Browse Prior Art Database

3D Cable-Based Cartesian Metrology System

IP.com Disclosure Number: IPCOM000125626D
Original Publication Date: 2004-May-01
Included in the Prior Art Database: 2005-Jun-09

Publishing Venue

National Institute of Standards and Technology

Related People

Robert L. Williams II: INVENTOR [+3]

Abstract

A novel cable-based metrology system is presented wherein six cables are connected in parallel from ground-mounted string pots to the moving object or tool of interest. Cartesian pose can be determined for feedback control and other purposes by reading the lengths of the six cables via the string pots and using closed-form forward pose kinematics. This article focuses on a sculpting metrology tool, assisting a human artist in generating a piece from a computer model, but applications exist in manufacturing, rapid prototyping, robotics, and automated construction. We present experimental data to demonstrate the operation of our system, we study the absolute accuracy and also measurement resolution, and we discuss various error sources. The proposed real-time cable-based metrology system is less complex and more economical than existing commercial Cartesian metrology technologies.

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Page 1 of 30

3D Cable-Based Cartesian Metrology System

Robert L. Williams II

Ohio University Athens, Ohio

James S. Albus and Roger V. Bostelman

NIST

Gaithersburg, MD

Submitted to the:

Journal of Robotic Systems

May, 2003

Keywords: metrology, cable-based metrology, cables, wires, string pots, rapid prototyping, robotics, automated construction.

Contact information:

Robert L. Williams II

Associate Professor

Department of Mechanical Engineering 257 Stocker Center
Ohio University
Athens, OH 45701-2979
Phone: (740) 593-1096
Fax: (740) 593-0476
E-mail:williar4@ohio.edu

URL: http://www.ent.ohiou.edu/~bobw

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3D Cable-Based Cartesian Metrology System

Robert L. Williams II

Ohio University, Athens, Ohio

James S. Albus and Roger V. Bostelman

NIST, Gaithersburg, MD

ABSTRACT

      A novel cable-based metrology system is presented wherein six cables are connected in parallel from ground- mounted string pots to the moving object or tool of interest. Cartesian pose can be determined for feedback control and other purposes by reading the lengths of the six cables via the string pots and using closed-form forward pose kinematics. This article focuses on a sculpting metrology tool, assisting a human artist in generating a piece from a computer model, but applications exist in manufacturing, rapid prototyping, robotics, and automated construction. We present experimental data to demonstrate the operation of our system, we study the absolute accuracy and also measurement resolution, and we discuss various error sources. The proposed real-time cable-based metrology system is less complex and more economical than existing commercial Cartesian metrology technologies.

1. INTRODUCTION

      Many applications in robotics, construction, and manufacturing require effective real-time measurement of Cartesian pose of end-effectors, tools, and materials. Current technologies in use for pose metrology include machine vision, photogrammetry, theodolites, laser interferometry, magnetic tracking, stereo optical image registration, and acoustic methods; many of the technologies are complex and expensive. The current article presents a novel system for Cartesian pose measurement using six cables (whose lengths are sensed via passive string pots with torsional-spring tensioning) connected to the end-effector. The proposed system is relatively simple and economical.

      This idea is related to cable-suspended robots; the literature in this area is growing, starting with the NIST (National Institute of Standards and Technology) RoboCrane1 and the McDonnell-Douglas* Charlotte2. The kinematics, dynamics, control, and applications of cable-suspended robots are topics of current interest3,4,5.

      NIST was also the innovator behind passive cable-based metrology. The Robot Calibrator6 used three cables meeting at a single point, measured by three string encoders, and was used to calibrate a PUMA robot, position only. A similar idea was implemented7 for partial-pose (position) calibration of an industri...