Abstract:
An improved, rotatably articuable scanner for reading and decoding bar codes in connection with the sale of retail articles is disclosed. An ultra-compact, lightweight, low-cost, self contained, visible laser diode (VLD) bar code scanner is provided with a great range of functionality and versatility. A scan head housing an optical subsystem is rotatably connected with a tower housing. The heat-generating electronic components are located in the tower housing away from heat-sensitive optical components located in the scan head. The scanner presents an extremely small footprint, and provides for its mounting in virtually any orientation and location. 
     The optical subsystem uses a basket-type mirror array configured around a rotating planar folding mirror, driven by a compact cup (brushed) DC motor. The scanner features a short optical beam path. The organization of components within the scan head and tower housings, as well as the partitioning thereof between the two, provides for convection-cooled operation of the optical subsystem. The center of mass of components in the scan head is located near an axis of rotation of the scan head, thereby making the scanner extremely stable despite its small footprint. Ease of field maintenance and calibration of the optical subsystem is very simple because the replaceable components thereof are decoupled from the remaining components and replacement parts do not require optical alignment.

Description:
This application is a continuation of U.S. Ser. No. 08/325,967 filed Oct. 20, 1994 now U.S. Pat. No. 6,065,676, May 23, 2000 which is a divisional of U.S. Ser. No. 07/870,689 filed Apr. 17, 1992 abandoned. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     This application relates generally to bar-code scanners such as those used in connection with point-of-sale (POS) terminals wherein coded retail items are presented to the scanner along a counter, the scanner automatically reads the bar code and communicates the retail item information to the POS terminal for transacting the sale of the item, inventory control, pricing, accounting, receipting, etc. More particularly, the invention concerns such a scanner that is miniaturized to produce a small, lightweight, low-cost, self-contained scanner the head of which is rotatably articuable and which can be mounted virtually anywhere and in any orientation. 
     Prior art POS terminal-connected mounted scanners require a large amount of retail outlet counter space and are relatively high-cost. Smaller scanners typically have relatively shallow and narrow viewing angles, or ranges, and thus are provided with extendable, retractable features, e.g. articuable, multiple arms enabling them to be extended and retracted for positioning adjacent a retail article. Of course, such require much manipulation by the retail sales associate and thus are inconvenient to use, as the scanners&#39; heads must be constantly, or at least periodically, repositioned. Moreover, such scanners have been rendered smaller by removing much of the scanning electronics to a separate housing that requires under-counter space, which is at a premium. Essentially, the oversize problem is merely moved to another location, rather than being addressed and resolved. Known scan heads also have a larger volume than the scan head of the invention, which contributes to the lack of mounting flexibility in such scan heads. 
     There is a growing need for smaller, lighter weight bar-code rotatably articuable scanners that are versatile and inexpensive for use by retailers. There is also a growing need for rotatably articuable scanners that provide high performance, easily reachable scanning area that read bar codes quickly and accurately when retail articles are presented, with their bar codes generally facing the scanner, in a natural presentation or arc-sweeping motion by the retail sales associate. There is a growing need for rotatably articuable scanners that accommodate the variety of retail counter layouts of numerous retail outlets, and are interface-compatible with the variety of POS terminals that may be found therein. 
     Accordingly, certain aspects of the present invention may meet one or more of the following objects: provide a highly functional rotatably articuable scanner that is extremely compact, yet extremely versatile in terms of compatibility with existing POS terminal interfaces and retail counter configurations. 
     To provide such scanners that are capable of reading a bar code from an article independent of the axial orientation of the bar code relative to the scanner, and requiring only that the bar code be within a defined field of view of the scanner. 
     To provide such a rotatably articuable scanners having improved viewing angles and depths to achieve higher scanning accuracy and reliability. 
     to provide such scanners in an easily and quickly adjustable orientation to accommodate the idiosyncracies of various retail counter configurations and checker preferences. 
     To provide such a rotatably articuable scanners at extremely low cost of manufacture and field maintenance. 
     To meet the above objectives in a scanner that is unimposing and attractive. 
     Recent advances in bar code scanners have made it possible to scan bar codes generally independent of the axial orientation of the bar code relative to the read axis of the scanner. The so-called asterisk scan pattern, consisting of plural lines crossing generally at their centers with their endpoints being spaced apart in a generally circular arc, can be used to read conventional linear bar codes used in retailing, without concern for the orientation of the surface of the bar code about the axis of the asterisk scan pattern, because at least one of the lines of the pattern will extend thereacross. One such bar code scanner producing an asterisk scan pattern is described in U.S. Pat. No. 4,939,356 issued Jul. 3, 1990 to Rando, et al., entitled BAR CODE SCANNER WITH ASTERISK SCAN PATTERN (which patent is commonly assigned with the present application) the disclosure of which is incorporated herein by this reference. 
     Another important, relatively recent advance in bar code scanners is the use of the so-called “basket” reflecting mirrors arrangement in which a Erusto-conical array of fixed planar mirrors is disposed circumferentially around a centrally located rotating mirror, wherein the basket mirrors and rotating mirror operatively are associated with a laser preferably disposed within a tubular member collinear with the axis on which the central mirror rotates to produce a variety of scan patterns including such an asterisk scan pattern. One such basket-type scanner useful in producing an asterisk scan pattern is described in U.S. Pat. No. 4,699,447 issued Oct. 13, 1987 to Howard, entitled OPTICAL BEAM SCANNER WITH ROTATING MIRROR (Reexamination Certificate B1 4,699,447, dated Jul. 3, 1990) (which patent is commonly assigned with the present application) the disclosure of which also is incorporated herein by this reference. 
     Briefly summarizing the invention, an extremely compact, lightweight, low-cost, self-contained, visible laser diode (VLD) printed bar code scanner is provided with a great range of adjustability and versatility. Preferably, a scan head housing the optical subsystem is fixedly rotatably connected with a tower housing the heat-generating electronic components of the scanner. The scan head housing contains a spin motor control reflected light pattern detector, while the tower housing contains a bar code decoder and communication means, connectable with a conventional POS terminal via a multiple physical/electrical interface bulkhead located in a base for the tower housing. The scanner presents an extremely small footprint, and provides for its mounting in virtually any orientation and location. The scanner of the invention provide for handsfree scanning and one-handed adjustability. 
     Preferably, the optical subsystem uses a basket-type dispersal/collecting mirror array configured around a rotating planar folding mirror driven by an extremely compact cup (brushed) DC motor. Most of the optical components within the laser bean&#39;s path, as well as most of the mounting structures and housing components may be rendered in injection molded plastic to reduce weight and cost. The organization of components within the scan head and tower housings, as well as the partitioning thereof between the two, provides for convection cooled operation of the optical subsystem and rotation of the scan head, which has a center of mass near the scan head&#39;s axis of rotation, thereby making the scanner extremely stable despite its small footprint. Ease of depot and field maintenance and calibration of the optical subsystem is very simple because the replaceable components and subsystems may be easily removed and replaced without the need for realignment of the optical system. The scan head may be easily removed from the tower housing for convenience of maintenance and repair. 
