New Publications are available for Robot and manipulator mechanics
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New Publications are available now online for this publication.
Please follow the links to view the publication.Study on automatic feeding in hot stamping production line
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.1036
The material feeding in hot stamping is quite different from traditional cold stamping. This paper described some key issues of automatic high-temperature steel plate feeding, some analysis and studies were done about gripping method, clamping force, local and whole plate temperature drop in transferring process, and some ideas about robot manipulator' design were proposed with that.Inverse kinematics computation in robotics using conformal geometric algebra
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.1527
Conformal geometric algebra is a kind of new geometric representation and geometric computation tool. In this paper, an approach to the inverse kinematics of a serial manipulator is presented based on the conformal geometric algebra. First, the basics of the conformal geometric algebra are introduced. Then, an algorithm for the inverse kinematics of a 5-dof serial manipulator is presented, which can be able to comprehend without prior knowledge of geometric algebra. (5 pages)The magnetic field analysis and optimization of permanent-magnetic adhesion device for a novel wall-climbing robot
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.1531
The climbing-wall robot based on permanent-magnet adsorption is always concentrated on tracked-type, but robot with this type is deficient flexibility when it moves. In this paper, a new permanent-magnet adhesion device of an adjustable pole is introduced in the wheel-type robot, the device can provide 1500 N force when the air gap between the device and wall is 4 mm to meet load requirement in working state, and at this time the magnetic flux leakage is very small. While permanent magnetic force is almost approach zero when device in non-operating state, so the robot can up and down the wall conveniently. The mathematic model is established by Finite Element Method to calculate and design magnetic field. The finite element software is used to analyze and optimize the magnetic field distribution, magnetic field intensity as well as the structure size which will affect magnetic field intensity to the device. Optimization results show that every parameter has a different influence on adsorbability of the device when it changes. Ratio between the maximum and minimum of adsorbability in two states is more than 5666 times when structure is designed reasonably. (5 pages)Constraint forces applied on limbs of 3-RPS parallel manipulator in static equilibrium
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.1526
To know constraint forces of joints in static equilibrium is one of the important bases for mechanical design. As a 3 degree-of-freedom (dof) in-parallel manipulator, 3-RPS is has found wide applications. Static characteristics of 3-RPS are presented in this paper taking gravity into account. With constructed static equilibrium equations of 3-RPS, constraint forces of passive joints applied on each link have been obtained. Static analysis shows that each link is subjected to push/pull, bending and twisting torque in general. In particular, when centre of mass (CM) of link is on line through centres of joints fixed on platform and base respectively, or when gravity is omitted, each link will not bear twisting moment. Finally an example is provided to demonstrate static characteristics of 3-RPS. (5 pages)Research on detection system for coal mine detection robot based on the technology of information fusion
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.1529
China have a large of coal resources, while the accidents due to gas explosions, gushing water, fire and other factors often happened every year. This paper presents a system of robot's sensors and obstacle avoidance which suitable for detecting mine environmental information. The sensor system that composed of gas sensors, temperature sensors, pressure sensors and obstacle avoidance sensors, enable the robot to finish the detection of mine information successfully and play an important role in taking rescue work favorably. The system of obstacle avoidance is mainly composed of industrial computer and its board. The robot can realize the intelligent and autonomous obstacles-avoiding movement in mine by an advanced navigation technology of fuzzy neural network based on T-S model. The simulation experiments show that this system of sensors can achieve security obstacle avoidance, and detect the information in mine accurately and timely which can support accurate foundation for rescue work. (5 pages)Web services based mechatronics product conceptual design and its application in robot arm and underactuated wrist
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.2043
Conceptual design is an early stage of the whole mechatronics product development process, which involves the generation of solutions to satisfy the design requirements. It is a crucial issue how to help designers to find proper principle solutions from all knowledge repositories to support conceptual design. This paper proposes a web services based conceptual design methodology in a distributed knowledge resource environment, which can be used to design innovative mechatronics product. The design of service robot arm and underactuated wrist is given as an example, which demonstrates that the methodology is obviously useful.Research on path planning for coal mine detection robot
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.1530
Aiming at the path planning for coal mine detection robot in unknown static environment, a path planning method is propounded which couples behavioural dynamics with rolling scan information. Firstly, the method of sub-target's choice is provided using heuristic function according to the rolling scan information L it is local environment information L which is obtained by sensors. Then path planning is divided into trending to target behaviour and obstacle avoidance behaviour L their behaviour state and behaviour pattern dynamics modes are established L and then one autonomous local path planning technology is implemented using behaviour dynamics mode in a single rolling scan region. Connecting a series of local paths tandem according to continuity, the global path planning is accomplished ultimately. The method has a simple principle and low calculating burden L smooth path and high applied value. The method's efficiency and adaptability is verified by simulation experiment. (5 pages)Kinematic control of a redundant manipulator using inverse-forward adaptive scheme
