Abstract:
An automatic tape measure having a tape retraction prevention device to prevent unintended retraction of the tape into a housing caused by increasing the strength of a return spring. A tape assembly is received in the housing and includes a tape selectively received on a reel, the return spring and a cassette for receiving the reel. A motor is coupled with a power source, a drive assembly, the tape assembly and a switch assembly to control extension and retraction of the tape. The drive assembly couples the motor with the tape assembly and includes at least one gear. The tape retraction prevention device includes a pawl that may engage with the gear to prevent rotation of the drive assembly and, in turn, unintended retraction of the tape into the housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not Applicable.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable.  
       BACKGROUND OF THE INVENTION  
       [0003]     This invention relates generally to a tape measure and, more particularly, to an automatic tape measure that utilizes a retraction prevention mechanism with the drive assembly for maintaining extension of the tape.  
         [0004]     Automatic tape measures are generally used to measure an existing object or as a tool for marking and measuring distances. The tape is automatically extended from the front wall of the housing using a motor, a drive assembly, and a reel. The reel is typically rotatably coupled to and positioned within the housing. The tape is wound on the reel which includes a recoil spring that assists in retracting the tape. The motor rotates the drive assembly which extends the tape out of the housing. The drive assembly includes a combination of gears and rollers that are coupled with the motor and engaged with the tape. The motor may then activate the drive assembly which, in turn, extends the tape out of the housing a desired amount. However, in the standard embodiment, the motor only assists with extension of the tape, not retraction. As stated above, the recoil spring assists the reel in rewinding the tape.  
         [0005]     When the tape has been extended a desired amount, the drive assembly remains engaged with the tape. The resistance of the motor to being rotated backwards prevents the spring from recoiling the tape. Thus, in order for retraction to occur, the drive assembly must be disengaged from the tape to allow the recoil spring to retract the tape and the motor is deactivated. One design issue, however, with the recoil spring is the difficulty of the recoil spring to retract the tape when it has been extended a great distance. A solution to this problem is to increase the tension of the recoil spring such that it more readily provides for tape retraction when the drive assembly is disengaged from the tape. However, when the tension of the spring is increased to provide for greater retraction power, the rewind force of the recoil spring often overcomes the braking force naturally provided by the non-activated motor and, thus, will retract the tape when the motor is deactivated even though the drive assembly is still engaged with the tape. When the braking force of the motor is overcome, a “creeping” of the tape back into the housing occurs from the extended position. This is due to the large recoil force of the recoil spring tending to urge the retraction of the tape via the reel by overcoming the natural braking force of the motor.  
         [0006]     Thus, it would be desirable to manufacture an automatic tape measure with a drive mechanism that utilizes a recoil spring for retraction, but which also provides a retraction prevention mechanism that prohibits the recoil spring of the drive mechanism from automatically retracting the tape by overcoming the braking force provided by the motor.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     This invention is directed to an automatic tape measure with a retraction prevention mechanism. The tape measure contains a housing, a tape assembly, a motor, a drive assembly, and a retraction prevention mechanism. The housing is a container configured to hold the tape assembly, the motor, and the drive assembly. The tape assembly preferably includes a tape, a reel, and a cartridge or cassette. A switch assembly is used in conjunction with the drive assembly and reel to extend and retract the tape. Extension of the tape is provided via an extension button and retraction of the tape is provided via a retraction button, both of the switch assembly.  
         [0008]     The drive assembly includes a motor, a drive gear, a ratchet gear, a ratchet wheel, and a drive wheel. The drive assembly is positioned within the housing such that the drive wheel contacts the tape to extend it from the housing. It is understood that pressing the extension button causes an output from the motor, through a combination of gears and rollers, to extend the tape from within the housing. Pressing the retraction button causes retraction of the tape within the housing by disengaging the drive assembly from the tape. Once disengaged, a recoil spring coupled to the reel causes the tape to retract within the housing. The recoil spring provides a rewind force on the reel to cause retraction.  
         [0009]     The tape measure also includes a retraction prevention device. In one embodiment, the retraction prevention device includes a ratchet pawl. The ratchet pawl is pivotably mounted to a lower portion of an inner housing. The ratchet pawl is biased into contact with the ratchet gear by a torsion spring. The ratchet pawl permits rotation of the ratchet gear in a first direction of rotation when the tape is being extended from the housing. However, when the ratchet gear attempts to rotate in a second direction, the ratchet pawl engages the ratchet gear. Thus, the ratchet pawl prohibits the retraction of the tape within the housing due to the recoil spring overcoming the braking force of the motor. Retraction of the tape may then only occur by pressing the retraction button to disengage the ratchet pawl from the ratchet gear, as well as the drive assembly from the tape.  
