Inductive Micro Encoders

DN Staff

July 15, 2009

2 Min Read
Inductive Micro Encoders

Using MEMS technology to miniaturize the design, new inductive micro encodertechnology from Maxon Motoroffers a unique, miniaturized feedback solution. Thefirst implementation of the technology is mounted on the shaft of an EC6brushless DC motor, which extends the length of the motor/encoder combinationby only 1 mm.

"We believe the MILE micro inductive encoder, which is only 6 mm indiameter, is the world's smallest inductive encoder," says Paul McGrath, aregional sales manager for Maxon Motor USA."The inductive encoder technology itself is not new, but it's the firsttime this has been implemented on such a small scale."

The general principle used in inductive encoders is that the inductanceof one or more coils changes in relation to the material in their proximity. Asemi-circular iron core representing the material measure, for example, couldbe directed to a coil which then changes its inductance. But there aredrawbacks to simple inductive encoders, such as the temperature dependence ofthe soft iron/ferrite. External magnetic fields can also change thepermeability of the material used, well below saturation point.

This is why new highly accurate inductive encoders are ironless, and thecontrast is generated with eddy currents. McGrath says inductive encodershave been featured in larger motors for a long time, but have not been producedfor micromotors until now.

Compared to optical, magnetic and magnetive resistive encoder solutions,the new technology offers a series of benefits in specific applications. The new MILE encoder delivers 64 pulses at upto 120,000 rpm and offers three channels including a line driver and integratedcommutation outputs. Typical application areas include medical technology,robotics and harsh environment industrial applications.

McGrath says the new encoder can be compared, in some respects, to aminiature resolver. The design utilizes eddycurrent induced changes to an otherwise balanced, high frequency magnetic fieldto excite the integrated differential coils.And for that reason, it offers some of the traditional advantages of aresolver including robust operation against electromagnetic interference, dust,oil and magnetic fields. An integrated,factory-set look-up table also makes it possible to correct repeatable errorsin real-time by comparing measured raw parameters to values in the look-uptable. The result is an almost perfectlinearity of the sensor.

The first implementation of the MILE encoder technology is supplied mountedon the shaft of a motor, with further implementations to come in the nearfuture.

Using MEMS technology to miniaturize the design, new inductive micro encoder technology from Maxon Motor offers a unique, miniaturized feedback solution.

Inductive Micro Encoders A

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