Abstract:
A stepper motor includes the following. A rotatable hub. A first shaped memory alloy (abbreviated to SMA) rotary-driver, which when heated undergoes a shape change to rotationally couple with the hub and rotate the hub in a predetermined direction, and which can be deformed to reverse the shape change to rotationally uncouple from the hub. A first return spring connected with the first SMA rotary-driver for deforming the first SMA rotary-driver, when no longer heated, to reverse the shape change of the first SMA rotary-driver and rotationally uncouple the first SMA rotary driver from the hub. A second SMA rotary-driver, which when heated undergoes a shape change to rotationally couple with the hub and rotate the hub in the predetermined direction, and which when can be deformed to reverse the shape change to rotationally uncouple from the hub. A second return spring connected with the second SMA rotary-driver for deforming the second SMA rotary-driver, when no longer heated, to reverse the shape change of the second SMA rotary-driver and rotationally uncouple the second SMA rotary-driver from the hub. A control device for heating the first and second SMA rotary-drivers in succession and only one at a time. Thus, the first and second SMA rotary-drivers can take turns to stepwise rotate the hub in the predetermined direction.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to the field of photography, and in particular to motors for cameras such as used for film winding purposes. More specifically, the invention relates to a stepper motor with a shaped memory alloy rotary-driver. 
     BACKGROUND OF THE INVENTION 
     Prior art U.S. Pat. No. 5,279,123 mentions that shaped memory alloy (abbreviated to SMA) devices are well known in the art to undergo a martensitic (diffusionless) transition dependent upon the temperature applied to the SMA device. The SMA device when heated above its transition temperature undergoes a shape change to a memorized shape and when cooled below its transition temperature reverses the shape change from the memorized shape to an original shape. This change in shape can be used to provide mechanical work. 
     Often, as disclosed in prior art U.S. Pat. No. 5,459,544 issued Oct. 17, 1995, the SMA device is a metallic wire. When electrical current is applied to lead wires connected to opposite ends of the SMA wire, the SMA wire is heated to due to electrical resistance and it shrinks or contacts, i.e. recovers, to a memorized shape. When the electrical current is cut, the SMA wire cools to extend, i.e. deform, to an original shape. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a stepper motor comprises: 
     a rotatable hub; 
     a first shaped memory alloy (abbreviated to SMA) rotary-driver, which when heated undergoes a shape change to rotationally couple with the hub and rotate the hub in a predetermined direction, and which can be deformed to reverse the shape change to rotationally uncouple from the hub; 
     a first return spring connected with the first SMA rotary-driver for deforming the first SMA rotary-driver, when no longer heated, to reverse the shape change of the first SMA rotary-driver and rotationally uncouple the first SMA rotary driver from the hub; 
     a second SMA rotary-driver, which when heated undergoes a shape change to rotationally couple with the hub and rotate the hub in the predetermined direction, and which when can be deformed to reverse the shape change to rotationally uncouple from the hub; 
     a second return spring connected with the second SMA rotary-driver for deforming the second SMA rotary-driver, when no longer heated, to reverse the shape change of the second SMA rotary-driver and rotationally uncouple the second SMA rotary-driver from the hub; and 
     a control device for heating the first and second SMA rotary-drivers in succession and only one at a time, whereby the first and second SMA rotary-drivers can take turns to stepwise rotate the hub in the predetermined direction. 
     According to another aspect of the invention, a method of rotating a film spool in a film winding direction in a camera comprises the steps: 
     heating a first shaped memory alloy (abbreviated to SMA) rotary-driver to undergo a shape change, which rotationally couples the first SMA rotary-driver with the film spool and rotates the film spool a predetermined angle in the film winding direction; 
     discontinuing heating the first SMA rotary-driver to allow a first return spring to reverse the shape change of the first SMA rotary-driver, which rotationally uncouples the first SMA rotary-driver from the film spool; 
     heating a second shaped memory alloy (abbreviated to SMA) rotary-driver to undergo a shape change, which rotationally couples the second SMA rotary-driver with the film spool and rotates the film spool the predetermined angle in the film winding direction, ; and 
     discontinuing heating the first SMA rotary-driver to allow a first return spring to reverse the shape change of the first SMA rotary-driver, which rotationally uncouples the first SMA rotary-driver from the film spool. 
