By replacing a template-based automotive seat inspection system with an electronic laser-scanning approach, Johnson Controls saved $60,000 in template costs and reduced validation time for PT Cruiser designfrom almost four months to three weeks.
Building 24 sets of templates to test all the possible seat configurations for the vehicle would have taken three months. Testing the 360 seats required by DaimlerChrysler would have taken another three weeks. Instead, the quality department opted to capture seat contours using an NVision 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 three weeks.
"The main benefit of using the NVision laser scanner was the time savings because we had to delay production until the testing was completed," says Rosa Leyva, division quality manager 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 has grown into a multi-billion dollar corporation since its inception in 1885, with worldwide business in automotive systems and building controls. In the automotive market, the company provides 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, including DaimlerChrysler, Ford, General Motors, Honda, Nissan, 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 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 Mexican city. The PT Cruiser has four different seats: Driver, front passenger, 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. Johnson 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 24 sets of templates would have been needed to test each of the 12 different seat models. At a cost of approximately $2,500 per set, this represented a cost of $60,000
In addition to cost, the other drawback to this approach was the time it would have taken. Producing the templates would have consumed about three months. Testing the 360 seats would have taken another three weeks, which delays PPAP approval.
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 objectsand are not rugged enough to survive in the plant environment.
The only system that met Johnson Control's requirements was the NVision laser scanner. The major components of the NVision laser scanning system are a 3D laser sensor, an arm or position-sensing device on which the sensor is attached, a PC, and the software that extracts, displays, and manipulates the data. The scanner’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 NVision laser scanner can be configured with several commercially available position-sensing mechanisms.