Showing papers in "Robotica in 1991"

Identifiable Parameters and Optimum Configurations for Robots Calibration

Abstract: This paper presents a general method to identify the geometric parameters of robots. An algorithm is given to calculate the identifiable geometric parameters. The robot location and the tool location parameters are taken into account. The algorithm is generalized to tree structure robots. The problem of selecting the optimum robot configurations to be used during the identification is discussed and a solution is proposed.

Dextrous telerobotics with force feedback — An overview part 2: control and implementation†

Abstract: The control stategy for a dextrous masters is different from the general case of bilateral teleoperation since it models the human hand in much more detail. Such a model is discussed together with the selection of actuators used for force feedback control. Existing prototypes of dextrous masters with force feedback are then reviewed. These are the Servo Controlled Manipulator Device, the Portable Dextrous Force Feedback Master (P.D.M.F.F.), the Remote Handler, and the Advanced Multiple DOF Force Reflective Hand/Wrist Master.

Dextrous Telerobotics with Force Feedback – An Overview. Part 1: Human Factors†

Abstract: Complex tasks that need to be performed through teleoperation led to the development of multifinger robot hands. A dextrous master is a multi-DOF controller which is worn by the operator in order to teleoperate these anthropomorphic hands. Force feedback is very useful when there is interaction with the environment. Providing force feedback to dextrous masters is an area of active research. We outline some of the human factors that influence the design of such masters. Of obvious importance is the hand geometry and the desired number of degrees of freedom. Additional criteria relate to the force perception of the hand. Finally, the man-machine impedance is of importance, since at the man/machine interface there are two impedances acting in series. One is the effective impedance of the human operator holding the master controller, the second is the impedance of the master controller being manipulated.

Optimal trigonometric robot joint trajectories

Abstract: Interpolation of a robot joint trajectory is realized using trigonometric splines. This original application has several advantages over existing methods (e.g. those using algebraic splines). For example, the computational expense is lower, more constraints can be imposed on the trajectory, obstacle avoidance can be implemented in real time, and smoother trajectories are obtained. Some of the spline parameters can be chosen to minimize an objective function (e.g. minimum jerk or minimum energy). If jerk is minimized, the optimization has a closed form solution. This paper introduces a trajectory interpolation algorithm, discusses a method for path optimization, and includes examples.

Manufacturing of a Scara Type Direct-Drive Robot with Graphite Fiber Epoxy Composite Material

Abstract: A SCARA type direct-drive robot which can be used in the assembly operation of printed circuit boards was designed and manufactured with graphite fiber epoxy composite material. The optimum stacking angle of the graphite fiber which gives the minimum deflection of the composite robot arm was calculated by the energy method and the manufacturing method of the box-type cross section of the robot arm with composite materials was developed.In order to compare the dynamic characteristics of the composite material robot arm with a conventional material robot arm, an aluminum robot arm which has the same dimensions and thickness of the composite robot arm was manufactured.The static and dynamic characteristics of the composite material robot arm such as static deflection, natural frequency and damping as well as weight saving were considerably improved compared to those of the aluminum robot arm.

Iterative Generation of Virtual Reference for a Manipulator

Abstract: Virtual reference is defined as the signal for a closed-loop System so that the response tracks the desired path perfectly. It is proposed to obtain a virtual reference signal suitable for a manipulator to track a predetermined trajectory using repetitive operations. Thus the algorithm ensures that the difference between the desired and the manipulator trajectories will become negligible as the number of operations approaches infinity if the manipulator is compensated for properly by local feedback. This algorithm uses a dual System to recursively improve the reference signal. Such a System has the advantage of being simple to design. The derivation of this algorithm is based on functional analysis. The effectiveness is confirmed by two experimental results.

Time-optimal Trajectories for Robot Manipulators

Abstract: A computational technique for obtaining minimum-time trajectories for robot manipulators is described in this paper. In the analysis, limitations to link movements due to design constraints are taken into consideration. Numerical examples based on a two-link planar robot arm shows the feasibility of the technique proposed. A physical explanation for the general characteristics of the observed trajectories is also presented. The importance of appreciating optimal control issues in designing robot manipulators and in planning robot workstation layouts is emphasised.

