Monolithic sensor base body with 3D milling technology

A monolithic base body, the monolith, is milled from a block of high-strength aerospace aluminum and then measured. This monolith, with joints thinner than a hair, is the core of the load cell and is decisive for the measuring performance. On the way to this stage of development, simple monolithic systems were manufactured in a first step. Next, the team in Aachen succeeded in developing a monolith with a multi-transmission lever system and having it manufactured by a local supplier. All levers - three in number - are milled from a single block of material and there are no screw connections along this force transmission path that could cause measurement errors, such as drifting of the measured value. The three transmission stages allow high preloads. When a product is loaded, the product weight is compensated with a very small electromagnetic force, whereby the low current flow reduces the heating of the measuring system to a minimum. This makes it possible to realize 10,000 calibratable steps across all measuring ranges. This successful prototype development also included other technology components such as a magnet system, coil and position detector.

Completion of a sensor with additional technology components in Košice

The success of the development contributed to the decision to purchase a 5-axis milling machine and set up mechanical production with pre-assembly of this EMFR sensor at the state-of-the-art production site in Košice, which is managed centrally by Minebea Intec Aachen. After assembly of the add-on parts such as the magnet system, coil and position detector, the pre-assembled sensor is subjected to extensive testing.

Final assembly of the load cell and testing in Aachen

At the Aachen plant, the pre-assembled sensors are completed with electronics, a housing and other add-on parts. The now complete load cells are tested in a climate chamber over their entire temperature range. Not only the zero point of the load cell is measured. The climate chamber also contains weights that are automatically applied at different temperatures. The data obtained is converted into correction parameters and stored in the load cell's electronics. The now temperature-compensated load cell is then checked again against the metrological data.

Load cell for maximum throughputs of up to 600 items per minute

The special electronics were developed especially for fast, dynamic weighing. Parts of the measurement algorithms are carried out digitally. In contrast to analog load cells, the EMFR load cell delivers finished weight values on the digital interface at a very high data rate of up to 2,000 measured values per second for high-performance applications with extremely short measuring times. With such a high sampling rate, these load cells operate virtually in real time.

The load cells can be extended to include a conveyor belt for product transport, called, the weighing belt. It has special requirements in terms of accuracy in order to reliably enable the dynamic measurement of products. The weighing belts are developed and built at the Minebea Intec site in Aachen. The combination of load cell and weighing belt, also known as a weighing kit, is a proven combination when it comes to dynamic weighing with product transport.

The EMFR load cells from Minebea Intec are now also available for OEM applications for direct machine integration. This allows customers to benefit from the full expertise of the development center in Aachen.

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