This paper presents development of energyefficient and fault-tolerant control of multiphase nonsinusoidal PM synchronous machines by making use of the Hamiltonian of optimal control theory. An analytical solution for the optimallinearization control is derived in a closed-form from the maximum principle formulation to linearize the machines and at same time to maximize machine efficiency for non-constant operational torque and speed while automatically deferring output voltage saturation. The controller can achieve voltage-totorque linearization even for faulty motors with open-circuited phase(s) making it suitable for high-risk applications. Experimental results are appended to underpin the performance of the energy-efficient controller.

The projection-based control of a rather general class of robots subject to linear and quadratic inequality constraints pertinent to unilateral contacts and friction cones is presented. The controller can also take into account other physical constraints levied by actuator saturation limits and/or existence of some unactuated joints, and can minimize actuation effort for redundant systems. Moreover, since the controller is not based on derivation of minimal-order dynamics model, it can easily handle contact switching. Therefore, a single controller can be used for different constraint conditions, which is very appealing for applications such as legged robots or grasping robots. The orthogonal decomposition of the generalized force vector yields the primary and secondary control inputs, which are used for motion control and interaction control, respectively. It is shown that the problem of minimizing actuation effort subject to the constraints due to the friction cones, unilateral contacts, and actuation limitations, can be transcripted into an optimization programming in terms of the secondary control variable. The latter optimization problem has a quadratic cost function accompanied by a set of quadratic and linear inequality constraints plus linear equality constraints that can be solved by barrier methods.

This paper presents a non-minimal order dynamics model for many analysis, simulation, and control problems of constrained mechanical systems passing through singular configurations during their motion by making use of linear projection operator. The distinct features of this model describing dynamics of the dependent coordinates are: i) The mass matrix M̅(q) is always positive definite even at singular configurations; ii) matrix equation is skew symmetric, where all nonlinear terms are lumped into vector C̅(q, q̇)q̇ after elimination of constraint forces. Eigenvalue analysis shows that the condition number of the constraint mass matrix can be minimized upon adequate selection of a scalar parameter called “virtual mass” thereby reducing the sensitivity to round-off errors in numerical computation. It follows by derivation of two oblique projection matrices for computation of constraint forces and actuation forces. It is shown that projection-based model allows feedback control of dependent coordinates which, unlike reduced-order dependent coordinates, uniquely define spatial configuration of constrained systems.

This paper focuses on optimal and seamless guidance of robotic manipulators, in both pre- and post-grasp phases, to capture and stabilize a tumbling and drifting free-floating object. All dynamics parameters of the object are assumed to be unknown with the exception its mass and the trace of the inertia matrix. In the pre-grasping phase, an optimal trajectory is planned to intercept a grasping point on the target with zero relative velocity subject to acceleration limit and adequate target alignment while minimizing the fly time and/or distance. In the post-grasping phase, the manipulator damps out the targets's angular and linear momentums as quickly as possible subject to the constraint that the magnitude of the exerted force and torque remain below their pre-specified values. The unknown parameters in addition to the relative linear and angular velocities of the target needed for the motion planning are estimated by a Kalman filter estimator. Finally, an end-to-end validation of the robotic operation for grasping and stabilizing a tumbling/drifting free-floating object using the proposed robot motion planning scheme is presented by combination of experimental and simulation results.

Time delay in attitude sensors is one of the performance limiting factors in controlling the satellite attitude. In this paper, we investigate attitude control of a fully actuated satellite in presence of constant and known delay in attitude measurement. The proposed controller consists of a matrix gain which is computed by solving a time varying matrix differential equation depending on the time delay. We assume that the moment-of-inertia matrix of the satellite is unknown. The controller guarantees asymptotic convergence of the satellite attitude and angular velocity to their desired values in presence of delay. Finally, a simulation example is presented that illustrates performance of the proposed controller in presence of delayed attitude measurement.

Visually guided robotic capturing of a moving object often requires long-term prediction of the object motion not only for a smooth capture but because visual feedback may not be continually available, e.g., due to vision obstruction by the robotic arm, as well. This paper presents a combined prediction and motion-planning scheme for robotic capturing of a drifting and tumbling object with unknown dynamics using visual feedback. A Kalman filter estimates the states and a set of dynamics parameters of the object needed for long-term prediction of the motion from noisy measurements of a vision system. Subsequently, the estimated states, parameters, and predicted motion trajectories are used to plan the trajectory of the robot's end-effector to intercept a grapple fixture on the object with zero relative velocity (to avoid impact) in an optimal way. The optimal trajectory minimizes a cost function, which is a weighted linear sum of travel time, distance, cosine of a line-of-sight angle (object alignment for robotic grasping), and a penalty function acting as a constraint on acceleration magnitude. Experiments are presented to demonstrate the robot-motion planning scheme for autonomous grasping of a tumbling satellite. Two robotics manipulators are employed: One arm drifts and tumbles the mockup of a satellite, and the other arm that is equipped with a robotic hand tries to capture a grapple fixture on the satellite using the visual guidance system.

