The stability of the hybrid position/force control for manipulators is examined using Lyapunov's direct method for decentralized controllers which are in the form of linear feedback of projected joint errors. This paper aims in clarifying the kinematic instabilities that have been reported to exist for the original hybrid control scheme using the Jacobian inverse for mapping cartesian errors to joint errors, and which have been later remedied in a control scheme using the Jacobian pseudoinverse. Stability conditions demonstrate the importance of the joint error projection matrix and the contact state. Experimental results for a 2-degrees-of-freedom planar manipulator using a PUMA 560 are given both in free space and in contact with a stiff wall.

The objective of this work is to allow subsea teleoperative tasks to be performed efficiently even when all communication between human operator and remote robot is via an acoustic link. This paper describes the integration of remote site cameras into the teleprogramming system. Images from these cameras may be used for calibrating and maintaining the world model as well as for aiding the operator in diagnosing and recovering from unexpected events. The constrained communications channel forces the adoption of an intelligent approach to image transmission. The system automatically selects windowing and subsampling parameters while varying frame rates and task execution speeds to match that which the system can support given available bandwidth and computational constraints. Examples are presented from tests in which an operator in Philadelphia controlled a robot manipulator mounted on an underwater vehicle submerged off the Massachusetts coast.

Presents a collaborative effort to design and implement a cooperative material handling system by a small team of human and robotic agents in an unstructured indoor environment. The authors' approach makes fundamental use of the human agents' expertise for aspects of task planning, task monitoring, and error recovery. The authors' system is neither fully autonomous nor fully teleoperated. It is designed to make effective use of the human's abilities within the present state of the art of autonomous systems. The authors' robotic agents refer to systems which are each equipped with at least one sensing modality and which possess some capability for self-orientation and/or mobility. The authors' robotic agents are not required to be homogeneous with respect to either capabilities or function. The authors' research stresses both paradigms and testbed experimentation. Theory issues include the requisite coordination principles and techniques which are fundamental to a cooperative multiagent system's basic functioning. The authors have constructed an experimental distributed multiagent-architecture testbed facility. The required modular components of this testbed are currently operational and have been tested individually. The authors' current research focuses on the agents' integration in a scenario for cooperative material handling.

The teleprogramming system is a supervisory control approach to time delayed teleoperation that incorporates predictive graphics and reactive skills to accomplish dexterous manipulation tasks in the presence of significant time delay. This paper presents an experimental effort to validate the teleprogramming system using the GRASP Laboratory of the University of Pennsylvania as the operator station and the TROPICS Laboratory of the Jet Propulsion Laboratory as the remote site. The teleprogramming experiment involved operator supervisory control of a robot performing puncture and slice operations on the thermal blanket securing tape of a satellite repair mission sub-task This experiment was successfully performed in August, 1994 using the Internet as the sole medium of communication. During experimentation, messages experienced time-varying time delay between three and fifteen seconds with an average delay of approximately six seconds.

In many teleoperation applications including undersea and shallow space operations, communication time delay limits the applicability of force reflecting master-slave devices. We instead employ teleprogramming, a supervisory control approach to remote manipulation. A behavior-based controller, constructed under the principles of the subsumption architecture, fulfils the need for semi-autonomy at the remote site prescribed by supervisory control. In this paper we present an interface allowing operator interaction with the behavior-based controller. The use of a behavior-based controller provides a rich means of presenting diagnostic and kinesthetic state information to the operator when used with diagnostic interfaces previously developed. We demonstrate the supervisory control system on a GRASP Laboratory mock-up of a slicing task performed during a satellite repair operation where a robot held knife cuts securing tape along seams of panels of a thermal protection blanket.>

The teleprogramming system employs a supervisory control approach where operator interaction with a virtual environment directs the actions of a remote manipulator operating semi-autonomously. We focus on the detection, diagnosis, and recovery from unexpected situations frequently arising during normal operation. The teleprogramming system employs a single thread approach to error recovery that is inherent in the system design. We perform two experimental tasks, each highlighting a different role for the operator, using the teleprogramming system with a simulated communication time delay of 10 seconds. In the first task of inserting and extracting bolts, the operator assumes the role of "task level reasoning" or task planning and sequencing, task state reasoning, and diagnostic procedure generation. In the second task, puncturing and slicing duct tape, the operator performs "action level reasoning" or diagnosing and correcting unexpected situations and determining success of actions. Our experimental results indicate that complex tasks can be accomplished when the operator is provided multiple and overlapping forms of feedback.>

