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.

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.

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.

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.

The constraints on the physical limit should be considered in a kinematic redundancy resolution problem of a robot. This paper proposes a new optimization scheme to resolve kinematic redundancy of the robot while considering physical constraints. In the proposed scheme, quadratic inequality constraints are used in place of linear inequality constraints, thus a quadratically constrained optimization technique is applied to resolve the redundancy. It is shown that the use of quadratic inequality constraints considerably reduces the number of constraints. Therefore, the proposed method reduces the problem size considerably and makes the problem simple resulting in computational efficiency. A numerical example of a 4-link planar redundant robot is included to demonstrate the efficiency of the proposed optimization technique. In this example, simulation results using the proposed method and another well-known method are compared and discussed.

This paper addresses the swing-free transport of simply suspended objects which cannot be grasped by robot manipulators, and therefore, must be carried by a hook or a similar device attached to the manipulator endpoint. Two methods are presented to stop the suspended object in a swing-free state at the end of a move/gross motion; (1) limiting transportation time, thus stopping the manipulator at the instant when the object completes one or more full cycle(s), and (2) adjusting traveling time of each section of a three-piece continuous trajectory provided that a given transportation time is unchanged. A hydraulically actuated robot manipulator carrying a compound pendulum was employed as an experimental system to test the methods. Simulation and experimental results are presented to demonstrate the feasibility of both methods. It is concluded that while limiting transportation time is not a preferred way to eliminate swing at the end of the move as it depends on the period of oscillation of the suspended object, the latter is a more practical and applicable method and is valid for moves of any length. The results reveal that by properly planning the acceleration of the transporting device, a robot manipulator or a similar device such as a crane, a swing-free stop is obtainable. The proposed approaches are simple and easy to implement.

This work focuses on the dynamic modeling of a flexible robotic manipulator with two flexible links and two revolute joints, which rotates in the horizontal plane. The dynamic equations are derived using the Newton-Euler formulation and the finite element method, based on elementary beam theory. Computer simulation results are presented to illustrate this study. The dynamic model becomes necessary for use in future design and control applications.

In this paper a procedure is proposed for a rational and optimum use of robots. It is the result of the lessons learned by the author in the course of his consultancy and teaching activities on manipulative tasks and programming capabilities of robots.

One of the chief aims of this paper is educational, and has been set on the basis of students' practice with robots in the Laboratory of Robotics at the University of Cassino, Italy. A second goal consists in highlighting and teaching how robots' versatility and flexibility can be easily exploited during robot's operation when a task is properly modelled through elementary actions. An elementary action, representing a small manipulative operation and consisting in one or few simple instructions given in robot language, can be easily performed by the robot's programming capability. Some examples have been reported to better illustrate the ideas and the procedure proposed, whose main advantage, also from an educational viewpoint, consist in providing a simpler method for analysing manipulations for robot design and programming.

Cooperating multiple robots may experience slips between their end-effectors and the object when making no rigid grasps, as is the case of manipulating fingers. Consequently, these slips make the robotic system unsuccessful in executing a job properly and can even cause a failure of control. Contact-point slips can be avoided by defining multiple constraints on grasping forces and usable workspace, but these constraints limit the utilization of a robotic system. The researchers working on finger grasps and multiple robots cooperation with contact have always been assuming no slips at the contact points. However, in normal practice, one has to encounter this problem. Hence, this paper has taken this contact-point slip problem as its main topic and theme of work. Consequently, the slip phenomenon is analyzed thoroughly and then generalized for a multiple robot system manipulating a geometrically regular-shaped object. Different slip configurations are introduced and methods for their detection are proposed. This detection does not consider dedicated sensors neither for the object's posture nor for the slip detection. It, rather, utilizes only the finger-tip position information usually available from the kinematics based on very common sensors available with the manipulator. Utilizing the proposed methodology, it is possible to detect the end-point slips in most of the cases and realize an exact task execution and stability of control, with a minimum number of sensors.

This paper proposes a navigation system for a non-holonomic mobile robot. The navigation is based on a “look and move” approach. The aim is to define intermediate points called sub-goals through which the robot must pass. This algorithm is particularly suitable for navigation in an unknown environment and obstacle avoidance. Between two successive sub-goals, a shortest path planning solution is adopted. We have adopted the “Dubins' car” because of the environment perception sensor, a 180° laser scanner. In order to minimize the calculation time, the theoretical results of shortest path are approximated by simple equations. The navigation algorithm proposed can be used either in a structured or unstructured environment. In this context the local map construction is based on the segmentation of a structured environment; so for an unstructured environment, a suitable algorithm must be used instead.

One of the most important drawbacks of real robots is their lack of flexibility to changes in the environment or of the task. This paper presents a method enabling a visually guided robot to coordinate its movements with the vision processes. This method has been tested with a manipulator tracking maneuvering targets. The learning phase is performed in about one hour of repeated movements. After that, the robot can perform smooth and fast reaching movements and easily drop small objects into the wagon of a model train moving on an arbitrary trajectory.