Linear-wavelet models applied to the identification of a two-link manipulator

This paper shows that a wavelet network and a linear term can be advantageously combined for the purpose of non linear system identification. The theoretical foundation of this approach is laid by proving that radial wavelets are orthogonal to linear functions. A constructive procedure for building such nonlinear regression structures, termed linear-wavelet models, is described. For illustration, sim ulation data are used to identify a model for a two-link robotic manipulator. The results show that the introduction of wavelets does improve the prediction ability of a linear model.

Predictive computed-torque control of a PUMA 560 manipulator robot

This paper describes the integration of constrained predictive control and computed-torque control, and its application on a six degree-of-freedom PUMA 560 manipulator arm. The real-time implementation was based on SIMULINK, with the predictive controller and the computed-torque control law implemented in the C programming language. The constrained predictive controller solved a quadratic programming problem at every sampling interval, which was as short as 10 ms, using a prediction horizon of 150 steps and an 18th order state space model.

Joint servoing for robust manipulator force control

An experimental and theoretical comparison is made of force control performance with different types of innerloop joint servoing techniques. The problem of disturbance rejection and sensitivity to plant dynamics variations (robustness) is addressed. Position, velocity, strain gauge derived joint torque, and current servos are designed and implemented on a specially instrumented industrial robot, and the end-effector force feedback performances achieved are compared. Joint strain derived torque servoing is found to provide the best overall robust force control performance. Experimental results of the robust hard-on-hard contact achieved with the novel force controller implementation based on joint torque sensing are provided. Conclusions are drawn on the force control performance achievable on a geared robot given the joint servoing technique.

Automated robotic grinding by low-powered manipulator

A new robotic grinding process has been developed for a low-powered robot system using a spring balancer as a suspension system. To manipulate a robot-arm in the vertical plane, a large actuator torque is required due to the tool weight and enormous gravity effect. But the actuators of the robot system always exhibit a limited torque capacity. This paper presents a cheap and available system for precise grinding tasks by a low-powered robot system using a suspension system. For grinding operations, to achieve position and force-tracking simultaneously, this paper presents an algorithm of the hybrid position/force-tracking scheme with respect to the dynamic behavior of a spring balancer. Material Removal Rate (MRR) is developed for materials SS400 and SUS304. Simulations and experiments have been carried out to demonstrate the feasibility of the proposed system.

The Octahedral Hexarot - a novel 6-DOF parallel manipulator

A novel 6-DOF parallel kinematic manipulator named the Octahedral Hexarot is presented and analyzed. It is shown that this manipulator has the important benefits of combining a large positional workspace in relation to its footprint with a sizable range of platform rotations. These features are obtained by combining a rotation-symmetric actuating arm system with links in an octahedral-like configuration. Thus the manipulator consists of a central cylindrical column with six actuated rotating upper arms that can rotate indefinitely around the central column. Each upper arm is connected to a manipulated platform by one 5-DOF lower arm link. The link arrangement of the Octahedral Hexarot is inspired by the original Gough platform. The manipulated platform is an equilateral triangle and the joint positions on the upper arms approximately form an equilateral triangle. A task dependent optimization procedure for the structural parameters is proposed and the workspace of the resulting manipulator is analyzed in depth.

Embedded vision-based autonomous move-to-grasp approach for a mobile manipulator

This paper proposes a vision‐based autonomous move‐to‐grasp approach for a compact mobile manipulator under some low and small environments. The visual information of specified object with a radial symbol and an overhead colour block is extracted from two CMOS cameras in an embedded way. Furthermore, the mobile platform and the postures of the manipulator are adjusted continuously by vision‐based control, which drives the mobile manipulator approaching the object. When the mobile manipulator is sufficiently close to the object, only the manipulator moves to grasp the object based on the incremental movement with its head end centre of the end‐effector conforming to a Bezier curve. The effectiveness of the proposed approach is verified by experiments.

Automation of a complex transfer operation using a polar manipulator

Purpose – The objective of this paper included developing a polar robot (SPBot) for rotating and transferring car engine block (CEB) around and along two different axes in a confined workspace envelope.

Design/methodology/approach – The complex transfer operations of the CEB requires sweeping complete surface of the half sphere, and thus a polar robot is best suited to such a task in a confined space. Considering the limited space for this operation, a specially designed manipulator is built comprising 2 degrees of freedom driven by electrical servo motors. Also due to the special form of CEB, an especially designed pneumatic gripper is developed. Kinematics models, static and dynamic equations, together with trajectory planning for such a manipulator are described.

Findings – The high-speed complex transfer in a limited environment is successfully implemented.

Originality/value – The developed polar robot provides for complex transfer operations that significantly increases the speed of the product line and thus reducing the cycle time from 60?s using manpower to just 20?s using the robot.

Kinematic analysis and workspace determination of hexarot-a novel 6-DOF parallel manipulator with a rotation-symmetric arm system

Parallel mechanisms possess several advantages such as the possibilities for high acceleration and high accuracy positioning of the end effector. However, most of the proposed parallel manipulators suffer from a limited workspace. In this paper, a novel 6-DOF parallel manipulator with coaxial actuated arms is introduced. Since parallel mechanisms have more workspace limitations compared to that of serial mechanisms, determination of the workspace in parallel manipulators is of the utmost importance. For finding position, angular velocity, and acceleration, in this paper, inverse and forward kinematics of the mechanism are studied and after presenting the workspace limitations, workspace analysis of the hexarot manipulator is performed by using MATLAB software. Next, using the obtained cloud of points from simulation, the overall borders of the workspace are illustrated. Finally, it is shown that this manipulator has the important benefits of combining a large positional workspace in relation to its footprint with a sizable range of platform rotations.