Jacobian matrix, then external force estimation is achieved, but measurement and modeling inaccuracies cause incorrect force projection
Solution Approach 1:
The patent segments the joint forces into two distinct components: effective forces acting on the TCP (tool center point) and crushing forces acting on robot surfaces at distances from the TCP. This segmentation is achieved by decomposing the joint force vector into components that lie in the range space of the Jacobian transpose and components in the null space, allowing independent monitoring of each force type with appropriate safety thresholds.
2Ease of operation
If joint moments from contact forces at distance from TCP are projected using pseudo-inverse, then force estimation is performed, but zero-space components result in very small estimated forces without safety reaction
Solution Approach 1:
The patent extends the traditional force monitoring by adding a new dimensional component - the null space projection of joint forces. While conventional methods only monitor the range space component (effective forces on TCP), this invention monitors both the range space and null space components separately. The null space component captures crushing forces at robot surfaces that would otherwise be lost, creating an additional monitoring dimension that detects forces previously invisible to the control system.
3Measurement precision
If conventional force monitoring is used, then TCP contact forces are detected, but forces on robot surfaces at distance from TCP are missed
Solution Approach 1:
The patent implements a feedback mechanism where joint forces are continuously measured by torque sensors, decomposed into effective and crushing force components, and used to trigger appropriate safety reactions. The system provides continuous feedback about both TCP contact forces and surface crushing forces, allowing the robot to respond appropriately to different types of environmental interactions based on real-time force component analysis.
Data Source
Figure 1~2
AI summary
A method according to the invention for monitoring a kinematically redundant robot (1) comprises the steps: detecting (S10, S20) joint forces (τ, T̂e) which act in the joints of the robot; Determination (S30) of an external effective force (f̂w) between a robot-fixed reference (TCP) and an environment on the basis of the detected joint forces; Determination (S40) of a further monitoring variable (τ̂NS), which is at least essentially independent of an external force acting on the robot-fixed reference, on the basis of the detected joint forces; and monitoring (S50, S60) the ascertained external effective force and the ascertained additional monitoring variable.