A nonlinear iterative learning method for robot path control

Abstract: An iterative learning control method is proposed for a class of non-linear dynamic systems with uncertain parameters. The method, in which non-linear system model is used, employs the model algorithmic control concept in the iteration sequence. A sufficient condition for convergency is provided. Then the method is shown to be applicable to continuous-path control of a robot manipulator.

Robotic assembly by slight random movements

Abstract: In this paper we develop a compilant system that permits robotic assembly of chamferless pieces. The idea is to absorb the positioning error between parts to be inserted by giving one of them a planar random movement. An actuator consisting of two axes (X and y) operated by an electromagnetic System is fitted to the work table; when its inputs are pseudo-random binary signais (P.R.B.S.) random motion is obtained. The trajectories of the actuator are analysed depending upon the P.R.B.S. parameters and a peg-in-a-hole assembly task is carried out. Experimental results show that large positioning errors can be compensated for chamferless insertions.

Concepts of Augmented Image Space and Transformed Feature Space for Efficient Visual Servoing of an “Eye-in-Hand Robot”

Abstract: For efficient visual servoing of an “eye-in-hand” robot, the concepts of Augmented Image Space and Transformed Feature Space are presented in the paper A formal definition of image features as functionals is given along with a technique to use defined image features for visual servoing Compared with other known methods, the proposed concepts reduce the computational burden for visual feedback, and enhance the flexibility in describing the vision-based task Simulations and real experiments demonstrate that the proposed concepts are useful and versatile tools for the industrial robot vision tasks, and thus the visual servoing problem can be dealt with more systematically

On the design of a direct drive 5-bar-linkage manipulator

Abstract: The 5-bar-linkage manipulator configuration is well suited to many industrial robotic applications. Aside from kinematic suitability, the dynamic equations are greatly simplified due to a decoupling of the manipulator inertia matrix. The design also lends itself to the use of direct drive motors. However, these motors must be capable of providing a high continuous torque to counter gravitational loading in the conventional manipulator design. In this paper, the static and dynamic design of the 5-bar-linkage manipulator is analysed. A technique is proposed whereby the motor torque requirements may be reduced to a fraction of those required in the conventional design, while simultaneously retaining the advantage of a decoupled inertia matrix. Details of a prototype manipulator and experimental results of its performance are presented.

Task–Driven Extraction of Object Contour by Human Haptics: Part 1

Abstract: The extraction of contour information from objects is essential for purposes of grasping and manipulation. We proposed that human haptic exploration of contours, in the absence of vision, would reveal specialized patterns. Task goals and intrinsic system capacities were assumed to constrain the breadth of processing and the precision with which contour is encoded, thus determining parameters of exploration and ultimately producing movement synergies or “contour exploration procedures.” A methodology for testing these assumptions is described, and the most frequently observed procedures are documented in Part 1. Part 2 will further analyze the procedures, test predictions, and develop implications of the research. The paper (2 parts) is novel in its study of human manipulative behavior from a robotic standpoint; it is thus of interest to robotics research workers interested in the long-term goals of robot manipulation and those interested in an anthropomorphic approach to robotics studies.

A multi-agent environment in robotics

Abstract: The use of Multi-Agent Systems as a Distributed AI paradigm for Robotics is the principal aim of our present work. In this paper we consider the needed concepts and a suitable architecture for a set of Agents in order to make it possible for them to cooperate in solving non-trivial tasks. Agents are sets of different software modules, each one implementing a function required for cooperation. A Monitor, an Acquaintance and Self-knowledge Modules, an Agenda and an Input queue, on the top of each Intelligent System, are fundamental modules that guarantee the process of cooperation, while the overall aim is devoted to the community of cooperative Agents. These Agents, which our testbed concerns, include Vision, Planner, World Model and the Robot itself.

