Currently, most plastic components are produced by large, expensive, plastic injection-molding machines. These machines force molten plastic under enormous pressure into intricate molds to cast specific parts such as electromechanical connectors. Once formed, the molded parts must be checked to determine the presence and dimensions of wire protectors, insulation bases, and fixing elements.
Merten (Wiehl-Bomig, Germany) manufactures a number of such appliance connection boxes. Rather than manually inspect the finish parts, Merten contracted its sister company, Pulsotronic Merten GmbH (Wiehl, Germany), to develop a gravity-fed-parts machine-vision system to inspect at a rate of approximately 40 parts per minute.
Dubbed the Video Check system, the finished system implements a two-stage PC-based vision system. During operation, electromechanical connectors are gravity fed individually from a hopper at the top of a tilted chute. Parts slide down the chute and pass through a light beam sensor that triggers an ET200S programmable logic controller (PLC) from Siemens (Karlsruhe, Germany). In turn, this PLC actuates a pneumatic stop that halts the connector under the first camera-vision stage. Here, the connector is illuminated using red light-emitting diode (LED) Vicolux lighting panels from Vision and Control (Suhl, Germany) and imaged using a CVM-1 monochrome 1300 x 1030 x 8-bit CCD camera from JAI Camera Solutions (Glostrup, Denmark). According to Klaus Strack, Pulsotronic sales manager, LED lighting was chosen because its intensity could be adjusted to automatically compensate for different production environments.
After images are captured using a PCI-based PCI-MVSG frame grabber from Matrix Vision (Oppenweiler, Germany), they are processed using the Pulsotronic Director PC-based machine-vision software package. This PC-based imaging software allows developers to construct a number of machine-vision routines using a set of primitive functions such as image capture, histogram, and filtering. In the first stage of the connector inspection, this software is used to determine the presence of a number of surface contacts on the electrical connector. This inspection was performed by first defining regions of interest within the connector image and then performing a pattern-matching operation to determine the presence or absence of surface contacts.
After the surface contacts are inspected, the pneumatic stop is again opened, allowing the inspected part to slide under gravity to a second pneumatically controlled image-inspection stage. The purpose of the second stage is to compute the exact dimensions of the connector. To accomplish this, Pulsotronic employs an S6ASS1500 telecentric LED condenser from Sill Optics GmbH (Wendelstein, Germany) that uniformly illuminates the connector from underneath. To image the backlit connector, another JAI CVM-1 camera is used but is coupled to a S5LPJ6020 telecentric lens, also from Sill Optics. With a working distance of 190 mm and a magnification of 0.1, the telecentric lens permits the imaging of the connector across its 65 x 48-mm area.
The captured images by the second JAI CCD camera are digitized by the Matrix Vision PC-based PCI-MVSG frame grabber. The Pulsotronic Director software analyzes the critical dimensions of the captured images to within 0.01 mm. During both inspection tests, images are displayed on a PC-based TFT flat-screen monitor. From this display console and a Siemens OP170B flat panel monitor, operators can view the results of the tests and store them in database format for further analysis.
