Method of forming a variably stressed spring for a tape measure

Abstract

A tool, such as a tape measure, including a spring-based retraction system is shown. The spring-based retraction system is driven by a spiral spring, that has a variable preformed stress profile along the length of the spring.

Description

[Technical Field]

[0001] This invention generally relates to the field of tools. More specifically, this invention relates to measuring tapes, retractable rulers, etc., which include a spring retraction system with variable stress. [Previous Technology]

[0002] None [Summary of the Invention]

[0003] One embodiment of the present invention relates to a measuring tape, the measuring tape including a helical spring coupled between the measuring tape strip and the measuring tape housing, such that when the measuring tape strip extends from the housing, the spring stores energy and releases energy to drive the measuring tape strip to retract. The force (e.g., measured in the diameter of the free coil) varies along the length of the helical spring.

[0004] In a particular embodiment, the helical spring has an inner end, an outer end, a length extending between the inner and outer ends, and a first length segment adjacent to the outer end. The stress within the first length segment, measured as the free coil diameter, decreases along the length of the first length segment. In this embodiment, because the free coil diameter is inversely proportional to the stress within the spring, the free coil diameter increases along the length of the first length segment. In a particular embodiment, the free coil diameter increases in the direction toward the outer end of the helical spring.

[0005] Other features and advantages are set forth in the detailed description following this document, and some may be understood by those skilled in the art upon review of the description, or by examining the embodiments shown in the description and its claims, as well as the accompanying drawings. It should be understood that the above overview and the detailed description following this document are illustrative.

[0006] The accompanying drawings are provided to offer a further understanding and are incorporated in and constitute a part of this application. The drawings disclose one or more embodiments and, together with the description, illustrate the principles and operation of those embodiments.

Implementation Method

[0014] Please refer to the figures for general details, which illustrate a variable stress helical spring and related manufacturing method for a tape measure retraction system according to one exemplary embodiment. Many embodiments of the tape measure described herein include an innovative retraction system comprising a variable stress helical spring designed to provide a number of desired retraction characteristics, including reducing the tape measure retraction speed and tape measure acceleration.

[0015] Generally speaking, in a specific tape measure design, a spring stores energy during the retraction of the tape measure and applies force to a spool, causing the tape measure to rewind on the spool during retraction. Many variations of the spring design, such as spring energy, torque curve, spring constant, etc., are chosen to ensure that the spring's operation results in a satisfactory degree of tape measure retraction. In this tape measure, the spring design is a function of many parameters related to the tape measure's retraction, including the tape measure's width, length, shape, and material, friction within the tape measure spool / retraction system, the mechanical efficiency of converting spring energy into tape measure retraction, the desired tape measure speed / acceleration during retraction, etc. Therefore, for a given set of tape measure mechanical parameters and a given desired retraction speed / acceleration, the spring system within the tape measure must store and release a given amount of energy during retraction.

[0016] In a typical tape measure design, a helical spring is used to provide the retraction energy, and in such designs, the length and / or width of the helical spring are general spring parameters adjusted to provide more or less retraction energy required for a particular design. For example, in this conventional tape measure, a longer or wider helical spring is typically used to generate the retraction force required for a longer tape measure blade, a heavier tape measure blade, a faster retraction speed, etc.

[0017] As described herein, the applicant has designed numerous innovative tape measure retraction systems that utilize helical springs with varying degrees of pre-induced or pre-stressed tension along the length of the helical spring. In particular, the degree of pre-stress is reduced in the helical spring section adjacent to the reel or spring housing. The applicant believes that by reducing the degree of pre-stress in certain portions of the tape measure helical spring, such as the outer section, the maximum torque delivered by the spring can be reduced, and the slope of the torque curve can be decreased, while delivering a sufficiently high initial or preloaded torque.

