Design, development, control and performance investigations of a sitting/ lying type lower limb rehabilitation robot

Abstract

This thesis proposes a new lower limb rehabilitation robot which can assist the therapist to conduct various rehabilitation treatments in sitting/lying posture. It is a stationary system designed for the patients in bedridden state (early phase of recovery). The proposed lower limb rehabilitation robot consists of a vertical planar parallel manipulator along with a serial planar passive orthosis (exoskeleton/supporting system) to generate physiological motion in the sagittal plane. The proposed rehabilitation robot is named as “ANKUR-LL” (A Neurorehabilitation Kinematic Utility for Rehabilitation of Lower Limb).In the early stage of recovery, the patients have no control or sometimes slight control over their limb movements. At this stage limbs need to be given continuous passive motion treatment, to trigger the motor nerves for faster recovery. This needs a system of good range of motion capabilities to provide the required range of operating space and speeds for the rehabilitation therapies. The difficulty observed with the available systems is the high moving inertial parts, high infrastructure cost (expensive), safety brakes in rotary joints, etc. The main limitation or issue experienced by the commercial manipulators is, the dynamic behavior dominates the motion behavior at high speed operations. To deal with this kind of circumstances a new rehabilitation robot is proposed and analyzed for its motion capability in this thesis.Proposed rehabilitation robot’s kinematic arrangement along with its forward and inverse solutions are presented and discussed. The basis of selection of proposed configuration is discussed. The proposed system isrealized in virtual environment and detail design is prepared. The detail design is validated for the strength of the critical joints and fixtures. Furthermore, the system dynamics is derived along with an interactive graphical simulator to understand the behavior of the over-constrained manipulator-orthosis system.Further, to fulfil the motion requirement which can handle variability in payload and unknown model parameters, a robust motion control scheme is proposed. The effectiveness and usefulness of the proposed manipulator is shown with the implementation of the motion controller through the computer based numerical simulations using a clinical gait motion pattern. The controller robustness is further analyzed at different working conditions. In comparison to the conventional controllers, the proposed control scheme possesses few advantages namely better robustness, less chattering, high precision and can work in the presence of parameter uncertainties. Afterwards, the proposed motion control scheme is also validated on an in-house fabricated prototype through motion control experiments. From the demonstration, the proposed manipulator has certain advantages over existing stationary lower limb rehabilitation trainers namely, simple design, larger workspace, higher stiffness, modular design and low cost.