This work presents a 2D human model and its use in a novel gait analysis framework, which only requires a stereo camera to produce impressive results for the inverse kinematics, inverse dynamics, as well as ground reaction forces during gait. The model is designed to resemble the human body in the sagittal plane, with anatomical landmarks used as keypoints in the inverse kinematics calculations that yield accurate estimates of the joints' motion during gait. The gait dynamics are formulated in compact form, allowing the simultaneous estimation of internal joint torques, as well as ground reaction forces via the solution of a fully-defined system of linear algebraic equations. The proposed framework offers an affordable alternative to costly gait analysis systems, and can have various applications in robotics and in biomechanics.

This paper introduces a virtual gravity controller for underactuated biped robots. A bio-inspired model of passive bipedal walking is used as the basis for the controller's design. An analytical expression of the controller is obtained, allowing on-line implementations of the developed control scheme. Following a design modification tailored to the controller, the robot is able to reproduce its passive gait even on level-ground. The results are verified via independent high-fidelity physics simulations of the real robot's digital twin. The active robot demonstrates significant dynamic convergence to the passive model's dynamics, with only minor motorization efforts. The developed control scheme showcases robustness and energetic efficiency, and leads the way to a design-oriented approach in active biped locomotion.

To accurately accomplish on-orbit tasks using Space Manipulator Systems (SMS), advanced model-based controllers, dependent on the knowledge of SMS parameters, can be employed. However, these parameters may change on orbit for several reasons. Also, during an SMS task, excitation of flexible appendages, such as solar panels, or fuel sloshing may introduce significant end-effector errors. Therefore, controllers robust to parametric uncertainty and disturbances are needed. A robust controller attractive due to its small computational effort is the Linear Parameter Varying (LPV) gain-scheduled controller. However, its design for spatial SMS is not trivial and has not been studied yet. Therefore, the aim of this work is to study and compare robust controllers and examine their applicability to SMS. An LPV plus H∞controller is compared with a Model-Based PD, and a Model-Based PD plus H∞controller, in the presence of parametric uncertainty, noisy measurements and disturbances, using a planar example. The criteria considered include: (i) Design Complexity, (ii) Trajectory Errors, (iii) Required Torques, and (iv) Computational Effort.

Space manipulator system (SMS) maneuvers can excite flexible appendages, while fuel sloshing effects impact its dynamics and performance. To predict this behavior and control such systems, sloshing and flexible appendages are modeled. A novel system identification scheme is developed, which identifies all parameters required for the reconstruction of system dynamics despite unmeasurable sloshing and modal states. This is achieved by two identification experiments. In Exp.1 all unmeasurable states are eliminated, while in Exp.2 the unmeasurable sloshing states are eliminated, and a novel estimator is used for the unmeasurable modal states. The significance of accurate SYSID in controller design and performance is demonstrated by simulating a 3D SMS controlled by model-based and robust controllers. In both cases, using the identified parameters results in significant robust control performance enhancement.

Efficient and thorough vineyard inspection is crucial for optimizing yield and preventing disease from spreading. Manual approaches are labor-intensive and prone to human error, motivating the development of automated solutions. Precision viticulture benefits greatly from access to photo-realistic 3D vineyard maps and from capturing intricate visual details necessary for accurate canopy and grape health assessment. Generating such maps efficiently proves challenging, particularly when employing cost-effective equipment. This paper presents a novel vineyard inspection and 3D reconstruction framework implemented on a Robotic Platform (RP) equipped with three stereo cameras. The framework’s performance was evaluated on an experimental synthetic vineyard developed at NTUA. This testing setup allowed experimentation under diverse lighting conditions, ensuring the system’s robustness under realistic scenarios. Unlike existing solutions, which often focus on specific aspects of the inspection, our framework offers a top-down approach, encompassing autonomous navigation, high-fidelity 3D reconstruction, and canopy growth assessment. The developed software is available at the Control Systems Laboratory’s (CSL) bitbucket repository [1].

Analytical expressions are derived for actuator demands in quadrupedal locomotion of constant speed and height by using a reduction from a trot/ pace 6-bar model to a single-legged model and employing two widely used two-segmented leg architectures, the serial and the parallel. A method is developed that outputs optimal gait characteristics and leg designs for a robot to move with maximum efficiency or speed. Also, generic guidelines are presented, which answer questions such as: which speed should be selected for maximum efficiency, or which is the optimal leg architecture (serial/ parallel) and leg length for maximum efficiency or speed.

This paper studies a passive biped walker with knees and biomimetic feet and its behavior, as a function of key parameters. The model includes a continuous dynamic representation of the knee joint's interaction with a viscoelastic kneecap, as well as a complete kinematic description of feet that are designed to mimic the human rollover shape. First, the analytical model is derived and studied numerically for its passive walking capabilities. Then, the model is verified through independent simulations in a different platform. Finally, to increase the efficiency of its passive gaits and to map out its walking capabilities, the model is investigated parametrically. The methods used as well as the results obtained can offer significant assistance in the field of designing passivity-based biomimetic walking robots and prosthetic devices.

This paper studies the effects of replacing pin-joint knees in passive dynamic bipedal walkers with biomimetic four-bar knees. The kinetic model of the four-bar knees is presented in detail, and an analytical model of the passive walking dynamics is derived. The resulting four-bar kneed biped is compared with a pin-joint kneed walker, for their passive walking performance. The geometry of the four-bar knees used in the study is based on human anatomical data. It is found that the biomimetic four-bar knee configuration works to the advantage of the biped, especially around the extended-knee singular position. The four-bar knees are found to overperform the pin-joint ones, resulting in significant reduction of peak impact loads and energetic expenditure.

In this paper, we study the effect of alternative leg designs on energy consumption in legged locomotion. Focusing on gaits with constant horizontal velocity and constant height we introduce models of two simplified parallel and serial designs with realistic mechanical and actuation parameters. The analysis yields the distribution of power demands in the leg workspace, leading to useful conclusions related to mechanical power antagonism and actuator electric losses. Mechanical antagonism occurs not only in parallel but also in serial legs causing extensive power waste, since one actuator contributes to the locomotion task and the other consumes power with no contribution to it. Based on the analysis, we propose a new leg design that minimizes the total actuation power consumption criterion given a nominal robot toe trajectory.

To control a free-floating robotic system with uncertain parameters in OOS tasks with high accuracy, a fast parameter identification method, previously developed by the authors, is enhanced further and used concurrently with a controller. The method provides accurate parameter estimates, without any prior knowledge of any system dynamic properties. This control scheme compensates for the accumulated angular momentum on the reaction wheels (RWs), which acts as a disturbance to the robotic servicer base. While any controller using parameter information can be used, a transposed Jacobian controller, modified to include RW angular momentum disturbance rejection, is employed here. Threedimensional simulations demonstrate the method's validity.

