Intelligent vision system for PCB production

Channing Automation has combined the most advanced motion control with state of the art vision technology from Omron in its latest generation of high speed electronics production machinery.

Channing Automation has set new standards of excellence for PCB eyelet insertion by combining the most advanced motion control with state of the art vision technology from Omron in its latest generation of high speed electronics production machinery.

From its Plymouth base, Channings has made and exported PCB machinery for many years, during which time it has supplied most of the major home electronics producers plus more specialised companies like AB Automotive, and TV manufacturers Toshiba, Hitachi, Pansonic, JVC.

Lowe Opta.

It steadily develops the designs of its machines as technologies advance and as new techniques become available.

For instance it has already used vision systems on earlier projects, but has now broken new ground by integrating this technology with motion control.

"I always think it is a sign that a new technology has reached a significant level of maturity when you start integrating it into the whole machine design rather than using it as a 'standalone add-on'," says John Channing, founder and managing director of the company.

"Vision and motion are natural partners, which when combined together along with some processing intelligence form a very powerful and almost humanistic system.

A typical board will need around 100 eyelets inserting into it for through hole soldering after the electronic components are mounted upon it.

Naturally, the boards have to be produced in considerable volumes, so the speed of insertion required is high.

"Our previous generation of machines could insert eyelets in about 0.75 seconds each.

One of our objectives with the latest design was to get the cycle time down to below 0.5 seconds, and we are achieving this comfortably.

But quality is also paramount.

Most PCB boards are produced to a quality-assured regime where there is practically no tolerance of substandard production.

Two sizes of PCB eyelets are in common use, 2mm and 3mm, and most current machines insert these into the boards to within an accuracy of 0.3mm.

At the extremes of this tolerance the physical insertion is poor and copper can be lifted of the PCB.

This is likely to lead to poor soldering, low conductivity, and a completely failed joint and hence rejection of the whole board as substandard.

"Our goal here was consistent accuracy within 0.1mm, and in fact we are almost always twice as good as this," says Channing.

Boards are fed into the insertion area and the vision system searches the first hole, which is used as a datum or reference for the rest of the holes, the approximate position of which is derived from CAD data.

The camera is backlit absolutely square on to the required position of the hole.

Therefore, the camera will see the hole as a silhouette and, using special filtering functions built into the F150-2, its edges are sharpened up to match the hole's actual edges.

The vision system's processor will then use simple mathematical calculations to find the exact centre of the hole and if this is displaced from the target position the processor generates the necessary correction signal (which may be single of two axis) for the motion controller.

With the exact centre of the datum hole perfectly positioned, the rest of the holes in the board should line up accurately, although the vision and motion system remains active and checks/corrects each hole in turn before insertion of the eyelet.

"By starting with the first hole positioned perfectly, and keeping the system fine tuning for each subsequent hole, we are able to achieve staggering levels of accuracy every time, and at faster production times than ever before," enthuses Channing.

"Initially I was a bit worried about a big learning curve as we adopted all this new high technology, but in fact both of Omron's pieces if kit proved very user friendly.

The motion controller, their MC 402, is mounted inside a standard plc, so programming it was no different than normal.

Being integral with the PLC, its processing time is unencumbered by transmission delays to a separate unit, and this was critical considering the typical cycle time of 0.3-0.4 seconds.

Channing was equally impressed by the Omron F150-2 vision system, which he says makes his previous non-intelligent systems look decidedly pedestrian.

The camera uses a zoom lens to enlarge the 2mm or 3mm holes to the full size of the 484x512 pixel screen.

Sub pixel processing then increases this resolution four fold.

"We have always pushed back the boundaries for automated PCB production, so I am used to innovation and technology leaps.

Combining vision and motion has produced possibly the greatest breakthrough our market will experience this decade.

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