This paper describes an onboard automated hybrid reasoning system for terrain safety assessment using multiple heterogeneous sensors onboard a spacecraft. An innovative feature of this system is integration of multiple sensing modalities and different reasoning engines into a unified approach. Three different frameworks for representation of data uncertainty are considered: fuzzy set theory, Bayesian probability theory, and Dempster-Shafer belief theory. The hybrid reasoning system is composed of three subsystems, namely, multisensor fusion, multidecision fusion, and tier-based fusion selection, where each tier represents a range of spacecraft altitudes. Simulation results are presented to illustrate the multisensor decision fusion methodology described in this paper. The developed capabilities will enable future spacecraft to land safely in more challenging planetary regions with scientifically interesting terrain features.

In this paper, multiple on-board sensors are used to assess the terrain safety in real-time during spacecraft descent. A linguistic, fuzzy rule-based reasoning engine is used to determine terrain safety from sensor measurements and, together with information about required fuel consumption and site science return, provide a figure-of-merit for all possible landing sites. Additional fuzzy rule-sets are used to address spatial and temporal dependence in the reasoning process in order to arrive at a final score for each potential landing site. This landing score is used to retarget the spacecraft if the original landing site is found to be hazardous. Simulation studies are presented for illustration.

In this paper, we present an approach to transfer human expertise for learning off-road navigation behavior to an autonomous mobile robot. The methodology uses the concept of humanized intelligence to combine principal component analysis and neural network learning to embed human driving expertise onto mobile robots. The algorithms are tested in the field using a commercial Pioneer 2AT robot to demonstrate autonomous traversal over rough natural terrain.

This paper presents a new method for integrating terrain maps into a reactive navigation strategy of field mobile robots operating on rough terrain. The method incorporates the Regional Traversability Map, a fuzzy map representation of traversal difficulty of the regional terrain, into the navigation logic. A map-based regional navigation behavior provides speed and direction recommendations based on the current status of the robot. In addition, recommendations from two sensor-based reactive behaviors, local avoid-obstacle and regional traverse-terrain, are fused with the map-based regional behavior to construct a comprehensive navigation system. The algorithms are tested both in graphical simulations and in the field using a commercial Pioneer 2AT robot to demonstrate traversal over rough natural terrain.

Presents a fuzzy terrain-based path planning method for planetary rovers operating on rough natural terrain. The focus of this approach is on planning an optimally safe path of minimum traversal cost, which is calculated from linguistic descriptors of terrain traversability. The method incorporates the traversability map, a fuzzy map representation of traversal difficulty of the terrain, into the path planning logic. The search methodology uses a traversal cost function that is derived directly from this traversability map. The path planning method is developed in detail and experimental results are presented.

Presents novel measures of terrain traversability at three different ranges, namely local, regional and global traversability indices. The local traversability index is related, by a set of linguistic rules, to local obstacles and surface softness within a local perception range, measured by on-board sensors mounted on a robot. The rule-based regional traversability index is computed from the terrain roughness and slope that are expected from video images of the terrain within a regional perception range obtained by on-board cameras. The global traversability index is obtained from a terrain topographic map, and is based on natural or man-made surface features, such as mountains and craters, within the global perception range. Each traversability index is represented by four fuzzy sets with linguistic labels {poor, low, moderate, high}, corresponding to surfaces that are unsafe, moderately unsafe, moderately safe or safe for traversal, respectively. These indices are used to develop a behavior-based navigation strategy for a mobile robot traversing a challenging terrain. The traversability indices form a basis of three navigation behaviors, namely local, regional and global traversal behaviors. These behaviors are integrated with a goal-seeking behavior to ensure that the mobile robot reaches the goal safely while avoiding obstacles and impassable terrain segments. The paper concludes with an illustrative graphical simulation study.

Operational safety and health monitoring are critical matters for autonomous field mobile robots such as planetary rovers operating on challenging terrain. This paper describes relevant rover safety and health issues and presents an approach to maintaining vehicle safety in a mobility and navigation context. The proposed rover safety module is composed of two distinct components: safe attitude (pitch and roll) management and safe traction management. Fuzzy logic approaches to reasoning about safe attitude and traction management are presented, wherein inertial sensing of safety status and vision–based neural network perception of terrain quality are used to infer safe speeds of traversal. Results of initial field tests and laboratory experiments are also described. The approach provides an intrinsic safety cognizance and a capacity for reactive mitigation of robot mobility and navigation risks.

