Abstract:
A power-return tape measure uses a retainer to help keep a retraction spring in the proper position. The tape measure may have a reel with an interior central cavity with a post extending therethrough. A spring is wound substantially within the central cavity and mounted to the post so as to provide a retraction bias. A cap is secured to the reel so as to substantially enclose the reel&#39;s central cavity and the spring. The retainer is disposed between the spring and the cap. The cap has a first hole of a first size and the retainer has a second hole of a second, smaller, size. The post extends through the second hole with a sliding fit and through the first hole in spaced relation to the cap. The post and the retainer substantially close off the first hole. A main case substantially encloses the reel.

Description:
BACKGROUND OF THE INVENTION 
     Modern tape measures (or “tape rules”) typically include a coiled tape that is spring-biased towards associated retracted position. A housing generally surrounds and protects the tape and a retraction spring and includes an opening through which a distal end of the tape extends. Typically, the tape measure housing consists of two housing halves that are joined together by one or more screws. In addition, one of the housing halves typically includes an inwardly pointing integral post that provides an anchoring point for one end of the retraction spring. During assembly, a blade winding reel is placed over the post with the retraction spring engaged by the post, and the other housing half is then joined to the first housing half with the reel captured therebetween. During use, the distal end of the tape is pulled away from the housing; when released, the spring pulls the tape back into the housing so that the tape returns to the retracted position. The retracted tape is wound on the reel in the form of a convolute coil, with the reel rotatably supported by the housing. 
     One important consideration when designing commercially available tape measures is that the tape measure should be able to function even after being repeatedly dropped, as frequently occurs on a construction site. Dropping the tape measure subjects the tape measure to substantial shock loadings that sometimes lead to the retraction spring becoming pinched or otherwise misaligned with respect to the anchoring post, quickly rendering the tape measure unusable. 
     Another consideration in designing tape measures is that the presence of dirt and other contaminants inside the housing may tend to degrade the performance of the retraction mechanism, by adding friction, increasing wear, and other mechanisms. However, providing a completely sealed housing is impractical, particularly given the need to pay out the tape measure blade in a convenient manner and the extreme cost pressures present in the marketplace. 
     Accordingly, there remains a need for improved tape measure designs, particularly those that have a more robust design, an preferably designs that address one or more of the problems outlined above. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a power-return tape measure, and/or a method of assembling a power-return tape measure, that employs a distinct internal retainer to help keep a retraction spring in the proper position relative to its anchoring post. 
     In one embodiment, the tape measure comprises a main case having first and second sidewalls and a peripheral wall extending between the sidewalls. A tape measure blade is coiled about a drum assembly in a conventional fashion. Also as is conventional, the drum assembly includes a drum having side flanges disposed generally parallel to the main case sidewalls and a core therebetween. The core of the drum generally defines a central cavity. The drum assembly further includes a drum cap secured to the drum so as to substantially enclose the central cavity. The drum assembly also includes a disc disposed internal to the central cavity and adjacent the drum cap. The drum cap has a first hole of a first diameter and the disc has a second hole of a second diameter smaller than the first diameter. The disc may be metallic and should have a periphery radially larger than the first hole. The power-return retraction spring is wound substantially or entirely within the central cavity and mounted to a post so as to provide a retraction bias for the tape blade. The post may include a slot, with the spring mating to the post via the slot. The post is disposed between the first and second sidewalls and extends through the central cavity, the first hole, and the second hole. The post extends through the second hole with a sliding fit and through the first hole without touching the drum cap. For example, the post may be spaced from the edge of the first hole so that there is a uniform gap therebetween. At least one of the sidewalls may include an inwardly pointing boss that cooperates with the first hole to provide a rotational bearing surface for the drum assembly. The other sidewall may also have a boss that cooperates with other features of the drum assembly to provide another bearing surface on the other side of the drum. 
     In another embodiment, the tape measure may comprise a tape measure blade coiled about a reel, the reel having an interior central cavity. A post extends through the central cavity. A spring is wound substantially or entirely within the central cavity and mounted to the post so as to provide a retraction bias for the tape blade. A cap is secured to the reel so as to substantially enclose the central cavity and the spring. A retainer is disposed between the spring and the cap. The retainer is distinct from both the reel and the cap and may advantageously be metallic and disc shaped. The cap has a first hole of a first size and the retainer has a second hole of a second size smaller than the first size. The post extends through the second hole with a sliding fit and through the first hole in spaced relation to the cap. The post should rotationally fixed relative to the main case. The post and the retainer substantially close off the first hole. A main case substantially encloses the reel. 
