maxon sensor - maxon motor - #1

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32 maxon sensor Technology – short and to the point May 2010 edition / subject to change 90° e Phase shift A,B 360° e CycleIndex puls widthPhase shift of index pulseChannel AChannel BChannel I Representation of the output signal of a digital encoder N SNS Schematic design of a magnetic encoder B IA Schematic design of an opto-electronic encoder maxon sensor Technology – short and to the point Sensors maxon offers a series of sensors. Their characteristics are: Digital incremental encoder – Relative position signal suitable for positioning tasks – Rotation direction recognition – Speed information from number of pulses per time unit – Standard solution for many applications DC tachometer – Analog speed signal – Rotation direction recognition – Not suitable for positioning tasks Resolver – Analog rotor position signal – Analog speed signal – Extensive evaluation electronics required in the control system – For special solutions in conjunction with sinusoidal commutation in EC motors Digital Incremental Encoder Encoder signals The encoders provide a simple square signal for further processing in the control system. Its impulses can be counted for exact positioning or determining speed. Channels A and B pick up phase shifted signals, which are compared with one another to determine the rotation direction. A “home” pulse (index channel I) can be used as a reference point for precise determination of rotation angle. The line driver produces complementary signals A–, B–, I- which help to eliminate interference on long signal lines. In addition, this electronic driver installed in the encoder improves signal quality by steeper signal edges. Magneto-resistant (MR) principle In an MR-encoder, the multipole magnetic disc mounted on the motor shaft produces a sinusoidal voltage in the MR sensor. The typical encoder signals are created by interpolation and electronic signal refinement. Characteristics – Needs very little space – No protruding parts – High number of pulses by interpolation – Different number of pulses can be selected – Index channel possible – Line driver possible Magnetic principle with Hall sensors On the magnetic MEnc-Encoder a small multipole permanent magnet sits on the motor shaft. The changes in magnetic flux are read by Hall sensors and fed into the electronics as channel A and B. Characteristics – Small design – 2 channels A and B – No line driver possible – Low number of pulses Optical principle The opto-electronic principle (example: HEDL HEDS, Enc22) sends an LED light through a finely screened code wheel that is rigidly mounted onto the motor shaft. The receiver (photo transistor) changes light/dark signals into corresponding electrical impulses that are amplified and processed in the electronics. Characteristics – Needs large space with protruding part – High number of pulses – Index channel possible – Line driver possible – High accuracy Inductive eddy current principle In the inductive MILE encoder, a high-frequency magnetic field is brought onto a structured copper disc and the angle-dependent field displacement measured. Characteristics – Very robust against magnetic and electrical fields as well as contamination – Very high speeds possible – High precision. Interpolation errors are largely compensated for by a look-up table – Index channel and line driver available – Absolute interface (SSI) on request 1 End cap 2 Electrical connections motor and encoder 3 Print 4 MR sensor 5 ASIC 6 Magnetic multi-pole wheel 7 Encoder housing 8 Motor connections 9 Motor = Solid measure + Carrier of solid measure Program – Digital MILE encoder – Digital MR encoder – Digital Hall effect encoder – Digital optical encoder – DC Tacho – Resolver