Abstract:
A dual wheel exposure counter comprising a rotatable tenths counter wheel having a series of at least two spaced units, and a rotatable unit counter wheel having a series of ten spaced units and a rotating member which rotates the tenths counter wheel to change by one unit when the unit counter wheel is rotated to change by ten units, is characterized in that a retaining member engages the tenths counter wheel to prevent rotation of the tenths counter wheel and can be moved temporarily out of engagement with the tenths counter wheel to permit the tenths counter wheel to be rotated to change by one unit, and the unit counter wheel includes an actuating member separate from the rotating member that moves the retaining member temporarily out of engagement with the tenths counter wheel when the unit counter is rotated to change by ten units, whereby the rotating member can then rotate the tenths counter wheel to change by one unit.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to the field of photography, and in particular to a dual wheel type of exposure counter for a camera. 
     BACKGROUND OF THE INVENTION 
     Practically every camera that is available today includes an exposure counter. The exposure counter provides a visible indication of the number of film frames that remain available to be exposed on a filmstrip in the camera, i.e. the current number of exposures that can be made on the filmstrip. Alternatively, the exposure counter can provide a visible indication of the number of film frames actually exposed on the filmstrip, i.e. the number of exposures already made. In either case, the exposure counter includes a numerical scale of successive exposure count indicia that are evenly spaced from one another. The scale of indicia at least range from the number “1” which indicates either that only one frame remains available to be exposed on the filmstrip, or only one frame has been actually exposed, to a higher number which is the maximum number of exposures, for example “15”, “24” or “40”. Each time the filmstrip is advanced one frame increment, the exposure counter undergoes an indicia change equivalent to one frame, which can be one less or one more than the previous number. 
     Early prior art U.S. Pat. No. 1,642,818 issued Sep. 20, 1927 discloses a dual wheel type of exposure counter comprising a count-by-unit counter wheel having ten evenly spaced units and a single actuating pawl, and a count-by-tenths counter wheel having ten evenly spaced units which are the same as the ten units of the unit counter wheel and respective peripheral teeth which correspond to the ten units of the tenths counter wheel. The actuating pawl on the unit counter wheel successively engages the peripheral teeth on the tenths counter wheel to rotate the tenths counter wheel to change by one unit in response to each rotation of the unit counter wheel to change by ten units. The ten units on the unit counter wheel and the ten units on the tenths counter wheel are designated “0”, “1”, “2”, “3”, “4”, “5”, “6”, “7”, “8”, “9” on respective top sides of the two counter wheels. The unit counter wheel is incrementally rotated ten times to move the designations “1”, “2”, “3”, “4”, “5”, “6”, “7”, “8”, “9”, “0” on the unit counter wheel successively into and out of a counter window in the housing of the camera. When the designation “0” on the unit counter wheel is moved into the counter window, following movement of the designation “9” on the unit wheel out of the counter window, the actuating pawl on the unit counter wheel engages one of the peripheral teeth on the tenths counter wheel to incrementally rotate the tenths counter wheel to move one of the designations “0”, “1”, “2”, “3”, “4”, “5”, “6”, “7”, “8” “9” on the tenths counter wheel out of the counter window and move the next higher designation on the tenths counter wheel into the counter window. This can provide a frame count from “01” to “99”, which is particularly useful when a relatively long length of film is used in the camera. However, a possible problem is that the engagement of the actuating pawl on the unit counter wheel with any one of the peripheral teeth on the tenths counter wheel is momentary, rather than continuous. Consequently, when the actuating pawl is not engaged with one of the peripheral teeth, a mechanical shock to the exposure counter, for example should the camera be dropped, could move the tenths counter wheel to be out of count. 
