Vision systems keep UK "solutions provider" competitive

Citation

(2003), "Vision systems keep UK "solutions provider" competitive", Assembly Automation, Vol. 23 No. 1. https://doi.org/10.1108/aa.2003.03323aaf.001

Vision systems keep UK "solutions provider" competitive

Vision systems keep UK "solutions provider" competitive

Keywords: Machine vision, Cognex

A culture of continuous system improvement pays ongoing dividends. Twenty Cognex In-Sight machine vision sensors are helping a world-beating assembly "solutions provider" JEB Engineering of Mildenhall, Suffolk, stay competitive in the manufacture of electronic components (Plate 1). JEB makes a variety of high volume, high quality components for some of the world's most famous companies. Recently, Cognex In-Sight vision sensors were instrumental in achieving dramatic operational improvements for them in the manufacture of an interconnnect system for an ink-jet printer cartridge.

Producing this type of component requires handling tiny parts at very high speed - in this case at over 4,000 pieces per minute. Unit costs must be low if overseas competitors are to be kept at bay and to make matters even more challenging, reacting quickly to market demand is critical to success.

Plate 1 In-sight machines vision sensors from Cognex

There is only one way to achieve all this, according to Production Manager Mark Isaacson, and that is to develop highly automated production lines and keep on improving them. Never stand still, because someone, somewhere, is about to capture your next order. "People tend to assume that English suppliers cannot beat overseas competitors but we have done it many times. We often make our own components to ensure higher quality, and our costs are always competitive. All it takes is the will, the experience and the right investments. But it involves constantly re-appraising equipment performance, constant self-assessment and above all, a culture of continuous improvement."

The machines making the interconnects (there are two) have been improved dramatically in the past 2 years. "To achieve that", said Isaacson, "it's necessary to find out exactly how your system is working and where its bottlenecks are, or where defects are highest. You take the worst, find a way to eliminate it, then go on to the next important one."

To understand how this happens it is useful to look at the challenges involved in assembling the JEB interconnect. The product comprises a plastic moulding measuring approximately 3 cm × 1.5 cm, into which are inserted 52 gold-plated pins, each approximately 3 mm long and held in place by tiny springs to ensure that the tips provide a good electrical contact with the printer head. Each pin has a "dunch" or flange near its outer end, which stops it falling through the moulding. This asymmetric profile means it must be correctly oriented before insertion and as the pins are being inserted at the rate of 340-350/min this requires a fast and precise way to prove that each pin is oriented correctly.

There are two identical assembly lines based on Bihler platforms. For each line, pins are pneumatically transported by air-tubes from a nearby pin sorter, which is the key to accurate and timely manufacture. Springs are delivered from a separate hopper-based feeder. On each line, mechanical handling systems insert groups of pins into the mouldings as they pass by on a tape-conveyor, with optical and electrical tests performed immediately afterwards to eliminate faults and reduce losses as soon as possible.

From each pin sorter, vibrator bowls deliver a continuous stream of pins into the air-tubes. Because pins can exit a bowl in one of two orientations (flange to front - wrong - and flange to rear - correct) a weir is placed just prior to the air-tube to tip wrongly oriented pins into the correct state. The vision camera looks down onto the line just after the weir and the arrival of a pin in its field of view triggers the software to check that it is properly oriented. Correctly-oriented pins are allowed to pass into the air-tube while wrongly-oriented pins are blown off the line by means of an air blast controlled by the vision system, and returned to the bowl for re-cycling. Each pin sorter is controlled according to the demand of the assembly line itself, to balance the number of parts being delivered through the air-tubes and avoid over-loading or under-loading of the mechanical handling systems.

Ten bowls and corresponding air-tubes are needed to keep up with the machine's current production rate of 45 parts per minute, which equates to 4,815 pieces being assembled each minute. Average efficiency has risen from 60 to 80 per cent over 2 years. How has this been achieved? Said Isaacson, "Obviously fast, accurate pin delivery is critical to overall production, so we closely monitor the efficiency of each bowl. If you have good production data it's very easy to see the efficiency of each bowl are and as production demand inevitably increases, so you can easily identify which problem area needs to be addressed."

"Component handling systems like vibrator bowls are always a potential source of trouble. We could see that improving overall efficiency was important and this required that each bowl performed at its best thus minimising downtime. Recently we found that the inspection system was our biggest limiting factor."

At the time, the inspection system was pneumatic/mechanical based (through-beam sensors) and was limiting production to about 40 parts per minute, with lots of attendant maintenance problems, so a vision-based alternative was a natural choice for speeding output. "We have used automated vision systems in this line for some years", said Isaacson, "but it is the current range of low-cost, easily-programmed options that really made our choice easy for inspecting the pins. The Cognex In-Sight cameras we use at each bowl were very easy to install and the hand-held programming tool and the spreadsheet-based programs mean that our inspection regime could be configured very easily. Ethernet connectivity was a bonus." Each camera is used with an LED backlight to illuminate the pin from underneath. The only maintenance is regular cleaning of this backlight, and camera threshold adjustments to compensate for the slight variations in the colour of gold plating.

Six PLCs control the two-machine assembly line, communicating with each other over Ethernet. The main PLC provides master control, while others are dedicated to various sub-sections of each line, including the pin sorters and the systems which pack the assembled connectors into transportation tubes.

Production data from about 300 sensors on the machine is collated and processed by the main PLC and various operator display screens enable production to be accurately monitored, although Isaacson says that a fully-trained operator can usually "see" how the machine is performing just by looking and listening. A feed to a desktop PC also allows production data to be fed into a spreadsheet for external use. Ethernet gives quicker reaction times than the previous proprietary network and has also contributed to making the machine go faster. Currently connected by a hub, the network will soon have its own switch to improve data transmissions even further.

A measure of the success of the culture of continuous improvement is given by the fact that over the past 2 years output has been increased by 50 per cent, labour costs have been decreased by a third and costs overall reduced by 25 per cent.

For further information contact: Katrina Dixon, Cognex UK, Units 7-9, First Quarter, Blenheim Road, Epsom, KT19 9QN, UK. Tel: 0800 0180018; Fax: 01372 754 150; E-mail: kdixon@cognex.com