Stanford Manipulation Group - Human Centered Robotics



	Human-Centered Robotics In recent years, there has been great interest generated in the emerging fields of service and medical robots. These applications are part of a growing area of human-centered robotics. This area involves the close interaction between robotic manipulation systems and human beings, including direct human-manipulator contact. In such applications, traditional figures of merit such as bandwidth, maximum force and torque capability, and reachable workspace, do not fully encompass the range of metrics which define the requirements of such systems. Specifically, human-centered robotic systems must consider the requirement of safety in addition to the traditional metrics of performance. Thus, it is the challenge of human-centered robotics to successfully blend often competing requirements of safety and performance. The Stanford Robotics Laboratory has initiated a research effort to design a human-centered, inherently-safe robotic manipulator. While the design and development effort include all aspects of manipulator design, the primary focus has been on addressing the limitations of the mechanical system and its impact on safety and performance. We have focused on efforts to reduce the manipulator weight and inertia to improve its inherent safety characteristics while maintaining performance levels expected of modern manipulators. DECMMA Actuation Approach A critical component to this work has been the development of a new actuation approach that seeks to relocate the major source of actuation effort from the joint to the base of the manipulator. This can substantially reduce the effective inertia of the overall manipulator by isolating the reflected inertia of the actuator while greatly reducing the overall weight of the manipulator. Performance is maintained with small actuators collocated with the joints. Our approach partitions the torque generation into low and high frequency components and distributes these components to the arm location where they are most effective. We refer to the overall approach as Distributed Elastically Coupled Macro Mini Parallel Actuation (DECMMA). The DECMMA approach is analogous to the design of robotic manipulators for use in zero gravity. Under such conditions, gravity induced torques do not exist. Joint actuators provide torques related only to the task, such as trajectory tracking and disturbance rejection, both of which are primarily medium to high frequency in content. We achieve the zero gravity analogy by compensating for gravity torques and low frequency torques using the low frequency actuator located at the base of the manipulator. With the effects of gravity and low frequency torques compensated, joint torque requirements become similar to those encountered by a zero gravity robotic manipulator. However, unlike robotic manipulators designed for space applications, the DECMMA joint actuators do not require a large gear reducer to achieve the required torque and power densities. Thus, the impedance of DECMMA approach, and its resulting safety characteristics, is superior to that of current space robotic manipulators. . . Implementation of the DECMMA Approach Implementation of the DECMMA approach is essentially a trade off between safety, performance, and design complexity. However, this design trade is not necessarily a zero-sum game. Recall that the primary reason for the introduction of our new actuation approach was to (1) reduce contact impedance and (2) maintain task performance levels. If the task is performed by a manipulator's end effector, then high frequency torque and force capabilities need only be provided at the end effector. The dynamics of a redundant manipulator is bounded by the dynamics of the outermost degrees of freedom which span the task space. In the case of a redundant manipulation system, such as a dual manipulator - mobile base system, the mobile base degrees of freedom need not employ our new actuation approach to maintain task performance levels which, due to the redundancy of the system, are bounded by the outer six degrees of freedom. Another possible approach is to design the wrist such that required task torques are small, as would be the case for a compact wrist design. In this case, the wrist actuation could be provided by smaller conventional EM actuators. The large DC and low frequency torques provided by the base actuators of the DECMMA approach would not be required. The higher impedance of the wrist actuators would not compromise safety because impact loads would be limited by the inner three degrees of freedom. Thus, our new human friendly actuation approach can be implemented in a manner which maximizes the safety and performance characteristics while minimizing the additional complexity associated with the its dual actuation approach. . To facilitate the development and demonstrate the effectiveness of the DECAMMA approach, we have designed and built a two axis prototype robotic arm which incorporates the important characteristics of the DECMMA approach. Lessons learned from experimental work performed on the two-axis test bed are being incorporated into the design of a four degree of freedom DECCMA actuated manipulator. . "Playing