Slip Control for a Wheelchair

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Tech ID: 14-060 Patents: US Patent Publication NO. 2016/0250930 Description: Electric Ground Vehicles (EGVs) such as electric automobiles, golf carts, and electric powered wheelchairs are increasing in use since they are energy efficient, environmentally friendly, and reduce oil dependency. However, when traveling across slippery surfaces, EGVs become susceptible to lateral slip. Our developed novel technology mitigates slip using feedback control. The essential components are the following: a reference model based on mass-damper system, a trajectory tracking controller for each wheel, and a maximum tractive force estimator. The reference model generates the desired acceleration, velocity, and position of the vehicle based on user inputs, for example, the position of the steering wheel and throttle or the commands from a joystick displacement. The user inputs are mapped to force and torque inputs to the reference model. The commanded trajectory is mapped to the desired wheel trajectories using the controller. The maximum tractive force estimator determines the minimum of the maximum tractive forces that can be applied to each wheel by the surface the wheel is traversing. An associated lower bound on the mass of the reference model is used to determine when one or more of the wheels has been required to follow a trajectory that requires more than the estimate of the min-max tractive force, such that it can be inferred that slip has occurred or may soon occur. Subsequently, the value of the mass parameter in the reference model is reduced to help ensure that future slip will not occur.