Design and Control of a Force-reflecting Haptic Interface for Teleoperational Grasping

In this paper the design of a multi-finger force-reflecting haptic interface device for teleoperational grasping is introduced. The haptic interface or “master” controller device is worn on the human operator’s hand and measured human finger positions are used to control the finger positions of a remote grasping manipulator or “slave” device. The slave may be a physical robotic grasping manipulator, or a computer-generated representation of a human hand such as used in virtual reality applications. The forces measured by the robotic slave, or calculated for the virtual slave, are presented to the operator’s fingertips through the master providing a means for improved human sensation of presence and better control of grasping tasks in the slave environments. Design parameters and performance measures for haptic interfaces for teleoperation are discussed. One key performance issue involves the high-speed display of forces during initial contact, especially when interacting with rigid surfaces. The present design reduces slave controller computational requirements and overcomes actuator response time constraints thus addressing the problematic issue of the display of rigid bodies. The design presented utilizes a planar four-bar linkage for each finger, to represent each finger bend motion as a single degree of freedom, and to provide a finger bend resistance force that is substantially perpendicular to the distal finger pad throughout the full 180 degrees of finger bend motion represented. The finger linkage design, in combination with a remote position measurement and force display assembly, provides a very light weight and low inertia system with a large workspace. The concept of a replicated finger is introduced which, in combination with a decoupled actuator and feed forward control, provides improved performance in transparent free motion, and rapid, stable touch sensation of initial contact with rigid surfaces. A distributed computation architecture with a PC based haptic interface controller and associated control algorithms are also discussed.