Assembly processes of the wire harness in the car body
Mr Kosel is a research coordinator.
The wire harness is the first component to be installed by the car manufacturer in the still ‘naked’ car body. It is delivered in a sack that can weigh up to 100 kg. The workers first have to unfold and roughly lay out the tangle of cables. A car today has more than a thousand cables as well as several hundred racks. The more autonomous the vehicles become in the future, the more cables will be added. This includes cables for sensors that collect data and train the AI and cables that ensure networking with the outside world. Other examples include redundant power supplies for failure protection for steering or braking systems. If you picture the cable harness as a widely ramified nervous system that reaches into every corner of the car body, it becomes increasingly difficult to ensure that the nerves do not become kinked or pinched in the tight installation spaces.
Sub-project 4 represents the transition from the wire harness component to the overall automotive product. This is the moment when the wire harness and the associated management shell are ‘transferred’ to the vehicle and integrated into the overall management shell. This means that all collected information is merged into one complete picture. The contents could also be made available for the further lifecycle and other processes.
Objective of the sub-project:
The analysis of the actual assembly process will serve as a basis for further tasks, namely to make possible optimisations. The challenge here will be to determine the necessary data requirements and parameters for automated assembly and to store them in the management shell. Until now, assembly has always been carried out manually because there are no available automation solutions. Assembling flexible parts with the help of robotics requires super-skilled robots with fine motor skills that can fold the smallest latches in a locking mechanism. The wire harnesses would have to be recognised by the robot, no matter how close together the cables are. Moreover, the position of the cables is always different because of flexibility variations, to name just a few difficulties on the way to automation. Another aspect is that each wire harness is unique. Until now, it has not been worth programming robots for a batch size of 1. The idea for this sub-project is to develop an idea of what robot-assisted assembly could look like in the future.
The management shell is the enabler for automation if semantically described data is available and can be accessed in an automated manner. A great step that would make it possible for robots to lift the wire harness into the car body, lay it out there and connect it would be for machines to receive information such as: how is the body constructed? Where are the openings? What are the interfering contours? Where are the assembly points for clips and plugs?
An important process step in sub-project 4 is the assembly of the wire harness at the OEM and the electronic connection. In addition to this last process step, it is now important to hand over the management shell to the OEM and to include other processes, such as service and recycling processes.
In order to assemble the wire harness in the car body, various robotic work steps are necessary. When all product and process data are aggregated in the management shell, these processes must be carried out automatically by a robot in the future. However, how can the work steps in the assembly process be translated into a data model? The data model of the assembly will not only contain the type designation of machines, but also their properties and further information about the robot as well as the tools or grippers mounted on the robot arm.
Figure 1: Assembly of the wire harness in the vehicle
An automated zero point detection in the vehicle can be used to establish a uniform coordinate system for the assembly. When a new request is sent to the production line, all target coordinates can now be defined via the management shells of the car body and wire harness. The loads and ranges can be calculated.
The tasks are dealt with in greater detail in four work packages:
- WP4.1 Management shell of the relevant assembly components
- WP4.2 Selection of the processes to be automated
- WP4.3 Documentation of the requirements for the process
- WP4.4 Concept for the assembly of the wire harness
WP4.1 Management shell of the relevant assembly components:
It can be assumed that the wire harness will have one management shell, while the car body will have its own. This way, the robot on the assembly line knows the design data and can interpret it and follow up with appropriate actions. An example: How much a wire harness may be pulled before it breaks. The analysis of the environment is another important point, because several robots may have to work in parallel, especially in threading processes. If, for example, wires are laid from the interior to the engine compartment, robots have to thread them. To accomplish this task, they must be coordinated with each other. This requires the corresponding data, such as the speed at which the threading is carried out.
The current work priority includes the provision of process data, analogous to sub-project 3, where we are already a bit further along and know which data is needed for which process step. Tasks such as the semantic description of work instructions and parameters are also part of this process because they ensure that machines or robots can talk to each other.
WP4.2 Selection of the processes to be automated:
The easiest way to illustrate automation is to use an example. A process is sought to replace a task that is currently still mainly carried out manually. Data from this task is derived, stored in the management shell and finetuned for digitalisation, which can eventually lead to automation.
WP4.3 Documentation of the requirements for the process
In work package 4.3, requirements are collected that are necessary for the robot to be able to perform a movement. From this information, the project team derives movement simulations that would be transferred to the robot controller in the form of an Emily file. The goal is for the robot to execute the movement with the help of the file.
WP4.4 Concept for the assembly of the wire harness
In the reality of automated assembly, cameras could be used to detect cables. This would help an assembly robot understand coarse and fine localisation. As a result, it could know that only the wire harness of the boot lid can actually be located in a certain area. In the next step, shape recognition and bar codes could help identify the correct plugs/connectors.
This or something similar is the approach in another independent project, ARENA2036, which deals with the robotic handling of wire harnesses in assembly and production and is scheduled to launch on 1 January 2023. The project is called ‘Robohandling’. There is already an understanding that collaboration makes sense here.