This paper presents a new strategy for behavior-based navigation of field mobile robots on challenging terrain, using a fuzzy logic approach and a novel measure of terrain traversability. A key feature of the proposed approach is real-time assessment of terrain characteristics and incorporation of this information in the robot navigation strategy. Three terrain characteristics that strongly affect its traversability, namely, roughness, slope, and discontinuity, are extracted from video images obtained by on-board cameras. This traversability data is used to infer, in real time, the terrain Fuzzy Rule-Based Traversability Index, which succinctly quantifies the ease of traversal of the regional terrain by the mobile robot. A new traverse-terrain behavior is introduced that uses the regional traversability index to guide the robot to the safest and the most traversable terrain region. The regional traverse-terrain behavior is complemented by two other behaviors, local avoid-obstacle and global seek-goal. The recommendations of these three behaviors are integrated through adjustable weighting factors to generate the final motion command for the robot. The weighting factors are adjusted automatically, based on the situational context of the robot. The terrain assessment and robot navigation algorithms Are implemented on a Pioneer commercial robot and field-test studies are conducted. These studies demonstrate that the robot possesses intelligent decision-making capabilities that are brought to bear in negotiating hazardous terrain conditions during the robot motion.

The concepts of local, regional, and global traversability indices have been introduced by the author (1999, 2000, 2001). These indices represent the suitability of a terrain for traversal by a mobile robot at different scales of resolution. This paper utilizes these indices to develop a navigation strategy for a mobile robot traversing a challenging terrain. The traversability indices form the basis of three navigational behaviors; namely, traverse-local, traverse-regional, and traverse-global behaviors. These behaviors are blended with the seek-goal behavior to ensure that the mobile robot reaches the goal safety while avoiding obstacles and impassable terrain segments. The paper is concluded by an illustrative graphical simulation study.

This paper presents a rule-based fuzzy traversability index that quantifies the ease-of-traversal of a terrain by a mobile robot based on real-time measurements of terrain characteristics retrieved from imagery data. These characteristics include, but are not limited to slope, roughness, hardness, and discontinuity. The proposed representation of terrain traversability incorporates an intuitive, linguistic approach for expressing terrain characteristics that is robust with respect to imprecision and uncertainty in the terrain measurements. The terrain assessment method is tested and validated with a set of real-world imagery data. These tests demonstrate the capability of the terrain classification algorithm for perceiving hazards associated with terrain traversal.

Presents a strategy for autonomous navigation of field mobile robots on hazardous natural terrain using a fuzzy logic approach and a measure of terrain traversability. The navigation strategy comprises three simple, independent behaviors: seek-goal, traverse-terrain, and avoid-obstacle. The recommendations from these three behaviors are combined through appropriate weighting factors to generate the final steering and speed commands that are executed by the robot. The weighting factors are produced by fuzzy logic rules that take into account the current status of the robot. This navigation strategy requires no a priori information about the environment, and uses the on-board traversability analysis to enable the robot to select relatively easy-to-traverse paths autonomously. Field test results obtained from implementation of the proposed algorithms on the commercial Pioneer All Terrain rover are presented. These results demonstrate the real-time capabilities of the terrain assessment and fuzzy logic navigation algorithms.

To tackle the singularity problem, the SC (singularity-consistent) approach was introduced. It achieves very stable control at and around a singularity with feasible joint velocities and no directional error in the end-effector velocity. This approach is very suited for a direct manual teleoperation system because of its errorless character for the direction. Until now, it was applied for the teleoperation of a nonredundant manipulator. In this paper, the SC approach for a 7-DOF manipulator will be addressed. To derive the whole properties of the SC approach, analytical studies for both the adjoint and the determinant of the Jacobian are necessary. However, it is very difficult to realize this goal, since the kinematics of a 7-DOF manipulator is quite complicated. Therefore, here, we establish a method to apply the SC approach to a 7-DOF manipulator numerically without analyzing the kinematic properties. This method, though, cannot realize the whole properties of the SC approach but a stable control at and around the singularities is achieved which is the most important and demanded property of the SC approach. Moreover, this method can also be applied for any type of articulated manipulator if its Jacobian can be defined. The results of our approach have been confirmed by experiments with graphics model.

