1. 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 a relatively long single line scan line near the reader in a compact bar code reader.
2. 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 rectangle. 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 are 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. Nos. 4,387,297 and 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 hand-held or stationary scanner.
In the laser beam scanning systems known in the art, a single laser light beam is directed by a lens or other optical components along the light path toward a target that includes a bar code symbol on the surface. The moving-beam scanner operates by repetitively scanning the light beam in a line or series of lines across the symbol by means of motion or a scanning component, such as the light source itself or a mirror disposed in the path of the light beam. The scanning component may either sweep the beam spot across the symbol and trace a scan line across the pattern of the symbol, or scan the field of view of the scanner, or do both. The laser beam may be moved by optical or opto-mechanical means to produce a scanning light beam. Such action may be performed be either deflecting the beam (such as by a moving optical element, such as a mirror) or moving the light source itself. U.S. Pat. No. 5,486,944 describes a scanning module in which a mirror is mounted on a flex element for reciprocal oscillation by electromagnetic actuation. U.S. Pat. No. 5,144,120 to Krichever et al., describes laser, optical and sensor components mounted on a drive for repetitive reciprocating motion either about an axis or in plane to effect scanning of the laser beam.
Another type of bar code scanner employs electronic means for causing the light beam to be deflected and thereby scan a bar code symbol, rather than using a mechanical motion to move or deflect the beam. For example, a linear array of closely spaced light sources activated one at a time in a regular sequence may be transmitted to the bar code symbol to simulate a scanned beam for a single source. Instead of a single linear array of light sources, a multiple-line array may also be employed, producing multiple scan lines. Such type of bar code reader is disclosed in U.S. Pat. No. 5,258,605 to Metlitsky et al.
Bar code reading systems also include a sensor or photodetector which detects light reflected or scattered from the symbol. The photodetector or sensor is positioned in the scanner in an optical path so that it has a field of view which ensures the capture of a portion of the light which is reflected or scattered off the symbol, detected, and converted into an electrical signal. Different photodiode arrangements are described in U.S. Pat. Nos. 5,635,700; 5,682,029; and 6,213,399.
In retroreflective light collection, a single optical component e.g., a reciprocally oscillatory mirror, such as described in Krichever et al. U.S. Pat. No. 4,816,661 or Shepard et al. U.S. Pat. No. 4,409,470, both herein incorporated by reference, and U.S. Pat. No. 6,114,712, filed Oct. 9, 1996, scans the beam across a target surface and directs the collected light to a detector. The mirror surface usually is relatively large to receive as much incoming light as is possible, only a small detector is required since the mirror can focus the light onto a small detector surface, which increases signal-to-noise ratio.
Of course, small scan elements are preferable because of the reduced energy consumption and increased frequency response. When the scan element becomes sufficiently small, however, the area of the scanning mirror can no longer be used as the aperture for the received light. One solution is to use a staring detection system (a non-retroreflective system) which receives a light signal from the entire field which the scanned laser spot covers.
In non-retroreflective light collection, the reflected laser light is not collected by the same optical component used for scanning. Instead, the detector is independent of the scanning beam, and is typically constructed to have a large field of view so that the reflected laser light traces across the surface of the detector. Because the scanning optical component, such as a rotating mirror, need only handle the outgoing light beam, it can be made much smaller. On the other hand, the detector must be relatively large in order to receive the incoming light beam from all locations in the scanned field.
Electronic circuitry and software decode the electrical signal into a digital representation of the data represented by the symbol that has been scanned. For example, the analog electrical signal generated by the photodetector may be converted by a digitizer into a pulse width modulated digitized signal, with the widths corresponding to the physical widths of the bars and spaces. Alternatively, the analog electrical signal may be processed directly by a software decoder. See, for example, U.S. Pat. No. 5,504,318.
The decoding process of bar code reading systems usually works in the following way. The analog signal from the sensor or photodetector may initially be filtered and processed by circuitry and/or software to remove noise, adjust the dynamic range, or compensate for signal non-uniformities. Samples may then be taken of the analog signal, and applied to an analog-to-digital converter to convert the samples to digital data. See, for example, U.S. Pat. No. 6,170,749, which is herby incorporated by reference. Alternatively, analog circuitry may be used to digitize the shape of the signal.