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.1727
The inverse kinematic (IK) relationship of a manipulator is a one-to-many map which can not be learnt using a feed-forward neural network (FFN). The usual method is to learn the forward kinematic relationship using a FFN and then obtaining the IK solution through inversion of the approximate forward model. The accuracy of the inverse kinematic solution thus obtained is limited by the accuracy of the forward model. However, it is not possible to learn the forward kinematic map accurately even with a large network size and a large training data set. Moreover, one needs to resolve redundancy while solving IK in order to make use of available dexterity effectively. These limitations of a conventional network inversion-based scheme are overcome by using an inverse-forward adaptive scheme where the idea is to learn a local solution around the current joint angle configuration rather than trying to learn the global solution through an accurate forward model. It is shown that the accuracy of the IK solution thus obtained, is almost independent of the accuracy of the forward model. The redundancy is resolved by using a KSOM-SC network architecture as a hint generator for initializing the inverse-forward adaptive scheme. The efficacy of the proposed scheme is demonstrated through simulations and real-time experiment on a 7 DOF PowerCube manipulator. A simple obstacle avoidance task is performed to demonstrate the redundancy resolution process. (6 pages)Optimal control and design of flexible manipulators based on LQR output feedback
http://dl-live.theiet.org/content/conferences/10.1049/cp_20061095
The construction of lightweight manipulators with a larger speed range is one of the major goals in the design of well-behaving industrial robotic arms. Their use leads to higher productivity and less energy consumption than is common with heavier, rigid arms. However, due to the flexibility involved with link deformation and the complexity of distributed parameter systems, modeling and control of flexible manipulators still remain a major challenge to robotic research. Mechatronic design is a global optimization of the overall system. As a flexible manipulator, the overall system is the integration of link dynamics, DC motor equation, measuring sensors and the selected controller. The optimization process results in an optimal link geometric distribution, an optimal controller structure subject to the performance requirement. A rectangular beam is considered and divided into N segments equally along with the beam spatial coordinate. Case studies based on LQR formula are considered. The LQR feedback is as an inner loop followed by an adaptive iterative algorithm (IHR) as an outer loop searching for the beam width distribution. The mechatronic design procedure is addressed through detailing the integration of the inner loop with the outer loop. Also, the responses for step-type disturbance and step input are carried out to show the system robustness.An improved algorithm for inverse kinematics solution of redundant modular robots
http://dl-live.theiet.org/content/conferences/10.1049/cp_20061116
It is difficult to get solutions that can meet the requirements of high positioning accuracy and real time control simultaneously among the infinite solutions of a redundant robot. Based on weighted least-norm method (WLNM), an optimized algorithm for inverse kinematics solution of redundant modular robots, with which the joint limits can be avoided, is presented in this paper. According to the characteristic of robot global wrist organ, the position and pose of the robot tag end can be resolved separately, therefore the computing time is reduced without decreasing the solution accuracy. Recently, an Intravehicular Robot Service System's Ground Demonstration for Space Station has been built in the Space Robot Lab of Bupt, and the operation object of the demonstration is a 9-DOF modular reconfigurable robot. Through the experiments of pulling drawers and pressing buttons by the 9-DOF robot, the accurate and real-time solutions are given to show the applicability and effectiveness of the proposed algorithm. The experiment results demonstrate that the positioning accuracy is up to ±2.0 mm and single-step computing time is less than 1 ms.Kinematics analysis of a parallel machine tool based on genetic algorithms
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060977
This paper presents the kinematics analysis of a novel 5-UPS/PRPU 5-degree-of-freedom parallel machine tool based on genetic algorithms. The characteristic of the parallel machine tool is described and the mathematic expression of the 5-UPS/PRPU parallel machine tool's velocity mapping matrix is derived. The genetic algorithms is introduced in the search of the singular configuration and the extrema of the kinematics performance of the parallel machine tool. The non-singular workspace of the parallel machine tool and the corresponding extrema of the kinematics performance evaluation indices are obtained. The numerical analysis results prove the effectiveness of the algorithm.Kinematic properties of wheeled mobile robots in round ducts/pipes
http://dl-live.theiet.org/content/conferences/10.1049/cp_20061094
To solve the motion control problem of wheeled mobile robots in round ducts/pipes, kinematic properties of wheeled mobile robots in round ducts/pipes are analyzed. The description of posture and motion of a single wheel on a plane is applied to the wheel rolling on the wall of round ducts/pipes by dint of the tangent plane of the cylinder at the contacting point. The trajectory and velocity of the center of a single wheel pure rolling in round ducts/pipes are educed. Geometric constraints of two-wheel robots and three-wheel robots in round ducts/pipes are analyzed respectively. With the theory of instantaneous screw of a rigid-body motion, the kinematic properties of type (1,1) two-wheel robots, type (1,1) three-wheel robots, moving in round ducts/pipes is presented and discussed respectively. Simulation results are presented to show the trajectory of the center of a single wheel pure rolling on the wall of round ducts/pipes, the virtuality of the geometrical restriction equations and performance of the instant screw of the wheeled mobile robots in vertical round ducts.Kinematics analysis of active reflector supporting mechanism for FAST