Operational safety and health monitoring are critical matters for autonomous field mobile robots such as planetary rovers operating on challenging terrain. The paper describes relevant rover safety and health issues and presents an approach to maintaining vehicle safety in a navigational context. The proposed rover safety module is composed of two distinct components: safe attitude (pitch and roll) management and safe traction management. Fuzzy logic approaches to reasoning about safe attitude and traction management are presented, wherein sensing of safety status and perception of terrain quality are used to infer safe speeds of traversal. Results of field tests and laboratory experiments are also described. The approach provides an intrinsic safety cognizance and a capacity for reactive mitigation of navigation risks.

This paper presents a novel technique for real-time measurement of terrain characteristics and incorporation of this information into the navigation strategy of an autonomous mobile robot. The proposed methodology utilizes a fuzzy logic framework for on-board analysis of terrain traversability, and develops a set of fuzzy navigation rules that guide the rover toward the safest and the most traversable terrain. In addition, a simple goal-seeking behavior is used to drive the rover from its initial position to a user-specified goal position. The overall navigation strategy, consisting of terrain-traverse and goal-seeking behaviors, requires no a priori information about the environment, and uses the on-board traversability analysis to enable the rover to select easy-to-traverse paths to the goal autonomously. The terrain traversability navigation rules are tested and validated with a set of physical rover experiments. These experiments demonstrate the real-time capability of the terrain assessment and fuzzy navigation algorithms.

A traversability index is introduced as a new and simple measure for traversability of planetary surfaces by mobile robots. This index is developed using the framework of fuzzy logic, and is expressed by linguistic fuzzy sets that quantify the suitability of the terrain for traversal based on its physical properties, such as slope and roughness. The traversability index is used for classifying planetary surfaces, and provides a simple means for incorporating the terrain quality data (out to about 10 metres) into the rover navigation strategy. A set of fuzzy navigation rules is developed using the traversability index to guide the rover toward the safest and the most traversable terrain. In addition, another set of fuzzy rules is developed to drive the rover from its initial position to a user-specified goal position. These two rule sets are integrated in a two-stage procedure for autonomous rover navigation without a priori knowledge about the environment. A computer simulation study is presented to demonstrate the capability of the rover to reach the goal safely while avoiding impassable terrains.

A new approach to real-time collision avoidance for position-controlled conventional 6-DOF and dexterous 7-DOF arms is developed, and supportive experimental results are presented. The collision avoidance problem is formulated and solved as a position-based force control problem. Virtual forces representing the intrusion of the arm into the obstacle safety zone are computed in real time using a spring-damper model. These forces are then nullified by employing an outer force control loop which perturbs the Cartesian commands for the arm position control system. The approach is implemented and tested on a 7-DOF RRC arm and a set of experiments are conducted in the laboratory. These experiments demonstrate perturbations of the end-effector position and orientation, as well as the arm posture, in order to avoid impending collisions. The proposed approach is simple, computationally fast, requires minimal modification to the arm control system, and applies to whole-arm collision avoidance for 7-DOF arms.

In October 1996, a research and development task was initiated at JPL to develop and demonstrate nonlinear contact control schemes for the dexterous robotic arms planned for the Space Station. This paper reports on the progress made to-date in this task. Specifically, the paper introduces a new class of contact controllers comprised of a nonlinear gain in cascade with a linear fixed-gain PI force controller and PD compliance controller. The nonlinear gains used are simple hyperbolic functions of force error and contact force, respectively. The stability of the closed-loop systems incorporating nonlinear PI and PD controllers are investigated using the Popov stability criterion. Experimental results are presented to demonstrate the efficacy of the nonlinear force and compliance control schemes for a dexterous 7-DOF arm. These results highlight the advantages of the proposed nonlinear contact controllers compared to conventional fixed-gain controllers.

This paper describes the approach and algorithms developed for real-time model-based obstacle detection and distance computation for the NASA Ranger Telerobotic Flight Experiment. Objects of interest, such as manipulator arms or the ranger vehicle and solar arrays, are modeled using a small set of component types: edges, polygonal faces and cylindrical links. Link positions are computed using standard forward kinematics, and distances between object components are computed directly using equations derived from geometry. Prioritized lists of potential obstacles for each manipulator link eliminate needless distance computations and assure that the most likely obstacles are checked, even if the computation is terminated early due to real-time constraints. A test program, utilizing a 3D graphical simulation and providing a graphical user interface for operator control, has been developed and used to test and demonstrate obstacle detection. An earlier paper (1996) described how the obstacle detection results are utilized for collision avoidance.

