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 position signal, suitable for positioning without a 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, IMR, GAMA, TSX (magnetic encoders) − Enc, HEDS, HEDL, RIO (optical encoders) − DC-Tacho, Resolver (analog sensors) − EMT (magnetic absolute encoder)
1 End cap 2 Electrical connections motor and encoder 3 PCB 4 MR sensor 5 Magnetic multi-pole wheel 6 Encoder housing 7 Graduated disk 8 Encoder fork coupler 9 Flange 10 Solid measure 11 Sensor with housing
Take a look at the ENX 22 EMT encoder.
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 electron- ics may limit the maximum possible counts per turn of the encoder. − The higher the counts per turn and the accuracy, the easier it is to achieve a smooth, jolt-free operation even at low speeds. − The maxon controllers can be configured for encoders with low (at least 16 cpt) or high counts per turn. For positioning systems, the following applies: − The higher the counts per turn, the more accurate the positioning. At 500 counts (2000 statuses), a mechanical angle resolu- tion of 0.18° is achieved. This is usually much higher than the precision of the mechanical drive components. − 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 position as a bit sequence which is transmitted at the clock rate of the controller with a suitable pro- tocol (SSI, BiSS-C). The resolution is 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 un- ambiguously over several revolutions. They are able to detect motor revolutions even without a power supply. At start-up, the motor position over multiple revolutions is thus known.
Recommendations on encoder selection ( ✓ ) Conditionally applicable *OPT, ENC, HEDL, HEDS 1 very high speed ✓ ✓ ✓ ✓ ( ✓ ) ✓ 2 very low speed ( ✓ ) ( ✓ ) ✓ ✓ ✓ 3 precise position ( ✓ ) ( ✓ ) ( ✓ ) ✓ ✓ 4 line driver possible ✓ ✓ ✓ ✓ ✓ 5 index channel possible ✓ ✓ ✓ ✓ 6 compact design ✓ ( ✓ ) ✓ ✓ ✓ ✓ 7 dust, dirt, oil ✓ ✓ ✓ ✓ ✓ ( ✓ ) 8 external magnetic fields ( ✓ ) ( ✓ ) ( ✓ ) ✓ ✓ ✓ 9 ionising radiation ✓
Representation of the output signal of a digital encoder 90° e Phase shift A,B 360° e Cycle
Channel A
Channel B
Channel I
Index puls width Phase shift of index pulse
CW
76 Technology – short and to the point
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