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Frontiers of Mechanical Engineering

Front Mech Eng    2012, Vol. 7 Issue (2) : 219-230
A total torque index for dynamic performance evaluation of a radial symmetric six-legged robot
Kejia LI1(), Xilun DING1, Marco CECCARELL2
1. Robotics Institute, School of Mechanical Engineering and Automation, Beijing University of Aeronautics and Astronautics, Beijing 100191, China; 2. Laboratory of Robotics and Mechatronics, University of Cassino, 03043 Cassino, Italy
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This article focuses on the dynamic index and performance of a radial symmetric six-legged robot. At first the structure of the robot is described in brief and its inverse kinematics is presented. Then the dynamic model is formulated as based on the Lagrange equations. A novel index of total torque is proposed by considering the posture of the supporting legs. The new index can be used to optimize the leg’s structure and operation for consuming minimum power and avoiding unstable postures of the robot. A characterization of the proposed six-legged robot is obtained by a parametric analysis of robot performance through simulation using the presented dynamic model. Main influences are outlined as well as the usefulness of the proposed performance index.

Keywords six-legged robots      dynamic modeling      performance index     
Corresponding Authors: LI Kejia,   
Issue Date: 05 June 2012
 Cite this article:   
Kejia LI,Xilun DING,Marco CECCARELL. A total torque index for dynamic performance evaluation of a radial symmetric six-legged robot[J]. Front Mech Eng, 2012, 7(2): 219-230.
Fig.1  The radial symmetric six-legged robot
Fig.2  Different gaits of the radial symmetric six-legged robot.
(a) Insect gait; (b) mammal gait; (c) mixed gait
Fig.3  Two groups of possible solutions for a leg
Fig.4  The posture of supporting leg 1.
(a) Stable posture; (b) unstable posture
Tab.1  Six examples of leg design
Fig.5  The joint torques during motion of leg 1.
(a) The torque of hip pitching joint; (b) the torque of knee joint
Fig.6  The value of index and for six design examples.
(a) Index ; (b) index
Case 1Case 2Case 3Case 4Case 5
Tab.2  Different lengths of and
Case 1Case 2Case 3Case 4Case 5
Tab.3  Different groups of m and m /kg
10% change of L2 and L310% change of m2 and m310% change of step length10% change of joint angles
τ12 change20%0.43%2.2%4.3%
τ13 change40%Neglect10%Neglect
Tab.4  The effect of different parameters to the joint torques of supporting legs
Fig.7  Results of simulation for different length of leg.
(a) Torque of hip pitching joint; (b) torque of knee joint
Fig.8  Results of simulation for different mass distribution of leg.
(a) Torque of hip pitching joint; (b) torque of knee joint
Fig.9  Results of simulation for different step length.
(a) Torque of hip pitching joint; (b) torque of knee joint
Fig.10  Results of simulation for different posture of supporting legs.
(a) Torque of hip pitching joint; (b) torque of knee joint
Fig.11  The robot walks in four different poses.
(a) Pose 1; (b) pose 2; (c) pose3; (d) pose 4
Smax/mTtot of one stepTtot of per meterTime spent per meter/s
Pose 10.2693.4359.237.7
Pose 20.21270.6333.029.4
Pose 30.1541.727813.3
Pose 4000
Tab.5  Results form numerical simulation for total torque and time spent in four different poses
Fig.12  The robot walks by four different step lengths.
(a) ; (b) ; (c) ; (d)
Step length/mTtot of one stepTtot of per meterTime spent per meter
Tab.6  Results form numerical simulation for total torque and time spent in the same pose
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