Oscillation Damping, Collision Detection and Reaction for a Multi-Elastic-Link Robot Arm


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Oscillation Damping, Collision Detection and Reaction for a Multi-Elastic-Link Robot Arm
Malzahn, Jörn
Bertram, Torsten
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TU Dortmund, Lehrstuhl für Regelungssystemtechnik
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In first place, elasticity in the links of robot arms and structurally comparable mechatronic systems such as construction machines, fire rescue turntable ladders, cherry pickers or automobile concrete pumps is a highly undesired effect. It prolongs settling times and deteriorates the positioning accuracy. Therefore substantial mechanical design efforts are commonly taken to avoid link elasticity in these mechanisms. The presented work approaches from the contrary perspective and intentionally introduces intrinsic structural compliance in the links of an experimental robot platform. The motivation is to exploit the added intrinsic link compliance to reduce the overall robot weight, to cut costs, to add positioning tolerance as well as to add contact force sensing capabilities to the system. The video shows, how robust and rapid settling as well as disturbance rejection can still be accomplished by devising control algorithms [1,2] based on per link strain measurements. In addition, the derivation and identification of mathematical models that accurately describe the load and joint configuration dependent static end effector deflections allows -- through software -- for the compensation of the inaccuracy of the mechanism [3]. The feasibility of time critical and precise end effector positioning for an elastic link arm has been exemplified with ball catching experiments before [4] (http://www.youtube.com/watch?v=P4 i k...). With the mechanical imperfections compensated by the developed inner loop control software, the video demonstrates, how the intrinsic link compliance can be exploited to actively shape the apparent arm compliance, to sensitively sense contact forces, to safely react to accidental collisions as well as to enable intentional physical human machine interaction. The control scheme behind these features uses an identified model of the residual damped arm dynamics [5]. This model is way simpler to derive and identify than a holistic arm model including the oscillatory and actually infinite dimensional arm dynamics. An identified linear mapping from the strain readings acquired close to the hubs on each passively compliant link and the motor torques turns each link into load side joint torque sensors. This way the video shows that collision detection and reaction techniques originally developed by other authors for rigid or elastic joint robots can be readily adopted for the use with elastic link robots [6]. The provided results imply that link elasticity is not necessarily just a problem. In contrast, the devised control concepts are able to compensate for the machine imperfections reveal promising new perspectives. Time-line: 00:12 Introduction to the experimental setup 00:36 Exp I: Oscillation Damping: step motion 00:48 Exp II: Oscillation Damping: harmonic disturbance 02:10 Exp III: Collision detection and reaction: blunt impacts with a balloon 02:37 Exp IV: Collision detection and reaction: sharp impacts with a balloon 03:02 Exp V: Collision detection and reaction: sharp impacts with a Christmas ball 03:23 Exp VI: Collision detection and reaction: sharp impacts with a human arm 03:47 Exp VII: Interaction in zero gravity mode For more information on the project please visit:http://www.rst.e-technik.tu-dortmund....
oscillation damping
collision detection
flexible robot
elastic link
flexible link
force control
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