Development and control of a series elastic actuator equipped with a semi active friction damper for human friendly robots

• Whole realization process of a successful implementation of a variable impedance actuator.
• Comprehensive analysis on the effects of compliance and variable physical damping.
• Mechatronic implementation of the variable impedance actuator.
• Introduction of a novel mechanical impedance estimator for measuring physical damping.
• Experimental results validate the analysis and the whole mechatronic system.

Compliance is increasingly being incorporated in the transmission of robotics actuation systems to cope with unpredictable interactions, improve the robustness of the robot and in some cases its efficiency. However, compliance also introduces some drawbacks as e.g. reduced bandwidth of the controlled system and typically underdamped vibration modes which decrease the accuracy and stability margin of the controlled system. To tackle these issues, variable physical damping has recently been incorporated in such actuation systems. This paper presents the analysis, development, control, identification and experimental evaluation of a novel actuation system which embodies transmission characteristics such as passive compliance and variable physical damping. The first part of this paper introduces an analysis on how these two physical properties affect the performance of the actuation system with the second part analysing the mechatronic design and control in detail. Furthermore, a novel damping estimation method is presented. Results are presented to validate the results obtained in the analysis section advantages gained by employing such actuation approach and to show the effectiveness of the actuation unit in replicating and estimating desired mechanical impedance values.