BACKGROUN D OF THE INVENTION

The present invention relates generally to optical code readers and, more specifically particularly, concerns an autofocus light source module useful in optical code readers, and the like.

Anyone who has shopped in a modern supermarket is familiar with optical code readers, in this case a bar code scanner, which facilitate rapid checkout by scanning barcodes imprinted on product packages. This is a relatively undemanding application of barcode reading, as a package is essentially brought to a standstill by the operator for purposes of reading the bar code. However, the barcode reader still must have a reasonable range of distances of operation, since the user cannot place a barcode at precisely the same location every time.

One form of optical scanner commonly used with l inear barcodes projects a laser beam at a remote optical code and scans the beam l inearly along the direction of the barcode. More of the laser beam is reflected from the light areas of the barcode than the dark areas (the bars), so the light reflected from the barcode, when sensed at the scanner, contains a sequence of bright and dark portions corresponding, respectively, to the spaces and bars of the barcode, respective!) .

Accurate detection of the light and dark areas of the barcode requires that a well focused light source, typically one providing infrared laser light, be scanned over the barcode, to make an accurate determination regarding which areas are light or dark and, in particular, where the transition between the light and dark areas occurs. A common approach is to focus the light source to a specific position where the barcode is expected to be and to restrict the beam diameter by passing the beam through an aperture of predefined size. Restricting the beam diameter increases the depth of field and. therefore, the operating range over which the light source provides illumination sufficiently focused to allow accurate decoding of the optical code. The range can be increased by reducing the aperture, but only at the expense of reducing overall illumination. That is, a substantial increase in the brightness of the light source becomes necessary. In an effort to extend this operating range, such light sources have been provided with an autofocus mechanism, which includes a movable lens element. This usually yields an effective operating range for many applications.

In many applications, an optical code scanner must be hand-held, placing severe limitations on the size and weight of the device. It should be kept in mind that, in addition to the movable lens element, there would also be at least one stationary lens element in the light source module. The reader would further include a movable mirror to scan the light emitted by the source, a driver to move the mirror, optics to focus the light reflected from the remote optical code, and a photo diode (often an array), all of which need to be closely located to the light source, usually on a single mounting board.

Figure I is a sectional view of a prior art autofocus light source module 10 used in a hand-held barcode scanner. The source of light is a light emitting diode (LED) 12, which emits infrared laser light forwardly, to the right in the figure, typically through a transparent face 12a. At a distance from the LED 12, an aperture and lens assembly 14 is mounted to the rear of a carriage 16, on which is also mounted a winding or coil 1 8. Inward of coil 18. carriage 16 is hollow and fits slidingly over a yoke portion 20a of a frame 20. Frame 20 also includes an exterior portion 20b. which extends rearwardly over carriage 16. On the inside of portion 20b. a magnet assembly 22 is mounted so as to oppose coil I 8.

In operation, magnet assembly 22 and coil 1 8 cooperate to define a linear actuator.

Magnet assembly 22 directs a magnetic field through the coil 1 8. Application of an electrical current to the coil causes it to interact electromagnetically with magnetic assembly 22 so as to slide forwardly or rearwardly (depending on the direction of the current in the coil). LED 12 and frame 20 are mounted in a fixed relationship, so the sliding movement of carriage 16 varies the distance between LED 12 and lens 14 (and between lens 14 and at least one stationary lens), causing the light emitted by the LED to be focused.

A serious shortcoming of lighting module 10 is that it occupies a substantial amount of space. It will be appreciated that there is a minimum distance between diode 12 and the lens of assembly 14. determined by the focal length of the lens. Furthermore, this distance must be at least as great as the full distance traveled by lens assembly 14. Also, yoke 20a must have a sufficient length to accommodate the full distance traveled by lens assembly 14.

Therefore, the forward end of frame 20 must be at a distance from diode 12 equal to at least twice the full distance traveled by lens assembly 14. Module 10 will occupy the full distance from the rear end of diode 1 2 to the forward end frame 20. This distance is just too great for a typical hand-held scanner, and it would be desirable to decrease it substantially.

SUMMARY OF THE INV ENTION

In accordance with one aspect of the present invention, a case made of a magnetic material is provided on an LED serving as the source of light in an autofocus lighting module employing a linear actuator for lens focus. The LED is then used as the yoke for the linear actuator by mounting a coil around the case and a magnet assembly around the coil. The coil is mounted to a carriage which extends forward of the diode for a distance equal to the minimum required distance between the lens and diode, and a lens assembly is mounted to the forward end of the carriage. Since this module will require only sufficient clearance in front of it to accommodate the full distance traveled by the lens, the total length it will occupy is approximately the minimum possible length.

BRIEF DESCRI PTION OF THE DRAWINGS The foregoing brief description and further objects, features, and advantages of the present invention will be understood more completely from the following detai led description of a presently preferred, but nonetheless illustrative, embodiment in accordance with the present invention, with reference being had to the accompanying drawings, in which:

Figure 1 is a sectional view of a prior art autofocus light source module 10 used in a hand-held barcode scanner; Figure 2 is a cross-sectional view of an embodiment 1 10 of an autofociis lighting module in accordance with the present invention;

Figure 3 illustrates an LED 12 ^" with a conventional case and a sleeve 1 3 thereover to provide the layer of magnetic material:

5 Figures 4(A) and 4(B) are schematic representations of the cooperation between assembly 14 and fixed lens L:

Figure 5 Illustrates the magnetic field strength in a linear driver stage of the type shown in Figure 2; and

Figure 6 is a magnetic field diagram, similar to Figure 5, with the laser diode 12 being I O a conventional one in which the case is made of a non-magnetic material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Figure 2 is a cross-sectional view of an embodiment 1 10 of an autofocus lighting

1 5 module in accordance with the present invention. Certain elements in module I 10 are identical to those in module 1 0 of Figure I and bear the same reference characters. The source of light for the module I 10 is the LED 12, which preferably emits infrared laser light. LED 12 is mounted on a substrate S, such as a circuit board. LED 12 has a case or cap C made of a magnetic material, preferably SPCC, Nl, Kovar (Co + Ni) or another soft magnetic 0 material.

