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Case Studies Collaborative Robots

Nov 30, 2018 — Schunk, a manufacturer of robot grippers, uses a collaborative robot in the pre-assembly process. A robot equipped with a camera takes base housings from a container and brings them to the worker. The robot also tightens screws, closes air connections on the gripper and strips excess glue. Meanwhile, workers complete tasks requiring high dexterity.

In the production of modern gripping systems numerous product variants are being manufactured, and provided in different batch sizes. The grippers were assembled manually on conventional assembly workstations up to now. Associated with this are one-sided physical strain, the danger of injuries, for example during chamfering, and comparatively high costs for purely manual activity. The goal of one HRC project at the SCHUNK smart factory was to use HRC systems to increase employee flexibility, reduce workplace monotony, improve ergonomics, and reduce manual cost per item.

Instead of completely automating processes, partial automation is currently gaining in importance, in which the strengths of humans and the strengths of robotics are brought together synergistically. The driving forces behind human/robot collaboration (HRC) are relieving the workforce of stressful or monotonous work steps, improving ergonomics in the workplace, especially against the background of demographic change, making work processes more flexible, increasing efficiency and optimizing logistics, handling and loading processes. This need for change also affects the production of SCHUNK, the competence leader for gripping systems and clamping technology.

Careful workplace analysis as a starting point

Before the project started, the SCHUNK team analyzed which change processes are associated with the introduction of an HRC application. On the one hand, it is important to create the technical prerequisites for standard-compliant workplace operation and thus legal certainty for the operators and, on the other hand, to gain the acceptance of the employees for the robot as a colleague.

In the course of a work process evaluation, SCHUNK identified workplaces and work steps, which are suitable for the conversion to an HRC application. Assessment criteria were the required programming effort, the integration effort within the entire process chain, and the controllability of the hazard analysis. At the same time, jobs with moderate-duty cycle requirements and process chains of manageable complexity were preferred. Stations were selected, where a particularly effective ergonomic and mental relief is achieved and collaboration times and interventions are initially rather low. Another key factor in the selection of jobs was the fact that the special strengths of the robots and the workers could be clearly distinguished from each other. Because if employees can continue to bring their strengths into the overall process in a secure manner, this promotes acceptance. For the pilot projects, employees were selected and included at an early stage, who have a high degree of technical affinity and curiosity.

Division of labor based on strengths

One of the use cases is the pre-assembly of gripping tools. In this application, a 7-axis lightweight KUKA LBR iiwa 7 R800 robot, on whose DIN ISO 9409-1-A-50 flange a modified SCHUNK Co-act EGP gripper is equipped with an integrated black-and-white industrial camera, removes various base housings from a universally usable transport container, and takes them to the worker. The camera detects the exact position of the basic housing, and it is transferred to the robot in the form of correction signals. Workpiece clamping is form-fit from the inside. The gripping force of the gripper with an inherently safe design is limited to a maximum of 140 N. The different sizes of the supplied workpieces are recognized, the corresponding product is classified, and the processing parameters adjusted. Other monotonous and so far purely manually executed subtasks are the screwing in of set-screws, the closing of air connections on the gripper, and the stripping of screw glue. In a second implementation phase, these steps were automated. This eliminates the worker’s least favored steps and reduces the risk of injury. Between the delivery of the blanks and the finishing of the workpiece, additional assembly tasks have to be carried out which are completed more effectively by the worker: The insertion of spring elements and sealing rings, an initial haptic functional test and the attachment of further individual components. They all require situational adaptation, which is one of the essential strengths of humans.

While the worker is mounting the gripper, the robot performs other tasks in parallel, such as part feeding or chamfering of components. © image: SCHUNK
While the worker is mounting the gripper, the robot performs other tasks in parallel, such as part feeding or chamfering of components. © image: SCHUNK

Regular safety checks, training, and acceptance analyses

For ensuring the standard compliant equipment of the workplace risk assessments and space-related safety assessments were carried out. Moreover, the acceptance by the DGUV, and the occupational safety monitoring measures during operation were examined, on whether the biometric limit values were complied with in the event of a collision. In addition, employees deployed at the HRC position receive regular training in handling the robot, and in the effectiveness of the safety measures. In addition, satisfaction is determined in regular survey rounds. It has shown that above all the first contact with the robot has a considerable influence on the acceptance of the employees. The appearance of the robot as well as the subjective feeling of safety are decisive in this respect.

As soon as the employee finishes his or her task, he or she will confirm via a tap that the robot can pick up the component. © image: SCHUNK
As soon as the employee finishes his or her task, he or she will confirm via a tap that the robot can pick up the component. © image: SCHUNK

Conclusions and recommended actions+

The experience gained from this use case has shown: Workers must be able to experience with HRC solutions right from the start that they can master the work processes, determine the processes, and rely on the function of the safety systems. Anyone, who begins with too fast robot movements, or who irritates employees with constant error messages, will suffer an uprising within a very short time. The decisive factor is that the human always sets the pace. He/she must not be driven or limited in any way by the robot. And most importantly: The area of occupational safety and the works council must be included in the considerations right from the start.

In the economic evaluation of HRC projects, SCHUNK considered other factors besides the immediate efforts and costs:

  • Transition to more flexibility in production in the form of multi-machine operation
  • Minimizing the overhead of workpiece feeding and steering, which would generate high costs in full automation of mass production
  • Increased system availability through the possibility of rapid response and courageous safe intervention, as well as by avoiding mini-stops due to terminals or small faults
  • Reduction of quality costs through process optimization
  • Robotic use for process steps that are monotonous, mentally demanding, but essential for the overall quality, such as gluing and automated testing.
  • Increased employee satisfaction and positive health effects for the workers

An additional benefit opens up by a partial automation, as it extends the sphere of activity of a worker or avoids the conversion of entire existing systems. Likewise, if increased process efficiency and quality are achieved by humans by taking over set-up, commissioning, or control tasks.



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