Page 647 - Mechatronics with Experiments

ELECTRIC ACTUATORS: MOTOR AND DRIVE TECHNOLOGY 633
hysteresis and eddy current losses are given based on measured data as a function of field
intensity and frequency,

∗
P = f(B , w) (8.121)
C max
where B is the maximum flux density, and w is the frequency of change in magnetic
max
flux. The nonlinear function f(⋅) is defined as numerical graphs for different lamination
materials by manufacturers. Notice that the core loss data for different materials is given
per unit mass of the material. Total core loss for a given mass of motor application,
P = m ⋅ P ∗ (8.122)
C C
Hence, the designer can estimate the core losses for a given design using the manufacturer
supplied data.

8.2.3 Friction and Windage Losses

These losses are significant at very high speeds due to the air resistance between the rotor
and stator. The energy loss due to air resistance is called the windage loss. Energy loss due
to bearing friction is called the friction loss. They are taken into account by increasing the
resistive loss by a safety factor, since it is very difficult to accurately model friction and
windage losses, that is
P = 0.1 ⋅ P (8.123)
F R

8.3 SOLENOIDS

8.3.1 Operating Principles of Solenoids
A solenoid is a translational motion actuator with a rather limited motion range. Solenoids
are used in fluid flow control valves and small range translational displacement actuators.
A solenoid is made of (Figure 8.17),

1. a coil,
2. a frame which is a material with high permeability to guide the magnetic flux,
3. a plunger which also is made of high permeability material,
4. a stopper (and a centering spring in most cases), and
5. a bobin, which is a plastic or non-magnetic metal on which coil is wound. It is non-
magnetic so that there is no short circuit for the flux between the coil and plunger.

Flux lines
Coil Frame
Bobin
Plunger
Stop

Mounting thread
x
(a) (b)
FIGURE 8.17: Solenoid components and its design: pull and push types.