maxon sensor Technology − short and to the point
Encoder maxon offers a range of different encoders. Their main characteristics are: Digital incremental encoders − Relative position signal, suitable for positioning tasks − Direction of rotation detection − Speed information from number of pulses per unit of time − Standard solution for many applications Digital absolute encoders − Absolute single-turn position signal, suitable for absolute positioning within one motor revolution − Solution for special applications without homing procedure − Option to generate commutation signals DC tacho − Analog speed signal − Direction of rotation detection − Not suited for positioning tasks Resolver − Analog signal transmission − More complex evaluation electronics required in controller − For special industrial solutions Encoder signals Digital incremental encoders Position changes (relative position) are trans- mitted to the controller as square pulses. The controller evaluates these pulses for precise positioning or speed measurement. The signal transmission is implemented via two phase- shifted channels (A and B) that are compared to determine the direction of rotation. Usually the phasing of channels A and B applies for operation in a clockwise direction (CW), relative to the motor shaft seen from the outside. The maxon controllers evaluate the signal edges. This results in a four times higher positioning resolution relative to the counts per turn of the encoder. The technical term for this is quad counts or states. The absolute position can be determined by homing to a fixed posi- tion. The signal edges of index channel I can be used for a precise reference position.
Program − MILE (inductive encoders) − EASY, MAG, MR, MEnc (magnetic encoders) − Enc, HEDS, HEDL, AEDL, RIO (optical encoders) − DC-Tacho, Res (analog sensors)
1 End cap 2 Electrical connections motor and encoder 3 PCB 4 MR sensor 5 Graduated disk 6 Magnetic multi-pole wheel 7 Encoder housing 8 Solid measure 9 Flange
10 Sensor with housing 11 Encoder fork coupler
Key points for encoder selection These are the main characteristics of maxon incremental encoders: − Counts per turn (increments) − Accuracy − Use of an index channel − Use of a line driver − Maximum supported speed − Suitability for special ambient conditions (dust, oil, magnetic fields, ionizing radiation) Encoders and maxon controllers − The input frequency of the control electronics may limit the maximum possible counts per turn of the encoder. − The higher the counts per turn and the ac- curacy, the easier it is to achieve a smooth, jolt-free operation even at low speeds. − maxon controllers can be adjusted for ope- ration at low or high speeds, as well as for encoders with low or high counts per turn. For positioning systems, the following applies: − The higher the counts per turn, the more ac- curate the positioning. For 500 counts (2000 quad counts), a mechanical angle resolution of 0.18° is achieved. This is usually much higher than the precision of the mechanical drive components (e.g. due to gear backlash or the elasticity of drive belts). − In positioning controllers, only encoders with an integrated line driver should be used (e.g. RS422). This prevents signal loss and accumulated positioning errors due to elec- tromagnetic interference. − Positioning applications often required the encoder's index channel for precise determi- nation of a reference point.
The line driver is a driver built into the encoder to improve the signal quality through steeper edges. Additionally, it generates the comple- mentary signals A, B, and I. Differential signals make it possible to eliminate faults during transmission. Absolute encoders Absolute encoders return the absolute posi- tion as a bit sequence for transmission with a suitable protocol (SSI, BiSS-C) at the clock rate of the controller. The resolution given as a bit length; e.g. 12-bit equals 4096 positions. Single-turn absolute encoders output the posi- tion only within one motor revolution. Multi-turn absolute encoders determine the position unambiguously over several revolutions. They frequently have the capability to detect motor revolutions even without a power supply. At start-up, the motor position is determined over multiple revolutions.
Recommendations on encoder selection ( ✓ ) Conditionally applicable
Representation of the output signal of a digital encoder 90° e Phase shift A,B 360° e Cycle
*OPT, ENC, AEDL, HEDL, HEDS 1 very high speed 2 very low speed 3 precise position 4 line driver possible 5 index channel possible
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6 compact design 7 dust, dirt, oil
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Index puls width Phase shift of index pulse
8 external magnetic fields ( ✓ ) ( ✓ )
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9 ionising radiation
Technology – short and to the point
September 2020 edition / subject to change
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