     Unprecedented functionality and versatility in an ultra-compact bar code scanner is achieved by minimizing the length of the optical beam path, reducing component size, partitioning the optical subsystem from the associated electronics and choosing, configuring and mounting components of both for optimal compactness in an easily assembled, maintained and operated form. 
     These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the scanner housing of the invention, with a scan head depicted in an operating position. 
     FIG. 2 is a schematic system block diagram of the scanner made in accordance with its preferred embodiment. 
     FIG. 3 is a right side elevation of the scanner housing and optical subsystem that forms a part of the scanner, with portions broken away to show detail 
     FIG. 4 is front elevation of the scanner of FIG. 3, with portions broken away to show detail. 
     FIG. 5 is a left side elevation of the scanner housing, with portions broken away to show interior detail. 
     FIGS. 6 is a rear elevation of the scanner housing. 
     FIGS. 6A-6D are greatly enlarged fragmentary sections taken from FIG. 6 showing, respectively, a labyrinth seal detail details of the window mounting, attachment of a base to a tower housing, and an alternate base embodiment. 
     FIG. 7 is an exploded isometric view of the mounting for a scan head. 
     FIGS. 7A,  7 B and  7 C are medial section front elevations of alternate embodiments of the scan head mounting. 
     FIG. 8 is a bottom plan view of a base of the scanner of FIG. 1, illustrating the cable routing mechanism of the preferred embodiment. 
     FIG. 8A is a bottom plan view of the base depicting a cover therefor. 
     FIG. 9 is schematic circuit diagram of the spin motor monitoring circuit that forms part of the electronics of the scanner. 
     FIG. 10 is a fragmented right side elevation of the scanner housing and optical subsystem showing an optical beam path. 
     FIG. 11 is a reduced-scale top plan view of the scanner housing. 
     FIG. 12 is an end-on elevation of a window of the scanner housing, taken generally along the lines  12 — 12  of FIG.  4 . 
     FIG. 13 is a schematic circuit diagram of the shadow detector feature of the preferred embodiment o the invention. 
     FIG. 14 is a schematic block diagram of the scanner circuitry depicting thermal separations characteristics of the scanner. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the drawings, and initially to FIG. 1, the scanner of the invention is depicted generally at  20 . Scanner  20  includes a scan head, or scan module,  22  which is adjustably, rotatably mounted on a scanner tower  24 , which, in the preferred embodiment, in turn is mounted on a scanner base  26 . The scanner includes a scanner housing  21  which is bifurcated into a scan head housing and a tower housing, which will be described below in greater detail. The scanner of the invention is an ultra-compact device which contains all of the optics and electronics in a single housing. There is no requirement for external components other than a power supply, which is generally provided in a conventional, connected, point-of-sale terminal, or an AC/DC power module. 
     Referring now to the block diagram of FIG. 2, scan head, or scan module,  22  includes a scan pattern generator  28 , collection optics  30 , processor means  31  which includes a detector and pre-amp  32  and a signal processing means, or circuit, or mechanism,  34 . The components within scan head  22  are connected by a flexible interconnect  36  to the electronics contained in tower  24 . Flexible interconnect  36  includes a wiring harness  38  (FIG. 4) and a rotation mechanism  40 , the latter of which, in the preferred embodiment, takes the form of a splined positioning mechanism  41  (FIG.  7 ). 
     Scanner tower  24  includes a decoder  42 , a communications interface  44 , and a power conversion/distribution mechanism, or power converter,  46 . 
     Scanner  20  is connected, by a cable  48 , to a host point-of-sale (POS) terminal  50 . Terminal  50  supplies a 12 VDC power source  52  to power conversion/distribution mechanism  46  in tower  24 , which distributes required DC power levels to various components of scanner  20 . It will be understood that POS terminal  50  is of any conventional design and is generally used to determine item identification from the decoded data supplied by the scanner, which ultimately would result, for example, in the generation of a sales or charge receipt Of course, other applications of the code scanner are within the scope of the invention and other sources of power may be provided. 
     A communication means is provided for communicating the information from scanner  20  to an external device  50 . In the preferred embodiment, communication means includes a microprocessor, shown as being part of decoder  42  (FIG. 2) executing firmware within a memory, also part thereof, and communications interface  44 . Those of ordinary skill in the art will appreciate that communications means may have any desired physical and logical interface protocol that enables scanner  20  to communicate over a cable  48  with an external terminal or other device, such as POS terminal  50 . In the preferred embodiment, communication means includes a multiple interface, by which is meant that it supports a plurality of terminal interface standards, including RS232, OCIA and 46XX, and a clock-selection scheme implemented in circuitry and firmware associated with the microprocessor that permits scanner  20  to communicate in any one of these protocols depending upon what terminal is connected and/or which standard is desired. 
     It should be appreciated that while scanner  20  is generally intended to be used with the conventional UPC printed bar code and/or industrial printed bar codes, the scanner is operable to read any type of coded indicia which may be used to identify an object, such as embossed or engraved codes, arrangements of geometric forms and various types of three dimensionally encoded information, so long as appropriate decoding electronic circuits are provided. Referring again to FIG. 1, as used herein, “printed code” or printed bar code” should be understood to include any coded indicia of any type, such as that shown at  55 , located on a surface, which may be on the article itself, as depicted at  54 , using any process, including those described above, which is capable of being scanned by a scan, or light, pattern, such as that depicted in FIG. 1 at  56 . Scan pattern  56 , in the preferred embodiment, is generally conical in shape, having a central axis  57 , and is made up of 11 scan lines, for reasons that will become apparent 
     Processor means  31 , and now referring to FIGS. 1 and 2, generates a digital signal representative of scanned code  55 , which is identified in FIG. 1 as a bar signal. The signal is characterized by a bi-level, low voltage transition between two voltage level which represents a transition in a bar code at light-to-dark and dark-to light edges. 
     Scanner Housing 
     Turning now to FIGS. 3 through 6, components of scanner  20  will be described in greater detail. Scan head  22  includes a scan head housing  58 , which is formed of three separate pieces in the preferred embodiment The three pieces of scan head housing  58 , which also is referred to herein as a scanner housing first portion, or first housing, are joined together by interlocking parts, eliminating the necessity for any type of fasteners or adhesive binding Scan head housing  58  includes an outboard portion  60 , an inboard portion  62 , and a bezel  64 . A flexible catch  66  is located on outboard portion  60 , which interlocks with a conformal catch receiver  68  in inboard portion  62 . A labyrinth seal  70 , best shown in FIG. 6A, includes a projection  72  on outboard portion  60 , and a receiver  74  on inboard portion  62 . Seal  70  is more than adequate to prevent the incursion of dust and undesirable humidity to the interior of scan head  22  when the scan head is stored or used. Ribs  76  are provided at intervals along the interior of inboard portion  62  to rigidize scan head housing  58 . 
