Bidirectional antagonistic variable stiffness actuation: Analysis, design & Implementation

The variable stiffness actuation concept is considered to provide a human-friendly robot technology. This paper examines a joint concept called the bidirectional antagonistic joint which is a extension of antagonistic joints. A new operating mode called the helping mode is introduced, which increases the joint load range. Although the joint can not be pretensioned in the helping mode, it is shown that a stiffness variation is possible, assuming a suitable torque-stiffness characteristic of the elastic elements. A methodology to design such characteristics is presented along with several example cases interpreted in a torque-stiffness plot. Furthermore, a stiffness adaptation control scheme which ensures mechanism safety is described. Finally, the design methodology and the control are evaluated on an implementation of a bidirectional antagonistic joint.

Authors

• Florian Petit
• Maxime Chalon
• Werner Friedl
• Markus Grebenstein
• Alin Albu-Schäffer
• Gerhard Hirzinger

Keywords

• Robot sensing systems
• Humans
• Service robots
• Torque control
• Robotics and automation
• Design methodology
• Safety
• Protection
• Actuators
• USA Councils
• Variable Stiffness
• Variable Stiffness Actuators
• Operation Mode
• Elastic Elements
• Actuator
• Horizontal Axis
• Electrical Engineering
• External Load
• Different Signs
• Load Distribution
• Changes In Stiffness
• Joint Stiffness
• Joint Torque
• Real Constants
• Motor Torque
• Motor Position
• Range Of Stiffness
• External Torque
• Stiffness Characteristics
• Stiffness Control
• Torque Curve