Identification and Compensation of a Robot Kinematic Parameter for Positioning Accuracy Improvement

Abstract: This paper presents a simple identification method of the actual kinematic parameters for a robot with parallel joints It is known that Denavit–Hartenberg's coordinate System is not useful for nearly parallel joints In this paper, the coordinate frames are reassigned to model the kinematic parameter between nearly parallel joints by four parameters The proposed identification method uses a straight ruler about 1 m long A robot hand is placed by using a teaching pendant at the prescribed points on the ruler, and the corresponding error function is defined The identified kinematic parameters, which make the error function zero, are obtained by the iterative least square method based on the singular value decomposition In the compensation of joint angles, only the position is considered because the usual applications of robot do not require a precise orientation control

Constrained motion control of manipulation robots―a contribution

Abstract: The problems concerning the control of constrained motion of manipulation robots are discussed in the paper. Two general problems of hybrid position/force control are considered: the problem of interaction between position and force control and the problem of contact between a robot and an environment. Some promising solutions to these problems are identified. It is shown that adaptive control is necessary to solve these problems. A new control scheme is proposed and results of computer simulations are presented

ELITE : a goal oriented vision system for moving objects detection

Abstract: A specially designed system for movement monitoring is here presented The system has a two level architecture At the first level, a hardware processor analyses in real-time the images provided by a set of standard TV cameras and, using a technique based on the convolution operator, recognizes in each frame objects that have a specific shape The coordinates of these objects are fed to a computer, the second level of the system, that analyses the movement of these objects with the aid of a set of rules representing the knowledge of the context The system was extensively tested on the field and the main results are reportedThe whole system can work as a controlling device in robotics or as a general real-time image processor as well as an automatic movement analyser in biomechanics, orthopedic and neurological medicine

Force-Controlled Assembly of two Objects with a Two-arm Robot

Abstract: The use of a two-arm robot for assembling two objects, with each being held by one arm, is presented. The assembly task is decomposed into an approach phase and an assembly phase. For each phase, we propose a solution for describing the task. For the approach phase, we suggest to describe the task with respect to a mobile reference frame, attached to the end effector of one of the arms. This allows us to take advantage of the redundancy of the system. For the assembly phase, we propose two solutions, both involving some kind of force control. The first one is based upon a position control similar to the one used for the approach phase, with an updating of the reference position through a measurement of the contact forces. The second scheme is derived from a symmetrical hybrid control scheme initially proposed by Uchiyama and Dauchez to control a two-arm robot handling a single rigid object. The main results of this scheme are summarized, and the way of using it for an assembly task is presented. Finally, the experimental setup we have installed to validate our theoretical results is described.

A Distributed PC-Based Control System for Education in Robotics

Abstract: The paper presents an educational system for teaching and research in robotics which consists of a manipulator, controller and a PC compatible host computer. The advanced design of host-computer user-interface software makes the system very suitable for teaching. It allows the user not only to follow the system states but also to change the control structure on-line. In the first part of this paper the architecture of the system, window-oriented user interface, specially designed robot language and several build-in students lessons will be described as well as the data acquisition system and advanced graphical capabilities. In the second part of this paper the executive controller architecture is described. Besides the manipulator control function and IO operations, the controller supports communication with the hostcomputer. The controller is programmable, i.e. it executes various tasks within user-defined and build-in students lessons. By the use of simple host-computer commands the controller can execute various algorithms both for trajectory generation and dynamically compensated digital servo control. The dynamic model components in the feed-forward and feed-back control loop can be selectively included and changed during the manipulator's motion. Experimental results with a 4-link educational robot are presented.

A Variational Approach for Modeling Flexibility Effects in Manipulator Arms

Abstract: This paper presents a general technique to model flexible components (mainly links and joints flexibilities are considered) of manipulator arms based on Castigliano's theorem of least work. The robotic arms flexibility properties are derived and represented by the matrix of compliance coefficients. Such expressions can be used to determine the errors due to the robotic tip deformations under the application of a set of applied loads at the tip in a Cartesian space. Once these deformations are computed, they may be used to correct for the positional errors arisen from the robotic structural deformations in the motion control algorithms.

Motion planning for multiple robots with multi-mode operations via disjunctive graphs

Abstract: A new approach to motion planning for multiple robots with multi-mode operations is proposed in this paper. Although sharing a common workspace, the robots are assumed to perform periodical tasks independently. The goal is to schedule the motion trajectories of the robots so as to avoid collisions among them. Rather than assigning the robots with different priorities and planning safe motion for only one robot at a time, as is done in most previous studies, an efficient method is developed that can simultaneously generate collision-free motions for the robots with or without priority assignment. Being regarded as a type of job-shop scheduling, the problem is reduced to that of finding a minimaximal path in a disjunctive graph and solved by an extension of the Balas algorithm. The superiority of this approach is demonstrated with various robot operation requirements, including “non-priority”, “with-priority”, and “multicycle” operation modes. Some techniques for speeding up the scheduling process are also presented. The planning results can be described by Gantt charts and executed by a simple “stop-and-go” control scheme. Simulation results on different robot operation modes are also presented to show the feasibility of the proposed approach.

