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Inspection cells help to drive up quality.

For launch of its new Polo passenger car, Volkswagen acquired a body-in-white shopfloor inspection system. Two turnkey robot cells were to be installed in the welding plant next to the car body assembly lines. Specifications required measuring robot systems equipped with automated part load/unload stations and operator protection devices. Other requirements included DMIS application software with local PLC supervisors and proprietary SPC software. The system had to be designed with a suitable substructure to allow the plant floor to hold the weight of the measuring systems.

VW selected the DEA BRAVO 4308/2 OS, by DEA-Brown & Sharpe Systems Group, Torino, Italy. Consisting of two BRAVO 4308 OS measuring robots with a compound measuring envelope of 6000x29 1/2 mm, each robot is equipped with the IW 42C two-axis servo wrist and an anti-crash protection device on the spindle. The servo wrist permits accurate probe orientation in space for sheet metal measurement and assures full part accessibility by handling lengthy probe extensions for inside car body measurements with no loss of accuracy. Each cell is controlled by CHORUS F2, an industrial grade DMIS-based measuring software for operations such as in-process sheet metal gaging and free-form surface inspection. It offers 10-axis control within a single part program for multiarm inspection cell management with automatic collision protection.

An automatic part handling system minimizes machine downtime by feeding parts to the cell via two motorized shuttles from two load/unload stations on each side of the machine. Each station has a gantry crane that loads the part to be inspected from the welding line onto the loading station pallet and takes it back when the measuring cycle is completed. While one part is being inspected, another is loaded into the other loading station pallet.

According to Jakob Dyck, body production manager, VW replaced fixed gages with measuring robots to increase panel and body-in-white inspection throughput and to generate real-time inspection data. "In the past, using fixed gages, we were only able to inspect one body assembly at the end of the production batch and no detailed diagnosis was possible when a problem occurred. Hard gages did not give us the ability to control the process because they don't provide statistical data. The BRAVO's measuring velocity allows increased inspection sampling rates to keep pace with the production line output," he says.

Each cell checks one full body plus a complete set of subassemblies. Dimensional data are sent to VW's proprietary SPC software for real-time trend analysis and process monitoring. "BRAVO allows intelligent feedback decisions to be taken for maintaining product quality. If the preset quality limits are exceeded by one or more elements, we can launch diagnostics sub-programs that check the critical areas," says Mr Dyck. He also says that BRAVO identifies problems quickly, allowing for immediate attention to the problem.

CHORUS' routines for sheet metal gaging simplify and speed-up inspection and part program generation. At run time, the sheet metal routines overcome element mispositioning. If an element is not present, automatic skip cycles allow the machine to continue the part program without stopping, reducing machine downtime.

For more information from DEA-Brown & Sharpe, N Kingstown, RI.
COPYRIGHT 1997 Nelson Publishing
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Copyright 1997 Gale, Cengage Learning. All rights reserved.

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Publication:Tooling & Production
Date:Nov 1, 1997
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