231 research outputs found

    A shared position/force control methodology for teleoperation

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    A flexible and computationally efficient shared position/force control concept and its implementation in the Robot Control C Library (RCCL) are presented form the point of teleoperation. This methodology enables certain degrees of freedom to be position-controlled through real time manual inputs and the remaining degrees of freedom to be force-controlled by computer. Functionally, it is a hybrid control scheme in that certain degrees of freedom are designated to be under position control, and the remaining degrees of freedom to be under force control. However, the methodology is also a shared control scheme because some degrees of freedom can be put under manual control and the other degrees of freedom put under computer control. Unlike other hybrid control schemes, which process position and force commands independently, this scheme provides a force control loop built on top of a position control inner loop. This feature minimizes the computational burden and increases disturbance rejection. A simple implementation is achieved partly because the joint control servos that are part of most robots can be used to provide the position control inner loop. Along with this control scheme, several menus were implemented for the convenience of the user. The implemented control scheme was successfully demonstrated for the tasks of hinged-panel opening and peg-in-hole insertion

    A Distributed System for Robot Manipulator Control, NSF Grant ECS-11879 Fourth Report

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    This is the fourth annual report representing our last year\u27s work under the current grant. This work was directed to the development of a distributed computer architecture to function as a force and motion server to a robot system. In the course of this work we developed a compliant contact sensor to provide for transitions between position and force control; developed an end-effector capable of securing a stable grasp on an object and a theory of grasping; developed and built a controller which minimizes control delays; explored a parallel kinematics algorithms for the controller; developed a consistent approach to the definition of motion both in joint coordinates and in Cartesian coordinates; developed a symbolic simplification software package to generate the dynamics equations of a manipulator such that the calculations may be split between background and foreground

    Robotic Exploration of Surfaces With a Compliant Wrist Sensor

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    This paper presents some results of an ongoing research project to investigate the components and modules that are necessary to equip a robot with exploratory capabilities. Of particular interest is the recovery of certain material properties from a surface, given minimal a priori information, with the intent to use this information to enable a robot to stand and walk stably on a surface that is unknown and unconstrained. To this end, exploratory procedures (ep\u27s) have been designed and implemented to recover penetrability, material hardness and surface roughness by exploring the surface using a compliant wrist sensor. A six degree-of-freedom compliant wrist sensor, which combines passive compliance and active sensing, has been developed to provide the necessary flexibility for force and contact control, as well as to provide accurate position control. This paper describes the compliant wrist and sensing mechanism design along with a hybrid control algorithm that utilizes the sensed information from the wrist to adjust the apparent stiffness of the end-effector as desired

    Control Software of Robot Compliant Wrist System

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    The compliant wrist combining passive compliants and sensor has been developed in GRASP laboratory. The device provides the robot system the necessary flexibility which accommodates transitions as the robot makes contact with the environment, corrects positioning error in automatic assembly, avoids high impact forces and protects the surface from damage. The device also supplies the displacement sensing of the passive compliance so that active feedback control is possible. This report is intended to serve as a reference material to introduce the control software of the robot compliant wrist system developed and implemented in the lab. The detail discussion on system performance and parameters selection can be found in the thesis [3]. The rest of material is organized as follows. Section 2 introduces the compliance control methods of robot manipulators. The historic development of both passive and active compliance method is discussed. The advantages and disadvantages of the methods are investigated. Based on the unsolved problems in this issue, the six-degree freedom compliant wrist is developed, and the design feature is presented. Section 3 discusses the hybrid position/force control scheme using the sensing information from the device. The positioning error due to load or external force when robot moves in free space is compensated for, so that the effective stiffness is increased. In force control when robot is constrained by environment, the trajectory is modified by sensed force, so that the effective stiffness is decreased. Section 4 deals with the implementation of the control scheme. Various programs have been developed to perform the hybrid control operations, such as hybrid control demonstration, surface tracking, edge tracking, insertion and pulling out, and writing operation. The programs have been successfully implemented in the experiments. Definition and selection of the parameters in the programs are discussed. Section 5. is the source code of control scheme which has been implemented in PUMA 560 with index machine in GRASP Laboratory. The control is executed on a MicroVax I1 using the RCI primitives of RCCL

    On the Robot Compliant Motion Control

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    Teleprogramming: Remote Site Research Issues: (Dissertation Proposal)

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    This document proposes the development of the remote site workcell for teleoperation with significant communication delays (on the order of one to 20 seconds). In these situations, direct teleoperation becomes difficult to impossible due to the delays in visual and force feedback. Teleprogramming has been developed in order to overcome this problem. In teleprogramming, the human operator interacts in real time with a graphical model of the remote site, which provides for real time visual and force feedback. The master arm and the manipulator/model interactions, given predefined criteria of what types of motions are to be expected. These commands are then sent via a communication link, which may delay the signals, to the remote site. Based upon a remote world model, predefined and possibly refined as more information is obtained, the slave carries out commanded operations in the remote world and decides whether each step has been executed correctly. The remote site receives commands sent via the delayed communication link. These commands must be parsed and translated into the local robot control language, which includes insertion of dynamic parameters that are not generated by the master system. The commands are then executed by the hybrid position/force controller, and the resulting motions monitored for errors. This proposal addresses the following remote site issues: low level manipulator control using an instrumented compliant wrist for sensory feedback, higher level command execution implementing dynamic parameters, and remote manipulator tool usage and control

    Human machine interaction via the transfer of power and information signals

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    Robot manipulators are designed to perform tasks which would otherwise be executed by a human operator. No manipulator can even approach the speed and accuracy with which humans execute these tasks. But manipulators have the capability to exceed human ability in one particular area: strength. Through any reasonable observation and experience, the human's ability to perform a variety of physical tasks is limited not by his intelligence, but by his physical strength. If, in the appropriate environment, we can more closely integrate the mechanical power of a machine with intellectually driven human hand under the supervisory control of the human's intellect, we will then have a system which is superior to a loosely-integrated combination of a human and his fully automated robot as in the present day robotic systems. We must therefore develop a fundamental approach to the problem of this extending human mechanical power in certain environments. Extenders will be a class of robots worn by humans to increase human mechanical ability, while the wearer's intellect remains the central intelligent control system for manipulating the extender. The human body, in physical contact with the extender, exchanges information signals and power with the extender. Commands are transferred to the extender via the contact forces between the wearer and the extender as opposed to use of joystick (master arm), push-button or key-board to execute such commands that were used in previous man amplifiers. Instead, the operator becomes an integral part of the extender while executing the task. In this unique configuration the mechanical power transfer between the human and extender occurs in addition to information signal transfer. When the wearer uses the extender to touch and manipulate an object, the extender transfers to the wearer's hand, in feedback fashion, a scaled-down value of the actual external load which the extender is manipulating. This natural feedback force on the wearer's hand allows him to feel the scaled-down value of the external forces in the manipulations. Extenders can be utilized to maneuver very heavy loads in factories, shipyards, airports, and construction sites. In some instances, for example, extenders can replace forklifts. The experimental results for a prototype extender are discussed
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