This paper describes the approach followed in the design of a service robot for health care applications. Under the auspices of the NASA Technology Transfer Program, a partnership was established between JPL and RWI, a manufacturer of mobile robots, to design and evaluate a mobile robot for health care assistance to the elderly and the handicapped. The activities of the first phase of the project include the development of a multi-modal operator interface, and the design and fabrication of a manipulator arm for the mobile robot. This paper describes the architecture of the system, the features of the manipulator arm, and the operator interface.

The paper presents experimental results that demonstrate a new approach to real-time collision avoidance for 7-DOF arms. The collision avoidance problem is formulated and solved as a force control problem. Virtual forces opposing intrusion of the arm into the obstacle safety zone are computed in real time. These forces are then nullified by employing an outer feedback loop which perturbs the arm Cartesian commands for the inner position control system. The approach is implemented and tested on a 7-DOF RRC arm and a set of experiments are conducted in the laboratory. These experiments demonstrate perturbations of the end-effector position and orientation, as well as the arm configuration, in order to avoid impending collisions. The approach is simple, computationally fast, requires minimal modification to the arm control system, and applies to whole-arm collision avoidance.

This paper considers the problem of controlling the motion of highly redundant manipulators to achieve a desired set of tasks. The paper develops two real-time control modules for implementation with the Sequential Modular Architecture for Robotics and Teleoperation (SMART) which has been developed at Sandia National Laboratories. SMART provides a "generic" framework within which individual subsystems can be combined, simulated, and implemented for real-time control of complex robotic systems. Control modules developed in the paper include an adaptive gravity compensation controller and a real-time redundancy resolution strategy. The adaptive gravity compensation controller is a position regulation strategy that requires no information regarding the manipulator dynamic model or payload and can be proven to be passive. The redundancy resolution strategy uses a damped-least-squares (DLS) inverse kinematic formulation. The example controller modules are demonstrated through computer simulation on a 20-DOF serpentine manipulator.

The paper presents experimental results that demonstrate a new approach to real-time collision avoidance for 7-DOF arms. The collision avoidance problem is formulated and solved as a force control problem. Virtual forces opposing intrusion of the arm into the obstacle safety zone are computed in real time. These forces are then nullified by employing an outer feedback loop which perturbs the arm Cartesian commands for the inner position control system. The approach is implemented and tested on a 7-DOF RRC arm and a set of experiments are conducted in the laboratory. These experiments demonstrate perturbation of the end-effector position and orientation, as well as the arm configuration, in order to avoid impending collisions The approach is simple, computationally fast, requires minimal modification to the arm control system, and applies to whole-arm collision avoidance.

This paper describes an online approach to whole-arm collision avoidance for the NASA Ranger Telerobotic Flight Experiment. Using a geometric world model, minimum distances and nearest points between parts of the active dexterous 7-DOF manipulator and potential obstacles are computed by the Ranger obstacle detection software. Obstacle data is then used to compute virtual repulsive forces which perturb the operator-commanded manipulator Cartesian motions in order to avoid collisions. The virtual forces are computed at the tool-tip for end-effector position perturbation, at the wrist for end-effector orientation perturbation, and on the upper and lower arm links for arm angle perturbation. The paper also describes the software development environment, utilizing a 3D graphical simulation and providing a graphical user interface for display and operator command. Results of several test runs illustrating end-effector position and orientation perturbation, as well as arm angle perturbation, are presented.

This paper describes the architecture and performance of a PC-based configuration controller for dexterous 7-DOF manipulators. The computing platform is a 486-based personal computer equipped with a bus extender to access the robot Multibus controller, together with a single-board computer as the graphical engine, and a parallel I/O board to interface with a force-torque sensor mounted on the manipulator wrist. The Windows environment is enhanced by the iRMX real-time operating system that runs the configuration control algorithms for redundancy resolution. The position control algorithm is executed every 2.5 ms; motions can be simulated and displayed in real-time by the graphical engine on a separate monitor. The results of several experiments carried out with a Robotics Research manipulator have shown motion control capabilities comparable to those obtained with more extensive computing systems, thus validating the use of PCs for dexterous manipulator control. PC-based motion controllers for RRC arms, incorporating the configuration control software, are currently produced by the Robotics Research Corporation.

