1. Robodogs

The American public has greeted the arrival of the Robodog with a great deal of enthusiasm, but not the animal rights lobby. The Robodog is, in fact, an ordinary police dog that has been equipped with the latest high tech systems, and is still under control of a human handler.

A path planning method is presented based on non-autonomous dynamic modeling of open-loops in articulated systems. It is assumed that one part of the mechanical system is submitted to specified motions laws, while movements of the complementary part are free. Thus, motion optimization is related to free joint movements but it is achieved on the basis of the dynamic model of the whole mechanical system. This approach introduces a non-autonomous state equation of a special type in the sense that it can not only depend on the running time but also on the unknown travelling time. The cost function to be minimized involves the travelling time and the actuating inputs. Optimization is achieved by applying the Pontryagin Maximum Principle which yields a new optimality condition concerning the travelling time dependency of the stated problem. Two simulation examples are presented. The first one shows how the developed technique makes possible both the reducing and mastering the dynamic complexity of a four degrees of freedom-vertical manipulator. Set at four degrees of freedom, the second one deals with a redundant planar manipulator characterized by a mobile base that is submitted to a specified driving motion.

New methods have been developed to control a mechanism's realtime Cartesian motion along spatially complex curves such as Non-Uniform Rational B-splines (NURBS). The methods dynamically map the critical trajectory parameters between parameter space, Cartesian space, and joint space. Trajectory models that relate Cartesian tool speeds and accelerations to joint speeds and accelerations have been generalized so that they can be applied to most classes of robots and CNC mechanisms.

A simple and efficient predictor-corrector method uses finite difference theory to predict the parametric changes required to generate the desired curvilinear distances along the trajectory, and then correct the erorrs arising from this prediction. Polynomial approximation methods successfully approximate joint speeds and accelerations rather than require a closed-form inverse Jacobian solution.

The numerical algorithms prove to be time bounded (fixed number of computational steps), and the generated trajectories are smooth and continuous. Both simulation and physical experiments using an Open-Architecture Controller demonstrate the feasibility and usefulness of the developed trajectory generation algorithms and methods. The methods can be conducted at trajectory rates greater than 100 Hz, depending on mechanism complexity.

This paper presents a novel approach for seam tracking using ultrasonics. An ultrasonic seam tracking system has been developed for robotic welding which tracks a seam that curves freely on a two-dimensional surface. The seam is detected by scanning the area ahead of the torch and monitoring the amplitude of the waves received after reflection from the workpiece surface. Scanning is accomplished by using two ultrasonic sensors (a transmitter and a receiver) mounted on a stepper motor such that the transmitter angle is the same as the receiver angle. The motor is mounted on the end-effector just ahead of the welding torch and covers a ninety degree arc in front of the torch. If there is no seam then the receiver receives most of the transmitted waves after reflection, but if there is a seam then most of the transmitted waves are dispersed in directions other than that of the receiver. The system has been tested and is very robust in the harsh environments generated by the arc welding process. The robustness of the system stems from using various schemes such as time windowing, a waveguide, air and metal shields, and an intelligent sensor manager. This ultrasonic system offers some distinct advantages over traditional systems using vision and other sensing techniques. It can be used to weld very shiny surfaces, and is a very economical method in terms of cost as well as computational intensity. The system can be used to detect seams less than 0.5 mm wide and 0.5 mm deep.

This paper presents the design and development of a laboratory facility constituting a constrained planar flexible manipulator system. The system is designed for experimental investigations within research programmes involving flexible manipulator systems. An outline of a generic design procedure for flexible manipulator systems is given. The design criteria developed through this procedure account for the strength and stiffness of the manipulator and the required transducers and instrumentation. These are considered in detail and the system designed accordingly. Finally, practical problems encountered are highlighted and methods of dealing with such problems are presented and discussed.

This paper addresses the tracking control problem of robotic manipulators with unknown and changing dynamics. In this study, nonlinear dynamics of the robotic manipulator is assumed to be unknown and a control scheme is developed to adaptively estimate the unknown manipulator dynamics utilizing generic artificial neural network models to approximate the underlying dynamics. Based on the error dynamics of the controller, a parameter update equation is derived for the adaptive ANN models and local stability properties of the controller are discussed. The proposed scheme is simulated and successfully tested for trajectory following tasks. The controller also demonstrates remarkable performance in adaptation to changes in manipulator dynamics.

It is well known that computed torque robot control is subjected to performance degradation due to uncertainties in robot model, and application of neural network (NN) compensation techniques are promising. In this paper we examine the effectiveness of neural network (NN) as a compensator for the complex problem of Cartesian space control. In particular we examine the differences in system performance of accurate position control when the same NN compensator is applied at different locations in the controller structure. It is found that using NN to modify the reference trajectory to compensate for model uncertainties is much more effective than the traditional approach of modifying control input or joint torque/force. To facilitate the analysis, a new NN training signal is introduced and used for all cases. The study is also extended to non-model based Cartesian control problems. Simulation results with three-link rotary robot are presented and performances of different compensating locations are compared.

Variable structure control is applied to an underactuated two and three-link robot. Control laws are developed to invert the robot from its stable, downward equilibrium position to an inverted position. This maneuver is accomplished by pumping energy into the system with the variable structure controller. A linear balancing controller is activated once the robot nears the inverted position. Numerical simulations are presented for both the two and three-link robot.

Isotropic velocity radius (IVR) and isotropic acceleration radius (IVR) are proposed as local performance indices to quantify the dynamic responsiveness of a multi-arm robot as regards the velocity effects. These performance measures are defined on the basis of the acceleration set describing the effects of actuator torques, velocity of the manipulated object, and gravity upon the acceleration of the object. An algorithm is presented to obtain an explicit expression for calculating these measures by decomposing the torque-related non-square matrix into square matrices without using the concept of pseudo-inverse for the planar multi-arm robot composed of arms each with two joints.

Numerical examples for a planar robot with two 2R arms show that the proposed concepts are effective in representing the acceleration capability and velocity effects of a multi-arm robot.

This paper identifies the need for a new range of end effectors suitable for non-rigid products and introduces a novel non-contact gripping device. The end effector operates on the principle of generating a high-speed flow between the end effector and product surface thereby creating a vacuum which levitates the product. The lifting forces and conditions are theoretically discussed. The experimental results are presented using the end effector that has been operated to lift non-rigid food materials such as jelly blocks.

A link position tracking controller is formulated for an n-link, rigid, revolute, serially-connected robot. The controller generates torque commands to the individual robot links based on adaptive estimates of the system parameters and measurements of only link positions. A filtering technique, based on the link position signal, is used to alleviate the need for velocity measurements. A complete development of the controller is presented along with a proof of semiglobal asymptotic link position-velocity tracking performance. Experimental validation of the proposed controller on the Integrated Motion Inc. (IMI) two-link direct drive robot is also presented. Several extensions to the basic controller are described that consider the use of fixed parameter estimates.

The UK Magnetics Society's one-day seminar Advances in Instrumentation for Magnetics Measurements was held at the University of Wales Cardiff on 10 July 1996. Ten presentations were made during the event which was attended by over 65 participants.

1. The International Federation of Robotics expects to have a presence on the World Wide Web by the time this issue of Robotica is published. The URL will be http://www.ifr.org. The IFR Web pages will include information about the Federation's activities as well as links to its member associations in Europe, Asia, North America and Australia.