Abstract:
A compact retro-reflective module for use in electro-optical bar code readers includes components arranged to fold outgoing and incoming light along crossed optical paths. The module is convertible between generating one-dimensional and two-dimensional scan patterns to read bar code symbols.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part application of U.S. patent application Ser. No. 09/223,482, filed Dec. 30, 1998 now U.S. Pat. No. 6,491,222, which is a continuation-in-part of U.S. patent application Ser. No. 09/048,418, filed Mar. 26, 1998, now U.S. Pat. No. 6,114,712, which is a continuation-in-part of U.S. patent application Ser. No. 08/727,944, filed Oct. 9, 1996 now abandoned. This application is also a continuation-in-part of U.S. patent application Ser. No. 09/379,153, filed Aug. 23, 1999, now U.S. Pat. No. 6,283,372, which is a division of U.S. patent application Ser. No. 09/167,880, filed Oct. 7, 1998 now U.S. Pat. No. 6,412,697, which is a continuation of U.S. patent application Ser. No. 08/595,162, filed Feb. 1, 1996, now U.S. Pat. No. 5,861,615, which is a continuation of U.S. patent application Ser. No. 08/153,053, filed Nov. 17, 1993, now U.S. Pat. No. 5,504,316. This application is related to U.S. Pat. No. 5,821,521 and to U.S. Pat. No. 5,705,799. All of said patents and applications are hereby incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     FIELD OF THE INVENTION 
     The field of the invention relates to electro-optical readers or scanning systems, such as bar code symbol readers, and more particularly to the optical path design in a scanning module for use in applications requiring particularly compact bar code readers. 
     DESCRIPTION OF THE RELATED ART 
     Electro-optical readers, such as bar code symbol readers, are now very common. Typically, a bar code symbol comprises one or more rows of light and dark regions, typically in the form of rectangles. The widths of the dark regions, i.e., the bars and/or the widths of the light regions, i.e., the spaces, between the bars encode information in the symbol. 
     A bar code symbol reader illuminates the symbol and senses light reflected from the regions of differing light reflectivity to detect the relative widths and spacings of the regions and derive the encoded information. Bar code reading type data input systems improve the efficiency and accuracy of data input for a wide variety of applications. The ease of data input in such systems facilitates more frequent and detailed data input, for example, to provide efficient inventories, tracking of work in progress, etc. To achieve these advantages, however, users or employees must be willing to consistently use the readers. The readers therefore must be easy and convenient to operate. 
     A variety of scanning systems is known. One particularly advantageous type of reader is an optical scanner which scans a beam of light, such as a laser beam, across the symbols. Laser scanner systems and components of the type exemplified by U.S. Pat. No. 4,387,297 and No. 4,760,248 which are owned by the assignee of the instant invention and are incorporated by reference herein have generally been designed to read indicia having parts of different light reflectivity, i.e., bar code symbols, particularly of the Universal Product Code (UPC) type, at a certain working range or reading distance from a handheld or stationary scanner. 
     A variety of mirror and motor configurations can be used to move the beam in a desired scanning pattern. For example, U.S. Pat. No. 4,251,798 discloses a rotating polygon having a planar mirror at each side, each mirror tracing a scan line across the symbol. U.S. Pat. No. 4,387,297 and No. 4,409,470 both employ a planar mirror which is repetitively and reciprocally driven in alternate circumferential directions about a drive shaft on which the mirror is mounted. U.S. Pat. No. 4,816,660 discloses a multimirror construction composed of a generally concave mirror portion and a generally planar mirror portion. The multimirror construction is repetitively reciprocally driven in alternative circumferential directions about a drive shaft on which the multimirror construction is mounted. All of the abovementioned U.S. patents are incorporated herein by reference. 
     In electro-optical scanners of the type discussed above, the “scan engine” including the laser source, the optics, the mirror structure, the drive to oscillate the mirror structure, the photodetector, and the associated signal processing and decoding circuitry all add size and weight to the scanner. In applications involving protracted use, a large heavy hand-held scanner can produce user fatigue. When use of the scanner produces fatigue or is in some other way inconvenient, the user is reluctant to operate the scanner. Any reluctance to consistently use the scanner defeats the data gathering purposes for which such bar code systems are intended. Also, a need exists for compact scanners to fit into small compact devices, such as notebooks. 
     Thus, an ongoing objective of bar code reader development is to miniaturize the reader as much as possible, and a need still exists to further reduce the size and weight of the scan engine and to provide a particularly convenient to use scanner. The mass of the moving components should be as low as possible to minimize the power required to produce the scanning movement. 
     It is also desirable to modularize the scan engine so that a particular module can be used in a variety of different scanners. A need exists, however, to develop a particularly compact, lightweight module which contains all the necessary scanner components. 
     SUMMARY OF THE INVENTION 
     OBJECTS OF THE INVENTION 
     It is an object of the present invention to reduce the size and weight of components used to produce scanning motion of the light beam, and to collect the reflected light. 
     A related object is to develop an electro-optical scanning system which is both smaller and lighter in weight. 
     It is yet a further object to produce a module which may be manufactured conveniently, and at low cost. 
     A related object is to provide a module which may be assembled easily. 
