Abstract:
A scanning system and method of data reading in which the scanning system is provided with a dithering assembly that is compact, easy to assemble, and configured to protect the more delicate scanning components, such as flexures, from damage due to external mechanical shock. In a preferred construction, the dithering assembly includes a dither mount and a mirror mount, each mount having an arm adapted to matingly engage one another. In particular, the dither mount arm may include a socket configured to receive a ball member protruding from the mirror mount arm.

Description:
BACKGROUND 
     The field of the present invention relates to optical systems for data reading and particularly to a scanning system having improved resistance to shock and vibration. 
     Typically, a data reading device such as a bar code scanner illuminates a bar code and senses light reflected from the code to detect the bars and spaces of the code symbols and thereby derive the encoded data. In a common system, the scanner includes a housing and a scan module comprising a light source, one or more scanning mechanisms, a detector, and optics and signal processing circuitry. 
     A variety of scan modules and their scanning mechanisms are known as described in, for example, U.S. Pat. Nos. 5,475,206 and 5,629,510 or U.S. application Ser. No. 08/934,487, each of these disclosures hereby incorporated by reference. Such scanning mechanisms typically comprise rotating polygon mirror assemblies and dithering or oscillating mirror assemblies. Dithering assemblies typically comprise a cantilevered mirror and a drive means or dithering motor for moving the mirror. 
     FIG. 1 illustrates a dithering assembly  100  comprising a mirror/magnet assembly  110 , drive coil  106 , feedback coil  108 , bending member or flexure  112 , and mounting member  114 . The mounting member  114  is mounted to a suitable chassis (not shown). The mirror/magnet assembly comprises mirror  102 , mirror bracket  103 , drive magnet  104 , and feedback magnet  105 . The bracket  103  holds mirror  102  and is pivotally supported on the mounting member  114  via flexure  112 . Bending of flexure  112  results in rotation of the mirror/magnet assembly  110  about an axis substantially parallel to mirror  102 , perpendicular to the plane of FIG.  1 . 
     Due to the cantilevered ditherer configuration and the sensitive components used to construct the scanner, current scanners are relatively sensitive to shock and are often damaged before they would have worn out for other reasons. Handheld scanners are particularly subjected to shock and have been equipped with shock protection such as by mounting the scan module to the interior of the housing body via shock mounts as described in U.S. Pat. No. 5,475,206. 
     Other shock protection includes a pin-in-hole arrangement that typically comprises a moving pin associated with the cantilevered mirror, and a stationary hole associated with the support structure (e.g., the chassis). Since during dithering (rotating) operation, there is no lateral motion of the pin within the hole, the required clearance inside the stationary hole need only be sufficient to accommodate process and temperature variations. 
     While the pin-in-hole arrangement may protect the flexure from yielding during overflexure or buckling, its assembly is often difficult. Assembly can be made easier by increasing the diameter of the hole. However, a larger hole diameter affords less protection against higher shock levels when compared to the level of protection afforded by a smaller hole diameter. Furthermore, once the pin is properly positioned inside the hole, should the level of shock protection need to be changed, the hole diameter itself must be changed. 
     In an attempt to overcome some of the problems inherent with the pin-in-hole arrangement, dithering assemblies have been equipped with shock mounts. Mounting the flexure to the mounting member via shock mounts, as described in, for example, U.S. Application entitled “FLEXIBLE DITHER MOUNT WITH ROTATION,” Svetal et al., filed Sep. 3, 1998 with Express Mail Label No. EM351172541US, hereby incorporated by reference, advantageously permits the diameter of the stationary hole to be larger than the diameter would be without the shock mounts. However, this design may increase manufacturing costs as well as the overall size of the scanning mechanism. Having recognized these conditions, an improved scanning system resistant to shock and vibration is desired. 
