Siemens SINUMERIK 840D Function Manual page 787

Effects on the gear stage change
Gear stage change in the part program
The actual gear stage signaled from the PLC is read by the NC when starting a part program.
If, at this instant in time, a value of "0" is read for the actual gear stage, then the next gear stage
change is executed and the gear stage change dialog is performed by the PLC. If a value
greater than "0" is read, then already in the program a comparison is made between the
requested and active gear stage. If both gear stages are the same, the gear stage is not
changed and a possibly programmed path motion is not interrupted.
Gear stage change in synchronized actions, FC18 and DBB30
The actual gear stage signaled from the PLC is always evaluated by the NC when the gear
stage is changed. The gear stage is always changed if a value of "0" is read from the NC. When
reading a value greater than "0", a comparison is made between the requested and active gear
stage. The gear stage is only changed with the PLC if the two values are not equal and the NC/
PLC interface signal DB31, ... DBX82.3 (change over gear) is then output.
Boundary conditions
● Output of DB31, ... DBX16.0-2 = 0
When the gear is disengaged, the PLC must enter gear stage 0 in the NC/PLC interface
DB31, ... DBX16.0-2 (actual gear stage A to C).
● Enabling the gear stage change
The precondition for a gear stage change after reaching gear stage 0 is the general enable
of the gear stage change via via machine data:
MD35010 $MA_GEAR_STEP_CHANGE_ENABLE (assign parameters to the gear stage
change)
MD35090 $MA_NUM_GEAR_STEPS (number of gear stages set up)
MD35092 $MA_NUM_GEAR_STEPS2 (2nd gear stage data set: Number of gear stages
that have been created) if MD35010 $MA_GEAR_STEP_CHANGE_ENABLE, bit 5 = 1
(tapping without compensating chuck)
● PLC user program/ POWER ON ASUB
The PLC user program or POWER ON ASUB should ensure that when the gear is
disengaged (gear stage 0) before spindle motion, a gear stage change request is
programmed. For instance, this can be realized with M41 in the ASUB. Spindle motion such
as e.g. in JOG or in axis operation does not generate any gear stage change itself.
Example
Example for the sequence to select the first gear stage after POWER ON
1. POWER ON.
2. The PLC user program determines, in the mechanical environment, the "Gear is
disengaged" state.
3. The PLC transfers the "Gear is disengaged" state to the NC by setting:
DB31, ... DBX16.0-2 = 0
4. Part program start or POWER ON ASUB.
Axes and spindles
Function Manual, 06/2019, A5E47437747B AA
S1: Spindles
18.4 Configurable gear adaptations
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