     FEATURES OF THE INVENTION 
     Briefly, and in general terms, the present invention provides a retro-reflective scan module in an electro-optical reader operative for directing a light beam to, and for detecting light reflected from, a bar code symbol to be read. The module includes a generally planar, rectangular support such as a printed circuit board, a light source such as a laser, an optical element such as a curved collection mirror, a reciprocally oscillatable scan mirror, and a sensor such as a photodiode. 
     In a preferred embodiment, the laser beam from the laser passes through an aperture in the collection mirror along a first optical path to impinge on the scan mirror. Light collected by the collection mirror is directed to the sensor along a second optical path. The laser beam impinging on the scan mirror is swept along a third optical path to the symbol for reflection therefrom. The reflected light impinging on the scan mirror is directed along a fourth optical path to the collection mirror. 
     In accordance with the invention, the second and third paths cross, thereby resulting in a compact design in which the laser and the sensor are located away from each other at opposite end regions of the support. The compact module has the form factor of a rectangular parallelepiped having dimensions less than 20.6 mm×14.2 mm×11.4 mm. 
     In accordance with another feature of this invention, the laser beam emitted by the laser does not directly impinge on the scan mirror, but instead, directly impinges on a fold mirror which reflects the laser beam to the scan mirror. The fold mirror may be reciprocally oscillated in order to obtain two-dimensional scanning of the symbol, or may not be oscillated in order to obtain one-dimensional scanning. When not oscillated, the fold mirror is effectively stationary and acts as a fixed mirror. A drive for the fold mirror is selectively disabled in order not to oscillate the fold mirror. 
     The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. Further features of the invention are set out in the appended independent claims, and further preferred features are set out in the dependent claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partially sectioned view of an optical assembly according to the invention; 
     FIG. 2 a  shows a side view of a gun-type scanner suitable for use with the optical assembly of FIG. 1; 
     FIG. 2 b  is a front view of the scanner of FIG. 2 a;    
     FIG. 2 c  is a plan view of the scanner of FIG. 2 a;    
     FIG. 2 d  is an exemplary hand-held optical scanner, suitable for use with the optical assembly of FIG. 1; 
     FIG. 2 e  is an exemplary hand-held combined computer terminal and optical scanner, again suitable for use with the optical assembly of FIG. 1; 
     FIG. 3 shows an optical assembly from which a scanning beam exits at a non-90° angle; 
     FIG. 4 is a flow chart showing operation of the scanner of FIGS. 2 a-c;    
     FIG. 5 a  shows a thin flexible band drive of known type; 
     FIG. 5 b  shows an improved thin flexible band; 
     FIG. 6 is an exploded view showing the mounting of the thin flexible band of FIG. 5 b;    
     FIG. 7 shows the components set out in FIG. 6 in assembled form; 
     FIG. 8 shows an optical assembly in a housing in cut-away form; 
     FIG. 9 shows a 2D scan motion scanner assembly; 
     FIG. 10 is a schematic plan view corresponding to FIG. 9; 
     FIG. 11 shows an alternative scan assembly configuration; 
     FIG. 12 is an end view corresponding to FIG. 11; 
     FIG. 13 a  illustrates the scanning plane in a conventional assembly; 
     FIG. 13 b  illustrates the scanning plane in an assembly of the type shown in FIG. 11; 
     FIG. 14 shows an alternative bar code reader housing; 
     FIG. 15 is a view similar to FIG. 10, but showing a more compact design; and 
     FIG. 16 is a view of another compact design similar to FIG.  15 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a low cost optical assembly, for creating a scanning laser beam for use in a bar code reader. 
     The optical assembly comprises two essentially separate portions, the “static optics”  10  and the scanner motor drive  12 , both mounted to a common support or printed circuit board (PCB)  14 . Before the structure of the assembly is described in detail, it may be helpful to provide a brief overview of the operation of the device. The light beam  16  from a semiconductor laser  18  passes through a molded plastics lens  20  and is turned through 90° by total internal reflection from a prism  22 . After exiting the prism, the beam passes through an aperture  24  in a collector mirror  26 , and impinges onto an oscillating scanning mirror  28 . This produces a scanning outgoing light beam  30 , which is directed toward an indicia (not shown) to be read. Although the mirror  28  is shown as being angled, this is merely a drawing representation to render the shape and operation of the mirror clearer. The mirror sweeps a beam in the plane of the paper on which the drawing is presented, and orthogonal to the PCB  14 . 
     Reflected light  32  from the indicia is first received by the scanning mirror  28 , which directs it onto a concave surface  34  of the collector mirror  26 . This focuses the light via an aperture  36  and a filter  38  onto a photodetector  40 . The photodetector output signal is then passed on to suitable electronics within the PCB  14  by an electrical coupling  42 . 
     The scanning mirror  28  is mounted at  44  for oscillation about an axis, this being achieved by virtue of the interaction between a permanent magnet  46  and a driven electromagnetic coil  48 . A suitable driving signal is applied to the coil, via the PCB  14  and coil electrical contact  50 . The scanner motor drive  12  shown in FIG. 1 is exemplary, and may be replaced with any type of mechanism for effecting a scanning motion of the laser beam in one or two dimensions. For example, the scanner motor drive could comprise any of the configurations disclosed in U.S. Pat. No. 5,581,067 and No. 5,367,151, both of which are incorporated by reference. In this way, the static optics assembly  10  may be used as a component in a variety of scanner designs. 