     According to another aspect of the invention, a motorized camera comprises: 
     a main body part including a chamber for a film spool having an engageable end portion; 
     a driven hub rotatable in a film winding direction, longitudinally extending into the chamber, and configured to coaxially engage the engageable end portion of the film spool in the chamber to rotate the film spool in the film winding direction; 
     a first drive ring which encircles the hub, is rotatable in the film winding direction to coaxial engage with the hub and rotate the hub in the film winding direction, and is rotatable in a reverse direction to disengage from the hub; 
     a first shaped memory alloy (abbreviated to SMA) rotary-driver having one end connected to the first drive ring and another end fixed to the main body part, which when heated undergoes a shape change to rotate the first drive ring in the film winding direction, and which can be deformed to reverse the shape change; 
     a first return spring having one end fixed to the main body part and another end connected with the first drive ring to rotate the first drive ring in the reverse direction to deform the first SMA rotary-driver, when no longer heated, to reverse the shape change of the first SMA rotary-driver; 
     a second drive ring which encircles the hub, is rotatable in the film winding direction to coaxial engage with the hub and rotate the hub in the film winding direction, and is rotatable in the reverse direction to disengage from the hub; 
     a second SMA rotary-driver having one end connected to the second drive ring and another end fixed to the main body part, which when heated undergoes a shape change to rotate the second drive ring in the film winding direction, and which can be deformed to reverse the shape change; 
     a second return spring having one end fixed to the main body part and another end connected with the second drive ring to rotate the second drive ring in the reverse direction to deform the second SMA rotary-driver, when no longer heated, to reverse the shape change of the second SMA rotary-driver; and 
     a control device for heating the first and second SMA rotary-drivers in succession and only one at a time, whereby the first and second SMA rotary-drivers can take turns to stepwise rotate the hub in the film winding direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded front bottom perspective view of a motorized camera which includes a stepper motor with a shaped memory alloy (abbreviated to SMA) rotary-driver for film winding, in a preferred embodiment of the invention; 
     FIG. 2 is an exploded rear bottom perspective of the motorized camera; 
     FIG. 3 is an assembled front bottom perspective view of the motorized camera; 
     FIG. 4 is an assembled rear bottom perspective view of the motorized camera; 
     FIG. 5 is an exploded front bottom perspective view of the stepper motor; 
     FIGS. 6,  7 ,  8  and  9  are exploded views similar to FIG. 5, showing sequential steps in the operation of the stepper motor; and 
     FIG. 10 is a schematic diagram depicting a control device for the stepper motor. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is disclosed as being embodied preferably in a motorized camera. Because the features of a motorized 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. 1-4 partially show a motorized camera  10  including a main body part  12 . The main body part  12  as seen in FIG. 2 has a rearwardly open cartridge receiving chamber  14  for a conventional film cartridge  16  with a filmstrip  18 , a rearwardly open backframe opening  20  at which successive sections of the filmstrip are exposed, and a rearwardly exposed film take-up chamber  22  that contains a film take-up spool  24  for winding the exposed film sections into an exposed film roll  26 . Front and rear cover parts for the main body part  12 , and a film door for closing the cartridge receiving chamber  14 , are not shown. As is typical, the film cartridge  16  includes a cartridge film spool having an accessible spool end  28  which may be engaged within a center opening  30  in the accessible spool end to rotate the cartridge spool in a film winding direction  32 . This is done to wind the exposed film into the film cartridge  16 . 
     A driven hub or spindle  34 , rotatable in the film winding direction  32 , longitudinally extends through an ingress hole  36  in the main body part  12  and into the cartridge receiving chamber  14 . See FIGS. 1-4. This allows a forked free end  38  of the hub  34  to be located within the center opening  30  in the accessible spool end  28  of the cartridge spool, to coaxially engage the cartridge spool in order to rotate the cartridge spool in the film winding direction  32 . 
