5
5.5 SIMODRIVE POSMO A functions
5-174
Siemens AG 2013 All Rights Reserved
SIMODRIVE POSMO A User Manual (POS1) – 08/2013 Edition
The following must also be observed:
The function ”travel to fixed stop” causes an externally forced rotation
delay and therefore an externally forced torque that must be below the
permissible torques indicated in Chapter 2.5.1 for POSMO A
– 75 W
and 2.5.2 for POSMO A
– 300 W. The electrical torque limiter is inef-
fective here!
The torque must therefore be limited with mechanical measures for
forced braking. The endstop therefore cannot be designed to be per-
manently fixed; rather, it must be flexible enough that the forced brak-
ing process is extended over a specific minimum time Δt. The minimum
time results from:
The translated moment of inertia of the motor = J
Mot
i
The speed at the gearbox output (N
Shaft
,) at which the endstop is
approached. The speed must be entered in rad/s for computational
inspection.
The maximum permissible gearbox torque
For the POSMO A – 75 W with i = 162 : 1 and a speed of 18 rpm (cor-
responds to a motor speed of 2916 rpm) yields, for example
Δt =
N
Shaft
(J
Mot
i
2
)
M
max_perm
=
48 N m
= 65 ms
18 rpm
2 π
60 smin
–1
(0.00006 kg m
2
162
2
)
The mechanical system of the fixed stop according to
the diagrams in Table 5-7 must therefore be designed to be flexible
enough that the motion is not braked abruptly, but is extended over at
least 65 ms. The centrifugal masses that are braked to a standstill by
the mechanical endstop comprise not only the moment of inertia of the
motor (as in the above example), but all moments of inertia and linearly
moved masses participating in the motion. For the event that the me-
chanical forced braking takes place unevenly, a corresponding safety
factor must be accounted for in the brake time calculation.
As an alternative to a carefully soft design of the endstop, the mechani-
cal limitation of the torque during forced braking can also be imple-
mented with a coupling on the gearbox output. The coupling then ex-
hibits the required flexibility k
rot
in the direction of rotation, whereby only
the translated motor moment of inertia need then be considered as
centrifugal mass.
k
rot
=
N
Shaft
2
max_perm
=
= 410 N m rad
–
18 rpm
2 π
60 smin
–1
(0.00006 kg m
2
162
2
)
(J
Mot
i
2
)
Upon transfer of the maximum permissible torque for this gearbox, the
coupling twists by approx. 1/10 rad, in other words about 6 degrees.
The user must check whether this much twisting can be accepted.
5 Description of the Functions
02.9908.0405.13
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