A novel compliant actuator with load-dependent variable stiffness: Design concept and control

Lu Lu, Jiawei Li, Cong Wang, Dan Strassberg

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1 Scopus citations


To develop the next generation of high-performance robots capable of working in human environments, it is required that the joint actuators have variable stiffness to achieve both precision motion control and ability of reaction under unexpectedly huge impact caused by collision with obstacles or human. Variable stiffness actuators (VSA) partially realize such objectives by employing an auxiliary input to change the joint stiffness. However, it requires prior information of external load condition. Load sensors or online load estimation techniques need to be implemented to detect sudden unexpected load for stiffness adjustment, adding complexity to the system with bandwidth issues. In this paper, we propose a new design of compliant actuator in which the stiffness automatically varies depending on the unexpected external load. A novel doubly-clamped box structure is used to connect the load inertia to the motor inertia. Specifically, the load inertia is confined inside a box clamped by two stoppers on two opposite sides with two pre-compressed springs. A secondary motor connects to the load inertia through another spring, compensating for known unbalanced forces such as gravity, Coriolis force and inertia force. It is shown that if the unexpected external load force is below the pre-compression force of the springs, the load inertia will be confined exactly within the box and the system behaves like a rigid actuator, otherwise one of the springs will be further compressed and the system behaves like a compliant actuator. Such a mechanical structure has the ability of achieving both precision motion control and automatic reaction under unexpectedly huge external impact, without the need of additional load sensing/estimation. Control algorithms for accurate position tracking under potentially huge unexpected load is developed for this new type of actuator. Simulations are conducted to verify the effectiveness of the design concept and control.

Original languageEnglish (US)
Title of host publicationMechatronics; Mechatronics and Controls in Advanced Manufacturing; Modeling and Control of Automotive Systems and Combustion Engines; Modeling and Validation; Motion and Vibration Control Applications; Multi-Agent and Networked Systems; Path Planning and Motion Control; Robot Manipulators; Sensors and Actuators; Tracking Control Systems; Uncertain Systems and Robustness; Unmanned, Ground and Surface Robotics; Vehicle Dynamic Controls; Vehicle Dynamics and Traffic Control
PublisherAmerican Society of Mechanical Engineers
ISBN (Electronic)9780791850701
StatePublished - 2016
EventASME 2016 Dynamic Systems and Control Conference, DSCC 2016 - Minneapolis, United States
Duration: Oct 12 2016Oct 14 2016

Publication series

NameASME 2016 Dynamic Systems and Control Conference, DSCC 2016


OtherASME 2016 Dynamic Systems and Control Conference, DSCC 2016
Country/TerritoryUnited States

All Science Journal Classification (ASJC) codes

  • Control and Systems Engineering
  • Industrial and Manufacturing Engineering
  • Mechanical Engineering


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