Abstract:
A non-retroreflective axial scan module has a light source for producing a light beam directed, a scan element disposed receptive of the light beam to provide a scanning light beam, a photodetector for receiving light from the scanning beam reflected by a dataform for producing a signal corresponding thereto and optics for restricting the field of view of the photodetector to the vicinity of a scan line formed by the scanning light beam on the dataform all supported in a housing having a volume of less than about one cubic inch.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the field of beam scanning, and in particular, to the use of scan modules for scanning and/or reading dataforms such as bar codes. 
     Two types of scan modules which scan bar codes and detect light reflected therefrom are retroreflective and non-retroreflective scan modules. An example of a retroreflective scan module is disclosed in U.S. application Ser. No. 09/275,858, filed Mar. 24, 1999, the disclosure of which is incorporated herein by reference. 
     A non-retroreflective axial scan module is disclosed in U.S. Pat. No. 5,506,394, the disclosure of which is incorporated herein by reference. The scan element used in the non-retroreflective scan module in the &#39;394 patent is a so-called axial scanner, for example, wherein a light source, such as a laser diode, produces a beam directed along an axis and a movable scan element is disposed along the axis and receives the beam to provide a scanning light beam directed generally along the axis. This provides for a scan engine or module having a narrow width. 
     Retroreflective and non-retroreflective scan modules are also known wherein the scanning is not axial, but rather a beam from a laser diode is projected in a direction normal to the outgoing scanning beam prior to being applied to a movable scanning element. 
     The non-retroreflective scan module disclosed in the &#39;394 patent has a number of disadvantages, in particular, the photodetector therein is not capable of receiving light reflected from a bar code without also receiving a considerable amount of noise caused by ambient light. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to provide an improvement in an axial non-retroreflective scan module wherein optics are provided to restrict the field of view of the photodetector to the vicinity of a scan line formed by the scan element. 
     Like an imaging system, a non-imaging collector such as the one disclosed in U.S. Pat. No. 5,778,133 increases signal, but unlike an imaging system, it does nothing to decrease the field of view. In fact, non-imaging collectors are generally used where large fields of view are desired. They are therefore a poor choice for a single line scanner. The collection system of the present invention increases signal and reduces field of view. 
     Another object of the present invention is to provide a pen scanner which comprises a pen housing with a writing element at one end and a non-retroreflective scan module mounted in the pen housing to emit the scanning light beam from the other end. The pen scanner is preferably self-contained and has a power source in the pen housing which can comprise a rechargeable or replaceable battery, power management circuitry, signal processing and decoding circuitry and communications circuitry to output data from the device. The communications circuitry is preferably wireless and can use the laser light source itself, a radio frequency transmitter or a light emitting diode. 
     A further object of the present invention is to utilize the non-retroreflective scan-module in a keychain scanner or a pendant scanner configuration. 
     A still further object of the present invention is to provide a scan module of either the non-retroreflective or retroreflective type and of either the axial and non-axial type, wherein the housing thereof comprises a block mounting a light source, scan element, photodetector and optics and wherein the block is mountable on a printed circuit board having signal processing and decoding circuitry thereon to output a signal from the photodetector to the signal processing and decoding circuitry. Alternatively, the photodetector.can be mounted on the motherboard, with the block carrying the optical filter and photodiode aperture. In this case, the block carries the laser with its focusing optics, the scan motor and the collection optics (if used). It can also carry the optical filter for the. photodiode and an aperture that the photodiode receives light through. The block retains all optical components in proper alignment. 
     The printed circuit board may be a motherboard for another device which utilizes a scanning input. For example, the motherboard can be.a printed circuit board for a personal digital assistant, a cell phone or any other electronic device which may also require a scanning capability. In this way, the circuitry for the scan module is already provided on the circuit board and one need only mount the block with the aforesaid scanner elements thereon to scan and decode bar codes and the like. 
     Another object of the present invention is to provide a mounting assembly for a non-retroreflective scan module, so that it can be easily and removeably mounted in a device housing or the like. 
     Still another object of the present invention is to provide an improvement in an axial non-retroreflective scan module wherein the laser is pulsed at a frequency to enable the electronics to distinguish between signal and noise. 
     These and other objects and advantages of the present invention will be achieved in accordance with the present invention as disclosed in the following description when read in conjunction with the attached drawings, wherein: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A-1C are top, front and side views of a scan module according to the present invention; 
     FIGS. 2A-2C are side, front and top views of another embodiment of a scan module according to the present invention; 
     FIGS. 3A-3C are side, front and top views of a further embodiment of a scan module according to the present invention; 
     FIGS. 4A-4C are side, front and top views of still another embodiment of the scan module according to the present invention; 
     FIG. 5 is a pen scanner according to the present invention; 
     FIG. 6 is an illustration of another embodiment of a scan module in accordance with the present invention; and 
     FIGS. 7A-7C illustrate optical AGC according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIGS. 1A-1C, a first embodiment of a scan module  10 A according to the present is shown. In this embodiment, a laser focus and scan mirror drive assembly  13  is disposed between two printed circuit boards  11  and  12 . Alternatively, one board can be used with all of the circuitry thereon. The laser focus and scan-mirror drive assembly is the axial non-retroreflective assembly disclosed, for example, in U.S. Pat. No. 5,506,394. The assembly produces a beam along axis A which is then scanned through a window  18  between lines S—S, as shown in FIG.  1 A. 
