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The assembly systems with parallel arms from Möve-Metall are equipped with Turck's inductive RI angle sensors to ensure that screws are inserted exactly to specifications

Möve-Metall, a company based in Thuringia, Germany produces assembly devices with parallel arms or other so-called reaction arms. Möve-Metall designs and produces assembly and testing equipment for car parts suppliers. The company developed a parallel arm with position detection for use in assembly processes. This enables the position measuring of the screw and rivet processes and reliably prevents incorrectly assembled parts.

“A screwdriver device is clamped on the parallel arm. The operation is based on the principle of the parallelogram and ensures the precise and repeatable positioning of the screwdriver”, says Michael Zimmermann, technical manager of the company. The position monitoring at the three joints of the parallel arm is provided by Turck inductive angle sensors. A beneficial spin-off of this is the fact that the forces involved with the assembly processes can be measured as well. This eliminates the effect of reaction torques on the user.

The parameters for each screw set are stored in the controller. If the operator wishes to screw in the first screw, he guides the arm to the appropriate position. The controller registers the correct position and releases the power or the compressed air for the screwdriver (first OK). The operator screws in the screw until the controller has registered the required number of screwdriver rotations (second OK) and the required torque has been reached (third OK), which guarantees that the screw is seated correctly. Only when these three OKs have been registered by the controller can the next screw be fitted: If the sequence was programmed beforehand, it is only possible to fit the screw that was stored in the controller as the second screw.

Tolerant sensors

“The position monitoring is relatively new. This offers an additional level of safety for the assembly process and is also easy to implement with the inductive angle sensor. A great benefit of the Turck sensor is its non-contact operation, thus requiring no mechanical connection to the positioning element. The four millimeter tolerance for the offset of the positioning element helps us considerably with the assembly process: we no longer have to fit so precisely and protect the sensor from contact, since slight impacts do not impair measuring”, Zimmermann explains.

Another benefit of the RI angle sensor is its immunity to magnetic fields and metal environments. The majority of other sensors on the market either have a mechanical connection between the rotary encoder and the sensor, or are susceptible to magnetic environments produced by large motors or welding equipment.