| 1. |
- Björkenstam, Staffan C, 1981, et al.
(författare)
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A framework for motion planning of digital humans using discrete mechanics and optimal control
- 2017
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Ingår i: Proceedings of the 5th International Digital Human Modeling Symposium. - : Federal Institute for Occupational Safety and Health. ; , s. 64-71
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Konferensbidrag (refereegranskat)abstract
- In this paper we present a framework for digital human modelling using discrete mechanics and optimal control. Discrete mechanics is particularly well suited for modelling the dynamics of constrained mechanical systems, which is almost always the case when considering complex human models interacting with the environment. We demonstrate that, by using recently developed recursive dynamics algorithms, we are able to efficiently use discrete mechanics in direct optimal control methods to plan for complex motions. Besides a proper mechanical model, an appropriate objective function is paramount to achieve realistic motions as a solution to an optimal control problem. Hence, several different objective functions, such as for example minimum time or minimum applied torque over the joints, are compared, and the resulting motions are analyzed and evaluated. To further improve the model, we include basic muscular models for the muscles of the shoulder, arm and wrist, and examine how this affects the motions.
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| 2. |
- Björkenstam, Staffan C, 1981, et al.
(författare)
-
Inverse Dynamics for Discrete Geometric Mechanics of Multibody Systems with Application to Direct Optimal Control
- 2018
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Ingår i: Journal of Computational and Nonlinear Dynamics. - : ASME International. - 1555-1423 .- 1555-1415. ; 13:10
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present efficient algorithms for computation of the residual of the constrained discrete Euler-Lagrange (DEL) equations of motion for tree structured, rigid multibody systems. In particular, we present new recursive formulas for computing partial derivatives of the kinetic energy. This enables us to solve the inverse dynamics problem of the discrete system with linear computational complexity. The resulting algorithms are easy to implement and can naturally be applied to a very broad class of multibody systems by imposing constraints on the coordinates by means of Lagrange multipliers. A comparison is made with an existing software package, which shows a drastic improvement in computational efficiency. Our interest in inverse dynamics is primarily to apply direct transcription optimal control methods to multibody systems. As an example application, we present a digital human motion planning problem, which we solve using the proposed method. Furthermore, we present detailed descriptions of several common joints, in particular singularity-free models of the spherical joint and the rigid body joint, using the Lie groups of unit quaternions and unit dual quaternions, respectively.
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| 3. |
- Roller, Michael, et al.
(författare)
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Optimal control of a biomechanical multibody model for the dynamic simulation of working tasks
- 2017
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Ingår i: ECCOMAS Thematic Conference on Multibody Dynamics.
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Konferensbidrag (refereegranskat)abstract
- In this contribution a framework for digital human modelling using optimal control of a biomechanical multibodymodel is presented. The skeleton of the human body is represented as a multibody system, actuated by simplifiedHill muscles. Motions of the digital human model are generated by optimal control with different objective functions.The optimal control problem is discretized by the DMOCC approach, using a variational integrator for the constrainedequations of motion. With this approach, the task of "lifting of a box from a lower to a higher position" is simulatedas a test example. Both arms are modeled with seven degrees of freedom each, actuated by 29 muscles. In the optimalcontrol problem an arbitrary grasp position is included, as well as frictional contact between the box and the hand.
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