     In order to detect light reflected from a dataform, such as a bar code, a photodetector  14  is provided. In order to restrict the field of view F—F of the photodetector, a collection lens  16  is disposed along one side of the module and the photodetector is recessed back behind the collection lens as shown. Disposed between the lens  16  and the photodetector  14  is a filter  15  for filtering out wavelengths other than those of the laser diode in assembly  13  and optionally, a slit aperture  17  which is configured to be long and narrow and aligned with the image of the scan line on a dataform as imaged by lens  16  onto photodetector  14 . The filter can be between the lens and symbol if desired, but it will be larger and more expensive. The slit size is dependent upon the geometry of the system. In this way, the field of view of the photodetector  14  is limited to the vicinity of the scan line on the bar code and the photodetector can therefore be larger than the image of the scan line. 
     Alternatively, the photodetector  14 , such as a photodiode, itself can be long and thin and thereby have a width matching the scan line image, as is shown in FIG.  1 C. The photodiode surface size is also dictated by the geometry of the system. In this embodiment, the slit aperture is optional. Although FIGS. 1A-1C illustrate the photodiode and lens on one side of the assembly  13 , it can also be mounted on the other side or above or below the assembly  13 . Alternatively, two photodiodes can be used with one on either side of the assembly or above and below the assembly If the lens and detector are above or below the plane of the scanned laser the images on the detector will move up and down on the detector as the symbol is moved closer or further away, due to parallax. In this case, the photodiode aperture has to be enlarged in the vertical direction, or the laser will be out of view at some distances. Enlarging the aperture (or shape of the photodiode) increases field of view, decreasing ambient light immunity. This is still better than a bare photodiode. 
     FIGS. 2A-2C illustrate another embodiment  10 B of the present invention wherein the photodetector  14  is disposed so that its surface is parallel to the scan axis A and to the plane of the scan beam and it is disposed between the assembly  13  and window  18 ′ as shown. In order to direct light reflected from a bar code to the photodetector, a reflector  20  is disposed behind the window  18 ′ and it is preferably a parabolic reflector, although it can also be a spherical elliptical or cylindrical reflector. 
     In the embodiment as shown, the photodetector or photodiode  14  is configured to limit the field of view to the vicinity of the scan line as imaged by the reflector  20  thereon. 
     This embodiment is more compact than that of FIGS. 1A-1C, since all of the scanning elements are enclosed in the housing of the assembly  13 . However, the reflector  20  and the photodiode  14  can be disposed on the side of assembly  13  or above or below assembly  13 , as in scan module  10 A. 
     FIGS. 3A-3C illustrate a further embodiment of the present invention. In this embodiment, the photodiode  14  and filter  15  are mounted on a PC board  22  installed in front of the assembly  13 . The plane of the photodiode is parallel to the axis A and thus a fold mirror  20 ′ is provided to direct light reflected from a bar code. In order to limit the field of view of the photodetector to the scan line image, a fresnel collection lens  21  is provided, which is preferably part of window  18 ′, but which can be separate therefrom. The lens can also be spherical or cylindrical, or it can be a conventional (non-fresnel) lens. 
     This embodiment is more compact than that of FIGS. 1A-1C , since all of the scanning elements are enclosed in the housing of the assembly  13 . However, the reflector  20  and the photodiode  14  can be disposed on the side of assembly  13  or above or below assembly  13 , as in scan module FIGS. 4A-4C illustrate a still further embodiment  10 D of the invention. In this embodiment, the photodiode is again in front of the assembly  13 , however the photodiode is facing in the axial direction A and has the filter  15  therewith and is mounted on a board  22 ′. 
     In this embodiment, the collection lens  23  is preferably spherical or cylindrical and is part of window  24 , although it could also be separate therefrom. 
     Moreover, the photodiode has a width.to match the scan line image formed by the collection lens  23 . 
     This embodiment is more compact than that of FIGS. 1A-1C, since all of the scanning elements are enclosed in the housing of the assembly  13 . However, the reflector  20  and the photodiode  14  can be disposed on the side of assembly  13  or above or below assembly  13 , as in scan module  10 A. 
     Instead of using the optics for restricting the field of view of the photodetector, ambient light can be distinguished from signal by pulsing the laser beam produced by the laser diode. The beam is pulsed at a frequency preferably greater than 5 times the highest frequency of the baseband signal. One would then, for example, use a bandpass or narrow band filter to separate the signal generated by reflected laser light from ambient (noise) light. For a hand held scanner working at 36 scans per second, the typical highest frequency of a baseband signal is approximately 30 kHz so that the beam is pulsed out at least 150 kHz and preferably about 450 kHz. 
