BECKHOFF EL7037 - Manual (Page 150)

Commissioning
Fig. 173: Effect of the modulo tolerance window - modulo target position 0° in positive direction
Example:
An axis is positioned to 0°, with the result that subsequently the actual position of the axis is exactly 0°. A
further modulo travel command to 360° in positive direction results in a full turn, with the subsequent modulo
position of the axis of once again being exactly 0°. If the axis comes to a stop somewhat in front of or behind
the target position for mechanical reasons, the next travel command does not behave as one would expect.
If the actual position lies slightly below 0° (see fig. 9, below left), a new travel command to 0° in the positive
direction leads only to a minimal movement. The deviation that arose beforehand is compensated and the
position is subsequently exactly 0° once more. If the position lies slightly above 0°, however, the same travel
command leads to a full revolution in order to reach the exact position of 0° again. This problem occurs if
complete turns by 360° or multiples of 360° were initiated. For positioning to an angle that is significantly
different from the current modulo position, the travel command is unambiguous.
In order to solve the problem, a “Modulo tolerance window” (Index 8020:0F [ } 183]) can be parameterised.
This ensures that small deviations from the position that are within the window do not lead to different axis
behaviour. If, for example, a window of 1° is parameterised, in the case described above the axis will behave
identically, as long the actual position is between 359° and 1°. If the position exceeds 0° by less than 1°, the
axis is re-positioned in positive direction at a modulo start. In both cases, a target position of 0° therefore
leads to minimum movement to exactly 0°. A target position of 360° leads to a full turn in both cases.
For values that are within the window range, the modulo tolerance window can therefore lead to movements
against the specified direction. For small windows this is usually not a problem, because system deviations
between set and actual position are compensated in both directions. This means that the tolerance window
may also be used for axes that may only be moved in one direction due to their construction.
EL70x7 150 Version 1.0