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The Merits of Passive Compliant Joints in Legged Locomotion: Fast Learning, Superior Energy Efficiency and Versatile Sensing in a Quadruped Robot

Matej Hoffmann1,2, Jakub Simanek3   

  1. 1. iCub Facility, Istituto Italiano di Tecnologia, Genova 16123, Italy
    2. Artificial Intelligence Laboratory, Department of Informatics, University of Zurich, Zurich 8050, Switzerland
    3. Department of Measurement, Faculty of Electrical Engineering, Czech Technical University in Prague, Prague 166 27, Czech Republic
  • 收稿日期:2016-06-01 修回日期:2016-12-01 出版日期:2017-01-10 发布日期:2017-01-10
  • 通讯作者: Matej Hoffmann E-mail:matej.hoffmann@iit.it
  • 作者简介:Matej Hoffmann1,2, Jakub Simanek3

The Merits of Passive Compliant Joints in Legged Locomotion: Fast Learning, Superior Energy Efficiency and Versatile Sensing in a Quadruped Robot

Matej Hoffmann1,2, Jakub Simanek3   

  1. 1. iCub Facility, Istituto Italiano di Tecnologia, Genova 16123, Italy
    2. Artificial Intelligence Laboratory, Department of Informatics, University of Zurich, Zurich 8050, Switzerland
    3. Department of Measurement, Faculty of Electrical Engineering, Czech Technical University in Prague, Prague 166 27, Czech Republic
  • Received:2016-06-01 Revised:2016-12-01 Online:2017-01-10 Published:2017-01-10
  • Contact: Matej Hoffmann E-mail:matej.hoffmann@iit.it
  • About author:Matej Hoffmann1,2, Jakub Simanek3

摘要: A quadruped robot with four actuated hip joints and four passive highly compliant knee joints is used to demonstrate the potential of underactuation from two standpoints: learning locomotion and perception. First, we show that: (i) forward loco-motion on flat ground can be learned rapidly (minutes of optimization time); (ii) a simulation study reveals that a passive knee configuration leads to faster, more stable, and more efficient locomotion than a variant of the robot with active knees; (iii) the robot is capable of learning turning gaits as well. The merits of underactuation (reduced controller complexity, weight, and energy consumption) are thus preserved without compromising the versatility of behavior. Direct optimization on the reduced space of active joints leads to effective learning of model-free controllers. Second, we find passive compliant joints with po-tentiometers to effectively complement inertial sensors in a velocity estimation task and to outperform inertial and pressure sensors in a terrain detection task. Encoders on passive compliant joints thus constitute a cheap and compact but powerful sensing device that gauges joint position and force/torque, and — if mounted more distally than the last actuated joints in a legged robot — it delivers valuable information about the interaction of the robot with the ground.

关键词: compliant joints, legged robots, underactuated robots, learning locomotion, haptic terrain classification, force and tactile sensing

Abstract: A quadruped robot with four actuated hip joints and four passive highly compliant knee joints is used to demonstrate the potential of underactuation from two standpoints: learning locomotion and perception. First, we show that: (i) forward loco-motion on flat ground can be learned rapidly (minutes of optimization time); (ii) a simulation study reveals that a passive knee configuration leads to faster, more stable, and more efficient locomotion than a variant of the robot with active knees; (iii) the robot is capable of learning turning gaits as well. The merits of underactuation (reduced controller complexity, weight, and energy consumption) are thus preserved without compromising the versatility of behavior. Direct optimization on the reduced space of active joints leads to effective learning of model-free controllers. Second, we find passive compliant joints with po-tentiometers to effectively complement inertial sensors in a velocity estimation task and to outperform inertial and pressure sensors in a terrain detection task. Encoders on passive compliant joints thus constitute a cheap and compact but powerful sensing device that gauges joint position and force/torque, and — if mounted more distally than the last actuated joints in a legged robot — it delivers valuable information about the interaction of the robot with the ground.

Key words: underactuated robots, legged robots, compliant joints, force and tactile sensing, haptic terrain classification, learning locomotion