In the case of encoders with increment-coded reference marks, multiple reference marks are distributed evenly across the entire travel distance. The absolute position information, relative to a specific zero point of the measurement system, is determined by counting the individual measuring increments between two reference marks. The absolute position of the scale defined by the reference mark is assigned to precisely one measuring increment. Before an absolute reference can be created or the last selected reference point found, the reference mark must be passed over. In the worst-case scenario this requires a rotation of up to 360°. To determine the reference position over the shortest possible distance, encoders with increment-coded reference marks are supported (e.g. HEIDENHAIN ROD 280C).
The reference mark track contains multiple reference marks with defined increment differences. The tracking electronics determines the absolute reference when two adjacent reference marks are passed over after just a few degrees of rotation.
Rotary system
| Number of pulses P 0572 | Number of reference marks | Basic increment G Nominal Increment A P 0630 | Basic increment G Nominal increment B P 0631 |
|---|---|---|---|
| 18 x 1000 lines | 18 basic marks + 18 coded marks = Σ 36 | Reference measure A = 1000 lines corresponding to 20° | Reference measure B 1001 lines |
Tabelle: Example of a rotary system
Bild: Schematic view of circular graduations with increment-coded reference marks
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Increment-coded reference measure B, large increment (1001 lines): P 0631 ENC_CH3_NominalIncrementB |
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Increment-coded reference measure A, small increment (1000 lines): P 0630 ENC_CH3_NominalIncrementA |
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Zero point: The pulses per revolution are entered in parameter P 0572 ENC_CH3_Lines (e.g. 18x1000). A sector increment difference of +1 and +2 is supported. One mechanical revolution is precisely one whole multiple of the basic increment A. |
Tabelle: Reference marks
Linear system
Bild: Schematic for a linear scale
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Pitch periods (TP): (P 0572 ENC_CH3_Number of lines) |
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Reference marks |
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Increment-coded reference measure A (small reference mark interval) (P 0630 ENC_CH3 Nominalincrement A) |
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Increment-coded reference measure B (large reference mark interval) (P 0631 ENC_CH3 Nominalincrement B) |
Tabelle: Reference marks, linear system
Homing method for increment-coded encoders:
Method -6: Increment-coded encoders with negative direction of rotation
Method -7: Increment-coded encoders with positive direction of rotation
Copyright © LTi DRiVES GmbH, Januar 2013, ID-Nr.: 0842.26B.1-00 DE