         [0010]     In another embodiment, the retraction prevention mechanism includes a ratchet pawl and a disc with a pair of depending ears. The ratchet pawl of this embodiment is not biased into contact with the ratchet gear by a spring, but is instead biased to a disengaged position. When the motor is inactive and the rewind force of the recoil spring overcomes the braking force of the motor, the tape will initially begin to retract within the housing. However, during this initial retraction, the ears of the disc will contact the ratchet pawl and move it into contact with the ratchet gear. At this point the ratchet pawl is engaged with the ratchet gear and, thus, unintentional retraction of the tape is prevented. Retraction of the tape may then only occur by pressing the retraction button to disengage the drive assembly from the tape. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0011]     These and other objectives and advantages of the present invention will be more readily apparent from the following detailed description of the drawings of the preferred embodiment of the invention that are herein incorporated by reference and in which:  
         [0012]      FIG. 1  is a cross-sectional side-elevation view of a tape measure of the present invention with a portion of the cassette cut away;  
         [0013]      FIG. 2  is an enlarged, fragmentary side-elevation view of the tape measure of  FIG. 1  with portions thereof cut away to show more detail of the various internal components and a drive mechanism engaged with the tape;  
         [0014]      FIG. 3  is a side-elevation view of the tape measure of  FIG. 2  with the drive mechanism disengaged from the tape;  
         [0015]      FIG. 4  is a cross-sectional side-elevation view of an alternate embodiment of a tape measure of the present invention with a portion of the cassette cut away and illustrating a ratchet pawl disengaged from a ratchet gear; and  
         [0016]      FIG. 5  is a cross-sectional, fragmentary, perspective view of the tape measure of  FIG. 4  with the ratchet pawl engaged with the ratchet gear by an ear of a disc. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     With initial reference to  FIG. 1 , an automatic tape measure according to the principles of the present invention is designated generally with the reference numeral  10 . The tape measure  10  includes a housing  12 , a tape assembly  14 , a drive assembly  16 , and a retraction prevention mechanism  18 . The housing  12  includes a pair of opposed sidewalls  20 ,  22 , top and bottom walls  24 ,  26 , and front and rear walls  28 ,  30 . It should be understood that the sidewall  20  is not shown as that portion of the housing  12  has been removed from the Figures to permit viewing of the interior of the housing  12 . The housing  12  is preferably two halves that mate in clamshell fashion, and is constructed from molded plastic, however, any suitable material may be used. The housing  12  is configured to define a container that houses the tape assembly  14 , the drive assembly  16 , and the retraction prevention mechanism  18 .  
         [0018]     The tape assembly  14  includes a tape  32 , a reel  34 , a recoil spring  36  (not shown), a cartridge  38 , and a switch assembly  40 . The tape  32  is wound on the reel  34  such that a bottom surface  42  of the tape faces outwardly, as is understood by one of ordinary skill in the art. The cartridge  38  is a two-piece shell that houses the tape  32 , the reel  34  and the recoil spring  36 . The recoil spring is coupled on one end with the reel  34  and on another end with the cartridge  38 , such that rotation of the reel  34  with respect to the cartridge causes a change in the tension of the recoil spring  36 . The cartridge  38  contains a pair of depending tabs  44  that permit attaching it to the sidewall  22  of the housing  12 .  
         [0019]     The extension of the tape  32  from the housing  12  is controlled by the switch assembly  40  and the drive assembly  16 , as will be further discussed below. Both the switch assembly  40  and the drive assembly  16  are electrically coupled to a power source  46 , as is understood by one of ordinary skill in the art. During extension, the tape  32  is guided by a roller  48  located adjacent the bottom wall  26  and near the front wall  28 . The tape  32  includes a hook  50  and extends through an opening  51  in the front wall  28 , as is understood by one of ordinary skill in the art.  
         [0020]     The switch assembly  40  is preferably located in the top wall  24  of the housing  12  and includes extension and retraction buttons  52 ,  54 . It will be appreciated by one of ordinary skill in the art that the buttons  52 ,  54  of the tape assembly  14  allow for forward movement and rearward retraction of the tape  32  via the drive assembly  16  and the recoil spring  36 , respectively. The recoil spring  54 , when permitted, retracts the tape  32  into the housing  12 .  
         [0021]     Referring now to  FIGS. 1 and 2 , the drive assembly  16  will be discussed. The drive assembly  16  is positioned within the housing  12  to contact the bottom surface  42  of the tape  32  as it is on the reel to extend the tape  32  from the housing  12 . The drive assembly  16  includes a motor  56  (not shown), a ratchet gear  58 , a ratchet wheel  60 , a pair of swingarms  62 , and a drive wheel  64 . The motor  56  is located in an inner housing  66 , the inner housing  66  being attached to the tape housing  12 . The motor  56  includes an output axle  68  with a drive gear  70  attached thereto. The motor  56  is powered by the power source  46 , as is understood by one of ordinary skill in the art.  