     First, second, third and fourth identical drive rings  40 ,  42 ,  44  and  46  (having the same diameter) are compactly stacked parallel and adjacent to one another, encircling the hub  34 , and supported for rotation in the film winding direction  32  and a reverse direction  48  at a nest or cavity  50  in the main body part  12 . See FIGS. 1-5. The hub  34  includes a known ratchet  52  having a circular (continuous) array of identical peripheral teeth  54  which are similarly inclined to allow them to be individually engaged to rotate the hub only in the film winding direction  32 . The first, second, third and fourth drive rings  40 ,  42 ,  44  and  46  each have a pair of identical inner teeth  56  spaced 180° apart for separately engaging any two of the peripheral teeth  54  spaced 180° apart on the ratchet  52 , to coaxially engage any one of the drive rings with the hub when any one of the drive rings is rotated in the film winding direction  32 . The inner teeth  56  of the respective drive rings  40 ,  42 ,  44  and  46  are flexible to be bent out of engagement with the peripheral teeth  54  of the ratchet  52  when any one of the drive rings is rotated in the reverse direction  48 , and they are resilient to resume their original shape when disengaged from the peripheral teeth of the ratchet. 
     First, second, third and fourth identical shaped memory alloy (abbreviated to SMA) rotary-drivers  58 ,  60 ,  62  and  64  each have one of their ends  66  connected to the respective drive rings  40 ,  42 ,  44  and  46  at individual peripheral fasteners  68  on the drive rings and another of their ends  70  fixed to the main body part  12  within individual slots  72  in the main body part. See FIGS. 1,  2  and  5 . The first, second, third and fourth SMA rotary-drivers  58 ,  60 ,  62  and  64  are evenly spaced 45° apart about the hub  34  and are similarly curved generally in a c-configuration to individually contract (recover) curvewise when heated to undergo a shape change to a memory shape, and they can individually expand (deform) curvewise when no longer heated to reverse the shape change. This is shown in FIGS. 5-9. When the first, second, third and fourth SMA rotary-drivers  58 ,  60 ,  62  and  64  are successively contracted curvewise as shown in FIGS. 6-9, they successively rotate the respective drive rings  40 ,  42 ,  44  and  46  an angle of 45° in the film winding direction  32  to rotate the hub  34  a total of 180° in the same direction. Conversely, when the first, second, third and fourth SMA rotary-drivers  58 ,  60 ,  62  and  64  are individually expanded curvewise as shown in FIGS. 7-9 and  5 , the respective drive rings  40 ,  42 ,  44  and  46  are successively rotated an angle of 45° in the reverse direction  48  without similarly rotating the hub  34  (because the inner teeth  56  of the respective drive rings are bent out of engagement with the peripheral teeth  54  of the ratchet  52 ). 
     First, second, third and fourth identical return springs  74 ,  76 ,  78  and  80  each have one of their ends  82  connected to the respective drive rings  40 ,  42 ,  44  and  46  within individual peripheral holes  84  in the drive rings and another of their ends  86  fixed to the main body part  12  within individual slots  88  in the main body part. See FIGS. 1,  2  and  5 . The first, second, third and fourth return springs  74 ,  76 ,  78  and  80  are evenly spaced 45° apart from one another about the hub  34  and are similarly curved generally in a c-configuration to individually be distorted curvewise from an original shape when the respective SMA rotary-drivers  58 ,  60 ,  62  and  64  contract curvewise due to being heated, and they can individually recover curvewise back to their original shape to reverse the shape change of the respective SMA rotary-drivers when the respective SMA rotary-drivers are no longer heated. This is shown in FIGS. 5-9. When the first, second, third and fourth SMA rotary-drivers  58 ,  60 ,  62  and  64  are successively heated they contract curvewise as shown in FIGS. 6-9 to successively rotate the respective drive rings  40 ,  42 ,  44  and  46  an angle of 45° in the film winding direction  32 . The successive rotation of the respective drive rings  40 ,  42 ,  44  and  46  in the film winding direction  32  successively deforms the first, second, third and fourth return springs  74 ,  76 ,  78  and  80  curvewise from their original shape. Conversely, when the first, second, third and fourth SMA rotary-drivers  58 ,  60 ,  62  and  64  are successively no longer heated, the first, second, third and fourth return springs  74 ,  76 ,  78  and  80  successively contract curvewise as shown in FIGS. 7-9 and  5 , and they successively rotate the respective drive rings  40 ,  42 ,  44  and  46  an angle of 45° in the reverse direction  48 . The successive rotation of the respective drive rings  40 ,  42 ,  44  and  46  in the reverse direction  48  reverses the shape change of the respective SMA rotary-drivers  58 ,  60 ,  62  and  64 . 
