Abstract:
A spring tape suitable for use in spring motor applications where reactive torque varies with rotational deflection. An elongate elastic element is advanced lengthwise and is laser cut into longitudinally complementary shapes which are separated and subsequently pre-stressed into rolls which are cut to length for assembly into a spring motor.

Description:
BACKGROUND OF THE INVENTION 
     It is known to provide spring motors having longitudinally symmetrical tapered flat tapes that produce variable reactive forces. Early examples are disclosed in a 1952 U.S. Pat. No. 2,609,193 to Foster, and in later U.S. Pat. Nos. 3,194,343 and 3,194,344 to Sindlinger. Foster discloses a so-called “A”-type spring motor, and Sindlinger discloses a so-called “B”-type spring motor. 
     In a B-type motor, a length of pre-stressed tape, or ribbon, is wrapped around first and second spools rotatable about spaced parallel axes. Each spool has a circular hub and a pair of circular flanges extending outwardly from the hub in spaced parallel relation. The tape is wrapped about the spool hubs such as in the manner described in referenced Sindlinger patents to form a spring motor assembly. In such an assembly, when one of the spools, such as the driver spool, is rotated about its axis, the tape element reacts as it separates from the driven spool, and causes either more, or less, torque to be required to rotate the driver spool. Either spool may be connected to a variety of prime mover mechanisms, such as a lanyard wrapped about a pulley, so that linear motion of the lanyard is converted to rotational motion. A simple practical application of this mechanism can be found in counterweighting window sashes and window treatments wherein the present invention also finds utility. 
     In published, but abandoned, U.S. Patent Application published as No. 2009/0108511 A1, several variations of a tapered spring tape are disclosed. In one such variation, illustrated in  FIGS. 10 and 11 , the tape has a single longitudinal straight edge and a single tapered edge extending between opposite ends. While such a tape may provide some theoretical advantages, the Published Application does not disclose any information about how to manufacture such a tape efficiently. 
     While the disclosed patented and published flat tapered tape spring motor mechanisms may function satisfactorily for their intended purposes, none is capable of being manufactured efficiently. Thus, there is a need for a flat tapered tape spring that is capable of being manufactured efficiently using commercially available equipment employed in a novel process. Moreover, there is a need for a tapered flat tape B-motor that can be used effectively in product display tethering applications, such as currently provided by the PULLBOX® product manufactured by applicant&#39;s assignee Vulcan Spring and Manufacturing, Inc. of Telford, Pa. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view the major components of a so-called B-type spring motor; 
         FIG. 2  is a plan view of the motor illustrated in  FIG. 1 ; 
         FIG. 3  is an elevational view of the motor illustrated in  FIG. 2 ; 
         FIG. 4  is an end elevational view taken on line  4 - 4  of  FIG. 3 ; 
         FIG. 5  is a sectional view taken on line  5 - 5  of  FIG. 2 ; 
         FIG. 6  is a plan view of the spring tape form shown prior to winding into a form suitable for assembly into the motor of  FIG. 1 ; 
         FIG. 7  is an elevational view similar to  FIG. 3  but of a modified embodiment; 
         FIG. 8  is an end view similar to  FIG. 4  but of the modified embodiment; 
         FIG. 9  is a sectional view similar to  FIG. 5 , but of the modified embodiment; 
         FIG. 10  is a plan view similar to  FIG. 6  but of a tape used in the modified embodiment; 
         FIG. 11  is a plan view of a length of tape prior to being cut to length to form the tape of  FIG. 10 ; and 
         FIG. 12  is a schematic view illustrating the process for making spring tapes, such as the one illustrated in  FIG. 10 . 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings,  FIG. 1  illustrates in perspective the major elements of a B-type flat spring motor  10 . These elements include a drive spool  12 , a driven spool  14 , and a flat tape spring element  16  wrapped around the spools  12 ,  14  in the manner illustrated. As best seen in  FIG. 5 , each spool, such as spool  14 , is characterized by a central cylindrical hub  18  and a pair of circular flanges  20 ,  22  extending radially outward in spaced parallel relation from the hub  18 . The gap between the hub and the inner surfaces of the flanges provides space for the tape spring  16  to occupy as it is displaced from one spool to the other during operation of the motor. By way of example, when a torque is applied to the driver spool  12  in the counter-clockwise direction of the arrow shown in  FIG. 1 , the tape  16  advances rightward under the spool hub from a location over the hub on the driven spool  14 . The action and reaction of the spring tape is well known and need not be further discussed in detail at this juncture. 
     In one aspect of the invention, as best seen in  FIG. 6 , the flat spring element  16  is elongate and has end portions  16   a  and  16   b  located at opposite ends of a tapered intermediate portion  16   c . The spring element  16  has an elongate guide edge  17   a  that extends the full length of the spring element, and has a free edge  17   b  that tapers relative to the guide edge  17   a  between the opposite end portions  16   a  and  16   b . One of the end portions  16   b  has a short transverse edge portion that cooperates with the guide edge  17   a  to define the minimum width of the tape at one end portion thereof. The opposite end portion  16   a  extends transversely across the full width of the tape. This shape is that of a right trapezoid in plan. Preferably, as best seen in  FIG. 5 , the hub  19  on the companion spool  12  is frustoconical. As seen in  FIGS. 3 ,  4  and  5 , the guide edge  17   a  engages the inside surfaces of the spool flanges to keep the tape properly centered as the tape moves, and the frusto-conical surface of the spool hub  19  assists in this function. 