http://dl-live.theiet.org/content/conferences/10.1049/cp_20061084
In the application of active reflector units supporting mechanism for a large spherical radio telescope (five-hundred meter aperture spherical radio telescope: FAST), a spatial three-degree-of-freedom (DOF) parallel mechanism combining two degrees rotation and one degree translation is investigated. In this paper, the mechanism is described in detail and its inverse kinematics solutions are derived. The parasitic motion of this mechanism is analyzed, and the relationships between the parasitic motions and independent motions of the mechanism are illustrated, followed by the Jacobian matrix of the velocity equation. The distribution of conditioning index on the workspace of the mechanism is obtained. And the workspace of the mechanism is numerically generated. The analysis results prove that the parasitic motion is neglectable compared to the independent motion in this application and the mechanism can be used as the supporting mechanism of spherical radio telescope.Study on large radius of spherical fiducial surface of bearing of highspeed railway forming base on virtual axis
http://dl-live.theiet.org/content/conferences/10.1049/cp_20061109
It is popular to use the method of mold grinding at home and abroad when a cylindrical roller-bearing of highspeed railway is proceeded, however it couldn't realize a continuous processing. It's needed to make axis of roller swing around a fixed axis and roller rotate around self-axes in order to realize a continuous processing, which needs a mechanism swinging around fixed axis. Because a diameter of spherical surface of cylindrical roller-bearing exceeds five meters, the dimension of a swinging mechanism must be very huge, which makes moment of inertia become great and limit the swinging speed. This mechanism isn't practical. In view of this situation, a 4-RPR structure based on the theory on parallel robot was brought forward to realize a mechanism swinging around virtual axes. Its dimension and moment of inertia are so small that the continuous processing of rollers could be gotten. The direct and inverse kinematic models are established in this paper.Vibration controllability of underactuated robots with flexible links
http://dl-live.theiet.org/content/conferences/10.1049/cp_20061072
The controllability analysis of underactuated robots with flexible links is the important preparatory step to efficiently control the system. In this paper, based on the dynamic model using the assumed mode method, controllability of a planar 3DOF underactuated manipulator with one passive joint and the 3-rd flexible link is analyzed in two stages. Firstly, neglecting the elastic deformations of the link, the state controllability results of the corresponding rigid system at various actuator placements is directly introduced from the preceding study; secondly, the structural vibration controllability of underactuated flexible one is investigated according to the state controllability result. It is shown that the vibration controllability of an underactuated flexible manipulator is both joint-configuration-dependent and actuator-placement-dependent. If an underactuated rigid robot is not state controllable, then the vibration controllability of the corresponding flexible one is uncertain and meaningless. By comparing the simulation of the modal accessibility index of two vibration controllable systems at different actuator placements, a conclusion can be drawn that the system with the second passive joint is easier than the one with the third passive joint to control the vibration of flexible link. Finally, the proposed method is extended to n-DOF underactuated flexible robots with one passive joint.Architecture singularity analysis for a class of parallel manipulators
http://dl-live.theiet.org/content/conferences/10.1049/cp_20061097
The present investigates the architecture singularity of a class of parallel manipulators. In general, singularity of parallel manipulators can be categorized into inverse and forward kinematic singularities. Based on the kinematics, the inverse Jacobian matrix of the parallel manipulator is factorized into three parts as: limb length diagonal matrix, structure parameter matrix and the motion parameter matrix so that the singularity analysis becomes convenient. Because each limb length is not zero, there does not exist inverse singularity. Only forward kinematic singularity exists in the parallel manipulators. The forward kinematic singularity is divided into architecture singularity and motion singularity. Architecture singularity is global and results in no solutions for forward kinematics. It should be avoided at the design stage. The class of parallel manipulators becomes architecture singularity as long as their six vertices of the platform are placed in a quadratic curve. Since the architecture singularity can be algebraically expressed, the constraints to avoid the undesired effects of the architecture singularity can be straightforwardly implemented for the design of the parallel manipulators and the planning of workspace and trajectory.Kinematics and dynamics analysis of maintenance manipulator
http://dl-live.theiet.org/content/conferences/10.1049/cp_20061082
A new approach is developed to model dynamic behaviors of robot manipulator. The process is realized through equivalent elements and the equivalent system of forces. Firstly, the concept of element pseudo-mass matrix is proposed based on the equivalent principle of elements, then establishes pseudo-mass matrix of the equivalent system through assembling units normatively, based on finite element thought. Secondly, dynamical modeling equations are produced base on the generalized dynamic equation and concepts of the equivalent system and vector of force. The expression is concise, standard and convenient for using with computer normatively. At last, the approach is used to generate the dynamic equations of five-DOF maintenance manipulator, and the dynamic response of the manipulator is obtained. The results of simulation are the same as those of ADAMS.Research on the hybrid cam-linkage mechanism realizing trajectory
http://dl-live.theiet.org/content/conferences/10.1049/cp_20061099
