Volvo places great emphasis on manufacturing quality, safe, comfortable, and environmentally friendly cars. To this end, the company has placed added emphasis and research into the manufacturing of its seats.
High quality standards led the company to invest in a system that allows it not only to subject the seats to extreme climatic conditions, but also to provide authentic simulation of the motions of a wide range of different vehicle occupants. An OccuBot testing system, developed jointly by Lear and Kuka, is fitted with a special protective suit and located in a climatic chamber to re-create the motions of a human driver, thereby testing the durability of the seats.
Volvo previously tested seats using a pneumatic seat tester. This system, however, could only place a 2-D load on the seats, carrying out either horizontal or vertical motions, and was not designed for extreme temperatures. Rubbing and rotational motions, which often occur during driving, could not be produced.
“There were a number of reasons for investing in a new seat testing system,” said Eva Richardson, Project Manager at Volvo. “One such reason, as an example, is the new system’s increased capacity. In our old seat tester, we could only test one seat in four weeks, and even then the results were not entirely satisfactory. The robot, on the other hand, tests the durability of five seats simultaneously over a period of just 10 weeks.”
The OccuBot system works day and night in varying temperatures, and its program is only interrupted to inspect the seats. Six seats are set up around the robot in the climatic chamber, and the robot then executes a series of preprogrammed seat motions in sequence. For this purpose, it is fitted with a special fixture on its wrist for holding a cushioned device that resembles the form of a human body. The robot makes this dummy sit down and stand up again, and rubs and pushes it in all directions. Force/torque sensors enable the robot to reproduce human movements and sense the force that is applied in the process. It can be flexibly programmed and has a high degree of repeatability.
The measuring system provides six measurement dimensions for forces and torques. This provides the user with data about the actual forces being exerted on the contact surface between the dummy and the seat.
It is possible to compensate for the static forces of the dummy itself in order to prevent them from giving rise to additional dynamic forces. The robot motions are also regularly adjusted in relation to the wear on the test object. To adapt the overall system to a new seat, it is necessary to redefine the base coordinate system. The friction between the dummy and the seat is also measured. As soon as a preset limit value is reached, the dummy reduces the load on the seat.
The robot and climatic chamber are controlled externally from a main computer. To protect the robot against the extreme fluctuations in temperature and air humidity, it is clothed in a special three-layer fabric that is coated on the outside, similar to an astronaut’s space suit. Beneath this material, the temperature for the robot is maintained at a constant 20°C (68°F). This is achieved by pumping in cool air at three points.
A number of safety measures were incorporated into the design of the system. One example is a “Stop” button situated just above the floor, which enables the system to be stopped by an operator lying on the ground. “This may appear strange at first glance,” Richardson said, “but when the chamber is operated at low temperatures, frost deposits on the floor could cause the operator to slip; under certain circumstances the operator may not be able to get back up again.”
The system, which can only be started from outside, stops immediately if a door is opened. An alarm is activated if gas escapes, for example, in the case of a defective seat heater. The air-conditioned room is large enough to park a car in. In such cases, the robot and its equipment can be stowed in such a way that other test apparatus can be accommodated. “It was important for us that the system should remain flexible in terms of its range of possible applications,” Richardson said.