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IP 240 Positioning

10.6.2 Backlash Compensation during Reference Point Approach

Compensation of the backlash during reference point approach ( Section 10.13.1) is similar to

compensation during positioning.

Synchronization is attained only when the reference point is approached in a positive direction.

Decisive for evaluation of the direction is the instant at which the preliminary contact signal

(connected to the IP's IN input) changes back to zero.

Since the position is normally not known following power-up, the approach to the reference

point is normally begun after traversing to a starting point. The actual value of the starting point

must therefore be less than the negative edge of the preliminary contact signal.

The direction of travel for reference point approach must always be specified by the S5 CPU.

Note

In order to ensure that synchronization is always done at the same place, the

direction of travel for the reference point approach may not be changed

following the negative edge at the IN input until the zero mark has been reached

(synchronization).

10.7 Actual Value Generation

The IP 240 computes an internal signed count by counting the encoder pulses and evaluating the

phase displacement between encoder pulse trains A and B. You can influence the conversion of

this count into the actual value by

• configuring the required resolution and

• specifying a zero offset.

The actual value stored on the IP 240 is updated in every module firmware cycle, and can be read

out over the S5 CPU.

Counting direction

The IP 240 counts the acquired encoder pulses

• up when the B signal is the leading signal.

• down when the A signal is the leading signal.

Fig. 10-16. Counting Direction in Positioning Mode

A signal

B signal

”Up” counting ”Down” counting

Changing the counting direction

To change the counting direction, you must interchange the following:

• for symmetrical encoders, interchange A/A and B/B

• for asymmetrical encoders, interchange A* and B*

EWA 4NEB 811 6120-02a

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Siemens IP-Module Especificaciones Pagina 189