ADVANCES IN ROBOTIC TECHNIQUES

1. Robotics in Medicine

There have been a number of reports in this section of the progress being made in applying robotic techniques to medical processes. High on the list of achievements in this area have been the attempts to help in surgical operations. Already reports here have dealt with improved aids for surgeons with increased facilities for viewing and of producing images of the patient's progress. Indeed, operations assisted by links with remote centres of expertise and with internet information databanks are no longer unusual. All of these facilities and devices have been, in the main, aids to the operating medical staff but automated surgery still remains a remote goal, although there are many experimental systems in existence. From the Pennsylvania Hershey Medical Centre, USA, however, comes a report of a truly robotic heart surgeon called Zeus. On this occasion it appears that Zeus is not some robotics researchers speculative design for an automated medical robot but a working system that is starting its medical trials in a real-life hospital.

It is, indeed, a pleasure to edit this special issue of Robotica entitled Design and Applications. This consists of revised and updated papers presented during the 26th International Symposium on Industrial Robots (ISIR), which was held on 4–6 October, 1995, in Singapore. The theme of the symposium was “Competitive Automation: New Frontiers, New Opportunities”. Ninety-six papers were presented by authors from twenty-five countries around the world. Three keynote presentations were made by Dr. Joseph Engelberger, best known as the ‘Father of Industrial Robots', Prof. Yukio Hasegawa, a world renowned professor from Japan and Mr. Walter Reis, from Germany (then the Chairman of the International Federation of Robotics).

In programming robot manipulators to carry out a wide variety of tasks it would be desirable to create a CAD system in which these tasks can be programmed at the task level, leaving the fine-grained detail of path planning and collision detection to the system. This paper describes the theoretical background to such a system, by providing a model in which robot motions are represented using multivariate B-splines, a standard representation for free-form shapes in the CAD environment. The paper also describes algorithms which take this representation and apply it to collision detection and path-planning.

This paper aims to develop a complete algorithm to determine the robot motion and the scene structure using a monocular vision system. It is based on straight lines and significant points extracted on them. In this way, an agreement between the problems to extract or to match points and the limitations of infinite lines to compute structure and motion is established. Many geometrical relations of the lines in the scene are exploited to clear up the coupling between the rotation and the translation of the camera. Several real images have been used to validate the proposed method. The algorithm has been considered for navigation of a mobile robot moving in man-made environments.

Industrial robots have a high positioning accuracy and stiffness but their work spaces are limited because their bases are fixed to the ground. To enlarge the work spaces, this paper proposes a novel mechanism, a wire suspended manipulator with three degrees of freedom. First, the kinematics of the mechanism is derived from both force and geometric constraints. Second, the volume of the work space is numerically calculated. After the evaluation of manipulability of the wire suspended system, guidelines for designing parameters are studied.

This paper considers the problem of controlling the motion of nonholonomic mechanical systems in the presence of uncertainty regarding the system model and state. It is proposed that a simple and effective solution to this problem can be obtained by first using a reduction procedure to obtain a lower dimensional system which retains the mechanical system structure of the original system, and then adaptively controlling the reduced system in such a way that the complete system is driven to the goal configuration. This approach is shown to be easy to implement and to ensure accurate motion control despite measurement and model uncertainty. The efficacy of the proposed control strategy is illustrated through computer simulations and preliminary hardware experiments with nonholonomic mechanical systems arising from both explicit kinematic constraints and symmetries of the system dynamics.

This paper examines the problem of link position tracking control of robot manipulators with bounded torque inputs. An adaptive, full-state feedback controller and an exact model knowledge, output feedback controller are designed to produce semi-global asymptotic link position tracking errors. Simulation results are provided to validate the theoretical concepts, and a comparative analysis demonstrates the benefits of the proposed controllers.

Force and position sensors have been widely used in robots to realize compliance and precise control. Traditional force/position control methods were studied and developed by the inverse dynamics for decades. Generally speaking, the controller contains two parts: One is the error-driven part that guarantees system stability; another is the identification model of inverse dynamics that can compensate for system influence. In practical control engineering, a system inverse dynamics or its identification model is not easy to obtain, even when using nonlinear estimation methods. Moreover, the complicated control algorithm cannot be implemented in on-board microprocessors because of the limited speed and memory. Thus, a simplified control method using a forward system model is introduced in this paper. Since the direct dynamics of the system can be more easily obtained than the inverse dynamics, this, in turn, simplifies the control structure and increases control speed. Therefore, the proposed control policy has a wider practical application.

This paper presents a new method to analyze the closed-form kinematics of a generalized three-degree-of-a-freedom spherical parallel manipulator. Using this analytical method, concise and uniform solutions are achieved. Two special forms of the three-degree-of-freedom spherical parallel manipulator, i.e. right-angle type and a decoupled type, are also studied and their unique and interesting properties are investigated, followed by a numerical example.

We present a new algorithm for fine motion planning in geometrically complex situations. Geometrically complex situations have complex robot and environment geometry, crowded environments, narrow passages and tight fits. They require complex robot motions with coupled degrees of freedom. The algorithm constructs a path by incrementally building a graph of linearized convex configuration space cells and solving a series of linear optimization problems with varying objective functions. Its advantages are that it better exploits the local geometry of narrow passages in configuration space, and that its complexity does not significantly increase as the clearance of narrow passages decreases. We demonstrate the algorithm on examples which other planners could not solve.

