Quality control in the assembly plant

If a business is to succeed, it is important to strive for the right quality. This is done in Smart Fabriker projects with the help of various quality controls. When a product, component or service is to be purchased, it is expected that it will meet certain requirements if it is to compete. A well-functioning quality control should limit productivity as little as possible, while identifying errors as early as possible in the process.

In the assembly plant's production process, the quality of the product is ensured by three different steps: scanning of the hole profile on the base component, control of the mounting process and strength control with shaking rig. To perform the first two steps, a robot (Yumi from ABB) is used in a collaborative application, see image below. The main purpose of the robot in the application is to help the installer during the assembly sequence and the quality control to use it in quality control came as a natural part of the application. The station is also equipped with an event camera that continuously records and stores the last 7 seconds of the assembly process. The camera is triggered in the event of any errors in the process and the film can thus be used for further troubleshooting.

Kvaliteteskontroll Monteringsfabriken
Assembly factory with camera including laser for quality control of geometry (1), cameras in respective robot arm (2) and event camera (3).

The first step, scanning the hole profile on the base component, takes place at the beginning of the manufacturing process. The robot for the base component passes a SICK camera (Trispector 1030) to read its hole profile before mounting begins. The camera scans the profile, measures the distances between the various holes in the component, and then sends an OK signal if the distances are within the predetermined tolerances. In the event that the check does not produce an approved result, the process stops, and the responsible operator is noted about what happened. In this way, one can easily find any faults early in the process and thus avoid what would have become unnecessary quality losses on finished product.

Kontroll Av Basdetalj
3D image of the product's basic component where distance between holes (green arrows) is measured.

Follow-up of the assembly process is the second step in quality control. It is implemented using the robot's integrated vision cameras, see below. After the installer places the springs, the robot ensures that the springs are in place by taking a picture at the position of the springs and thus that the installer has completed the step correctly. It is of great importance that this is checked as it is not possible to see the error later in the process when the springs are compressed inside the product.

Kontroll Av Fjädrar
Check with vision that the springs are mounted.

When the product is to be put together, the robot has another function, to ensure that the screws are pulled in the correct order. In order to achieve a working traceability when collecting measurement data from the screwdrivers (torque and angle), it is important to have the right set of data for the correct screw. This is ensured by having a specific order in which the screws are attached. The robot's task is thus to review the process by positioning itself parallel to the screwdriver and taking a picture. If the screwdriver is not at the correct screw, the screwdriver cannot be started, see image below.

Kontroll Av Skruvdragare
Check that the screws are tightened in the correct order.

The last step for quality control is strength testing with a shaking rig. Unlike the other parts, this step is not directly integrated into the assembly process itself. Torque is carried out on a separate shaking rig and is used to simulate customer use.


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This article is categorised as Intermediate  |  Published 2019-05-26  |  Authored by Johan Bengtsson