Based on the analysis of current situation and application prospect of hybrid electromechanical system, the concept of hybrid cam-linkage mechanism is proposed and its significance is expounded. The basic form of hybrid-driven mechanism is given and its kinematic principle is analyzed. Take realizing ellipse path with scheduled timing mark as example, the design method of hybrid cam-linkage generating path is introduced. Providing the parametric equation of the path that the mechanism generate, formulae are derived by kinematic analysis and from these formulae, the theoretical contour equation of the cam is obtained, and then the rotational angle of servo-motor which actuates the crank is solved through computer programming. Using the graphic solution, the flexible workspace and path characteristic of hybrid cam-linkage mechanism is analyzed, and the conclusions are verified by computer simulation, and then the design principle of path is proposed. The kinematic analysis and path characteristic of hybrid cam-linkage mechanism provides more theoretical basis for further study on its dynamic characteristic and geometric optimization issues of mechanism system.Research on path-planning method of a redundant modular robot
http://dl-live.theiet.org/content/conferences/10.1049/cp_20061115
The more complicated anticipant trajectory should be followed by the end-effector of a robot to meet the complex tasks of it, which is a hard job to a general industry robot, but the required path-planning can be realized by a redundant modular robot because of its less joint space limitation. An algorithm for three-dimensional spatial ellipse path-planning is presented in this paper in accord with the characteristic of the redundant modular robots. In this algorithm, the spatial trajectory is simplified to the one in two-dimensional plane by transformation of coordinates firstly, then the differential motion vector of end-effector is deduced by the method of linear interpolation with parabolic transition field, finally the differential increment of joint space is resolved by the inverse kinematics solution, even one or more joints damaged, the required trajectory can be realized continuously by Jacobian matrix reconfiguration. Through the simulations of a 9-DOF redundant modular robot, the results demonstrate that the tracking accuracy is up to ±2.2 mm, which verifies the applicability and effectiveness of the proposed algorithm, and it can be generalized to other styles of curves such as parabola, hyperbola, starlike line etc.Robots and Automated Manufacture
http://dl-live.theiet.org/content/books/ce/pbce028e
<p xmlns="http://pub2web.metastore.ingenta.com/ns/">To serve its purpose, an industrial robot must be harnessed to a manufacturing task, be it welding, assembly, adjustment or the inspection of food products. Complex tasks are likely to require offline programming, both for economy of equipment use and to permit computer simulations for collision avoidance. Vision and other sensory systems are helping to extend the capabilities of robots, while programming techniques are making their use more accessible to the shop floor.</p>Needle dynamics modelling and control in prostate brachytherapy
http://dl-live.theiet.org/content/journals/10.1049/iet-cta.2011.0449
Although ‘Needle steering’ is considered a challenge in needle insertion strategies, needle control becomes a crucial training tool for evaluating surgeon’s skills in such critical incision. In this study, a model-based dynamics equation for the needle movement through the soft tissue is developed. In the proposed control scheme, the force estimation calculated through the simulated tissue deformation data and the dynamic finite element as the tissue model, is used as the force feedback. To point out the role of mechanical properties of the soft tissue, an inverse dynamics control method is used to demonstrate the system performance in presence of uncertainty in tissue mechanical parameters. Moreover, it is shown that the uncertainty in the tissue mechanical parameters dramatically affects the system performance as well as causing instability. Hence subsequently, a robust control approach is designed to compensate for the undesirable effect of parameter uncertainty in the system.Mapping between different kinematic structures without absolute positioning during operation
http://dl-live.theiet.org/content/journals/10.1049/el.2012.1085
When creating datasets for modelling of human skills based on training examples from human motion, one can encounter the problem that the kinematics of the robot does not match the human kinematics. Presented is a simple method of bypassing the explicit modelling of the human kinematics based on a variant of the self-organising map (SOM) algorithm. While the literature contains instances of SOM-type algorithms used for dimension reduction, this reported work deals with the inverse problem: dimension increase, as we are going from 4 to 5 degrees of freedom.Actuator fault detection and adaptive accommodation control of flexible-joint robots
http://dl-live.theiet.org/content/journals/10.1049/iet-cta.2011.0508
This study presents a fault detection and adaptive accommodation control scheme for flexible-joint (FJ) robots with model uncertainties and multiple actuator faults. It is assumed that the value and occurrence time of multiple actuator faults are unknown. A fault detection scheme is designed to detect the first actuator fault of uncertain FJ robots and the fault detectability characterising the class of actuator faults is analysed. Then, we design an adaptive fault accommodation control scheme with prescribed performance bounds, which characterise the convergence rate and maximum overshoot of tracking errors to accommodate the actuator faults and to compensate the effect caused by them. The proposed accommodation controller is developed based on the dynamic surface design and the adaptive technique. From the Lyapunov stability theorem, it is proved that all signals of the closed-loop system are semiglobally uniformly ultimately bounded and tracking errors are preserved within prescribed performance bounds regardless of actuator faults that occur after the first fault detection. A simulation example of a three-link FJ robot is provided to illustrate the effectiveness of the proposed scheme.Adaptive robust time-varying control of uncertain non-holonomic robotic systems
http://dl-live.theiet.org/content/journals/10.1049/iet-cta.2010.0655