     As shown in FIG. 10, a control device  90  for heating the first, second, third and fourth SMA rotary-drivers  58 ,  60 ,  62  and  64  in succession and only one at a time includes a known current supply  92  for supplying electrical current to the respective SMA rotary-drivers to heat the respective SMA rotary-drivers, first, second, third and fourth normally open switches  94 ,  96 ,  98  and  100  which when individually closed connect the current supply to individual pairs of wire leads  102  and  104  to the respective SMA rotary -rivers and when individually re-opened disconnect the current supply from the respective SMA rotary-drivers, a known exposure counter  106  for indicating that a last available exposure has been made, a known timer  108  for indicating each time a predetermined time interval has elapsed, a known film presence sensor  110  for indicating that the filmstrip  18  is completely wound into the film cartridge  16 , and a known logic control  112  connected to the exposure counter and the timer for closing and re-opening the respective switches to supply electrical current from the current supply to the respective SMA rotary-drivers in succession and only one at a time beginning with the exposure counter indicating that the last available exposure has been made and ending with the film presence sensor indicating that the filmstrip is completely wound into the film cartridge, and in accordance with each time the timer indicates that the predetermined time interval has elapsed. 
     Operation 
     When the exposure counter  106  indicates to the logic control  112  that the last available exposure has been made, the logic control activates the timer  108  and simultaneously closes the first switch  94 . Closing the first switch  94  connects the current supply  92  to the first SMA rotary-driver  58  to heat the first SMA rotary-driver. The first SMA rotary diver  58  when heated is contracted curvewise to undergo its shape change to the memory shape, which rotates the first drive ring  40  an angle of 45° in the film winding direction  32  to similarly rotate the hub  34  and to distort the first return spring  74  curvewise from its original shape. This is shown in FIG.  6 . 
     As the first drive ring  40  completes its rotation of 45°, the timer  108  indicates to the logic control  112  that the predetermined time interval has elapsed. The logic control  112  then closes the second switch  96  and re-opens the first switch  94 . Re-opening the first switch  94  disconnects the current supply  92  to the first SMA rotary-driver  58 , which ends heat to the first SMA rotary-driver and allows the first return spring  74  to contract curvewise to its original shape to rotate the first drive ring  40  an angle of 45° in the reverse direction  48  to reverse the shape change of the first SMA rotary-driver  58 . This is shown in FIG.  7 . Closing the second switch  96  connects the current supply  92  to the second SMA rotary-driver  60  to heat the second SMA rotary-driver. The second SMA rotary-driver  60  when heated is contracted curvewise to undergo its shape change, which rotates the second drive ring  42  an angle of 45° in the film winding direction  32  to similarly rotate the hub  34  and to distort the second return spring  76  curvewise from its original shape. This is shown in FIG.  7 . 
     As the second drive ring  42  completes its rotation of 45°, the timer  108  indicates to the logic control  112  that the predetermined time interval has elapsed. The logic control  112  then closes the third switch  98  and re-opens the second switch  96 . Re-opening the second switch  96  disconnects the current supply  92  to the second SMA rotary diver  60 , which ends heat to the second SMA rotary-driver and allows the second return spring  76  to contract curvewise to its original shape to rotate the second drive ring  42  an angle of 45° in the reverse direction  48  to reverse the shape change of the second SMA rotary-driver  60 . This is shown in FIG.  8 . Closing the third switch  98  connects the current supply  92  to the third SMA rotary-driver  62  to heat the third SMA rotary-driver. The third SMA rotary-driver  62  when heated is contracted curvewise to undergo its shape change, which rotates the third drive ring  44  an angle of 45° in the film winding direction  32  to similarly rotate the hub  34  and to distort the third return spring  78  curvewise from its original shape. This is shown in FIG.  8 . 
