A mobile wheeled robotic device is considered. The device has been developed in MSU Institute of mechanics for the purpose of transporting and orienting an electron accelerator for beam therapy. The device is composed of a horizontal platform with four wheels and a manipulator. Each wheel is mounted in a fork capable of rotating around its vertical axis relative to the platform and can at the same time rotate around its horizontal axis in a regular way. Each wheel is a driving and steering wheel at the same time; it is activated by two independent motors. The manipulator has four degrees of freedom relative to the platform. The platform with steering wheels can move without wheel slipping only in case when the fork orientation and wheel angular velocities comply with certain conditions. These conditions are in the first place obligatory for the program values of fork rotation angles and wheel angular velocities that must be computed for automatic control of the platform motion or for its manual control by an operator. The report presents equations of platform motion that involve non-holonomic constraints. A semi-natural modeling system for the process of motion control of this device has been developed. The system includes a human operator, who controls the automatics of the device by means of a 3-DOF joystick. The control process involves setting a desired velocity of the center point of the platform and its angular velocity. The controlling computer calculates the program values of fork rotation angles and wheel speeds. Target calculated values are implemented by means of servo systems. The integration of the motion equations of the device is done during supervisor-controlled (with a human operator) motion of the device. A virtual platform and its manipulator are shown on a PC monitor, implementing visualization of this robotic device. Thus the operator can visually evaluate the accuracy of performing the desired motion. Control of the manipulator is also done in a supervisor-based mode.
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