     Bezel  64 , and now referring to FIG. 6B, is constructed to snap-fit over portions  60  and  62 , thereby to maintain the two portions in a sealed relationship. The bezel includes a shade portion  78  which extends outwardly from housing  58  when assembled, and a closure portion  80 , having a rib  82  thereon which is received in a conformal depression  84  located about the periphery of outboard portion  60  and inboard portion  62 . 
     The construction of outboard portion  60 , inboard portion  62  and bezel  64  is such that the three components have a snap-fit, and may be assembled or disassembled without the use of any tools whatsoever. Outboard portion  60  and inboard portion  62  have a window retaining receptacle  86  formed about the free ends thereof, which receive a soft durometer seal  88  therein, which in turn receives a window  90 . 
     This arrangement of mating, joining elements-including catch  66 , receiver  68 , the components of the labyrinth seal  70  and the interlocking of bezel  64  to scan head housing  58 —provides a hinge-like opening for the inboard and outboard portions of housing  58 . A similar construction is used to join components of tower  24 . The external volume of tower  24  preferably does not exceed approximately 492 cm 3  (31.5 in 3 ), more preferably does not exceed approximately 459 cm 3  (28 in 3 ), and is in the preferred embodiment approximately 433 cm 3  (26.4 in 3 ). The external volume of scan head  22  preferably does not exceed approximately 574 cm 3  (35 in 3 ), more preferably does not exceed approximately 524 cm 3  (32 in 3 ) and is in the preferred embodiment approximately 492 cm 3  (31.5 in 3 ). The total external volume of the scanner, including scan head  22  and scanner tower  24 , but excluding base  26 , preferably does not exceed approximately 1229 cm 3  (75 in 3 ), more preferably does not exceed approximately 1065 cm 3  (65 in 3 ), most preferably does not exceed approximately 967 cm 3  (59 in 3 ) and is in the preferred embodiment approximately 949 cm 3  (57.9 in 3 ). As used herein, volume refers to the displacement volume of a solid structure having the same exterior surfaces as scanner  20 . 
     Still referring to FIGS. 3 through 6, scanner tower  24  is, in the preferred embodiment, a two-piece structure, the first piece of which includes part of a mounting  40  for scan head  22 . Referring now to FIG. 7, in the preferred embodiment of scanner  20 , mounting  40  includes a splined positioning mechanism  41  which has a head ring  102  on scan head  22 , a tower ring  104  on tower  24  and a rotation limiter  106 , which is operable, in the preferred embodiment, both to limit rotation of scan head  22  relative to tower  24  to a rotation of 270° in a single plane and physically to retain the scan head on tower  24 . In its maximum laterally extended position, i.e. when rotated 90° from its at-rest position to a horizontal position, scan head  22  increases the projected footprint of the entire scanner housing to something preferably less than approximately 129 cm 2  (20 in 2 ). It may be seen then that the retail counter space occupied by scanner  20  is extremely small whether the scanner is deployed for operation or is stowed in its atrest configuration. 
     Head ring  102  includes plural splines  108  and plural retaining dogs  110 , which are mounted on a cylindrical structure  112 . Cylindrical structure  112  and its splines and dogs are received in tower ring  104 , wherein the splines engage plural teeth  114  to positively lock scan head  22  in a desired operating or stowage position relative to scanner tower  24 . A spring  116  is carried on rotation limiter  106 . Spring  116  may be compressed in order to slip rotation limiter over retaining dogs  110  and through slots  118 , whereupon rotation limiter  106  may be rotated and to position retaining dogs  110  over dog retainers  120  in order to retain rotation limiter on cylindrical structure  112 . Spring  116  will urge rotation limiter  106  away from tower ring  104 , thereby retaining splines  108  within teeth  114 . 
     Scan head  22  may be easily rotated by pulling the scan bead relatively away from scanner tower  24 , thereby disengaging splines  108  from teeth  114 . The scan head may be rotated relative to the tower as desired. Incremental, or stepwise, rotation in 15° steps up to 180° rotation (in one direction) and in 15° steps up to 90° (in the opposite direction), or 270° total, is provided in the preferred embodiment, which limitation is provided by a circle element  122  on rotation limiter  106  which cooperates with a channel  124  on tower ring  104  to limit rotation along a scan head rotation axis  126 . In the preferred embodiment, circle element  122  subtends an angle of 60°, while a stop portion  124   a  of channel  124  subtends an angle of 30°, thereby limiting the rotation of scan head  22  relative to tower  24  to 270°, which is nominally a 90° rotation rearward from the at-rest position shown in FIG  4 , and a 180° rotation from the at-rest position. Such rotation limits enables the scanner to be mounted not only in the depicted upright position on base  26 , but allows sufficient rotation of scan head  22  relative to tower  24  to allow mounting of the scanner to an under-counter surface, walls, and POS terminals. limiting the rotational adjustability of scan head  22  relative to scanner tower  24  ensures that flexible interconnect  36  is not unduly torqued and stressed. 
     Splined positioning mechanism  41  allows for the positioning and adjusting of scan head  22  thereby to reposition the scan pattern relative to the entire scanner without physical movement of the entire scanner. Known scanners are either fixed, thereby lacking adjustability and any ergonomic considerations, or are hand held, thereby limiting the ability of the user to manipulate objects being scanned, or have inconvenient or cumbersome adjustment mechanisms. The positioning mechanism of the invention provides the ability to position and positively lock the scan head in a desired position for indefinite periods of time, without slippage or otherwise unintended rotation. 
     In addition to the preferred embodiment of the mounting for scan head  22  previously described, several alternative forms are useable to accomplish the goal of positioning scan head  22  relative to tower  24  and maintaining the relative position over the course of operation. 
     The first alternate embodiment of mounting  40  is depicted in FIG. 7A, is depicted generally at  40   a  and is referred to herein as a push-button release. Mounting  40   a  incorporates a button  330  which is located in scan head  22 , which is urged to an engaged position, depicted in FIG. 7A, by a spring  332 . Button  330  includes a spline-bearing portion  334 , which extends through an opening  336  in scan head  22  and opening  338  in tower  24 . As depicted in FIG. 7A, tower  24  includes an alignment portion  340  which is received in a conformal aligmnent portion  342  in scan head  22 . 
     Spline-bearing portion  334  includes a number of splines  344  carried thereon, which interact with conformal splines  346  on tower  24 . When button  330  is in its engaged position, the splines align with one another in an engaged relationship, thereby locking scan bead  22  relative to tower  24 . If it is desired to rotate scan head  22  relative to tower  24 , button  330  is pressed inwardly, in the direction of arrow  348 , thereby disengaging the splines on the button and on the tower, permitting relative rotation between scan head  22  and tower  24 . The provision of button  330  allows one-handed adjustment of scanner  20 . 
