For a class of robot arms, a proportional-derivative (PD) controller plus gravity compensation yields the global asymptotic stability for regulation tasks, and some proportional-integral-derivative (PID) controllers guarantee local regulation without gravity cancellation. However, these controllers cannot render asymptotic stability for tracking tasks. In this paper, a simple decentralized continuous sliding PID controller for tracking tasks that yields semiglobal stability of all closed-loop signals with exponential convergence of tracking errors is proposed. A dynamic sliding mode without reaching phase is enforced, and terminal attractors, as well as saturated ones, are considered. A comparative experimental study versus PD control, PID control, and adaptive control for a rigid robot arm validates our design.

We describe a new robot architecture: the collaborative robot, or cobot. Cobots are intended for direct physical interaction with a human operator. The cobot can create smooth, strong virtual surfaces and other haptic effects within a shared human/cobot workspace. The kinematic properties of cobots differ markedly from those of robots. Most significantly, cobots have only one mechanical degree of freedom, regardless of their taskspace dimensionality. The instantaneous direction of motion associated with this single degree of freedom is actively servo-controlled, or steered, within the higher dimensional taskspace. This paper explains the kinematics of cobots and the continuously variable transmissions (CVT) that are essential to them. Powered cobots are introduced, made possible by a parallel interconnection of the CVT. We discuss the relation of cobots to conventionally actuated robots and to nonholonomic robots. Several cobots in design, prototype, or industrial testbed settings illustrate the concepts discussed.

Intelligent assist devices (IADs) are a new class of hybrid devices for direct, physical, interaction with a human operator in shared workspaces. These devices-designed for the assembly line worker-can reduce ergonomics concerns that arise due to on-the-job physical and cognitive loading, while improving safety, quality and productivity. Cobots, a sub-set of IADs, implement software defined virtual guiding surfaces while providing some amplification of human power. They exemplify the central theme of this paper-that humans are critical in many assembly operations and ergonomics tools that enable them to perform their duties are necessary. The paper describes broad design principles for human-machine interaction in these industrial settings. Prototype industrial cobots designed for testing and validation are described.

Identifying and implementing high fidelity scaling laws in scaled teleoperated systems is still a challenge. We propose the use of additional information (e.g., auditory and tactile) to complement and supplement the normal visual and force channels and thereby provide sensory enhancement when performing delicate tasks. We support our proposal by presenting experimental results from tests performed by humans on a hybrid hardware-software telemanipulation system. Our results show that integrating auditory and tactile feedback improved the performance of the operator.

A sequence replanning/control method is proposed to overcome geometric uncertainties of the slave environment in our a priori knowledge of a discrete-event-based tele-task model. A class of controlled Petri net (CPN) is adopted as a modeling tool of tele-robotic part-mating process and the discrete-event control policy of the process is formulated on the basis of the CPN model. In the case when an unexpected state transition occurs due to the uncertainty of the slave environment, recovery paths and their costs are extracted from the a priori knowledge and one of them to minimize the given cost is chosen as the replanned sequence in order for the slave process to escape from the unexpected state and resume the nominal plan.

We address the problem of controlling contact forces generated when the fingers of a robot close on an object or make contact with surfaces in the robot's environment. The use of controllable fingertip materials is proposed to enhance system performance and avoid contact instability problems that can arise with noncollocated sensors and actuators. We describe a novel fingertip employing an electrorheological fluid and present the results of experiments to evaluate its capabilities when used with a robot contacting a stationary object at various speeds. Having characterized the fingertip behavior as a function of applied voltage, we turn to the question of optimal control, Using a simplified dynamic model of a robot equipped with a controllable electrorheological fingertip, we obtain a piece-wise optimal solution for the fingertip damping as a function of time, to minimize settling time while satisfying constraints on the contact forces.

We propose a robot controller for stably executing all phases of contact tasks involving discontinuities due to the introduction or removal of contact forces. Systems executing such tasks are characterized by ambiguous right hand sides in the differential equations of motion. Consequently, our approach develops upon ideas from generalized dynamical systems (GDSs), an orthogonalization principle, the Hertz contact model, and model-based adaptive control. The result is an asymptotically stable controller that discontinuously switches among three possible configurations based on the contact situation. The method is used to tune the controller independently for both position and constrained motion as also for reducing contact forces during the process of making contact with the environment. The underlying theory is first described. Then the controller synthesis and proof of its asymptotic stability, based on Lyapunov's method, are presented. The idea is illustrated with a simulation of a simple task.>

The issue of controlling contact forces generated when the fingers of a dextrous device first close on an object is addressed. The use of active fingertips is proposed to enhance the system performance and avoid contact instability problems resulting from noncollocated sensors and actuators. A first step towards exploring this issue is the study of an idealized controllable fingertip making contact with an object. The authors provide analytical and simulation studies to identify ideal fingertip characteristics to achieve a desired performance for a simple contact problem. An investigation of the performance of more realistic fingers with limited controllability follows. Preliminary experimental results for a prototype semi-active fingertip that uses an electrorheological fluid to achieve active damping control are provided. A brief summary of future experimental plans to implement such active fingertips in simple manipulation tasks is presented.>

Preliminary experiments are presented concerning the use of tactile sensing to enhance the flexibility and robustness of robotic manipulation. A simple two-fingered manipulator with very clean dynamics has been constructed to focus on tactile and force sensing in manipulation. Manipulation is characterized by constantly changing mechanical systems, as fingers make or break contact or start to roll or slide on the surface of a grasped object. It is important to detect these changes since control schemes must change to match the varying task requirements. Following the human model, it is shown that dynamic tactile sensors can reliably detect the changing contact conditions. In a simple grasp-lift-replace task, use of these sensors enables the manipulator to cope with uncertainty in object location and task forces.>

The authors present an attempt to model soft robot fingertips filled with powders or plastic fluids. They propose two rolling models, adapted from hot metal rolling and extrusion, and discuss the factors that affect the choice of appropriate models. The integration of energy losses in the dynamic equations of motion is then considered. Initial simulation studies have shown that soft fingertips can help stabilize the grasp and reduce the demands on the control system. The viscoplastic nature of the finger tips affects the dynamics of manipulation by dissipating energy. The coin snap problem is given as an example to demonstrate this effect.>