Research Papers

Handling Actuator Saturation as Underactuation: Case Study With Acroboter Service Robot

[+] Author and Article Information
Ambrus Zelei

MTA-BME Research Group on Dynamics
of Machines and Vehicles,
Budapest H-1111, Hungary
e-mail: zelei@mm.bme.hu

László Bencsik

MTA-BME Research Group on Dynamics
of Machines and Vehicles,
Budapest H-1111, Hungary
e-mail: bencsik@mm.bme.hu

Gábor Stépán

Department of Applied Mechanics,
Budapest University of Technology
and Economics,
Budapest H-1111, Hungary
e-mail: stepan@mm.bme.hu

1Corresponding author.

Contributed by the Design Engineering Division of ASME for publication in the JOURNAL OF COMPUTATIONAL AND NONLINEAR DYNAMICS. Manuscript received May 13, 2016; final manuscript received September 14, 2016; published online December 5, 2016. Assoc. Editor: Ahmet S. Yigit.

J. Comput. Nonlinear Dynam 12(3), 031011 (Dec 05, 2016) (5 pages) Paper No: CND-16-1237; doi: 10.1115/1.4034868 History: Received May 13, 2016; Revised September 14, 2016

Model-based control methods such as inverse dynamics control and computed torque control encounter difficulties if actuator saturation occurs. However, saturation is a common phenomenon in robotics leading to significant nonlinearity in system behavior. In this study, the saturation of the actuator torques is considered as a temporary reduction of the number of independent control inputs. The reduction of the number of actuators leads to an underactuated control problem which typically involves the handling of differential algebraic equation systems. The saturated system may become especially complex when intricate combinations of the actuator saturations appear. A servoconstraint-based inverse dynamics control method for underactuated multibody systems is applied for the treatment of actuator torque saturation. In case of human-friendly robots, the problem of saturation cannot be avoided on the level of trajectory planning because unexpected human perturbations may take place, which result in such abrupt changes in the desired trajectory that lead to saturation at some actuators. A case study for the service robot Acroboter shows the applicability of the proposed approach.

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Fig. 1

Actuator saturation: nonlinear connection between commanded and real control input

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Fig. 2

Planar mechanical model (left) and free-body diagrams (right) of the Acroboter platform

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Fig. 3

Numerical results for specific cases (I), (II), and (III): path

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Fig. 4

Numerical results for specific cases (I), (II), and (III): servoconstraint violations

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Fig. 5

Numerical results for specific cases (I), (II), and (III): control inputs




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