What may seem futuristic to outsiders is already part of everyday life for some employees at the BMW Group plant in Berlin: working directly with a robot. As soon as the assembly worker has inserted the motorcycle rim into the centering machine, two APAS production assistants positioned to the right and left of the centering system take over the bolting process. An industrial screwdriving spindle is attached to each of the two robot arms; man and machine alternate and use the same workspace - without any safety fence. Sounds dangerous? It's not. Because the solution has been tested for safety and approved for working with people.

Robot plus screwing tool

This unique implementation of human-robot collaboration (HRC) combines two APAS assistant collaborative robots with a high-precision, automatic screwdriving spindle from the Bosch Rexroth 350 screwdriving system. The task of the creative synthesis of robotics, screwdriving and safety technology is to tighten the pre-assembled spokes in the correct sequence with repeat accuracy and to a precisely specified torque. The fact that the industrial robot can operate in the immediate vicinity of the assembly worker without a safety fence is due to the black sensor skin that surrounds both the APAS assistant and the screwdriving spindle and capacitively detects the surroundings. The system stops the movement before contact is made. Once the close-up area is clear again, the robot continues at the same point.

The basis for problem-free collaboration is the safety technology integrated into the APAS assistant. It creates a collision-free space in which man and machine can interact productively and safely. "The great advantage of hybrid workstations like this one is that they can be retrofitted with relatively little effort without having to change the surrounding micrologistics," says APAS Product Manager Wolfgang Pomrehn, who is responsible for collaborative robotics at Bosch Rexroth. "HRC is therefore a cost-effective alternative to full automation. Examples like this show how flexibly the factory of the future can be designed and that people will continue to play a central role in it."

Holistic solution

An important motivation for the Industry 4.0 project in motorcycle assembly was to gain experience for other potential HRC applications in series assembly. Bosch Rexroth was awarded the contract for the implementation due to its interdisciplinary expertise and range of solutions in both areas - collaborative robots and high-end screwdriving technology. Instead of costly special machine construction, the BMW Group thus received a complete, ready-to-install system that is made up of tried-and-tested standard components and also meets the required PL d, Cat. 3 safety standard.

In addition to high repeat accuracy for reproducible results, the requirements for the screwdriving solution also included seamless documentation. The Generation 350 screwdriving spindle and controller easily meet this requirement, as they are able to react to the individual screwdriving process in real time and, for example, immediately detect a defective thread. Process quality and reliability are therefore guaranteed in every case. As the complete tightening curve is recorded in each case, a wide range of characteristic data can be monitored - including the target torque, which is crucial for the correct tensioning of the spokes in the wheel.

Pilot successful, planning continues

The application has been running productively in two-shift operation since October 2020. The assembly employees have accepted the solution well, the experience gained with the HRC solution is passed on internally in training courses and helps to identify further potential areas of application, including assembly line assembly with continuous flow operation. The APAS modular system covers a wide range of application scenarios, especially as the industrial robot can be quickly and flexibly integrated with Kuka technology and the widely used mxAutomation PLC interface. Engineering is also simple, as the system is designed and programmed in a familiar robotics environment. This means that existing systems can also be efficiently supplemented or expanded.

In view of growing market volatility and increased demands on manufacturing flexibility, hybrid workstations with human-robot collaboration are proving to be a cost-effective way of increasing productivity in series production. Bosch Rexroth not only offers suitable standard components for this, but also the necessary industrial experience and interdisciplinary process expertise. "The APAS project at the BMW Group plant in Berlin is a good example of how manufacturing companies can tackle new problems with fresh ideas," says Wolfgang Pomrehn. "Based on a shared focus on technology and results, a piece of manufacturing of the future has been created here that sensibly combines the strengths of people and technology."