motor springs Factors Affecting Design
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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 > 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. > 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. > 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 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). > 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 > 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. >