A methodology for implementing arbitrary foot shapes in the passive walking dynamics of biped robots is developed. The dynamic model of a walking robot is defined in a way that allows shape-dependent foot kinetics to contribute to the robot's dynamics, for all convex foot shapes regardless of the exact foot geometry: for the developed method, only the set of points describing the foot profile curve is needed. The method is mathematically derived and then showcased with an application. The open-source pose estimation system OpenPose is used to determine the foot profile that enables the rigid-foot passive robot to reproduce the ankle trajectory of the actively powered, multi-DOF human foot complex. The passive gait of the biped robot walking on the specified foot shape is simulated and analyzed, and a stable walking cycle is found and evaluated. The proposed model enables the study of the effects of foot shape on the walking dynamics of biped robots, eliminating the necessity of solely using simple, and analytically defined geometric shapes as the walking robots' feet. The method can be used for foot shape optimization towards achieving any desired walking pattern in walking robots.

Space manipulator systems in orbit are subject to link flexibilities since they are designed to be lightweight and long reaching. Often, their joints are driven by harmonic gear-motor units, which introduce joint flexibility. Both of these types of flexibility may cause structural vibrations. To improve endpoint tracking, advanced control strategies that benefit from the knowledge of system parameters, including those describing link and joint flexibilities, are required. In this paper, first, the equations of motion of space manipulator systems whose manipulators are subject to both link and joint flexibilities are derived. Then, a parameter estimation method is developed, based on the energy balance during the motion of a flexible space manipulator. The method estimates all system parameters including those that describe both link and joint flexibilities and can reconstruct the system full dynamics required for the application of advanced control strategies. The method, developed for spatial systems, is illustrated by a planar example.

A novel identification method is developed which identifies the accumulated angular momentum (AAM) of spinning reaction wheels (RWs) of an uncooperative satellite captured by a robotic servicer. In contrast to other methods that treat captured satellite's RWs as non-spinning, the developed method provides simultaneously accurate estimates of the AAM of the captured satellite's RWs and of the inertial parameters of the entire system consisting of the robotic servicer and of the captured satellite. These estimates render the system free-floating dynamics fully identified and available to model-based control. Three-dimensional simulations demonstrate the method's validity. To show its usefulness, the performance of a model-based controller is evaluated with and without knowledge of the captured satellite's RWs AAM.

Quadrupedal locomotion skills are challenging to develop. In recent years, deep Reinforcement Learning promises to automate the development of locomotion controllers and map sensory observations to low-level actions. Moreover, the full robot dynamics model can be exploited, but no model-based simplifications are to be made. In this work, a method for developing controllers for the Laelaps II robot is presented and applied to motions on slopes up to 15°. Combining deep reinforcement learning with trajectory planning at the toe level, reduces complexity and training time. The proposed control scheme is extensively tested in a Gazebo environment similar to the treadmill-robot environment at the Control Systems Lab of NTUA. The learned policies produced promising results.

The parameter estimation of space manipulator systems on orbit is studied, whose manipulators are subject to joint flexibilities. To improve path planning and tracking capabilities, advanced control strategies that benefit from the knowledge of system parameters are required. These parameters include the system inertial parameters as well as the stiffness and damping parameters, which describe joint flexibilities. During operation some of these parameters may change or be unknown. Estimation methods based on the equations of motion are sensitive to noise, while methods based on the angular momentum conservation, while they are tolerant to noise, they cannot estimate the parameters that describe joint flexibilities. A parameter estimation method, based on the energy balance, applied during the motion of a space flexible-joint manipulator system in the free-floating mode, is developed. The method is tolerant to noise and can reconstruct the system full dynamics. It is shown that the parameters estimated by the proposed method can describe the system dynamics fully. The application of the developed method is valid for spatial systems; it is illustrated by a planar 7 degrees of freedom (DoF) example system.

An optimal leg sequence selection method is developed, which maximizes hexapod robot stability, considering feasible gaits, motion modes, and terrain slope. A novel and fast search method is employed to find the most stable leg sequence for a given gait; if no such sequence exists, the next fastest stable gait is chosen and the most stable leg sequence for this gait is selected. The method can be based on any stability measure; here the Force-Angle Stability Margin criterion is employed that is sensitive to top-heaviness, and inertial and external forces. Results show that the developed method senses instabilities accurately and selects the best leg sequence for maximum stability far faster than exhaustive searches, offering distinct advantages when varied external forces are applied.

This paper presents the mathematical derivation and experimental validation of a computational model, which accurately predicts static, large-strain deformations of tendon driven non-slender soft-arm manipulators subjected to gravity. The large strain behaviors are captured by employing the Green-Lagrange strain and by deriving analytical expressions for the variation of the equivalent Young modulus of the structure due to the large strains. No simplifying assumptions are made regarding the curvature of the structure, the stretching or the compression. Furthermore the paper proposes an iterative method for numerically solving the resultant non-linear system of coupled differential equations and demonstrates a number of application scenarios. The model is experimentally validated using a set-up comprising one segment of tendon driven soft-arm, which integrates stretchable and compressible hyperelastic (rubber-type) materials into its non-homogeneous back bone structure.

This paper studies the effects of varying rollover curvature on the passive dynamic gait of a biped walker. The dynamic model of a compliant biped robot is extended with the implementation of semielliptical feet, to mimic human rolling-radius progression during a step. The process of modeling the semielliptical foot shape and integrating its kinematics to the biped's dynamics is presented in detail. The passive dynamic behavior of the biped for elliptic feet of various dimensions is investigated through numerical simulations to provide results about gait stability, walking speed, energetic efficiency, and impact force levels. The concept of energetic efficiency in passive walking is discussed thoroughly, and an efficiency comparison methodology is proposed. Finally, it is shown that the biomimetically-inspired semielliptical foot profile can lead to higher gait efficiency. The results of this study can be used to optimize energetic efficiency in biped walking machines and/or gait assisting prosthetic equipment by means of foot shape optimization.

This paper presents an efficient method of stabilizing the gait of an underactuated biped with compliant legs and semicircular feet. First, the model is defined, incorporating elements that are often present in experimental biped robots. The biped's passive behavior is studied through numerical simulations that provide insight into the gravity's contribution as an energy input to the system. Based on this study, it is shown that an augmented biped -with the addition of a counterweight joint at the hip- is able to perform stable gaits with minimal input. This design is implemented easily as it does not require ankle torques; instead, both motors are mounted at the biped's hip. The control law used for the stabilization is the combination of virtual-gravity components with non-linear PD terms. The stable gaits performed by the augmented biped on level floor strongly resemble the passive gaits of the original biped walking on a slope, resulting in an efficient, natural-like motion of low transport cost.

This paper introduces alternative behaviors described by the SLIP model when it is subject to a range of initial conditions. A non-dimensional SLIP model and a numerical return map search scheme are used to determine fixed points as a function of non-dimensional leg stiffness and vertical displacement under friction constraints. A SLIP model behavior analysis is performed, using an analytical stance phase approximation, by diverging from the fixed points, i.e. by increasing/decreasing initial horizontal velocity, and/or touchdown angle. The results show that beyond the regular fixed points, the SLIP model performs an alternative, stable behavior that repeats itself every two cycles of motion. We call these 2nd-order fixed points and the regular ones 1st-order fixed points. A numerical simulation scheme was developed to investigate 2nd-order fixed points for a wide range of horizontal velocities and touchdown angles. Results show that 2nd-order fixed points respecting the friction cone constraints exist that can lead to a number of different behaviors such as high jumps, obstacle avoidance of different heights, or backward motion.

