Vision and Imaging Sensors / Detectors
Color Sensors: Quick and Economical
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A new class of simple, compact and especially cost-effective color area sensors is employed by a leading German transmission manufacturer in a pilot application for inspecting colored sealing plugs. The dustproof and splashproof sensors can "learn" up to 16 different color samples without programming, save them internally and complete up to 30 inspections per second.
The Saarbrücken plant of the ZF Getriebe GmbH is the headquarters of the car driveline technology division of the ZF Friedrichshafen AG. Here, 4-speed, 5-speed and 6-speed automatic transmissions for passenger cars are developed and manufactured. Since the beginning of production in 1973, this plant - which employs more than a fifth of all people working in the Saarland area automotive industry - has produced over 10 million transmissions. Clients include leading carmakers worldwide.
A daily output of approximately 4000 transmissions in 14 basic types and 120 models requires strictly organized, highly automated production processes and a perfect quality management, which integrates every step - no matter how small. This therefore also includes the inspection of simple sealing plugs before and after the washing of the transmissions. These plugs cover the connections for the cooling system and prevent washing water from entering the transmission interior. Since the washing creates internal pressure, it has to be made certain that the plugs have not been pushed out of the coupling holes.
A new Sensor Class closes the Gap
For this reason, the proper fit of the yellow, white or orange colored plugs is automatically checked - and has been for quite some time - with intelligent cameras from Siemens. Before the washing, where other characteristics are inspected as well, the intelligent camera SIMATIC VS 710 is the top choice for acquiring the complex grayscale images and for comparing them with the nominal samples.
"After the washing, only the presence of the plugs needs to be checked," says Klaus Kimmling, responsible for factory automation IT tasks at ZF. "Even the more simple industrial camera systems on the market are actually too oversized for this, which is why we have been searching for a long time for an equally rugged, but cost-optimized solution."
Kimmling finally found the right product in the new color area sensor SIMATIC MV220, which is rounding out the product spectrum of Siemens Automation and Drives (A&D) in the lower performance segment of the image-processing systems - above the conventional binary sensors.
ZF prefers to employ automation technology from Siemens throughout, which has proven to be durable, reliable and available at any time. The Saarbrücken plant has always belonged to the initial users of new Siemens automation technology and thoroughly tested the new color area sensor in a pilot project.
"One of our core requirements was to be able to adjust the sensor quickly and easily to different inspection tasks without complex programming or profound image processing knowledge," states Kimmling. This is a mandatory requirement, since sealing plugs of different colors and at different locations are employed by the various transmission types.
Advantageous for the application in the rough production environment is the dustproof and splashproof enclosure construction of the MV220, which meets the IP65 degree of protection and integrates all required components and features. Besides the actual color area sensor, these include an I/O interface for the digital data exchange with the controller, a laser-based alignment aid as well as the lighting. With its compact dimensions of 113 x 35 x 90 (W x H x D in mm), only a very small space is taken at the production line.
Automated Inspection
At the top of the device, a control panel is located - with only a few steps, up to 16 OK-images can be taught and stored in the sensor, which are then analyzed and compared to photos taken of the test items. The exposure time, white balance and brightness correction are automatically adjusted by the device. The focusing takes place semi-automatically. That is, the operator or setup technician only has to pay attention to the detection window, which can be sized via an adjusting screw from 40 x 30 to 200 x 150 mm to match the task.
The inspection of the sealing plugs after the washing runs fully automatic. Via data storage units of the RFID system Moby I from Siemens attached to the assembly carts, the present transmission type is identified and transmitted by the visualization system WinCC to the inspection stand controller, a SIMATIC S7 300. This controller activates the corresponding OK-image via the digital inputs of the color area sensor, briefly stops the assembly line and triggers the photo shot at the right moment.
The MV220 is capable of up to 30 pictures per second and can thus also inspect considerably smaller objects in rapid succession. In doing so, the color area sensor offers two basic operating modes: the "matching mode" for inspecting areas for all colors and the "recognition mode" for identifying specific, colored characteristic in a defined quantity, as is the case here with the transmission plugs. The classification of the inspection result takes place in the sensor and is sent back to the mobile data storage unit via the digital outputs, the controller and the visualization system. The data storage unit thus contains a complete product history.
To check the correct functioning of the inspection system itself, ZF runs a so-called reference master - a "faulty" transmission without plugs - through the inspection stand three times a day. Possible downtimes of the overriding control system - for instance due to maintenance - are bridged by an offline table in the controller, which always locally stores the last 10 transmission types checked.
Rugged and Stable
Klaus Kimmling himself has configured the new color area sensor for this pilot application and praises the intuitive teach-in procedure as well as the variable adjustment of the image window and object distance. "This shortens our changeover times without having to forego powerful image processing features."
The inspection system has been running stably and reliably for more than five months and fulfills the tasks assigned very economically.
Birgit
Gottsauner
Siemens AG
Automation and Drives
A&D PT 7 MP
Nürnberg, Germany