     Although a light masking aperture  36  may be used in front of the photodetector  40 , as shown in FIG. 1, for increasing the depth of focus of the photodetector, the same effect can be achieved without an aperture by appropriately specifying the area of the photodetector  40  itself. 
     Another key feature of the invention is that the aperture  24  is located in a position in the collector mirror  26  so that the beam path of the outgoing laser beam striking the mirror  28  is offset from the optical axis of the reflected light from the concave surface  34  of the collector mirror  26 . In particular, the aperture  24  is located below the optical axis of the collector mirror  26 , as shown in FIG. 1 (and in the corresponding components in FIG.  11 ). 
     The important consequence of such design placement of the outgoing and return beam paths is that it permits an internal placement of the assembly in a compact housing configuration as that shown in FIG. 2 d , in which the assembly of FIG. 1 is mounted on a printed circuit board (PCB)  214  with the outgoing beam parallel to the plane of the PCB. Note also that the assembly is situated in the housing so that the outgoing beam is substantially orthogonal to the surface of the window  218 . The window  218  is depicted in the figure as being substantially perpendicular to the PCB  214  and flush with the outer surface of the housing  210 . The same positioning of the window is illustrated in another configuration in the embodiment of FIG. 2 e . Such mechanical designs are easy to manufacture, and enable a very compact reader to be designed. 
     Situating the window orthogonal to the outgoing laser beam, however, results in partial internal reflection of the outgoing light back in the same direction and therefore into the assembly. The possibility of using such a window and module configuration with the optical assemblies in the prior art would be counter to good design for optimum performance since in such configurations the reflected light from the window would be captured by the light collecting portion and directed to the photodetector, where it would be detected together with the returning reflected light from the bar code symbol, and create a very noisy signal. If the amount of reflection were substantial, the light could even flood the photodetector and overpower the signal of the returning reflected light from the bar code symbol. Bar code readers utilizing such modules or optical assemblies with prior art optical path designs would avoid such difficulties by typically utilizing a window that was mounted at an acute angle with respect to the outgoing laser beam (see, for example, the placement of the windows in the bar code readers depicted in U.S. Pat. No. 4,387,297; No. 4,409,470; No. 4,816,660; and No. 5,280,164). Any internal reflection from such tilted windows would be in a direction away from the optical assembly, thereby reducing the noise of the signal received by the photodetector. Such tilted window configurations require, however, more effort to implement mechanically, and increase the overall size of the housing. 
     The design of the optical path in the scan module according to the present invention permits the scan module to be mounted on a PCB, such as shown in FIG. 2 d , so that the window can be placed flush with the surface of the housing and consequently orthogonal to the emitted laser beam. The scan module could also be mounted flush against the window for an even more compact arrangement. Although reflected light from the window is returned in the direction of the beam path of the outgoing laser beam, in the optical path design of the assembly of FIG. 1 the outgoing laser beam optical path is different from the optical axis of the reflected light from the light collecting portion. Thus, such internally reflected light would not be directed by the light collecting portion to the photodetector  40 , and therefore would not affect the signal from the light reflected by the bar code symbol. 
     The implementation of the above-described offset outgoing and return light paths does not require the use of an apertured collector mirror  26 . The laser light source and the photodetector must be positioned with respect to one another simply so that the emitted light beam partially reflected by the window and reflected by the light-collecting portion does not illuminate the photodetector, i.e., by having spaced-apart, or offset, optical axes. 
     The optical assembly shown in FIG. 1 may be incorporated within any type of fixed or portable optical scanner, for example, the scan-type scanner of FIGS. 2 a-c , the hand-held scanner shown in FIG. 2 d , or the hand-held computer terminal/scanner shown in FIG. 2 e.    
     Referring to FIGS. 2 a  to  2   c , a hand-held, gun-type scanner of ergonomic design is shown. The scanner includes a scanner body designated generally  100  including a handle portion  102  and a head portion  104 . The handle portion  102  is configured to be held upright in the user&#39;s palm and has a forward portion including a trigger  106  positioned preferably to be operable by the user&#39;s forefinger. The head portion  104  is provided at the top of the handle portion  102  and includes a front face including a scanning window  108  and a bulbous rear portion extending rearwardly from the handle  102  to rest on or above the user&#39;s hand in use. 
     The scanner  100  is pivotably fixed to a base portion  110  about a pivot axis  112  provided at the lower end of the handle  102 . The base includes a flat bottom face  114  and extends outwardly from the handle portion both forward and rear and to the sides such that the assembly as a whole can be placed freestanding stably on a supporting surface. The scanner  100  is arranged to pivot on the base  110  in the forward/backward direction. The base  100  provides an interface between the scanner  100  and a host (not shown) by a cable  116 . The cable  116  can simply carry power or can also include a data path either for control information to be passed to the scanner or for data ready to be downloaded to the host from the scanner  100 . 
     The base  110  includes on its underside  114  a pressure switch of any suitable known type (not shown), release of which indicates to a processor in the scanner that the scanner is being operated in hand-held mode. Accordingly the scanner switches to triggered mode indicating that reading will only take place when trigger  106  is activated. 