The servomotors used in the joints of a manipulator or wheels of a rover in high risk applications, such as space applications, should be capable of continued functional operation even if insulation failure or open-circuit of a winding occur. This paper presents a fault-tolerant (FT) torque con troller for brushless motors that can maintain accurate torque production with minimum power dissipation subject to current limitations even if one of motor phases fails. The controller is developed based on the Fourier series model of the motor back-EMF waveform and the cogging torque. The faulty phase is detected from the covariance of the estimation error of a voltage observer. Subsequently, the phase currents of the remaining phases are optimally reshaped so that the motor accurately generates torque as requested while minimizing power loss subject to maximum current limitation of the current amplifiers. A closed-form solution to the optimization programming problem is found by using the Kuhn-Tucker theorem; rendering the control approach suitable for real-time implementation. Experimental results illustrate the capability of the FT controller to achieve ripple-free torque performance during a phase failure at the expenses of increasing the mean power loss by 28%.

This paper presents optimal torque control of brushless DC motor with any back-emk waveform that minimizes power dissipation subject to voltage and current limits of the motor's drivers/amplifiers. When one or more phases reach the voltage or/and current limits, the controller optimally reshapes the stator currents of the remaining phases for continuing accurate torque production. This allow the motor to operate above the rated speed and torque that would be achieved without current reshaping. In the event that an open-circuit or short-circuit of a winding occurs, the torque controller can also isolate the faulty phase in order to generate torque as requested given the voltage and current constraints of the healthy phases. A closed-form solution for the optimal phase currents is obtained rendering the control algorithm suitable for real-time implementation. Experimental results illustrate the capability of the controller to achieve precise torque production during voltage/current saturation of the motor's drivers or a phase failure.

Bilateral teleoperation systems have been extensively utilized for implementing tasks in remote or hazardous environments. However, due to the cognitive limitations of the human operator, efficient teleoperation of complex robotic system operating in cluttered environments has been difficult to achieve. In this paper, we study the control problem of a semi-autonomous teleoperation system, where the redundant slave robot can autonomously satisfy several constraints while tracking the position of the master robot in the task space. Considering heterogeneous master and slave robots, we first develop a control algorithm to ensure task space position and velocity tracking between the master and slave robots in the presence of dynamic uncertainties and communication delays. The redundancy of the slave robot is then utilized for achieving sub-task control, such as singularity avoidance, joint limits, and collision avoidance. The control algorithms for the proposed semi-autonomous teleoperation system are validated using numerical simulations on a non-redundant master and a redundant slave robot.

This paper investigates 3-dimensional Simultaneous Localization and Mapping (SLAM) and the corresponding observability analysis by fusing data from landmark sensors and a strap-down Inertial Measurement Unit (IMU) in an adaptive Kalman filter (KF). In addition to the vehicle's states and landmark positions, the self-tuning filter estimates the IMU calibration parameters as well as the covariance of the measurement noise. Examining the observability of the 3D SLAM system leads to the the conclusion that the system remains observable provided that at least one of these conditions is satisfied i) two known landmarks of which the connecting line is not collinear with the vector of the acceleration are observed ii) three known landmarks which are not placed in a straight line are observed.

The equality and inequality constraints on constraint force and/or the actuator force/torque arise in several robotic applications, for which different controllers have been specifically developed. This paper presents a unified approach to control a rather general class of robotic systems with closed loops under a set of linear equality and inequality constraints using the notion of projection operator. The controller does not require the kinematic constraints to be independent, i.e., systems with time-varying topology can be dealt with, while demanding minimum-norm actuation force or torque in the case that the system becomes redundant. The orthogonal decomposition of the generalized force yields the tangential (potent) and normal (impotent) components leads. The tangential component is obtained using projected inverse dynamics control law, while the optimal normal component is found through solving a quadratic programming problem, in which the equality and inequality constraints are derived to be equivalent to the originally specified ones. Finally, a case study is presented to demonstrate how the control technique can be applied to multi-arms manipulation of an object.

