Disturbance observer based adaptive robust control of bilateral teleoperation systems under time delays

Bilateral teleoperation technology has caused wide attentions due to its applications in various remote operation systems. However, to really realize teleoperation requirements, there still exist some challenging control issues: a) the communication delay between master and slave manipulators may lead to system instability or performance decreasing; b) in some applications, the sensors are not easily set up to measure the environmental external force; c) various manipulator modeling uncertainties need to be considered carefully in order to achieve good control performance. In this paper, the disturbance observer is designed based on the slave manipulator dynamics to observe the unmeasurable environmental force. When the environmental force is modeled as a general linear regression form, its unknown parameters can be estimated online by the least square adaptation law. A novel communication structure is proposed where only the master trajectory is transmitted to the slave side, and the transmission signal from the slave to the master is replaced by those estimated environmental parameters. This design can avoid solving the complicated passivity problem under communication delays and having the trade-off between the system stability and control performance, and thus has the potential of achieving the excellent control performance and the guaranteed robust stability simultaneously under arbitrary time delays. The sliding mode control and the force compensation of disturbance observer are integrated subsequently to deal with various manipulator modeling uncertainties, so that the excellent synchronization performance can be achieved. The simulation on single DOF manipulators is carried out and the results show the effectiveness of the proposed control algorithm.