[0018] It is understood that the free coil diameter of the prestressed portion of the spring is inversely proportional to the torque delivered from the prestressed spring portion. Therefore, in the embodiments described herein, the helical spring has a free coil diameter that increases in the spring segment adjacent to the outermost end (outer shell end) of the spring, thus forming a helical spring with a lower maximum torque and a flatter torque curve than a standard measuring tape spring without reduced stress near the outer end. The applicant believes that this configuration reduces the maximum retraction speed, thereby reducing the force of the measuring tape strip striking the measuring tape housing and also reducing / eliminating the whipping that occurs in the last few feet of the measuring tape retraction.

[0019] Referring to Figures 1 and 2, a length measuring device (e.g., a measuring tape 10) is disclosed according to an exemplary embodiment. The measuring tape 10 includes a rollable measuring tape strip 14 and a housing 18. Generally, the measuring tape strip 14 is an elongated material that includes a plurality of marked measuring marks, and in a particular embodiment, the measuring tape strip 14 is an elongated metal material (e.g., steel) that includes an outermost end coupled to a hook assembly (e.g., hook assembly 26). The measuring tape strip 14 may include a plurality of coatings (e.g., polymer coatings) to help protect the measuring tape strip 14 and / or the markings on the measuring tape strip.

[0020] As shown in Figure 1, a variable-length extension 22 of the measuring tape 14 can retract and extend from the housing 18. As detailed later, the retraction of the measuring tape 14 is provided by a variable-prestressed helical spring. A hook assembly 26 is fixedly coupled to an outer end 30 of the measuring tape 14.

[0021] As shown in Figure 2, the non-extended portion of the measuring tape 14 is wound around a spool 34, which is surrounded by a housing 18. The spool 34 is rotatably disposed around an axis 38 of the measuring tape 10, and a retraction mechanism 42 is coupled to the spool 34 and configured to drive the spool 34 around the axis 38, thereby providing power for the retraction of the measuring tape 14. The retraction mechanism 42 includes an elongated helical spring that provides retraction energy to the retraction mechanism 42, as will be described in detail later; the helical spring can vary its stress along its length. A measuring tape locking member 46 is configured to selectively engage the measuring tape 14 to limit the retraction mechanism 42, such that the extended portion 22 of the measuring tape 14 remains at the desired length.

[0022] Referring to Figure 1, the housing 18 includes a first sidewall 50, a second sidewall 54, and a peripheral wall 58 connecting the first sidewall 50 and the second sidewall 54. The first sidewall 50, the second sidewall 54, and the peripheral wall 58 define an indentation 62, as shown in Figure 2, which covers the spool 34 and the retraction mechanism 42. Referring to Figure 1, the first sidewall 50 and the second sidewall 54 have a generally circular outline 66. In other embodiments, the sidewalls may be rectangular, polygonal, or any other desired shape. Many portions of the housing 18 may be co-molded or individually formed from an elastic material, such as natural or synthetic rubber. In the disclosed configuration, the housing 18 is formed by a housing cushion 70 and a support leg 74 extending from the lower portion 78 of one of the peripheral walls 58.

[0023] A slot 82 is defined along the front portion 86 of one of the peripheral walls 58. The slot 82 provides an opening in the tape measure housing to allow the tape measure locking member 46 to extend into the housing 18. In addition, the slot 82 provides a length sufficient to allow the tape measure locking member 46 to move relative to the housing 18 between the locked and unlocked positions.

[0024] Below the slot 82, a notch 90 is provided in the peripheral wall 58. The notch 90 has an arch 94, which corresponds to the arched cross-sectional profile of the measuring tape 14. The notch 90 allows the measuring tape 14 to retract and extend into the recess 62 defined within the housing 18.

[0025] As shown in Figures 1 and 2, the measuring tape 10 includes a finger protection assembly 98. The finger protection assembly 98 includes a protective member 102 and a protective member support member 106. As shown in Figure 1, the portion of the protective member 102 on the outside of the housing 18 is generally U-shaped and extends downward from the housing 18. As shown in Figure 2, when the measuring tape 14 is in the retracted position, one rear surface of the hook assembly 26 abuts against the protective member 102. As detailed later, in at least some embodiments, the helical spring of the retraction system 42 is configured by variable prestress to reduce the maximum torque and / or torque slope applied to the spool 34 / measuring tape 14 during retraction when the hook assembly 26 approaches the protective member 102. This reduction in the maximum torque results in a lower maximum retraction speed of the measuring tape 14, thereby reducing the force exerted on the hook assembly 26 when it contacts the protective member 102 when the measuring tape 14 is fully retracted.