This paper presents a simple online approach for motion control of rover-mounted manipulators. An integrated kinematic model of the rover-plus-manipulator system is derived which incorporates the nonholonomic rover constraint with the end-effector task. The redundancy introduced by the rover mobility is exploited to perform a set of user-specified additional tasks during the end-effector motion. The configuration control approach is utilized to satisfy the nonholonomic rover constraint, while accomplishing the end-effector motion and the redundancy resolution goals simultaneously. This framework allows the user to assign weighting factors to the rover movement and manipulator motion, as well as to each task specification. The computational efficiency of the control scheme makes it particularly suitable for real-time implementation. The proposed method is applied to a planar two-jointed arm mounted on a rover, and computer simulation results are presented for illustration.

This paper presents a simple and robust approach to achieving collision avoidance for kinematically redundant manipulators at the control-loop level. The proposed scheme represents the obstacle avoidance requirement as inequality constraints in the manipulator workspace, and ensures that these inequalities are satisfied while the end-effector tracks the desired trajectory. The control scheme is the damped-least-squares formulation of the configuration control approach implemented as a kinematic controller. Computer simulation and experimental results are given for a Robotics Research 7 DOF redundant arm and demonstrate the collision avoidance capability for reaching inside a truss structure. These results confirm that the proposed approach provides a simple and effective method for real-time collision avoidance.>

This paper present a new adaptive scheme for motion control of robot manipulators. The proposed controller is very general and computationally efficient since it does not require knowledge of either the mathematical model or the parameter valves of the robot dynamics, and is implemented without calculation of the robot inverse kinematic transformation. It is shown that the control strategy is globally stable in the presence of bounded disturbances, and that in the absence of disturbances the ultimate bound on the size of the residual tracking errors can be made arbitrarily small. Computer simulation results are given for a PUMA 560 manipulator, and demonstrate that accurate and robust trajectory tracking are achieved by using the proposed controller. Experimental results are presented for a PUMA 560 manipulator and confirm that the control scheme provides a simple and effective means of obtaining high performance trajectory tracking.>

This paper describes the design and implementation of a real-time control system with multiple modes of operation for a mobile redundant dexterous manipulator. The manipulator under study is a seven degree-of-freedom (DOF) arm from Robotics Research Corporation, mounted on a motorized platform. The manipulator-plus-platform system has 2-DOF for the task of hand placement and orientation. The redundancy resolution is achieved by accomplishing two additional tasks using the configuration control technique. The system allows a choice of arm angle control or collision avoidance for the seventh task and platform placement or elbow angle control for the eighth task. In addition, joint limit avoidance task is automatically invoked when any of the joints approach their limits. The system is robust to singularities, and also provides the capability of assigning weighting factors to end-effector and redundancy resolution tasks. The motion control algorithms are executed at 1.1 ms on two MC68040 processors in a VME-bus environment running the VxWorks real-time operating system. The paper describes the hardware and software components of the VME environment. Experimental results are also presented.>

This paper addresses the problem of controlling a manipulator in compliant motion while in contact with an environment having an unknown stiffness. Admittance control is used as an explicit force control scheme in which a force setpoint is specified and is tracked by the force compensator. Two adaptive PID and PI force compensators are proposed. The compensators ensure robust tracking of step force setpoints and rejection of constant disturbances. Since the environmental stiffness can typically vary by several orders of magnitude, compensator adaptation is used to ensure a stable and uniform system performance. Dynamic simulation results for a 7 DOF Robotics Research arm are presented to demonstrate the efficacy of the proposed admittance control scheme in executing contact tasks.>

This paper presents two adaptive schemes for compliance control of redundant manipulators. The first scheme is developed using an adaptive impedance control approach for torque-controlled manipulators, while the second strategy is an adaptive admittance controller for position-controlled manipulators. The proposed controllers are very general and computationally efficient since they do not require knowledge of the manipulator dynamic model or parameter values of the manipulator or the environment, and are implemented without calculation of the inverse dynamics or inverse kinematic transformation. It is shown that the control strategies are globally stable in the presence of bounded disturbances, and that in the absence of disturbances the ultimate bound on the size of the system errors can be made arbitrarily small. The capabilities of the proposed admittance controller are illustrated through laboratory experiments with a Robotics Research Corporation seven degree-of-freedom (DOF) manipulator.>