     Referring now to FIG. 7B, a mounting  40   b  is depicted. Mounting  40   b  is a modification of the push-button configuration of FIG.  7 A. Scan head  22  includes a spline bearing portion  350  which extends into tower  24 . A retaining ring  352  is urged inwardly in tower  24  by a spring  354  to maintain scan head  22  in an engaged position with tower  24 . Scan head  22  includes splines  356  and spline bearing portion  350  includes splines  358 , which engage one another. 
     In order to rotate scan head  22  relative to tower  24 , the scan bead is pulled outwardly along rotation axis  126  so that splines  356  and  358  disengage, thereby permitting relative rotation of scan bead  22  relative to tower  24 . 
     Referring now to FIG. 7C, mounting  40   c  is depicted. Mounting  40   c  includes a projection  362  on scan head  22 , which extends into a conformal scan head projection  364  on tower  24 . Serrated, or checkered, regions  366 ,  368  are provided on the mating surfaces of scan head  22  and tower  24 , respectively, to provide a frictional lock between the scan head and the tower. A retainer  370  is fixed to projection  362  and provides a reaction surface for a spring  372  which urges the checkered portions towards one another. The checkered area may be formed of non-conformal surfacing, which relies solely on a friction fit to maintain relative position between scan bead  22  and tower  24 , or, the regions may be formed with serrations, such as conformal teeth, so that distinct, repeatable orientation of scan head  22  relative to tower  24  may be achieved. 
     A variation of mounting  40   c  may include the provision of a locking knob, whereby the scan head is positively locked relative to the tower. Such a conFIGuration is by far the least expensive to construct, however, requires two-handed operation to adjust the scan head relative to the tower. 
     The mounting, or rotational hinged design, is desired to provide a minimum of 90° of rotation between the scan head and the tower, but, because of the presence of harness  36  which extends between scan bead  22  and tower  24 , is best restricted from full, 360° rotation. A compromise position, as set forth in connection with the preferred embodiment, is to provide 270° of rotation between scan head  22  and tower  24 . 
     In order to remove scan head  22  from tower  24  for servicing, the mounting must be disassembled. Such disassembly will generally be accomplished from the towerside of the hinge and will require removal of the internal components of the tower, which will be described next. 
     Referring now to FIGS.  1  and  4 - 6 , scanner housing  21  includes a second housing portion, or tower housing,  98 . Housing  98  includes a tower cover  130  which fits on a tower first piece  100  by means of a flexible catch  132  and a catch receiver  134 , which are constructed similarly to the same-named structures on scan head housing  58 . A labyrinth seal  70  is provided between the two pieces of tower housing  98 . The housing includes integrally formed snap fittings, which, in the preferred embodiment, include a latch  136  on first piece  100  and a receiver  137  on cover  130 , which hold the two halves of the tower housing together. 
     The tower housing snap-fits onto scanner base  26 , which has a generally flat appearance. The base has an upper surface which receives tower  24  thereon, wherein the two elements snap-fit together. In the preferred embodiment, a grip  138  on base  26  fits in a notch  139  in tower  24 . The base also has a lower surface and spaced-apart sides about the periphery thereof. 
     Briefly referring now to FIGS. 5,  8  and  8 A, base  26  includes a receptacle  140  for receiving a cable connector  142 , for connecting a cable  48  from scanner  20  to POS terminal  50 . Receptacle  140  extends between the upper and lower surfaces of the base, and provides for the connection of connector  142  to a plug which is located in tower  24 . In some instances, it may be desirable or necessary to route cable  48  out of base  26  through various ports  144  formed in the side of base  26 . To this end, cable guides  146  are provided, which define multiple cable paths on the lower surface of base  26  and which serve to route cable  48  to a desired port at the periphery of the base, thereby further increasing the versatility and mounting configurability of scanner  20 . As depicted in FIG. 8A, a cover  148  may be provided to partially enclose the bottom of base  26 , thereby retaining cable  48  in the base. 
     Returning now to FIGS. 4 and 5, tower first piece  100  is intended to receive two printed circuit boards (PCBs)  280 ,  282  therein, and includes mounting points  150  for fastening the PCBs thereto. For the sake of compactness, it will be appreciated that the PCB assemblies made in accordance with the preferred embodiment of the invention may be single or multi-layered and use, wherever possible, surface-mount electronic. components. 
     Referring to FIGS. 6C and 6D, key-hole mounting structures  152  are provided to affix tower  24  to a surface, such as a counter underside, or directly to a POS terminal. When structures  152  are used, the alternate form  26   a  of the base is used. Importantly, mounting structures  152  permit lightweight, ultra-compact scanner  20  to be positioned and oriented virtually anywhere and anyway. For example, scanner  20  may be affixed by structures  152  (and corresponding post pairs, not shown) to the ceiling, on a wall on the side of a terminal, on a counter or even in a doorway, if desired. 
     The Optical Subsystem 
     Referring now to FIGS. 3 and 4, an optical subsystem, shown generally at  160 , will be described. Optical subsystem  160  includes a chassis  162  which is contained within scan head  22 . Chassis  162  includes mounting points  164  which receive shock mounts  166  thereon. Shock mounts  166  are received on optical subsystem chassis retainers  168  on outboard portion  60  of scan head housing  58 . Optical subsystem  160  may be seen also to include scan pattern generator  28  and collection optics  30  (which, it will. be understood, share certain elements, ie. the window, the basket, the rotating mirror, the motor control). 
     The Light Source 
     Scanner  20  incorporates a visible laser diode (VLD) as a source of coherent light which is projected from scan head  22  onto the object being scanned. A VLD light source  169  is contained within VLD housing  170 , which is secured to a VLD housing mount  172 . VlD  169  emits a coherent light laser beam typically in the 600 nm to 800 nm range. 
     Mount  172  is constructed so that VLD housing  170  is fixed to the mount, but is adjustable relative to chassis  162  in two orthogonal planes. Adjustment is accomplished by an adjustment mechanism  173 , which includes a VLD adjusting screw  174 , which accounts for alignment, in a first plane, or about what will be referred to herein as a Y-axis. A first PCB  176  is carried on the VLD housing mount  172  and contains the circuitry which drives the VLD within VLD housing  170 . VLD housing mount  172  is secured to chassis  162  by means of a single screw-type fastener  178 . A second VLD adjusting screw  180  provides alignment of VLD housing  170  in a second plane orthogonal to the first, or about what will be referred to herein as an X-axis. Chassis  162  includes PCB mount  182 , which grasps one side of a PCB  184 , and two other PCB mounts  186 ,  188 , which grasp the other side of PCB  184 . 
     The Optical Basket 
     Importantly contributing to the high functional density of scanner  20 , an optical basket  190  is included as part of the optical subsystem and includes a truncated frustoconical structure having an array of plural facets  192  about the internal periphery thereof in what will be referred to herein as a substantially continuous, generally circular or annular array. Facets  192  are coated with a mirror-element  194 , thus together forming an array of plural reflecting elements in the optical basket Mounting pins (not shown) are provided to properly align optical basket  192  in an optical basket mounting structure, shown generally at  198 . Optical basket mount  198  includes pin receptacles (not shown) for receiving the mounting pins, a mounting flange  202  for receiving the periphery of the optical basket therein, and clips (not shown) for holding basket  190  in place. 