The authors propose a joint torque sensing technique making use of the existing structural elasticity of robots. The technique provides joint torque sensing without reducing the stiffness of the robot or changing the mechanical structure of the joints. The elasticity of the flexsplines of the harmonic drives is utilized to measure the joint torque. The flexsplines are flexible thin cups, made from steel, in the harmonic drives that are driven by the wave generators. A finite-element analysis of the flexsplines shows that a special configuration of strain gauges, mounted on the flexspline, has to be employed to eliminate errors in sensor information due to rotation of the wave generator. Characteristics of the torque sensor are examined experimentally. The linearity and the dynamic response are almost the same as those of a conventional sensing technique. For a one-link robot arm, both theoretical and experimental investigations support the validity of the sensing technique.>

A joint torque sensing technique for robots with harmonic drives is proposed. Elasticity of harmonic drives is utilized to measure the joint torque. The technique provides joint torque sensing without reducing the stiffness of the robot and changing the mechanical structure of the joints. A finite-element analysis of flexsplines, which are flexible thin cups made from steel in harmonic drives, is performed. The analysis shows that a special configuration of strain gauges on the flexspline has to be employed to eliminate errors in sensor information due to rotations of wave generators. Characteristics of the torque sensor are examined experimentally. The linearity and the dynamic response are almost the same as those of a conventional sensing technique. Both theoretical and experimental investigations support the validity of the proposed sensing technique.>

The authors present a method to compute inverse kinematics in parallel for robots with a closed-form solution, and distinguish a pipelined solution from a parallel solution. Although both increase the system throughput, only the parallel solution reduces the computational latency. The computational task of computing inverse kinematics is partitioned with one subtask per joint, and all subtasks are computed in parallel. The intrinsic dependency among subtasks is removed by linear extrapolation through the gradient of the inverse kinematic functions and joint velocity information. The simplicity of the solution makes it easily applicable to any robot manipulator with a closed-form solution. Examples are used to illustrate the effectiveness and efficiency of the algorithm. Implementation of the algorithm on a multiprocessor system is described.>

A method of computing inverse kinematics in parallel for robots with a closed-form solution is presented. The computational task of computing each inverse kinematics solution is partitioned with one subtask per joint, and all subtasks are computed concurrently. The intrinsic dependency among subtasks is removed by linear extrapolation through the gradient of inverse kinematic functions and joint velocity information. The high degree of concurrency and naturally balanced concurrent subtasks of the system significantly reduce the latency of the inverse kinematics evaluation. Compared with a serial solution, the algorithm results in a reduction of the time of execution by a factor proportional to the number of joints when implemented on a multiprocessor system. Its simplicity makes it easily applicable to any robot manipulators with closed-form solutions. Examples are used to illustrate the effectiveness and the efficiency of the algorithm. Implementation of the algorithm on a multiprocessor system is also discussed.>

A compliant wrist combining passive compliance and a displacement sensor has been developed for a robot manipulator to be used in assembly operations. The wrist provides the necessary flexibility to accommodate transitions as the robot makes contact with the workpiece, to correct positioning error, and to avoid high impact forces in automatic assembly. Sensing from the device makes it possible to actively control the contact forces or to compensate the positioning error during motion and contact. The design features of two prototypes of the device are described. A hybrid position force control scheme using the device and incorporating the passive compliance in the design is presented. Two basic primitives in the assembly process, edge tracking and insertion operation with the compliant wrist, are investigated. A fuzzy controller is presented to assign velocity instead of evaluating force zones in insertion. The experimental results show that the system provides a feasible and economical solution to the provision of necessary compliance in automated assembly and manufacturing.>

A computational analysis and a comparison of line-oriented representations of general (i.e. rotational and translational) spatial displacements of rigid bodies are presented. Four mathematical formalisms for effecting a general spatial screw displacement are discussed and analyzed in terms of computational efficiency in performing common operations needed in kinematic analysis of multilinked spatial mechanisms. The corresponding algorithms are analyzed in terms of both sequential and parallel execution. It is concluded that the dual-unit quaternion representation offers the most compact and most efficient screw transformation formalism but that line-oriented methods in general are not well suited for efficient kinematic computations or real-time control applications. Owing to line-based geometry, underlying its definition, screw calculus represents a set of valuable tools in theoretical kinematics. However, the mathematical redundancy inherent in Plucker coordinate space representation makes the screw calculus computationally less attractive than the corresponding point-oriented formalisms.>

Three-dimensional modeling of rotations and translations in robot kinematics is most commonly performed using homogeneous transforms. An alternate approach, using quaternion-vector pairs as spatial operators, is compared with homogeneous transforms in terms of computational efficiency and storage economy. The conclusion drawn is that quaternion-vector pairs are as efficient as, more compact than, and more elegant than their matrix counterparts. A robust algorithm for converting rotational matrices into equivalent unit quaternions is described, and an efficient quaternion-based inverse kinematics solution for the Puma 560 robot arm is presented.>

