Abstract:
A micro-optical system with autofocus capability utilizing micro electro-mechanical systems (MEMS) to vary the focus of the beam achieving increased depth of field and improved poor quality reading. The disclosed micro-optical system includes a light source, a micro-optical element positioned adjacent the light source, a detector configured to provide detection information based at least in part on a location of an object, a processor configured to calculate and transmit, and an actuator configured to adjust the relative spacing of the micro-optical element and the light source based at least n part on the actuation information received. In another embodiment, end-user or OEM focus is disclosed wherein the scanner is varied by altering the focus parameters input by the user. In this embodiment, the focus parameters are dependent on the application for which the scanner is to be used. For example, the device may be configured to have a very small “waist” or “spot” to read extremely small barcodes for applications where space for barcode labels is limited or where barcodes are deliberately made unobtrusive. Similarly, a methods of use of the present invention are also disclosed.

Description:
BACKGROUND OF THE INVENTION 
     The field of the present invention relates to data reading systems, and particularly to an optical system for reading bar codes such as found on consumer products (i.e. a UPC code), the system having improved depth of field and focusing through incorporation of micro electro-mechanical systems. The system is suitable for a variety of stationary or handheld scanners. 
     Bar code scanners, as any optical system, depend upon focused optics for effective and accurate performance. In a detection system such as a bar code scanning device employing a focusing lens, a light source such as a laser, laser diode, or non-coherent light source (e.g., light emitting diode) emits light which passes through and is focused by the focusing lens. The object containing the bar code is passed through the focused beam and if the bar code is sufficiently close to the beam focal point, reflected light from the bar code may be detected resulting in a successful scan. Specifically, the detected light reflected from the bar code is read by the scanner that then creates a signal based on the characteristics of the detected light. Because different barcodes create reflected light having different and unique characteristics, which are detectable by the scanner system, it is possible to assign data to a specific barcode based on the signal produced by the reflected light from the barcode. 
     As known by one skilled in the art, a focal point is typically not a discrete point but may be referred to as a “waist” which is the position along the beam axis where the “cone” of light from the light source reaches a minimum spot size, usually as measured in a direction parallel to the direction of spot motion. 
     A problem arises when the bar code or object being scanned does not fall sufficiently close to the focal point or waist, that is, when the beam spot is too large or too small to successfully read a symbol. By way of example, in a supermarket checkout application, a product bearing a UPC bar code label is passed at a certain distance in front of the window of a checkout scanner. The checkout scanner is designed with a scanning beam with a waist of a given diameter positioned at a certain distance from the window where the bar code is expected to pass. The checkout clerk must become familiar with the proper distance to pass the object in front of the window, that is, the bar code must pass sufficiently close to the scanner focal point or waist (i.e. within its depth of field) in order to achieve a successful scan. 
     However, in some applications, it may be desirable for the scanning device to function over a range of distances. U.S. Pat. No. 5,945,670 to Rudeen et al. discloses a variable aperture device that is electronically controllable for selectively adjusting the waist location of the outgoing beam. U.S. Pat. No. 5,438,187 to Rudeen et al. discloses using a laser beam to different distances via a focusing lens having multiple zones. U.S. Pat. Nos. 5,770,847 and 5,814,803 to Olmstead disclose image readers systems with multi-focus lenses. In systems as disclosed in U.S. Pat. No. 4,818,886, the position of the detector or the light source itself is moved—changing the object distance. 
     Another attempt at providing multiple depths of field is described in U.S. Pat. No. 4,560,862 which uses a rotatable optical polygon mirror having a plurality of facets, each mirror facet being of a different curvature. As the polygon mirror rotates, a different mirror facet reflects the beam from the light source along an optical path, each mirror facet providing a corresponding focal plane. The device multiplexes the signal to read the signal received from the various focal planes. Since the rotating polygon mirror also scans the outgoing beam, the device may also not be readily compatible with existing scanner designs and only allows a certain number of discrete focal points (one focal point for each mirror facet). Moreover, changing between selected sets of focal points would require replacing mirror facets or making some other hardware adjustment or modification. 
     Accordingly, the present inventor has recognized the desirability for a system for actively focusing a data reader/scanner which can change the focus parameters at low power and nearly instantaneously as the scanner reads the bar code. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a focusing system and method of focusing for a data reader, in a preferred configuration comprising a micro-optical system. 
     In a preferred application, the focusing system can vary the optimum waist focus distance as the bar code symbol is read in order to maintain an optimum focus and reduce or eliminate “false” reads or non-reading of the bar code symbol because the waist was either too small or too large. Furthermore, the focusing system may include a micro-optical system which utilizes advanced technology in order to make the scanner extremely compact so that the device is easily fabricated and suitable for use with such devices as pen scanners, hand scanners, wrist-mounted scanning devices, and other applications where it is desirable to have an extremely compact, robust scanning device. In one embodiment, the system comprises a scanning device that is mounted on a silicon substrate using micro-electromechanical systems (MEMS) technology. 
