Cartesian impedance control for a variable stiffness robot arm

The variable stiffness actuation (VSA) technology has been recently developed and applied in robotic arms. Mechanism robustness, high peak torque and velocity, and stiffness adjustment flexibility are key benefits of VSA joints. However, the achievable Cartesian stiffness by uncoupled VSA joints is limited. Therefore we suggest and analyze the use of an active impedance controller in combination with the passive joints to further increase the stiffness range. An algorithm to optimize the passive and active Cartesian stiffness is proposed to achieve a desired Cartesian stiffness as precise as possible. The algorithm was implemented and tested on the VSA robot DLR Hand Arm System. Experimental results and measurements of the active/passive impedance algorithm are shown.

Authors

• Florian Petit
• Alin Albu-Schäffer

Keywords

• Joints
• Robots
• Impedance
• Optimization
• Jacobian matrices
• Vectors
• Matrix decomposition
• Robotic Arm
• Variable Stiffness
• Impedance Control
• Variable Arm
• Cartesian Impedance Control
• Active Control
• Range Of Stiffness
• Passive Stiffness
• Passive Joint
• Diagonal Matrix
• Lagrange Multiplier
• Inequality Constraints
• High Stiffness
• Positive Definite Matrix
• Definite Matrix
• Equality Constraints
• Stiffness Matrix
• Frobenius Norm
• Low Stiffness
• Joint Stiffness
• Positive Definite
• Least Squares Problem
• Robot Configuration
• Elbow Joint
• Control Series
• Cartesian Position
• Joint Torque
• Stiffness Behavior
• Passive Elements
• Problem Of Finding