     The control system is illustrated in more detail in the flow chart of FIG.  4 . It will be seen that a continuous loop is maintained by a suitable controller establishing whether or not the pressure switch is activated (step  150 ). If the pressure switch is deactivated, then triggered (hand-held) mode is entered (step  152 ); further discussion of relevant features may be found in U.S. Pat. No. 5,151,581, incorporated herein by reference. 
     In the alternative mode, where the pressure switch is activated, continuous scanning (hands-free) mode  154  is entered. In this mode, a presentation scan pattern is always activated allowing all items to pass in front of the scanner to be scanned. This can be used, for example, at a retail sales point such as a checkout stand. Accordingly the arrangement allows dual mode operation. 
     The scanner  100  shown in FIG. 2 a-c  is an omnidirectional scanner but the gun-type configuration provides the benefits of a conventional one-dimensional scanner. 
     In addition, the adjustable angle provided by the incorporation of a pivot axis  112  allows the scanner as a whole to be positioned at any desired pivot angle for ease of reading and also allows the base to be angled to a comfortable position when in hand-held mode. 
     The main body  100  and base  110  are preferably modular such that one or other components can be changed at minimum expense to arrive at, for example, a cordless embodiment. Optionally a mode button  118  is additionally provided on the upper face of the head  104  (see FIG. 2 c ) allowing the user to select a scanning pattern of any desired type, for example, based on the bar code symbols or other indicia to be read, or the scanning conditions. In addition indicator lights such as LEDs are provided at  120  which can indicate, for example, the mode of operation of the scanner, whether it is in hands-free or hand-held mode, and so forth. 
     Referring now to FIG. 2 d , reference numeral  210  generally identifies a hand-held scanner in an alternative embodiment. The scanner may alternatively be gun-shaped, or any suitable configuration may be used. The scanner is manually operable, for example, by a trigger (not shown). As known from the above-identified patents and applications incorporated by reference herein, a light source component, typically but not necessarily a laser, is mounted inside the scanner shown at block  210 . The light source emits a light beam along a transmission path which extends outwardly through a window  218  that faces indicia, e.g., bar code symbols, to be read. Also mounted within the block  210  is a photodetector component, e.g., a photodiode, having a field of view, and operative for collecting reflected light returning through the window  214  along a path from the symbol. 
     The optical assembly of FIG. 1 is mounted within or as part of the block  210 . 
     In whichever scanner type the arrangement is provided, operation is generally the same. The photodetector generates an electrical analog signal indicative of the variable intensity of the reflected light. This analog signal is converted into a digital signal by an analog-to-digital converter circuit. This digital signal is decoded by a decode module  222 . The decode module  222  decodes the digital signal into data descriptive of the symbol. An external host device  224 , usually a computer, serves mainly as a data storage in which the data generated by the decode module  222  is stored for subsequent processing. 
     The block  210  and decoder  222  are mounted on a PCB  214 . In operation, each time a user wishes to have a symbol read, the user aims the scanner at the symbol and pulls the trigger or otherwise initiates reading of the symbol. The trigger is an electrical switch that actuates the drive means. The symbol is repetitively scanned a plurality of times per second, e.g., more than  100  times per second. As soon as the symbol has been successfully decoded and read, the scanning action is automatically terminated, thereby enabling the scanner to be directed to the next symbol to be read in its respective turn. 
     In addition, the head need not be a portable hand-held type as fixedly mounted heads are also contemplated in this invention. Furthermore, the heads may have manually operated triggers, or may be continuously operated by direct connection to an electrical source. 
     The oscillations need only last a second or so, since the multiple oscillations, rather than time, increase the probability of getting a successful decode for a symbol, even a poorly printed one. The resonating reflector has a predetermined, predictable, known, generally uniform, angular speed for increased system reliability. 
     Turning now to FIG. 2 e , there is shown an alternative hand-held optical scanner including additional features, this time taking the form of a scanning terminal  326 . The terminal comprises a hand-held case  328  having a data display screen  330  and a data input keypad  332 . The optical assembly of FIG. 1, within the case  328 , produces a scanning light beam which extends outwardly through a window  334  which faces the indicia to be read. Light reflected from the indicia passes back through the window  334  and impinges on the photodetector component, for example a photodiode, which creates a returning light output signal. The information content within that signal may be stored in an on-board memory (not shown) or may be downloaded to a remote computer via a data port  336 . Alternatively, the information may be transmitted via a radio frequency signal produced by an on-board radio transmitter/receiver  338 . 
     In one embodiment the motor drive used to obtain scanning action is preferably a “taut band element” drive. This type of drive is fully described in, inter alia, U.S. Pat. No. 5,614,706 and No. 5,665,954 which are commonly assigned herewith and incorporated herein by reference. In essence, the arrangement includes an optical element such as a lightweight mirror mounted on a thin flexible strip (the “taut band”) mounted across an electromagnetic coil. A permanent magnet is attached to the optical element which interacts with a varying magnetic field created when an AC signal is applied to the coil to cause repetitive torsional motion in the flexible strip. As a result, the optical element oscillates providing scanning motion. 