     In the preferred embodiment, basket  190  has a diameter at its wide end of approximately 4.6 cm (1.8 in). This greatly contributes to the compactness of scanner  20 . It is possible to provide, for a specific application, a scanner having basket diameters of up to about 7.7 cm (3 in), with a corresponding decrease in functional density, however, the preferred range is between about 3.8 cm (1.5 in) and 5.1 cm (2 in). 
     Scanner Motor and Circuit 
     A scanner motor  210  is provided to drive a scanning or rotatable mirror  212 , which preferably is received on the end of a motor shaft  214 . Surprisingly, it has been determined that motor  210  preferably is of a relatively compact “cup” style, by which generally is meant motor  210  preferably is a DC brushed motor, rather than being of the brushless style. Motor  210  is carried on a motor mount  216  which is secured to chassis  162  by a single screw, and is held in place by protrusions  218 , which extend upwardly from the base of chassis  162  When optical subsystem  160  is assembled, scanning mirror  212  is centrally located within optical basket  190 . 
     Use of DC brushed motor  210  in scanner  20  realizes many advantages over prior art scanners. First, it is much more efficient, and thus produces much less heat. Second, it requires simpler motor drive control and monitoring circuitry, thus further enabling a compact scanner. In accordance with the preferred embodiment, the contact points of the brushes (not shown) of DC brushed motor  210 , which is otherwise of conventional design, are of gold (Au), although it is believed that they may be made of one or more precious metals that tend to have a long life, high corrosion-resistance and not subject to frictional particulate wear and/or electro-erosion. The motor used in the preferred embodiment operates on five volt DC power and spins nominally at 5500 rpm. While the motor control circuit used in the preferred embodiment of the invention is conventional for the most part, the motor spin monitoring circuit deserves special mention. 
     Turning for a moment to FIG. 9, which is a simplified schematic block diagram illustrating how a controller circuit  298 , also referred to herein as a motor spin monitoring circuit, operates. In connection with a DC voltage V selectively impressible via a switch S thereacross, the preferred motor spin monitoring circuit may be seen to include a motor winding sense resistor R 1  which develops a voltage thereacross that is proportional to the instantaneous current in the winding of a spin, or scanner, motor M, first and second, corresponding, DC-decoupling capacitors C 1 , C 2  series connected as shown between either side of resistor R 1  and the inputs of a first voltage comparator  302 . Grounding resistors R 2 , R 3  are provided for reference purposes. Resistors R 1 , R 2 , R 3 , capacitors C 1 , C 2  and comparator  302  may be seen to form a current sensor that is connected with the drive terminals of motor M for producing a signal that is proportional to a defined characteristic, e.g. frequency, of the current through the excitation winding thereof. 
     Importantly, the voltage input to comparator  302  is only differentially compared, as between the high and low sides of current sense resistor R 1 , rather than being compared with an absolute DC voltage reference level. This renders the spin monitoring circuit much simpler and less dependent upon the absolute current characteristics and other conditions of the winding of motor M, which tend to vary over time. Thus, comparator  302  acts as a zero-crossing detector to produce an output pulse sequence signal representative of a current condition of motor M, e.g. its frequency, which is indicative of whether motor M is spinning. A microprocessor, e.g. the one that is a part of decoder  42 , may monitor the output signal produced by comparator  302  and, if the frequency of the measured pulse sequence therein falls below a predefined threshold frequency, then the laser beam may be turned off (followed by the turning off the drive signal to motor M). 
     A defined output signal characteristic of comparator  302  thus represents the condition of whether motor M is spinning in accordance with a first motor winding characteristic, e.g. current, and a corresponding, predefined criterion, e.g. frequency. It will be appreciated that any suitable current characteristic may, in accordance with the invention, be compared with any predefined criteria to determine whether motor M more probably is spinning or has stopped. 
     For redundancy, the voltage across the same winding of motor M also is monitored by a second voltage comparator  300  (which of course may be part of the same comparator as is used to monitor current conditions), with the winding voltage similarly DC decoupled by the provision therewith of corresponding, series-connected capacitors C 3 , C 4  and similarly grounded through grounding resistors R 4 , R 5 . Resistors R 4 , R 5  and capacitors C 3 , C 4  may be seen to form a voltage sensor connected with the drive terminals of motor M for producing a signal proportional to the back EMF across the excitation winding thereof An output pulse sequence signal from comparator  300 , which similarly is reference level-independent in accordance with the discussion above regarding current characteristic monitoring, thus represents the condition of whether motor M is spinning in accordance with a second motor winding characteristic, e.g. voltage, and a second defined criterion, e.g. frequency. The pulsed output of comparator  300  similarly may be monitored by a microprocessor to determine whether it remains above a predefined threshold frequency, and if it is determined that the measured frequency is below the threshold frequency then motor M may be stopped (and the laser beam turned off). 
     So long as both output signals of comparators  300 ,  302  meet predefined criteria, it is assumed that motor M is spinning. But if either output fails to so meet the criteria, then such is treated as an indication that motor M has stopped spinning, for whatever reason, which in rotating mirror-type laser systems would result in a fixed coherent beam of light of relatively high energy that might exceed allowable regulatory limits. In such case, and importantly now with redundancy that avoids prior art failures to detect such a stilled or stopped spin motor, the laser beam is inactivated, or turned off, to avoid such a condition. Thereafter, the drive to the scanning mirror motor may be turned off. Those skilled in the art will appreciate that the reverse sequence would be better used in restarting a laser scanner, i.e. the motor would first be turned on and, when the motor is up to speed, the laser beam would be activated. 
     The above described motor spin monitor, or motor spin-monitoring circuit, may be seen to avoid exceeding allowable regulatory limits that might result from a condition in which the non-rotation of rotating mirror  212  will produce no scanning, but instead will produce a fixed, non-patterned, laser spot. It will be appreciated that alternative current and voltage characteristics may be sensed, e.g. amplitude, phase, etc, and alternative criteria may be used to determine whether motor M still is spinning or has stopped, and that such are within the scope of the present invention. It also will be appreciated that there may be numerous applications for the invented motor spin-monitoring circuit in any laser system having a normally rotating mirror element which is used to produce a scanned light pattern. Thus, its application in the present printed code scanning system represents only one such application for the circuit within the broad scope of this aspect of the invention. 
     The Scanning Mirror Referring again to FIGS. 3 and 4, scanning mirror  212  includes a mirror cradle  219 , which has a mounting portion  220  including a receptacle  222  for motor shaft  214 . A counter-balance  221  is located on mounting portion  220  to balance mirror  212 . Tabs  223  are provided to properly position the mirror proper in the cradle. 
