Passive teleoperation of hydraulic systems

Hydraulic machines have been widely used in a variety of high power applications. Typically these machines are operated by an operator. In past research the interaction safety between the operator and the machine was seldom investigated. This dissertation addresses the interaction stability issue by exploiting the safety guarantees offered by passive systems. The hydraulic machine considered in this dissertation is a 2-DOF hydraulic backhoe teleoperated by a 2-DOF, electro-mechanical, force-feedback capable joystick (master). The impediment to applying the concept of passivity to hydraulics is that hydraulic systems, in general, do not behave like passive systems. An algorithm was presented which ensured that single-stage proportional valves, a key element in any hydraulic system, behave like passive devices. Using such a passive valve, a passive 2-DOF hydraulic backhoe (slave) is constructed by cascade interconnection of passive subsystems. Given a passive master and a passive slave, this dissertation proposes a systematic approach to design teleoperation control systems (based on bondgraphs) which ensure that the master and slave satisfy certain coordination and passivity requirements. Bondgraphs are used as they offer benefit of representing power flow in a dynamic system. Bondgraph based control is designed in three stages. In the first stage, a coordination control law is determined which ensures that the master and slave systems remain coordinated when teleoperated. The control law is determined based on system inversion ideas. By representing the coordination control law using bondgraphs it is possible to determine the power necessary to maintain coordination of the master and slave systems. In the second stage, desired dynamics of the coordinated teleoperated system are chosen based on the application. The desired dynamics (desired locked system) should be passive with respect to a power supply rate. In the third stage, a passive control law is determined so as to ensure that the coordinated system behaves dynamically like the desired locked system hence in turn ensuring that the teleoperated system is passive with respect to a power supply rate. The proposed passive control ensures that the joystick teleoperated backhoe (1) is coordinated thus guaranteeing performance, (2) is passive with respect to an appropriate power input thus guaranteeing interaction safety and (3) can behave like 4th order system or a 2nd order system based on the choice of desired dynamics. The proposed passive control algorithms is experimentally verified and the benefits achieved by dynamically tuning the passive teleoperated system are documented. It is also shown that the proposed control design method can be extended to ensure passive teleoperation of arbitrary order passive master and passive slave systems.