Abstract
This work addresses the fundamental need for continued improvement in human-machine interfaces. Of particular interest is the need for force feedback to the operator to provide the ability to interact physically with the synthetic environment. In order to allow for natural contact and control over the position, orientation, and motions of objects within the computer-generated environment, a new haptic interface device is under development that applies arbitrary forces to the digits of the human hand. This work describes the design and development of the hardware prototype of a robot manipulator intended to provide a force interface between a human operator and a computer-based dynamic model. The basis of the new device is in the coupling of the robot and human through the interaction of an electric current and a magnetic field. The device positions a strong magnetic field near wire coils mounted on the fingers, and forces are generated by electrical current moving within the magnetic field. The device consists of a mechanical exoskelton manipulator that maintains a constant position relative to the finger digits by means of an optical feedback tracking system. The kinematic linkage design of the exoskelton haptic interface device has been developed to maintain constant relative position of magnetic fields around the coils as each finger flexes through its range of motion. The relative position error is measured using a light source attached to the finger and a photo sensor mounted on the manipulator. The position of the exoskelton is controlled by correcting for the error between the center of the coil and the center of the magnetic yoke. The absolute position of the fingers is determined using the manipulator joint angles and the forward kinematic equations. The finger position is used as an input to the computer model, which generates appropriate interaction forces based on the inputs and the simulation parameters. The current prototype tracks one digit of the hand using two degrees of freedom, and can apply two independent virtual forces along the finger. The robot exoskelton is controlled by a digital computer, which combines sensor measurements with model simulation results to generate both trajectory and force commands. In this paper, the design and analysis of the mechanical exoskelton device and the development of a closed loop control algorithm to track the hand motion are discussed. A dynamic model of ISU exoskelton is developed and experimental results for the system are presented using some typical virtual environments, including interaction with a “hard” surface, a simple mass-spring-damper “yo-yo”, and interaction with a compliant “ball”. These results show that the electro-magnetic interface generates adequate force levels for perception of virtual objects by the exoskelton.
