Abstract In many applications, it suffices to know a lower bound on the distance between objects, instead of the exact distance itself, which may be more difficult to compute. Such an easy‐to‐compute lower bound on the distance between two nonconvex polyhedra is presented here, which does not require a decomposition of the original polyhedra into convex entities. Furthermore, a suitable preprocessing of the polyhedra permits lowering the effort needed to compute this lower bound, and improves its quality. Experimental evidence is presented of the promise of this approach for assembly applications. © 2006 Wiley Periodicals, Inc.

Abstract This paper presents a reconfigurable ankle rehabilitation robot to cover various rehabilitation exercise modes. The designed robot can allow desired ankle and foot motions, including toe and heel raising as well as traditional ankle rotations, since the mechanism can generate relative rotation between the fore and rear platforms as well as pitch and roll motions. In addition, the robotic device can be reconfigured from a range of motion (ROM)/strengthening exercise device to a balance/proprioception exercise device by simply incorporating an additional plate. Further, the action of the device is twofold in the sense that while a patient's foot is fastened firmly to the ROM/strengthening device for task specific training, that person can also stand on the balance/proproception device. To perform each mode of ROM, strengthening, and proproception exercises, aunified position‐based impedance controlis systematically developed taking into account the desired position and velocity. © 2005 Wiley Periodicals, Inc.

This paper studies the human arm's sensory-motor control mechanism in reaching movements. First, we formulate both the kinematics and dynamics of a two-link planar arm model with six redundant musc...

Abstract This paper studies the human arm's sensory‐motor control mechanism in reaching movements. First, we formulate both the kinematics and dynamics of a two‐link planar arm model with six redundant muscles. The nonlinear muscle dynamics is modeled based on several biological understandings. We then show the stability of the overall system and perform some numerical simulations. By considering the internal forces induced by the redundant muscles, we show that the damping factors in each joint can be regulated, and as the result, it can realize humanlike quasistraight line reaching movements. In addition, we also propose the gravity compensation method at the muscle input level and present the result of numerical simulation to verify the usefulness of this method. © 2005 Wiley Periodicals, Inc.

In this paper, we propose an optimal design for a passive haptic device with brakes and its control method. The inability of a brake to generate torque significantly affects the performance of a multi-DOF haptic device, in that a desired force can be generated only approximately in some workspace and, in some cases, the device may become stuck contrary to the user's intention. In this research, these limitations are analyzed by means of the so-called passive force manipulability ellipsoid. Through the analysis, performance indices are developed for evaluating the limitations associated with passive haptic devices. Optimization is conducted for a 5-bar mechanism with redundant actuation, and a coercive force approximation scheme is developed to avoid unsmooth motion during the wall-following task along the virtual wall. It is experimentally shown that the performance in relation to the limitations is greatly improved for the optimized mechanism. © 2005 Wiley Periodicals, Inc.

In navigation that involves several moving agents or robots that are not in possession of each other's plans, a scheme for resolution of collision conflicts between them becomes mandatory. A resolution scheme is proposed in this paper specifically for the case where it is not feasible to have a priori the plans and locations of all other robots, robots can broadcast information between one another only within a specified communication distance, and a robot is restricted in its ability to react to collision conflicts that occur outside of a specified time interval called the reaction time interval. Collision conflicts are resolved through velocity control by a search operation in the robot's velocity space. The existence of a cooperative phase in conflict resolution is indicated by a failure of the search operation to find velocities in the individual velocity space of the respective robots involved in the conflict. A scheme for cooperative resolution of conflicts is modeled as a search in the joint velocity space of the robots involved in conflict when the search in the individual space yields a failure. The scheme for cooperative resolution may further involve modifying the states of robots not involved in any conflict. This phenomenon is characterized as the propagation phase where cooperation spreads to robots not directly involved in the conflict. Apart from presenting the methodology for the resolution of conflicts at various levels (individual, cooperative, and propagation), the paper also formally establishes the existence of the cooperative phase during real-time navigation of multiple mobile robots. The effect of varying robot parameters on the cooperative phase is presented and the increase in requirement for cooperation with the scaling up of the number of robots in a system is also illustrated. Simulation results involving several mobile robots are presented to indicate the efficacy of the proposed strategy. © 2005 Wiley Periodicals, Inc.

This paper presents a dynamic virtual environment tool for training operators and to prove different control schemes in telerobotic systems, and describes virtual reality environments used in teleoperated robotic systems. In the presented tool, the kinematic and dynamic model of the remote environment which is manipulating the operator is considered. The paper also describes how time delays in the communication channel can be easily added to the simulator, in order to analyze their effects in the teleoperated system. Finally, some experimental results achieved with this virtual teleoperated system are shown. With the presented dynamic simulator, different control schemes designed to overcome the time delay problem could be tested. © 2005 Wiley Periodicals, Inc.

This paper proposes an algorithm for robot perception of impedance, which can be used as a fundamental technique for real-time and qualitative perception of physical constraints imposed on the robot's end-effector. This algorithm (1) estimates the impedance that represents the motion-force relation of the end-effector; (2) calculates the uncertainties of the estimates; and (3) detects discontinuous changes in the impedance. The estimated impedance can be used to recognize local dynamic properties of the environment and temporary constraint conditions imposed on the end-effector. The detected discontinuities can be used to segment the manipulated tasks and to recognize the geometric structure of the environment. This method can be implemented in both autonomous and remote-controlled robots because it is designed separately from control methodologies. Results of preliminary experiments are presented. © 2005 Wiley Periodicals, Inc.

When processing laser detection and ranging (LADAR) sensor data for scene interpretation, for example, for the purposes of feature extraction and/or data association in mobile robotics, most previous work models such devices as processing range data which follows a normal distribution. In this paper, it is demonstrated that commonly used LADARs suffer from incorrect range readings at changes in surface reflectivity and/or range discontinuities, which can have a much more detrimental effect on such algorithms than random noise. Most LADARs fall into two categories: coaxial and separated transmitter and receiver configurations. The latter offer the advantage that optical crosstalk is eliminated, since it can be guaranteed that all of the transmitted light leaves the LADAR and is not in any way partially reflected within it due to the beam-splitting techniques necessary in coaxial LADARs. However, they can introduce a significant disparity effect, as the reflected laser energy from the target can be partially occluded from the receiver. As well as demonstrating that false range values can result due to this occlusion effect from scanned LADARs, the main contribution of this paper is that the occurrence of these values can be reliably predicted by monitoring the received signal strength and a quantity we refer to as the “transceiver separation angle” of the rotating mirror. This paper will demonstrate that a correct understanding of such systematic errors is essential for the correct further processing of the data. A useful design criterion for the optical separation of the receiver and transmitter is also derived for noncoaxial LADARs, based on the minimum detectable signal amplitude of a LADAR and environmental edge constraints. By investigating the effects of various sensor and environmental parameters on occlusion, some advice is given on how to make use of noncoaxial LADARs correctly so as to avoid range errors when scanning environmental discontinuities. © 2005 Wiley Periodicals, Inc.

This paper addresses the co-design of biologically-plausible vision-based algorithms applied to control the reactive behaviors of mobile robots and, especially, the control of collision avoidance in unknown and dynamic worlds. Our main tools are programmable logic devices like FPGA (field programmable gate arrays) to implement real-time perception/actions schemes. © 2005 Wiley Periodicals, Inc.