Zero-defect mounting of 3.5 Million headrests

The company KriTec Sondernmaschienvertriebs GmbH, Lüdenscheid, Germany co-operates closely with Automotive industry and supplier industry for years, if it concerns handling systems, volume plants as well as assembly plants with testing facilities.

Together with their partner, the company ALTEC, the total concept of the here presented machine to the assembly and quality control of head rests was realized. The company ALTEC has responsibility itself for the control and construction of the switch cabinet.

Highest quality in the automobile industry

The German automobile industry has an excellent reputation world-wide .At the basis is among other things the high claim of quality to the finished building groups. Life and limb are endangered, when errors arise, particularly in safety-relevant building groups. For this reason more than ever inspection systems are in demand like the intelligent vision system used in this case, that guarantees 100% manufacturing and assembly quality.

3.5 million head rests per year error free

The KriTec assembly line installs a complete head rest holder from four individual parts. This takes place over eight individual assembly and control stations. Due to the high claim of quality it is necessary, to constantly control the assigned components within the consecutive assembly line. When a partly assembled case at a control station is identified as being abnormal, the tool carrier is marked and those cases are not continued to be processed, but are removed at the end. The assembly and control output that KriTec assembly line achieves amounts to 3.5 million rests per year. In the process two intelligent vision sensors are used.

Process with 8 manufacturing and control stations

In the first station the head rests are inserted into the tool carrier. If the tool carrier is completely equipped, it drives to the first control station, station 2. The intelligent vision sensor checks whether a burr is present in the admission for the head rest. For this the head rest case is examined with a standard flat light. Due to the thereby generated high contrast one is independent of the different bright and dark decoration colors; all colors can be examined with the same camera focus. The openings in the head of the case present themselves as white surfaces, which are judged on quality by surface size. An existing burr clearly makes the given surface smaller. In this case the sensor gives an error signal after 40 ms measure time and the tool carrier is marked.

At the third station the shank spring is installed into the plastic case. All movements, which are needed for it, are realized with pneumatic valves of the company FESTO. After assembly the seat of the shank spring is inspected at station 4. It is important, to determine with the inspection whether the spring slipped laterally or in the height. The cases are lighted with a standard Hf ring light. Because the head rest case has a recess at that spring admission, which reflect differently with the existing bright and dark decoration colors, the lateral misalignment of the shank spring must be measured, depending upon color, at the spring top or at the spring shank. For this six of the sixteen possible measuring windows for edge identification are used. The vision sensor places all four results of measurement of the distances of the spring to the plastic cases at one’s disposal at the digital 24 V-exits.

Which results of measurement are taken for evaluation, is stated on a seventh measuring window, which is specified to detect whether the plastic case has a bright decoration. This spring shank has a prominent break in range of the spring top. Via two measuring windows, which enable vertical edge identification, the absolute position of the spring in Y-direction is determined and evaluated. The processing of all nine measuring windows and the evaluation happens within 55 ms.

At the stations 5 and 6 the head rest assembly is finished. A u-shaped spring is brought into the head of the plastic case and locked with a pressure piece. The seventh station inspects the function of the two pressure pieces, by means of two pressure absorbers. The 0-10 V-signals of the pressure absorbers are put into the PLC and evaluated. Station 8 channels the parts out that were detected as incorrect at the three test stations. In this way 100% quality is guaranteed.

Simple quality control made possible

About the topic quality assurance Mr. Klaus Krie, managing director of the KriTec GmbH said: We attach great importance to a process-safe assembly and test sequence. Therefore the entire production with good and bad parts is automatically logged with an operating data logging system. The assembly log can at any time be seen and evaluated. A rising error rate of one station is thus detected in time and the error cause can be eliminated soon.