J.E. Colgate

Robust control of dynamically interacting systems

Dynamic interaction with the environment is fundamental to the process of manipulation. This paper describes an approach to the design of ‘interaction controllers’ and contrasts this with an approa...

Issues in the haptic display of tool use

Our group is interested in using haptic display for training tool use. Applications include training doctors to use tools during surgery, and training astronauts to use tools during EVA. This paper describes some of the challenges of creating realistic haptic perceptions of tool use. Many of these challenges stem from the importance of unilateral constraints during tool use. Unilateral constraints occur whenever rigid bodies collide, resisting the interpenetration of the bodies, but not holding the bodies together. To identify unilateral constraints, a tool/environment simulation must perform collision detection. To respond properly to a collision, the simulation must estimate the forces that ensue, and integrate the equations of motion. All of these computations must occur in real time, and the simulation as a whole must be stable (to ensure the users safety). Approaches to these problems are described.

Mechanics and control of swimming: a review

The bodies and brains of fish have evolved to achieve control objectives beyond the capabilities of current underwater vehicles. One route toward designing underwater vehicles with similar capabilities is to better understand fish physiological design and control strategies. This paper has two objectives: 1) to review clues to artificial swimmer design taken from fish physiology and 2) to formalize and review the control problems that must be solved by a robot fish. The goal is to exploit fish locomotion principles to address the truly difficult control challenges of station keeping under large perturbations, rapid maneuvering, power-efficient endurance swimming, and trajectory planning and tracking. The design and control of biomimetic swimming machines meeting these challenges will require state-of-the-art engineering and biology.

T-PaD: Tactile Pattern Display through Variable Friction Reduction

In this paper we discuss the theory, design and construction of a haptic display for creating texture sensations through variations in surface friction. Ultrasonic frequency, low amplitude vibrations between two flat plates have been shown to create a squeeze film of air between the two plate surfaces thereby reducing the friction (Salbu, 1964; Weisendanger, 2001). We show that a reduction of friction will also occur between a human finger and a vibrating plate. Thus, a vibrating plate can serve as a haptic interface. The amplitude of vibration can also be correlated to the amount of friction reduction between the plate and the finger. Varying the surface friction between the finger and the haptic interface is a way of indirectly controlling shear forces on the finger during active exploration. Using finger position and velocity feedback on the display allows for the creation of spatial texture sensations

Design of components for programmable passive impedance

A form of impedance control is proposed which addresses the issue of stability and provides for the programming of robots for interactive tasks. Passive mechanical elements, specifically springs and dampers, are incorporated into the drive of a robot. The impedance of the robot is programmable because the stiffness and damping coefficients of these mechanical elements are themselves programmable. The design of these elements and their use are outlined. Prototype springs and dampers have been fabricated, and their performance in theory and in practice is discussed.<<ETX>>

Design of a four degree-of-freedom force-reflecting manipulandum with a specified force/torque workspace

It is noted that the performance of force-reflecting hand controllers, also called manual interfaces or manipulanda, is at present limited more by mechanical design than by computing hardware. Some of the important mechanical features of a high-performance manual interface are low inertia, low friction, high stiffness, backdriveability, high output force capability, multiple degrees-of-freedom, and sizable range of motion. A four-degree-of-freedom manipulandum that utilizes a three-degree-of-freedom parallel-link mechanism was designed to incorporate these features. The kinematic design of the manipulator prompted the definition of a force/torque workspace as the volume of operation within which certain maximum desired endpoint forces and torques can be achieved, given actuators of limited output. The design requires low actuator torques, is small in size, and does not approach joint limits in the workspace.<<ETX>>

Power and impedance scaling in bilateral manipulation

A power and impedance scaling bilateral manipulator (such as an extender or a macro-micro bilateral manipulator) can greatly enhance the manual capabilities of a human operator, but it can also compromise the inherent stability of the operator. A condition for the robust stability of an operator/bilateral manipulator environment system is derived using the structured singular value. The application of this condition is illustrated with several examples of power and impedance scaling via a two-channel bilateral manipulator.<<ETX>>

Guaranteed stability of haptic systems with nonlinear virtual environments

Design of haptic systems that guarantee stable interaction is a challenging task. Virtual environments are typically highly nonlinear-resulting in a nonpassive discrete-time model. This paper will investigate how nonlinear mass/spring/damper virtual environments can be designed to guarantee the absence of oscillations and other chaotic behavior in the signal presented to the human operator. In particular, delayed and nondelayed implementation of the mass/spring/damper virtual environment is considered, revealing a nonintuitive result with regard to the allowable local stiffness.

Passive robotics: an exploration of mechanical computation

A passive wrist, of fixed design, can be programmed to execute a wide range of useful control laws. Considered in particular are wrists whose actuators are unpowered hydraulic cylinders, the ports of which are coupled to one another via variable-conductance constrictions. The wrist is programmed by selection of these conductances, much as an analog computer is programmed. The range of control laws such a device can compute is characterized mathematically.<<ETX>>

KineAssist: a robotic overground gait and balance training device

The KineAssist is a robotic device for gait and balance training. A user-needs analysis led us to focus on increasing the level of challenge to a patients ability to maintain balance during gait training, and also on maintaining direct involvement of a physical therapist (rather than attempting robotic replacement.) The KineAssist provides partial body weight support and postural torques on the torso; allows many axes of motion of the trunk as well as of the pelvis; leaves the patients legs accessible to a physical therapist during walking; servo-follows a patients walking motions overground in forward, rotation, and sidestepping directions; and catches a patient who begins to fall. Design and development of the KineAssist proceeded more rapidly in the context of a small company than would have been possible in most research contexts. A prototype KineAssist has been constructed, and has received FDA approval and IRB clearance for initial human studies. We describe the KineAssists motivation, design, and use.