     SUMMARY OF THE INVENTION 
     To these ends, the present invention is directed to a scan module and scanning mechanism including a dithering assembly that is compact, easy to assemble, and configured to protect the more delicate scanning components, such as flexures, from damage due to external mechanical shock. In a preferred construction, the dithering assembly includes a dither mount and a mirror mount, each mount having an arm adapted to matingly engage one another. In particular, the dither mount arm may include a socket configured to receive a boss of the mirror mount arm. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of a previous dithering assembly comprising a cantilevered mirror and a dithering motor for moving the mirror; 
     FIG. 2 is a side view of a handheld scanner as may be utilized by a preferred embodiment; 
     FIG. 3 is a diagrammatic side view of an example scan module; 
     FIG. 4 is a top view of a dither scanning mechanism according to a preferred embodiment; 
     FIG. 5 is a cross-sectional view of the dither scanning mechanism taken along line  5 — 5  of FIG. 4; 
     FIG. 6 is a detailed top view of the boss and socket configuration of FIG. 4; 
     FIG. 7 is a perspective view of a dither scanning mechanism according to another preferred embodiment; and 
     FIG. 8 is a detailed perspective view of the dither scanning mechanism of FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiments will now be described with reference to the drawings. For clarity of description, any element numeral in one figure will represent the same element if used in any other figure. 
     FIGS. 2-3 illustrate an example of a bar code reader  10  configured as a handheld gun-shaped device constructed of a lightweight plastic housing having a head portion  12  and pistol-grip type handle portion  14 . The head portion  12  contains a removable scan module or assembly  50  that contains a light source, a detector, and the optics and signal processing circuitry. 
     The scan assembly  50  may also include one or more scanning mechanisms, as shown for example in FIG. 2 as a first dithering mirror assembly  56  and a second rotating polygon mirror assembly  54  driven by motor coils  53 . The light source of the scan assembly  50  typically includes a laser diode  52  producing a light beam  55  which is scanned by one or more mirror assemblies  54 ,  56  and then exits the window  18 . The components may be mounted to a suitable chassis and contained within an enclosure the sides of which may be part of the chassis or integrated into printed circuit boards  60 ,  62 ,  66 . 
     The scanner  10  may be attached to a host  5  via a cable  20 , connected or incorporated into a portable data terminal, or may be cordless, powered by an internal battery, communicating with the host via wireless link or storing data in memory for periodic download, such as when integrated in a portable data terminal. A light-transmissive window  18  in the front end of the scan head portion  12  permits outgoing light beam  55  to exit and the incoming reflected light to enter. The user aims the reader  10  at a bar code symbol and actuates a trigger  16  on the handle portion  14  to activate the light source and scanning mechanism to scan the beam  55  across the bar code symbols. 
     FIGS. 4-6 illustrate a dithering mirror assembly  200  according to a first preferred embodiment. The dithering assembly  200  includes a mounting member or dither mount  202  mounted to a suitable chassis or housing member  204 . A bending member or flexure  208  has a support or fixed end attached to the dither mount  202  and a free or movable end attached to a mirror bracket or mirror mount  206 . A mirror  212  is mounted to the mirror mount  206  and supported by the flexure  208  in a cantilevered fashion so as to pivot about a center of rotation or pivot point  210 . 
     The mirror  212  is oscillated or dithered about pivot point  210  via dithering motor  218 . While the dithering motor  218  may comprise an array of different components and configurations such as for example those described in U.S. application Ser. No. 60/026,536, incorporated herein by reference, FIGS. 4-6 illustrate a dithering motor  218  that includes permanent magnets  220 ,  221  disposed on opposite sides of the mirror  212 . Electromagnetic drive coils  222 ,  223  as controlled by a suitable controller drive the permanent magnets. When engaged, the dithering motor  218  bends flexure  208 , resulting in rotation of the mirror  212  about an axis substantially parallel to the mirror  212 , perpendicular to the plane of FIG.  4 . 
     Turning in detail to FIGS. 4-6, the mirror mount  206  is substantially U-shaped in cross-section as defined by a pair of opposing arms  206   a ,  206   b  joined together at one end via a straight section  206   c . The mirror  212  is mounted to the straight section  206   c  on the exterior of the mirror mount  206  opposite arms  206   a ,  206   b.    