     Another embodiment comprises a scanner having an adjustable focus which could be varied “in the field” for optimum performance in a variety of applications. In this way, the scanner is varied by altering the focus parameters input by the user, wherein the focus parameters are dependent on the application for which the scanner is to be used. For example, the device may be configured to have a very small “waist” or “spot” to read extremely small barcodes for applications where-space for barcode labels is limited or where barcodes are deliberately made unobtrusive. Alternatively, for applications where the barcode label is of poor quality, the scanner may be configured to have a large waist or spot size in order to resolve voids or ambiguities in the barcode. 
     In an alternative embodiment, a focusing system comprises a focus aperture that may be nearly instantaneously varied through the use of an electronic actuator. In this manner, the focus aperture is widened or narrowed to optimize for a variety of bar sizes. Such a configuration is particularly suitable for applications where there are voids in printed bars in that a large waist size better integrates over these voids and increases the accuracy of the scanner. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is a scanning system according to a first embodiment wherein relative movement of a light source and a micro-lens is used to alter the waist size of a scanning beam. 
     FIGS. 2A-2B show a scanning system according to an alternate embodiment wherein an adjustable aperture is used to alter the waist size of a scanning beam, wherein FIG. 2A illustrates a linearly adjustable aperture for controlling the waist size of a scanning beam and FIG. 2B illustrates a rotationally adjustable aperture for controlling the waist size of a scanning beam. 
     FIG. 3 is a schematic of a preferred scanner apparatus suitable for application with the preferred embodiments. 
     FIGS. 4A-4B schematically illustrate the variation in waist size of a scanning beam from a scanner system, wherein FIG. 4A shows the alteration in waist size as one moves farther downstream the scanning beam and FIG. 4B shows the alteration in waist size relative to the configuration of FIG. 4A when the micro-lens and light source are moved closer relative to each other. 
     FIG. 5 illustrates an alternate embodiment of scanner system wherein relative movement of a light source, and a micro-lens is used to alter the waist size of a scanning beam. 
     FIGS. 6A-6B are flow charts graphically illustrating steps involved in a scanning method according to a preferred embodiment, wherein FIG. 6A shows the steps involved in the operation of a scanner system including a detector and processor and FIG. 6B shows an alternate method in a scanning system which does not require a detector and includes an optimization feedback loop. 
     FIGS. 7A-7B show a comb-drive actuator suitable for use with a preferred embodiment wherein FIG. 7A shows the comb-drive actuator in “closed” configuration and FIG. 7B shows the comb-drive actuator in a spaced “open” configuration. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments will now be described with reference to the attached figures. As used herein, “downstream” refers to a location farther away from the light source while “upstream” refers to a location closer to the light source. 
     FIG. 1 is a schematic of a scanner system  20  according to a first embodiment comprising a light source  15  disposed such that light emitted therefrom is incident a micro-optical element comprising a micro-lens  10 . Although the invention is described with reference to a micro-lens  10 , it can be understood that a variety of micro-optical elements are suitable for this application, including, for example, a curved micro-mirror, gradient index lenses, binary optical elements, or diffractive optical elements such as micro-holographic elements. In a preferred embodiment, the light source  15  is a laser diode, however, the system  20  is suitable for use with various light sources, including: a coherent light source such as a laser or laser diode, a non-coherent light source such as a light emitting diode, or combinations thereof. Furthermore, the micro-lens  10  may be comprised of one or more optical elements selected from the group consisting of: spherical, Fresnel and aspheric lenses or mirrors, holographic optical elements, and combinations thereof. Alternatively, a micro-optical element may comprise a curved micro-mirror or a micro-holographic element instead of micro-lens  10 . Although, for simplicity, the preferred embodiments will be described using a micro-optical element comprising a micro-lens  10 , the systems are generally applicable using alternate micro-optical elements as described above. 
     In the embodiment shown in FIG. 1, the micro-lens  10  of the scanner apparatus  20  is preferably mounted on a longitudinally adjustable base portion  30  which is adjustable from a first position relative to the light source  15  to a second position downstream from the first position. In a preferred embodiment, the base portion  30  may be adjustable using a micro-actuator such as a MEMS comb-drive  80  such as shown in FIGS. 7A and 7B. A suitable comb-drive actuator  80  may be manufactured and integrated into a silicon substrate such as substrate  30  as shown in FIG.  1 . Generally, as shown in FIGS. 7A and 7B, a comb-drive actuator  80  includes interdigitated finger structures or “combs”  82  and  84  having fingers  85  and  87  which can be actuated by electrostatically exciting the resonance of polysilicon microstructures parallel to the plane of a silicon substrate such as a computer chip. The combs  82 ,  84  come in interdigitated pairs: one part, the stator  82 , is generally physically anchored to the substrate  30  but isolated from it electrically with the lens attached directly to the corresponding comb  84 . 
