By Henrik Schunk
A case study in human-robot collaboration (HRC) at SCHUNK reveals the steps required to have manufacturers and machines work in harmony
By Henrik Schunk
August 8, 2019 – In the production of modern gripping systems, a large number of product variants are manufactured and provided in different batch sizes.
So far, the grippers have been assembled manually on conventional assembly workstations. One-sided physical strain, the danger of injuries – for example, during deburring – and comparatively high costs for purely manual activity are associated with manual assembly.
The goal of one human-robot collaboration (HRC) project at the SCHUNK Smart Factory in Lauffen, Germany 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 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, which manufactures gripping systems and clamping technology.
Careful workplace analysis
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 that 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 was 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 who have a high degree of technical affinity and curiosity were selected and included at an early stage.
Division of labour
One of the use cases is the preassembly of gripping tools: In the application, a seven-axis lightweight KUKA LBR iiwa 7 R800 robot – on whose DIN ISO 9409-1-A-50 flange, a modified SCHUNK Co-act EGP gripper with integrated blackand-white industrial camera was integrated – removes various base housings from a universally usable transport container and takes them to the worker.
The exact position of the basic housing is optically detected by the integrated camera and transferred to the robot in the form of correction signals. The workpiece handle is formfitting from the inside. The gripping force of the gripper with a 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 the air connections on the gripper and the stripping of screw glue. In a second implementation phase, these steps were also automated. This eliminated the workers’ least favoured steps and the risk of injury was reduced. Between the delivery of the blanks and the finishing of the workpiece, additional assembly tasks have to be carried out that 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.
Regular checks and analyses
Risk assessments and space-related safety assessments were carried out for the standard-compliant equipping of the workplace. In addition, at the time of acceptance by the DGUV [German Social Accident Insurance, a national association of professional organizations and insurance companies] and during occupational safety monitoring measures, workers checked 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 been 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.
Recommendations for action
The experience gained from this use case shows that with HRC solutions, workers must be able to experience 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 robot movements that are too fast or that irritate 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 by the robot. And most importantly: The area of occupational safety and the works council must be included in the project considerations right from the start.
In the economic evaluation of HRC projects, SCHUNK considered other factors besides the immediate expenses and costs:
- Flexibility of production in the form of multi-machine operation
- Minimizing the overhead of workpiece feed 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
Partial automation provides an additional benefit, as it extends the sphere of activity of a worker or avoids the conversion of entire existing systems. Likewise, if humans take over set-up, commissioning or control tasks, it achieves increased process efficiency and process quality.
Henrik Schunk is the CEO of SCHUNK.
This article originally appeared in the Summer 2019 edition of Robotics Insider, Manufacturing AUTOMATION’s quarterly e-book focused on robotics.