     If the motor is used in applications where low operating noise is desired, a tapered spring tape  24  of the configuration illustrated in  FIG. 10  is desirable. This tape configuration possesses modified end portions that tend to cause the motor to run quietly. In this embodiment, the end portions  25  and  26  of tape  24  have full width sections at both opposite ends of the tapered section  27 . As in the  FIG. 6  embodiment, the tapered section  27  has a guide edge  27   a  and a free edge  27   b . The guide edge  27   a  runs the full length L of the tape, and the free edge  27   b  extends for less than the full length by the dimensions L1 and L2. The lengthwise extent, L1 and L2 of each end portion corresponds to at least X. π. D of the spool hub about which each end portion is to be wrapped. The letter “X” equals the number of complete wraps needed to provide adequate hub/flange/tape engagement for centering the tape ends between the spool flanges during initial periods of extension and retraction of the spring tape. The letter “D” equals the diameter of the spool hub. As seen in  FIGS. 3 and 4 , the guide edge  17   a  continually engages one flange on both driver and driven spools to provide proper centering of the tape as it advances and retracts. The free edge tapers at a constant rate and provides the force that varies with length. In this embodiment a frusto conical spool hub  19  ( FIG. 5 ) is not required. 
     Regardless, of which spring tape embodiment is desired, both can be produced by essentially the same process using the same equipment, as illustrated schematically in  FIG. 12 . In the process, an indeterminate length  30  of flaccid metal tape, preferably of high tensile strength spring steel, is provided on a supply roll  32 . The tape  30  is unrolled and advanced lengthwise, such as horizontally, between support and drive rollers  31  and  33 . While being advanced, the tape  30  is cut by a laser beam B directed downwardly from a head  38  which is moveable transversely relative to the longitudinal path of movement of the tape  30 . The laser beam B makes a linear cut  40  in the tape to provide a free edge  40  that extends at an angle across the longitudinal medial axis M of the tape  30 , but does not extend all the way across the tape  30 . At predetermined intervals, the laser beam B makes a transverse cut  44  connected to the linear cut  40 . The transverse cut  44  forms a continuous free edge in a saw tooth configuration as illustrated in Section A-A downstream of the laser head  38 . To make this cut, either the longitudinal motion of the tape is briefly halted, or the laser head  38  is moved above the tape at a velocity that is synchronized with the velocity of the tape. It should be apparent that the rotational speeds of the drive rolls  31  and  33  are synchronized by suitable controls with the motion of the laser head  38 . 
     The continuous free edge cuts  40  and  44  form the tape into undulating complementary shapes on opposite sides of the medial axis M downstream of the laser beam B. As the cut tape advances, it engages a stationary separator nose  48  that splits the tape into two identical complementary shaped strips, Section B-B and Section C-C. One of the strips, Section C-C, advances downwardly onto a storage roll  46  for subsequent use. The other strip Section B-B advances horizontally into a spring coiler  50  which pre-stresses the strip by known techniques, and then cuts the stressed strip to a desired length. The operation of the spring coiler  50  is coordinated with the linear speed of the tape  30 . Also, a suitable slack provider may be emplaced between the separator nose  48  and the coiler  50 , as well known in the art. The thus-coiled tapered spring tape  30  is discharged into a collection bin  52  for further processing, such as customary heat treating, before being assembled into a spring motor. Preferably, the end portions of the tape are formed with keyholes for engaging fastener lugs on the spool hubs, as known in the art. 
     In the above-described process, the spring tape  30  is cut completely widthwise in the coiler  50  by means of a die  51 . When the cut is aligned with the transverse cuts, shown in Section B-B, the resulting strip has a wide end, and a narrow end, and yields a tape form as illustrated in  FIG. 6 . Such a tape spring is useful in applications where a very quiet running motor is not required. 
     It is important to note that Section B-B is the complement to Section C-C. Thus, it can be further processed in the same manner as Section B-B, as by being removed from its storage reel and fed into the same, or a parallel, coiling machine. The point is that the complementary cutting ensures that none of the material of the flaccid starting tape material  30  is wasted. 
     In order to produce the spring tape embodiment of  FIG. 10 , the laser cutting beam B is held stationary adjacent one, or the other, edges of the tape for brief periods of time as the tape advances. As a result, the laser beam B cuts the tape lengthwise for predetermined lengths L1 and L2 before resuming its transverse crosswise motion, as described above. This causes the opposite ends of the tape to have full width sections at both opposite ends, as shown in  FIGS. 10 and 11  for purposes previously discussed. 
     In the illustrated embodiment, the undulating free edge is linear, having tapered sections and transverse sections. There may, however, be applications where these undulating free edges may have a long-wave sinusoidal shape. Whether the free edge is linear, or long-wave sinusoidal, or a is composed of combination of curved and straight sections, the important aspect of efficient production is to provide complementary shapes on opposite sides of the medial axis of the tape so that minimal material is wasted in making the finished tape element.