Quadrupedal trotting gaits of constant forward velocity and body height are studied. A method is developed, which is structured upon analytical expressions derived from the dynamics of a reduced single-legged model comprised of a point mass, and two actuated rotational joints. The inputs of the method include the robot mass, the leg and actuator properties, and the desired forward velocity, yielding all robot body feasible trajectories and their energy footprints. Thus, the method predicts the maximum forward velocity of a trotting quadruped; it also suggests energetically optimal combinations of body height and step length for a given forward velocity.

To accomplish tasks with high accuracy, advanced control strategies that benefit from the knowledge of system parameters are required. However, during operation some of them may change, or be unknown. In this paper, a novel parameter estimation method is proposed, which is based on the conservation of the angular momentum of a space manipulator system in the free-floating mode. The estimated parameters are combinations of spacecraft, manipulator and payload parameters and render the system full dynamics identified and applicable to model-based control. The algorithm requires only measurements of joint angles and rates, and spacecraft attitude and angular velocity. No information about spacecraft and joint accelerations or joint torques, which include substantial noise, is required. Thus, in contrast to other methods using the equations of motion, the proposed method is insensitive to sensor noise. Moreover, it does not require the prior knowledge of any system parameters and can be applied to free-floating systems with more than one manipulators. The application of the proposed method is illustrated by a 3D example.

This paper introduces a leg design method aiming at speed maximization for quadruped robots with two-segment compliant legs, in trotting and bounding. The proposed method is an effort to address the leg design challenge in a holistic way, exploiting the coupling between gait parameters, leg design parameters and hardware constraints, while remaining control scheme independent. Optimal body trajectories and footfalls are derived using a simplified centroidal dynamics model, whereas joint trajectories and torques are computed by a more complex dynamic model, incorporating actuation parameters and constraints. The method is applied using real robot parameters to yield an optimal leg design, validated through a realistic trotting simulation experiment. In this experiment, the robot achieves accelerating motion from stance towards the maximum speed predicted by the method.

While legged locomotion is a rapidly advancing area in robotics, several issues regarding the performance of such robots on deformable ground are still open. In this paper, we generate a pronking gait on a quadruped robot using a controller, which takes into account the effects of ground deformation. The controller, initially developed for monopods, is modified appropriately to operate for quadrupeds. The robot uses a reaction wheel to retain a desired body pitch. The dynamic models of leg motor drivetrains and of the reaction wheel are incorporated and their importance in the design of legged robots is highlighted. Simulation results show good performance in reaching commanded apex heights and forward velocities when traversing various deformable terrains, demonstrating that the developed controller is quite promising.

This paper studies the effect of a flexible linear torso on the dynamics of passive quadruped bounding. A reduced-order passive and conservative model with translational spinal joint and springy legs is introduced. Numerical return map studies reveal the existence of a confined area of fixed points generating high-speed cyclic bounding motions by exploiting the natural dynamics of the model. The corresponding motion features extensive bidirectional spine deformation. The model displays interesting techniques that result in high-speed locomotion, such as increased flight phase duration and stride length. The obtained results show that the corresponding robot gaits and the associated performance resemble those of its natural counterparts even though the spinal joint lies beyond the bioinspired regime.

We present the design of a backstepping controller for a triangular over-actuated marine platform, controlled by three rotating jets. Our goal is the stabilization of the position and the orientation of the platform, under realistic environmental disturbances, such as wind forces, wave forces and hydrodynamic forces. Actuator thrust and angle dynamics, as well as settling delays, in the rotation of the jets and in the response of the desired thrust, are included in the algorithm, despite the presence of an allocation scheme. Thrust and angle velocity, limitations are also taken into account. A Thrust Upper Limit (TUL) manipulation heuristic is introduced in order to reduce the thrust requirements and the energy consumed. The performance of the developed backstepping controller is compared to the case with and without the TUL. Simulation results show that the use of the heuristic reduces energy consumption.

Terrain compliance is a critical parameter for the performance of legged locomotion. In this work, a single actuator monopod robot hopping on rough compliant terrain is considered. Based on our controller for flat compliant terrains, this paper introduces the necessary modifications, which allow the robot to tackle the disturbance of small inclinations. Using the developed method, the robot is examined on its performance to traverse rough terrains, while maintaining the goals of reaching a desired height and forward velocity. As the increased compliance and inclination alter the energy requirements from the controller actuator, the Cost of Transport (CoT) index for a number of scenarios is studied. The correlation between terrain parameters and the CoT is presented, and useful conclusions, which can aid the understanding of the behavior of legged robots in realistic terrains are extracted.

We propose a biomechatronics-based master/slave topology which is going to provide an Extended Physiological Proprioception (EPP)-equivalent control but without the use of a harness, cineplasty, or Bowden cable. The proposed control uses an implanted micro servo actuator. The original Bowden-cable EPP topology is compared to the proposed one and their simulation results are presented. The simulation results are encouraging since they indicate the materialization potential of the topology, both in terms of control and of low power, two essential factors in making the presence of an implant in the human body feasible. This control topology will provide a modern EPP-equivalent control scheme for upper-limb prostheses without the disadvantages of previous EPP configurations but with the control advantages of proprioceptive feedback.

The modeling and control of a vectoring tricopter UAV are developed in this article. The UAV is actuated by three thrust motors, each guided by suitable actuators, thus forming a platform able to independently track any desired attitude and trajectory. The derivation of the equations of motion is followed by the development of a vectoring controller that is supplemented by an allocation strategy. Both are based on geometric feedback linearization techniques, resulting in a singularity-free control law, taking into account the inertia effects of the main body, of the motors, and of the vectoring dynamics (actuators). A stability proof is developed validating the effectiveness of the control strategy under bounded disturbances. Simulations showcase the developed controller and tricopter performance.

This work addresses the optimal selection of propulsion components for a multi-rotor aerial vehicle (MRAV), for a given payload, payload capacity, number of rotors and flight duration. A steady state model is developed for motors, propellers, electronic speed controllers (ESC), and batteries, using a simplified analysis. Based on technical specifications of batteries, motors and ESCs, component functional parameters are expressed as a function of an equivalent length. Propeller models are developed using experimental data. An optimization program is developed, which calculates the optimal design vector, employing as objective function the energy consumption or the vehicle diameter. Using this program, the influence of the payload and of the number of rotors on the design vector and the MRAV size is studied. The results obtained by the program were compared successfully to existing commercial MRAVs.

Recently, there has been growing interest in biomimetic underwater vehicles. To exploit the full workspace of this kind of vehicles, depth control is needed and plays a critical role. Although depth control for large vehicles such as submarines has been addressed, this issue for low-cost, small-scale underwater vehicles has not received attention. In this paper, the depth control of a small robotic fish is studied, and implemented with the use of a small dc pump. The depth system dynamics are developed and limitations rising from the low-cost, small-scale actuators and sensors are described. A controller with limited feedback is designed, implemented and validated both by simulations and experiments. It is expected that this controller will add an important dimension to depth control of low-cost, energy-efficient small underwater vehicles.

