TRICONEX 4351B 3721 8312 describes the basic components of a typical servo motion system
Figure 1 depicts the basic components of a typical servo motion system using standard Laplacian notation. In this figure, the servo drive closes the current loop and is simply modeled as a linear transfer function G(s) . Of course, the servo drive will have a peak current limit, so this linear model is not entirely accurate, but it does provide a reasonable representation for our analysis. In its most basic form, a servo drive receives a voltage command that represents the desired motor current. The motor shaft torque T is related to the motor current I and the torque constant K t . The equation shows this relationship.
For discussion purposes, the transfer function of a current regulator, or indeed a torque regulator, can be approximated in units of the relatively low frequencies of motion that we are interested in, so we make an approximation as shown below.
The servo motor is modeled as a total inertia J , a viscous damping term b , and a torque constant K t . The total inertia term consists of the servo motor and load inertia. It is also assumed that the loads are rigidly coupled such that the torsional stiffness places the natural mechanical resonance point well beyond the bandwidth of the servo controller. This assumption allows us to model the total system inertia as the sum of the motor and load inertia at the frequency we can control. If coupler dynamics are incorporated, a more complex model is required.
The actual motor position q(s) is usually measured by an encoder or resolver connected directly to the motor shaft. Again, the basic assumption is that the feedback device is rigidly mounted, so its mechanical resonance frequency can be safely ignored. The external shaft torque disturbance, Td , is added to the torque produced by the motor current, resulting in a torque that can be used to accelerate the total inertia J.
LENZE EA-4/10
LENZE EVF8212-E
LEUZE DDLS 200/200.2-50-M12
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LEYBELOD TURBOVAC 361
LEYBELOD 850-400-G1
LEZE EVS 9325-ES
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LUST VF1410LHFS41
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LAM Research 810-017034-005
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