At Lear Corp.’s production facility in Besigheim, Germany, multiple shifts of workers assemble car seats just-in-time. Assemblers must work quickly while meeting strict quality requirements.

For the past two years or so, a robot has helped the workers produce high-quality, error-free seats. The UR5, made by Danish manufacturer Universal Robots, screws together the seat and rest frames just prior to final assembly. Operating around the clock in three shifts, the robot locates, measures and tightens nearly 8,500 screws every day, resulting in shorter throughput time and greater process reliability.

Because its assemblers had limited automation experience, Lear selected a robot that is low maintenance, and easy to control and program. Equally important, the company needed a small, mobile robot that could be used alongside humans in a limited-space production area.

Systems integrator Faude Automatisierungstechnik recommended Lear use the UR5, a six-axis robot that weighs just 18 kilograms. It has a reach of 85 centimeters and a lifting capacity of 5 kilograms. Faude knew that Lear would like the robot’s intuitive user interface.

Programming is done by either pressing arrow keys on a touchpad (indicating where the robot should move) or grabbing the robot arm and showing it how to perform a certain action. This simplicity enabled Lear to familiarize employees with the robots in only one day.

Lear also likes that the robot can be used directly alongside humans without any safety shielding. As soon as an employee comes in contact with the robot arm and a force of at least 150 newtons is exerted, the robot arm automatically stops operating. This safety mode is in accordance with the European ISO standard.

The UR5 is installed above a conveyor belt. Workers manually position screws on both sides of the seat before placing it on the conveyor. The seat also is equipped with a transponder containing individual identification data.

When the seat passes the robot, it reads the transponder and tightens the screws using an attached electric screwdriver. Process data is documented by the screwdriver, which applies up to 35 newton-meters of torque at a prespecified rotational angle.

“Because the seats can be in slightly different positions, the robot uses a Flexvision image processing system that locates each screw within a grid of 50 millimeters square,” says Esben Ostergaard, chief technology officer of Universal Robots. “Using 2D measurements and a camera, the robot quickly positions the bit exactly on the head of the screw at the correct angle of rotation.”

The image processing system also enables the robot to immediately spot errors. For example, if screws are missing on a seat, the robot issues an error notification. A Lear employee then moves the seat to a reworking station and manually installs the missing screws.

Ostergaard says the robot and vision system cost nearly 50,000 Euro ($67,000)—but that amount was recouped after just a few months. He says that, thanks to the UR5’s energy-efficient design, ongoing operating costs are manageable.

Lear is examining whether it can integrate the same car-seat assembly system into the company’s other production plants across Europe. The company is also considering using the UR5 for other processes, including joining, bonding and sawing.

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