This study addresses the trajectory tracking control problem of dynamic non-holonomic robotic systems in chained form in presence of parametric and non-prarametric uncertainties. At first, a global adaptive tracking controller is designed by exploiting the full use of the backstepping technique. Then, the proposed controller is modified to preserve its robustness to non-parametric uncertainties. In contrast to most of the previously developed kinematic and dynamic tracking controllers, the proposed controller makes all tracking errors and parameter estimation errors be at least globally uniformly ultimately bounded (GUUB) and exponentially converge to a small ball containing the origin. A Lyapunov-based stability analysis is presented to guarantee the GUUB stability of the tracking errors. The controller is applied to a non-holonomic wheeled mobile robot and simulation results are presented to illustrate the effectiveness of the proposed control law.Output feedback tracking control of uncertain non-holonomic wheeled mobile robots: a dynamic surface control approach
http://dl-live.theiet.org/content/journals/10.1049/iet-cta.2011.0169
This study addresses the trajectory tracking control problem of electrically driven wheeled mobile robots under non-holonomic constraints in the presence of model uncertainties without velocity measurement. By defining a suitable set of output equations, a new input–output model of wheeled mobile robots is developed, which helps the designer utilise the classic control algorithms of robot manipulators. An observer-based trajectory tracking controller is proposed for the new wheeled mobile robot (WMR) model. Then, in order to reduce the design complexity, the dynamic surface control approach is effectively exploited to propose a tracking controller considering the actuator dynamics. Adaptive robust techniques are also adopted to cope with the parametric and non-parametric uncertainties in the WMR model. A Lyapunov-based stability analysis is utilised to guarantee that tracking and state estimation errors are uniformly ultimately bounded. Simulation results are presented to illustrate the feasibility and efficiency of the proposed controller.Effective neural remedy for drift phenomenon of planar three-link robot arm using quadratic performance index
http://dl-live.theiet.org/content/journals/10.1049/el_20080455
A quadratic performance index is investigated for the online neural remedy for drift phenomenon of redundant robot manipulators. Computer simulations performed based on a three-link planar robot arm show the efficacy of such a quadratic-index based neural-remedy scheme.Validity and feasibility of intelligent Walkbot system
http://dl-live.theiet.org/content/journals/10.1049/el.2009.0879
The first study to highlight the validity and feasibility of the innovative exoskeletal Walkbot system is presented. The Walkbot is a locomotor retraining robot designed to provide gait impairment for the systematic reacquisition of locomotor skills. Neuromechanical data obtained from kinematic and electromyographic (EMG) measurements yielded excellent validity and consistency. Linear regression analysis for kinematic hip and knee angle data showed R<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sup>=0.8604 and R<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sup>=0.9265, respectively. The coefficient of variation also showed consistent EMG amplitudes in the selected ankle muscles at two independent velocities. The preliminary data provide promising evidence of locomotor retraining.LQR gain-schedule controller for vertical line following
http://dl-live.theiet.org/content/journals/10.1049/el.2010.0947
A novel guidance controller for UAVs to follow a line in the vertical plane based on the well-known linear quadratic regulator (LQR) theory is proposed. Robustness margins are derived based on Lyapunov stability analysis, and an efficient way to design the controller using performance prediction is suggested.Nonholonomic motion planning based on optimal control for flight phases of planar bipedal running
http://dl-live.theiet.org/content/journals/10.1049/el.2011.1712
Presented is a novel approach for online trajectory modification of joint motions to transfer a free open kinematic chain, undergoing flight phase, from a specified initial configuration to a specified final configuration. Formally, it is assumed that a nominal trajectory, computed offline, can reorient the kinematic chain (reconfiguration problem) for a given angular momentum on a time interval. A modification algorithm of body joints, based on optimal control, is developed such that for different angular momentums and time intervals, the same reconfiguration problem can be solved online. This approach can be utilised for space robotics applications and online computation of planar running trajectories during flight phases.Anatomy of a robot
http://dl-live.theiet.org/content/journals/10.1049/et_20080113
Stirling Paatz of robot integrators Barr & Paatz describes the kinematics of an industrial robot.Robonaut flies in [humanoid space robot]
http://dl-live.theiet.org/content/journals/10.1049/et.2010.1719
Robonaut is the first humanoid robot ever sent into space.It is designed to look and behave much like a space-suited human. Robonaut's grasping skills and sensitivity to touch are markedly finer than those of a space-walking astronaut, because its slender fingers have no need for thick gloves. A set of 14 brushless motors in each forearm drive the hands. Robonaut's gold-plated head is articulated at the neck, allowing a similar freedom of movement to a human head. The torso is built from aluminium, with Kevlar and Teflon padding to protect it from fire and micrometeorite impacts. The torso and arms are covered with a custom-fitted fabric skin that secures the electrical wire harnesses and keeps dust away from the mechanical joints. The 'foot' is an adaptor that clicks into various attachment points on the outside of the space station, or on the end of long and similarly articulated robotic boom arms that are already part of the station's external equipment.Development of 6-axis force/moment sensor for a humanoid robot's foot
http://dl-live.theiet.org/content/journals/10.1049/iet-smt_20070019
The development of a 6-axis force/moment sensor considering adult weight for an intelligent foot of humanoid robot is described. To walk on uneven terrain safely, the foot should perceive the applied forces <i xmlns="http://pub2web.metastore.ingenta.com/ns/">Fx, Fy</i> and <i xmlns="http://pub2web.metastore.ingenta.com/ns/">Fz</i> and moments <i xmlns="http://pub2web.metastore.ingenta.com/ns/">Mx, My</i> and <i xmlns="http://pub2web.metastore.ingenta.com/ns/">Mz</i> to itself and control itself using the forces and moments. The applied forces and moments should be measured from a 6-axis force/moment sensor attached to the foot, which is composed of <i xmlns="http://pub2web.metastore.ingenta.com/ns/">Fx, Fy, Fz, Mx, My</i> and <i xmlns="http://pub2web.metastore.ingenta.com/ns/">Mz</i> sensors in a body. Each sensor has different rated loads because the applied forces and moments to foot in walking are different. Therefore one of the important tasks in developing the sensor is to design each sensor with the different rated loads and the same rated output. A 6-axis force/moment sensor for a humanoid robot's foot was developed using parallel plate-beams. The structure of the sensor was newly modelled, and the sensing elements (plate-beams) of the sensor were designed using theoretical analysis. Then, the 6-axis force/moment sensor was fabricated by attaching strain gauges on the sensing elements, and the characteristic test of the developed sensor was carried out. The rated outputs from the theoretical analysis agree well with that from the characteristic test.Velocity controller with friction compensation
