Simulation and control of an active stewart platform for docking and berthing of space vehicles
- Paper number
IAC-06-C1.3.01
- Author
Dr. Michael Hardt, SENER Ingeneria y Sistemas, S.A., Spain
- Coauthor
Mr. Jose Ramón Villa, SENER Ingeneria y Sistemas, S.A., Spain
- Coauthor
Mr. Peter Urmston, European Space Agency (ESA)/ESTEC, The Netherlands
- Coauthor
Mr. Oscar Gracia, European Space Agency (ESA)/ESTEC, The Netherlands
- Coauthor
Mr. Daniel Cocho, SENER Ingeneria y Sistemas, S.A., Spain
- Year
2006
- Abstract
The International Berthing and Docking Mechanism (IBDM) currently being developed by the European Space Agency (ESTEC) in concurrence with SENER Ingeniería y Sistemas S.A. under Contracts 19427/05/NL/GM and 19607/06/NL/GM, consists of an actively controlled Stewart platform mounted upon a spacecraft for the purpose of rendezvousing with other spacecrafts. An androgynous counterpart in passive mode is similarly mounted on the opposite vehicle. The active platform controls the contact transition forces occurring at collision and proceeds to dampen these forces until a zero relative velocity has been achieved. The 3-3 Stewart platform configuration assembly consisting of six parallel linear actuators has a high payload-to-weight ratio and can effectively dampen the contact forces resulting from a wide range of different spacecraft configurations. The control algorithm presented here for accomplishing this purpose is a 6-DOF impedance controller based upon a quaternion attitude representation. The pseudoinverse of the force Jacobian translates the required control forces to commanded forces at the six linear actuators. An impedance control approach permits redefining the contact dynamics to simulate a nonlinear spring-damper with adaptable characteristics. Soft damping is defined at initial contact while the spring and damping forces are significantly increased as the platform approaches the limits of its manoeuvrability workspace. Alternative hybrid control approaches which consider explicitly the contact surface are unsuitable due to the surface complexity and configuration uncertainty. The measurement information received by the controller are the 6-DOF contact force measurements plus the extension range measurements of each of the supporting linear actuators. The problem of robustly and quickly estimating the entire platform configuration from the actuator range measurements is addressed here. This corresponds to the forward kinematics problem for which closed-form solutions are generally not available. A dynamic filtering algorithm is used in which the state prediction step is based upon a Newton iteration over the kinematic constraints including the velocities. The entire dynamic model and controller has been validated in a Matlab / Simulink environment. The control strategy on the microcontroller is subsequently validated in real-time in closed-loop together with the Simulink plant model running with dSpace. The success of this rapid prototyping development environment is dependent upon a highly efficient implementation in Simulink of the Stewart platform multibody dynamics including the contact dynamics. The modelling techniques are described which are based upon a distributed representation of the dynamics combined using a penalty-based approach. Simulation and performance results are presented.
- Abstract document
- Manuscript document
IAC-06-C1.3.01.pdf (🔒 authorized access only).
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