[0026] Please refer to FIG. 3, which discloses an exploded view of the measuring tape 10 of FIG. 1 according to an exemplary embodiment. The measuring tape 10 includes a spring, such as a helical spring 100 as shown. Generally, the helical spring 100 is coupled between a rod 108 and the measuring tape strip 14 (or a reel 34) such that the helical spring 100 stores energy during the extension of the measuring tape strip 14 and releases energy during the retraction of the measuring tape strip 14 to drive the measuring tape strip 14 to wind onto the reel 34. In some embodiments, the helical spring 100 is mounted within a spring cylinder 104 positioned within the reel 34. In other embodiments, the helical spring 100 is mounted directly within the reel 34.

[0027] Referring to Figure 4, a pre-strained coil of steel 110 used to form the helical spring 100 is disclosed. The helical spring material 110 is a strip or band of elastic material (e.g., metal, steel, etc.) having a central body section 116 extending between a first end 112 and a second end 114. It is understood that when assembled into the measuring tape housing 18, the helical spring 100 is wound within the spring coil 104 or spool 34 such that the first end 112 is coupled to the measuring tape strip 14 or spool 34, and the second end 114 is coupled to the rod 108 (or coupled to the housing 18). As shown in Figure 4, the end 112 has an ear-like shape to facilitate frictional coupling to a receiving hole or slot in the measuring tape strip 14 or spool 34; similarly, the end 114 has an ear-like shape to facilitate frictional coupling to a receiving hole or slot in the rod 108.

[0028] As shown in FIG4, the spring material 110 is formed such that the metal material has a reduced prestress force that varies along at least a portion of its length, which is revealed as a stress-reducing section 120. FIG4 reveals the stress-reducing section 120 by the prestress force formed within the spring material 110 (and necessarily the spring 100), measured at different locations along its length, namely near the end 112 (which becomes the outer end of the spring 100 when mounted in the reel 34). As shown in FIG4, the stress-reducing section 120 has a free coil diameter of 13 mm at position 1, 13.13 mm at position 2, 13.26 mm at position 3, 13.39 mm at position 4, and 13.52 mm at position 5. In this particular embodiment, position 5 is adjacent to the end 112, position 4 is located inward along the length of the spring 100, and so on.

[0029] In other embodiments, the diameter of the free coil near the outer end of the spring 100 is substantially larger than the diameter of the free coil in the body or central portion of the spring 100. In some embodiments, the diameter of the free coil of at least a segment of the spring 100 adjacent to the outer end of the spring 100 is 2, 4, 5, 20, 50, 75, or 100 times the diameter of the free coil in the body or central portion of the spring 100. In a particular embodiment, the diameter of the free coil in a segment within 1 meter of the outer end 112 of the spring 100 is 20 mm, 50 mm, 100 mm, and 1000 mm. In a particular embodiment, the diameter of the free coil in a segment of the spring 100 within 1 meter of the outer end 112 of the spring 100 is between 20 mm and 1000 mm, between 50 mm and 1000 mm, between 20 mm and 100 mm, or between 50 mm and 500 mm. In these embodiments, the free coil diameter at the central portion of the spring 100 is between 10 mm and 20 mm, more specifically between 13 mm and 15 mm. In these embodiments, these determined free coil diameters are the average free coil diameter along the length of the spring segment within 1 meter of the outer end 112 of the spring 100. In other embodiments, these determined free coil diameters are estimated free coil diameters measured at at least one location along the length of the spring segment within 1 meter of the outer end 112 of the spring 100.

