Magnetic multiturn sensors that use the GMR effect (giant magnetoresistance) work without contact, provide absolute position values, do not require a reference run and do not need a power supply or buffer battery to detect the rotations. In many mobile and industrial applications, they are therefore a practical alternative to multi-turn potentiometers or optical encoders.
These versatile sensors are now also used in robotics, for example in robots for military or police units, which are used for bomb threats, for example.


For many applications, multiturn angle sensors based on conventional functional principles are rather unsuitable, e.g. because they require a permanent power supply, work with wear-prone gears or are too complex and therefore too expensive for the area of application. To remedy this, Novotechnik has integrated GMR technology for rotation detection into the RSM-2800 series of multiturn sensors. The non-contact sensors can detect and store 2 to 16 revolutions without an external power supply and buffer battery, and the value can be set. The resolution of the analog interface is 16 bits. Speeds of up to 800 rpm are possible. Using digital interfaces (SSI, SPI), up to 18 bit total resolution (angle and rotation) can be achieved. The sensors are also
extremely accurate. the typical linearity deviations are less than 0.05 % over the entire measuring range. As the sensors are also very robust, they can also be used in a wide range of off-road applications. In the telemax PRO precision manipulator, for example, from Telerob Gesellschaft für Fernhantierungstechnik mbH, they detect the position of the so-called flippers on which the remote-controlled robot moves.


Universal genius with a long range

"Our telemax PRO can certainly be described as a universal genius due to its climbing and obstacle capabilities, the large manipulator reach and reach height and the numerous
tools it has on board," explains Dr. Andreas Ciossek, Product Manager at Telerob. Andreas Ciossek, Product and Innovation Manager at Telerob.
The versatile device is very compact with transport dimensions of 800 mm long, 400 mm wide and 750 mm high. Without the battery, it weighs a maximum of 77 kg and reaches a speed of 10 km/h in the high-speed version.
Depending on the surface, it can handle inclines of up to 45°, climb over 500 mm high obstacles or stairs, overcome 600 mm wide trenches and move loads of up to 20 kg with its 7-axis manipulator. All in all, this makes the telemax PRO an ideal helper when it comes to reaching potentially dangerous objects even in difficult positions in the event of a bomb threat, e.g. in luggage compartments or under airplane seats.

The complex movement sequences, e.g. when opening doors or pieces of luggage, can be conveniently controlled via the Tool Center Point control system, especially as almost all typical movement sequences are pre-programmed. "The tool magazine with automatic tool change is also practical.
The operator does not have to move the robot back if, for example, a different tool is required on site," continues Ciossek. "This saves time, which is very convenient for those affected by an airport or train station closure, for example."


Precise position detection for remote steering

The position of the flipper, i.e. the construction consisting of the wheel drive and tracks, must be precisely recorded so that the telemax PRO can be moved to the place of use in a targeted manner. This task is performed by the magnetic multiturn sensors from Novotechnik, which are installed on each of the four drive axles. A multiturn is not actually required for this application, but the telemax PRO proved to be the right choice. Due to the compact dimensions of the vehicle, the installation space is very limited. The sensors are therefore
not mounted at the rear of the wheel axle as is normally the case, but offset to the side to save installation space. For this purpose, the axle diameter is translated to a significantly smaller gear wheel for the sensor. One revolution of the drive wheel axle thus becomes six revolutions, for example, which the sensor counts for exact position detection.

Selecting the right sensor was not easy for the remote handling technology specialists; a number of alternatives were tested. "In the end, there were many reasons in favor of the RSM-2800," sums up Ciossek. "It is very smooth-running and, with the functions we wanted, it is the smallest and also the cheapest product we found on the market. With
a diameter of just 28 mm, it was easy to integrate." The functional principle also suited the application:

Thanks to the GMR effect, rotational speeds can be stored without current

The multiturn works on a micromagnetic basis and uses the GMR effect (giant magnetoresistance). This is observed in structures that consist of alternating magnetic and non-magnetic thin layers with a thickness of a few nanometers. The effect causes the electrical resistance of the structure to depend on the mutual orientation of the magnetization of the magnetic layers; it is significantly higher with magnetization in opposite directions than with magnetization in the same direction. This difference can be used to detect and simultaneously store rotations using a specially designed sensor element with several resistor segments, even in a de-energized state. The position value is output as an SSI signal, for example. Variants with a digital SPI or analog interface are available.

The RSM-2800 is also very robust and therefore ideally suited for use with the telemax PRO. It meets the requirements of protection class IP67 as standard, i.e. it is dustproof and protected against temporary submersion. There are therefore no problems when the manipulator is working outdoors in the rain or driving through a puddle. Shocks and vibrations do not impair its function either. The sensor housing is made of high-quality, temperature-resistant plastic.
Mounting brackets with slotted holes allow easy mounting and convenient mechanical adjustment. The backlash-free plug-in coupling allows quick and easy installation. The sensor is insensitive to dirt and moisture. The electrical connection is made via a shielded cable that is molded into the housing. Pre-assembled connection plugs, e.g. M12, are also available for true plug-and-play.

These features open up a wide range of applications for the RSM-2800. The compact multiturn solution can eliminate the need for complex gearbox solutions in many places, thus helping to reduce overall costs. Areas of application include printing machines, drive and steering systems, as rope length encoders, for door and gate drives, in mobile machinery, paper machines, lifting platforms or generally as a replacement for multi-turn potentiometers or encoders