A planning and control methodology for manipulating passive objects using orbital servicers in zero gravity has been developed by the authors. In this work, a parametric sensitivity analysis of the proposed model-based control for the motion of the passive object, in terms of parametric uncertainties, is presented. A linearization methodology is used to provide a scheme with which the controller robust behavior, in terms of parametric uncertainty, can be ascertained a-priori, without the need of running experiments. The system robust performance is illustrated in realistic 3D scenarios and verified via simulations.

Legged locomotion is a rapidly advancing area in robotics, yet still a large number of open questions exist. This work focuses on the foot-terrain interaction and its effect on the motion of a one-legged system. This interaction is usually tackled by disregarding some of the effects of ground deformation like permanent deformation and compaction. Inspired by other areas of engineering, an impact dynamics model is developed, allowing a more thorough study of the behavior during fast dynamic walking. This approach can be regarded as a viscoplastic one. The monopod controller presented in previous work is extended to cope with deformable terrains, based on energy dissipation considerations, without requiring the knowledge of the ground parameters. Simulation results prove the validity of the theory presented.

One of the most demanding tasks for a robotic servicer is capturing a target. During this task, the mechanical systems can be subject to large forces for short duration (impacts). In space servicers, these impacts may render the capturing of a target impossible without the use of undesirable fuel-consuming maneuvers. This paper presents an approach for minimizing impact reactions, using the Center of Percussion (CoP), a characteristic of rigid bodies rotating around an axis. This work generalizes and delineates the exact requirements for its use. Application of CoP in multibody systems is demonstrated using the Newton-Euler Algorithm. Implementation guidelines are discussed. Simulations of a planar space robot system, and a three-dimensional PUMA-like manipulator on a satellite base confirm the benefit of using the CoP during tasks that include impacts.

This paper presents the analysis, design, and closed-loop motion control of a mobile microrobotic platform capable of micrometer positioning on a plane. The mobile microrobot, including chassis, actuators, drives, microprocessor, and electronics, is of low cost (less than $20), can be fabricated rapidly and is made of commercially available components. Its motion is induced by centrifugal forces generated by two vibration motors installed inside the platform body. The asynchronous operation of the vibration motors is shown by simulation to result in planar motions of two degrees-of-freedom locally, with micrometer resolution. A motion controller has been designed to generate controlled motions using sets of motor angular velocities. A prototype has been developed and used to validate the motion principle and the controller efficacy. Open loop experiments show that the platform motion resolution is approximately 20 μm, while its speed is greater than 2 mm/s. Closed-loop experiments demonstrate a 5 μm resolution, i.e., a fourfold improvement compared to the open loop experiments. The low cost, the rapid fabrication, and the micrometer motion resolution suggest that this microrobotic platform is a promising solution for low-cost microfactories, where a group of such robots performs high throughput, advanced microassembly of microsystems.

Free-floating space manipulator systems have spacecraft actuators turned off and exhibit nonholonomic behavior due to angular momentum conservation. Such systems are subject to path dependent Dynamic Singularities (DS) that complicate their path planning. Due to the existence of DS its workspace is restricted. The Cartesian space path planning of free-floating space robots is studied and a novel path planning technique allowing the end-effector to follow a desired path avoiding any DS is proposed. Since the path is predefined, the method yields the appropriate initial system configurations that avoid dynamically singular configurations during the motion. Therefore, it allows effective use of the entire robot workspace. The proposed method is applicable to both planar and spatial systems and it is demonstrated using straight-line paths. The application of the method is illustrated by two examples.

Space exploitation will require efficient techniques for manipulating passive objects on-orbit. This work presents a manipulation technique that utilizes both on-off thrusters and manipulator proportional forces to handle passive objects on orbit, canceling the effect of limit cycles on the objects. The system dynamics including the unilateral constraints and the on-off thrusting are discussed. Using a two-layer optimization process, a planning strategy for the trajectory tracking motion of a passive object including optimal end-effector contact point selection, is developed. The manipulation strategy is illustrated using a 3D scenario. A model-based controller adapted to the special characteristics of the system is presented and its response is discussed. The performance of the proposed manipulation system is shown to be promising, while it reduces excessive thruster fuel consumption.

The determination of a rigid-body position and orientation from the position of a number of its points is one of the fundamental problems in kinematics. This problem arises in robotics, biomechanics, automatic guided vehicles, real-time control of space structures, etc. Under ideal conditions, it is possible to apply classical methods to find a body's position and orientation. However, in the presence of noise, these methods yield results that are unreliable and inconsistent. Two existing and a new method for determining position and orientation from noisy point coordinate data are presented. The theoretical analysis of the methods combined with an extensive simulation process led to conclusions about their behavior in different situations. The proposed method yields better orientation estimates than the other two methods, yielding reliable results both for absolute and relative position measurements and for low and high noise levels.

Space exploitation will require efficient techniques for manipulating passive objects on orbit. This work presents a manipulation concept that utilizes both the on-off thrusters and manipulator proportional forces to manipulate passive objects on orbit more efficiently. The system dynamics arising from the unilateral constraints and the on-off thrusting are discussed. The manipulation concept is illustrated using a simplified one-dimensional model. A novel controller based on backstepping and Lyapunov stability is presented and its performance, stability and robustness are discussed. The performance of this system is compared to that of a standard using on-off thrusters only, and is shown to use less fuel.

This paper presents the design and practical implementation of an autonomous dynamic positioning scheme, i.e., the stabilization of linear and angular velocities as well as the position and orientation, of a novel triangular floating sea platform. The required closed-loop forces and moments must be provided by three rotating pump jets, located at the bottom of three partly submerged cylinders located at the three corners of the platform. With this control configuration the platform is over-actuated, i.e., it has more control inputs than degrees of freedom (DOF). Design rules that maximize the manipulability of the platform, and a control allocation scheme that allows goal realization without violating thruster capabilities are developed. Simulations results, including environmental disturbances, are presented that demonstrate the performance of the controller, and the allocation scheme employed.

Dynamic stability allows running animals to maintain preferred speed during locomotion over rough terrain. It appears that rapid disturbance rejection is an emergent property of the mechanical system. In running robots, simple motor control seems to be effective in the negotiation of rough terrain when used in concert with a mechanical system that stabilizes passively. In this paper, we show that a quadruped robot could be able to perform self-stable running behavior in significantly broader ranges of forward speed and pitch rate with suitable mechanical design. The results presented here are derived by studying the stability of passive dynamics of a quadruped robot running in the sagittal plane in a dimensionless context and can be summarized as: (a) the self-stabilized behavior of a quadruped robot for a particular gait is related to the magnitude of its dimensionless inertia, (b) the values of hip separation, normalized to rest leg length, and the leg relative stiffness of a quadruped robot affect the stability and should be in inverse proportion to its dimensionless inertia, and (c) the self-stable regime of quadruped running robots is enlarged at relatively high forward speeds.

