This paper deals with the kinematic calibration of the Argos mechanism which is a novel, spherical parallel structure having 3 rotational degrees of freedom. Its design is based on 3 actuators carrying a pantograph each which are connected to the end-effector by means of 3 spherical joints. Two different calibration models are introduced. The first one models mechanical deviations in all parts except for the spherical joints and the assumption that they are moving on a perfect circle (“model 27”). The second model considers only deviations which affects the orientation of the end-effector but not its position assuming that the mechanism remains spherical (“model 9”). A measurement set-up allows to measure the full pose (position and orientation) of the end-effector with respect to its base. These measurement data are used to identify the parameters of the two calibration models resulting in an accuracy improvement of RMS (root mean squares errors) of a factor of 5.3 for the orientation and a factor of 3.4 for the prediction of the position.

A 6-DOF motion bed is proposed as a nonlinear robust observer to solve the forward kinematics problem of a Stewart platform. The stability of the estimation error dynamics is proved via Lyapunov stability analysis and the error dynamics shows practical stability. An observer design algorithm which tackles the nonlinearity and uncertainty both in the system and in the output is presented by a new arithmetic Riccati equation. The estimation performance for the algorithm is verified using both simulations and experiments. The equation employs the bounding condition computed from the platform dynamics.

In this paper, the use of algebraic and trigonometric splines for the trajectory planning of robot manipulators is discussed. First, the two methods are analyzed and compared in detail; then, a strategy, which involves a combined use of the two schemes to perform sudden changes in a predefined trajectory (e.g. in case of obstacle avoidance) is proposed. Results show that the main interest in using trigonometric splines lies especially in the task of connecting two separate pieces of cubic splines, as overshoots are significantly reduced, although the continuity of velocity, acceleration and (in case) jerk is guaranteed.

This paper presents a novel method for ultrasound speed compensation in ultrasonic robot tracking. It employs optimization algorithms to estimate the best value of the ultrasound speed for every computation of the robot end-effector position. Compared with the other existing method for ultrasound speed compensation, this method has the advantage that no extra equipment is required to monitor the environment conditions (temperature etc.). The simulation, which is described at the end of this paper, shows that the real trajectory is extracted with very good precision from a set of distorted data caused by serious ultrasound speed drifting.

This paper describes an algorithm for generating a tripod turning gait which, when given an arbitrarily located turning centre, firstly maximises the rotation angle (angular stride) and then secondly optimises the stability. It does not require a specific walking machine layout or leg workspace shape, and it can deal with changes in the position of the CG caused by walking on a gradient or by uneven loading.

In this paper, a new application of the ZMP (Zero Moment Point) control law is presented. The objective of this control method is to obtain a smooth and soft motion based on a real-time control. In the controller, the ZMP is treated as an actuating signal. The coordinates of the robot body are fed back to obtain its position. The proposed control method was applied on two different biped robots, and its validity is verified experimentally.

An approach to planning time-optimal collision-free motions of robotic manipulators is presented. It is based on using a negative formulation of the Pontryagin Maximum Principle which handles efficiently various control and/or state constraints imposed on the manipulator motions, which arise naturally out of manipulator joint limits and obstacle avoidance. This approach becomes similar to that described by Weinreb and Bryson, as well as by Bryson and Ho if no state inequality constraints are imposed. In contrast to the penalty function method, the proposed algorithm does not require an initial admissible solution (i.e. an initial admissible trajectory) and finds manipulator trajectories with a smaller cost value than the penalty function approach. A computer example involving a planar redundant manipulator of three revolute kinematic pairs is included. The numerical results are compared with those obtained using an exterior penalty function method.

In this paper we consider the problem of coordinating multiple motion devices for welding. We focus on the problem of coordinating a three-axis positioning table and a six-axis manipulator. The problem is complex as there are nine axes involved and a number of permutations are possible which achieve the same movements of the weld torch. The system is redundant and the robot has singular configurations. As a result, manual programming of the robot system is rather difficult to complete.

Our approach to the coordination problem is based on a subdivision of tasks. The welding table is coordinated to align the weld point surface to be anti-parallel to the gravity direction. The six-axis robot is constrained to move the weld torch along the weld trajectory. Robot coordination is achieved by placing the positioning table in a good maneuverability position, i.e. far from its singular configurations and far from the motion limits of the six-axis arm and the motion limits of the track. While considering multiple criteria, including the welding orientation, a Genetic Algorithm was employed to globally optimize six relevant redundant degrees of the multiple robotic system for welding. The joint angles of the arm were generated by inverse kinematics. Our method of redundancy coordination is superior to pseudo-inverse techniques, for it is more global and accurate.

Teleoperation, one of the oldest areas of robotics, has experienced considerable growth in the last two decades. Main causes for this trend are the need for increased safety levels for human operators and lower production costs. In this work, a three d.o.f. local manipulator (two d.o.f. for force and one d.o.f. for torque) is developed. This hand controller, intended for robot or mobile teleoperation systems, has force reflection in two axes and torque reflection in the third axis. using a robotic hand developed at INAUT as a remote device, laboratory experiments on each axis (one at a time) have shown good results. An impedance controller at the remote system allows one to carry out interactive tasks with the environment such as polishing, insertion and grinding, where it is necessary to control and accommodate the interaction forces and torques in order to avoid hazards for both the manipulated objects and the remote robot.