     In another embodiment, a method of assembling a tape measure includes providing a main case having a boss thereon; providing a reel having a central cavity; providing a tape measure blade convolutionally wound on the reel; providing a post having a slot therein; anchoring a spring to the post via the slot, the spring disposed substantially within the central cavity and operative to bias the blade towards being wound on the reel; providing a retainer having a first hole therein, the first hole sized to slidably engage the post; placing the retainer over an end of the post and moving the retainer toward the spring; capturing the retainer in the central cavity between the spring and a cap connected to the reel, the capturing including positioning the cap so that the post extends through the second hole therein in spaced relation to the cap; rotationally supporting the reel for rotation relative to the housing via the boss and second hole; and substantially enclosing the post, the reel, the spring, the retainer, and the cap in the housing. The main case may have distinct first and second case portions, with the first case portion including the boss. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of one tape measure embodiment constructed in accordance with the present invention. 
     FIG. 2 is a perspective view of one embodiment of a tape measure housing in accordance with the present invention with some elements removed for clarity (e.g., screws, clip, etc.). 
     FIG. 3 is a perspective view of one embodiment of a post suitable for the present invention. 
     FIG. 4 shows a partial cross-sectional view of the center of the tape measure of FIG. 1 without the blade. 
     FIG. 5 shows a simplified side view of the retraction spring, post, and reel with the cap and retainer removed. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As illustrated in FIG. 1, a tape measure, generally designated  10 , is shown constructed according to the present invention. The tape measure  10  includes a coilable measuring tape or blade  12  and an associated housing  20 . The distal end of the tape  12  may advantageously include an end hook  14  to prevent it from being retracted into the housing  20 . A tape-biasing device, such as a retraction spring  99  (FIG.  5 ), is operatively connected to the tape  12  to bias the tape  12  towards a retracted orientation. A locking mechanism, including a toggle  16  or similar actuator is provided to aid in controlling the movement of the tape  12  into and out of the housing  20 . One or both sides of the housing  20  may include a clip  18 , as desired. As the general design and operation of power-return tape measures are well known in the art, additional detailed discussion of some components is omitted herein for brevity. However, additional discussion may be found in U.S. Pat. Nos. 4,527,334; 4,976,048; and 6,349,482, which are incorporated herein by reference. 
     The housing  20  typically includes a main case or shell  30  and a grip element  36  mounted on the shell  30 . The housing  20  preferably has a generally squarish shape, with a rounded upper-rear corner and may have a slightly projecting nose, as shown in FIGS. 1-2. The housing  20  includes an opposing pair of sidewalls  32  and an interconnecting peripheral wall  34  that help define an internal chamber  29  (FIG. 4) that houses the coiled portion of the tape  12 , a suitable tape-biasing device, and portions of the locking mechanism. As shown in the Figures, the peripheral wall  34 , and thus the shell  30 , may be thought of as having a top  22 , a bottom  24 , a front  26 , and a rear  28 . The housing  20  typically includes an opening  27  near its lower-front corner that connects to the internal chamber  29 . The distal end of the tape  12  extends through this opening  27 . The housing  20  is preferably sized to fit within a user&#39;s hand, and also conveniently stored on a work belt or in a toolbox. 
     As shown in FIG. 2, the shell  30  may be constructed from two portions, a right-hand portion  30   a  and a left-hand portion  30   b , joined together by suitable screws  38 , as is known in the art. The external configurations of both the shell portions  30   a , 30   b  and the grip element portions  36  may advantageously be symmetrical if desired, but this is not required. Indeed, the two portions  30   a , 30   b  may have different internal and external configurations, depending on the internal workings of the tape measure  10 , also as is known in the art. However, as the present invention primarily relates to the internal configuration of the tape measure  10 , the details of the external configuration of the shell  30  are not important to understanding the present invention, and the following discussion will focus on the internal structure of the tape measure  10 . More information on possible external configurations of the housing  20  may be found in U.S. patent application Ser. No. 10/174,629, filed Jun. 19, 2002 and entitled “Tape Measure Housing with Grip Element,” which is incorporated herein by reference. 
     As shown in FIG. 4, a post  40  is disposed between the respective sidewalls  32 , internal to the housing, and provides an anchoring point for the retraction spring  99  (FIG.  5 ). The post  40  may be formed integrally with one or both of the housing shell portions  30   a , 30   b , or may be a distinct therefrom. As the later arrangement is believed advantageous, the discussion following will assume that the post  40  is a distinct part, although either arrangement is intended to fall within the scope of the present invention. 
