W.E.T. Automotive Systems AG, based in Odelzhausen near Munich, is one of the world’s leading manufacturers of car seat heaters and associated temperature control components. Other activities of the company, founded in 1968, include the development and production of cable assemblies, flat cables and industrial heating elements. Principal customers of the W.E.T. group, which has subsidiaries in Canada, Malta, Mexico, Hungary and the USA, are the automotive industry and its tier-one suppliers. With a workforce of over 2500, the ISO 9001/2, VDA 6.1, QS 9000 and TS 16949-certified company achieved total sales of approximately €130 million for the last business year.
Growing market for car seat heating systems
Car seat heaters, which account for about 90 percent of the company’s business, have undergone major further development at W.E.T. Successful research in the areas of durability, new applications, performance and economy has helped the Bavarian firm to conquer the number one slot in the world market for car seat heaters, with a market share in excess of 50 percent. Numerous patents also testify to the company’s technological superiority. The continually growing global market for car seat heaters is thus opening up new opportunities. Between 1995 and 2000, the percentage of cars fitted with seat heaters rose from 3.7 to 12.8 percent.
For car seat heaters, technical perfection is not enough; they must also satisfy a wide range of different customer requirements. These requirements cover the diversity of seat types necessary for different car models on the one hand, and the different production conditions of the seat manufacturers on the other. This is why W.E.T. offers a range of different installation options. The spectrum ranges from simple heating pads for DIY installation, to products designed to be sewn into seats and systems that are installed by means of backfoaming.
The basic materials and system components used for the seat heaters must be tested continuously and optimized in accordance with the test results. Standard qualification testing includes thermographic imaging, tests in climatic chambers and the mechanical durability test series, e.g. with Occubot VI, that are required by the automotive industry.
Occubot VI as a mechanical process
In the Occubot VI process, a KUKA KR 150 robot verifies whether or not heaters integrated into car seats or seat parts withstand the mechanical stress which they are subjected to during the lifetime of the car. Occubot VI is a flexible, programmable, load- and position-controlled test system. This method, which works with force/torque sensors, reproduces the motions and loads of a human body using dummies, thus replacing a wide range of costly, customized test devices with hydraulic or pneumatic drives. Occubot VI allows realistic simulation, for example, of someone getting into and out of the seat (ingress/egress test), or of strong pulsation or vibration during driving. In addition, there are jounce and squirm, rear fatigue, truck driver and clutch operation tests.
Apart from the KUKA robot with its controller and control panel, the Occubot VI system consists of the force/torque sensor system, the system software including the application, setup and configuration programs, and the various dummies.
The measuring system used in the control loop with the robot controller provides six measurement dimensions for forces and torques and ensures absolute accuracy. For three forces, the system records three torques. The forces and torques are measured continuously at the interpolation cycle rate of the robot controller. The system saves path offsets in a file for subsequent test evaluation.
The software converts all the forces measured by the sensor to a virtual coordinate system. This provides the user with data about the actual forces and torques being exerted on the contact surface between the dummy and the seat. It is also possible to compensate for the static forces of the dummy in order to prevent its weight from giving rise to additional dynamic forces. The robot motions are also regularly adapted in relation to the wear on the test object.
Flexible robot
The flexibility of the procedure, which results from the use of a six-axis jointed-arm robot, makes it possible to configure the system for combined operation with three different tests on three different seats at the same time. This means, for example, that the robot can complete one program at night and then switch automatically to the next program.
The path profiles of the robot result from a combination of different test motions. For complex tests, the operator enters a series of points to which the KR 150 executes smooth motions in sequence and with different forces. All robot motions are defined as motions of the tool center point relative to the Base coordinate system. This means that to adapt the overall system to a different seat, it is merely necessary to redefine the Base coordinate system. The user is aided by a utility program which calculates the current robot position.
Basic knowledge of programming is sufficient as the system software is embedded in the robot programming. Another factor contributing to the overall user-friendliness is the fact that, after a stop, the robot can always resume motion at exactly the point where it stopped.
Tests “around the clock”
At W.E.T. Automotive Systems, the Occubot VI tests run “around the clock” seven days a week. Before a new test series is started, the home position of the seat is measured and the mechanical test sequence is defined. The operator also specifies how current is to be supplied to the heater being tested. As soon as it receives the start signal, the KUKA robot starts the durability test. It moves the SAE (Society of Automotive Engineers) dummy mounted on its wrist in such a way as to simulate the stress on the seat heater caused by part of the driver’s body, e.g. thigh or buttocks. The full force of the robot, provided by its load-bearing capacity of 150 kg, is seldom required.
W.E.T. uses the KUKA robot for all tests with four or more axes, for more extensive simulations, and high-frequency sinusoidal test applications for driving simulation. When asked what requirements he places on a robot system, the user mentions short cycle times and high repeatability. In particular, however, he emphasizes the need for flexibility. One example of the flexibility of the KR 150 is that when the heater in a seat being tested ceases to function, the robot automatically moves on to the next seat and resumes testing there.
Technical considerations were the deciding factor in the choice of a robot from KUKA Roboter GmbH, Augsburg. Given that the KR 150 is in operation around the clock, the geographical proximity of the company was an additional bonus as W.E.T. expects prompt service in order to guarantee permanent availability.
Author: Jürgen Warmbold, freelance technical journalist, 27327 Martfeld, Germany