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 MIL-HDBK-1038
springs) when the drive is operating in the micro-drive mode. The arrangement is
"fail safe" due to the electric circuitry that sets the main brakes in case of
clutch disengagement due to loss of power.
4.4.5.1
Toothed (Clutch) Couplings. Micro-drive connection to the main drive may
also be a toothed coupling with interlocking radial teeth on its two clutch
plates. The height of the teeth is approximately 1/16 inch and their
sides are tapered for easier engagement. The coupling tooth engagement is enabled
only when the main drive brakes are set. A jogging feature is provided to shift
the micro-drive clutch plate to position its teeth for alignment with the main
drive clutch plate. A limit switch is required to sense the fully engaged
position of the clutch and permit the energization of the micro-drive and release
of the main drive brakes. Because of the sensitivity of full engagement of the
coupling teeth to the short operating stroke, NCC policy is to prohibit their use
on new cranes.
4.4.6
Gear Motors. Gear motors (or motor reducers) combine the electric motor
and gear reducer into a single, compact base or flange mounted unit. The electric
motor may be of any type, but the most common is the 1800 RPM AC squirrel cage.
The gear reducer selections include parallel shaft (in-line or offset) right angle
bevel gear, worm gear, planetary, cycloidal, or combinations of these types. The
first gear (pinion) of the gear reducer is normally pressed and keyed to the motor
shaft. Gear motor applications are limited to low-power drives such as travel
and rotate drives, and various operating mechanisms.
4.4.7
Painting and Corrosion Protection. Purchased mechanical-electrical
components are usually painted by their manufacturers. They should be painted for
corrosion protection in the same manner as the mechanical components. See
paragraph 4.3.6.41 for specific requirements.
4.5
Electrical. All electrical components are standard commercial items
designed, manufactured, and rated according to the applicable industry standards.
Only those components that comply with the requirements of the National Electrical
Manufacturers Association (NEMA) Industrial Control Systems (ICS) standards and of
Underwriters Laboratories (UL) documents, or those of other established nationally
or internationally recognized approving organizations, may be used on Navy cranes.
Such electrical components are described in detail in the manufacturers' catalogs
and advertising literature. Furthermore, installation of electrical conductors
and equipment must comply with the National Electrical Code; for installations not
covered by the code, it is to be complied with to the greatest extent practicable.
Both direct current (DC) and alternating current (AC) electrical systems
are utilized on Navy cranes. DC power is normally available at the older Navy
shore facilities and is often used on larger cranes with on-board diesel engine
generated power. Newer Navy shore facilities and smaller cranes, especially
underrunning and cantilever types, are AC powered. Some electrical components may
be used in either system; however, their DC and AC rating must be noted because
they may be significantly different.
4.5.1
Crane Electrical Systems. Electrical systems on cranes are classified
according to their basic functions drive power, control, and ancillary service.
The particular drive motor types, in combination with the appropriate controls,
define the crane drive systems and their operating characteristics.
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