[0030] In many embodiments, the length of the central portion of the spring 100 is greater than the length of the segment of the spring 100 with lower, reduced prestress. In many embodiments, the length of the central portion is at least 5 times, more specifically at least 10 times, and more specifically at least 50 times the length of the segment of the spring 100 with lower, reduced prestress adjacent to the outer end 112.

[0031] Please refer to FIG5, which illustrates a system 200 and related method for forming a variable stress helical spring (e.g., spring 100) according to an exemplary embodiment. System 200 includes a feed 202 of a sheet (e.g., metal strip) or strip material 204. The metal strip 204 deviates from the feed 202 and moves through a leveling station, revealing opposing calendering rolls 206. The metal strip 204 is then heated in a heating station 208, and the ear-shaped ends 112, 114 are formed into a strip 204 in a stamping station 210.

[0032] Next, the metal strip 204 passes over a roller 212 and moves to a stress station 214. The stress station 214 is configured to generate different degrees of prestress at different locations on the metal strip 204 as the metal strip passes through the station. In the illustrated embodiment, the stress station 214 includes a rod 216 that contacts the metal strip 204 at different locations, causing different degrees of deformation in the metal strip 204. This different degree of deformation relates to the variable stress along the length of the spring when the spring 100 is wound inside the measuring tape housing 18.

[0033] In this embodiment, the rod 216 moves relative to the metal strip 204 in the direction 218 of the arrow. When the metal strip 204 passes around the rod 216, the rod 216 moves toward the metal strip 204 to reduce the bending radius generated in the metal strip 204. Reducing the bending radius via the rod 216 increases the deformation of the metal strip 204, thus increasing the stress formed in a specific length direction portion of the metal strip 204, resulting in a lower free coil diameter (i.e., tighter winding) at the higher deformation portion of the metal strip 204. Conversely, when the rod 216 moves away from the metal strip 204, the bending radius generated in the metal strip 204 when passing around the rod 216 increases. Increasing the bending radius via the rod 216 reduces deformation, thus reducing the stress formed in a specific length direction portion of the metal strip 204, resulting in a lower free coil diameter (i.e., less tight winding) at the lower deformation portion of the metal strip 204. Therefore, in this embodiment, by changing the position of the rod 216 relative to the metal strip 204, different stresses are formed along the length of the metal strip 204 in the longitudinal direction.

[0034] Following the stress station 214, the metal strip 204 is then wound around a storage device surrounding the mandrel 220 to form the spring material 110. In the schematic diagram of FIG5, the metal strip 204 is wound around the mandrel 220 in a bending direction opposite to that caused by the rod 216 within the stress station 214. Therefore, in the orientation of FIG5, the metal strip 204 bends around the rod 216 in a counterclockwise direction 222 as indicated by the arrow, and is wound around the mandrel 220 in a clockwise direction 224 as indicated by the arrow.

[0035] Referring to Figure 6, the spring 110 is shown in a free or slack state before being wound around the reel 34. As shown in Figure 6, the spring 110 has a central section 130 with a generally fixed free coil diameter, which occupies most of the length of the spring 110. As shown in Figure 6, the low-stress region 120 has a free coil diameter that is significantly larger than that of the central section 130.

[0036] Figure 7 shows a torque curve of a standard measuring tape spring, having a fixed free coil diameter as shown in curve 140, and a schematic torque curve of spring 100. In the illustrated embodiment, the spring represented by curve 140 is the same as spring 110 (e.g., same material, width, thickness, length, etc.), except for the reduced stress as described herein. As can be seen from Figure 7, the maximum torque applied by spring 100 is less than the maximum torque of the spring represented by curve 140, and the slope of the torque curve applied by spring 100 is less than that of curve 140.

[0037] It should be understood that the drawings illustrate exemplary embodiments in detail, and that this application is not limited to the details or methods described in the specification or shown in the drawings. It should also be understood that the terminology is for illustrative purposes and should not be considered as limiting.