     Scanning mirror  212 , also referred to herein as a driven or rotating or deflecting mirror, includes a flat reflective surface  224  which includes a zone one area  224   a  or first region, and a zone two area  224   b , or second region. 
     Mirror flatness in zone one is, in the preferred embodiment, approximately 4 fringes/cm (10 fringes/in), while mirror flatness in zone two may be relaxed slightly to approximately 12 fringes/cm (30 fringes/in). The optical flatness of the surfaces is achieved through a precise injection molding process to tolerances which are extremely small, such tolerances demanding exceptionally careful handling and processing, in order to produce mirror surfaces which result in the highly efficient scanner disclosed herein. The performance of scanner  20  is uncompromised by its ultra-compactness and relatively low cost. Mirror surface  224  is deposited on scanning mirror substrate  225 , which is secured to cradle  219  by double-sided adhesive tape in the preferred embodiment. 
     System Cooling—Scan Head 
     Another important feature of rotating mirror  212  is that it provides air movement within scan head  22  in order to provide some degree of cooling to the heatproducing electronic components in the scan head, including the VLD (which is conventionally heat-sinked, as shown), and the motor drive and motion detection circuitry included on two small PCBs mounted within scan head  22 . In some instances, it may be desirable to add additional vanes to mirror  212  in order to provide more air movement. Of course, such must be done with proper regard to preserving the low and balanced mass of all rotating, or driven, elements. Alternately, shaft  214  of motor  210  may be extended through the other end of the motor and a fan blade assembly may be attached thereto. 
     An important feature of the scanner of the invention is the minimal heat transmission from tower  24  to scan head  22 . It has been demonstrated that an increase of as little as 1° C. within the 45° C. to 50° C. upper operating temperature range, will result in a decrease of several thousand hours of life in the VLD. Additionally, the design of the optical aperture in accordance with the preferred embodiment, e.g. the selection, dimensioning and arrangement of the basket and associated components of the beampath director, allows the VLD source to be driven at a lower current, which also results in a longer VLD life. The scanner is constructed to provide thermal partitioning in order to maintain acceptable temperatures within the scanner housing. Thermal partitioning will be more fully discussed later herein. 
     The Window 
     Window  90  is mounted in scan head  22  and is operable to bend the beam emanating from VLD housing  170  to direct the beam, by means of a series of beam-directing elements, towards other components of the optical subsystem. Window  90  includes a generally planar support structure  230  which has a number of components projecting rearwardly from an interior side  230   a . Support structure  230  is also operable to rigidize scan head  22 . The exterior side  230   b  of structure  230  faces outwardly from housing  58 . The first components are interlocking posts  232  which cooperate with grips  234  on chassis  162  to secure and stabilize window  90  in a proper position relative to the rest of the optical subsystem Alignment pins  236  are provided and are received in pin receivers  238  on chassis  162 . Stops  240  cooperate with the flat front peripheral surface  242  of optical basket  190  to further rigidize the important positional and orientational relationships between window  90  and optical basket  190 . Grips  234 , arms  232  and the front surface  242  of basket  190  make up what is referred to herein as a basket stabilizing structure  243 . 
     A first mirror mount  244  is provided on the rear surface of mirror  90  and includes a first turning, or directing, mirror  246  carried thereon. A second mirror mount  248  is fixed to window  90  and carries a mirror substrate  249  thereon. A second turning mirror  250 , having formed therein a collecting mirror  251 , is formed on substrate  249 . Second turning mirror  250  also includes a dispersing mirror  252  which is, in the preferred embodiment, located centrally within collecting mirror  251 . Known scanning devices utilize mirror surfaces exclusively to fold or bend light beams, such as that designated  253 . The mirrors in the scanner of the invention use curved mirrors, which are effective to not only bend, but also to focus, the light beams. The mirrors located on window  90  comprise what is referred to herein as beam-directing elements. The details of the formation of the first, second and third mirrors will be described in greater detail later herein. 
     In the preferred embodiment, collecting mirror  251  has a concave ellipsoid configuration and is operable to both turn and to focus light which strikes it Mirror  251 , also referred to herein as a convergence region, or second mirror zone  1 , is constructed to a first specified optical smoothness and accuracy. 
     Dispersing mirror  252  has, in the preferred embodiment, a hyperboloid convex curvature and is also operable to turn light which strikes it while simultaneously causing the light to spread, or disperse. Mirror  252 , also referred to herein as a divergence region, or second mirror zone  2 , is constructed to a second specified optical smoothness and accuracy. The curvatures in the drawings are greatly exaggerated. 
     The Optical Path 
     Referring now to FIG. 10, an optical path is depicted generally at  254  and includes a transmitted light beam path  254   a  (dash-dot line) which emanates from VLD housing  170 , is directed towards first mirror  246 , and impinges on dispersing mirror  252  and scanning mirror  212 . As scanning mirror  212  rotates, the beam is directed towards the facets  192  of optical basket  190 , and is directed out through a transparent portion, or first region,  256  of window  90  where it forms what is referred to as an asterisk (*) light pattern when it strikes an object to be scanned (refer briefly to FIG.  1 ). 
     Return scattered, or what is referred to loosely herein as reflected, light, in the form of a reflected light beam path  254   b  (dashed line), returns from a bar code within the field of view of scanner  20  to scan head  22  through transparent window portion  256 . There it is reflected from facets  192  of basket  190  onto scanning mirror  212  and thence onto second mirror  250 , where it is directed to an optical detector  260  through a filter  262  on PCB  184 . Filter  262  may be an interference filter, which may be formed of coated mylar, and which allows light in a bandpass nominally centered on the wavelength of the VLD selectively to pass therethrough. The signal from optical detector  260  is then processed by a pre-amp carried on PCB  184 . The mirror components of scanner  20  are referred to collectively herein as a beam-path director  258 . 
     A feature of basket  190  is the inclusion of a gap, or notch,  264  in one side thereof, which provides a passage for beam path  254   a  through a side of the basket. Gap  264  allows further compaction of the components of scanner  20 . 
     Returning to the mirrors which are provided in optical subsystem  160 , and with reference to FIGS. 3,  4  and  10 , it should be appreciated that, in order to maintain a structure in scan head  22  having as low a mass as possible, the optical elements thereof are formed, as much as practical, of plastic or polymer material. This includes the mirrors which are used in the optical subsystem With the exception of directing mirror  246 , which in the preferred embodiment is formed of conventional reflective material deposited on glass, the remaining collecting mirror  251 , dispersing mirror  252 , scanning mirror  212  and mirrors  194  in optical basket  190  are all formed by vacuum-depositing reflective, optical coating material on a plastic substrate. This enables the substrates, such as basket  190 , scanning mirror  212  and substrate  249  for mirrors  251  and  252  to be injection molded, thereby forming light, durable, low cost and optically smooth and accurate structures that may serve as a substrate for the reflective material. In the preferred embodiment, mirrors  246  and  250  are attached to their respective mounts/substrates with double-sided adhesive tape. 
