Basic Concepts - Siemens SIMATIC SIMOSTEP 1FL3041 Functional Description

10 Stepping motor parameters and characteristics
10.1

Basic concepts

Step angle
Number of steps
Holding torque
Systematic angle
tolerance
Control and stepping
frequency
Speed
Torques
10-2
A number of certain parameters and characteristics must be known for
examining and selecting a stepping motor. Each stepping motor has its
specific properties in conjunction with the power controller used; these
properties are represented by characteristic curves. To facilitate an
understanding of their contents and meaning, the essential parameters
and the usage of the characteristics are explained here.
A step refers to a motor shaft rotation by the step angle ; the step is
initiated by a control pulse.
The number of steps specifies the number of steps the rotor performs per
revolution. The number of steps can be adjusted for a 3-phase stepping
motor.
The rotor is held in each step position due to the DC excitation of the coils
unless its holding torque M
The systematic angle tolerance per step ∆α
number of angular minutes a step may deviate from the nominal step
angle.
With a continuous sequence of control pulses at a control frequency f
the motor shaft will also execute a sequence of steps at the (same)
stepping frequency f .
Z
From a specific control frequency onwards (depending on motor type and
mechanical load) the step-by-step movement of the motor shaft verges
into a continuous rotary movement. The following then applies fro the
speed n of the motor:
n = α/360° · f
Z
If the rotating motor shaft is subjected to a load torque M
continue to follow the control frequeny synchronously unless the load
torque exceeds a certain limit, i.e. the maximum torque at maximum slew
stepping rate M .
Bm
In this case, the rotor cannot follow the control frequency any more, and a
step "loss" will occur, where control frequency and stepping frequency are
no longer identical.
Such a situation can be avoided by selecting the correct motor and by
controlling it correctly
is exceeded on the motor shaft.
H
specifies the maximum
s
· 60 r.p.m. (f [Hz])
z
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02.05
, the motor will
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FM-STEPDRIVE/SIMOSTEP (FB)
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