Those skil led in the art wil l appreciate that it is not necessary that the LED case itself be made of a magnetic material. For example, it might be desirable to use an LED with a conventional case and simply provide a sleeve over the case which is made of a magnetic material. Thus the invention merely contemplated that a layer of magnetic material be 5 provided about the LED to serve as a yoke, although that layer may be the can itself.

Whenever reference is made in the present document to the LED case, it wil l be understood to also refer to the instance in which the magnetic layer is separate from the case, such as when it is a sleeve. Figure 3 illustrates an LED 12' with a conventional case and a sleeve 13 thereover to provide the layer of magnetic material. This structure may be substituted for0 case 12 in Figure 2.

A coil 1 8 is mounted around the case C of LED 1 2 so that the case can serve as a yoke. Coil 1 8 is mounted so as to be capable of sliding movement over case C. The forward end of coil 18 is mounted to a carriage I 16 having passageways 1 16a, 1 16a. Supports 30. 30 are mounted to substrate S so as to project forwardly therefrom and into passageways 1 16a, 1 16a. Supports 30, 30 are shaped and dimensioned to slide freely within passageways 1 16a. I 16a. whereby carriage I 16 is supported for sliding movement relative to substrate S. An aperture and lens assembly 14 is mounted at the front of carriage 1 16 for movement therewith.

A permanent magnet assembly 22 is mounted to substrate S so as to extend about coil 18. defining therewith a linear actuator having case C as a yoke. Assembly 22 may comprise individual magnets or single magnet polarized to produce an inwardly directed magnetic field the passes through the winding of coil 1 8. In either case, assembly 22 and coil 1 8 are so constructed and oriented that their electro magnetic interaction causes the coil to move along the axis of case C. In applying an electric current to coil 18 will cause it to interact electromagnetically with magnet assembly 22, causing it to move forward or backward, depend upon the direction of the electric current appl ied to coil 1 8. This movement is applied to aperture/lens assembly 14 causing it to move relative to at fixed lens L, adjusting the focus of light emitted from LED 12. It will be appreciated that this mode of operation involves distance sensing electronics for the barcode and control electronics for coil 1 8 which controls the direction and duration of coil current. However, these are common to autofocus systems of this type and will not be discussed further. Module 1 10 further includes a magnet 50 mounted to carriage 1 16 via an extension

45. A Hall effect integrated circuit (IC 40) and is mounted to one of the supports 30 so as to be opposed to and aligned with magnet 50. In operation. IC 40 senses a change in magnetic field when assembly 14 moves forward, since it moves out of alignment with magnet 50. and the magnetic field to which it is exposed changes. Moreover, Hall elements, such as IC 40 are extremely sensitive to such changes and will therefore provide a high resolution indication of lens position. The inclusion of a lens position makes possible to control a bar code scanner when the bar code moves at high velocities relative to the scanner, for example on a high speed production line. Hall effect devices useful in this application are available commercially from Asahi Kasei EMD Corp. (see http://'www.asahi- kasei .CQ. ip/ake/en/funct ion/minute. html). As explained above, the m inimum distance between the front of diode 12 and the lens of assembly 14 is determined by the focal length of the lens. With the present invention, the front to rear dimension of carriage I 16 can be approximately equal to that minimum distance. Enough unobstructed space must be left in front of assembly 14 to permit the assembly to 5 move to its most forward position. However, the distance from the rear of diode 12 to the front of assembly 14 is that most forward position is the m inimum amount of space needed for the autofocus module, and essentially this minimum can be achieved with the present invention.

Figures 4(A) and 4(B) are schematic representations of the cooperation between

I O assembly 14 and fixed lens L. For convenience of description, the components of the lighting module associated with moving assembly 14 are not shown. In Figure 4(A). assembly 14 is at its most forward position. In this position, the aperture of the assembly masks a substantial portion of the light emitted from diode 12. This results in an effective aperture diameter φι at the forward end of lens L. On the other hand, with assembly 14 in its rearmost position

1 5 (Figure 4(B)). much more of the light emitted from diode 12 passes through the aperture. resulting in an effective aperture diameter φι ^" which is substantially greater than φι and a greater focus distance. It will be appreciated that these may vary, depending upon the particular application. However, it is clear that the effective aperture increases substantially with increased focus distance. Therefore, the amount of illumination delivered to the target 0 increases, desirably, with distance of the target, resulting in more consistent intensity of illumination.

Figure 5 Illustrates the magnetic field strength in a linear driver stage of the type shown in Figure 2. That is. one in which the laser diode 12 has a case C made of a magnetic material, which serves as the yoke for the driver. The scale on the left i llustrates how the5 strength of the magnetic field is represented in color. Figure 6 is a magnetic field diagram, similar to Figure 5, with the laser diode 12 being a conventional one in which the case is made of a non-magnetic material. Comparing Figures 5 and 6, It will be appreciated that, when the laser diode has a case is made of a magnetic material (Figure 5), the magnetic filed induced in coil 1 2 is substantially stronger and more uni form than when the laser diode has a0 case made of non-magnetic material Although a preferred embodiment of the invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that many additions, modifications, and substitutions are possible without departing from the scope and spirit of the invention as defined by the accompanying claims.