A variety of mirror and motor configurations can be used to move the beam in a desired scanning pattern. A scanner which produces an elongated scan line is described in U.S. Pat. No. 5,621,203. 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. Nos. 4,387,297 and 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 multi-mirror construction composed of a generally concave mirror portion and a generally planar mirror portion. The multi-mirror construction is repetitively reciprocally driven in alternative circumferential directions about a drive shaft on which the multi-mirror construction is mounted. U.S. Pat. No. 6,247,647 describes an arrangement for providing either a multiple line, or single line, scan pattern by means of a controller. All of the above-mentioned US patents are incorporated herein by reference.
In electro-optical scanners of the type discussed above, the implementation of 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 as components all add size and weight to the scanner. In applications involving protracted use, a large, heavy 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 an interchangeable compact slim and module to fit into small compact devices, such as notebooks, portable digital assistants, pagers, cell phones, and other pocket appliances.
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 module and to provide a relatively thin or flat scan module, so that the single scan line can be elongated close to the reader. 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 appliances. A need exists, to develop a particularly compact, lightweight module which contains all the necessary scanner components for such applications.
Objects of the Invention
It is an object of the present invention to provide a module for use in a bar code reader capable of emitting an elongated scan line close to the module.
It is another object of the invention to provide a module that emits a scan line over and parallel to the top surface of the module.
It is a further object of the present invention to provide a non-retroreflective scan module with multiple photodectectors.
It is still further object of the present invention to provide collection optic in a scan module with adjusts the optical power as a function of position on the scan line.
A related object is to provide a non-retroreflective electro-optical scanning module which is both thinner, smaller and lighter in weight then using discrete optical components, while providing a collector area of at least 20 mm2.
It is yet a further object to produce a module having a step-shaped form factor which may be manufactured with a print circuit board forming the base of the module.
Additional objects, advantages and novel features of the present invention will become apparent o those skilled in the art from this disclosure, including the following detailed description, as well as by practice of the invention. While the invention is described below with reference to preferred embodiments, it should be understood that the invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional applications, modifications and embodiments in other fields, which are within the scope of the invention as disclosed and claimed herein and with respect to which invention could be of significant utility.
Features of the Invention
Briefly, and in general terms, the present invention provides a scan module for use in bar code reading systems for reading indicia having portions of different light reflectivity and located on a target at a distance from the scan module, including a generally rectangular module including a support having a generally planar base and planar peripheral sides orthogonal thereto: a laser light source mounted on the support for producing a light beam; a scan mirror mounted on the support in spaced relationship to the light source and positioned so that the light beam from the light source is directed by the scan mirror along a first optical path to a fold mirror mounted on the support which directs the light beam along a second optical path exterior to the scan module in the direction of the target. There are further provided a drive moving the scan mirror so that the light beam is moved in a scanning pattern substantially parallel to the peripheral sides of the support and across the indicia to be read; and at least one sensor mounted on the support for directly receiving reflected light from the target and converting the reflected light in to an electrical signal.
According to another aspect of the invention there is provided an optical scan module having mounted thereon a light source for emitting a light beam; and a scanning assembly for receiving said light beam and for generating therefrom a scanning beam directed to the bar code symbol to be scanned so that the emitted scanning beam is longer than the side of the module which the scanning beam passes over enroute to the target.
According to yet another aspect the invention there is provided a small-size optical scan module in the form factor of a substantially rectangular, step-shaped, parallelepiped module having dimensions approximately 42 mmxc3x9724 mmxc3x9711 mm. In the first embodiment, on one of the larger sides (i.e. preferably a peripheral side 42 mmxc3x9724 mm there is mounted thereon a light source for emitting a light beam, a scanning assembly for receiving said light beam and for generating therefrom a scanning beam directed to an indicia to be read, at least one photodtector and collection optics arranged to received reflected light from the symbol and to direct it to said detector.
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.