     Later prior art U.S. Pat. No. 5,809,351 issued Sep. 15, 1998 discloses a dual wheel exposure counter comprising a tenths counter wheel having a series of six evenly spaced units and six evenly spaced actuated members, and a unit counter wheel having a series of ten evenly spaced units and a single actuating member which successively actuates the actuated members to rotate the tenths counter wheel to change by one unit in response to each rotation of the unit counter wheel to change by ten units. The six units on the tenths counter wheel are designated “5”, “4”, “3”, “2”, “1”, “0”, and the ten units on the units counter wheel are designated “9”, “8”, “7”, “6”, “5”, “4”, “3”, “2”, “1”, “0”. The unit counter wheel includes an opposed-end concentric channel having an opening between opposite ends of the channel. The single actuating member of the unit counter wheel constitutes a protuberance which is positioned in the opening to leave respective ingress and egress spaces in the opening between the protuberance and the opposite ends of the channel. The actuated members are positioned on the tenths counter wheel for the protuberance to drive one of the actuated members out of the channel through the egress space to rotate the tenths counter wheel to change by one unit and move another of the actuated members into the channel through the ingress space, each time the unit counter wheel is rotated to change by ten units. The fact that one of the actuating members is always in the channel serves to prevent any unintended rotation of the tenths counter wheel with respect to the unit counter wheel. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a dual wheel exposure counter comprising a rotatable tenths counter wheel having a series of at least two spaced units, and a rotatable unit counter wheel having a series of ten spaced units and a rotating member which rotates the tenths counter wheel to change by one unit when the unit counter wheel is rotated to change by ten units, is characterized in that: 
     a retaining member engages the tenths counter wheel to prevent rotation of the tenths counter wheel and can be moved temporarily out of engagement with the tenths counter wheel to permit the tenths counter wheel to be rotated to change by one unit; and 
     the unit counter wheel includes an actuating member separate from the rotating member that moves the retaining member temporarily out of engagement with the tenths counter wheel when the unit counter is rotated to change by ten units, whereby the rotating member can then rotate the tenths counter wheel to change by one unit. 
     According to another aspect of the invention, an exposure counting method for a dual wheel exposure counter comprising a rotatable tenths counter wheel having a series of at least two spaced units, and a rotatable unit counter wheel having a series of ten spaced units and which rotates the tenths counter wheel to change by one unit when the unit counter wheel is rotated to change by ten units, is characterized by the steps of: 
     elastically biasing a retaining member into engagement with the tenths counter wheel to prevent rotation of the tenths counter wheel when the unit counter wheel is rotated to change less than ten units; and 
     moving the retaining member relative to the unit counter wheel to move the retaining member out of engagement with the tenths counter wheel when the unit counter wheel is rotated to change by ten units, to permit the unit counter wheel to then rotate the tenths counter wheel to change by one unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a dual wheel exposure counter which is a preferred embodiment of the invention; 
     FIG. 2 is a top plan view of the dual wheel exposure counter as seen in FIG. 1; and 
     FIGS. 3-5 are top plan views of the dual wheel exposure counter illustrating its operation. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is disclosed as being embodied preferably in a camera. Because the features of a camera are generally known, the description which follows is directed in particular only to those elements forming part of or cooperating directly with the disclosed embodiment. It is to be understood, however, that other elements may take various forms known to a person of ordinary skill in the art. 
     Referring now to the drawings, FIGS. 1 and 2 depict a dual wheel exposure counter  10  preferably for use in a camera, not shown. The exposure counter  10  comprises a rotatable count-by-unit counter wheel  12  having a concentric series of ten evenly spaced consecutive units on its top side  14  and a rotatable count-by-tenths counter wheel  16  having a series of five evenly spaced consecutive units on its top side  18 . The ten consecutive units on the top side  14  of the unit counter wheel  12  are designated “0”, “9”, “8”, “7”, “6”, “5”, “4”, “3”, “2”, “1”. The five consecutive units on the top side  18  of the tenths counter wheel  16  are designated “4”, “3”, “2”, “1”, “0”. 
     The unit counter wheel  12  has a center (central) cavity  20 , and the tenths counter wheel  16  is seated in the cavity to make the two counter wheels have the same axis of rotation  22 . Thus, the unit wheel  12  and the tenths counter wheel  16  are concentric. See FIGS. 1 and 2. 
     The tenths counter wheel  16  has a center (central) opening  24  and an integral elastic cantilever beam  26  that projects into the center opening. The unit counter wheel  12  has an integral center rotation post  28  that projects into the center opening  24  in the tenths counter wheel  16 . The elastic beam  26  presses against the rotation post  28  with a sufficient friction force to make the tenths counter wheel  16  rotate with the unit counter wheel  12  in a clockwise direction  30  in FIGS. 1 and 2 when the tenths counter wheel is not prevented from being rotated in that direction. If the tenths counter wheel  16  is prevented from being rotated in the clockwise direction  30 , the unit counter wheel  12  can rotate relative to the tenths counter wheel because the rotation post  28  will overcome the friction force the elastic beam  26  exerts against it. Thus, the combination of the elastic beam  26  and the rotation post  28  function as what is often referred to as a “friction or slip clutch”. 
