An experimental study of collinear and planar arrays

Measurements are described that serve to verify a recently reported new theory of arrays of arbitrarily located parallel elements especially including ones that are collinear and staggered. Since the theory takes full account of the effects of mutual coupling in determining the distributions of current in each element of an array, the experimental studies involved the determination of distributions of current and charge as well as admittances and field patterns. Since the theory should be a good approximation for dipole elements well over a wavelength long, complete measurements are reported for arrays of both half-wave and full-wave elements in collinear and planar arrangements. Experimental and theoretical results are in good agreement.     

Teleoperation of a robot manipulator using a vision-based human-robot interface

Remote teleoperation of a robot manipulator by a human operator is often necessary in unstructured dynamic environments when human presence at the robot site is undesirable. Mechanical and other contacting interfaces used in teleoperation require unnatural human motions for object manipulation tasks or they may hinder human motion. Previous vision-based approaches have used only a few degrees of freedom for hand motion and have required hand motions that are unnatural for object manipulation tasks. This paper presents a noncontacting vision-based method of robot teleoperation that allows a human operator to communicate simultaneous six-degree-of-freedom motion tasks to a robot manipulator by having the operator perform the three-dimensional human hand-arm motion that would naturally be used to complete an object manipulation task. A vision-based human-robot interface is used for communication of human motion to the robot and for feedback of the robot motion and environment to the human operator. Teleoperation under operator position control was performed with high accuracy in object placement on a target. Semi-autonomous traded and shared control using robot-vision guidance aided in achieving a more accurate positioning and orientation of the end-effector for object gripping tasks.     

Robust learning control of a high precision planar parallel manipulator

End-point positioning accuracy and fast settling time are essential in the motion system aimed at semiconductor packaging applications. In this paper, a novel robust learning control method for a direct-drive planar parallel manipulator is presented. A frequency-domain system identification approach is used to identify the high frequency dynamic of the manipulator. A robust control design method is employed to design a stable, fast tracking response feedback controller with less sensitivity to high frequency disturbance and the control parameters are determined using genetic algorithm. A Fourier-series-based iterative learning controller is designed and used on the feedforward path of the controller to further improve the settling time by reducing the dynamic tracking error of the manipulator. Experimental results demonstrate that the planar parallel manipulator has significant improvements on motion performance in terms of positioning accuracy, settling time and stability when compared with traditional XY-stages. This shows that the proposed manipulator provides a superior alternative to XY-motion stages for high precision positioning.     

State-space system identification of robot manipulator dynamics

We have applied and evaluated system identification methods using both commercial software and dedicated subspace model identification software (MOESP). Results using the different software tools have been similar (but not identical) in accuracy and predictive power, the main differences being the time required for computation and occasional failures of one algorithm in delivery of a stable model. For linear model identification all methods tested failed to provide residuals, i.e. model misfit, uncorrelated with input and without significant autocorrelation. As a result, no linear stochastic innovations model could be formulated in any satisfactory manner. However, model-order tests based on singular values suggest that a low model order be sufficient for input–output modeling to within a modeling accuracy of 2–5%. Thus, the identification of a state-space model combined with a friction model provides effective means to modeling in robotics.     

Concurrent redesign of an underactuated robot manipulator

An interesting problem in robotics is to minimize the required time to force a manipulator to travel between two specific points (positioning time). In this paper a concurrent structure-control redesign approach is proposed in order to find the minimum positioning time of an underactuated robot manipulator, by considering a synergetic combination between the structural parameters and a bang–bang control law. The problem consists in finding the structural parameters of the system and the switching intervals of the bang–bang control that simultaneously minimize the positioning time, subject to the input constraint and the structural parameter constraint. The concurrent structure-control redesign approach is stated as a dynamic optimization problem (DOP). The projected gradient method is used to solve the DOP.The effectiveness of the proposed concurrent redesign approach is shown via simulation and experimental results on an underactuated system called the Pendubot.     

