Stability analysis and synthesis of statically balanced walking for quadruped robots

by Hardarson, Freyr

Abstract (Summary)
Walking robots have a potential to traverse certain types of terrain in a more efficient and stable manner than more conventional robots, using wheels or tracks. The property of walking robots that the contact with the ground is discontinuous gives them the ability to select footholds such that obstacles or holes are avoided. Other advantageous properties of walking robots are that they cause less damage to the terrain, active suspension is an intrinsic part of their structure, and they are omnidirectional, which gives them an advantage in maneuvering through cluttered and tight environments. The control of walking robots requires that the issue of stability against tipping over is treated in a more specific fashion than for wheeled robots, as there are discrete changes in the support of the robot when the legs are lifted or placed. The stability of the robot is dependent on how the legs are positioned relative to the body and on the sequence and timing in which the legs are lifted and placed. In order to reduce the risk of the robot losing stability while walking, a measure for the stability of the robot is typically used in the gait and motion planning, in order to avoid, or detect, that the robot could become unstable. The main contribution of the thesis is in the analysis of the stability of statically balanced quadrupedal gaits and how statically balanced walking can be achieved. The center of pressure, i.e. the point where the resultant of the ground reaction forces at the feet acts, is used to develop a stability measure, which is then used in the planning of the body motion. The stability measure is used to set appropriate bounds on the motion of the robot, to account for potentially destabilizing forces or moments. The motion of the robot is planned by determining the supporting force for each leg, which in turn will determine how the robot should shift its weight in order to remain statically balanced. The approach proposed in this thesis, therefore, solves simultaneously the problem of determining a statically balanced motion trajectory for the body, as well as, the distribution of forces to the feet, to compensate for the weight of the robot. A description of the implementation and experimental results are provided, using the quadruped robot WARP1. The experimental results demonstrate the walking capability of the robot, and its ability to handle inclined surfaces.
Bibliographical Information:


School:Kungliga Tekniska högskolan

School Location:Sweden

Source Type:Doctoral Dissertation

Keywords:legged locomotion; walking robots; mobile robots; stability measure; center of pressure; force distribution; kinematics; dynamics; gaits


Date of Publication:01/01/2002

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