     The post  40 , shown in FIG. 3, may include a column portion  42  and an anchoring (or base) portion  50 . The column portion  42  is generally elongate along axis  44 , and may advantageously have a generally circular cross-section split by slot  49 . The slot  49  extends from the terminal end  46  of post  40  toward the anchoring portion  50 . The terminal end  46  of post  40  may advantageously include a hole  48  that is intended to accept a fastener  60 , as described further below, and may include a chamfer if desired. The anchoring portion  50  of the post  40  includes a flange  52  and a plurality of ribs  54 . The flange  52  is disposed proximate the column portion  42 , and advantageously has a non-circular shape. The ribs  54  extend radially outward from the axis  44 , and may therefore be considered as extending generally normal to the axis  44 . There are preferably four ribs  54 , but other numbers of ribs  54  may also be used. The ribs  54  have a profile that is generally flat on the side toward the flange  52 , and slopes backward at an angle on the side away from the flange  52 , such as at an angle of 15° to 45°, a preferably approximately 30°. The ribs  54  may be of suitable size, such as approximately 0.006 to 0.010 inches in height. The portion of anchoring portion  50  having the ribs  54  thereon may be round, or may advantageously be non-circular with appropriate flats  56  or the like. Thus, the ribs  54  may extend circumferentially entirely around the post  40 , or may be interrupted by the flats  56 . The end of the anchoring portion  50  opposite the column portion  42  may also advantageously include a hole (not shown), similar to hole  48  in size and function. For more details of the post  40 , attention is directed to U.S. patent application Ser. No. 10/347,665, filed Jan. 21, 2003 and entitled “Tape Measure Housing with Post,” which is incorporated herein by reference. 
     Referring to FIG. 4, the post  40  advantageously mates to the sidewalls  32  of the housing shell  30  using corresponding bosses  70 , 74  in the sidewalls  32 . One sidewall, such as the sidewall  32  of the left half  30   b  of shell  30 , may include boss  70  which is substantially round in shape with a recess  72  intended to accept the terminal end  46  of post  40 . The other sidewall, such as the sidewall  32  of the right half  30   a  of shell  30 , may include a boss  74  with a more complex recess  76  with an upper portion corresponding in shape to the flange  52 , and a lower portion corresponding in shape to the ribbed area of the anchoring portion  50  of post  40 . The lower portion of recess  76  may be round in shape if desired, and should be sized so that there is a sliding fit between the wall defining the recess  76  and the anchoring portion  50  at a point between the ribs  54 . At least recess  72 , and preferably both recesses  72 , 76 , should include suitable through holes for allowing access to holes  48 , 58  in post  40  for securing fasteners  60  thereto. 
     The blade winding drum (or “reel”)  82  typically takes the commonly known bobbin-like form with two parallel flanges  84  and an intervening core  86 . The tape blade  12  is wound about the core  86  in a convolute coil, with the inner portion of the core  86  providing a central cavity  88  for substantially housing the retraction spring  99 . The spring  99  is anchored on one end to the post  40 , and provides a bias to retract the tape blade  12 . The spring  99  is disposed at least substantially, and optionally entirely, inside the central cavity  88  (see FIG.  5 ), as is known in the art. The drum  82  is rotatably mounted in the housing  20 , with the post  40  extending through the central cavity  88 . As discussed above, the slot  49  of the post  40  typically engages and anchors one end of the spring  99 . The spring  99  is held in the slot  49 , at least partially, by a drum cap  90  and retainer  94 . The drum cap  90  is preferably a generally annular plastic part that mates to the drum  82  so as to substantially enclose the central cavity  88  with the spring  99  therein. The drum cap  90  may mate to the drum  82  in any known fashion, with conventional interengaging snap fingers being a convenient approach. The center of the drum cap  90  includes a hole  92  for the post  40  to extend through. This hole  92  is sized substantially larger than the corresponding portion of the post  40  so that a gap is formed between the post  40  and the drum cap  90 . The hole  92  is intended to fit around boss  70  so that the drum  82  is rotatably supported by the resulting bearing surface created thereby. In addition, a retainer  94  is disposed just internal of the drum cap  90 . This retainer  94  preferably takes the form of a very thin metal disc, such as on the order of 0.003 inches thick. The retainer  94  also includes a hole  96 , preferably in the center thereof, for the post  40  to extend through. This retainer hole  96  is substantially smaller than hole  92  of the drum cap  90 . The hole  96  is preferably sized to be just larger than the corresponding portion of the post  40 , so that there is a sliding fit therebetween. 
