EuroWire May 2016

Technical article

Optical Wrap Defect Inspection for Cable By Craig Girdwood and Andrew McCloskey, Taymer International

Abstract The optical wrap defect inspection system significantly improves the quality control of wrapped cable. The surface and wrapping structure of the cable is continuously monitored by a machine vision system at production line speed. The wrap surface can be viewed live and/ or recorded for 100 per cent of the cable length. Surface and wrapping defects are identified, and images of the defects are recorded together with position information. Wrapping information including wrapping angle and overlap percentage can be monitored for changes. This technology improves the quality of the cable produced and prevents defective products from reaching the customer. 1 Introduction A critical quality issue created during the production of wrapped cable is surface defects and wrapping defects. Potential surface defects include scratches or holes, and potential wrapping defects include uneven wrapping, incorrect wrapping angle, tape peeling and tape tears. These defects are not only a cosmetic problem, but they can lead to the core being exposed to the surroundings, resulting in short circuits and failure of equipment. By identifying and detecting these defects during the production process, immediate corrective action can be performed and defective sections of product can be repaired or discarded. Utilising the constant and immediate feedback from the machine, operators and process engineers are able to pinpoint the root cause of the defects. The wrap defect inspection system utilises one or more high-speed cameras capturing real-time images of wrapped cable surfaces. The wrap inspector software is able to accurately measure

wrapping distance and angle, as well as determine both the type and size of a wide range of surface defects and wrapping defects. Surface and wrapping defects as small as 0.1mm can be detected and an alarm triggered. When a defect is detected a digital image is enhanced, magnified and displayed on a remote monitor, enabling the operator to verify the defects. This allows operators to determine the type of defect, to identify false positives (eg, a water droplet), or even detect surface blemishes (eg, surface discolouring, scratches). The wrapping angle and distance measurements for the entire cable are saved to a database along with a record of any surface or wrapping defect information. The defect information includes defect type, size and location on the cable in metres or feet. This allows defects to be isolated quickly by operators after production is completed. The wrap inspector system is able to be easily integrated into existing production lines and performs well for various types of wrapped cables and convoluted armouring. The wrap inspector system makes sure that any problems are discovered prior to any defective products being sent to customers. The lifetime of the lights can be over 50,000 hours of usage and they are the only consumable part. Detection Technique Limitations 2.1 Laser Diameter Gauges A laser diameter gauge is used to detect bulges, and neck-downs. The machine uses a laser and shadow technology to measure the diameter of the cable. The diameter measurement is extremely accurate and can be used to classify bulges or neck-downs. 2 Current Defect

However, there is no way to truly know if the defect detected is an actual defect. For example, a dust particle or water droplet on the cable would increase the diameter measurement, resulting in a false positive. 2.2 Spark Tester A spark tester is equipment that can be used to detect pinhole-type defects. The machine creates a spark when there is a pinhole that exposes the core of the cable – conductive metal. However, if a pinhole does not expose the core, the spark is not created. But the pinhole that is not a through hole is still a defect since over time the pinhole could expand and expose the core of the cable. Also, for products without a core (pipe, hose, tubing) or products without a conducting core (fibre optic cable), spark testers are not applicable. 2.3 Vision Systems Prior configurations of surface defect detection systems were unable to identify and measure convolutions of the product. These systems were limited to ignoring the convolutions to identify significant defects such as pinholes or significant bulges or shape changes. The wrap inspection system has been improved with additional image processing software and alternative camera configurations that identifies the wrapped cable profile and can measure parameters and detect variations in the wrapping that are considered defects.

3 Machine Vision

Inspection System

3.1 Optical Mechanical Design The wrap defect inspection system consists of one or more high resolution cameras and adequate lighting to capture images of cable moving at speeds more than 1,200 feet (400 metres) per minute. Using multiple cameras, 360-degree coverage of the cable surface can be achieved. The system produces high quality images at these speeds with a very high frame rate.

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May 2016