Robotic capture of a tumbling target-satellite means that the space robot's hand and the target grapple point arrive at a rendezvous point with the same velocity and then the chase vehicle mechanically connects into the target using a grapple device. This paper is focused on optimal control of the space manipulator in the postcapture phase so as to bring the tumbling non-cooperative satellite to rest in minimum time while ensuring that the magnitude of the interaction torque between the manipulator and target remains below a prescribed value. First, we seek fast detumbling maneuvers of the target satellite subjected to the torque restriction. The theory of optimal control and Pontryagin's principle are applied to obtain a closed-form solution for the optimal path planning problem, giving a great deal of insight: the vector of the interaction torque is aligned opposite to the direction of the instantaneous angular momentum vector. Second, a coordination control for combined system of the space robot and the target satellite, which acts as the manipulator payload, is developed so that the robot tracks the optimal path while regulating the attitude of the chase vehicle to a desired value. A preliminary illustrative example is appended.

This paper focuses on the guidance of a robot manipulator to capture a tumbling satellite and then bring it to state of rest (detumbling). First, a coordination control for combined system of the space robot and the target satellite, which acts as the manipulator payload, is presented so that the robot tracks the optimal path while regulating the attitude of the chase vehicle to a desired value. Subsequently, two optimal trajectories for the pre- and post-capture phases are designed. In the pre-capturing phase, the manipulator maneuvers are optimized by minimizing a cost function which includes the time of travel and the weighted norms of the end-effector velocity and acceleration, subject to the constraint that the robot end-effector and a grapple fixture on the satellite arrive at the rendezvous point with the same velocity. In the post-grasping phase, the manipulator dumps the initial velocity of the tumbling satellite in minimum time subject to the constraint that the magnitude of the torque applied to the satellite remains below a safe value. Simulation and experimental results are appended.

A heavy payload attached to the wrist force/moment (F/M) sensor of a manipulator can fail the conventional impedance controller to establish a desired impedance due to the non-contact components of the force measurement, i.e., the inertial and gravitational forces of the payload. This paper proposes an impedance control scheme for such a manipulator to accurately shape its force-response without needing any acceleration measurement. Therefore, no wrist accelerometer or a dynamic estimator for compensating the load inertial forces are required. The impedance controller is further developed using an inner/outer loop feedback approach that allows not only to overcome the robot dynamics uncertainty, but also to specify the target impedance model in a general form, e.g., a nonlinear model. The stability and convergence of the impedance controller are analytically investigated, and the results show that that control input remains bounded provided that the desired inertia is selected to be different from the payload inertia. Experimental results demonstrate that the proposed impedance controller is able to accurately shape the impedance of a manipulator carrying a relatively heavy load according to a desired impedance model.

This paper presents tracking and set point controllers for parallel mechanism based on the notion of a projection operator. The controller reported here works whether the system is overactuated or not; plus one does not need to derive the minimal-order dynamics model of the system. Since the dimension of projection matrix is fixed, the projection-based controller does not need to change its structure whenever the mechanical system changes its topology or number of degrees of freedom. Moreover, the derivation of the projection-based controller seems to be simpler than the inverse dynamics controller derived using Lagrange-D'Almbert formulation. This is because the structure of the former controller can be obtained from the Jacobian matrix of the constraints, which, in turn, can be deduced from the linkage geometry. The stability of the projection-based controllers are rigourously proved, while the condition for the controllability of parallel manipulators is also derived in detail. Finally, experimental results are appended.

This paper focuses on the design and test results of an adaptive variation of Kalman filter (KF) estimator based on fusing data from Inertial Measurement Unit (IMU) and two Real Time Kinematic (RTK) Global Positioning Systems (GPS) for driftless 3-D attitude determination and robust position estimation of mobile robots. GPS devices are notorious for their measurement errors vary from one point to the next. Therefore in order to improve the quality of the attitude estimates, the covariance matrix of measurement noise is estimated in real time upon information obtained from the differential GPS measurements, so that the KF filter continually is ¿tuned¿ as well as possible. No a priori knowledge on the direction cosines of the gravity vector in the inertial frame is required as these parameters can be also identified by the KF, relieving any need for calibration. Next, taking advantage of the redundant GPS measurements, a weight least-squares estimator is derived to weight the GPS measurement with the ¿good¿ data more heavily than the one with ¿poor¿ data in the estimation process leading to a robust position estimation. Test results are presented showing the performance of the integrated IMU and two GPS to estimate the attitude and location of a mobile robot moving across uneven terrain.