This paper presents a new recursive algorithm of robot dynamics based on the Kane's dynamic equations and Newton-Euler formulations. Differing from Kane's work, the algorithm is general-purpose and can be easily realized on computers. It is suited not only for robots with all rotary joints but also for robots with some prismatic joints. Formulations of the algorithm keep the recurrence characteristics of the Newton-Euler formulations, but possess stronger physical significance. Unlike the conventional algorithms, such as the Lagrange and Newton-Euler algorithm, etc., the algorithm can be used to deal with dynamics of robots containing closed chains without cutting the closed chains open. In addition, this paper makes a comparison between the algorithm and those conventional algorithms from the number of multiplications and additions.

This paper suggests an efficient approach to collision avoidance of a practical two-robot system. The approach is based on the C-space of one robot, and we consider only two and three dimensional C-space in which nearly all industrial manipulators can be reasonably represented for collision avoidance problems. The C-space of one robot is discretized with the concentric circles or spheres centered at the goal configuration. We then introduce the concept of free arc which is a set of the candidate configuration points on the concentric circle or sphere at each sampling time to avoid collisions. It is represented simply with respect to the coordinate frame attached to the goal configuration. The free arc is used as a tool for collision avoidance of a two-robot system and sub-optimality can be considered in determining a collision-free path. The main contribution of this paper is that it provides a method to construct C-obstacles in a time-varying environment more efficiently than the existing methods (e.g. slice projection method1) by restricting the search space at the expense of sacrificing completeness. Thus, it enables us to implement a practical collision avoidance algorithm for a two-robot system with decreased computational cost. Simulation results for two 2-d.o.f. manipulators and two PUMA robots are presented to show the efficacy of the proposed method.

This paper provides a solution to the composite adaptive output feedback tracking control problem for robotic manipulators. The proposed controller utilizes an update law that is a composite of a gradient update law driven by the link position tracking error and a least squares update law driven by the prediction error. In order to remove the controller's dependence on link velocity measurements, a linear filter and a new prediction error formulation are designed. The controller provides semi-global asymptotic link position tracking performance. Experimental results illustrate that the proposed controller provides improved link position tracking error transient performance and faster parameter estimate convergence in comparsion to the same controller using a gradient update law.

A new numerical method for the solution of the inverse position analysis of serial manipulators is presented. The main feature of the method that makes it attractive with respect to the method available in the literature, is its ability to search out the inverse solution of any precision quickly.

The Shape Memory Alloy (SMA) is a device which is lightweight and small in volume. The SMA can be used as the actuator of a micro-robot, but it is difficult to design a controller to handle the highly nonlinear properties of the SMA. In this paper, a Fuzzy Walking Pattern (FWP) is proposed to control a small biped robot, using an SMA as the actuator. In fact, the desired walking pattern of the small biped robot is used to construct the FWP. The proposed FWP can control the biped robot under the desired walking pattern, and handle the exceptional case when the biped robot is subject to disturbance. The proposed FWP not only solves the control problem of the SMA, but also provides a new method in controller design of the biped robot. In addition, a transputer network is designed to impelement the FWP. Experimental results demonstrate the functions of the FWP.

This paper presents some problems dealing with the transportation of bulk and liquid materials. The robotization of the transport process by an elastic manipulator of an elephant trunk type is proposed. The design of an experimental stand and some results of statical and dynamical analysis are presented. In conclusion, some proposals describing the possibilities of utilising elastic manipulators for transport purposes are given.

This paper presents a kinematic analysis and design characteristics of an in-parallel manipulator developed for the probing task application that requires high precision, active compliance, and high control bandwidth. The developed manipulator is a class of six-degree-of-freedom in-parallel platforms with 3 PRPS (prismatic-revolute-prismatic-spherical joints) chain geometry. The main advantages of this manipulator, compared with the typical Stewart platform type, are the capability of pure rotation generation and the easy prediction of the moving platform motion. The purpose of this paper is to develop an efficient kinematic model which can be used for real-time control and to propose systematic methods to design the manipulator considering workspace, manipulability, resistivity, singularity, and the existence conditions of the forward kinematic solution. Particularly, we propose a new method for checking the singularity of the parallel manipulator using the translational and rotational resistivity measures. A series of simulation are carried out to show kinematic characteristics and performance of the manipulator mechanism. A prototype manipulator was built based on the kinematic analysis results.

This paper deals with the decision mechanism analysis and the design of bipedal trajectories, for the stepping motion. For that we have used biomechanical model of the human body and dynamic control scheme previously developed by Gorce. We based our study on an experimental protocol, in order to determine behavioural laws for the task execution. We have developed a biped trajectory generation process, taking into account the biped height and the obstacle dimensions. Furthermore, we characterize the stepping motion feasibility by introducing a security notion, and we define an “Admissible control Domain”, which relies on the relative position of the biped to the obstacle and the obstacle dimensions. This domain definition has led us to define the biped behavioural strategies facing an obstacle: the biped executes the task at an accurate “chosen distance”, or stops or takes another way. Experimentations have allowed to validate simulations results.