Vrije Universiteit Brussel


Soft Arm

Introduction

Repetitive manual handling of heavy loads is common in assembly and is a frequent cause of lower back disorders. This can have a significant impact on the quality of life and has a serious economic cost. Manipulators are robotic systems designed to avoid these problems. They assist people in performing heavy-duty tasks.

Most of the commercially available manipulators use a counterweight, which limits their use to handling loads of a specific mass. Others are electrically or hydraulically actuated. This usually makes them heavy, complex and expensive.

The use of the PPAM actuator allows us to tackle these issues and develop a manipulator that combines ergonomics, operator safety, low cost, low weight and ease of operation.

The goal of our research is to develop a proof-of-concept manipulator that will be used in direct contact with an operator, without expensive force or torque sensors and without user interaction through control elements (such as joysticks). We are working towards a system that behaves as follows: when the operator wants to move a load attached to the manipulator, he/she starts moving it as if there were no manipulator. By measuring the muscle gauge pressures, the system can estimate the forces applied by the operator and assist him in accomplishing the desired load movement. Ideally, moving a 30 kg load would feel like moving a 3 kg load. The direct interaction between operator and load (without intermediary control tools) allows for very precise positioning.

The main requirement for any mechanical device that is used in the immediate environment of people is safety. The PPAM actuators greatly contribute to the overall safety of the manipulator system: they allow for a lightweight construction, there is no danger of electrocution and, most important of all, the muscles are inherently compliant. The controller will also enhance safety, since there is no fundamental difference between forces generated by a collision and forces applied by an operator. The system will always tend to move away from people or objects it collides with.

Issues that have to be dealt with in the design include matching the nonlinear force-length characteristic of the PPAM to the requirement of being able to carry and move the load throughout the entire working area and making sure that the applied operator pressure can be estimated accurately enough in all manipulator positions. The main control challenge in this highly nonlinear system is obtaining a natural feel for the operator

At present, the hardware setup of a small-scale manipulator is nearing completion. It consists of two PPAM actuated links in inverse elbow configuration. A controller for the system is currently being developed.

Movies and pictures

  • A movie (1.5 MB) of the manipulator moving:


  • Two movies illustrating the inherent compliance of the system.
    In the first movie, all muscle pressures are kept at 1.5 bar (150 kPa). It is clear that the system is very compliant.
    In the second movie, all pressures are set to 3 bar (300 kPa). The system remains very compliant, but it feels a lot stiffer.
    Pressure = 1.5 bar (2 MB) Pressure = 3 bar (2 MB)

  • Movie of an operator interacting with the system. The operator gently guides the manipulator.


  • Some pictures (click to enlarge):


Financial support

This research is supported by the Fund for Scientific Research - Flanders (Belgium), grant FWOKN147.

Publications

International journal papers

  • Proxy-Based Sliding Mode Control of a Planar Pneumatic Manipulator
    M. Van Damme, B. Vanderborght, B. Verrelst, R. Van Ham, F. Daerden and D. Lefeber.
    International Journal of Robotics Research, Vol. 28, issue 2, 2009, p. 266-284.
    Impact factor: 1.591 (2006)
    http://ijr.sagepub.com/cgi/content/abstract/28/2/266

  • Sliding Mode Control of a 2-DOF Planar Pneumatic Manipulator
    M. Van Damme, B. Vanderborght, R. Van Ham, B. Verrelst, F. Daerden, D. Lefeber.
    Transactions of the ASME - Journal of Dynamic Systems, Measurement, and Control, Vol. 131, Issue 2, 2009.
    Impact factor: 0.658 (2006)
    http://link.aip.org/link/?JDS/131/021013

Conference papers

  • Modeling Hysteresis in Pleated Pneumatic Artificial Muscles
    Van Damme Michael, Beyl Pieter, Vanderborght Bram, Van Ham Ronald, Vanderniepen Innes, Versluys Rino, Daerden Frank, Lefeber Dirk
    2008 IEEE International Conference on Robotics, Automation & Mechatronics (RAM 2008), September 22 - 24, Chengdu, China, pp. 471-476
    Best Paper Award.

  • Proxy-Based Sliding Mode Control of a Manipulator Actuated by Pleated Pneumatic Artificial Muscles
    Van Damme Michael, Vanderborght Bram, Van Ham Ronald, Verrelst Bjorn, Daerden Frank, Lefeber Dirk
    ICRA2007 -- 2007 IEEE International Conference on Robotics and Automation, pp. 4355-4360

  • Proxy-Based Sliding Mode Control of a 2-DOF Pneumatic Manipulator
    Van Damme Michael, Vanderborght Bram, Van Ham Ronald, Daerden Frank, Lefeber Dirk
    Book of Abstracts 26th Benelux Meeting on Systems and Control, pp. 127-127 (2007)

  • Proxy-Based Sliding Mode Control of a Planar Pneumatic Manipulator
    M. Van Damme, B. Vanderborght, R. Van Ham, F. Daerden, D. Lefeber
    CLAWAR 2006 -- 9th International Conference on Climbing and Walking Robots and the Support Technologies for Mobile Machines, September 12 - 14, 2006, Brussels, Belgium, pp. 402 - 406

  • Design and Control of a "Soft" 2-DOF Planar Pneumatic Manipulator
    M. Van Damme, R. Van Ham, B. Vanderborght, F. Daerden and D. Lefeber
    Proceedings of the 15th International Symposium on Measurement and Control in Robotics, 08-10 November 2005, Brussels, Belgium.

  • Design of a "Soft" 2-DOF Planar Pneumatic Manipulator
    Van Damme M., Van Ham R., Vanderborght B., Daerden F., & Lefeber D.
    CLAWAR 2005: 8th International Conference on Climbing and Walking Robots and the Support Technologies for Mobile Machines, 12Ė15 September 2005 - London, U.K., p 559-566

  • A Pneumatic Manipulator used in Direct Contact with an Operator
    Van Damme M., Daerden F. & Lefeber D.
    Proceedings of the 2005 IEEE International Conference on Robotics and Automation, Barcelona, Spain, April 2005, p. 4505-4510.

  • Design of a pneumatic manipulator in direct contact with an operator
    Van Damme M., Daerden F. & Lefeber D.
    Proceedings of the 35th International Symposium on Robotics, Paris, France, 2004.

Researcher: MichaŽl Van Damme
Promotor: Frank Daerden Up

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