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Successful control of contact transitions is an important capability of dextrous robotic manipulators. In this paper we examine several methods for controlling the transition from free motion to constrained motion, with an emphasis on minimizing fingertip load oscillations during the transition. A new approach, based on input command shaping, is discussed and compared with several methods developed in prior research. The various techniques were evaluated on a one-axis impact testbed, and we present results from those experiments. The input shaping method was found to be comparable, and in some cases superior, to existing techniques of contact transition control.

We describe an approach for making the capability of manufacturing processes manifest to designers starting with the earliest stages of geometry specification. The approach involves a dialogue among design and manufacturing agents over the Internet. The dialogue focuses on the specification and exchange of process capability models for establishing "design rules on-demand" to ensure manufacturability. The models include both declarative knowledge and, for those aspects of the process that are difficult to represent declaratively, platform-independent procedural code which is automatically loaded onto the designers' machines. The approach is being implemented using agents, written in the Java 2 language, which exchange feature-based capability models. The approach is being tested initially on machining and shape-deposition processes.

In studying grasping and manipulation we find two very different approaches to the subject: knowledge-based approaches based primarily on empirical studies of human grasping and manipulation, and analytical approaches based primarily on physical models of the manipulation process. This chapter begins with a review of studies of human grasping, in particular our development of a grasp taxonomy and an expert system for predicting human grasp choice. These studies show how object geometry and task requirements (as well as hand capabilities and tactile sensing) combine to dictate grasp choice. We then consider analytic models of grasping and manipulation with robotic hands. To keep the mathematics tractable, these models require numerous simplifications which restrict their generality. Despite their differences, the two approaches can be correlated. This provides insight into why people grasp and manipulate objects as they do, and suggests different approaches for robotic grasp and manipulation planning. The results also bear upon such issues such as object representation and hand design.

Pathologies including stroke and multiple sclerosis can leave patients with impaired tactile and proprioceptive sensation, which contributes to their difficulty in performing everyday tasks. We present the results that indicate that a combination of fingertip force sensing and vibrational feedback can help patients with multiple sclerosis improve their performance in manipulation tasks. The feedback can take the form of an "event cue" in which patients are alerted when forces at the fingertips stray outside of a recommended range, or proportional feedback, in which trains of vibration pulses are correlated directly with the fingertip forces. While both types of feedback allow the patients to handle objects with more accurate force control, the former approach is more successful and preferred by subjects with mild impairment while the latter approach appears to be most effective for patients with severe impairment.

Force sensing is an essential requirement for dexterous robot manipulation. We describe composite robot end-effectors that incorporate optical fibers for accurate force sensing and estimation of contact locations. The design is inspired by the sensors in arthropod exoskeletons that allow them to detect contacts and loads on their limbs. In this paper, we present a fabrication process that allows us to create hollow multimaterial structures with embedded fibers and the results of experiments to characterize the sensors and controlling contact forces in a system involving an industrial robot and a two-fingered dexterous hand. We also briefly describe the optical-interrogation method used to measure multiple sensors along a single fiber at kilohertz rates for closed-loop force control.

The authors consider the detection of small surface features, such as cracks, bumps, and ridges, on the surface of an object during haptic exploration and dexterous manipulation. Surface feature definition and detection are essential for intelligent haptic exploration and modeling of unknown objects. First, the authors review the representation of object surface geometry and present definitions of features based on local surface curvature. These definitions depend on both the geometry of the robot fingertips and the object being explored. It is also shown that the trajectory traced by a round fingertip rolling or sliding over the object surface has some intrinsic properties that facilitate feature detection. Several algorithms for feature detection based on feature definitions are described and compared, and simulated and experimental results are presented for feature detection using a hemispherical fingertip equipped with a tactile sensor.

We present a new tactile display for use in dexterous telemanipulation and virtual reality. Our system renders the location of the contact centroid moving on the user’s fingertip. Constructed in a thimble-sized package and mounted on a haptic force-feedback device, it provides the user with concurrent feedback of contact location and interaction forces. We believe such a design will enable more versatile object manipulation and richer haptic interactions. To evaluate this display concept, we conducted two perceptual experiments. First, human subjects judged object curvature using both direct manipulation of physical models and virtual manipulation via the device. Results show similar levels of discrimination in real and virtual interactions, indicating the device can effectively portray contact information. Secondly, we investigated virtual interactions with rolling and anchored objects and demonstrated that users are able to distinguish the interaction type using our device. These ...