Presents a simple and computationally efficient approach of online coordinated control of mobile robots consisting of a manipulator arm mounted on a mobile base. The effect of base mobility on the end-effector manipulability index is discussed. The base mobility and arm manipulation degrees of freedom are treated equally as the joints of a kinematically redundant composite robot. The redundancy introduced by the mobile base is exploited to satisfy a set of user-defined additional tasks during the end-effector motion. A simple online control scheme is proposed which allows the user to assign weighting factors to individual degrees-of-mobility and degrees-of-manipulation, as well as to each task specification. The computational efficiency of the control algorithm makes it particularly suitable for real-time implementations. A computer simulation study is presented for a spatial three-jointed manipulator mounted on a one-DOF mobile platform, and demonstrates the online coordination of mobility and manipulation.

Presents two simple and computationally efficient schemes for force tracking using impedance control. The schemes generate the reference position trajectory required to produce a desired contact force despite lack of knowledge of the environmental stiffness and location. The first scheme uses direct adaptive control to generate the reference position online as a function of the force tracking-error. The second scheme utilizes an indirect adaptive strategy in which the environmental parameters are estimated online, and the required reference position is computed based on these estimates. Simulation studies are presented for a 7-DOF Robotics Research arm using full arm dynamics and demonstrate that the adaptive schemes are able to compensate for uncertainties in both the environmental stiffness and location, so that the end-effector applies the desired contact force while exhibiting the specified impedance dynamics.

Graphics simulation and real-time implementation of configuration control schemes for a redundant seven-degree-of-freedom (7-DOF) Robotics Research arm are described. The arm kinematics and motion control schemes are described briefly. This is followed by a description of a graphics simulation environment for 7-DOF arm control on the Silicon Graphics IRIS Workstation. Computer simulation results are presented to demonstrate elbow control, collision avoidance, and optimal joint movement as redundancy resolution goals. The laboratory setup for experimental validation of motion control of the 7-DOF Robotics Research arm is then described. The configuration control approach is implemented on a Motorola-68020/VME-bus-based real-time controller, with elbow positioning for redundancy resolution. Experimental results demonstrate the efficacy of configuration control for real-time control.>

Applications of the configuration control approach to motion control of redundant 7 DOF (degree-of-freedom) arms are described. This approach provides a unified framework for resolution of redundancy to accomplish a broad range of objectives. The configuration control approach is briefly described, and a graphics simulation environment for control of 7 DOF Robotics Research arms is discussed. Computer simulation results are presented to demonstrate elbow control, obstacle avoidance, and optimal joint motion as redundancy resolution goals for the 7 DOF arm.>

A kinematic analysis of anthropomorphic 7 DOF serial link spatial manipulators with revolute joints is presented. To determine joint angles uniquely for a given end-effector position and orientation, the redundancy is parameterized by a scalar variable which corresponds to the angle between the arm plane and a reference plane. The forward kinematic mappings from joint-space to end-effector coordinates and arm angle and the augmented Jacobian matrix which gives end-effector and arm angle rates as functions of joint rates are given. Conditions under which the augmented Jacobian becomes singular are given and are shown to correspond to the arm being either at a kinematically singular configuration or at a nonsingular configuration for which the arm angle ceases to parameterize the redundancy.>

A robust control scheme to accomplish accurate trajectory tracking for an integrated system of manipulator-plus-actuators is proposed. The control scheme comprises a feedforward and a feedback controller. The feedforward controller contains any known part of the manipulator dynamics that can be used for online control. The feedback controller consists of adaptive position and velocity feedback gains and an auxiliary signal which is simply generated by a fixed-gain proportional/integral/derivative controller. The feedback controller is updated by very simple adaptation laws which contain both proportional and integral adaptation terms. By introduction of a simple sigma modification to the adaptation laws, robustness is guaranteed in the presence of unmodeled dynamics and disturbances.>

The author presents a simple decentralized adaptive control scheme for multijoint robot manipulators based on the independent joint control concept. The control objective is to achieve accurate tracking of desired joint trajectories. The proposed control scheme does not use the complex manipulator dynamic model, and each joint is controlled simply by a PID (proportional-integral-derivative) feedback controller and a position-velocity-acceleration feedforward controller, both with adjustable gains. Simulation results are given for a two-link direct-drive manipulator under adaptive independent joint control. The results illustrate trajectory tracking under coupled dynamics and varying payload. The proposed scheme is implemented on a MicroVAX II computer for motion control of the three major joints of a PUMA 560 arm. Experimental results are presented to demonstrate that trajectory tracking is achieved despite coupled nonlinear joint dynamics.>

