Siemens SINUMERIK 840C Installation Instructions Manual page 852

10.94
•
Setting up without a reference point
Where there is no reference cam, e.g. for reasons of cost.
NC MD 1808* bit 0 = 1 is set, i.e. a SIPOS absolute encoder is installed.
The machine is traversed manually in "JOG" or "incremental" mode to the customer's
chosen reference point.
Calculating the absolute encoder offset:
Machine system = SIPOS absolute encoder value + absolute offset
Absolute offset = machine system - SIPOS absolute encoder value
Where the following is valid:
• Machine system = desired absolute position = reference point value
• SIPOS absolute encoder value = displayed absolute position (actual value)
The calculated absolute offset must be entered in MD 396* and declared valid through setting
of MD 1808*, bit 3. After the next control power-up, the displayed actual position is
synchronized with the machine system and the status signal "Reference point reached" is set.
Notes:
• If NC MD 396* has a value other than 0, this value must be taken into account because it
is contained in the SIPOS absolute encoder system (= displayed actual value).
Suggestion: Set NC MD 396* before synchronization.
• When the SIPOS absolute encoder is set up with reference point approach an overrun
control is carried out automatically. An overrun results because the absolute encoder is
15
absolute to ±2 revolutions and it cannot be ruled out that on setup an overrun of 0 to
2 15 revolutions from the zero position will occur.
• When setting up without a reference point the customer must carry out the overrun
control. All absolute values used must then have the format ± 99999999 input units.
• If a value larger or smaller than ± 99999999 input units results from the calculation of
the absolute offset by the machine system - SIPOS absolute encoder value, it must be
corrected as follows:
Absolute offset > 99999999:
Absolute offset <-99999999:
:
Example
a) Calculated absolute offset = 130000000
correction: absolute offset = 130000000 - 199999999 = - 69999999
b) Calculated absolute offset = - 130000000
correction: absolute offset = - 130000000 + 199999999 = +69999999
© Siemens AG 1992 All Rights Reserved
SINUMERIK 840C (IA)
12.11.1 SIPOS absolute encoder up to SW 4
Absolute offset - 199999999
Absolute offset +199999999
6FC5197- AA50
12 Functional Descriptions
12–77