Nowadays, robots produce car bodies almost without human intervention. However, a lot of manual work is still required to assemble the interior. There are several hurdles to overcome for the assembly of plastic parts with robots: special sensor technology, complex programming and safety at work in human-robot collaboration. EDAG PS does a lot of research in this direction in order to be able to use tactile robots in assembly.
Author: Daniel Roth
A glance at the assembly of modern vehicles shows that more than 80% of the work is still carried out by workers on the assembly line. The ability to quickly test and see whether assembled parts are properly and firmly seated is what characterizes human manpower. But tactile and sensitive robots such as an LBR iiwa from KUKA extend the possibilities significantly. He is able to determine whether a part placed by him fits correctly.
Particularly challenging and an important part of research in this area is the topic of security. These robots operate in the immediate environment of humans and are not separated from them by protective grids or barriers. In fact, they work together with human colleagues (Man-Robot-Collaboration, MRK) because they partly provide them with production parts.
Independent research with tactile robots
EDAG PS is researching independently (without customer order) in the field of MRK and tactile robots. In the context of a master thesis on the topic "concept of an MRK plant for pre-assembly" Sebastian Häring explains how the assembly of a panel in the center console of a vehicle can be planned with a tactile robot and which advantages and disadvantages the different approaches have.
For the human-robot collaboration, there are four different types of cooperation between worker and machine:
The four types of human-robot collaboration. The Master's thesis examined cases 4 and 1. (Quelle, in Anlehnung:
Source (based in): Dietz, Thomas; Oberer-Treitz, Susanne; Kroh, Rüdiger (2015): Using human-robot cooperation economically. Würzburg
In the first and third scenario, sensors ensure that humans and robots cannot get too close to each other. In the 2nd situation, the robot is inactive and is moved by humans. In the fourth scenario, humans and robots can touch each other. In order to avoid injuries, the robot should move slowly and, in the event of a conflict, only exercise precisely defined maximum pressures on human tissue - something that the planning process should of course avoid.
The central point of the planning is therefore the safety at work of the employee who is mounting workpieces together with the robot. This increases the complexity of the planning process considerably because it influences the process, the layout of the machines, the robot system and possibly also the product to be manufactured.
Safety at work affects all areas of assembly.
The master thesis examines how an optimal interaction between a human being and a robot can look like when three elements are mounted in a central console. The primary goal is for the robot to insert the elements and use sensors to determine whether they are seated correctly.
The center console (picture above) is equipped with three inserts. The robot or worker must "clip them in" during assembly and check whether they are positioned correctly. The robot (LBR iiwa) has sensors in all its joints to determine the occurring moments and forces.
During the planning process, however, the focus is on the human being. A human being can act much more flexible than a robot. For example, it is easy for him to grasp loose parts and align them correctly. In addition, he can easily and quickly check visually whether the component to be processed is in proper condition. It is also important that humans do not have to wait for the robot or feel rushed by it.
Due to the spatial cooperation, however, the robot must move slowly for safety reasons. This means that in scenarios in which the robot has to mount all three parts, the worker has to wait too long. In this form of collaboration, throughput times are the shortest if the robot only mounts one part and the human being mounts two parts.
The human being (black element with the number "1") prepares part 3 for the robot to mount and installs parts 1 and 2 himself. Two center consoles are mounted at the same time. Man and robot work on different consoles.
Assembly can only be further accelerated if the robot can move faster. As a result, however, humans and robots must maintain a safety distance (case 1 of MRK, see above). For this purpose, however, numerous other safety elements (safety mats, protective fences, light grids) have to be installed which make production more expensive again. This is where the company has to consider and calculate what is more profitable.
With the new possibilities of tactile robotics, EDAG PS provides the knowledge to further develop and automate assembly and joining technology in automotive engineering. The master's thesis has shown where the special challenges in assembly are and what possible solutions look like, which on the one hand make economically sense and on the other hand guarantee the safety and health of the worker.
Would you like to optimise your factory in terms of human-robot collaboration or do you have additional questions about this blog post? Please feel free to contact me: firstname.lastname@example.org.