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10.94 12 Functional Descriptions
12.7.2 Description of the spindle modes
In main spindle drives, the torque is limited as follows (cf. Fig. 1):
• Constant torque up to rated speed n
n
: Torque = const
• Constant power above rated speed
up to breakdown speed n
k
: Torque 1 / n
• Power reduction at higher speeds up to n
max
: Torque 1 / (n*n)
Allowance is made for these characteristics in the control in the form of an acceleration
adaptation which is simple to parameterize:
• Constant acceleration (according to MD 478* as with previous SW) up to a freely settable
speed limit n
x
.
The speed limit nx is entered via a new MD 2471* - MD 2478* which parameter-set-
specific.
• Above speed limit nx, the acceleration rate is reduced according to the equation:
Acceleration= MD 478* n
x
/ n
n: Present speed
It may to be necessary to make allowance for the acceleration characteristic of the induction
drive which drops in proportion to 1/(n*n) above the speed range of constant power. This can
be achieved approximately by means of an additionally applied adaptation factor c (MD 2479* -
MD 2486*):
Acceleration= (MD 478*) for n n
x
Acceleration= (MD 478*) * [n
x
/ (n * c)+(c - 1) / c] for n>n
x
Fig. 3 Possible shapes of acceleration characteristic when adaptation factor is varied. For c = 1 (1 = 100 %),
the acceleration above speed limit nx is reduced in inverse proportion to the speed.
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Acceleration
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© Siemens AG 1992 All Rights Reserved 6FC5197- AA50
12–51
SINUMERIK 840C (IA)
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