Active Vibration Control of Flexible Robots Using Virtual Spring-damper Systems

When using robots for heavy loads and huge operating ranges, elastic deformations of the links have to be taken into account during modeling and controller design. Whereas for conventional rigid multilink industrial robots modeling can schematically be done by standard techniques, it is a massive problem to obtain an accurate analytic model for multilink flexible robots. But an accurate analytic model is essential for most modern controller design techniques, and modeling errors can lead to instability of the controlled system due to spillover since the eigenvalues of the system are only slightly damped. A new approach to active damping control for flexible robots is presented in this paper where the actuators act like virtual spring-damper-systems. As the spring-damper-element is a passive energy dissipative device, it will never destabilize the system and thus the control concept will be very insensitive to modeling errors. Basically, the two parameters, spring stiffness and damping constant of this system, are arbitrary and model independent. To satisfy performance requirements they are adjusted using knowledge of the system model. The more it is known about the system model, the better these parameters may be adjusted. The new input of the controlled system is a virtual variation of the spring base. The paper illustrates this technique with the help of a simple and easy to model one link flexible robot which is also available as a real laboratory testbed.