Magnetorheologically Damped Compliant Foot for Legged Robotic Application

The aim of this work is to enhance the controllability and the balance of a legged robot by improving the traction between the foot tip and the ground, since the stability of the robot can be influenced only during the phase when the foot is touching the ground. Within the framework of the hydraulically actuated quadruped robot, called HyQ, this paper presents an innovative solution for bouncing reduction between a robotic leg and the ground by means of a semi-active compliant foot. The compliant foot is custom-designed for quadruped walking robots and it consists of a linear spring and a magnetorheological damper. By utilizing magnetorheological technology in the damper element, the damping coefficient of the compliant foot can be altered in a wide range without any additional moving parts. The content of this paper is twofold. In the first part the design, the prototype and a model of the semi-active compliant foot are presented, and the performances of the magnetorheological damper are experimentally studied in quasi-static and dynamic cases. Based on the quasi-static measurements the damping force can be controlled in a range from 15 N to 310 N. From the frequency response measurements it can be analyzed that the generated damping force has a bandwidth higher than 100 Hz. The second part of this paper presents an online stiffness identification algorithm and a mathematical model of the HyQ leg. Using this model the relevant physical parameters are identified. A critical damping control law is proposed and implemented in order to demonstrate the effectiveness of the device that makes use of smart materials. Further on, drop-down experiments have been carried out to assess the performance of the proposed control law in terms of bounce reduction and settling time. In the test setup the HyQ leg was attached to a vertically sliding test setup and in the leg the compliant foot was mounted to the lower limb segment. With the total mass of 7 kg the robotic leg was dropped from the heights of 0.1 m, 0.2 m and 0.3 m. In the results it will be demonstrated that by real time control of the damping force 98% bounce reduction with settling time of 170 ms can be achieved.

[1]  Matthew M. Williamson,et al.  Series elastic actuators , 1995, Proceedings 1995 IEEE/RSJ International Conference on Intelligent Robots and Systems. Human Robot Interaction and Cooperative Robots.

[2]  Claudio Semini.  HyQ - Design and Development of a Hydraulically Actuated Quadruped Robot , 2010 .

[3]  Chee-Meng Chew,et al.  Series damper actuator: a novel force/torque control actuator , 2004, 4th IEEE/RAS International Conference on Humanoid Robots, 2004..

[4]  Mehdi Ahmadian,et al.  Investigating the magnetorheological effect at high flow velocities , 2006 .

[5]  Antonio Bicchi,et al.  Design and Control of a Variable Stiffness Actuator for Safe and Fast Physical Human/Robot Interaction , 2005, Proceedings of the 2005 IEEE International Conference on Robotics and Automation.

[6]  Michael Goldfarb,et al.  Enhanced Performance and Stability in Pneumatic Servosystems With Supplemental Mechanical Damping , 2010 .

[7]  Joel E. Chestnutt,et al.  The Actuator With Mechanically Adjustable Series Compliance , 2010, IEEE Transactions on Robotics.

[8]  Billie F. Spencer,et al.  Large-scale MR fluid dampers: modeling and dynamic performance considerations , 2002 .

[9]  B.J. Bass,et al.  System Identification of a 200 kN Magneto-Rheological Fluid Damper for Structural Control in Large-Scale Smart Structures , 2007, 2007 American Control Conference.

[10]  G. Oriolo,et al.  Robotics: Modelling, Planning and Control , 2008 .

[11]  Norman M. Wereley,et al.  A Magnetorheological Damper with Bifold Valves for Shock and Vibration Mitigation , 2007 .

[12]  Blake Hannaford,et al.  Measurement and modeling of McKibben pneumatic artificial muscles , 1996, IEEE Trans. Robotics Autom..

[13]  Bram Vanderborght,et al.  The Pneumatic Biped “Lucy” Actuated with Pleated Pneumatic Artificial Muscles , 2005, Auton. Robots.

[14]  Stefan Schaal,et al.  Compliant quadruped locomotion over rough terrain , 2009, 2009 IEEE/RSJ International Conference on Intelligent Robots and Systems.

[15]  G.A. Pratt,et al.  Series elastic actuator development for a biomimetic walking robot , 1999, 1999 IEEE/ASME International Conference on Advanced Intelligent Mechatronics (Cat. No.99TH8399).

[16]  Blake Hannaford,et al.  Artificial Muscles : Actuators for Biorobotic Systems , 1999 .

[17]  Michael Goldfarb,et al.  Design and control of a pneumatic quadrupedal walking robot , 2011, 2011 IEEE International Conference on Robotics and Automation.

[18]  Matti Pietola,et al.  Magnetorheological (MR) damper with a fast response time , 2008 .

[19]  Ferdinando Cannella,et al.  Design of HyQ – a hydraulically and electrically actuated quadruped robot , 2011 .

[20]  Nikolaos G. Tsagarakis,et al.  A variable physical damping actuator (VPDA) for compliant robotic joints , 2010, 2010 IEEE International Conference on Robotics and Automation.

[21]  G. G. Stokes.  "J." , 1890, The New Yale Book of Quotations.

[22]  Jerry Pratt,et al.  Series Elastic Actuators for legged robots , 2004, SPIE Defense + Commercial Sensing.

[23]  Seung-Bok Choi,et al.  Optimal design of a vehicle magnetorheological damper considering the damping force and dynamic range , 2008 .

[24]  R. Stanway,et al.  Controllable viscous damping: an experimental study of an electrorheological long-stroke damper under proportional feedback control , 1999 .

[25]  W. L. Wilkinson,et al.  Non-Newtonian Fluids : Fluid Mechanics, Mixing and Heat Transfer , 1960 .

[26]  Nader Jalili,et al.  A Comparative Study and Analysis of Semi-Active Vibration-Control Systems , 2002 .

[27]  Gene F. Franklin,et al.  Feedback Control of Dynamic Systems , 1986 .