A major goal in the electrical and electronics industry today is always better performance, a design with the smallest possible dimensions - whether to save space or to make devices less noticeable. For the production, however, the increasing miniaturisation of components is problematic, since handling it is very tiring for the employees, but conventional robot systems do not work finely enough to take on these tasks. The injection moulding and toolmaking expert Reiter HG Geiger Kunststofftechnik GmbH has now developed an automated system for high-precision tooling in cooperation with a mechanical engineering specialist: The system is capable of reliably isolating and gripping pins with a maximum diameter of only 0.6 mm and placing them with a tolerance of a few μm. As a result, it was not only possible to relieve the worker, but at the same time the risk of losing the tiny precision turned parts was also significantly reduced.
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For over-moulding, different contacts must be placed in a slide, including pins with a length less than 1 millimetre.
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In medical technology, Reiter has been producing a delicate thermoplastic part with overmoulded contacts for a long time. Slides with two injection cavities must be equipped with four metal components each. The dimensions, however, demanded the utmost concentration from the operators: The turned and plated parts are only 1.65 mm long and have a diameter of only 0.4 mm, and at the head only 0.6 mm. Inserting them manually into the provided tool slots, which provide much less than 0.01 mm of clearance, posed a major challenge for consistent product quality. "In addition, the work as a whole is rather monotonous, which makes it hard to stay focused", says Hans Kolb, process engineer at the Geiger Group, to which Reiter also belongs. Another disadvantage of the manual loading method is that surface coating is damaged, which makes the parts unusable.
Now that the number of parts needed in this field has steadily increased, the injection moulding company decided to partially automate this process. Finding a suitable solution to the problem, however, proved difficult despite the general, cross-industry automation trend, as the engineer discovered: "We presented our requirements to different vendors, but most of them did not trust their technique to handle such fine motor skills. A few of them at least looked at the current production processes - and gave up". After a successful test run of the basic technology with the only remaining mechanical engineering company, which had offered a solution, which was "necessary" according to Kolb, "because we hardly even believed that the task was even solvable", the design of the actual machine began.
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Reiter, together with a specialist in production equipment, developed a robot system that can detect and precisely use the contact pins despite their small dimensions.
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Vibration, vacuum and individual coding guide the pin into the hole
First hurdle was the separation of the contact pins in order to be able to grip them later. For this, a vibratory feeder bowl with a circumferential groove was used. The pins are moved by the vibrations into the channel and then move upwards for alignment. At the end of which waits a vacuum suction device, which receives the foremost contact in the series and positions it freely. A robotic arm grasps the pin, but without damaging it, and brings it to the slide.
In actual placement, another challenge to be met was the accurate insertion into the tool hole. For this purpose, the slide, as in the injection moulding machine itself, initially centred in the robot cell with the aid of short-stroke cylinders and then clamped to prevent slippage. In addition, each of these carriers is coded individually so that it can be identified by the system. "This is necessary because not all tool slides and holes can be made exactly the same in the 0.001 mm range. So that the robot finds the appropriate holes, it is therefore specially trained on each slide", says the process engineer. This allows the pin to be properly positioned, inserted and returned immediately.
Simple work by autonomous flow of complex processes
The entire process takes only a few seconds for all four pins per slide. The fully assembled change-over slide is placed in the injection moulding machine after a visual inspection and the over-moulding is started while the finished parts are removed and checked from the previous slide. The now empty carrier is then pushed back into the robot cell for refilling, resulting in a seamless cycle. In addition, the machine does the same task with a time delay for a second injection moulding workstation on the other side of the machine.
Since all the complex processes in the system are pre-programmed and run autonomously, it was very easy for the staff at Reiter to get used to working with the new robotic colleague. All components such as sensors, actuators and controllers communicate via Profibus and ensure that the robot follows the defined movement steps. The process itself is directly controlled by inserting or removing the slides: A green light indicates that a slide on one side is fully populated. The respective worker can then remove it through a small sliding door in the safety enclosure of the robot and insert an empty one.
Meanwhile, the robot arm is busy with another slide on the other side, ensuring that there is no risk of collision or injury to the open door. If, on the other hand, the access is opened without the green light signal being released, the robot stops immediately and does not continue its interrupted activity until the door is closed. The same applies if the large front door is opened, for example, to refill pins in the hopper. In addition, the system, which is very compact (1,000 x 800 x 2,000 mm), also has a control panel which, apart from reading the current operating data, is hardly needed in everyday life.
Better ergonomics and less material loss
The assembly robot has been proving its worth now for over a year in production at Reiter in Hilpoltstein. "The throughput rate is roughly in the range that we used to achieve with fully manual assembly," reports Kolb. "It is much more important, however, that the ergonomics of the employees has improved greatly because the strenuous handling of the extremely small inserts has been eliminated. Another positive effect is the higher assembly quality, which is reflected in a lower error rate. "Based on these good experiences, an expansion of the range of applications is conceivable. The machine would be ready: It was so generously designed already at the conception that it offers space for two more slide feeders.