This paper presents a new conceptual design for reconfigurable robots. Unlike conventional reconfigurable robots, our design does not achieve reconfigurability by utilizing modular joints. Rather, the robot is equipped with passive joints, i.e., joints without actuator or sensor, which permit changing the Denavit-Hartenberg (DH) parameters such as the link length and twist angle. The passive joints will become controllable when the robot forms a closed kinematic chain. Also, each passive joint is equipped with a built-in brake mechanism that is normally locked, but the lock can be released whenever the parameters are to be changed. Such a versatile and agile robot is particularly suitable for space application for its simple, compact, and light design. The kinematics and recalibration of this kind of reconfigurable robot are thoroughly analyzed. A stable reconfiguration-control algorithm is devised to take the robot from one configuration to another by directly regulating the passive joints to the associated, desired DH parameters. Conditions for the observability and the controllability of the passive joints are also derived in detail.

A unified formulation for deriving the equations of motion of constrained or unconstrained multi-body systems (MBS) in terms of (reduced) quasi-velocities is presented. In this formulation, the square-root of the mass matrix is used to transform disparate units into homogeneous units for all the quasi-velocities resulting the gauge invariance. We show that the square-root factorization of mass matrix and hence the quasi-velocities are not unique, rather they are related by unitary transformations. Subsequently, we show that a particular transformation leads to significant simplification of the dynamic modeling. The number of differentiations required to derive the equations of motion is reduced. This fact combined with the fact that the expression of the inverse of the mass matrix factorization can be given in a closed-form make the formulation suitable for symbolic manipulation or numerical computation. Moreover, in this formulation the equations of motion are decoupled from those of constrained force and each system has its own independent input (that is not attainable by other formulations). This allows the possibility to develop a simpler force control action that is totally independent from the motion control action. The structure of the formulation is also suitable for control purposes. Tracking control and regulation control of constrained multi-body systems based on a combination of feedbacks on the vectors of the quasi-velocity and the configuration variables (which may contain redundant variables) are presented.

A gauge-invariant formulation for deriving the equations of motion of constrained or unconstrained multi-body systems (MBS) in terms of (reduced) quasi-velocities is presented. We show that the square-root factorization of mass matrix and hence the quasi-velocities are not unique, rather they are related by unitary transformations. Subsequently, we show that a particular transformation leads to significant simplification of the dynamic modeling. In this formulation the equations of motion are decoupled from those of constrained force and each system has its own independent input (that is not attainable by other formulations). This allows the possibility to develop a simpler force control action that is totally independent from the motion control action. Moreover, the square-root of the mass matrix is used to transform disparate units into homogeneous units for all the reduced quasi-velocities making the formulation suitable for hybrid force/motion control of robots.

This paper is focused on an adaptive vision system for the guidance of a robot to intercept a non-cooperative target satellite with unknown dynamics parameters. A Kalman filter is developed to reliably estimate the states of the object as well as all of its inertial parameters - namely, the moment-of-inertia ratios, the center-of-mass location, and the orientation of the principle axes - from vision information. The estimates are then used to optimally plan the motion of the manipulator. The optimization performance index includes the time of travel and the weighted norms of the end-effector velocity and acceleration, and it is subject to the conditions that the robot end-effector and the satellite gasping point arrive at the rendezvous point with the same velocity and that the interception occurs within the robot reach. The variational method is used to find the optimal path, which turns out to be the solution of a fourth-order differential equation. Subsequently, a closed-form solution is obtained. The solution to the optimal terminal-time problem is also obtained from the Hamiltonian of the entire system. Experiments are conducted by using a robotic arm to move a satellite mockup according to orbital mechanics and measuring the satellite pose by a laser camera system. The results demonstrate a successful grasping even though the inertial parameters are not known by the control system.

The advantages of reconfigurable robots have been discussed in the specialized literature. Conventionally, reconfigurability was a direct result of using modular joints. In this paper we discuss the configuration control and recalibration of a different class of reconfigurable robots, one which is equipped with lockable cylindrical joints with no actuators or sensors. Such a robot can be as versatile and agile as a hyper-redundant manipulator, but with a simpler, more compact, lighter design. A passive joint becomes controllable when the robot forms a closed kinematic chain and the joint lock is released. After reconfiguration, the values of the passive joints are computed from the value of the active joints using inverse kinematics of the closed chain. That problem is solved using a globally uniformly asymptotically stable scheme based on closed-loop inverse kinematics (CLIK). An asymptotically stable reconfiguration controller is also devised that takes the robot from one configuration to another by directly regulating the values of the passive joints. The controller has a rather simple structure, which only relies on the robot gravity and kinematics models. Conditions for the observability and the controllability of the passive joints are also derived in detail, and some numerical results are reported.

Accurate torque control of a brushless motor requires the motor’s torque characteristics, which can be captured by a periodic function in motor angle. This paper presents a direct adaptive controller for torque control of brushless motors, which estimates the Fourier coefficients of the periodic function based on the measurements of motor phase voltage and angle. It will be analytically shown that the proposed adaptive controller achieves torque tracking regardless of the trajectories of input signals. Moreover, the adaptive controller does not rely on the modeling of the mechanical load, and that makes control implementation simple and modular. Experimental results obtained from the McGill/MIT motor have demonstrated that motor torque converges to the command torque.

