Driven format adjustment in inspection technology: lubrication-free and modular

How do you check 900 screws or 700 injection moulded parts per minute for damage? Anyone asking themselves this question will find the right answer at Gefra GmbH. Founded in 1995, the company specialises in developing automated systems for the fast and precise optical inspection and measurement of components.
The Optisort machines from Gefra GmbH utilise camera technology in conjunction with automated feeding and very fast computer systems. For the inspection, the test specimens are fed individually past the cameras via a conveyor belt. 360° inspections with four cameras are also possible. Finally, good parts are actively ejected and faulty parts are separated.
All of this happens at a speed that the human eye can barely keep up with. The systems inspect several hundred parts per minute, sometimes more than 50,000 pieces per hour.
With the continuous further development of the systems, even the mechanics, i.e. the feeding system, reached its limits due to the high speed. But the computing speed also reached its limit. After all, the system has to analyse the data from eight or ten cameras and make decisions within milliseconds.
To further optimise the systems, the lighting was redesigned to put the test specimens in the right light for the cameras. The distance between the lights and the test specimen varies depending on the product and previously required manual adjustment of the lights using an adjusting wheel with a scale.
The process therefore needed to be integrated into the programme, making it automated and reproducible. A crucial criterion for the linear technology required for this was that it should be able to work completely without lubricants. The drives must not emit any foreign substances that could impair the testing process. After all, the lighting units are located directly above, next to and below the objects to be inspected. The compact nature of the drive units was equally important. As electrical adjustment is offered as an option, it must be possible to integrate it into the existing design. And finally, the entire unit with motor, carriage and mounting should be supplied ready for installation from a single source.

In their search for suitable linear drives, the Gefra engineers found what they were looking for in our drylin® programme. In addition to linear guides, the drylin® portfolio also consists of bending-resistant linear axes that combine a slide made of the high-performance polymer iglidur® with a drive spindle. The drylin® E-programme (E for electric) was later developed based on these linear tables. These are complete linear drive units in which a stepper motor is connected to the axis via an optional flange and an optional claw coupling and drives it.
With this axis, Gefra has now created the prerequisite for integrating the luminaire adjustment into the PC control system and thus into the respective test plan.
The new driven linear adjustment was initially trialled in a system for testing seals. Four spindle linear stages of the type drylin® SAW-0630 with electric drive, motor flange and integrated claw coupling are used here, which are connected to the system's PC via a controller. The linear axes have a stroke of 60 mm, for which a NEMA 17 stepper motor is responsible, which moves loads of up to 1000 g with an accuracy of +/- 0.5 mm. The drives fit perfectly into the environment and thus fulfil Gefra's requirement to offer its customers the most modular driven linear adjustment possible. The goal of a lubrication-free realisation of the format adjustment was also achieved. This is because the slides of the SLW linear axis are fitted with sliding foils made of iglidur®, a special material that is self-lubricating and works reliably even without additional lubrication from the outside. This not only protects the test specimens from lubricating grease, but also saves customers regular maintenance work.