http://dl-live.theiet.org/content/journals/10.1049/iet-cta_20050101
The problem of velocity control concerning a manipulator arm is considered. It is assumed that the joint friction is described by a model that contains the Dahl effect. A joint velocity controller and a friction observer are expressed in terms of the normalised quasi-velocities (NQV). The controller with the observer is shown to be exponentially convergent. Some properties arising from the use of NQV are presented. The control strategy, including the friction observer, was tested in simulation on a 3 d.o.f. 3D, Direct Drive Arm robot.Adaptive tracking control of high-order non-holonomic mobile robot systems
http://dl-live.theiet.org/content/journals/10.1049/iet-cta.2008.0061
A backstepping-based tracking control design for uncertain mobile robot systems with non-holonomic constraints is presented. For avoiding the singularity and the necessity of the repeated differentiation of the virtual controller, high-degree polynomials of the affine functions are generally included in many existing kinematic controllers. That unfortunately would cause the possible blowup of the actuators for high-order kinematic systems (e.g. a trailer-type mobile robot) in high-speed motions. Regarding this, an exponentially modulated linear stabilising function is included in this design to alleviate such a difficulty. Next at the dynamic design level, an adaptive control algorithm is developed for attaining the global asymptotic tracking stability of the overall closed-loop system. Two case studies of a unicycle-like and a trailer-type wheeled mobile robots are conducted in the final to demonstrate the effectiveness of the proposed design.Tracking control scheme for an underwater vehicle-manipulator system with single and multiple sub-regions and sub-task objectives
http://dl-live.theiet.org/content/journals/10.1049/iet-cta.2010.0174
This study presents a novel tracking control scheme for an underwater vehicle-manipulator system (UVMS) where the proposed controller is not only used to track the prescribed sub-region but also allows the use of the self-motion to perform various sub-tasks (i.e. drag minimisation, obstacle avoidance and manipulability) because of the kinematically redundant system. In the proposed control scheme, the desired primary task of the UVMS is specified as two sub-regions that are assigned for the vehicle and end-effector. Despite the parametric uncertainty associated with the underwater dynamic model, the controller ensures the sub-task tracking without affecting the sub-region and attitude tracking control objective. The Lyapunov-type approach is utilised to design the controller and an extension to an adaptive-robust control scheme with multiple sub-regions and sub-task objectives is also performed to illustrate the flexibility of the approach. The presence of variable ocean currents creates hydrodynamic forces and moments that are not well known or predictable, even though they are bounded. Therefore the control task of tracking a prescribed sub-region trajectory is challenging because of these additive bounded disturbances. Furthermore, multiple sub-task criteria that are formulated using a weighted-sum approach are added to the control objective. Simulation results are presented to demonstrate the performance of the proposed control law.Co-ordinated collective motion patterns in a discrete-time setting with experiments
http://dl-live.theiet.org/content/journals/10.1049/iet-cta.2009.0338
In this study, the authors co-ordinated collective motion patterns for a group of autonomous vehicles with Cartesian co-ordinate coupling in a discrete-time setting and present experimental results to validate the theoretical results. The collective motion patterns include rendezvous, circular patterns and logarithmic spiral patterns. The authors first study the collective motion patterns for a group of autonomous vehicles with single-integrator kinematics in a discrete-time setting when there exists time delay. The conditions on the network topology, the sampling period, the time delay and the Euler angle are presented such that different collective motion patterns can be achieved. The collective motion patterns for a group of autonomous vehicles with double-integrator dynamics in a discrete-time setting in the presence of relative damping are studied. The conditions on the network topology, the sampling period, the damping factor and the Euler angle are presented such that different collective patterns can be achieved. Finally, the theoretical results are experimentally validated on a multi-robot platform.Robust tracking control for a class of uncertain electrically driven robots
http://dl-live.theiet.org/content/journals/10.1049/iet-cta.2008.0024
The problem of designing robust tracking controls for a large class of robots actuated by brushed direct current motors is addressed. This class of electrically driven robots can be perturbed by plant uncertainties, unmodelled time-varying perturbations and external disturbances. Adaptive neural network (or fuzzy) systems are employed to approximate the behaviours of uncertain dynamics, and the variable structure system control algorithm is used to efficiently eliminate the effect of both the approximation error and the time-varying perturbation. Consequently, a hybrid robust adaptive dynamic feedback tracking controller is developed such that all the states and signals of the closed-loop system are bounded and the asymptotic bound on the trajectory tracking error can be made arbitrarily small. Finally, simulation examples are presented to demonstrate the effectiveness and the tracking performance of the proposed control algorithm.Formulation and analysis of stability for spacecraft formations
http://dl-live.theiet.org/content/journals/10.1049/iet-cta_20050459