     The tenths counter wheel  16  has an integral rib  32  on the top side  18  of the tenths counter wheel that is uniformly curved partially about the rotation post  28  on the unit counter wheel  12 . Five evenly spaced stops  34 ,  36 ,  38 ,  40  and  42  corresponding to the five consecutive units “4”, “3”, “2”, “1”, “0” on the top side  18  of the tenths counter wheel  16  project from the rib  32  to be individually engaged to prevent rotation of the tenths counter wheel with the unit counter wheel  12  in the clockwise direction  30  in FIGS. 1 and 2. A retaining lever  44  is pivotally mounted on a support pin  46  to be urged via a torsion spring  48  to swing (pivot) a retaining finger  50  of the retaining lever against the rib  32 , for the retaining finger to engage any one of the stops  34 ,  36 ,  38 ,  40  and  42  on the rib to prevent rotation of the tenths counter wheel  16  in the clockwise direction  30 . The retaining member is pivotal about a pivot axis  52  that is parallel to the rotation axis  22  of the unit counter wheel  12  and the tenths counter wheel  16 . When the retaining finger  50  is in engagement with any one of the stops  34 ,  36 ,  38 ,  40  and  42 , a corresponding one of the five consecutive units “4”, “3”, “2”, “1”, “0” on the top side  18  of the tenths counter wheel  16  is visible in a known counter window  54  in a housing of the camera. For example, FIGS. 1 and 2 illustrate that when the retaining finger  50  is in engagement with the stop  34 , the unit “4” of the tenths counter wheel  16  is visible in the counter window  54 , and FIGS. 4 and 5 illustrate that when the retaining finger is in engagement with the stop  36 , the unit “3” of the tenths counter wheel is visible in the counter window. At the same time, one of the ten consecutive units “0”, “9”, “8”, “7”, “6”, “5”, “4”, “3”, “2”, “1” on the top side  14  of the unit counter wheel  12  is visible in the counter window  54  to the right of whichever one of the of the five consecutive units “4”, “3”, “2”, “1”, “0” of the tenths counter wheel  16  is visible in the counter window. Thus, FIGS. 1 and 2 show “40” in the counter window  54 , FIG. 4 shows “39” in the counter window, and FIG. 5 shows “38” in the counter window. 
     The unit counter wheel  12  has an integral peripheral actuating member  56  that is radially spaced from the rotation post  28  on the unit counter wheel. Each time the unit counter wheel  12  is rotated in the clockwise direction  30  as shown in FIGS. 3 and 4 to move the unit “0” on the top side  14  of the unit counter wheel out of the counter window  54  and move the unit “9” on the top side of the unit counter wheel into the counter window, the actuating member  56  pivots the retaining lever  44  beginning at a free end  58  of the retaining lever to swing the retaining finger  50  temporarily out of engagement with any one of the stops  34 ,  36 ,  38 ,  40  and  42  on the rib  32  on the top side  18  of the tenths counter wheel  16 . This permits the tenths counter wheel  16  to be temporarily rotated with the unit counter wheel  12  in the clockwise direction  30  as shown in FIGS. 3 and 4, to move one of the units “4”, “3”, “2”, “1”, “0” on the top side  18  of the tenths counter wheel out of the counter window  54  and move the next lower unit into the counter window. When the actuating member  56  departs from the free end  58  of the retaining lever  44 , the spring  48  returns the retaining finger  50  of the retaining lever to the rib  32 . The tenths counter wheel  16  is prevented from rotating with the unit counter wheel  12  in the clockwise direction  30  when as shown in FIG. 4 the next one of the stops  34 ,  36 ,  38 ,  40  and  42  on the rib  32  is moved into engagement with the retaining finger  50 . 
     A known sprocket wheel  60  has eight evenly spaced sprocket teeth  62  successively engageable with a known filmstrip  64  at respective evenly spaced perforations  66  in the filmstrip to rotate the sprocket wheel in a counter-clockwise direction  68  when the filmstrip is advanced a single frame increment in a film advance direction  70  as shown in FIGS. 3 and 4 and in FIG. 5, following each exposure of one frame of the filmstrip in the camera. A pinion  72  coaxially connected via a shaft  74  to the sprocket wheel  60  has successive evenly spaced teeth  76  that engage with respective evenly spaced teeth  78  of the unit counter wheel  12  to incrementally rotate the unit counter wheel in the clockwise direction  30  each time the filmstrip  64  is advanced in the film advance direction  70 . 