A noise-adaptive variant of the Kalman filter is presented for the motion estimation and prediction of a freefalling tumbling satellite as seen from a satellite in a neighboring orbit. A complete dynamics model, including aspects of orbital mechanics, is incorporated for accurate estimation. Moreover, a discrete-time model of the entire system which includes the state-transition matrix and the covariance of process noise are derived effectively in a closed form, which is essential for the real-time implementation of the Kalman filter. We will show that the translational and rotational measurements are coupled and consequently derive the corresponding observation matrix. The statistical characteristics of the measurement noise is formulated by a state-dependent covariance matrix. This model allows additive quaternion noise, while preserving the unit-norm property of the quaternion. The estimator takes the noisy measurements from a laser vision system with unknown and possibly varying statistical noise properties, and subsequently the estimator adaptively estimates the full sates, i.e., the pose and the velocities, in addition to the covariance of the measurement noise and the inertial parameters of the target satellite. Simulations and experiments conducted will demonstrate the quality performance of the adaptive estimator.

This work describes the design and development of a mechatronics testbed facility allowing high fidelity and low cost testing of a manipulator's joint-prototypes in a highly flexible environment. The testbed system consists of a set of load motors whose shafts are connected to those of the joint prototypes through some torque transducers. A controller modifies the dynamics of the load motors to match the nonlinear and coupled dynamics of a manipulator links. This is made possible by incorporating the measurement of joint angles, velocities, and joint torques as well as dynamics model of the manipulator links in a composite feedforward/feedback loop. The testbed system also permits thermal-vacuum testing in order to simulate a space-like hostile environment. This makes the facility particularly useful for development and validation of new joints for space manipulators. The system is experimentally validated by comparing trajectories of the joint angles, velocities, and torques of a set of joint prototypes obtained by installing them first on a real robot and then on the mechatronics testbed

A system emulation that can be used for testing a spacecraft control system with all of its hardware in place, in a 1-g laboratory environment, is presented. The system is comprised of a manipulator whose end-effector rigidly grasps a functional spacecraft, a six-axis force/moment (F/M) sensor placed at the interface of the spacecraft and the manipulator, and a control system. The controller takes the values of the force/moment as well as the manipulator's joint angles and velocities and issues torque command to drive the manipulator so that the motion of the spacecraft model in the presence of external forces replicates 0-g motion dynamics of a flight spacecraft. The control system can also modify the inertia! properties of the spacecraft so as to match those of an actual spacecraft, even if the latter is flexible and the former is rigid. The stability of the overall system is analytically investigated, and the results show that the system remains stable provided that the inertia! properties of two spacecraft are different. Important practical issues such as calibration and analysis of the sensitivity to noise and disturbance are also presented. Finally, the concept of the 0-g emulation of spacecraft is demonstrated by conducting an experiment using a robotic testbed at the Canadian Space Agency (CSA)

A procedure for the calibration of the force-moment sensor of a space robot is reported. In terrestrial applications, such sensors can be calibrated by measuring the sensor output while under known static loads, which are most easily applied using known weights. In zero-g environment, such an approach does not work. A viable alternative is to use the dynamic effects of the motion of a carried payload to load the sensor. For a rigid robot, the displacement of the payload can be inferred from joint-angle measurements using the robot kinematics. However, major space robots are structurally flexible, in which case establishing a similar inference is difficult. Therefore, it is assumed here that a payload with known mass properties is handled by the end-effector, and that the payload displacement is measured directly using a laser vision system. Then, considering the end-effector and the payload to be one rigid-body, their dynamics equations, which are the Newton-Euler equations, are used to design an adaptive observer that simultaneously generates estimates of the motion of the body and identities the calibration matrix of the sensor. In this paper, as a first step, the problem would be solved for planar robots. The performance of the adaptive observer would then be evaluated through simulations

This work presents a new paradigm and a conceptual design for reconfigurable robots. Unlike conventional reconfigurable robots, our design does not achieve reconfigurability by utilizing modular joints. Rather, the robot is equipped with passive joints, i.e., joints with no actuator or sensor, which permit changing the Denavit-Hartenberg parameters such as the link length and twist angle. The passive joints will become controllable when the robot forms a closed kinematic chain. Also, each passive joint is equipped with a built-in brake mechanism which is normally locked, but the lock can be released whenever the parameters are to be changed. Not only will such a manipulator have the versatility to perform different tasks but also it can be packed adequately within its designated space on the launch vehicle. Kinematics of such a robot is analyzed, and a stable control algorithm which can take the robot from one configuration to another is devised