it safe [human-friendly robots]" Zinn, M., Khatib, O., Roth, B., Salisbury, J.K. Robotics & Automation Magazine, IEEE Volume 11, Issue 2, June 2004 Page(s):12 - 21 "Towards a Human-centered Intrinsically-Safe Robotic Manipulator" Zinn, M., Khatib, O., Roth, B., Salisbury, J.K. IEEE Robotics and Automation Magazine, 11(2) 12-21, June 2004. "A New Actuation Approach for Human-friendly Robot Design" Zinn, M., Khatib, O., Roth, B., Salisbury, J.K. International Journal of Robotics Research, 23(4/5) 379-398, April-May 2004. "A New Actuation Approach for Human-friendly Robot Design" Zinn, M., Khatib, O., Roth, B. Proc. IEEE International Conference on Robotics and Automation, New Orleans, April 26-May 1, 2004, pp. 249-254. Vol.1 "Robots for the Human and Interactive Simulations" Khatib, O., Brock, O., Chang, K., Ruspini, D., Sentis, L., Viji, S. Proc. 10th IFToMM World Congress on the Theory of Machines and Mechanisms,, Tianjin, China, April 2004, pp. 1572-1576. "Human-Centered Robotics and Interactive Haptic Simulation" Khatib, O., Brock, O., Chang, K., Ruspini, D., Sentis, L., Viji, S. International Journal of Robotics Research, Vol 23, No. 2, Feb. 2004, pp.167-178. "Human-centered robotics and interactive simulation" Khatib, O Robotics, Intelligent Systems and Signal Processing, 2003. Proceedings. 2003 IEEE International Conference on Volume 2, 8-13 Oct. 2003 "Actuations Method for Human-Centered Robotics and Associated Control Challenges" Zinn, M., Khatib, O., Roth, B., Salisbury, J.K. Control Problems in Robotics, A. Bicchi, H. Christensen, and D. Prattichizzo (Eds.), STAR, Springer 2003, pp.105-120. "Actuation Methods For Human-Centered Robotics and Associated Control Challenges" Zinn, M., Khatib, O., Roth, B., Salisbury, J.K. Second Joint CSS/RAS International Workshop on Control Problems in Robotics and Automation, Las Vegas, NV, December 2002 "Human-centered Robotics and Haptic Interaction: From Assistance to Surgery, the Emerging Applications" Khatib, O. Proc. Third International Workshop on Robot Motion and Control, RoMoCo'02, Bukowy, Poland, November 2002, pp. 137-139. "Towards A Human-Centered Intrinsically-Safe Robotic Manipulator" Zinn, M., Khatib, O., Roth, B., Salisbury, J.K. Second IARP – IEEE/RAS Joint Workshop on Technical Challenges for Dependable Robots in Human Environments, LAS-CNRS, Toulouse, France, October 2002 "Towards A Human-Centered Intrinsically-Safe Robotic Manipulator" Zinn, M., Khatib, O., Roth, B., Salisbury, J.K. Proc. Second IARP - IEEE/RAS Joint Workshop on Technical Challenges for Dependable Robots in Human Environments, Toulouse, France, October 2002 "A New Actuation Approach for Human Friendly Robot Design" Zinn, M., Khatib, O., Roth, B., Salisbury, J.K. Proceedings of International Symposium on Experimental Robotics, Santa Angelo d'Ischia, Italy, July 2002 "A New Actuation Approach for Human Friendly Robot Design" Zinn, M., Khatib, O., Roth, B., Salisbury, J.K. Experimental Robotics VIII, B. Siciliano and Paolo Dario (Eds.) Star, Springer Tracts in Advanced Robotics, 2002, pp. 113-122. "Human-Centered Robotics and Interactive Haptic Simulation." Khatib, O., Brock, O., Chang, K., Ruspini, D., Sentis, L, Viji, S. Robotics Research, The Tenth Symposium, R. A. Jarvis and A. Zelinsky (Eds.) Star, Springer Tracts in Advanced Robotics, 2002, pp. 239-253. "Robots in Human Environments" Khatib, O., Yokoi, K., Brock, O., Chang, K., Casal, A. Archives of Control Sciences, special issue on Recent Developments in Robotics, Part I, vol. 11 (XLVII), no. 3/4, pp. 123-138, 2001. "Robots in Human Environments" Khatib, O. Proc. International Conference on Control, Automation, Robotics, and Vision, ICRACV2000, December 2000, Singapore, pp. 454-457. "Robots in Human Environments" Khatib, O., Yokoi, K., Brock, O., Chang, K., Casal, A. Proc. First Workshop on Robot Motion and Control (RoMoCo'99), Kiekrz, Poland, June 1999, pp. 213-221. "Robots in Human Environment" Khatib, O., Yokoi, K., Brock, O., Chang, K., Casal, A. Proc. Third International Workshop on Robot Motion and Control, RoMoCo'02, Poznan, Poland, 1999, pp. 213-221. "Robots in Human Environments: Basic Autonomous Capabilities" Khatib, O., Yokoi, K., Brock, O., Chang, K., Casal, A. International Journal of Robotics Research, vol. 18, no. 7, 1999, pp. 684-696. "Robots in Human Environment: Basic Autonomous Capabilities" Khatib, O., Yokoi, K., Brock, O., Chang, K., Casal, A. Proc. 1st International Workshop on Humanoid and Human-Friendly Robotics, Tsukuba, Japan, 1998, pp. III-2:1-11. "Design of Macro/Mini Manipulators for Optimal Dynamic Performance" Bowling, A, Khatib, O. Proc. IEEE International Conference on Robotics and Automation, Albuquerque, Volume 1, 20-25 April 1997 Page(s):449 - 454 vol.1 "Reduced Effective Inertia in Macro-/Mini-Manipulator Systems" Khatib, O. Robotics Research 5, Proc. 5th Int. Symposium, H. Miura and S. Arimoto, eds., Cambridge: MIT Press, 1990, pp. 279-284. "Inertial Characteristics and Dextrous Dynamic Coordination of Macro/Micro-Manipulator Systems" Khatib, O. RoManSy 7, CISM-IFToMM Symposium on Theory and Practice of Robots and Manipulators, Cracow, Poland, 1988. Acknowledgments The financial support of NSF grant EIA-9977717 is gratefully acknowledged. Last update: 08 - 2004 by M.Zinn .