In this article we compare theoretical and experimental trajectories obtained for sliding an object with the fingers of a dextrous hand. The experiments were conducted using a twofingered planar manipulator with soft fingers. Forceltorque sensors monitored the contact forces at the fingertips, and a vision system tracked the motion of the object. The predicted trajectories were obtained using a quasistatic sliding analysis and assuming Coulomb friction at the contacts. Close agreement between the predicted and experimental results indicates that quasistatic sliding analyses can be used for motion planning with soft sliding fingertips, provided that the average values of the contact forces and coefficient of friction are accurately known.

The goal of this article is to develop practical descriptions of the relationship between forces and motions in sliding manipu lation. We begin by reviewing the limit surface, a concept from the mechanics of sliding bodies that uses kinematic analysis to find the force and moment required to produce any given sliding motion. Next we provide experimental results showing that the limit surface only approximates the actual force-motion relationship. Then we look at other approximations that can be used to provide a simplified model useful in control, planning, and simulation of manipulation. These approximations include square pyramids, cones, ellipsoids, and ellipsoids with facets removed. Different approximations may be most appropriate, depending on the required computational speed and accuracy and the need to produce conservative results.

Shared control represents a middle ground between supervisory control and traditional bilateral control in which the remote system can exert control over some aspects of the task while the human operator maintains access to low-level forces and motions. In the case of dexterous telemanipulation, a natural approach is to share control of the object handling forces while giving the human operator direct access to remote tactile and force information at the slave fingertips. We describe a set of experiments designed to determine whether shared control can improve the ability of an operator to handle objects delicately and to determine what combinations of force, visual, and audio feedback provide the best level of performance and operator sense of presence. The results demonstrate the benefits of shared control and the need to carefully choose the types and methods of direct and indirect feedback.

Force sensing is an essential requirement for dexterous robot manipulation. Although strain gages have been widely used, a new sensing approach is desirable for applications that require greater robustness, design flexibility and immunity to electromagnetic noise. An exoskeletal force sensing robot finger was developed by embedding Fiber Bragg Grating (FBG) sensors into a polymer-based structure. Multiple FBG sensors were embedded into the structure to allow the manipulator to sense and measure both contact forces and grasping forces. In order to fabricate a three-dimensional structure, a new shape deposition manufacturing (SDM) process was explored. The sensorized SDM-fabricated finger was then characterized using an FBG interrogator. A force localization scheme is also described.

We describe research at the Stanford Dextrous Manipulation Lab centered around haptic exploration of objects with robot hands. The research areas include object acquisition and manipulation and object exploration with robot ngers to measure surface features, textures and friction. We assume that the robot is semi-autonomous; it can receive guidance or supervision from humans regarding object selection and grasp choice, but is also equipped with algorithms for autonomous ne manipulation, surface exploration and feature identi cation. The applications of this work include object retrieval and identi cation in remote or hazardous environments.

In this paper we describe ongoing work toward eventdriven dextrous manipulation. In this context, the events are primarily determined through tactile and force/torque sensing. We begin with a review of recent work in tactile event detection and its role in the control of manipulation. We then consider control issues, focusing on the problem of accomplishing smooth transitions as the constraints, dynamic equations and control objectives change from one phase of a manipulation task to the next. Smooth transitions are essential in dextrous manipulation because of the typically low inertias of the grasped object and the fingers Ñ the object accelerates quickly and the fingertip sensors produce large signals in response to disturbances at the contacts. Finally, we describe a language that we are developing to facilitate programming of dextrous manipulation tasks with multiple control modes and tactile sensors.

Fingertip suction is investigated using a compliant, underactuated, tendon-driven hand designed for underwater mobile manipulation. Tendon routing and joint stiffnesses are designed to provide ease of closure while maintaining finger rigidity, allowing the hand to pinch small objects, as well as secure large objects, without diminishing strength. While the hand is designed to grasp a range of objects, the addition of light suction flow to the fingertips is especially effective for small, lowfriction (slippery) objects. Numerical simulations confirm that changing suction parameters can increase the object acquisition region, providing guidelines for future versions of the hand.