     In the assembled form, the retainer  94  is disposed around the post  40 , between the spring  99  and the drum cap  90 . Because the hole  96  in the retainer  94  matches the diameter of the post  40  (assuming the post is round), the retainer  94  acts to keep the spring  99  firmly located within the slot  49  of the post  40 . However, the drum  82  is not limited to having rotational bearing surfaces that match the diameter of the post  40 , but are instead allowed to be the larger size of the hole  92  in the drum cap  90 . Thus, preferred embodiments of the present design allow for the drum  82  to have larger rotational bearing surfaces (hole  92  and boss  70 ), while also preventing the spring  99  from working itself laterally out of the slot  49  of post  40 . In addition, the close correlation between the size of hole  96  and the size of post  40  allows the retainer  94  to also act as a seal against intrusion of dirt and other contaminants into the central cavity  88 . Thus, the retainer  94  performs dual-functions in the preferred embodiments of the present design—retaining the spring  99  and better sealing the central cavity  88 . 
     For ease of reference, the combination of the drum  82 , the drum cap  90 , and the retainer  94  may be referred to herein as the drum assembly  80 . 
     The tape measure  10  may be assembled using mostly conventional techniques, with some modifications to accommodate that addition of the retainer  94 . The assembly process begins with the anchoring portion  50  of post  40  being mated to the half  30   a  of shell  30  that includes boss  74 . The end of the post  40  corresponding to the anchoring portion  50  is inserted into the recess  76  such that the ribs  54  bite into the boss  74 . This mating of the post  40  with shell half  30   a  may be accomplished using an arbor press if desired. With the post  40  mated to the shell half  30   a , the reel  82  and spring  99  are mounted to shell half  30   a , with one end of spring  99  being inserted into slot  49  (FIG.  5 ). It should be noted that the reel  82  is intended to be rotatably supported by the bosses  70 , 74  of the housing  20  when fully assembled. The reel  82  is then temporarily clamped to the shell half  30   a  and the “free end” of spring  99  is then rotated about the reel  82  so that a preload is placed on the spring  99 , typically using a powered winding tool/fixture. The free end of the spring  99  is routed out of the shell half  30   a , the retainer  94  placed over the spring  99  with the post  40  extending through hole  96 , and the retainer  94  slid down the post  40  towards the spring  99 . The drum cap  90  is then snapped onto the drum  82 , with the post  40  extending through hole  92 , but spaced from the edges of hole  92  (preferably uniformly spaced). The addition of drum cap  90  substantially encloses the central cavity  88  of the drum  82  with the spring  99  and retainer  94  captured therein. Indeed, the drum cap  90  pushes the retainer  94  laterally against the spring  99  in preferred embodiments. The tape blade  12  (with hook  14  attached) is then connected to the free end of the spring  99 , and the spring  99  released so that the blade  12  is wound onto the reel  82 . Preferably, the convolute coil formed by the blade  12  wrapped on the reel  82  is not higher than the reel&#39;s flanges  84 , but this is not required. The locking mechanism (e.g., toggle  16 , etc.) and other relevant internal components are then added along with the other half of the shell  30   b . Screws  38  are added to hold the housing halves  30   a , 30   b  together. The post mounting screws  60 , if used, are inserted through the corresponding sidewalls  32  and screwed into their respective holes in post  40 , thereby very firmly mounting the post  40  to the shell  30 . These holes in post  40  may be threaded, or alternatively the post mounting screws  60  may be self-tapping. If desired, one of the post mounting screws  60  may be used to attach the belt clip  18 . From this point, the assembly of the tape measure  10  continues in a conventional fashion, e.g., labels are added, testing, etc. 
     Shell  30 , drum  82 , and drum cap  90  are preferably made from a durable material such as a hardened plastic (e.g., ABS, polycarbonate, or the like). The post  40  is preferably distinct from the shell  30 , may be made from a different material. Preferably, post  40  is constructed from metal, such as steel or zinc alloys (e.g., a zinc-aluminum-magnesium-copper alloy known as zamak-5), using a die cast process. Using a metallic post  40  allows the post  40  to be of a smaller radial size while still retaining the requisite strength. The retainer  94  may be made from suitable plastics, but is preferably metallic. 
     It should be understood that the tape measures  10  of the present invention may also include other features, such as shock-absorbing bumpers proximate the opening  27 , specially coated blades  12 , reinforcing hooks  14 , various locking mechanisms, and like, all of which are known in the art. 
     The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.