[0038] Further modifications and alternative embodiments of the present invention will be made available to those skilled in the art through this specification. Accordingly, this specification should be interpreted as disclosure only. The constructions and configurations shown in many exemplary embodiments are also for disclosure purposes only. Although only a few embodiments are described in detail herein, many modifications (e.g., variations in the size, volume, structure, shape and location, parameter values, installation configuration, material use, color, orientation, etc. of many elements) can be achieved without substantially departing from the novel doctrine and advantages of the subject matter described herein. Some elements disclosed as integral may be composed of a plurality of components or elements, the positions of the elements may be reversed or changed, and the nature or number of discontinuous elements may be varied or changed. The order or sequence of any process, logical calculation, or method steps may be varied or changed according to alternative embodiments. Other alternatives, modifications, variations, and omissions may also be achieved in the design, operation, and configuration of exemplary embodiments without departing from the scope of the present invention.

[0039] Unless otherwise stated, any method described herein should be construed as having its steps performed in a specific order. Accordingly, the absence of a method claim specifying the order of its steps, or an explicit indication in the claim or specification that the steps should be limited to a specific order, does not imply any specific order. Furthermore, the article "a" used herein should include one or more components or elements and should not be construed as only one. Robust coupling as used herein refers to two components coupled such that when a force is applied to them, the components move together in a fixed positional relationship.

[0040] Many embodiments of the present invention relate to any combination of any intended features, and such any combination of features may be declared in this application or a future application. Any feature, element, or component of any of the above exemplary embodiments may be used alone or in combination with any feature, element, or component of the other embodiments described above. [Simplified Explanation of the Diagram]

[0007] [Figure 1] is a perspective view of the left side of the measuring tape according to the exemplary embodiment.

[0008] [Figure 2] is a perspective view of the right side of the measuring tape in Figure 1 of the exemplary embodiment.

[0009] [Figure 3] is an exploded view of the measuring tape in Figure 1 of the exemplary embodiment, showing a variable stress helical spring.

[0010] [Figure 4] is a top view of a metal strip used to form a variable stress helical spring according to an exemplary embodiment.

[0011] [Figure 5] is a schematic diagram illustrating the manufacture of a variable stress helical spring according to an exemplary embodiment.

[0012] [Figure 6] is a schematic diagram of a variable stress helical spring in the free state according to an exemplary embodiment.

[0013] [Figure 7] is a torque curve of a variable stress helical spring according to an exemplary embodiment compared with that of a general measuring tape spring.

Claims

1. A method for forming a variable stress spring for a measuring tape, comprising: providing a sheet spring material to a leveling station; moving the sheet spring material through the leveling station; moving the sheet spring material through a stress station, wherein the stress station deforms the sheet spring material such that varying degrees of stress are formed along the length of the sheet spring material; and, after the stress station, winding the sheet spring material around a mandrel in a storage device.

2. The method as described in claim 1 further includes: The sheet spring material is deformed, wherein a first portion of the sheet spring material is deformed through contact with a rod, the rod being configured to introduce a first bending radius into the first portion of the sheet spring material when the sheet spring material moves around the rod.

3. The method as described in claim 2 further includes: The rod is moved a certain distance away from the sheet spring material, so that the contact between the rod and the second part of the sheet spring material causes a second bending radius that is different from the first bending radius.

4. The method of claim 3, wherein the first portion of the sheet spring material has a first-level prestress, and the second portion of the sheet spring material has a second-level prestress; wherein the second-level prestress is different from the first-level prestress and varies along the length of the second portion; and wherein the first-level prestress is measured by the diameter of a first free coil, and the second-level prestress is measured by the diameter of a second free coil, wherein the diameter of the first free coil is smaller than the diameter of the second free coil.

5. The method of claim 1, wherein the leveling station comprises a pair of calendering rolls.

6. The method as described in claim 1 further includes: After the leveling station, the sheet spring material is heated.

7. The method as described in claim 1 further includes: An ear-shaped end is formed on the sheet spring material at the stamping station.

8. The method as described in claim 7 further includes: After the stamping station, the sheet metal spring material is passed around a roller.

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