         [0022]     The drive gear  70  is in engagement with the ratchet gear  58 . The ratchet gear  58  is located on a transmission axle  72 , the axle  72  being rotatably mounted with the inner housing  66 . As the motor  56  turns, the drive gear  70  transfers torque from the output axle  68  to the ratchet gear  58 . As best seen in  FIG. 2 , the ratchet wheel  60  is also coupled to the transmission axle  72 . Thus, as the ratchet gear  58  turns so does the ratchet wheel  60 . The ratchet wheel  60  is adjacent to and configured to frictionally engage the drive wheel  64 , as will be further discussed below.  
         [0023]     The swingarms  62  are generally kidney shaped, as illustrated, and are rotatably coupled to the transmission axle  72 . It should be understood that a swingarm  62  is located on each side of the ratchet wheel  60  and the drive wheel  64 . The swingarms  62  have an upper portion  74  and a lower portion  76 . The lower portion  76  depends downwardly from the axle  72  and has an aperture  78 . The apertures  78  on each swingarm  62  align to receive a wheel axle  80  to mount the drive wheel  64  thereon. The upper portion  74  contains an arm  82  with an aperture  84 . The apertures  84  on each arm  82  align to receive a pin  86 , the importance of which will be further described below.  
         [0024]     Continuing with the discussion of the drive assembly  16 , the drive wheel  64  will now be discussed. As stated above, the drive wheel  64  is mounted on the wheel axle  80  received between the swingarms  62 . As best seen in  FIG. 2 , the drive wheel  64  is frictionally engaged with the ratchet wheel  60 . During extension and rest, the drive wheel is also frictionally engaged with the bottom surface  42  of the tape  32 . Thus, rotation of the ratchet wheel  60  causes rotation of the drive wheel  64  which, in turn, contacts the bottom surface  42  of the tape  32  and causes it to extend from the housing  12 .  
         [0025]     The drive assembly  16  further includes an adjustment mechanism  88 , as shown in  FIGS. 2 and 3 . The adjustment mechanism  88  includes a generally vertical rod member  90 . The member  90  abuts an underside  92  of the retraction button  54  at an upper end  94  and abuts the pin  86  of the drive mechanism  16  at a lower end  96 , as will be further discussed below. The member  90  is guided by a pilot flange  98  extending horizontally from an upper portion  100  of the inner housing  66 .  
         [0026]     The adjustment mechanism  88  also contains a compression spring  102  and a tension spring  104 . The compression spring  102  surrounds the member  90  and is located between the pilot flange  98  and a flange  106  located proximate the upper end  94  of the member  90 . The compression spring  102  biases the member  90  and, thus, the retraction button  54  upwardly. The tension spring  104  extends between the pilot flange  98  and the drive mechanism  16 . An upper end of the tension spring  104  is coupled to the pilot flange  98  while a lower end of the tension spring  104  is coupled to the pin  86 . The tension spring  104  biases the swingarm  62  and, thus, the drive wheel  64  upwardly to maintain contact between the drive wheel  64  and the bottom surface  40  of the tape  32 , as will be further discussed below.  
         [0027]     Referring again to  FIG. 1 , the retraction prevention mechanism  18  will be discussed. The retraction prevention mechanism  18  includes a ratchet pawl  106 . The ratchet pawl  106  is pivotably coupled to a protrusion  108  located on a lower portion  110  of the inner housing  66 . The ratchet pawl  106  extends upwardly and engages the ratchet gear  58 . The ratchet pawl  106  is biased into contact with the ratchet gear  58  by a torsion spring  112 . As explained in greater detail below, the ratchet pawl  106  prohibits “creeping” of the tape  32  back into the housing  12  from its extended position by limiting the clockwise rotation of the ratchet gear  58 .  
         [0028]     Referring now to  FIGS. 1 and 2 , the operation of the tape measure  10  will be discussed. The tape is extended by depression of the extension button  52 . Depression of the extension button  52  activates the motor  56  and causes the output axle  68  to rotate in a clockwise direction, as is understood by one of ordinary skill in the art. The clockwise rotation of the output axle  68  causes clockwise rotation of the drive gear  70 . The clockwise rotation of the drive gear  70  causes counter-clockwise rotation of the ratchet gear  58  and, in turn, the transmission axle  72 . The counter-clockwise rotation of the transmission axle  72  rotates the ratchet wheel  60 , which is frictionally engaged with the drive wheel  64 , as seen in  FIG. 2 . The counter-clockwise rotation of the ratchet wheel  60  causes clockwise rotation of the drive wheel  64 , which, in turn, extends the tape  32  from the housing  12 .  