     FIG. 5 a  shows a taut band element drive of known type in more detail. In particular, coil  70 , flexible strip  72 , mirror  74  and permanent magnet  76  can be seen. The flexible strip  72  can be held against the coil  70 , for example, by a holding annulus  78 . An AC voltage applied to the coil is represented schematically at  80  and causes torsional oscillation represented schematically by arrow  82 . It will be apparent that this arrangement can replace the arrangement shown generally in FIG. 1 as mirror  28  and drive arrangement  44 ,  46 ,  48  in a manner apparent to the skilled reader. 
     In a further embodiment shown in FIG. 5 b , the flexible strip  72  is replaced by an elongate element  84  which is V-shaped in cross-section perpendicular to its elongate axis on which is mounted the mirror  74  and permanent magnet element  76 . The V-shaped element  84  extends across a coil or is otherwise appropriately mounted in the same manner as previous thin flexible element  72  and the permanent magnet  76  interacts with the AC magnetic field resulting in torsional deflection represented by arrow  86 . The V-shaped cross-section of the band increases its stiffness and in particular ensures that the torsional deflection is uniform or substantially uniform over the length of the band, the mirror  74  being mounted on the apex of the “V”. It will be appreciated that alternative configurations for the band cross-section can be contemplated such as X-, I-, H-, or W-shaped, as long as the requirements of torsional deflection and uniformity of that torsional deflection along the length of the band are maintained. 
     FIG. 6 shows in exploded form a practical mode of mounting the V-shaped element  84  of FIG. 5 b . Coil  70  is mounted on an E-configuration core  71   a  including a central arm  71   b  which is received in the central recess of the coil  70  and outer arms  71   c  and  71   d  which extend to either side of the coil and above it. A mounting plate  75   a  is received on the outer arm  71   c ,  71   d  of the E-core and extends above and across the coil  70 . The mounting plate  75   a  includes a central aperture  75   b  defining the space across which the V-shaped element  84  extends. The V-shaped element  84  includes limbs  84   a  extending to either side of its longitudinal axis symmetrically at either end and the center and is mounted on the mounting plate  75   a  across the aperture  75   b  in any suitable manner, for example, by securing the end limbs  84   a  to the upper face of the mounting place  75   a . Cooperatingly configured V-shaped connecting elements  85  are secured to the V-shaped element  84  and generally aligned with the limbs  84   a  and the mirror  74  is mounted on the connecting elements  85  at the apex of the V-shaped element. 
     Depending from the mirror  74  is a yoke  73  also substantially of V-shape but straddling the V-shaped element  84 , having its outer ends  73   a ,  73   b  attached to the rear of the mirror  74 . The yoke  73  has a central portion which extends away from the mirror  74  and has lateral tabs  73   c ,  73   d . The lateral tabs  73   c  and  73   d  are in register with the central limbs  84   a ,  84   b  of the V-shaped element and are attached thereto. The permanent magnet  76  is attached to the underside of the central portion of the yoke  73 , for example, to the underside of the tabs  73   c  and  73   d . Accordingly, the yoke  73  straddles the V-shaped element  84  such that the permanent magnet projects over or through the aperture  75   b  in the mounting plate  75   a  allowing optimum magnetic coupling with the coil  70 . When an AC current is applied to the coil  70 , the permanent magnet  76  oscillates which in turn gives rise to torsional flexing of the V-shaped element  84  and oscillation of the mirror  74 . The assembled arrangement is shown in FIG.  7 . 
     An assembled module incorporating the arrangement of FIG. 7 is shown in FIG. 8 in which it will be seen that a substantially cuboidal housing is incorporated. The direction of angular motion of the mirror is depicted by arrow A. 
     In another preferred embodiment, the type of motor drive used to oscillate the scan mirror can be a Mylar™ leaf spring supporting an unbalanced mirror assembly. In FIGS. 11-12 the mirror assembly is mounted to a Mylar leaf spring which flexes as the permanent magnet is driven by the AC coil imparting an oscillating force. 
     Yet a further alternative is a “micro-machined” mirror assembly as discussed in U.S. Pat. No. 6,102,294 and No. 6,059,188 according to which the mirror is driven back and forth directly by a suitable drive motor, preferably of very small dimension. Yet a further alternative is to use a mirror of known rotating polygon type as discussed in the introduction in relation to U.S. Pat. No. 4,251,798 according to which the mirror comprises a solid body having a plurality of faces angled to one another. As the body rotates, the beam is scanned by successive rotating faces of the polygon body. In one embodiment the Mylar motor can be used in an arrangement for one dimensional scanning while a V-shaped taut band element (described above) can be used for two-dimensional scanning, also as discussed in more detail below. 
     Turning now to the static optics assembly  10  shown in FIG. 1, it will be noted that the laser focusing lens  20 , the laser aperture  24  and the collection mirror  26  are all defined by a single molded plastics material member, shown in cross-hatching and indicated generally by the reference numeral  52 . The molded member  52  further acts to house and to locate the laser  18 , the filter  38  and the photodetector  40 . 
