Handle variance in automated screwdriving

In today's manufacturing environment, automation is essential for improving efficiency and productivity. One area where automation can be particularly beneficial is in screwdriving assembly. Traditional automation systems for screwdriving have been limited by their inability to handle variance in manufacturing workstations. This is because traditional systems require uniform conditions in order to function properly. In the real world, however, variance in the workspace is a regular occurrence.

Tightening processes are common in all manufacturing industries. In essence, the aim of these processes is to realize a secure connection between two or more parts by means of a screw or multiple screws. While this may seem straightforward, automating a tightening process is exceedingly difficult. This is due to several types of variance that arise in production workstations that involve screwdriving:

• Variance in the position of parts in the workstation. This makes the precise location of screw holes unpredictable. Position variance is particularly troublesome when parts cannot be fixed in a workpiece carrier. Even when parts are placed in a workpiece carrier, they can still vary in their position by up to a few millimeters.
• Variance in the part itself, a result of production tolerance, which can make the screw-hole location on a workpiece uncertain.
• Variance of the angle at which to insert a screw, owing to an unpredictable location of a screw hole or to unaligned screw holes when there are two or more parts that must be connected.

Getting around this complexity is nearly insurmountable for traditional automation systems, which require uniform conditions. As a result, many tightening tasks must be done with human hands. The same applies to nuts, studs, and flow-form screws.

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‍Partnership with DEPRAG to handle variance in automated screwdriving

We have partnered with DEPRAG — a specialist for screwdriving systems as well as specialized machines, robot cells, and assembly lines — to develop an automated screwdriving solution that can overcome these challenges. The solution combines DEPRAG's screwdriving technology with our AI-powered MIRAI vision system, which enables robots to perceive their workspace and correct their movement where needed. This makes MIRAI ideal for handling the variance that is inherent in screwdriving assembly.

Our joint automated screwdriving solution is suitable for different manufacturing applications, including the assembly of white goods, electronics, automotive parts, and agricultural machinery. The solution can be set up and ready for deployment in less than one working day.

Test case

Together with DEPRAG, we conducted and documented a test case. The aim was to drive four screws into an electronic module, joining a top piece with a base piece. Both MIRAI and DEPRAG’s screwdriving technology were attached to a Universal Robots UR16e. The task consists of four sections:

1. The robot positions the screw (fed to the screwdriver by the DEPRAG feeding system) 50-60 mm from the screw hole on the module. At this position, the robot’s native controller will hand over control to the MIRAI system.
2. The MIRAI system assumes control of the robot, positioning the screw tip 2 mm above the threaded hole.
3. The DEPRAG system assumes control. It inserts and secures the screw.
4. Under the guidance of its native controller, the robot pulls back and approaches the next hole in the electronic module (step 1). As it does, the screwdriver is fed a screw.

With this setup, the system is able to handle variance in the position of the electronic modular in the workstation as well as variance in the angle at which to insert the screws into the holes.

This automated screwdriving solution — or a modified version of it — is applicable to the assembly of white goods, electronics, automotive parts, agricultural machinery, and more. It can be set up and ready for deployment in less than one working day.