motor springs Factors Affecting Design0 pages

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factors affecting design

nnMOTOR SPRINGS nn

C MIN
STORAGE DRUMD2D2D1D4
D3
TORQUE OUTPUTDRUM
D3WT SEE DETAILS OFSPRING ENDS
C MIN
RECOMMENDED DISTANCE BETWEEN DRUM FLANGESEQUALS SPRINGS WIDTH (W)+1mm to 3mm
MAY BE INCREASED SYMBOLS W =Spring material widthT = Spring material thickness
L = Spring length (reference only)C =Distance between drum centres (min)D2 = Storage drum diameterD3 = Torque drum diameterD1 = Outside diameter of spring when fully wound on storage drum D4 = Outside diameter of spring when fully wound on torque drum >

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Fatigue Life

The fatigue life has a directeffecton the size of the spring
and the maximum torque outputavailable in the least
space.A comparison of various chartvalues illustrates the
effectfatigue requirements have on the size of the spring.
For any application the required number of cycles or
reversals should be estimated for the life of the equipment
or a replacementschedule.The fatigue life of a spring can be defined as either a full orpartial extraction and retraction of the spring i.e.the spring
can be exercised over its whole length and achieve the
average life expectation,however if itis exercised over any
one section of the spring repeatedly then thatsection can
be expected to fatigue when the total number of cycles
approaches the life predicted for the spring.Fatigue Life is nottime dependantunder normal operatingcircumstances;itis solely dependenton the number of
operations.However pollutants even in low concentrations can have theeffectof shortening the fatigue life through corrosion or
chemical attack,please refer to the statements regarding
uses and misuses of Spiroflex springs in our brochure andweb site and refer to Spiroflex if in doubt. >

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Mounting Details

A spring motor consists of the following,torque outputdrum,
Spiroflex spring and a storage drum.The storage drum is the
smaller of the two and is of a specified diameter.The Spiroflex
spring will grip the storage drum by its own inherentgripping
action.The torque outputdrum is the larger of the two and is also of aspecified diameter.The Spiroflex spring mustbe attached to
the drum in such a way thatsucceeding turns of
the spring will notbe raised by any
protrusions,(see diagrams).Both
drums are usually supplied by the
user according to the requirements
of his own application. >

nnHow the spring is assembled on drum nn

(notsupplied)

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END BEND A Outer end of spring to be firstwrap on storage drum.
The free end is then fastenedto the torque outputdrum sothatits curvature will be
reversed. AB

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Working Turns

The principal limitation on the total number of rotations of a Spiroflex spring motor is the spacerequirementof the amountof material involved.Working turns are quoted for the standard range
(see spring charts). >

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Speed and Acceleration

Free release of a charged Spiroflex spring motor,or any condition approaching free release,may
permitthe torque drum to throw off material faster than the storage drum can coil up.No such
limitation exists in the pull-outor charging partof the cycle,exceptfor sudden decelerations.
Wherever high-speed operation,sudden stopping or release are predictable service conditions,
experimental models should be employed to verify performance. Fully Wound Position
Unwound Position >

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Stop Mechanisms

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Issue No.1 (Mtr_spr_A/eng) If the driven mechanism does nothave its own limits,some stops or restraints should be included in
the design of the spring motor assembly to preventover-travel of the spring.In some applications
the travel of the motor assembly mustbe limited itself.The illustration shows a double stop
mechanism with the motor in both the wound and unwound positions.More often an automatic
stop is required only atthe end of the power stroke,in which case the device shown would be used
only on the outputdrum. >

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