Nonlinear computed torque control for a high-speed planar parallel manipulator

A new computed torque (CT)-type controller termed nonlinear CT (NCT) controller is developed and applied to a high-speed planar parallel manipulator. The NCT controller is designed by replacing the linear PD in the conventional CT controller with the nonlinear PD (NPD) algorithm. The stability of the parallel manipulator system with the NCT controller is proven using the Lyapunov theorem, and the proposed controller is further proven to guarantee asymptotic convergence to zero of both tracking error and error rate. The superiority of the proposed NCT controller is verified through the trajectory tracking experiments of an actual high-speed planar parallel manipulator, and the experiment results are compared with the CT controller.     

Design and control of robot manipulator with a distributed actuation mechanism

This paper presents a design methodology based on the distributed actuation principle to achieve a high-performance robot manipulator. Spatial movement of the actuation points provides several advantages such as high payload capacity, high efficiency and a light weight structure for the proposed robot manipulator. Based on the analysis, the distributed actuation mechanism using a single slider is adopted for the proposed manipulator. A prototype of the manipulator with two degrees of freedom is developed and controlled as an example. The efficacy of the proposed approach is verified experimentally.     

Robust control of a planar manipulator for flexible and contactless handling

Many industries require non-contact and flexible manipulation systems, such as magnetic or pneumatic devices. In this paper, we describe a one-degree-of-freedom position control of an induced-air flow surface. This device allows to convey objects on an air cushion using an original aerodynamic traction principle. A model of the system is established and the parameters are identified experimentally. A H_∞ robust controller is designed and implemented on the device in order to control the object position. Experiments with objects of various dimensions and materials are conducted and showed the robustness capabilities of the controller.     

Design and experimental study of a planar multibeam double-reflector aplanatic system

The results of design and experimental investigation of a multibeam planar three-layer double-reflector system in the millimeter wave band are presented. A Schwarzschild aplanatic reflector system with symmetric generatrices is considered. The system parameters have been chosen as a result of optimization of this system with the use of the method of physical optics and the Pareto criterion. A prototype of an integral quasi-optical system in the form of a multilayer printed circuit board containing an aplanatic double-reflector optical system illuminated by an array of 19 microstrip horns has been manufactured. Experimental studies have been performed at a frequency of 36 GHz; a set of beams with fan-shaped radiation patterns in a coverage sector of ±38° has been obtained. The experimental data are compared to the results of calculation.     

An experimental study on improving hybrid position/force control of a robot using time delay control

Robot position/force control has been a difficult task owing to the interaction between a robot and the environment. In addition to the dynamic instability, the interaction causes the following problems: (1) the dynamic coupling effect of the robot; (2) positional disturbance due to the uncertain surface of the environment with which the robot is in contact; and (3) vibration at steady state. To solve these problems, time delay control (TDC), well known for its robustness to plant uncertainties and disturbances, has been used as a baseline control law for hybrid control. In conjunction with TDC, the following three ideas were also used. (i) To reduce the dynamic coupling, a more accurate mass matrix was used instead of the constant mass matrix. (ii) To reject positional disturbance from the environment, force derivatives instead of position derivatives were used in the TDC law. (iii) Finally, to reduce the amplitude of the vibration at steady state, a novel scheme was adopted to enhance the resolution of A/D conversion for the force sensor. Experiments showed obvious improvements in the quality of the hybrid control, thereby clearly demonstrating the effectiveness of TDC with the proposed ideas.     

Neural network impedance force control of robot manipulator

The performance of an impedance controller for robot force tracking is affected by the uncertainties in both the robot dynamic model and environment stiffness. The purpose of this paper is to improve the controller robustness by applying the neural network (NN) technique to compensate for the uncertainties in the robot model. NN control techniques are applied to two impedance control methods: torque-based and position-based impedance control, which are distinguished by the way of the impedance functions being implemented. A novel error signal is proposed for the NN training. In addition, a trajectory modification algorithm is developed to determine the reference trajectory when the environment stiffness is unknown. The robustness analysis of this algorithm to force sensor noise and inaccurate environment position measurement is also presented. The performances of the two NN impedance control schemes are compared by computer simulations. Simulation results based on a three-degrees-of-freedom robot show that highly robust position/force tracking can be achieved in the presence of large uncertainties and force sensor noise     