     FIG. 5 illustrates an embodiment of the present invention wherein a pen housing  30  has any one of the modules  10 A- 10 D referenced as  10  in FIG. 5, so that the scan lines S—S can be emitted from one end thereof. The module  10  includes all of the signal processing and decoding circuitry thereon in one or two or more printed circuit boards forming the housing of the module. 
     Also included in the pen housing is a writing element  28 , which can be a retractable pen cartridge or fixed pen with a cap or the like, and batteries  29 A,  29 B which can be either replaceable or rechargeable AA or AAA batteries. Also included in the pen housing  30  is communications circuitry  40 . The communications circuitry may be circuitry which controls the laser in the module  10  to emit a pulsed output to indicate data. It can also include an LED which can indicate successful decodes when decoding is being carried out and which can also communicate data via pulsing of the light beam (other optical interfaces such as IRDA can also be used and returning data can be received by scanner photodiode). The decode LED can be actuated to transmit data. The circuitry  40  can also be a wireless RF transceiver for communicating data to a host or terminal. The device also includes power management circuitry  41  which is connected to the other components and saves power by shutting off the scan module after a successful decode or a time-out period and/or by staggering the activation of the various components to reduce peak power draws. For example, the circuitry may first turn on a scan motor and let it come up to full speed before laser turn on. Similarly, laser turn on may be delayed until the circuitry has gone through its initiation routine. This will not only reduce overall power drain on the batteries, but will also minimize current spikes (instantaneous) current draw. This is important with small batteries that have high internal resistance. 
     The components  10 ,  29 A,  29 B,  40  and  41  can also be used in a keychain or pendant form factor because of their compact size. FIG. 6 illustrates another embodiment of the present invention. In this embodiment, the module  100  can be any one of the scan modules  10 A- 10 D discussed hereinabove, or it can be a retroreflective and/or non-axial scan module. The module housing includes a block  110  on which a laser scanner assembly  130  including a laser source and a moveable scan element, as well as photodetector  140  and collecting optics  150 . The photodetector  140  generates a signal corresponding to light reflected from a dataform, such as a bar code, and this signal from the scan module is to be signal processed, such as by being amplified and digitized, and is thereafter decoded. This is carried out by signal processing and decoding circuitry. 
     In accordance with the present invention, the signal processing and decoding circuitry is preferably mounted on a printed circuit board  101 , so that one need only mount the module block  110  to the printed circuit board to connect the output of the photodetector to the circuitry or to direct collected light to the photodiode mounted on the circuit board. Other signals for the module, for example, a motor drive signal, a motor feedback signal, a laser drive signal and a laser feedback signal, would also be connected. This embodiment is particularly advantageous where the printed circuit board  101  is the motherboard for another device, such as a cellular phone, a personal digital assistant, a computer terminal or the like. In this case, the motherboard  101  can be constructed with all of the electronics thereon for the scan module, and in order to add the scanning functionality to the device, one need only mount the module block with its supported components shown in FIG. 6 to the motherboard and make the connections therebetween. 
     Power management circuitry and communications circuitry can also be mounted on the motherboard to give additional functionality to the scan module. 
     The modules  10 A- 10 D can be mounted in housings in a simple manner by the-use of a two screw mount disclosed in U.S. application Ser. No. 09/275,858, filed May 24, 1999, the disclosure of which is incorporated herein by reference. 
     Another advantage of the above disclosed systems is that they can be configured to provide “Optical AGC”. This kind of system reduces the change of signal level associated with variations in distance between the symbol and the scanner. Normally the signal received by the collection optics falls off with the square of the distance, as the symbol moves away from the scanner. This can require the use of electrical automatic gain control (AGC) circuitry, or of complex digitizing circuitry that can accommodate signals of widely varying amplitudes. Use of an optical AGC can allow increased working range of a scanner without using either of these things, and optical AGC can usually be implemented without adding any cost to a collection system. 
     To get this advantage, as shown in FIGS. 7A-7C, it is merely necessary to focus the collection system so that the image of the scan line  73 , on the detector  71  through aperture  70  is best when the symbol is far away from the scanner at L 1 , for example, for systems described above, which have a useable range of around two to two and a half feet, the system might be focused about one to two feet out and the detector is positioned near the focal length of the lens L f . FIG. 7A is a top view and FIG. 7B is a side view thereof. When a symbol is positioned closer than this, the image on the detector is out of focus, causing a blurry line, instead of a sharply defined line on the detector. As the symbol moves closer to the scanner, the blur increases until some of it falls on the masked area of the detector as shown in FIG.  7 C. When the symbol is very close, most of the light falls on the masked area, throwing away more and more signal as the symbol comes closer to the scanner. This reduces the signal compensating for the otherwise increasing signal that would have occurred from bringing the symbol closer, maintaining a more even signal level throughout the working range. This optical AGC can be used with a spherical lens  72  or a cylindrical or elliptical lens. 
     It is understood that the embodiments described hereinabove are merely illustrative and are not intended to limit the scope of the invention. It is realized that various changes, alterations, rearrangements and modifications can be made by those skilled in the art without substantially departing from the spirit and scope of the present invention.