     The preferred laser  18  is a semiconductor laser is mounted by conventional through-hole techniques on the PCB. The photodiode is preferably an SMD (“surface mounted device”) device as is the AC coil for the Mylar leaf spring motor. This eliminates the need for standoffs and hand-soldering or sockets, as are used on prior art scanners. Typically, the laser will be a standard packaged edge emitting laser. For minimum cost, the laser focusing is not adjustable, and the laser is simply installed with its mounting flange in contact with a shoulder molded as part of the molded member. This will position the laser accurately enough with respect to the molded focusing lens  20  to provide adequate performance within an inexpensive scanner. The fact that the focusing lens is molded as part of the same component as the shoulder  54  minimizes tolerance buildups that could otherwise cause improper focusing. 
     The laser is held in place within the molded member  52  by means of UV-curing cement. Since the plastics material of the molded member is transparent to UV-light, the cement may be cured by shining UV light through the member into the cavity within which the laser is positioned. Cement may be applied to the laser  18 , or to the molded member  52 , with the laser then being pushed into the cavity until it abuts the positioning shoulder  54 . The assembly may then be exposed to ultraviolet light for a few seconds, so curing the cement. If desired for higher performance, this method of retaining the laser also allows for a focusing adjustment to be made. In this case, the laser is gradually slid into the cavity while the output beam is being monitored. When correct focus is achieved, the assembly is exposed to UV-light, thus curing the cement and locking the assembly into place. 
     In the unadjusted assembly, it may be possible to eliminate the cement by spring-loading the laser up against the positioning shoulder  54 , for example, by means of a rubber or foam washer  56  between the PCB  14  and the bottom of the laser  18 . 
     As shown in the drawing, the laser  18  has downwardly-extending electrical leads  58  which are simply installed directly into the PCB  14 . This eliminates hand-soldering, but soldering could be used if desired. 
     The fact that the leads extend downwardly into the circuit board means that in a conventional laser, the beam will be directly upwardly perpendicular to the board. The prism  22 , previously described, is molded into the top of the molded member  52  to direct the vertical laser beam through the aperture  24  in the collector mirror  26  towards the scanning mirror  28 . The prism  22  uses total internal reflection to reflect the laser beam, so it is not necessary to coat the upper surface with a reflective coating. 
     To provide for further focusing of the laser beam, should it be desired, it would also be possible to shape the exit surface  60  of the prism. 
     It is desirable that, somewhere along its path, the laser beam should pass through a beam stop. The aperture  24  in the collector mirror  26  may serve this purpose. Alternatively, the lens  20  or the reflecting or exit surface of the prism  22  could provide the beam stop. 
     In fact it is preferred to keep the aperture  24  as small as possible which improves the collection capability of the collector mirror  26 . For example, the aperture  24  may be in the region of 0.5 mm in diameter. This provides an additional advantage as the resulting diffraction pattern gives rise to a light distribution following a Bessel function which is particularly well adapted for scanning indicia. 
     The molded member  52  needs to be secured to the circuit board  14 , and to that end, snaps  62 ,  64  are provided. These automatically latch onto the circuit board when the component is installed. Alternatively, posts on the lower side of the molded member may protrude through the board to be heat-staked onto the bottom of the board. Ultrasonic staking could also be used. 
     The collector mirror  26  is coated with a reflective coating so that light impinging upon it will be reflected downwardly toward the photodetector  40 . This coating may also cover that part  62  of the molded member that serves as a housing for the photodiode. This will render the optics assembly opaque in that area to prevent any light from reaching the photodiode except via the aperture  36  and the filter  38 . 
     This reflective coating may also serve another function. Typically, the coating will be a thin film of metal such as gold, aluminum or chrome. These films are electrically conductive. Accordingly, the film also acts as an electromagnetic interference (EMI) shield for the photodiode  40 . The use of a surface coating to protect the photodiode enables the usual EMI shield to be dispensed with, thereby eliminating both the cost of a separate shield and the labor to have it installed within the assembly. 
     The coating is electrically grounded by extending a projection  66  of the molded member into a small socket  68  in the PCB. Alternatively, the projection  66  could be press-fitted into a plated through-hole in the board. 
     The housing portion  62  of the molded member  52  not only acts to hold the optical filter  38  in place on top of the photodiode  40 , but also entirely surrounds the photodiode, thereby preventing stray light from reaching it. The aperture  36  in the housing may be small to limit the field of view of the detector, maximizing ambient light immunity. The aperture needs to be accurately located with respect to the collector mirror  26 , to allow the use of a minimum-sized field of view. Accurate relative positions of the aperture and the collector mirror are easily achieved since they are molded as a single part. 
     An alternative arrangement is shown in FIG.  3 . In certain circumstances it is desired to provide an arrangement in which the beam  30  leaves the optical assembly at an angle other than  90  to the vertical (relative to the PCB  14 ). For example, there may be instances in which the mounting requirements mean that the PCB  14  is mounted at a non-orthogonal position. In previous arrangements it has been necessary to overcome this problem by introducing additional spacers when mounting the PCB  14  such that the beam  30  leaves at the desired angle. This problem is solved in the arrangement according to FIG. 3 by adjusting the angle by which the beam exits the optical assembly to compensate for the mounting angle and remove the need to mount the PCB including a spacer. In the arrangement shown, this is achieved by altering the angle of the scanning mirror assembly  28 , which is of particular benefit as no adjustment of the laser mounting would be required. It will be appreciated that the remaining optics may also require adjustment to further compensate which adjustments can be easily achieved by the person skilled in the art. 
