A Study on the Control of a Manipulator Arm Using Flexible Hydraulic Actuators (FHA).

Abstract

In extreme environments, e. g., in space or in a vacuum pan, there are increasing numbers of cases where it is necessary to move and manipulate objects quickly with a large moment of inertia. Hence, it would be desirable to develop more powerful and lightweight actuators. At present, electric motors are used for space manipulators ; however, their capability is not sufficient in view of output torque-inertia ratio. An actuator proposed and developed here for hydraulic control in space is named a flexible hydraulic actuator (FHA) . This actuator consists of an oil-proof rubber core tube and tenacious string cords (aramid fiber) braided to cover it. During an increase in inner pressure, the FHA contracts in an axial direction about 30% of the full effective length, and its output force to axial direction is 1500 N max (3 MPa of inner pressure) whene the weight is 0.3kgf. The main features of the FHA are that there is no need for lubrication and that it is susceptible to leakage. The precise mathematical model of the FHA in static and dynamic behavior is derived and compared with experiments. It is also ascertained that the FHA responds sufficiently quickly. In addition, the dynamics of a single-armed manipulator model composed by the two FHAs are investigated experimentally. An angle position control of the system, including minor control of the internal pressure defference between the two FHAs, is discussed and is well-established. Moreover, we try to eliminate the effects of the system parameter change and disturbance employing the disturbance estimation observer. The results with the robust control are in good agreement with the response of the desired system model.