     Each arm  206   a ,  206   b  may include a boss. FIGS. 4-6 illustrate two preferred embodiments of bosses  214 ,  215  respectively associated with arms  206   a ,  206   b . Referring to arm  206   a , boss  214  may include an optional raised section  214   a  and a protruding section or ball member  214   b . If used, the raised section  214   a , orthogonally extending away from arm  206   a , provides additional rigidity and/or structural integrity to arm  206   a . Such additional structural support may be advantageous in countering gravitational forces. Ball member  214   b  extends away from and parallel to arm  206   a . Raised section  214   a  originates from the juncture of arm  206   a  and straight section  206   c , and runs along the entire length of arm  206   a  and ball member  214   b . As seen from the top in FIG. 4, the raised section  214   a  is substantially rectangular until a point near the end opposite the straight section  206   c . Here, the raised section  214   a  is substantially elliptical in order to correspond to the dimensions of ball member  214   b . When viewed from the top as shown in FIG. 4, the boss  214 , in its entirety, has a shape reminiscent of a thermometer. 
     Referring to arm  206   b , while boss  215  may include a raised section, FIG. 5 illustrates boss  215  as including only a protruding section or ball member  215   b . The ball member  215   b  extends away from and parallel to arm  206   b , in the same manner ball member  214   b  extends away from and parallel to arm  206   a . Ball member  215   b  also has a substantially elliptical shape, in the same manner as ball member  214   b.    
     Similar to the mirror mount  206 , the dither mount  202  includes a pair of opposing arms  202   a ,  202   b . As illustrated in FIG. 5, a bracket section  202   c  joins together one end of each of the mount arms  202   a ,  202   b . Opposite the bracket section  202   c , each mount arm  202   a ,  202   b  includes a trough or socket. Mount arm  202   a  includes socket  217 , whereas mount arm  202   b  includes socket  216 . Arcuate sidewalls  217   b  and, optionally, floor  217   a  define socket member  217 . While floor  217   a  provides no additional structural advantages, tooling of socket  217  is made easier if floor  217   a  is used to help define socket  217 . Sidewalls  217   b  are dimensioned to matingly engage ball member  214   b.    
     In the same manner as socket  217 , arcuate sidewalls  216   b  and, optionally, floor  216   a  may define socket  216 . While floor  216   a  provides no additional structural advantages, tooling of socket  216  is made easier if floor  216   a  is used to help define socket  216 . Sidewalls  216   b  are dimensioned to matingly engage ball member  215   b  of boss  215 . 
     When viewed in cross-section as shown in FIG. 5, each trough  216 ,  217  is substantially L-shaped. Each ball member  214   b ,  215   b  and socket  217 ,  216 , respectively work together to limit the deflection of the flexure  208  from overflexing or buckling when the dithering assembly  200  is subjected to an external shock or vibration. Since the flexure  208  is most likely to yield during buckling, the present invention allows for a small amount of deflection in buckling and a larger amount of deflection in bending. No protection is provided for in tension, as none is needed. 
     In particular, should the dithering assembly  200  be subjected to a front or buckling load B 1 , the flexure  208  will buckle and close the buckling gap G 1  between the ball members  214   b ,  215   b  and sockets  217 ,  216 . When the ball members  214   b ,  215   b  and sockets  217 ,  216  make contact, the flexure  208  is protected from further deformation, and possible yielding. Should the dithering assembly  200  be subjected to a side or bending load B 2 , the walls  216   b ,  217   b  defining the sockets  216 ,  217  wrap around the ball members  215   b ,  214   b  at the center of rotation  210  of the ditherer such that the walls  216   b ,  217   b  act as a side stop to limit travel of the ball members  215   b ,  214   b  within the sockets  216 ,  217 . In this manner, the flexure  208  is allowed to deflect during bending and close bending gap G 2  between ball members  214   b ,  215   b  and sidewalls  217   b ,  216   b , without overflexure of flexure  208  to the point of yielding. 