Structured motion planning in the local configuration space

Abstract: The minimum-time motion of robot manipulators is solved by defining a suitable time history for the arm end-effector to traverse. As the planning is performed in the configuration space, the uniqueness of the proposed algorithm emerges from the combination of both cubic and quadratic polynomial splines. Furthermore, the highly efficient time optimisation procedure could be applied to local segments of each joint trajectory, leading to a significant reduction of the travelling time. In addition, the ability to perform a search in the work space is granted, exploiting all possible options for an optimum motion. The method proposed considers all realistic physical limitations inherent in the manipulator design, in addition to any geometric constraints imposed on the path. Simulation programs have been written, and results are reported for the Unimation PUMA 560 robot manipulator.

A new simulation scheme for self-tuning adaptive control of robot manipulators

Abstract: In most dynamic adaptive control simulation of robotic manipulators, the Langrange–Euler (L–E) dynamic equations are first piecewise linearized about the desired reference and then discretized and rewritten in a state space form. This makes things very complicated and it is easy to make errors. What is more is that with a different reference this work must be done again. A new simulation scheme – Backward Recursive Self-Tuning Adaptive (BRSTA) – as it will be called, is suggested in this paper for adaptive controller design of robot manipulators. A two degree of freedom robot manipulator is used to verify the scheme in the condition of highly nonlinear and highly coupled system. A one degree of freedom robot manipulator is used for comparing both the forward and backward methods. The main advantages of this scheme include that it can be used for evaluating the self-tuning adaptive control laws and provide the initial process parameters for real-time control. And it is concluded here that the Newton–Euler (N–E) dynamic equations are equally well qualified as the Langrange–Euler (L-E) equations for the simulation of self-tuning adaptive control of robot manipulators.

A Distributed On-Line Trajectory Generator for Intelligent Sensory-Based Manipulators

Abstract: An algorithm is presented for the on-line generation of minimum-time trajectories for robot manipulators. The algorithm is designed for intelligent robots with advanced on-board sensory equipment which can provide the position and orientation of the end-effector. Planning is performed in the configuration (joint) space by the use of optimised combined polynomial splines, along with a search technique to identify the best minimum-time trajectory. The method proposed considers all physical and dynamical limitations inherent in the manipulator design, in addition to any geometric path constraints. Meeting the demands of the heavy computations involved lead to a distributed formulation on a multiprocessor system, for which an intelligent control unit has been created to supervise its proper and practical implementation. Simulation results of a proposed case study are presented for a PUMA 560 robot manipulator.

An efficient computational method of the Jacobian for robot manipulators

Abstract: A more efficient method for computing the Jacobian matrix for robot manipulators is developed. Compared with the existing methods, the number of required numerical operations is greatly reduced, making the proposed technique the fastest or the least expensive one for any general N degrees-of-freedom manipulator.

Evaluation of ultrasonic inspection and imaging systems for robotics using TLM modelling

Abstract: Airborne ultrasound based sensor systems have been applied to a variety of problems in robotics and advanced manufacturing. These include slot and hole inspection, and systems suitable for workspace imaging and autonomous guided vehicle (AGV) navigation. The transmission line matrix (TLM) method of modelling wave propagation has been used in the evaluation of these systems. The model gives both graphical and numerical outputs, and allows an improved understanding of the interaction of ultrasonic waves and targets to be obtained.

Adaptive Control of Nonlinear Dynamic SCARA Type of Manipulators

Abstract: Robotica / Volume 9 / Issue 03 / July 1991, pp 319 326 DOI: 10.1017/S0263574700006482, Published online: 09 March 2009 Link to this article: http://journals.cambridge.org/abstract_S0263574700006482 How to cite this article: Devendra P. Garg (1991). Adaptive Control of Nonlinear Dynamic SCARA Type of Manipulators. Robotica, 9, pp 319-326 doi:10.1017/S0263574700006482 Request Permissions : Click here