A formulation of stability for formation flying spacecraft is presented. First, a formation is defined via control interactions between the spacecraft. Then, stability is formulated on the basis of input-to-output stability with respect to a partitioning of the formation dynamics. The particular form of input-to-output stability used here is based on the peak-to-peak gain of a system from its input to its output. This formulation of stability is shown to be useful in characterising disturbance propagation in the formation as a function of the partition interconnection topology, and also in analysing the robustness of sensing, communication and control topologies. Stability analysis results are presented for hierarchical, cyclic and disturbance attenuating formations in terms of the input-to-output gains of the partitions in the formation. Finally, Lyapunov stability analysis results are provided in terms of linear matrix inequalities for a general class of formations.Distributed estimation, communication and control for deep space formations
http://dl-live.theiet.org/content/journals/10.1049/iet-cta_20050460
Spacecraft formations in deep space give a means of implementing science instruments on a physical scale not possible with an individual spacecraft. Interferometric imaging is one application requiring a large spacecraft separation and extremely high relative position precision in order to image planets in other solar systems. Deep-space missions typically also require a high-level of autonomy, and the proposed distributed architectures for control and coordination, that are consistent with these requirements. Each spacecraft estimates the full state of the formation in order to calculate its optimal control action. Disagreements between estimates on the spacecraft lead to unanticipated dynamics and it is shown how communication may be used to ameliorate the effect of these dynamics. The relationship between the communication topology and the closed-loop system dynamics is presented.Robust <i xmlns="http://pub2web.metastore.ingenta.com/ns/">H</i><sub xmlns="http://pub2web.metastore.ingenta.com/ns/">∞</sub> consensus analysis of a class of second-order multi-agent systems with uncertainty
http://dl-live.theiet.org/content/journals/10.1049/iet-cta.2008.0492
This study is concerned with consensus problems for a class of multi-agent systems with second-order dynamics. Some dynamic neighbour-based rules are adopted for the agents with the consideration of parameter uncertainties and external disturbances. Sufficient conditions are derived to make all agents asymptotically reach consensus while satisfying desired <i xmlns="http://pub2web.metastore.ingenta.com/ns/">H</i><sub xmlns="http://pub2web.metastore.ingenta.com/ns/">∞</sub> performance. Finally, numerical simulations are provided to show the effectiveness of our theoretical results.Friction and uncertainty compensation of robot manipulator using optimal recurrent cerebellar model articulation controller and elasto-plastic friction observer
http://dl-live.theiet.org/content/journals/10.1049/iet-cta.2010.0389
A model-free control scheme with the elasto-plastic friction observer is presented for robust and high-precision positioning of a robot manipulator. The traditional model-based adaptive controller requires information on the robotic dynamics in advance and thus undergoes robustness problem because of complex dynamics and non-linear frictions of a robot system. This problem is overcome by an employed model-free recurrent cerebellar model articulation controller (RCMAC) system and friction estimator for friction and uncertainty compensation of a robot manipulator. The adaptive laws of the RCMAC networks to approximate an ideal equivalent sliding mode control law and adaptive friction estimation laws based on the elasto-plastic friction model are derived based on the Lyapunov stability analysis. To guarantee stability and increase convergence speed of the RCMAC network, the optimal learning rates are obtained by the fully informed particle swarm (FIPS) algorithm. The robust positioning performance of the proposed control scheme is verified by simulation and experiment for the Scorbot robot in the presence of the joint dynamic friction and uncertainty.Adaptive position and trajectory control of autonomous mobile robot systems with random friction
http://dl-live.theiet.org/content/journals/10.1049/iet-cta.2009.0251
The authors present a robust adaptive control approach using model reference adaptive control (MRAC) for autonomous robot systems with random friction. First, a non-linear model of the robot system is approximated by feedback linearisation to derive a nominal control law. Next, a least square observer is constructed for the online estimation of friction dynamics. The authors derive a perturbed system model governing the friction estimation error and design an MRAC control to mitigate its effect. Also, stability conditions for the perturbed system model using the Lyapunov stability theory are derived. The authors demonstrate the success of the proposed control methodology through computer simulation, including a comparison to a traditional controller based on nominal dynamics.Adaptive formation tracking control of electrically driven multiple mobile robots
http://dl-live.theiet.org/content/journals/10.1049/iet-cta.2009.0280
An adaptive formation control method is proposed for multiple uncertain non-holonomic mobile robots at the actuator dynamics level. All parameters of the robot kinematics and dynamics, and actuator dynamics are unknown. The virtual structure with path parameters and the dynamic surface design methodology are combined to design a simpler adaptive formation control scheme than the previous backstepping-based control system. Using the Lyapunov stability theorem, the authors present the adaptation laws for tuning all unknown parameters of multiple mobile robots regardless of considering path parameters in the reference trajectories. In addition, it is proved that all signals in the total closed-loop system are semi-globally uniformly bounded and all formation tracking errors and synchronisation errors of the path parameters converge to an adjustable neighbourhood of the origin. Finally, simulation results demonstrate the effectiveness of the proposed approach.Further results on decentralised coordination in networks of agents with second-order dynamics
http://dl-live.theiet.org/content/journals/10.1049/iet-cta.2008.0263
