Using National Instruments LabVIEW and IMAQ for Visual Quality Control of a Filling Line

Author(s):
L. Vidal - CONTER Control de Energia
F. Serena - CONTER Control de Energia

Industry:
Consumer Goods

Products:
Vision, LabVIEW

The Challenge:
Implementing a quality control system in a Kinesias toiletterie production line.

The Solution:
Developing a PC-based system using IMAQ image acquisition boards controlled with LabVIEW and interfaced with the PLC controlling the production line.

Introduction
CONTER Control de Energia, S.A. is an engineering company with one division specialised in implementation of automation and industrial control. We developed asystem for automated visual inspection on a production line. We applied the system to a fully automated line consisting of a bottle positioning device, a filling unit, a cap device, a labelling system, and robots that place the bottles and set the boxes in pallets. The visual inspection system, which is located between the labelling system and the box device, takes care of the inspection of the front and back labelling as well as the code printed on the back label.

System Design
The system consists of a 400 MHz Pentium II PC running Windows NT. It contains three IMAQ PCI-1408 boards each connected to a progressive scanning CCD camera, with the electronic shutter fluctuating between 1/50 and 1/1,000 seconds. These cameras capture front, back, and code views of each bottle respectively. The PC-based system interfaces through LabVIEW to the PLC that controls the production line.

The lighting system is paramount to ensure the success of the image analysis. A high-frequency lighting system provides diffuse beam on the object to decrease glare on the labels and obtain a very uniform image.
Two photocells located beside the line generate a trigger pulse for each bottle. The PLC manages these signals and generates the trigger sequence of the cameras. These signals are connected to the trigger line of each board to start the acquisition process.

Following the acquisition process, LabVIEW and IMAQ Vision take care of the image processing by means of three programs running simultaneously, checking the references of the three views. The result of this image processing is transmitted to the PLC through the serial port. If the analysis reveals a failure, the PLC activates a pneumatic piston that knocks the flask off the line.

How the System Works
Because the maximum line speed is 7,200 units/hour, we have only 500 ms per bottle to carry out the complete analysis - acquisition and processing of the three images (front, back, and code). Thus, we have 166 ms to carry out each process. The acquisition program, developed on NI-IMAQ 2.1,runs simultaneously with the processing programs developed on IMAQ Vision 4.1.1

The first step of the analysis process is the localization of the object to get a reference point for all the regions of interest (ROIs). Each measurement ROI, which provides specific information on the bottle, is located according to the reference point and is characterised by constant parameters that determine the level in the grayscale to be detected. The distances between the different points provide information on whether the position between the different elements related to the bottle are correct. The front and back analysis detects vertical and horizontal shifting of the label and the correct position and orientation of the cap. The code analysis verifies the presence or absence of the code.

Advantages
After a close study of the management and system operation, we recommended using three PCI-1408 boards (with four video channels each) instead of a single one. This configuration avoids the loss of images that may occur as a result of the simultaneous triggering of several cameras.

The Result
This system has fulfilled the required specifications, so we can assure the quality level of the final product. This system is user-friendly for programmers and users, expanding the possibilities of using LabVIEW in industrial vision applications.

For more information, contact:

F. Serena and L. Vidal

CONTER Control de Energía

S.A., Parc Tecnològic del Vallès

Centre Empreses de Noves Technologies

08290 Cerdanyola (Barcelona) Spain

Tel: 34 93 5820313

Fax: 34 93 5820133

E-mail: conter@ptr.es

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