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Magnetic rotary sensors in machine engineering

Magnetic processes are frequently used among the measuring technologies for non-contacting rotary sensing. Novotechnik provides CANopen sensors for a paper filling system.

For non-contacting rotary sensing, a magnet is attached to the rotating shaft; the orientation of the magnetic field and thus the voltage signal of the sensor component, are changing with the rotation angle (Photo: Novotechnik)

In magnetic sensors relying on the Hall effect, a current flows through a Hall component. When a magnetic field is applied perpendicular to this, the Hall component yields a voltage that runs transversely in relation to the current. Since this voltage is proportionally related to the strength of the magnetic field, it allows for touchless rotary sensing with setups: All that is required is the attachment of a magnet onto a rotating shaft (Photo 1).

By combining several sensor elements and implementing the entire signal processing with a few components, it becomes possible to integrate complex systems into tiny spaces. Both non-contacting systems with shafts and systems without mechanical shaft couplings allow for measurements up to 360° and through several revolutions.

Novotechnik provides CANopen sensors of the RFC-4800 (Photo 2) series. Packaging specialist Papier Sprick, for instance, is using these sensors in his Speedman MAX (Photo 3) paper filling system. This system, for which a patent is pending, is advancing paper at speeds of up to 3,3 meters per second, yielding approx. three cubic meters of filling volume per minute. The machine is being „fed“ with recycled paper from the very same manufacturer. It is available in space-saving fold-out feeds of 360 or 2 200 running meters and has been awarded the “Blue Angel” label for environmentally friendly products. The paper filling system is suited for centralized packaging stations or as an end-of-line solution.

The RFC-4800 CANopen sensors (Photo: Novotechnik)

With the sensors’ different mechanisms and connectors, they can be integrated into a range of applications. They come with a variety of electrical interfaces: from CANopen, and various single- and multiple-channel designs with analog interfaces to SPI, SSI, and Incremental, up to IO-Link. The CANopen version is available in a one-channel or multichannel design, with one or two connectors. This allows for a stub connection or the loop-through of the network. The sensor uses the CiA 406 V 3.2 device profile and communicates according to CiA 301 V 4.2.0; LSS services to CiA 305 V 1.1.2. Programmable parameters are position, speed, cams, working areas, rotating direction, scale, offset, node-ID, and bit-rate (50 kbit/s to 1 Mbit/s).

There are also different contacting options available: The selection includes models with cable outlets, as well as 5-pin M12 connectors, and the AMP or Deutsch connectors favored for mobile applications. In the near future, the CAN protocol J1939 for utility vehicles will be supported as well.

Integration into the machine

Controlling the feeding speed and measuring the feed distance are essential for a smooth paper feed. These tasks had previously been accomplished with the aid of a cam switch attached to the rotating shaft, in combination with two proximity switches. While this setup worked well, it did have one distinct disadvantage. The installation process was too complex: The cam switch and the two proximity switches each had to be attached and aligned. Additionally, both sensors had to be wired. The magnetic rotary sensor, on the other hand, is much easier to install, and it almost seamlessly replaced the original solution, because the design chosen for this application yields an incremental HTL measuring signal.

The Speedman MAX is geared in particular towards consignors with high filling volumes or high numbers of units (Photo: Sprick)

The installation is closely related to the operating principle: For rotary sensing, a positioning magnet is attached to the rotating shaft, in close proximity to the drive. The orientation of the magnetic field, and thus the signals of the 15-mm flat sensor, are changing with the rotation angle. The integrated sensor circuit then converts this signal change into a signal output that is proportional to the rotation angle and provides it to the control unit. The fact that sensor and positioning magnet are physically separate components simplifies the installation process, as the sensor can be installed with an air gap of up to 1,4 mm in relation to the position marker. A marking identifies the correct orientation in relation to the sensor. The sensor housing is made of temperature-resistant plastic. The sensor is encapsulated and thus insensitive to contamination. The cables or single wires for the electrical connections are molded into the housing. Since the setup includes neither shaft nor bearing, and the measuring distance is variable, application-specific installation tolerances are not an issue.

In addition to industrial applications, they are also suited for mobile applications. After all, they can tolerate oscillations and vibrations of up to 20 g (in compliance with IEC 600658-2-6) as well as impacts of up to 50 g (6 ms, in compliance with IEC 68068-2-27), and they comply with the required EMC specifications. The allowable ambient temperature range is between -40 °C and +125 °C, and covers the protection requirements of IP67 and/or IP6K9K. The sensors provide measurements at a resolution of up to 14 bit. The (independent) linearity is around +/- 0,3 % and the repeatability at 0,1°. In addition to machine engineering and plant design, there are application fields found in floor conveyors, in construction, agricultural and forestry machinery, medical technology, as well as in wave power plants.


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