This paper describes the design and development of a mechatronic testbed facility which allows high-fidelity and low-cost testing of the joint prototypes of a manipulator in a highly flexible environment. The testbed system consists of a set of load motors whose shafts are connected to those of the joint prototypes through a set of torque transducers. A controller modifies the simple dynamics of the load motors to match the nonlinear and coupled dynamics of the manipulator links. This is made possible by incorporating the measurement of joint angles, velocities, and joint torques, as well as the dynamics model of the manipulator links in a composite feedforward/feedback loop. The stability of the overall system and the fidelity of the load emulator are investigated. The testbed system is constructed to permit testing in a space-like thermal/vacuum environment. Thus, the facility is particularly useful for development and validation of new joints and actuators for space manipulators. The system is experimentally validated by comparing trajectories of the joint angles, velocities, and torques of a set of joint prototypes obtained by installing them first on an actual robot, and then on the mechatronic testbed

The application of joint-torque sensory feedback (JTF) in robot control has been proposed in the past that, unlike the model-based controllers, does not require the dynamic model of the robot links. JTF, however, assumes precise measurement of joint torque and accurate friction model of the joints. This paper presents an adaptive JTF control algorithm that does not rely on these assumptions. First, the robot dynamics with JTF is presented in a standard form with a minimum number of parameters, where the inertia matrix appears symmetric and positive definite. Second, an adaptive JTF control law is developed that requires only incorporation of uncalibrated joint-torque signals, i.e., the gains and offsets of multiple sensors are unknown. Also, all physical parameters of the joints including inertia of the rotors, link twist angles, and friction parameters are assumed to be unknown to the controller. The stability analysis of the control system is presented. Experimental results demonstrating the tracking performance of the proposed adaptive JTF controller are presented.

The application of joint-torque sensory feedback (JTF) in robot control has been proposed in the past as a substitute for the computed torque method. A controller based on JTF does not require computation of link dynamics. However, the traditional JTF assumes precise measurement of joint torque. This paper presents an adaptive JTF control algorithm that does not rely on this assumption. First, the robot dynamics with JTF is presented in a standard form, where the inertia matrix appears symmetric and positive definite. Subsequently, properties of the dynamics is inves tigated and a condition on the number of parallel joint axes for dynamic decoupling is derived. This can lead to further simplification of control structure for a class of robots. Secondly, an adaptive control law is developed incorporating uncalibrated joint torque signals, i.e., the gains and offsets of multiple sensors are unknown, into the control system. No dynamic model of a robot link is required, and all physical parameters of the joints including inertia of the rotors, link twist angles, and friction parameters are assumed unknown to the controller. Stability analysis together with a condition for bounded control input are presented. The control algorithm is experimentally applied to a robotic arm and experimental results illustrate high tracking performance, albeit neither was the torque sensor calibrated nor the parameters were known.

This paper presents an emulating system for zero-gravity (0-G) emulation of a ground spacecraft in an earthbound (1-G) laboratory environment using a controlled manipulator. Such an emulating system allows testing of the spacecraft, e.g., a satellite, with all of its hardware in place, and it is applicable to the case of either a rigid spacecraft or a flexible spacecraft. The controller of the manipulator is developed to virtually change the mass properties of the ground spacecraft and to replicate either the free-space motion or the orbital motion dynamics of a flight-spacecraft. The stability of the system and the effects of disturbance and force sensor noise on the fidelity of the emulating system is thoroughly analyzed. The concept of the 0-G emulation of spacecraft is demonstrated by performing experiment for emulation of a satellite using a robotic testbed at the Canadian Space Agency (CSA).

This paper presents a unified approach for inverse and direct dynamics of constrained multibody systems that can serve as a basis for analysis, simulation, and control. The main advantage of the dynamics formulation is that it does not require the constraint equations to be linearly independent. Thus, a simulation may proceed even in the presence of redundant constraints or singular configurations, and a controller does not need to change its structure whenever the mechanical system changes its topology or number of degrees of freedom. A motion-control scheme is proposed based on a projected inverse-dynamics scheme which proves to be stable and minimizes the weighted Euclidean norm of the actuation force. The projection-based control scheme is further developed for constrained systems, e.g., parallel manipulators, which have some joints with no actuators (passive joints). This is complemented by the development of constraint force control. A condition on the inertia matrix resulting in a decoupled mechanical system is analytically derived that simplifies the implementation of the force control. Finally, numerical and experimental results obtained from dynamic simulation and control of constrained mechanical systems, based on the proposed inverse and direct dynamics formulations, are documented.