We present a method for controlling the forward speed and the apex height of a one-legged hopping robot over rough terrain, using a single actuator located at the robot hip. The control algorithm is comprised of two elements, the forward speed control and the height control. The only input to the system is the torque applied by the hip actuator. The control is demonstrated to perform tracking of desired forward speed trajectories and desired apex height trajectories. Simulation and experimental results on the SAHR (Single Actuator Hopping Robot) experimental setup are presented and compared. It is shown that the robot follows both trajectories closely in simulation as well as in experiment. Also the robot is tested successfully on a rough terrain course, which includes inclined ground and an abrupt drop in height of over 25% the length of the robot leg. The robot has no knowledge of its environment. Further, the robot is made to run over the course a number of times, to demonstrate the control robustness.

In legged systems design an important question applies to: "What can be inferred from the performance of a legged robot of a similarly configured system, but scaled to a smaller or larger size?" Our work attempts to answer this question and set the basis for a systematic approach in sizing legged robots. This paper focuses on the influence of permanent magnet DC electric drives on the size of quadruped running robots. The reason is twofold. First, many of the existing legged machines have used such actuators for propulsion. The second, the performance of electric motors scales differently from torque- speed requirements of legged robots. Specifically, we show that there exists a particularly sized quadruped running robot that is superior according to desired performance criteria, and under the existing technologic limitations and economic restraints. Therefore, valuable information on legged systems design and insight for optimizing the size of a quadruped robot emerges.

In this paper a novel multipart control is developed for a trotting quadruped robot. The control is designed to drive the quadruped to a steady-state motion with desired forward speed and apex height, using only one actuator per leg. The body pitching motion is controlled to be small. The controller is applied to the robot and the complete system is used to develop a parametric study for the robot. The study examines the behavior of the actuator effort and the leg touchdown angles, over a parametric region of both the robot physical parameters and the gait parameters. Interesting results appear, not previously reported, that may contribute to enhanced robot design and better gait selection for a given robot. Typical findings are that a robot should be lighter- weight when running on more slippery terrain, as well as that certain higher forward speeds require less actuator effort than other slower speeds.

In this work a novel control method is presented for controlling the forward speed and apex height of a special class of running quadruped robot, with a dimensionless inertia of 1, and one actuator per leg. Seeking to minimize the parasitic pitching motion in running, pronking is used as the target gait. The control design is based on the robot dynamics, allowing its application to a wide range of robots of the class studied. Moreover, the controller adjusts the robot speed and height, requiring knowledge only of the robot physical parameters. The control ensures that negative actuator work during the stance phase is zero, thereby reducing the power expenditure. Small, off-the-shelf DC motors are adequate for the control implementation, while results of application to a detailed robot model show good performance even when including leg mass, foot collision, motor limitations, foot slipping and other factors.

This paper considers the design of a novel closed- loop trajectory tracking controller for an underactuated robotic airship having 6 degrees of freedom (DOF) and 3 controls, on forward, yaw and pitch motions using two side thrusters. A backstepping methodology is adopted as a design tool, since it is suitable for the cascaded nature of the vehicle dynamics. It also offers design flexibility and robustness against parametric uncertainties which are often encountered in aerodynamic modeling and air stream disturbances. Indeed, in our simulations we assume a 10% error in all dynamic parameters and yet the controller performs position, orientation, linear and angular velocities tracking successfully. We also impose an additional air stream disturbance and the controller corrects the vehicle's trajectory successfully too.

This paper studies the capabilities of a microrobotic platform, driven by vibrating motors, to generate and impart micromanipulation forces of desired type and magnitude. First, an analysis is carried out on the nature of the actuation forces of the motion mechanism of the platform. The results demonstrate that the oscillating nature of these forces does not allow their direct use for micromanipulations. Consequently, further analysis is conducted to identify the conditions, under which the platform's actuation forces can be exploited for micromanipulations. To this end, a dynamic model of a single-dimensional pushing operation is developed, comprising the dynamics of the platform, the manipulator and the object. It is demonstrated by simulation that the forces imparted on the manipulated object depend on the physical parameters of the platform-manipulator system. Accordingly, a set of nonlinear equations involving platform-manipulator system parameters, is formulated that describes the conditions for developing micromanipulation forces of appropriate type and magnitude. The solution of this set of equations yields a range of parameter values, which are used as guidelines in the design and construction of a manipulator that is capable of applying smooth and controllable forces to manipulated objects. Using the parameter values suggested by the developed analysis, a needle type manipulator, appropriate for force feedback applications, is designed, built, and mounted on an experimental prototype of the microrobotic platform. Using this manipulator, experiments demonstrate the force capabilities of the microrobotic platform and verified the analytical and simulation results.

Conservation of angular momentum that introduces nonholonomic behavior, underactuation and time dependence, makes the trajectory planning of gymnastic robots difficult. By defining appropriate values for the initial angular momentum, a method is developed that can lead a mechanism to a desired final configuration from an initial given one, in prescribed time. This method is optimization-based and fully exploits the initial mechanism angular momentum. Obstacle avoidance during flight is achieved by setting additional constraints. The method results in smooth, small in magnitude, and therefore easily applicable joint torques.

In this paper a study is conducted on the force capabilities of centripetal force actuated microrobotic platforms. The aim is to exploit the centripetal forces generated by platform mounted vibrating micro-motors for micromanipulation purposes. First, an overview of the platform dynamics and motion capabilities is presented. The type of forces generated by the actuation mechanism as well as due to the impulsive interaction with the working environment are studied. Then design steps are proposed for (i) the reduction or elimination of undesired impulsive forces, (ii) the attenuation of the force ripple transmitted to the manipulated object. The outcome is a smooth, controllable force transmitted to the manipulated object. A cantilever is mounted on the platform and preliminary experiments are conducted.

In free-floating mode, space manipulator systems have their actuators turned off, and exhibit nonholonomic behavior due to angular momentum conservation. The system is underactuated and a challenging problem is to control both the location of the end effector and the attitude of the base, using manipulator actuators only. Physical limitations, imposed by system's dynamic parameters, are examined. Lower and upper bounds for base rotation, due to manipulator motions, are estimated. An analytical path planning method is briefly presented and appended by a technique which extends drastically the accessibility of final configurations and simplifies the free parameters selection. Based on this extension, a numerical approach is also derived and examples are given. The presented methodologies avoid the need for many small cyclical motions, and use smooth functions in the planning scheme, leading to smooth configuration changes in finite and prescribed time

This paper presents the motion analysis, design and position control of a novel, low cost, sliding micro-robot, which is actuated by centripetal forces generated by robot mounted vibration micro-motors. A new, two-micromotor design of the platform is presented, that improves system energy efficiency, and further does not necessitate for synchronous actuator operation and robot symmetry. The motion behavior of the micro-robot, for asynchronous actuation operation, is expressed analytically and simulation results are presented. A control strategy for microrobot x,thetasz, position control that employs two motor speed controllers, and a platform position controller is designed. The control system performance is evaluated through the simulation of a successful trajectory tracking task. A prototype of the micro-robot has been constructed and is presented

Free-floating space manipulator systems, have spacecraft actuators turned off and exhibit nonholonomic behavior due to angular momentum conservation. A path planning methodology for planar free– floating space manipulator systems is developed that allows simultaneous manipulator end-point and spacecraft attitude control using manipulator actuators only. The method is based on mapping the angular momentum to a space where it can be satisfied trivially. Smooth and continuous functions such as polynomials are employed driving the system to a desired configuration. It is shown that the method allows for smooth configuration changes in finite and prescribed time, without requiring small cyclical motions. Limitations are discussed and examples are presented.

