ADVANCED NEURO-ROBOTICS

1. ‘Robo Rat' project

United States scientists from SUNY Downstate Medical Centre have reported on a Robo Rat project that they have initiated. In a research paper published in Nature (May, 2002) they describe some of their remarkable results. It may soon be possible, we are told, that because of their researches, a remote-controlled living ‘Robo Rat' could be involved in numerous and varied applications. Their work is a spin-off from research to give paralysed people the ability to move and feel artificial limbs. The report of the project presents their findings and described how five rats carrying a special backpack, which contained a battery, radio receiver and brain stimulator, were controlled by a human operator sitting up to 500 yards away. The human operator was able to make them weave in and out of obstacles and navigated them over a course. Instead of using the traditional methods ofanimal training which associated behaviour with rewards, the researchers directly stimulated the parts of the animals' brains that responded to the movements of their whiskers and to receiving rewards of food. Electrical signals were sent to parts of the brain and provided a virtual contact to the animal's whiskers, showing them which way the operator wished them to go. In their research paper it is shown how by stimulaling these ‘whisker centres' the rats could be steered and by stimulating the brain's reward centre, they could reinforce the correct behaviour.

The passivity property of a noncollocated single-link flexible manipulator with a parameterized output is studied. The system can be characterized by either the irrational transfer function of an infinite-dimensional model or its truncated rational transfer functions. Necessary and sufficient conditions for these transfer functions to be passive are found. It is also shown that a non-passive, marginal minimum-phase, truncated transfer function can be rendered passive by using either the root strain feedback or the joint angular acceleration feedback. For the noncollocated truncated passive transfer function, a PD controller suffices to stabilize the overall system. Numerical results are given to show the efficacy of the proposed approaches.

The minimum-time path-following problem for non-redundant manipulator has already been analyzed and a number of efficient solution algorithms have been proposed. These algorithms can be applied also to redundant manipulators if the path is assigned in the joint space. If the path is assigned in the task space instead, how to exploit kinematic redundancy to reduce the execution time is still an open problem. In this paper it is proposed to follow a heuristic approach to choose between different solutions to the inverse kinematics problem that underlies the minimum-time path-following control problem. The aim is to obtain a joint-space path which configures the manipulator so as to improve acceleration/deceleration capabilities of the end-effector. This is obtained by penalizing the motion of joints with higher inertia-to-torque ratios. Numerical results are presented for an “easy-to-understand” three degree-of-freedom planar manipulator involved in two-dimensional paths.

The influence of ground irregularities on the behavior of a wheeled mobile robot (WMR) navigating on uneven surfaces is addressed. The paper studies the vibratory movements induced on the body of the WMR, in order to analyze its ability for carrying out on-board tasks, and on the accuracy of the data collected by its external sensorial systems. The adhesion capability of the wheels of the WMR on this uneven terrain is also studied, since it conditions the braking, traction and steering performance. The method is applied to the WMR RAM.

A method for the time suboptimal control of an industrial manipulator that moves along a specified path while keeping its end-effector orientation unchanged is proposed. Nonlinear system equations that describe the manipulator motion are linearized at each time step along the path. A method which gives control inputs (joint angular velocities) for time suboptimal control of the manipulator is developed. In the formulation, joint angular velocity and acceleration limitations are also taken into consideration. A six degree of freedom elbow type manipulator is used in a case study to verify the method developed.

This paper is concerned with a stability theory of motion governed by Lagrange's equation for a pair of multi-degrees of freedom robot fingers with hemi-spherical finger ends grasping a rigid object under rolling contact constraints. When a pair of dual two d.o.f. fingers is used and motion of the overall fingers-object system is confined to a plane, it is shown that the total degree of freedom of the fingers-object system is redundant for realization of stable grasping though there arise four algebraic constraints. To resolve the redundancy problem without introducing any other extra and artificial performance index, a concept of stability of motion starting from a higher dimensional manifold to a lower-dimensional manifold, expressing a set of states of stable grasp with prescribed contact force, is introduced and thereby it is proved in a rigorous way that stable grasp in a dynamic sense is realized by a sensory feedback constructed by means of measurement data of finger joint angles and the rotational angle of the object. Further, it is shown that there exists an additional sensory feedback that realizes not only stable grasp but also orientation control of the object concurrently. Results of computer simulation based on Baumgarte's method are presented, which show the effectiveness of the proposed concept and analysis.

The objective of the paper is to present a method of designing geometrical parameters of 3-dof orientation mechanisms. The parameters are to be determined for a given workspace, which in this case is described as a set of angles of orientation. An algorithm is presented, based on the equations of constraints which makes it possible to obtain the parameters of a manipulator. whose workspace involves the specified taskspace.

This paper describes an adaptive S-curve used to recover a tool path upon a system crash in the Windows operating system (OS). For a mechanism such as a robot or machine tool, the joint values, being delivered as setpoints to the servo-controller, are dynamically recorded by the real-time operating system also residing on the computer. The real-time OS can control the abort and record pertinent motion data after Windows OS crash.

Upon system recovery, the recovery trajectory generator examines the setpoints intervals to determine the current slow joint. At every trajectory step, and for the current slow joint, the S-curve velocity profile applies the joint entry state (position, speed, acceleration, and jerk) to interpolate the motion between the setpoints in a reverse direction. The other joints are proportionally interpolated (slowed) so that they pass through each setpoint simultaneously with the slow joint, but in a reverse direction.

The trajectory algorithm is optimal since the slow joint always uses the maximum allowable jerk to change the profile speed and acceleration for each trajectory step.

In this paper, we try to find an efficient and accurate dynamic model for a robot with spatial compliant links using the screw theory. After making some reasonable assumptions for the system, we introduce the Ding-Holzer method for system simplification. Instead of looking at the beam at rest, we consider the spatial forces and deflections of a moving elastic arm. We focus our study on the dynamic modelling problems of a compliant arm with six dimensional forces and deformations at the tip.

The paper is aimed at generating optimal gait cycles in the sagittal plane of a biped, the locomotion system of which has anthropomorphic characteristics. Both single and double support phases are globally optimised, considering incompletely specified transition postural configurations from one phase to the other. An impactless heel-touch is prescribed. Full dynamic models are developed for both gait phases. They are completed by specific constraints attached to the unilaterality of contact with the supporting ground.

A parametric optimisation method is implemented. The biped joint coordinates are approximated by cubic splines functions connected at uniformly distributed knots along the motion time. The finite set of unknowns consists of the joint coordinate values at knots, some gait pattern parameters at phase transitions, and the motion time of each phase. The step length is adjusted to the prescribed gait speed by the optimisation process. Numerical simulations concerning slow and fast optimal gaits are presented and discussed.

The purpose of the present study is to assess the influence of auditory and haptic signals on the manipulation performance in a virtual reality-based hand rehabilitation system. A personal computer, a tracker, and a data glove were included in this system. Three-dimensional virtual environments were developed. Forty volunteers were recruited to participate in a pick-and-place procedure, with three levels of difficulty and four feedback modes. Task time and collision frequency were the parameters used to evaluate their manipulation performance. It can be concluded that the haptics is a significant signal for improving a subject's performance at the high difficulty level.