         [0029]     As stated above, the ratchet pawl  106  is biased into contact with the ratchet gear  58  by the torsion spring  112 . Thus, as the ratchet gear  58  rotates in the counter-clockwise direction, the ratchet pawl  106  slides along and abuts the outer periphery of the ratchet gear  58 . However, should the ratchet gear  58  start to rotate in a clockwise direction, which can happen when the tape  32  is extended and the motor  56  is inactive, if the rewind force of the recoil spring  36  is sufficient to overcome the braking force of the motor  56 , the distal end of the ratchet pawl  106  will become engaged in the teeth of the ratchet gear  58 , as illustrated in  FIG. 1 , and prevent further clockwise rotation of the ratchet gear  58 . As such, the ratchet pawl  106  exists to prevent the “creeping” of the tape  32  back into the housing  12  by engaging the ratchet wheel  58  to prevent backward rotation of the drive assembly  16 .  
         [0030]     Intended retraction of the tape  32  will be discussed with reference to  FIGS. 2 and 3 .  FIG. 2  shows the drive wheel  64  engaged with the bottom surface  42  of the tape  32  for extension or holding of the tape  32 .  FIG. 3  shows the drive wheel  64  disengaged from the bottom surface  40  of the tape  32  to permit retraction of the tape  32  within the housing  12 . In order to retract the tape  32  within the housing  12 , the retraction button  54  is depressed. Depression of the retraction button  54  causes the button to contact the upper portion  94  of the member  90  and move the member  90  downwardly. This downward movement of the member  90  causes the lower portion  96  of the member  90  to contact the pin  86 . As shown in  FIG. 3 , contact with the pin  86  causes the swingarms  62  to rotate about the transmission axle  72 . This rotation causes the drive wheel  64  to disengage from the bottom surface  42  of the tape  32  and, thus, the tape  32  is allowed to freely retract within the housing  12  via the recoil spring  36 . To stop retraction, the user simply removes the downward pressure from the retraction button  54 . As shown in  FIG. 3 , once the downward pressure is removed, the compression spring  102  returns the retraction button  52  to its original rest position and the tension spring  104  rotates the drive wheel  64  back into contact with bottom surface  40  of the tape  32 .  
         [0031]     In another aspect, an alternate embodiment of the retraction prevention mechanism  18 A will be discussed. Referring now to  FIGS. 4 and 5 , the retraction prevention mechanism  18 A includes a disc  114  and a ratchet pawl  116 . The disc  114  is coupled to the ratchet wheel  58  via the transmission axle  72 . The disc  114  includes a pair of ears  118  depending therefrom and oriented in opposed relation to one another. The ratchet pawl  116  is pivotably coupled to the protrusion  108 . The ratchet pawl  116  includes a taper  120  at its upper end. The movement of the ratchet pawl  116  away from the ratchet gear  58  is limited by a stop  122 . The stop is a V-shaped protrusion that depends from the lower portion  110  of the inner housing  66 .  
         [0032]     Referring now to  FIGS. 4 and 5 , the operation of the tape measure  10 , specifically the extension and retraction of the tape  32 , for the alternate embodiment is the same as the previous embodiment discussed above. The only difference is the manner in which the retraction prevention mechanism  18 A operates. In this embodiment, the ratchet pawl  116  is not biased into engagement with the ratchet gear  58  as was the pawl  106  of the first embodiment. Instead, the pawl  116  is frictionally mounted to resist rotation by an external force (e.g., the ears  118  or the teeth of the ratchet gear  58 ). Once the force is removed, the pawl will remain in its present location until moved again by an external force. In this embodiment, should the rewind force of the recoil spring  54 , not shown, overcome the braking force of the motor  56 , the clockwise rotation of the ratchet gear  58  and in turn the disc  114 , would cause one of the ears  118  to contact the ratchet pawl  116  and move it into contact with the ratchet gear  58 , thus, preventing further backward movement of the drive assembly  16  and, in turn, unintended retraction of the tape  32 . It should be understood while the ears  118  move the ratchet pawl  116  into blocking engagement with the ratchet gear  58  during retraction, the ears  118  also move the ratchet pawl  116  out of blocking engagement with the ratchet gear  58  during extension and the taper  120  on the ratchet pawl  116  allows the ears  118  to ultimately pass by the ratchet pawl  116  during extension.  
         [0033]     The present invention has been described in relation to particular embodiments, which are intended in all respects to be illustrative rather than restrictive. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its scope.  
         [0034]     From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects set forth above, together with other advantages, which are obvious and inherent to the system and method. It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated and within the scope of the claims.