This paper addresses the combined problem of trajectory planning and tracking control for underactuated AUVs moving on the horizontal plane. A reference feasible trajectory for the position and orientation of the AUV is planned so that it is consistent with vehicle dynamics. Using these reference values the dynamics of the vehicle is transformed to the error one. Partial state-feedback linearization, backstepping and non-linear damping techniques are utilized to stabilize the above system and force the tracking error to a neighborhood about zero that can be made arbitrarily small. Simulation results that validate the proposed tracking methodology are presented and discussed.

This paper presents the analysis and design of a novel mini-robotic platform that is able to perform translational and rotational sliding with sub-micrometer positioning accuracy and develop velocities up to 1.5 mm/s. The platform actuation system employs vibration micro motors. The dynamic model of the platform and of its actuation system is presented, and analytical expressions are derived which provide design guidelines for the platform. Simulations are performed which verify the analytical results and demonstrate the platform capabilities. The platform design is simple, compact and of low cost. Also the energy supply of the mechanism can be accomplished in an untethered mode using simple means such as single cell batteries.

In this paper it is shown that, for a one-legged robot, there exists a particular passive gait, of all those possible, for which the dissipated energy per meter of travel is minimized. An analytical method is used to identify the optimal gait. A SLIP model of the robot is used to simplify the dynamics. Both mechanical and electrical losses are taken into account. A numerical analysis of a complete robot model follows, to evaluate the accuracy of the analytical prediction. Finally, the limitations imposed by a torque limited motor, with regard to the optimal gait, are studied.

An OpenGL/C++ real-time graphic environment, part of a training simulator for urological operations, is presented. The graphic environment simulates endoscope insertion in a small diameter deformable tube and is used with a low-force 5-dof force-feedback haptic mechanism. Piecewise Bezier interpolations are used for smooth urethra deformations. A novel particle-based model computes the forces and torques fed to the haptics. Realistic textures from medical databases are employed and a 25 fps refresh rate is achieved using the Rendering Thread method. The overall simulator software is made of three processes running on two distinct platforms, communicating via Ethernet and TCP/IP.

This work presents a design methodology, which aims at the minimization of the mass, inertia and joint friction for a low - force five - dof haptic device. The haptic device is optimized along a typical path with proper tolerances, rather than at some workspace operating point. The device, part of a training medical simulator for urological operations, consists of a two dof, 5-bar linkage and a three dof spherical joint. The requirement for reliable reproduction of low torques and forces lead to the need for minimization of device induced parasitic forces and torques. The multiobjective optimization employed is based on two objective functions that include mass/ inertia properties and joint friction. The kinematical and operational constraints are taken into account. The resulting optimized mechanism is substantially improved with respect to an existing device.

In this paper, we study the passive dynamics of quadrupedal bounding, based on a simplified model of our Scout II quadruped robot. Surprisingly, numerical return map studies reveal that passive generation of a large variety of cyclic bounding motion is possible. Most strikingly, local stability analysis shows that the dynamics of the open loop passive system alone can confer stability of the motion. Stability improves at higher speeds, which is in agreement with recent results from biomechanics. These results can be used in developing a general control methodology for legged robots, resulting from the synthesis of feed-forward and feedback models that take advantage of the mechanical system, and might explain the success of simple, open loop bounding controllers on our experimental robot.

Virtual reality is becoming very important for training medical surgeons in various operations. Interfacing users with a virtual training environment requires the existence of a properly designed haptic device. This paper presents the design and implementation of a new force feedback haptic mechanism with five active degrees of freedom (DOFs), which is used as part of a training simulator for urological operations. The mechanism consists of a 2-DOF, 5-bar linkage, and a 3-DOF spherical joint, designed to present low friction, inertia and mass, and to be statically balanced. The device is suitable for the accurate application of small forces and moments. All five actuators of the haptic device are base-mounted dc motors and use a force transmission system based on capstan drives, pulleys, and tendons. The paper describes the overall design and sizing considerations, the resulting kinematics and dynamics, the force feedback control algorithm, and the hardware employed. Experimental results are provided.

A haptic feedback mechanism with five active degrees of freedom (dof), part of a training simulator for urological operations, is presented. The mechanism consists of a 2-dof 5-bar linkage, and a 3-dof spherical joint. To reproduce very small forces and moments, the mechanism has low friction, inertia and mass, is statically balanced, and has a simple mass matrix. Roll-pitch-yaw motions of the tool result in motions of the corresponding actuator. Force feedback transmission is achieved via capstan drives and idler pulleys. The computation of the currents and the structure of the control loop are described.

Friction is responsible for several servomechanism problems, and their elimination is always a challenge for control engineers. In this paper, feedback model-based compensation of friction is used for servomechanism set point and tracking tasks. Basic friction models are tested and their influence on system response is examined using describing function analysis. Analytical predictions are compared to simulations and experimental results. Various control laws using friction compensation are compared experimentally. Results showed that for both types of tasks, the best response is obtained by a model-based control law with friction compensation using the general kinetic friction model.

A planning methodology for nonholonomic mobile manipulators that employs smooth and continuous functions such as polynomials is developed. The method decouples kinematically the manipulator from the platform by constructing admissible paths that drive it to a final configuration and is based on mapping the nonholonomic constraint to a space where it can be trivially satisfied. In addition, the method allows for direct control over the platform orientation. The developed transformation also maps Cartesian space obstacles to transformed ones and allows for obstacle avoidance by increasing the order of the polynomials that are used in planning trajectories. The additional parameters required are computed systematically. It is shown how the method can be extended for avoiding obstacles of any number.

This paper presents a novel approach to compute the rank-deficiency locus of nonsquare Jacobian matrices. This algorithm is based on the computation of the singular vectors associated to zero singular values of the Jacobian. Examples are provided to illustrate the application of the algorithm. Results an shown for a four degree-of-freedom and a seven degree-of-freedom manipulator.

Mobile manipulator systems, comprised of a mobile platform with one or more manipulators, are of great interest in a number of applications. This paper presents a planning and control methodology for such systems allowing them to follow simultaneously desired end-effector and platform trajectories without violating the nonholonomic constraints. Based on a reduction of system dynamics, a model-based controller is designed to eliminate tracking errors without requiring large gains. The sensitivity to parameter errors is examined and found to be negligible. The validity of the methodology is demonstrated using example systems.

This paper focuses on the development of a real-time graphical simulator engine for a forestry machine. The rigid body dynamics of the machine's manipulator are integrated with electrohydraulic actuator dynamics and joint controllers. System stiffness introduced by the closing valves, high order hydraulic dynamics, and an interpreted implementation are identified as the prime reasons for slowing down the integration. Successive models are proposed aiming at achieving a faithful machine simulator that can run in real-time. Simulation results obtained show very good prediction of an actual machine's behavior, with execution speeds improved by a factor of 35.