Application of rubber artificial muscle manipulator as arehabilitation robot

The application of a robot to rehabilitation has become a matter of great concern. This paper deals with functional recovery therapy, one important aspect of physical rehabilitation. Single-joint therapy machines have already been achieved. However, for more efficient therapy, multjoint robots are necessary to achieve more realistic motion patterns. This kind of robot must have a high level of safety for humans. A pneumatic actuator may be available for such a robot, because of the compliance of compressed air. A pneumatic rubber artificial muscle manipulator has been applied to construct a therapy robot with two degrees of freedom (DOF). Also, an impedance control strategy is employed to realize various motion modes for the physical therapy modes. Further, for efficient rehabilitation, it is desirable to comprehend the physical condition of the patient. Thus, the mechanical impedance of the human arm is used as an objective evaluation of recovery, and an estimation method is proposed. Experiments show the suitability of the proposed rehabilitation robot system     

Robust control of robot manipulator by model-based disturbance attenuation

In this letter, a model-based disturbance attenuator (MBDA) for robot manipulators is proposed and the stability of the MBDA in robot positioning problems is proved via Liapunov's direct method. This method does not require an accurate model of a robot manipulator and takes care of disturbances or modeling errors so that the plant output remains relatively unaffected by them. The output error due to the gravity or constant disturbance can be effectively eliminated by this method.     

Calculation of a robot manipulator model in the form of arecurrent neural net

A neural model for robot manipulator is proposed similar to the mathematical model of a robot manipulator in the form of a Lagrange-Euler equation. A learning algorithm based on the backpropagation method is given for a neural model. A numerical example of calculation of a neural model for Puma 560 robot is presented.     

Cooperative control of a human and a robot manipulator for positioning a cart on a frictionless plane

Robots may be expected to execute some tasks in cooperation with humans. Control systems for such robots should be appropriate to adapt to human characteristics in order to successfully accomplish the task. Pushing a cart on a frictionless plane in cooperation with a human is a basic example to such a task. To control the motion of an object from one point to another on a frictionless plane is impossible by only pushing in one direction without supporting it in the opposite direction, since as soon as the force is applied, the object will move without stopping its motion. In this paper, compliant cooperative positioning of a cart on a frictionless plane by a human and a manipulator is proposed using impedance control method with the parameters obtained from human–human cooperation.     

Implementation and experimental study of a multiprocessor system for real-time model-based robot motion control

This paper presents the design and implementation of a multiprocessor system for real-time robot motion control. Full inverse dynamics compensation control laws in both joint and Cartesian spaces are used for developing parallel computation algorithms. The algorithms are divided into subtasks which are distributed among a fixed number of processors based on heuristic scheduling algorithms. The control laws are real-time tested on an experimental robot. The results present a feasible way for improving controller performance of current industrial robots.<>     

An experimental study of a sea clutter model

A model for the radar cross section (RCS) of the sea has been developed in parallel efforts by scientists in both the United States and the Soviet Union, which is based upon the concept of a composite surface, i.e., one in which a slightly rough surface in the sense of Rice is superimposed on a larger swell structure. For angles off the normal, the model predicts the variation of the RCS with frequency, polarization, and incident angle of the illumination and further predicts an upper bound (saturation value) of the RCS with increasing roughness. The model has been collated with data collected by the Naval Research Laboratory four-frequency radar system in sea states ranging from 0 to 7. The results of the comparison have shown that the upper bound for the RCS exists and is closely approached in windspeeds in excess of 5 m/s. In addition, the data have confirmed the variation of RCS with frequency (UHF to X-band), grazing angle, and with polarization (H, V), provided that the "tilting" of the scattering surface by swell is taken into account in the region of shallow grazing angles.     

Force feedback control of robot manipulator by the accelerationtracing orientation method

The authors propose a novel approach to force and compliance control of multi-degree-of-freedom (DOF) robot manipulators. The acceleration tracing orientation method (ATOM) is applied to both controllers. The control law is described in the Cartesian space; however, the final command is the acceleration in the joint space. The interactive terms in each joint disturb and deteriorate the joint motion. The disturbance observer cancels out the total sum of these terms and enables each joint to trace the acceleration command. As a result, a robust control is possible in the force task. The testing of the proposed system in a three-DOF robot manipulator is discussed