Siemens SINUMERIK 840C - Manual (Page 815)

12 Functional Descriptions 06.93
12.7.2 Description of the spindle modes
When there is a request from the NC or PLC, the corresponding machine data of the
active gear ratio is used, which is:
– MD 427* to 434* ”Creep speed for M19” as max. speed during positioning
– MD 478* to 485* ”Acceleration time constant with position control” for
limiting the acceleration rate during acceleration and
deceleration
– MD 435* to 442* ”Gain factor” for the position controller
– MD 443* ”Position tolerance” for establishing the position window
(regardless of the active gear ratio)
If the gain factor is required to be changed in the positioning mode, the following will also
be needed:
– MD 469* ”Factor for gain changing”
The positioning sequence
This section describes in detail the principle of the positioning sequence since it is now
different from the conventional spindle control.
To begin with, it is necessary to distinguish between absolute positioning (M19 from NC or
PLC) and incremental positioning (M19tsr from command channel).
• Absolute positioning (M19)
The spindle is to be brought to a preset angular position as quickly as possible and
stopped there. Driving to a particular position is only possible if the spindle is synchronized
with the encoder, i.e. if the zero mark has been overtravelled once. It is only then that the
absolute position of the spindle can be defined.
1. Spindle synchronized with encoder
a) Spindle stopped
The spindle is driven to the preset position by the shortest path. This means that
the path to be traversed is always within the range -180 to +180°. Determining
the shortest path also determines the direction of rotation.
The maximum speed attained during positioning is the creep speed.
Speed characteristic for case 1a
n
t
Creep speed for M19
12–40 © Siemens AG 1992 All Rights Reserved 6FC5197- AA50
SINUMERIK 840C (IA)