     The angle involved is dependent on the particular consumer requirements but may be in the region of 45-90° to the PC board, more preferably in the range of 60-70° and most preferably 65° to the PCB. 
     FIGS. 11 and 12 show an alternative optical assembly and motor drive embodiment to FIG. 3 according to an embodiment of the invention. Although illustrating two-dimensional scanning, the arrangement of components may also be configured for one-dimensional scanning alone. The arrangement is mounted on a single base board  500  and includes a laser assembly  502  of suitable type, for example, of the type discussed above. In this embodiment, the laser assembly  502  may be mounted on the chassis including peripheral side  550 , which also acts as a heat sink for the laser. A beam from the laser assembly  502  is not folded, but directly passes through an aperture  504  in a collector mirror  506  and is reflected by a scanning mirror  508 . The returning beam is retro-reflected onto the collector mirror  506  and directed to a detector of suitable known type  510 . 
     Turning now to the drive assembly for the scanning mirror  508  in more detail, the mirror is mounted in conjunction with a permanent magnet  512  which interacts with a magnetic field provided by an AC current driven coil  514  to oscillate the mirror. The mirror is mounted relative to the base  500  via an attachment element  501  which is connected to the mirror by two Mylar springs  518 ,  520 . Although the mirror is mounted parallel to the base, the attachment element  516  is mounted at 25° to the horizontal base and the Mylar springs which extend perpendicular to the attachment strip  516  are hence at 25° to the vertical. Accordingly a scanning plane is defined at 25° to the vertical as discussed in more detail below. It will be appreciated, of course, that any appropriate angle can be selected. The scan angle is then defined by the amplitude of motion of the mirror and is preferably selected to be 50°. The mirror assembly is of the unbalanced type, that is, no counterweights are provided against the mirror mass as considered relative to the point of support. 
     The use of an unbalanced mirror, i.e., one in which no counterweights are provided in the mirror assembly, is particularly suitable in implementation in which the mirror is driven at a speed of greater than 100 scans per second. With an unbalanced mirror, since the attachment points of the mirror to the flexible springs are not the center of mass of the mirror assembly, while the mirror is at rest, gravity will exert a relatively greater force on the side of the mirror assembly having the greater mass, causing the mirror to “droop” on its heavier side and pull on the flexible springs. Of course, the effect of such force depends on the orientation of the scanner with respect to the force vector of gravity. The same “drooping” effect is present when the mirror is scanning at relatively low speeds, so in such applications the use of a balanced mirror would be preferred. A balanced mirror, however, requires additional mass be added to the mirror, or mirror assembly, which is a drawback in terms of operating design weight and consequently the power requirements. 
     In the embodiment of high speed operation (i.e., at more than 100 scans per second), the material composition, size, shape and thickness of the spring may be appropriately selected to achieve the desired resonant frequency. For example, for operation at approximately 200 scans/second, the selection of a Mylar spring with a thickness of 4 mils is appropriate. For operation at 400 scans/second, a stainless steel spring with a thickness of about  3  mils is preferred. 
     It will be seen that the mirror  508  is angled relative to the vertical to direct the scanning beam out of the upper face of the assembly. As with FIG. 1, although the mirror  508  is represented in FIG. 11 as being also angled out of a plane orthogonal with a plane of the paper, this is merely a drawing representation to render the figure clearer. It will be seen that the attachment element  516  includes limbs  522  and  524  extending to either side of the Mylar springs  518 ,  520 . These limbs are positioned within shaped recesses in side blocks  526 ,  528  allowing a certain amount of clearance for the limbs which provides adequate space for the desired scanning angle to be achieved while providing stops to limit the amount of oscillation of the mirror should a shock be imparted to the unit, for example, by dropping it. 
     Accordingly, a beam emitted by the laser assembly  502  incident on the mirror  508  is swept through an angle of 50° by the scanning mirror. However, the plane of sweep of the beam (the scan plane) is not at 90° to the base  500  but is at an angle constrained by the direction in which the magnet is driven to oscillate, i.e., the axis of flexing of the Mylar springs. This can be best be understood with reference to FIGS. 13 a  and  13   b . In FIG. 13 a  the laser beam  30  enters in the Y direction. The mirror and drive assembly are not shown but in FIG. 13 a  the normal mirror configuration is assumed, that is, the mirror is angled at 45° to the X-Z plane and is mounted to oscillate about the X direction. As a result a scan plane  530  is established in the Y-Z plane. However in FIG. 13 b  the mirror and mirror drive are mounted as discussed in relation to FIGS. 11 and 12. It will be seen, therefore, that the scan line is obtained in a plane  532  at 25° to the Y-Z plane. Again, any desired scan plane angle or scanning angle can be selected. 
     Accordingly a non-90° output angle of the beam as discussed in relation to FIG. 3 is achieved in a different manner. 