The authors present an inverse kinematic algorithm for a four-revolute-joint (4-R) spherical wrist that provides for a complete set of spatial orientations, is nonsingular, and is simple to implement with existing technology. The algorithm is a rate-controlled method that depends on the required Cartesian rate. In the process of presenting the algorithm, the authors have developed the fundamentals of differential motion with n-revolute-joint spherical wrists. The method is outlined and applied to a 4-R regional structure. The goal is to combine the 4-R spherical wrist with the 4-R regional structure to develop an 8-R manipulator that is free of internal singularities.>

Engineering mechanics is used to develop the initial grasp liftability chart, or IGLIC. Its primary usefulness is in planning and analyzing grasps for lifting frictionless objects. Candidate grasp configurations can be mapped onto the IGLIC to determine, first, whether the grasp can be used to lift the object and, second, the nature of liftoff. Even though the development is undertaken for the two-dimensional case, the results can be applied to three-dimensional objects which can be approximated as generalized cylinders, by considering appropriate cross sections of the cylinders.>

Three-dimensional modeling of rotations and translations in robot kinematics is most commonly performed using homogeneous transforms. An alternate approach, using quaternion/vector pairs as spatial operators, is discussed and analyzed. Sequential and parallel algorithms for some of the common spatial operations are given for both homogeneous transforms and quaternion/vector pairs and compared in terms of computational efficiency. The two approaches are shown to be essentially equivalent in the absence of the need for frequent renormalization of rotational operators.>

The design of an end effector under development at Pennsylvania University is reported. The rationale supporting this mechanism is explored, its geometry is described and experimental results from the first prototype are presented. The gripper has three fingers, one fixed with respect to the palm and the other two able to rotate synchronously about different points under the palm. Some ideas for future work are presented.>

A compliant wrist instrumented between a robot and its end effector provides a necessary compliance for assembly operations, and the displacement and force information generated from the wrist sensor can be utilized to actively control the end effector. The authors discuss the position compensation for the detection of the compliant wrist due to the gravity load and other external forces at the unconstrained space, and the force control as the robot is constrained with the environment. The system stability problem and dynamic performance are investigated for the different control laws, wrist parameters, and environment models. By analysis and simulation, some meaningful conclusions are obtained. The results are useful for design of the compliant wrist device and determination of the compensator law in the feedback loop.>

The ability of a robot manipulator to position its end-effector accurately depends not only on kinematic modeling of the robot but also on the dynamic execution of the transformation between end-effector coordinates and joint coordinates. The authors examine errors associated with various approaches of motion trajectory generation and evaluate them statistically. Two approaches to controlling errors are considered: VAL, which has been developed by them, and resolved motion rate control (RMRC), which is due to D.E. Whitney (1986).>

Introduces an algorithm by which the inverse kinematics of a robot manipulator with closed-form solution can be computed in parallel to reduce the computational complexity roughly by a factor of n, the number of joints of the manipulator. The authors study the errors introduced by the algorithm by constructing statistical models of the errors. They evaluate the algorithm on a PUMA 260 manipulator, which has six degrees of freedom with six revolute joints and a reach of approximately 0.5 m.>

Robot manipulator motions near the wrist degeneracy often cause excessive joint rates that cannot be satisfied by the joint actuators and thus result in both position and orientation errors. We have developed an inverse Jacobian control policy that bounds the excessive rates while guaranteeing the position accuracy and minimizing the orientation error of the end effector.

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Grasping by a two-dimensional hand comprised of a palm and two hinged fingers is studied. The mathematics of frictionless grasping is presented and used in the development of a planner/simulator, The simulator computes the motion of the object using an active constraint set method and assuming exact knowledge of the physical properties of the polygonal object, hand, and support.

The decentralized control of robot manipulators at low speed needs the calculation of the inertial and gravitational coefficients of the dynamic equations. The scheme of calculation of the generalized forces can then be divided into two parts: the calculation in background of the dynamic coefficients and the calculation in real time of the generalized forces [1]. A LISP program, due to its ability for symbolic manipulation, has been created for the automatic generation of these coefficients. The input to the program is a file containing the Denavit-Hartemberg parameters, masses, centers of gravity and moments of inertia of the links. The result is a C program that calculates the coefficients. The validity of the program has been demonstrated by numerical comparison with the Newton-Euler program. Two examples, the PUMA robot and the Stanford manipulator have been tested. The former needs only 270 multiplications and 220 additions for the manipulator with an arbitrary load, and 200 multiplications and 150 additions without load; the latter needs 160 multiplications and 120 additions with an arbitrary load and 120 multiplications and 100 additions without load. The total time of calculation of the coefficients in a 8086/8087 microprocessor needs only 22 milliseconds in background.