A simple approach for controlling the manipulator configuration over the entire motion, which is based on augmentation of the manipulator forward kinematics, is presented. A set of kinematic functions is defined in Cartesian or joint space to reflect the desirable configuration. The user-defined kinematic functions and the end-effector Cartesian coordinates are combined to form a set of task-related configuration variables as generalized coordinates for the manipulator. A task-based adaptive scheme is then utilized to control directly the configuration variables so as to achieve tracking of some desired reference trajectories throughout the robot motion. This accomplishes the basic task of desired end-effector motion, while utilizing the redundancy to achieve any additional task through the desired time variation of the kinematic functions. Simulation results for a direct-drive two-link arm are given to illustrate the proposed control scheme. The scheme has also been implemented for real-time control of three links of a PUMA 560 industrial robot, and experimental results are presented and discussed. The simulation and experimental results validate the configuration control scheme, and demonstrate its capabilities for performing various realistic tasks.>

A decentralized adaptive control is proposed to stabilize and track the nonlinear interconnected subsystems with unknown parameters. The adaptation of the controller gain is derived by using model reference adaptive control theory based on Lyapunov's direct method. The adaptive gains consist of sigma , proportional, and integral combination of the measured and reference values of the corresponding subsystem. The proposed control is applied to the joint control of a two-link robot manipulator, and the performance in computer simulation corresponds with what is expected in theoretical development.>

The author presents a simple decentralized adaptive control scheme for multijoint robot manipulators based on the independent joint control concept. The proposed control scheme for each joint consists of a PID (proportional integral and differential) feedback controller and a position-velocity-acceleration feedforward controller, both with adjustable gains. The static and dynamic couplings that exist between the joint motions are compensated by the adaptive independent joint controllers while ensuring trajectory tracking. The proposed scheme is implemented on a MicroVAX II computer for motion control of the first three joints of a PUMA 560 arm. Experimental results are presented to demonstrate the trajectory tracking is achieved despite strongly coupled, highly nonlinear joint dynamics. The control scheme presented is computationally very fast and is amenable to parallel processing implementation within a distributed computing architecture, where each joint is controlled independently by a simple algorithm on a dedicated microprocessor.>

The authors put forward a simple scheme for multivariable control of robot manipulators. The scheme is composed of an inner-loop stabilizing controller and an outerloop tracking controller. The inner loop utilizes a multivariable PD (proportional differential) controller to stabilize the robot by placing the poles at some desired location. The outer loop uses a multivariable PID (proportional integral differential) controller to achieve input-output decoupling and trajectory tracking. The gains of the PD and PID controllers are related directly to the linearized robot model by simple closed-form expressions. The controller gains are updated online to cope with variations in the robot model for gross motions and payload change. Alternatively, the use of high-gain controllers for gross motion and payload change are discussed.>

A new adaptive control scheme for direct control of manipulator end-effector to achieve trajectory tracking in Cartesian space is developed in this paper. The control structure is obtained from linear multivariable theory and is composed of simple feedforward and feedback controllers and an auxiliary input. The direct adaptation laws are derived from model reference adaptive control theory and are not based on parameter estimation of the robot model. The utilization of feedforward control and the inclusion of auxiliary input are novel features of the present scheme and result in improved dynamic performance over existing adaptive control schemes. The adaptive controller does not require the complex mathematical model of the robot dynamics or any knowledge of the robot parameters or the payload; and is computationally fast for on-line implementation with high sampling rates.

The paper presents a simple scheme for linear multivariable control of multi-link robot manipulators. The control scheme consists of multivariable feedforward and feedback controllers. The feedforward controller is the minimal inverse of the linearized model of robot dynamics and contains only proportional-double-derivative (PD2) terms. This controller ensures that the manipulator joint angles track any reference trajectories. The feedback controller is of proportional-derivative (PD) type and achieves stability and pole placement. This controller reduces any initial tracking error to zero as desired. The two controllers are independent of each other and are designed separately based on the linearized robot model and then integrated in the overall control scheme.