High-speed, high-precision measurement by machine vision.
South African machine vision specialist, Westplex, was presented a challenge when it contracted to design and manufacture a machine vision system for quality control at Autoliv South Africa. The system is required to handle and position three different types of small seat-belt parts, measure over 20 sizes on each part in three dimensions, with accuracies of 0,1 mm, at a rate approaching 55 parts per minute and then sort and categorise them by pass or type of failure.
The accuracy and speed the system is dependent on all of its components: cameras, lenses, lighting, parts handling and processing software. Non-optimal performance anywhere results in degradation of the entire system.
Cameras and data management
In order to measure the large number of sizes accurately in all three axes, six high-speed cameras were necessary. Cognex Insight vision sensor smart cameras were chosen, as they provide high resolution, powerful image analysis, part location functions and accurate measurement tools in a rugged industrial housing.
The Cognex cameras are connected via Ethernet to a server that coordinates the measurement results from the cameras and provides camera programming facilities. All of the data is reported on a shift, batch, day and month basis, showing the number of failures and their location as well as statistical information related to the tests.
One of the powerful characteristics of Cognex cameras is that all the vision analysis and measurement happens on the camera. They are IP67 compliant with a small form factor and a vast array of analysis capability. In this application, each camera was programmed for its specific test routine with all information fed back after each part inspection to the central computer. A tablet PC controls system operation through the associated PLCs and correlates the resultant data.
Lenses
Due to the high accuracy required, the use of telecentric lenses with image magnification independent of object distance was mandatory. Telecentric lenses from leading supplier, Opto Engineering, were chosen. Besides very high image resolution, the lenses provide uncommonly high telecentricity, depth of field and very low distortion.
Lighting
To cope with the multiple camera angles, measurement speed requirements and high reflectivity of the parts, innovative lighting configurations were devised. A combination of lights from CCS, a leader in machine vision lighting, and Westplex’s own in-house custom designed lights was provided the solution.
Parts handling
The specialised parts handling system of the machine was designed and manufactured by Techlyn. The parts being inspected are fed from one of two bowl feeders through a go/no-go gauge, a system of conveyor belts and robots then position the parts accurately in front of the cameras at rates up to 55 parts per minute.
Westplex supplied all the lights, cameras and optical components. It was also responsible for system engineering, software development and system integration. To date the system has been running reliably for over six months and machine vision has checked and recorded over a million parts.
For more information contact Brian Walker, Westplex, +27 (0)11 787 0473, [email protected], www.westplex.co.za
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