We develop strategies for fine motion planning for assembly by robot manipulators. In particular we consider the insertion problem. Our strategies are based on the control of orientation and force to achieve fine position control. These methods avoid the problems of wedging and jamming.

The design and implementation of a distributed robot manipulator controller based on a parallel architecture is introduced in this paper. We consider the robot manipulator as a robot force and motion server (RFMS) to the robot system to execute force and motion commands issued by the robot coordinator. In the server, computation is distributed to a number of processors to achieve a system capable of executing computation expensive tasks. The use of "c" programming language for both the system programming and the user interface provides a convenient environment to control such a system.

We present a method for the computation of the effective inertia, coupling inertia, and gravity loading terms for a manipulator with a load. The calculations are separated so as to consider the manipulator and the load independently. These inertial and gravity loading effects are additive and furthermore their computation need only be performed at a rate commensurate with changes in the configuration of the manipulator, not at the control sample rate. As an example we compute the terms for the PUMA manipulator. Taking advantage of the symmetries in the manipulator we need only 65 multiplications and 41 additions to compute all terms. The computations for a load requires an additional 160 multiplications and 101 additions if the load is considered as a point mass.

This paper analyzes the effects of the mechanical stiffness of end effector force sensors on the control of robot manipulators. Modeling of the general manipulator-sensor system is presented, along with a detailed investigation of a single joint case. Analytical and experimental results indicate that the use of a mechanically compliant sensor permits a more responsive force controlled system to be realized. In addition, an active compensator for sensor deflections was developed to recover the static positional stiffness of the manipulator.

This paper describes a control scheme designed to make a manipulator move as fast as possible within its velocity and acceleration constraints. The control system adapts itself to any given path but is still conceptually simple and requires relatively little computing power. The basic strategy is to have an optimization algorithm tune the output of a trajectory generator that drives individual control loops on the robot joints. The optimization process is iterative, using only measured data from real-time runs of the arm in each step.

A robot manipulator must be able to satisfy any consistent position and force specifications in a well-defined Cartesian coordinate frame. In this paper, we present a method to achieve such a hybrid control of position and force. While the desired compliance is specified in Cartesian space, the control is accomplished in joint space, thus effectively reducing the computation load. Results show that accurate position and force control is obtained.

RCCL is a robot programming system that enables a user to specify robot manipulator tasks employing a set of primitive system calls similar in spirit to those of the UNIX input-output system. The goals addressed in the RCCL system are: manipulator task description; sensor integration; updatable world representation; flexibility; wide range of applications; medium level robot programming; off-line programming; efficiency; manipulator independence; portability; foreground-background programming; Cartesian path programming; arbitrary path specification; tracking; force control.

A new Cartesian position control called resolved motion force control (RMFC) has been developed for robot manipulator. It adapts force convergence concept to control the Cartesian force and position instead of classical joint control. In this way, the changing configurations, gravity loading, and internal friction of the manipulator can be automatically compensated. Also, the method only uses the Jacobian transpose matrix such that it is applicable to more than six degrees-of-freedom manipulator without increasing the computational burden.

A structured programming and teaching system is described for a robot manipulator where stress is laid on the consistent integration of programming and teaching. In the PAL programming system being developed at Purdue University, tasks are represented in terms of structured Cartesian coordinates. Every motion statement is a request to position and orient the manipulator such that a position equation, representing a closed kinematic chain of homogeneous transformations, is satisfied. In the teaching process, the transformation which represents the position of the end of the manipulator is defined using the manipulator itself, and an equation relating any undefined transformations is obtained. By defining these equations during the interpretation of the task program and progressively solving them, the task is taught. The method is applicable both to practical industrial robot control and to intelligent robot control.

This paper describes a structured programming and teaching system for a robot manipuLator where stress is Laid on the consistent integration of programming and teaching. Tn the PAL programming system being developed at Purdue, tasks are represented in terms of structured Cartesian coordinates. Every motion statement is a request to position and orient the manipulator such that a position equation, representing a closed kinematic chain of homogeneous transformations, is satisfied. In the teaching process, the transformation which represents the position of the end of the manipulator is defined using the manipulator itself, and an equation relating any undefined transformations is obtained. By defining these equations during the interpretation of the task program and progressive by solving them, the task is taught. The method is applicabLe both to practical industrial robot control and to intelligent robot control.