Most studies on adaptive coordination of multi-robot systems assume exact knowledge of system kinematics and deal only with dynamic uncertainties. However, many industrial applications involve tasks in which a multi-robot system interacts with geometrically unknown environments. In this paper, we consider a multi-robot system grasping a rigid object in contact with a geometrically unknown surface. The proposed adaptive hybrid force-motion controller guarantees asymptotic tracking of desired motion and force trajectories while ensuring exact identification of constraint Jacobian matrix without persistency of excitation condition. The control signal is smooth and does not depend on contact force derivative. The proposed adaptive controller is robustified against environmental friction and nonparametric uncertainty in environment geometry. Simulation examples are presented to illustrate the results.

Most studies on adaptive coordination of multi-robot systems assume exact knowledge of system kinematics and deal with dynamic uncertainties. However, many industrial applications involve tasks in which a multi-robot system interacts with geometrically unknown environments. In this paper we consider a multi-robot system grasping a rigid object which is in contact with a frictionless surface with unknown geometry. The proposed adaptive hybrid force-motion controller guarantees asymptotic tracking of desired motion and force trajectories while ensuring exact identification of tangential and normal directions to the constraining surface without persistency of excitation condition. The control signal is smooth and no projection is used in parameter update law. A simulation example is presented to illustrate the results.

This paper presents an approach for control of constrained multibody systems based on a projected inverse-dynamics control scheme. The main advantage of the controller is that it works for constrained systems, which have joints with no actuator (passive joints), e.g. parallel manipulators. Also the controller minimizes actuation force, while it does not require the constraint equations be linearly independent. Therefore, the controller can cope with redundant constraint or singular configuration. It follows with development of a complementary controller for control of constraint force.

An emulating robot is required to verify functionality of a space robot, such as the special purpose dextrous manipulator (SPDM). Control of the emulating robot is very challenging; it requires matching the contact force frequency-response of the emulating robot and that of the space robot, attenuating sensitivity to force sensor noise, while maintaining contact stability in spite of uncertain environment impedance. A /spl mu/ synthesis based controller for minimizing the weighted distance between the realized and the specified force transfer functions, minimizing noise sensitivity, and maintaining closed-loop stability in spite of a broad variation of environment parameters (stiffness and damping) is proposed. Experimental results demonstrate robust performance of the controller.

This paper presents a unified approach for inverse and direct dynamics of constrained multibody systems that can be served as a basis for analysis, simulation, and control. The compactness of the dynamics formulation can result in computational efficiency. Furthermore, the acceleration is explicitly related to the generalized force by an introduced "constraint inertia matrix" which is proved to be always invertible. Thus a simulation may proceed even with the presence of redundant constraints or singular configurations. The generalized forces are decomposed onto two orthogonal subspaces which are considered as control inputs for controlling position and constraint force. The motion controller scheme, remarkably, requires no force feedback, proves to be stable, and minimizes actuation force. Finally, numerical and experimental results obtained from dynamic simulation and control of constrained mechanical systems, based on the proposed inverse and direct dynamics formulations, are documented.

To verify all robotic tasks involving a space robot interacting with environment, such as the special purpose dexterous manipulator, one should appeal to a simulation technique because the space robot cannot operate in an 1-g environment. However, to simulate dynamical behavior of a robot interacting with environment possess many difficulties due to complexity of the physical phenomenon involved during the interaction. In this work we develop an hardware-in-loop simulation technique, where a simulation of the space robot dynamics is combined with emulation of the contact dynamics by using a rigid robot prototype performing the contact task. The rigid robot is not dynamically or kinematically equivalent to the space robot, but it is controlled so that its endpoint dynamics replicates that of the space robot. Experimental results given from implementation of a single axis arm are presented.

A new torque control strategy for brushless motors with minimum torque ripple and minimum copper losses while maintaining the phase currents under magnetic (or current) saturation is presented. The optimal control, a nonlinear map from desired torque and position to the motor's phase currents, is the closed form solution to a quadratic programming problem. Experimental results demonstrate virtually ripple-free torque and improved tracking accuracy. In case of magnetic or current saturation, the maximum torque capability of the motor is considerably increased.

Analyses the performance and stability of a force/moment accommodation (FMA) loop closed around a joint rate controller. A synthesis methodology is given to select the gains of the accommodation controller. The bandwidth and coupling limitations of the FMA control architecture are discussed. It is shown that the closed-loop FMA exhibits natural decoupling when FMA acts on the "transpose Jacobian rate" controller. The theoretical developments in the paper are supported by simulation and experimental results.

