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(Original author: NVsion – www.nvision3d.com )
By replacing a seat inspection system based on templates with a laser scanning approach, Johnson Controls saved $84,000 in template costs and reduced validation time for PT Cruiser seats from almost four months to one week. Building 24 sets of templates to test all the possible seat configurations for this vehicle would have taken three months. Testing 360 seats, the number required by DaimlerChrysler, would have taken another three weeks. Instead, the quality department opted to capture seat contours using a laser scanner. The cost and three-month delay for building templates was avoided, and the scanner captured 3D coordinate data for all 360 seats in only one week. "The main benefit of using the scanner was the time savings since we had to delay production until the testing was completed," says Rosa Leyva, division quality manger at Johnson Controls' Toluca, Mexico Comfortseat operation. "But the scanner also gives more accurate information, which we are using to establish manufacturing tolerances."
Johnson Controls, Milwaukee, Wisconsin, has grown into a multi-billion dollar corporation since its inception in 1885, with worldwide leadership in two businesses: automotive systems and building controls. Overall company sales for 2000 totaled $17.2 billion. In the automotive market, the company is the global market leader in seating and interior systems for light vehicles including passenger cars and light trucks. Systems supplied include seating, overhead, door, instrument panels, storage, electronics, and batteries. All systems, except batteries, are sold to the original equipment automotive market. Major OEM customers include DaimlerChrysler, Fiat, Ford, General Motors, Honda, Mazda, Mitsubishi, Nissan, NUMMI, Peugeot, Renault, Toyota, and Volkswagen. The Plymouth, Michigan-based automotive operations of Johnson Controls supplies interior products for more than 20 million vehicles annually.
Testing for PPAP
Johnson Control's Comfortseat plant in Toluca, Mexico was awarded the contract to design and manufacture seats for DaimlerChrysler's popular PT Cruiser. The car itself is assembled at a DaimlerChrysler plant in the same city. The PT Cruiser has four different seats: the driver's, the front passenger's, and two rear seat options. Each of these four seats is available in three types of fabric, for a total of 12 unique seat models in all. Johnson Controls was required by the terms of the part production approval process (PPAP) to test 30 copies of each seat model, or 360 seats in all.
In the past, they would have done this by comparing each of the seats to a series of contoured plastic templates. Two sets of templates were needed per seat, one set for the seat cushion and another for the seat back. The templates were arranged on an inspection stand in a lattice-type arrangement that represented the critical contours of the seat. When a seat was placed next to the latticework of templates, it was required to line up to within the tolerances indicated by the OEM. In the case of the PT Cruiser that was +/- 12 mm. For this car, a total of twenty-four sets of templates would have been needed to test each of the 12 different seat models. At a cost of approximately $3,500 per set, this represented a cost of $84,000. In addition to the cost, the other drawback to this approach was the time it would have taken. Producing the templates would have taken about three months. Testing the 360 seats would have taken another three weeks. And during that entire time, production was on hold.
In an attempt to reduce the cost of seat testing and get new seats into production sooner, plant management investigated a number of other inspection technologies. The options available to them used either laser or white light scanning techniques to capture shapes. White light systems were not stable enough for the factory environment, however, and required highly skilled operators. Also, they were expensive. Small and inexpensive laser systems were ruled out because they do not produce enough laser power to scan dark objects and are not rugged enough to survive in the plant environment.
The only system that met Johnson Control's requirements was the ModelMaker from NVision, Dallas, Texas. The major components of the ModelMaker system are a 3D laser sensor, an arm or position-sensing device on which the sensor is attached, the PC, and the software that extracts, displays, and manipulates the data. The ModelMaker's sensor is a single viewpoint laser stripe sensor incorporating the illumination and sensing means to capture 3D data. Laser stripe sensors are significantly faster than simple laser point sensors. They work by projecting a line of laser light onto the object while a small CCD camera views the line as it appears on the surface. A dedicated interface card translates the video image of the line into more than 400 3D coordinates, allowing for a maximum data capture rate of 10,000 points per second. The result is a dense cloud of 3D data, which accurately describes the surface of the object.
The ModelMaker can be configured with several of the commercially available position-sensing mechanisms. Johnson Controls chose the FaroArm from FARO Technologies Inc., Lake Mary, Florida, over competing products because the FaroArm offered an extra degree of freedom. Rather than six degrees of freedom which most position-sensing devices have, the FaroArm offers seven. This was important because the extra range of motion makes it possible to reach any point on a seat.
More accurate information
The Comfortseat plant's first use of the ModelMaker as a seat inspection device was for the PT Cruiser seats. The first step in the new inspection process was locking the seat back or cushion into the inspection stand as before. The technician, who needed only two weeks of training to operate the ModelMaker, then held the laser sensor so that a line of laser light appeared on the seat. Then he moved the sensor over the surface of the seat while the coordinate data was rendered and displayed real-time on the PC screen. This process was repeated for all 360 seats. It required only one week, which allowed Johnson Controls to get the PT Cruiser seat into production about three and a half months sooner than if templates had been used.
In addition to speeding validation for these seats, the new inspection process is also used on an on-going basis. For each of the 12 seat models, the quality department identified 25 critical points. The x, y, z coordinates for these points, obtained from the scanner, were entered into an Excel spreadsheet where an average was obtained from the 30 seats tested. "This way, if a dimension on one seat was at the outer limit, the readings from the other seats brought it back into line," says Leonardo Quinaniar, supervisor of the test laboratory at the Comfortseat plant. These values were then used to set manufacturing tolerances, creating a master model against which seats are tested now that normal production has begun.
Using scanned data to create the master gives Johnson Controls a more accurate production testing method than it had in the past when template provided only a "pass" or "fail" evaluation. Using software called Metris, Johnson Control quality engineers perform a quantitative comparison between the values in master model and the coordinates of the seat being tested. If an area is out of tolerance, manufacturing can see exactly how much it is off. Although it was possible to measure the distance between the seat and the templates by hand, the accuracy was too poor for this to be of any value. With the scanned data, the measurement of any discrepancy is highly accurate, helping manufacturing determine the cause of any problems. For example, the laser measurements might show that the seat was being built too far to one side or another. With that information, manufacturing knows where to adjust the process to solve the problem. Now that normal production on the PT Cruiser seats is underway, Johnson Controls uses this approach to test 10 seats from each of the 12 seat models on a quarterly basis.
Another on-going use of the new inspection system is for validating engineering changes. "Any time there is an engineering change that affects a seat, we have to test it," says Daniel Guavarrama, manager of quality engineering at the Toluca Comfortseat plant. "In the past, that would have meant modifying the template or building new one, so there was always a delay of at least two months. Now, engineering changes can be accommodated more quickly because once the new seat is produced, it can be scanned immediately." Another benefit to using the laser scanner is that it saves space. "With templates you need a lot of room for production and assembly," says Leyva. "Templates took up a big portion of the chassis lab space. Since we replaced them with the scanner, we have put that space to other use."
As the PT Cruiser project proved, a laser scanner seat inspection system is superior to templates in four significant ways. It eliminates the cost of templates completely. It gets new seat designs into production sooner. It yields more accurate measurements. Finally, it allows Johnson Controls to react faster to engineering changes.
Download: PT Cruiser uses handheld scanner for seat inspection (PDF file)
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