Impedance control of a hydraulic servoactuator joint system is discussed. Impedance control imparts a desired behavior to a system, rather than controlling position or force individually. Due to nonlinear properties of hydraulic actuators, impedance control is difficult. The control strategy presented involves a combined feedforward and feedback control. An impedance filter modifies a desired trajectory according to a specified behavior. The modified trajectory is fed to a reduced-order model of the servoactuator hydraulic joint in order to reduce the effects of the nonlinear hydraulic dynamics. Position, velocity and pressure feedback loops compensate for the unmodeled dynamics. Simulation results show the strategy to be promising in providing impedance control to the joint. Special attention is given to the careful choice of impedance and control parameters to ensure smooth transition between contact and non-contact regimes, and to avoid actuator saturation. The developed controller is useful in achieving a desired behavior of hydraulic manipulators in contact tasks. It will provide the basis for a robust impedance control of the SARCOS high-performance hydraulic manipulator.

Space manipulators mounted on an on-off thruster-controlled base are envisioned to assist in the assembly and maintenance of space structures. When handling large payloads, manipulator joint and link flexibility become important, for they can result in payload-attitude controller fuel-replenishing dynamic interactions. In this paper, the dynamics model of an N-flexible-joint space manipulator is developed. The model of a three-flexible-joint manipulator mounted on a six-degree-of-freedom spacecraft is used to compare three different on-off thruster attitude control systems. Two variations of a classical control scheme are suggested to minimize such undesirable dynamic interactions, as well as thruster fuel consumption.

Impedance control was formulated originally to impose a desired behavior on a single manipulator interacting with its environment. In this paper, a new algorithm called multiple impedance control (MIC) is proposed for the cooperative manipulation of a common object. The general formulation for the MIC algorithm is developed and it is shown that under the MIC law all cooperating manipulators, and the manipulated object exhibit the same designated impedance behavior. At the same time, the potentiality large object inertia and other forces are taken into account. An estimation procedure for contact force determination is given which results in a good approximation even during an impact. Using an example, the response of the MIC algorithm is compared to that of the object impedance control. It is shown that in the presence of flexibility, the MIC algorithm results in an improved performance.

In this paper, modelling and identification of a hydraulic servoactuator system is presented. The importance of such a model is evident in further understanding the system and in order to develop a robust force controller. The model accounts for line losses, nonlinear orifice areas, hysteresis, friction, leakage, and load dynamics. System parameters are identified based on a high-performance hydraulic manipulator joint, and in particular, the elbow of the SARCOS slave manipulator. Specialized hardware was designed and constructed in order to help identify parameters, to allow line pressure measurements, and to validate the model. The model is verified by comparing simulation and experimental results in two modes: static and dynamic. The results prove to be very good. The developed model sheds light onto the subsystems in a hydraulic manipulator joint and will prove useful in the development of a robust force control algorithm.

Multiple impedance control (MIC) is a new algorithm which enforces a designated impedance on both a manipulated object, and all cooperating manipulators. In this paper, the MIC is applied to a space robotic system in which robotic arms, mounted on a free-flying-base, manipulate an object. The general formulation of the MIC is extended to include the dynamic coupling between the arms and the base. It is shown that under the MIC law, all participating manipulators, the free-flyer base, and the manipulated object exhibit the same designated impedance behavior. This guarantees good tracking of system manipulators and the object, in performing a manipulation task. A system of two cooperating two-link manipulators is simulated, in which a remote centre compliance is attached to the second end-effector. The object is grabbed with a pivoted grasp condition, i.e. both the translational and rotational motions of the object have to be controlled by end-effector forces. As simulation results show, the response of the MIC algorithm is smooth, even in the occurrence of an impact due to collision with an obstacle.

This paper focuses on modeling and parameter estimation for the electrohydraulic actuation system of an articulated forestry machine. The linear graph method is implemented in deriving mathematical models of the swing, boom and stick subsystems. Actuation dynamics are subsequently integrated with manipulator dynamics to result in a complete machine model. Identification procedures employed in estimating physical parameters are discussed. Model validation studies show good agreement between model predictions and experiments. The derived models will be used for designing a controller for coordinated endpoint motion, for prediction, and for a real-time graphical training simulator.

This paper focuses on the generation of dynamic models for an articulated forestry machine. Such models can be used for training simulators, for sizing components, and for control. The most complex model includes base compliance, and pendulum-like motions of the processing head suspended from an end-point. A Newton-Euler iterative method, implemented symbolically, is used to include base degrees-of-freedom due to the machine's compliant tires. Techniques and experiments designed to extract system parameters are described. Based on the obtained models, a novel valve-sizing methodology is outlined. Finally, simulation results of the machine's response are provided.

In this paper, modelling and identification of a hydraulic servoactuator system is presented. The development of the model is important for further understanding the system and for developing a robust force controller. A systems approach is used to model the various subsystems including the servovalve dynamics, fluid dynamics and the vane and load dynamics. Included in the model are line losses, leakage, and hysteresis. System parameters are identified using the elbow joint of the SARCOS slave experimental hydraulic manipulator. Specialized hardware was designed and constructed for this purpose. The model was validated by comparing simulation and experimental results. The correlation between model and actual system response proved to be very good. Hence, the developed model predicts well the system dynamic behavior and will prove useful in the development of a robust force controller.

Transpose Jacobian control is one of the simplest algorithms used in manipulator control. However, since it is not dynamics-based, poor performance may occur in applications where high speed tracking is required. In this paper, a modified transpose Jacobian algorithm is presented and applied to control of space free-flyers. This new algorithm employs stored data of the control command in the previous time step, resulting in improved performance. The gains of the modified algorithm do not need to be large, hence the noise rejection characteristics of the algorithm are improved. Stability analysis, based on Lyapunov's theorems, shows that both the standard and the modified transpose Jacobian algorithms are asymptotically stable. Simulations of both terrestrial and space applications show that the tracking performance of this new algorithm is comparable to that of computed torque algorithms, although it does not require a priori knowledge of plant dynamics.

This paper focuses on the modeling, parameter estimation, and model validation in open and closed-loop of an experimental forestry machine manipulator. Symbolic Newton-Euler and linear graph methodologies are used in deriving mathematical models of the swing, boom and stick subsystems. Actuation dynamics are integrated with manipulator dynamics to result in a complete manipulator and actuation model. Identification procedures employed in estimating physical parameters are discussed. Model validation studies show good agreement between model predictions and experiments. The models will be used for designing a controller for coordinated end-point motion and for a real-time graphical training simulator.

Mobile manipulators operating in field environments are susceptible to dangerous and costly rollover or tipover instabilities, particularly when operating on an uneven terrain or when exerting large forces or moments. By monitoring the static and dynamic tipover stability margins of a mobile manipulator it is possible to predict such tipover and take appropriate actions to prevent the tipover from occurring. This paper describes a scheme for automatic tipover prediction, and prevention, which uses the static and dynamic force-angle measures of tipover stability margin. Time-until-tipover prediction is accomplished using estimated gradients of the tipover stability margins, and prevention is accomplished using a combination of the manipulator and platform actuators. Simulation results demonstrate the efficiency and promise of the proposed scheme for automatic tipover prevention.

