Abstract
A two-wheeled robotic wheelchair (TWRW) has a better manoeuvrability than a conventional four-wheeled wheelchair. However, it is not statically stable near the upright posture or a posture desired by the rider, and an active stability controller is required. Stability control becomes more challenging when a TWRW is also required to move in a desired direction. To rely on wheels' motions to achieve both stability and direction control tend to impose a large burden on the wheels' driving motors or other types of actuators in terms of their driving torque and power consumption. Various disturbances in the system also affect the performance of the controller. To solve these problems, this paper presents a stability and direction controller based on the motion of a pendulum-like movable mechanism added to assist the wheels to produce control actions. The dynamic model of the TWRW is established through the Euler-Lagrange formulation in which the disturbances caused by model uncertainties and rider's motion are considered. A robust second-order sliding mode control is then developed for the stability and the direction control of a TWRW. Simulation results are presented to validate the effectiveness of the proposed method.
Highlights
A conventional robotic wheelchair consists of two driving wheels and two passive casters, where the driving wheels move actively for both mobility and stability of the wheelchair, while the passive casters provide a support for the wheelchair’s stability [1]–[3]
In this paper, a novel approach is proposed for stability and direction control of a two-wheeled robotic wheelchair (TWRW)
A pendulum-like movable mechanism is added to the TWRW to assist the driving wheels to achieve the both control objectives
Summary
A conventional robotic wheelchair consists of two driving wheels and two passive casters, where the driving wheels move actively for both mobility and stability of the wheelchair, while the passive casters provide a support for the wheelchair’s stability [1]–[3]. For a nonlinear system like a TWRW with different driving mechanisms, the common nonlinear controller Computed Torque Control can be applied for stability and direction control [15] In this controller, the control inputs (torques) are derived from nonlinear state feedback and closed loop tracking errors through the system dynamic model. Pendulum-like movable mechanism is added to the TWRW to assist the wheels for stability and direction control. Applying Equation (1), the dynamic model of TWRW in the conventional method can be derived and presented as [24]. Considering the added pendulum like movable mechanism, the overall kinetic and potential energy of TWRW is obtained as. To assist the wheels for stability and direction control, the input torque of added movable mechanism is defined as τp = β(τr + τl ).
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