     With respect to second turning mirror  250 , the mirror surface of collecting mirror  251  is constructed to a tolerance, or optical smoothness and accuracy, of ≦12 fringes/cm (≦30 fringes/in) off of a perfect ellipsoid curve. Dispersing mirror  252  is constructed to a tolerance, or optical smoothness or accuracy, of ≦4 fringes/cm (≦10 fringes/in) off of a perfect hyperboloid curve. Each of mirrors  251  and  252  have an axis of reflection,  251 A and  252 A in FIG. 10, respectively, which axes are angled relative to one another. In the preferred embodiment, this angle is 12°. Ideally, there would be no difference in the axes of reflection, but such construction would place the light from VLD  169  on the same path as the light going to detector  270 , which is not practical for this device. The mirrors are therefor angled to compensate for the differing location of the VLD and detector. 
     As optical basket  190 , in the preferred embodiment, has eleven facets, the asterisk pattern has eleven lines therein, which intersect at a focal point generally in the center thereof at a predefined distance from the scan head. 
     In the preferred embodiment, optical basket  190  is formed such that facets  192  have an angle of 52.15°, indicated as angle A, from a plane defined by the front surface  242  of the basket. Motor  210  is mounted such that shaft  214  is perpendicular to the front surface of the basket, while the flat mirror surface  224  of scanning mirror  212  is formed with an angle of 50° relative to an axis defined by shaft  214 , as indicated by angle B. Angles A and B are empirically selected based on the overall size of basket  190  and the desired number of scan lines which the scanner is to generate. Put another way, the surface area of each facet is the optically limiting aperture of the device. It is desirable to have non-parallel lines in the scan pattern. For this reason, an odd number of lines should be generated. A goal of providing an optical basket with an overall diameter of two inches or less was selected which, given the sensitivity of optical sensor  260 , dictated that eleven scan lines, and therefore eleven facets, will provide the requisite scan pattern having sufficient scattered light intensity to activate the optical sensor. It should be appreciated that fewer facets may be provided, as may more facets. For instance, a basket having as many as 15 facets may be provided, as may a basket having as few as 7 facets. There is, of course, a tradeoff between the number of facets, the size of facets with respect to height and width thereof, and the sensitivity of the optical detector which is used to provide the electronic signal representative of the code being scanned. The basket is one the most significant determining factors in the compactness of the scanner, so these tradeoffs are made, in the preferred embodiment, in what is believed to provide an optimal optical system 
     The diameter of basket  190  is determined by minimum scan line length needed at the free end of bezel  64 , along with the locations of the basket and motor. The scattered or reflected light also has an impact on the basket diameter and height of each facet. Although all of the facets in the preferred embodiment have equal angles with respect to the basket front face  242 , it is also feasible to design a basket having offset angles, which will result in a slightly different scan pattern. 
     It should be appreciated by those of ordinary skill in the art that it is the width of the basket facet which determines the length of an individual scan line. It is the overall area of a basket facet  194  and scanning mirror  212  which determines how much scattered light will ultimately be collected by mirror  251  and directed towards optical detector  270 . 
     As previously noted, motor  210  and motor mount  216  are fixed to chassis  162  with a single screw, and scanning mirror  212  is carried on motor shaft  214 . Given the selected angles between the reflective surfaces in optical basket  190  and mirror surface  224 , a tolerance is provided to the extent that mirror surface  224  is essentially decoupled from, so as to be outside of, the optical alignment path. This means that the motor, with its attached mirror, may be removed and replaced while the scanner is in the field, and the alignment provided by motor mount  216  and protrusions  218  is sufficient to align motor  210  and mirror surface  224  in order quickly and easily to restore the scanner to operation. Additionally, VLD housing  170  and mount  172  are easily removable and replaceable in the field. Motor mount  216  and VLD mount  172  make up what is referred to herein as an alignment mechanism which provides for selected, removable component (VLD light source housing  170  and motor  210 ) coupling and decoupling. This is an important advantage from both an assembly and field maintenance point of view, as the critical elements of the optical subsystem easily can be replaced without special calibration or alignment tools. 
     Motion Sensor Another feature of the scanner of the invention is the presence of a proximity or motion sensor  270  which is carried on PCB  184 , and which detects the presence of an object in the vicinity of the scanner as a change in the amount of light impacting thereon through an object sensor port  272  in window  90 . Briefly, the provision of object sensor  270  allows the electronic components of scanner  20 , specifically motor  210  and the VlD light source, to be shut down if there is no successful read for a predetermined period, which, in the preferred embodiment, is generally user adjusted to five minutes, and yet to be quickly re-activated by movement near the scanner which results in a change in ambient light. 
     Movement of an object in front of window  90  provides a “wake-up”, or start, signal to the electronics to activate the system and scan the object Sensor  270 , in the preferred embodiment, is sensitive to changes in ambient light, and specifically, is a shadow sensor, or detector,  271  which is sensitive to reductions in light. Put another way, sensor  270 , which includes shadow sensor  271  and circuitry required to generate the start signal, is shadow activated. If there has been no successful read for a five minute period, and there are no changes in ambient light, a timing circuit (not shown) will time-out and shut down power-consuming and heat-producing components such as VLD  169  and motor  210 , in that order. As soon as there is a reduction in the average amount of light entering sensor  270 , the scanner will wake up, first starting motor  210  and then activating VlD  169 . This scenario is used to wake up the scanner as a sales associate approaches the scanner, which will generally result in the casting of shadows in the vicinity of the scanner, which in turn will generate the wake up signal. 
     It has been discovered that, by the use of a cadmium sulfide (CdS)-type sensor  271  positioned as illustrated, scanner  20  can be activated to read printed code generally on a first pass. This fast “wake-up” is the result of using a cup motor  210  which has a fast start-up time. 
     FIG. 13 schematically illustrates in some detail motion detector  270 , also referred to herein as a “wake-up” circuit. Motion detector  270  includes a preferably cadmium sulfide (CdS) photo-sensitive resistor  271 , to detect the level of ambient light reaching scanner  20 . Photo-sensitive resistor, or photoresistor,  271  is located on PCB  184  mounted within scan head  22 , and is responsive to light entering scanner  20  through port  272  in window  90 . Numerous advantages flow from the use of a CdS photoresistor, including a low associated components count that greatly simplifies the detection circuitry, relatively slow frequency response that avoids false-positive responses to 120-Hz noise without resort to filtering; and a spectral response more like that of the human eye than previously known, silicon-based photo-sensitive diodes and resistors having lower sensitivity in certain lighting conditions. 