Mobile manipulators operating in field environments will be required to perform tasks on uneven terrain which may cause the system to approach, or achieve, a dangerous tipover instability. To avoid tipover in an automatic system, or to provide a human operator with an indication of proximity to tipover, it is necessary to define a measure of stability margin. This work presents a new tipover stability measure (the force-angle stability measure) which is easily computed and sensitive to topheaviness. The proposed metric is applicable to systems subject to inertial and external forces, operating over even or uneven terrains. Performance of the measure is demonstrated using a forestry vehicle simulation.

Studies the problem of large force/torque application using robotic systems with limited force/torque actuators. For such systems, the available workspace may be smaller than its reachable workspace. It is shown that redundancy increases the force capability and workspace of a robotic system. To plan redundant manipulator postures during force tasks, a new method based on a min-max optimization scheme is used. Unlike other norm-based methods, the proposed one guarantees that no actuator capabilities are exceeded, and that the required force/torque of the most loaded actuator is minimized. Examples that demonstrate the validity and usefulness of the proposed method are included.

Space manipulators mounted on an on-off thruster-controlled base are envisioned to assist in the assembly and maintenance of space structures. When handling large payloads, manipulator joint and link flexibility become important for it can result in payload-attitude controller fuel-replenishing dynamic interactions. In this paper, the dynamic behavior of a flexible-joint manipulator on a free-flying base is approximated by a single-mode mechanical system, while its parameters are matched with available space-manipulator data. Describing functions are used to predict the dynamic performance of three alternative controller/estimator schemes, and to conduct a parametric study on the influence of key system parameters. Design guidelines and a particular state-estimator are suggested that can minimize such undesirable dynamic interactions as well as thruster fuel consumption.

This paper analyzes the application of large force/torques by robotic systems with limited force/torque actuators. It is shown that such system may be able to apply a force/torque in some configurations only; therefore its useful force workspace is limited. To improve the force capabilities of a system, base mobility and/or redundancy can be employed. A planning algorithm is proposed which results in proper base positioning relative to a large-force quasi-static task. To plan redundant manipulator postures during large force-tasks, a new method based on a min-max optimization scheme is developed. Unlike norm-based methods, this method guarantees that no actuator capabilities are exceeded, and that the force/torque of the most loaded joint is minimized. Examples that demonstrate the validity and usefulness of the proposed methods are included.

In a number of industrial, space, or mobile systems applications, reaction forces and moments transmitted by a manipulator to its base are undesirable. Based on the force and moment transmission analysis, a three DOF redundant manipulator design is selected aiming at reactionless motions. Dynamic reaction forces are eliminated by using force balancing. Reaction moments are eliminated by following reactionless paths, whose planning is simplified by rendering the dynamics of the system decoupled and invariant. The value of the synergy between design and planning is demonstrated by example cases. An additional advantage of this design is that the manipulator can be used either as a redundant system, or as a two DOF reactionless system.>

Studies the motion control of a multi-arm free flying space robot chasing a passive object in close proximity. Free-flyer kinematics are developed using a minimum set of body-fixed barycentric vectors. Using a general and a quasi-coordinate Lagrangian formulation, two dynamics models are derived. Control algorithms are developed that allow coordinated tracking control of the manipulators and the spacecraft. The performance of model-based algorithms is compared, by simulation, to that of a transposed Jacobian algorithm. Results show that the latter can give reasonably good performance with reduced computational burden.>

Kinematic models for multiple manipulator space robotic systems are developed, as functions of body-fixed barycentric vectors. These models are used to define workspaces for single- and multi-manipulator free-floating systems. It is shown that following the capture of a large payload, the location of these workspaces in space changes, and their size is reduced. These effects, common in single- and multi-manipulator systems, must be taken into account during the planning of manipulation tasks in space. A procedure for manipulating a large payload is proposed. Given a payload and its desired path in space, this procedure yields an optimum grasping posture to ensure successful manipulation of the payload.

Some important dynamics and control problems unique to space robotic systems are discussed. Particular attention is paid to free-flying and free-floating space robots that might be used for such tasks as space station repair and construction. Advances in solving these problems are briefly reviewed. Three promising methods for planning and controlling the motion of space robotic systems are presented. It is suggested that a thorough understanding of the fundamental dynamics of these systems will result in effective solutions to their control problems.>

Nonholonomic behavior is observed in free-floating manipulator systems, and is due to the nonintegrability of the angular momentum. Free-floating manipulators exhibit dynamic singularities which cannot be predicted by the kinematic properties of the system and whose location in the workspace is path dependent. Trouble-free Path Independent Workspaces are defined. A joint space planning technique used to control the orientation of the spacecraft by using joint manipulator motions is reviewed, and its limitations are discussed. Finally, a cartesian space planning method that permits the effective use of a system’s reachable workspace by planning paths that avoid dynamically singular configurations is proposed and demonstrated by an example.

The coordinated control of space manipulators and their spacecraft is investigated. The dynamics of free-flying space robotic systems are written compactly as functions of the system barycentric vectors. A control technique is developed that includes requirements on a spacecraft's position and orientation as well as on its manipulator. This control scheme has the double advantage of allowing a system's motion to be planned to avoid impacts with is environment, and of maintaining a favorable manipulator configuration during the end-effector's motion. In addition, since a system's spacecraft can be moved, the workspace of its manipulator becomes unlimited. A transposed-Jacobian type controller with inertial feedback is developed, and an example is used to demonstrate this technique.>

It is suggested that nearly any control algorithm that can be used for fixed-based manipulators also can be employed in the control of free-floating space manipulator systems, with the additional conditions of estimating or measuring a spacecraft's orientation and of avoiding dynamic singularities. This result is based on the structural similarities between the kinematic and dynamic equations for the same manipulator but with a fixed base. Barycenters are used to formulate the kinematic and dynamic equations of free-floating space manipulators. A control algorithm for a space manipulator system is designed to demonstrate the value of the analysis.>

A study of the characteristics of control algorithms that can be applied to the motion control of space manipulators is reported. The results obtained show that nearly any control algorithm that can be applied to conventional terrestrial fixed-base manipulators, with a few additional conditions, can be directly applied to free-floating space manipulators. Barycenters are used to formulate efficiently the kinematic and dynamic equations of free-floating space manipulators. A control algorithm for a space manipulator system is designed to demonstrate the value of the analysis.>

Emulating on Earth the weightlessness of a manipulator floating in space requires knowledge of the manipulator's mass properties. A method for calculating these properties by measuring the reaction forces and moments at the base of the manipulator is described. A manipulator is mounted on a six-degree-of-freedom sensor, and the reaction forces and moments at its base are measured for different positions of the links of the manipulator as well as for different orientations of its base. A procedure is developed to calculate from these measurements some combinations of the mass properties of the manipulator. The mass properties identified are not sufficiently complete for computed torque and other dynamic control techniques, but do allow compensation for the gravitational load on the links of the manipulator, and for simulation of weightless conditions on a space emulator. The algorithm has been experimentally demonstrated on a PUMA 260 and used to measure the independent combinations of the sixteen mass parameters of the base and three proximal links of the manipulator.>