     FIG. 9 shows a second preferred embodiment in which two-dimensional scanning motion is achieved by using two mirrors each oscillating in an orthogonal plane. Multi-pattern scanners can be achieved by using two reflector X-Y motion as described in U.S. Pat. No. 5,581,070, No. 5,637,856 and No. 5,614,706, all of which are incorporated herein by reference. Preferably, the two reflectors are driven by a thin flexible element-type drive of the type shown in FIG. 5 a  or FIG.  7 . In particular, the optical module  10  emits a beam  30  through aperture  24  in collector  34  which is oscillated in a first direction, for example, the X direction by a first oscillating mirror  28   a  mounted on a first V-shaped element  84  and is then oscillated in a second direction, for example, the Y direction by a second mirror  28   b  mounted on a V-shaped band  84 . As a result, any desired scanning pattern can be achieved at the target as represented schematically by pattern  11 . 
     All of the elements are preferably provided in a single module as can be seen from the base layout depicted in FIG.  10 . In particular laser  18  emits an outgoing beam  30  through an aperture  34  in collector mirror  26 . The beam is oscillated in the X direction by mirror  28   a , and in the Y direction by mirror  28   b , giving rise to a scanning pattern shown schematically at  11 . The returning beam  32  returns along the reflection path and is directed onto the detector  40  by the collector mirror  26 . It will of course be appreciated that the arrangement is preferably used in conjunction with the optical assembly shown in FIG.  1  and the exact positioning and orientation of the parts will be apparent to the skilled reader. 
     FIG. 14 shows an alternative scan engine form factor and ergonomic housing variation for incorporation of the scanner described herein or any other suitably dimensioned scanner. In particular, the scanner is incorporated into a pen-type housing  600  having a scanning window  602 . The pen-type housing  600  is preferably elongate having broad front and rear faces  604 ,  606  and narrow side faces. The scanning window is preferably provided at the upper end of broad face  604 , at the opposite end to the pen “nib”  612 . Scanning can be triggered by one or more triggers  608 ,  610  provided, for example, on the side or front face of the pen housing  600 . The pen nib  612  can either be a conventional pen or an electronic pen. Because of the broad faces, the arrangement easily houses a scanner module of the type described herein. In addition, the positioning of the window  602  allows ergonomic scanning, and the positioning of a plurality of triggers allows left- or right-handed users to use the scanner with ease. It will be seen that the broad rear face  606  of the housing  600  contacts the user&#39;s palm in reading mode for comfort and ease of use while in the writing mode the narrow side face contacts the user&#39;s palm, so that the arrangement can be used normally as a pen. 
     Although the window  602  is shown in FIG. 14 with its shorter side parallel to the axis of the pen, alternatively the longer side may be positioned parallel to the axis with the direction of the scan line also parallel to the axis of the pen. 
     Turning now to FIG. 15, the illustrated arrangement is similar to that shown in FIG. 10 in which a laser  18 , a collection mirror  26  having an aperture  24 , a reciprocally oscillatable scan mirror  28 , and a sensor  40  are all mounted on a rectangular support such as printed circuit board  14 . The laser  18  emits a laser beam along a first optical path  30   a  through the aperture  24  to the scan mirror  28  for reflection therefrom. The collection mirror  26  reflects light impinging thereon along a second optical path  30   b  to the sensor  40 . The laser beam impinging on the scan mirror  28  is directed and swept along a third optical path  30   c  to the symbol for reflection therefrom. At least some of the light reflected off the symbol travels in a countercurrent direction along the third optical path  30   c  to impinge on the scan mirror  28  and is, in turn, reflected along a fourth optical path  30   d  to the collection mirror  26 . 
     The folded optical path makes for a very compact retro-reflective module  10  whose rectangular parallelepiped form factor has dimensions less than 20.6 mm×14.2 mm×11.4 mm. The laser  18  and sensor  40  are not located in a side-by-side relationship as in FIG. 1, but instead, are located at opposite end regions of the board  14 . 
     FIG. 16 is identical to FIG. 15, except that the laser  18  does not emit its laser beam directly through the aperture  24 , but instead, directs the laser beam initially to a fold mirror  29  for reflection therefrom through the aperture  24 . The fold mirror  29  is a planar, reciprocally oscillatable scan mirror, just like scan mirror  28 , except smaller in area. The fold mirror may be oscillated to sweep the laser beam reflected therefrom in a first scan direction. When operatively combined with the scan mirror  28  which sweeps the laser beam reflected therefrom in a second scan direction, the symbol is read with a two-dimensional scan pattern. Preferably, the first and second scan directions are mutually orthogonal. 
     This invention also contemplates that the fold mirror  29  be permanently fixed in position, in which event, the symbol is read with a one-dimensional scan pattern or a single scan line. Preferably, the fold mirror  29  is not permanently fixed, but instead, its drive is disabled during a one-dimensional reading mode. Upon re-enabling the drive during a two-dimensional reading mode, the two-dimensional scan pattern is generated. The disabling of the drive for the fold mirror may be achieved by the generation of a disabling control signal by the microprocessor and/or by the depression of a control switch by a user. 
     It will be understood that each of the features described above, or two or more together, may find a useful application in other types of scanners and bar code readers differing from the types described above. 
     While the invention has been illustrated and described as embodied in a scanning assembly in compact bar mode readers, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit and scope of the present invention. In particular it will be recognized that features described in relation to one embodiment can be incorporated into other embodiments as appropriate in a manner that will be apparent to the skilled reader. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims. 
     What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.