Technology

Increasing the degree of automation in assembly with new technologies and thus raising economic and qualitative potentials: For this goal, we are developing pitasc, a software for force-controlled assembly processes.

In contrast to other production areas, the degree of automation in assembly is low. Less than a fifth of the industrial robots used worldwide operate here. There are three main reasons for this circumstance: the variety of processes, the large wide variety and the challenge of creating the right contact from the specific combination of force and movement. 

• Assembly includes processes such as riveting, screwing, clipping, gluing, snapping, setting and hooking, i.e. the joining of parts by using forces. So far, the process has been solved in a task-specific manner. This means that current solutions do not scale sufficiently in robot programming .
• Variant diversity means: Products are increasingly personalized, even up to batch size 1, for example in final assembly in the automotive industry or in small and medium-sized companies. Reprogramming the robot each time and adapting it to specific variants is not economical.
• Assembly or joining always also means that there is contact between components. The process determines the type of contact and the robot must react appropriately. In this way, for example, manufacturing or position tolerances must be compensated.

Therefore, the following applies: Classic robot programming reaches its limits for assembly. It is too closely adapted to a specific task. Force control is often not supported or only for simple processes. For this reason, the Fraunhofer IPA offers solutions that enable fast programming according to the variants.

pitasc is structured as a modular system and offers program modules, the so-called force control and parameters. To use pitasc, an external control unit is connected, which gives the robot new capabilities during assembly.

The first component of pitasc, the program modules, enables subtasks such as contact set-ups, a search movement, telescoping, plugging in, using snap connections and much more. Applications can be assembled from these reusable modules. Currently, pitasc developers can combine the modules and create processes as they wish. In the future, system integrators will be able to implement this directly at the user’s end.

The second part of the solution is the force control. For this purpose, a sensor is attached to the robot flange. With the help of data evaluation, pitasc can compensate tolerances, for example, move until a contact occurs or either slide along surfaces or press until a set mating force is reached. In addition, the force control enables search and joining strategies, for example to detect a rivet hole or a top-hat rail, which can be offset by a few millimeters.

The third aspect of the solution is the parameterization of the modules. The task description is based on geometric features of workpieces and tools and not on poses of the robot. In this way, new variants can be easily mapped, as only new values of geometric features need to be specified while the force value is changed accordingly. The entire task description is independent from the installed robot. pitasc already supports several robot manufacturers (e.g. Universal Robots, Kuka, Denso, Franka Emika).