A six-axes force/moment sensor can be completely characterized by a 6/spl times/6 gain matrix whose elements can be estimated from a sequence of sensor outputs and applied forces. Unlike the conventional calibration procedure that uses an external hardware to produce the load forces, we present a calibration procedure that applies inertial forces as a result of movement of a manipulator payload in free space. The subsequent inertial forces and moments are calculated by using the Newton-Euler formulation assuming known inertial parameters (mass, center of mass, inertia tensor) of the payload. An extended Kalman filter is employed to perform the estimation of the sensor gain matrix based on the measurements of the manipulator velocity and the sensor outputs. The performance of the proposed estimator is evaluated by simulation.

This paper reports on advances in the design and development of a high performance direct-drive joint for robotics and automation. The key design aspects of the mechanical components, sensors, control architecture, and a hydraulically actuated dynamometer testbed are described. We also present a number of advanced implementations in control, motor torque control, and motion control using positive joint torque feedback. Experimental results illustrate outstanding performance regarding thermal response, torque ripple, reference trajectory tracking, torque disturbance rejection, and joint stiffness.

Hardware-in-the-loop simulation is an attractive tool to validate the functionality of space robots. It is the purpose of the hardware-in-the-loop simulation to make a rigid robot prototype behave, in contact/noncontact phases, as closely as possible to a given robot reference model that would be encountered in the real-world. We introduce a method for the hardware-in-the-loop simulation that is based on the projection of the generalized coordinates of the robot model into two subspaces representing independent and dependent coordinates. The independent coordinate is obtained via simulation by making use of its acceleration model expressed in a closed form. While, the dependent coordinate is obtained from the generalized coordinated of the linearized robot prototype acting as a double integrator on the input dependent-coordinate acceleration. It is followed by investigating the effect of external disturbance on the performance of the hardware-in-the-loop simulation, by the method of Lagrangian multiplier. Finally experimental results obtained from implementation of a single axis arm is presented.

As a partner in the International Space Station, Canada is responsible for the verification of all tasks involving the special purpose dextrous manipulator (SPDM). In this paper, the concept of an SPDM task verification facility (STVF) is described. The verification process involves three complementary stages. First, a real-time software simulator is used to verify the complete nominal and malfunction procedures. Next, the feasibility of a task involving contact is verified with the help of a hardware-in-the-loop simulator. Finally, a non real-time simulator is used to perform detailed parametric studies given the known tolerances on the components. The paper describes all three stages but emphasizes on the hardware-in-the-loop simulator, the only new facility within the STVF.

Positive joint torque feedback can compensate the detrimental effects of load torques on position tracking performance. However, with (real world) nonideal torque sources, simple unity gain positive torque feedback can actually deteriorate the performance, or even result in instability. An H/sup /spl infin// joint torque feedback is proposed which takes the dynamics and uncertainty of the actuator into account and minimizes the system's sensitivity to load torques. In our experimental direct-drive system, the H/sup /spl infin// positive torque feedback inner loop drastically improved the disturbance attenuation (25 dB) and load decoupling properties of a simple PID position controller.

The open-loop torque control of synchronous motors with minimum torque ripple and minimum copper losses is presented. The control problem is viewed as an optimization problem for the nonlinear mapping from desired torque and position to the motor's phase currents. The performance of the controller to produce virtually ripple-free torque and to enhance the precision of position tracking is demonstrated experimentally.

This paper addresses the dynamics and control of direct drive robots with positive joint torque feedback. We analytically derive the system dynamics in closed form. Even though it is coupled and nonlinear in general, it is substantially simpler than the robot link dynamics. We also derive conditions on the robot configuration which result in linear dynamics. Motion control laws for both cases are proposed.

Applying positive joint torque feedback in direct drive motor systems reduces the effect of external load torques. This is most beneficial when accurate position tracking is required in the presence of large disturbances or for complex loads as found in robotic manipulators. We formulate the problem of torque feedback in the presence of actuator dynamics. The problem of finding the optimal torque feedback which minimizes the maximum disturbance sensitivity is equivalent to the model-matching problem. The effect of the load on the rotor dynamics appears as a perturbation minimized by the proposed torque feedback. To synthesize the torque filter, only the actuator dynamics and a very rough knowledge about the mechanical load is required.

This paper presents a new model reference adaptive control method to control motor torque in direct drive reluctance motors in an accurate and ripple-free fashion. It is based on the motor's voltage equation and requires only measurements of motor angle, winding voltages and currents. In addition, we introduce a new optimal torque-to-current conversion which minimizes copper losses. Simulations of a reluctance motor with magnetically coupled phases demonstrate fast parameter convergence and accurate torque tracking.