We present a scheme by which a manipulator can identify when it is about to lose hold of a grasped object grasp forces, saving energy and reducing damage to deliso that it c~.n take preventive measures to maintain the cate objects. However, as the contact forces at the fingergrasp before slipping occurs. By detecting localized slips tips automatically adapt to variations in task loading or which precede gross slip between the gripping surface and surface conditions (e.g., the presence of dirt or moisture), a grasped object, a controller can reliably modify the grasp other advantages accrue which are probably more imporforce and prevent the object from slipping. The motiva-tant for everyday manipulation. In particular, closed-loop tion behind our sensor design comes from current physio-control of the normal/tangential force ratio at the fingerlogical research which reveals the importance of a textured tips is particularly useful for manipulation with sliding gripping surface in detecting these localized, or incipient, [Kao and Cutkosky 19921. Also, by keeping the contact slips and provides us with insight into human grasping forces small, the sensitivity and available dynamic range and manipulation strategies. By using our sensor as an of the tactile sensors is enhanced. This is partly because active gripping surface on a simple manipulator and mod-saturation of the sensors is avoided and partly because the C e eling our control strategy after humans, we are able to compliance of a fingertip decreases with increasing contact dynamically control the amount of force used to grasp ob-force. The deformation of a fingertip varies as 6x = c6f, jects, while preventing them from slipping. Our results where c is compliance (inverse of stiffness). Therefore, show that the sensor is not greatly affected by variations as the fingertips are pressed harder against a surface, the in the material properties of the grasped object and indi-relative change in skin and tissue deformation for a given cate that the force control strategy is adequately immune change in force decreases, and the fingertips become less to mechanical vibrations in the manipulator. sensitive. Finally, keeping the contact force slightly above the threshold for slipping ensures that micro-slips will often occur. This is useful because a change in the incidence

We describe the dynamic testing and control results obtained with an exoskeletal robot finger with embedded fiber optical sensors. The finger is inspired by the designs of arthropod limbs, with integral strain sensilla concentrated near the joints. The use of fiber Bragg gratings (FBGs) allows for embedded sensors with high strain sensitivity and immunity to electromagnetic interference. The embedded sensors are useful for contact detection and for control of forces during fine manipulation. The application to force control requires precise and high-bandwidth measurement of contact forces. We present a nonlinear force control approach that combines signals from an optical interrogator and conventional joint angle sensors to achieve accurate tracking of desired contact forces.

This paper presents a tool aimed at the design of compliant, under-actuated hands. The particular motivation is hands that will be used for an underwater robot to grasp a variety of objects, some of which may be delicate or slippery. The focus of the analysis is the problem of object acquisition. In comparison to many prior grasp analysis tools, the tool presented here models the dynamics of a hand, including actuation mechanisms, compliance and friction in an efficient formulation that permits one to evaluate variations in such quantities as phalange length, finger spacing, transmission ratios, and torsional joint stiffness when comparing hand designs. The analysis is demonstrated for a quasi-static object acquisition problem and leads to the computation of a vector space of three dimensional regions for which the hand will tend to center and stably grasp a compact object.

Multi-fingered robotic end-effectors have not yet made significant inroads into practical applications, partly due to the complexity of dextrous manipulation tasks. This paper develops an approach for assembling tasks from relatively simple phases which are punctuated by discrete events, signaling the transfer of operation to the next phase in a sequence. We examine the constraints active during phases, and develop methods for conducting smooth transitions between phases. Techniques for robust event detection in the presence of disturbances are also described. Experimental data is shown in support of the phase transition and event detection methods.

We describe a new tactile display for use in dexterous telemanipulation and virtual reality. Our system renders the changing location of a remote or virtual contact by moving a tactile element along the user's fingertip. Mounted at the endpoint of a haptic mechanism, our thimble-sized device concurrently displays contact location and interaction forces. We believe such a design will enable more versatile object manipulation for haptic interactions. To evaluate this display concept, we conducted two perceptual experiments. First, human subjects judged object curvature though direct manipulation of physical models and virtual manipulation with the device. Results show similar levels of discrimination in real and virtual interactions, indicating the device can effectively portray contact information. Second, we investigated virtual interactions with rolling and anchored objects and demonstrated that users can distinguish the interaction type using our device. These experiments provide insight into the sensitivity of human perception and suggest that even a simple display of the contact centroid location may significantly enhance telerobotic and virtual grasping tasks.