     Operation 
     FIGS. 1 and 2 show the unit “4” on the tenths counter wheel  16  and the unit “0” on the unit counter wheel  12  side-by-side in the counter window  54 , This indicates that forty frames on the filmstrip  64  are available for exposure in the camera. 
     After frame number “40” on the filmstrip  64  is exposed in the camera, the filmstrip is advanced a single frame increment in the film advance direction  70  as shown in FIGS. 3 and 4. The sprocket wheel  60  is rotated in the counter-clockwise direction  68  to similarly rotate the pinion  72 , to in turn incrementally rotate the unit counter wheel  12  in the clockwise direction  30  in FIGS. 3 and 4. 
     When the unit counter wheel  12  is rotated in the clockwise direction  30  as shown in FIGS. 3 and 4, the unit “0” on the top side  14  of the unit counter wheel is moved out of the counter window  54  and the unit “9” on the top side of the unit counter wheel is moved into the counter window. The actuating member  56  on the unit counter wheel  12  pivots the retaining lever  44  beginning at the free end  58  of the retaining lever to swing the retaining finger  50  temporarily out of engagement with the stop  34  on the rib  32  on the top side  18  of the tenths counter wheel  16 . This permits the tenths counter wheel  16  to be temporarily rotated with the unit counter wheel  12  in the clockwise direction  30  as shown in FIGS. 3 and 4, to move the unit “4” on the top side  18  of the tenths counter wheel out of the counter window  54  and move the next lower unit “3” into the counter window. When the actuating member  56  departs from the free end  58  of the retaining lever  44 , the spring  48  returns the retaining finger  50  of the retaining lever to the rib  32 . The tenths counter wheel  16  is prevented from rotating with the unit counter wheel  12  in the clockwise direction  30  when as shown in FIG. 4 the next stop  36  on the rib  32  is moved into engagement with the retaining finger  50 . At this time, the filmstrip  64  has been advanced a single frame increment in the film advance direction  70  and therefore its movement is ended. 
     FIG. 4 shows the unit “3” on the tenths counter wheel  16  and the unit “9” on the unit counter wheel  12  side-by-side in the counter window  54 , This indicates that thirty-nine frames on the filmstrip  64  are available for exposure in the camera. 
     Next, after frame number “39” on the filmstrip  64  is exposed in the camera, the filmstrip is advanced a single frame increment in the film advance direction  70  as shown in FIG.  5 . The sprocket wheel  60  is rotated in the counter-clockwise direction  68  to similarly rotate the pinion  72 , to in turn incrementally rotate the unit counter wheel  12  in the clockwise direction  30  in FIG.  5 . Since the actuating member  56  on the unit counter wheel  12  is out of range to pivot the retaining lever  44  to swing the retaining finger  50  temporarily out of engagement with the stop  36  on the rib  32  on the top side  18  of the tenths counter wheel  16 , the tenths counter wheel  16  is prevented from rotating with the unit counter wheel  12  in the clockwise direction  30  in FIG.  5 . Thus, the unit “3” on the top side  18  of the tenths counter wheel  16  remains in the counter window  54 , and the unit “9” on the top side  14  of the unit counter wheel  12  is replaced in the counter window with the next lower unit “8”. 
     The invention has been described with reference to a preferred embodiment. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention. For example, instead of there being five consecutive units “4”, “3”, “2”, “1”, “0” on the top side  18  of the tenths counter wheel  16 , there can be more or less unit. 
     Parts List 
       10 . dual wheel exposure counter 
       12 . unit counter wheel 
       14 . top side 
       16 . tenths counter wheel 
       18 . top side 
       20 . center cavity 
       22 . rotation axis 
       24 . center opening 
       26 . elastic beam 
       28 . rotation post 
       30 . clockwise direction 
       32 . rib 
       34 . stop 
       36 . stop 
       38 . stop 
       40 . stop 
       42 . stop 
       44 . retaining lever 
       46 . support pin 
       48 . torsion spring 
       50 . retaining finger 
       52 . pivot axis 
       54 . counter window 
       56 . actuating member 
       58 . free end 
       60 . sprocket wheel 
       62 . sprocket teeth 
       64 . filmstrip 
       66 . perforations 
       68 . counter-clockwise direction 
       70 . film advance direction 
       72 . pinion 
       74 . shaft 
       76 . teeth 
       78 . teeth