03.95 12 Functional Descriptions
12.7.2 Description of the spindle modes
Gear ratio changing
Gear ratio changing is only possible in the open-loop control mode. There can be up to eight
different ratios between motor and spindle.
A permitted range of speed can be laid down for each gear ratio by defining maximum and
minimum speed values. If the speed setpoint does not fall within the range of the gear ratio
that is currently active, the number of the required gear ratio is ascertained automatically and
entered into the interface to the PLC together with IS:CHANGE GEAR.
The PLC user program executes the gear change, acknowledges the request by resetting IS:
CHANGE GEAR and enters the new gear ratio into the interface.
If no suitable gear ratio for the programmed speed exists, no request for gear changing is
generated. The programmed speed is then transferred to the current gear ratio. So it is
important to ensure that there is always a suitable gear ratio available.
The behaviour of the spindle during gear ratio changing can be influenced by MD 521*, bit 5
"New S value after PLC acknowledgement". If the bit is set, the programmed speed setpoint
will only be accepted when the PLC has acknowledged gear ratio changing. This prevents an
unwanted increase in speed while still in the old ratio before changeover.
Data required
This section describes the data that is of particular significance to the open-loop control mode.
•Limiting the speed
Parameters for maximum and minimum speed limits can be assigned for each gear ratio.
Parameter assignment is effected through the machine data:
– MD 403* to 410* ”Max. speed” per gear ratio
– MD 411* to 418* ”Min. speed” per gear ratio
If a gear stage is not used, the value zero must be entered for the maximum speed of this
gear stage and not the value in the standard machine data.
Regardless of which gear ratio is active, the speed is limited by:
– MD 451* ”Max. chuck speed”
– MD 448* ”Min. motor speed”
– SD 401* ”Programmable spindle speed limit for G96”; programmed with
G92
– SD 403* ”Programmable spindle speed limit”; programmed with G26
•Limiting the acceleration
In order to avoid excessive acceleration when changing speeds, the setpoint is ramped up
or down accordingly by means of a ramp-function generator. The maximum value of
acceleration to be used is assigned by means of an acceleration time constant. A
separate acceleration time constant must be specified for each gear ratio employed:
– MD 419* to 426* ”Acceleration time constant without position control”
© Siemens AG 1992 All Rights Reserved 6FC5197- AA50 12–37
SINUMERIK 840C (IA)