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On the Kinematics and Dynamics of Dual-Gripper Robot Manipulator

Authors:

Yih T., University of Texas at Arlington, USA

Shiakolas P., University of Texas at Arlington, USA

Eluri B., University of Texas at Arlington, USA

Burks B., Providence Group Inc.,

Thompson B., RedZone Robotics, Inc.

ABSTRACT

A dual-gripper Remote Tool Delivery (RTD) system has been developed to retrieve radioactive wastes from underground storage tanks with internal structural members. The RTD system is equipped with two grippers at both ends of the system. A vertical translation mechanism (VTM) is added which enables the vertical lifting motion of the system. The vertical movement can be processed with each gripper operating on a separate structural member. The dual-gripper design and inclusion of the VTM distinguish the RTD system from other ordinary robotic systems. These special features provide greater dexterity and flexibility; yet, increase the complexity in modeling and analysis. There are four possible operating configurations for the RTD system. The first configuration is that gripper 1 grasps the structural member in the tank while gripper 2 is free to move in space to perform designated task. In other occasions, it is possible that gripper 2 grasps the structural member and gripper 1 performs the necessary task. These two configurations typify the RTD system as an open-chain robotic system. It is also possible that both grippers grasp separate or the same structural members simultaneously. This exemplifies the RTD system as a closed-chain mechanism. The kinematics, dynamics and simulation of the open-chain robotic configurations are investigated in this paper.

Key Words. Dual-Gripper robot manipulator, Kinematic modeling, Kinematics, Dynamics, Simulation.

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Robotic Calibration Issues: Accuracy, Repeatability and Calibration

Authors:

Conrad K., University of Texas at Arlington, USA

Shiakolas P., University of Texas at Arlington, USA

Yih T., University of Texas at Arlington, USA

ABSTRACT

The groundwork for a contact calibration methodology using a touch probe is developed for an articulated robot arm. This solution is framed within current calibration and metrology issues in robotics based upon the kinematical mechanical design of a serial link manipulator. Accuracy, repeatability, and resolution are explored and a simplistic approach is taken. This exercise is intended to lay the groundwork for exploring the feasibility of integrating a commercial product such as a force sensor or touch trigger probe on the end of a robot arm. Candidate processes and/or applications are identified. Findings indicate that an in-process contact calibration methodology that is accurate, repeatable, and cost effective would be a desirable solution.

Key Words. Robotic accuracy, repeatability, calibration, resolution

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Reduced-Order Model Matching Control Design for Gantry Robots

Authors:

Yang X., Georgia Institute of Technology, USA

Taylor D., Georgia Institute of Technology, USA

ABSTRACT

An important application of gantry robots is circuit board assembly, a chal-lenging task involving rapid point-to-point motions that tend to induce structural vibrations. Attempts to suppress such vibrations through model-based controller design must take into account the variation of the flexible dynamics with respect to placement head position. To circumvent the time-varying configuration-dependent mass distribution property of the flexible dynamics, this paper explores the potential of a controller design based instead on the rigid dynamics. This reduced-order approach to controller design is recommended for gantry robots with relatively sti .beams, since it o .ers an appropriate compromise between modeling/implementation requirements and performance potential. The proposed reduced-order controller is designed using a model-matching formulation to adjust the transient response, and an integral e .ect is included to reject friction force disturbances for satisfactory steady-state response. The reduced-order model matching controller has been implemented and tested on a prototype gantry robot. The experimental results confirm the viability of the new design and show its superiority over the more traditional PID controller.

Keywords: Gantry robots, flexible beams, structural vibration, point-to-point motion, reduced-order control, model matching control.

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