     A brief description of the operation of the circuit illustrated in FIG. 13 follows, and further explains how the advantages listed above are realized. The resistance of photo-resistor  271  varies in inverse proportion of the light falling thereon, and it and a +5 VDC-connected bias resistor R 6  form a voltage divider the AC output only (via a DC blocking, series-connected capacitor C 5  and a grounded, DC referencing resistor R 7 ) of which is connected to the negative input of an operational amplifier (OP AMP)  402 . The positive terminal of OP AMP  402  is biased to a relatively low reference or threshold DC voltage level by resistors R 8 , R 9  this reference level determining the level of change in resistance of photo-resistor  271  that is needed to trigger a WAKE-UP signal. OP AMP  402  acts as a voltage comparator, the output of which is a negative-going, 100-msec pulse signal that is treated by the microprocessor as a WAKE-UP command. A pull-up resistor R 10  biases the output of OP AMP  402  to a logic one level that is compatible with the microprocessor. 
     Those of skill in the art will appreciate that the sensitivity of motion detector  270  to decreases in ambient light reaching photoresistor  271  may be established by choosing appropriate reference voltage and bias resistors R 6 , R 7 , R 8 , R 9 . Accordingly, while a preferred setting is illustrated, it will be understood to be within the scope of the invention to modify the circuit topology, components and component values to produce a motion detector having any desired sensitivity, frequency and spectral response. The circuit topology and component values shown in FIG. 13 have been found to produce a responsiveness to decreases in ambient light in the vicinity of scanner  20  that obviates multiple passes of a coded object, for example, within the field of view of the scanner, by responding true-positively and quickly to such decreases by turning on scanner  20  and reading a printed code on the object the “shadow” of which was detected by motion detector  270 . 
     The Digital Module Referring again to FIGS. 2,  4  and  5 , a digital processing subsystem  278  having two PCB&#39;s, identified by the reference numerals  280  and  282 , are located in tower  24 . PCB  280  contains a power conversion/distribution mechanism  46 , and is connected to connector  142  and thence to cable  48 . PCB  282  carries decoder  42  and communications means, or a communication interface,  44  thereon. It will be appreciated that decoder  42  and interface  44  may be of conventional design, but preferably are rendered in very large-scale integrated (VLSI) circuits, most preferably surface mount devices, further to increase the functional density of scanner  20 . 
     As depicted in FIG. 2, the scan pattern generator  28  includes the VID light source module  169  contained in VLD housing  170 , the drive for the VLD, contained on PCB  176 , first mirror  246 , second mirror  250 , rotating mirror  212 , window  90 , and object sensor  270 . Additionally, a motor control circuit, or motor controller, for motor  210  is carried on PCB  176 . Optical, or object, sensor  270  is also mounted on the PCB. 
     The collection optics  30  include window  90 , optical basket  190 , rotating mirror  212 , and collecting mirror  251 . 
     Detector  260  and a pre-amp, collectively designated as block  32  in FIG. 2, are both carried on PCB  280 , as is the signal processing unit  34 . Wiring harness  38  is operable to connect to PCB  184  by means of plug  284  carried on the PCB, and connector  38   a , which is part of the wiring harness. The harness exits scan head  22  through a port  286  in rotational mechanism  40 , and connects by means of a connector  38   b  to a plug  288  on PCB  282 . PCB&#39;s  280  and  282  are interconnected by a mating plug arrangement  290 . 
     In the event that it is necessary to replace detector  260 , the detector easily may be replaced in the field along with PCB  280 . As in the case of scanning mirror  212 , although detector  260  is the ultimate destination of the optical path, the arrangement of chassis  162  and the other components of the scanner are such that replacement of PCB  280  with detector  260  thereon will permit very good optical alignment, thereby maintaining the system operational. 
     Referring momentarily to FIGS. 1 and 5, an OFF/ON switch  292  is located on PCB  280 , and is activated by a push button  292   a , which is mounted on tower  24 . A power-on, light emitting diode (LED) indicator  294  also is located on PCB  280 , and an associated viewing window  294   a  is carried on the tower. Scanner  20  is connected to cable  48  and its associated connector  142  by means of a plug  296 , which is also carried on PCB  280 . 
     Thermal Partitioning 
     Turning finally to FIGS. 2 and 14, it may be seen that thermal partitioning of the circuitry and components of scanner  20  has been optimized to increase the scanner&#39;s performance. FIG. 14 illustrates in schematic/tabular form the thermal partitioning of the preferred embodiment of the invention that results in approximately equal heat production form components contained within first and second housing portions, or scan head housing  58  and tower housing  98 . Those of skill in the art will appreciate from a brief review of FIG. 14 that, because power supply  46  and digital circuitry (including decoder  42  and the communications means) mounted on PCBs  280 ,  282  are located within tower housing  98 , it is estimated that in the preferred embodiment the heat produced within the tower housing does not exceed approximately 0.9 watt. It also will be appreciated that, because VLD  169 , motor control, detector  260 , signal processing  34  and motion sensor  270  circuitry are located within scan head housing  58 , it is estimated that in the preferred embodiment the heat produced within the scan head housing does not exceed approximately 1 watt during steady state operation, i.e., after startup of motor  210 , during which there briefly is up to an additional 0.3 watts of heat produced. It is believed that optical subsystem  160  operates accurately and reliably at such a level of heat within housing  21 . Although superior operation is achieved in the preferred embodiment by not exceeding the 1 watt heat production goat it is believed that the optical subsystem may operate effectively with heat production range of 1.1 watts to 1.3 watts, or more. 
     This substantially equal partitioning of the heat-producing components of scanner  20  between scan head  22  and the tower  24  render scanner  20  cool and accurate in extended operation, without the need for anything but convection cooling, as described herein. Thus, it will be appreciated that the preferred embodiment of the invention is believed optimally to have partitioned the electronic and optical components of the scanner in consideration of a number of factors, including the desirable separation of heat-producing from heat-sensitive components, the desirable approximately equal distribution of thermal density between the relatively rotatable scanner housing portions, and the desirable optimization of functional density of all components. It will be appreciated that this last goal of functional density is to some extent inconsistent with thermal separation and partitioning, and that scanner  20  in its preferred embodiment described herein is believed optimally to have traded off the various factors in achieving unprecedented performance in an ultra-compact printed code scanner. 
     The apparatus of the invention is now understood to provide a number of advantages over prior art code scanners, as well as important advantages in scanning mirror motor drive design. The herein described, ultra-compact scanner provides extreme versatility in positioning, orientation and mounting by its relatively rotatable, bifurcated housing portioning. It also provides unprecedented performance, in terms of code-reading accuracy and reliability because of the thermal partitioning of its optical and electrical components and its use of high-efficiency components that produce relatively little heat. In its modified embodiments, the scanner provides all of these advantages and the additional advantage that all such optical and electrical components may be contained within a singular housing suitable for hand held operation. In all disclosed embodiments, size, mass and heat are reduced, as well as manufacture, calibration and field maintenance costs minimized. 
     Accordingly, while preferred and alternative embodiments of the invention have been described herein, it is appreciated that further variations and modifications will become apparent to those skilled in the art and may be made within the scope of the invention.