This study investigates consensus problems for networks of second-order agents, where each agent can only access the relative position information from its neighbours. We first introduce two new protocols with and without time-delay. Then we provide a convergence analysis in three cases: (a) networks with fixed topology; (b) networks with switching topology; (c) networks with switching topology and time-delays. Several conditions are presented to make all agents asymptotically reach consensus while accomplishing some tasks such as moving to a common value and moving together with a constant velocity or with a constant acceleration. Finally, simulation results are provided to demonstrate the effectiveness of our theoretical results.Computed torque control-based composite nonlinear feedback controller for robot manipulators with bounded torques
http://dl-live.theiet.org/content/journals/10.1049/iet-cta.2008.0259
On the basis of the classical computed torque control method, a composite nonlinear feedback (CNF) design method for robot manipulators with bounded torques is presented. The resulting controller consists of two loops. The inner loop is for the full compensation for manipulators nonlinear dynamics and the outer loop is the CNF for stabilisation and performance enhancement. Stability analysis is carried out with an estimate of the domain of attraction specified in the presence of actuator saturation. In addition to the guaranteed stability properties, the controller takes advantage of a varying damping ratio induced by the CNF control. The varying damping ratio allows fast transient response without overshoot and compensates the effect of the frictions. It also takes advantage of the high-gain action embedded in the outer loop to compensate the friction effect. Simulation results demonstrate the effectiveness of the proposed design.Adaptive tracking control for a class of wheeled mobile robots with unknown skidding and slipping
http://dl-live.theiet.org/content/journals/10.1049/iet-cta.2010.0026
This study presents an adaptive tracking control approach for trajectory tracking of wheeled mobile robots with torque saturation in the presence of unknown skidding and slipping. The robot kinematics and dynamics are induced from the perturbed non-holonomic constraints. The adaptive control system using the kinematics transformed in polar coordinates is developed to compensate unknown skidding and slipping at the dynamic level of mobile robots with the input saturation. All signals of the controlled closed-loop system are uniformly bounded and the point tracking errors converge to an adjustable neighbourhood of the origin regardless of large initial tracking errors, input saturation and unknown skidding and slipping. Simulation results are provided to demonstrate the performance and stability of the proposed control scheme.Stability of a contact task for a robotic arm modelled as a switched system
http://dl-live.theiet.org/content/journals/10.1049/iet-cta_20060191
The task of stabilising an <i xmlns="http://pub2web.metastore.ingenta.com/ns/">n</i>-degree-of-freedom (dof) robot arm moving from free space to contact with a compliant surface is considered. A proportional derivative position controller with gravity compensation is used for the free motion and a parallel force/position controller for the contact task. The goal is to stabilise the robot in contact with the environment, exert a desired force and place the end-effector at a desired position. The robot is modelled as a switched system, and its stability is examined using hybrid stability theory by considering typical candidate Lyapunov functions for each of the two discrete system states. The stability analysis reveals that extra conditions involving control gains and control targets should be satisfied in order to guarantee asymptotic stability of the switched task in a Lyapunov sense. The system performance and robustness is illustrated by the simulation of a 3-dof planar robot.Adaptive tracking and obstacle avoidance for a class of mobile robots in the presence of unknown skidding and slipping
http://dl-live.theiet.org/content/journals/10.1049/iet-cta.2010.0644
An adaptive control approach is proposed for path tracking and obstacle avoidance of mobile robots considering unknown skidding and slipping. The proposed adaptive controller consisting of a kinematic controller and a torque controller for the dynamic model is derived to compensate the unknown skidding and slipping effect. From Lyapunov-stability analysis, it is proved regardless of unknown skidding and slipping that all signals of the controlled closed-loop system are semiglobally uniformly ultimately bounded, the point tracking errors converge to an adjustable neighbourhood of the origin outside the obstacle detection region and the obstacle avoidance is guaranteed inside the obstacle detection region. The performance and stability of the proposed control system are verified from simulation results.Convergence analysis for multiple agents with double-integrator dynamics in a sampled-data setting
http://dl-live.theiet.org/content/journals/10.1049/iet-cta.2010.0397
This study revisits the sampled-data consensus algorithm for agents modelled by double-integrator dynamics under both fixed and dynamic network topology. Totally different methods are employed to perform the convergence analysis. Under certain assumptions on the sampling period and the velocity damping gain, a necessary and sufficient condition is given for the agents under fixed network topology to reach consensus. In addition, the method employed in performing the convergence analysis for the fixed case can be further extended to achieve a similar result as that in the existing literature for the dynamical case in a more general setting. The consensus equilibria are also analysed for the system evolving under a special class of dynamic network topology.Path following of a class of non-holonomic mobile robot with underactuated vehicle body
http://dl-live.theiet.org/content/journals/10.1049/iet-cta.2009.0617
A new dynamic model for a class of two-wheeled mobile robot (2WMR), whose mass centre locates below its wheel axis, is presented. The dynamic model considered as the motion of an underactuated vehicle body can represent the time-varying horizontal distance of the mass centre with respect to the configuration centre. This model can describe the dynamic behaviours of the robot more accurately. By the computed torque approach, a sliding mode controller based on the adaptive gain to overcome the disturbances of the system is proposed. Integrating with the velocity controller, the whole control system is made up of two closed-loop structures. The control algorithm efficiency is confirmed through simulation in the MATLAB environment.