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.

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.

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.

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

In this paper, we describe a framework for the autonomous capture and servicing of satellites. The work is based on laboratory experiments that illustrate the autonomy and remote-operation aspects. The satellite-capture problem is representative of most on-orbit robotic manipulation tasks where the environment is known and structured, but it is dynamic since the satellite to be captured is in free flight. Bandwidth limitations and communication dropouts dominate the quality of the communication link. The satellite-servicing scenario is implemented on a robotic test-bed in laboratory settings

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

The work reported here was motivated by the development of manipulator systems comprising one long-reach, flexible-link subsystem, termed the macromanipulator, and a short-reach, rigid-link subsystem, called the micromanipulator. The flexural states of the macromanipulator, needed for controlling such systems effectively, are not usually measurable directly. For this reason, a state-estimation algorithm is proposed which uses the velocity and angular-velocity data of the micromanipulator base to estimate the flexural states of the macromanipulator. The velocity data are inferred from the acceleration signals delivered by a kinematically redundant set of triaxial accelerometers. The accelerometer signals are also utilized to calculate the translational and angular accelerations of the micromanipulator base, which are, in turn, used along with the dynamics equations of the micromanipulator to obtain the reaction force and moment acting between the two subsystems. Treating the force and the moment as inputs, the dynamics equations of the macromanipulator alone are used in the observer, thus reducing the order of the dynamics model. The state-output relations, on the other hand, are linearized in closed form to lower the computational cost. The relations thus obtained are then used in an extended Kalman filter to estimate the flexural states of the system.

The subject of this paper is a state-estimation algorithm which uses the twist data, velocity and angular velocity, of the base of a micro-manipulator, placed on the end-effector of its macro counterpart, to estimate the flexural states of the flexible links of the macro-manipulator. The twist data are inferred from the acceleration signals delivered by an accelerometer array $a kinematically redundant array of tri-axial accelerometers. The array signals can also be utilized to calculate the translational and angular accelerations of the micro-manipulator base, which are in turn used to obtain a set of dynamics equations for the macro-manipulator, thus reducing the order of the dynamics model. Next, the dynamics equations of the macro-manipulator and the state-output relations are linearized, the latter in closed form so as to lower the computational cost in a control loop. The relations thus obtained are then used in an extended Kalman filter to estimate the flexural states of the system.

An accelerometer-array attitude-calibration method is proposed. Being based on the compatibility of rigid-body point accelerations, this method can be applied to determine and account for the accelerometer installation errors with a high degree of accuracy. It is assumed that the number or three-axis accelerometers in the array is redundant in order to help reduce the effect of sensor noise, thereby obviating the Kalman-filtering of the signals. Procedures are developed to calculate the angular velocity and acceleration as well as the attitude of the body, all in the body frame. It is demonstrated that even large attitude errors can be dealt with via off-line iterative applications of the scheme.

Common packet channel (CPCH) access is an efficient approach to support packet data transmissions in a wideband code division multiple access (W-CDMA) system. This paper investigates a modified CPCH access method which provides prioritized services for various traffic classes. Each traffic type has a distinct transmit permission probability that is estimated at the new call initiation stage based on the status of CPCH channel occupancy. The differentiated service qualities are evaluated in terms of packet blocking rates. The overall system performance is also evaluated in terms of throughput.

We address issues concerning technology selection for non-real time, near real time and interactive data services for 3G W-CDMA systems. Specifically, we compare the packet mode of operation with the circuit mode of operation in UMTS W-CDMA. We show that the use of packet channels such as the common packet channel (CPCH) and forward access channel (FACH) lead to an order of magnitude higher spectrum efficiency as compared to use of the dedicated channels. We also show in an example and under a set of service mixture assumptions that their use lead to a factor of 3.3 higher spectrum efficiency in the downlink and 21 in uplink, and to more than two order of magnitude resource utilization efficiency gain in the range of 2-134. Finally, CPCH offers eightfold increase in throughput and capacity efficiency as compared to the random access channel (RACH). We find that the level of resource utilization gain is sensitive to the level of burstiness of traffic as is the case with the spectrum efficiency gain.

An algorithm for estimating the pose and twist of a rigid body using measurements made by a redundant number of on-board accelerometers is formulated. Redundancy helps reduce the effect of the accelerometer noise. This algorithm is based only on rigid-body kinematics because it is intended to be used for rigid bodies acted upon by forces and moments elusive to modeling. Procedures are developed to calculate the angular velocity and acceleration as well as the attitude of the body along with the velocity and position of the centroid of the pickup points, all in the body frame. It is shown that a small installation error can cause the integration results to become unstable. This instability is compensated for by means of a pose-measurement sensor.

With the rise of interest in wireless Internet and wireless packet data communications on one hand and explosion of interest in IP and packet-switched based networks on the other, it is beneficial to bring the packet switching capability to the air interface which is the last hop in network. The common packet channel (CPCH) has been included in the third generation wideband direct sequence code-division multiple access (3G W-CDMA) technical specifications to meet this growing demand and need in an efficient manner. This paper will address the CPCH benefits, applications, CPCH access method and comparison of various UMTS base node deployment scenarios.

This paper is a systems engineering overview of a state-of-art packet switched radio data system-the Mobitex system. RAM Mobile Data operates Mobitex systems in the US and the UK. Mobitex systems are also in operation in Scandinavia and Canada. The system architecture is 'open', which allows any company to enter the wireless data business by providing radio modems and/or application software conforming to the Mobitex interface specification. This paper first outlines the Mobitex network architecture, network protocol, RF system design and the Mobitex 'open' air interface. Finally, the spectral efficiency and response time for transmission of short messages using a wireless packet data network and present day analog cellular systems are compared. It is concluded that a wireless packet data network is superior to analog cellular systems both in terms of spectral efficiency and response time for short data messages.>