     As the third drive ring  44  completes its rotation of 45°, the timer  108  indicates to the logic control  112  that the predetermined time interval has elapsed. The logic control  112  then closes the fourth switch  100  and re-opens the third switch  98 . Re-opening the third switch  98  disconnects the current supply  92  to the third SMA rotary-driver  62 , which ends heat to the third SMA rotary-driver and allows the third return spring  78  to contract curvewise to its original shape to rotate the third drive ring  44  an angle of 45° in the reverse direction  48  to reverse the shape change of the third SMA rotary-driver  62 . This is shown in FIG.  9 . Closing the fourth switch  100  connects the current supply  92  to the fourth SMA rotary diver  64  to heat the fourth SMA rotary-driver. The fourth SMA rotary-driver  64  when heated is contracted curvewise to undergo its shape change, which rotates the fourth drive ring  46  an angle of 45° in the film winding direction  32  to similarly rotate the hub  34  and to distort the fourth return spring  80  curvewise from its original shape. This is shown in FIG.  9 . 
     As the fourth drive ring  46  completes its rotation of 45°, the timer  108  indicates to the logic control  112  that the predetermined time interval has elapsed. The logic control  112  then closes the first switch  94  and re-opens the fourth switch  100 . Re-opening the fourth switch  100  disconnects the current supply  92  to the fourth SMA rotary-driver  64 , which ends heat to the fourth SMA rotary-driver and allows the fourth return spring  80  to contract curvewise to its original shape to rotate the fourth drive ring  46  an angle of 45° in the reverse direction  48  to reverse the shape change of the fourth SMA rotary-driver  64 . Closing the first switch  94  connects the current supply  92  to the first SMA rotary-driver  58  to heat the first SMA rotary-driver. The first SMA rotary-driver  58  when heated is contracted curvewise to undergo its shape change, which rotates the first drive ring  40  an angle of 45° in the film winding direction  32  to similarly rotate the hub  34  and to distort the first return spring  74  curvewise from its original shape. This is shown in FIG.  6 . 
     This cycle is concluded after the film presence sensor  110  indicates to the logic control  112  that the filmstrip  18  is completely wound into the film cartridge  16 . 
     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, any number (at least two) of drive rings SMA rotary drivers, and return springs may be used. Also, the hub  34  may be used for any manner of film winding, i.e. it is not limited to winding the filmstrip  19  into the film cartridge  16 . 
     PARTS LIST 
       10 . motorized camera 
       12 . main body part 
       14 . cartridge receiving chamber 
       16 . film cartridge 
       18 . filmstrip 
       20 . backframe opening 
       22 . exposed film take-up chamber 
       24 . film take-up spool 
       26 . exposed fihn roll 
       28 . accessible spool end 
       30 . center opening 
       32 . film winding direction 
       34 . hub 
       36 . ingress hole 
       38 . forked free end 
       40 . first drive ring 
       42 . second drive ring 
       44 . third drive ring 
       46 . fourth drive ring 
       48 . reverse direction 
       50 . nest 
       52 . ratchet 
       54 . peripheral teeth 
       56 . inner teeth 
       58 . first SMA rotary-driver 
       60 . second SMA rotary-driver 
       62 . third SMA rotary-driver 
       64 . fourth SMA rotary-driver 
       66 . driver ends 
       68 . fasteners 
       70 . driver ends 
       72 . slots 
       74 . first return spring 
       76 . second return spring 
       78 . third return spring 
       80 . fourth return spring 
       82 . spring ends 
       84 . holes 
       86 . spring ends 
       88 . slots 
       90 . control device 
       92 . current supply 
       94 . first switch 
       96 . second switch 
       98 . third switch 
       100 . fourth switch 
       102 . wire leads 
       104 . wire leads 
       106 . exposure counter 
       108 , timer 
       110 . film presence sensor 
       112 . logic control