     Advantageously, such a pinless design only protects the flexure  208  in the directions that need protection, without overconstraining the dithering movement. Moreover, this embodiment minimizes manufacturing tolerances. In particular, as the flexure  208  is mounted between the mirror mount  206  and the dither mount  202 , and the bosses  214 ,  215  and sockets  217 ,  216  are located on the respective arms  206   a ,  206   b ,  202   a ,  202   b  thereof, small tolerances are easily achieved. For example, G 1  is presently a distance of approximately 0.003″. With small tolerances, the buckling gap G 1  can be reduced which improves shock protection. In addition, small tolerances keep the overall size of the dithering assembly  200  small. Further, the present invention obviates the manufacturing step of positioning a pin in a hole, or shock mounting the fixed side of the flexure  208 . Accordingly, such a pinless ditherer design also makes assembly easier, less complicated, and less costly. 
     FIGS. 7-8 illustrate a dithering mirror assembly  200  according to another preferred embodiment. This preferred embodiment is identical in all respects to the preferred embodiment illustrated in FIGS. 4-6, except for the different configuration of the boss  214  of arm  206   a . In particular, as shown in FIGS. 7-8, this boss  214  may optionally include a raised section  214   a . However, raised section  214   a  does not originate from the juncture of arm  206   a  and straight section  206   c  as it did in the earlier preferred embodiment illustrated in FIGS. 4-6. Rather, raised section  214   a  only extends away from arm  206   a  at a point near the end opposite the straight section  206   c  and from the top of ball member  214   b . The perspective views of FIGS. 7 and 8 illustrate the boss  214  of this embodiment to be substantially elliptical. While raised section  214   a  of boss  214  of this embodiment should offer more strength/reinforcement to arm  206   a  than an arm  206   a  without a raised section  214   a , if more rigidity is required, raised section  214   a  may be extended to run the entire length of arm  206   a  as shown in FIGS. 4-6. Accordingly, while FIGS. 4-8 illustrate three different embodiments for bosses  214 ,  215 , any combination thereof may be employed. 
     Additional shock protection may be used with any of the embodiments shown in FIGS. 4-8. For example, the scan assembly module  50  may be positioned within the scan head  12  and mounted to the interior of the scan head  12  by shock mounts as described in U.S. Pat. No. 5,475,206. Moreover, the individual printed circuit board and/or chassis elements  60 ,  62 ,  64 ,  66  may be provided with additional, separate shock mounting features. 
     For enhanced shock protection, the dithering assembly  200  may also include dither parking mechanisms as disclosed in U.S. Ser. No. 09/119,253, hereby incorporated by reference. In addition, the dithering assembly may include one or more travel stops  224 , as described in U.S. application Ser. No. 60/026,536 and incorporated herein by reference, for restricting the amplitude of the dithering motion to a maximum dithering amplitude and for assisting in the reversal of motion of the dithering assembly. For even greater shock protection, the dither mount arms  202   a ,  202   b  may be flexible, and the dither mount  202  itself may be mounted on a rotatable bracket, as described in U.S. application entitled “FLEXIBLE DITHER MOUNT WITH ROTATION,” Svetal et al., filed Sep. 3, 1998 with Express Mail Label No. EM351172541US. 
     The flexure  208  may be constructed from metal such as beryllium copper alloy, aluminum, steel, titanium, or plastic such as Mylar™, or combinations thereof. The dither mount  202  and the mirror mount  206  and their respective arms  202   a ,  202   b ,  206   a ,  206   b  may also be constructed from metal, plastic, rubber or other flexible material. Each of the mounts  202 ,  206  may be constructed in a single molded component or as a combination of parts. 
     Though the following examples are illustrated as applied to dithering mirror assemblies, the present invention may be applied to improving shock protection on other devices. For example, the present invention may be applied to a pivoting/oscillating light source or laser diode, a dithering/oscillating prism, a holographic element, etc.—essentially any device comprising a supporting structure which allows for movement of a mechanical scanning mechanism. 
     Thus while embodiments and applications of the present invention have been shown and described, it would be apparent to one skilled in the art that other modifications are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the claims that follow.