     In a comb-drive actuator  80  such as shown in FIGS. 7A and 7B, the displacement  84  between the combs  82 ,  84  is dependant on the applied voltage to the combs  82 ,  84 . Control of this voltage gives precise control of the movement of these comb microstructures. A comb-drive mechanism  80  may also include linear plates (not shown) suspended by a folded-cantilever truss or torsional plates suspended by spiral or serpentine springs (not shown). These mechanisms are generally fabricated from a doped polysilicon film. 
     Accordingly, in such a lateral-drive approach embodied in a comb-drive actuator  80 , a mechanical structure such as micro-lens  10  can be driven parallel to a substrate  40  by the comb-drive  80 . For example, a voltage applied to the interdigited “combs” electrically excites the combs and causes lateral movement of one comb relative to the other comb of the pair. Thus, the fingers  85  and  87  and the combs slide laterally relative to each other. In this manner, the distance between the optical element (such as a micro-lens) and the light source is selectively varied depending on the magnitude of the voltage applied to the comb-drive. Further details of a comb-drive actuator suitable for use with a scanner are shown and described in U.S. Pat. No. 5,025,346, incorporated by reference herein in its entirety. 
     Although a comb-drive actuator  80  is particularly suited for application with a scanner system  20 , it can be appreciated that a variety of micro-actuators may be used. For example, parallel plate capacitors may be used to generate a force transverse to the surface of a substrate  30 . In a parallel plate capacitor, the transverse force created is proportional to the square of the drive voltage applied to the capacitors and inversely proportional to the square of the gap between the capacitor plates. However, the parallel plate capacitor may be limited in its application as the effective range of motion for parallel plate actuators is generally less than 10 microns. In contrast, comb-drive actuators  80  may be configured to have a range of motion in excess of 100 microns. 
     A scanner constructed with a micro-actuator may be advantageously incorporated into a substrate such as a silicon computer chip. In this regard, a comb-drive offers an extremely compact actuation mechanism that enables the scanner to be suitably miniaturized for mounting on a computer chip. Alternatively, the base portion  30  may also be adjusted using a hydraulic drive, a rotary drive, thermal expansion, or any combination of the above which can be made suitably compact to enable placement for miniaturized applications. 
     For example, a micro rotary drive suitable for use with the preferred embodiments is described in U.S. Pat. No. 4,435,667, incorporated by reference in its entirety. In such a drive mechanism, a coiled spring material operates in much the same way as a traditional bimetallic metal strip (although preferably in a much smaller scale) wherein a signal from a signal generator causes the coiled spiral drive to coil and uncoil. Alternatively, a thermal drive unit may be used wherein the varying thermal properties between two joined micro-structures is utilized such that thermal activation of the micro-structures results in bending or deflection in the micro-structures such that linear deflection is possible. These alternative mechanisms for longitudinally adjusting the base portion may be applied by one skilled in the art following the teachings herein and will not be discussed in great detail herein. 
     Through the use of the longitudinally adjustable base portion  30 , a scanner may be configured to automatically adjust the focus of the resultant beam waist  25  in order to accommodate variously sized and positioned objects to be scanned. For example, as shown in FIG. 3, a scanner operates by focusing light emitted by a light source  15  through a micro-lens  10 . The focussed light may be redirected by a fold mirror  12  or, alternatively, may be focussed directly to a scanning mirror  14 . This scanning mirror will dither or reciprocate to produce a scanning beam  22  targeted on the object to be scanned  26 . Alternatively, the scanning mirror may also be replaced by a hologram, prism, polygon mirror, or other suitable scanning means for creating a scanning beam  22 . 
     Light reflected from the object to be scanned  26  is collected by a collection mirror or collection lens (not shown) which collects the reflected light and directs it to the photodetector  18 . The photodetector  18  creates a signal based on the characteristics of the reflected light gathered from the object to be scanned  26  wherein the signal created is unique to the object to be scanned  26 . In this manner, based on the signal created by the photodetector  18 , information or data (e.g., price) previously stored regarding a particular object to be scanned can be accessed for that object. 
     With scanners having a fixed focus, and consequently, a fixed field of view, the performance and accuracy of the scanner may be improved by positioning the object to be scanned at a specific distance from the scanner. The reason for this variation in performance is related to the size of the scanning beam at the object to be scanned. As shown in FIG. 4A, the farther from the scanner an object to be scanned is positioned, the wider will be the beam size  25  at that point. In FIG. 4A, the width of the beam W 3 , is less than that of beam width W 2 , which, in turn, is less than that of beam width W 1 . 
     In some instances, it may be desirable to have a larger beam size  25  in order to improve the performance and accuracy of the scanner. For example, in a bar code scanning application wherein the barcode to be scanned is of poor quality, i.e. has substantial voids, blurring, or other defects, it is desirable to have a larger waist which will integrate over those areas of the barcode which are free of defects. Alternatively, for some barcode scanner applications, it may be desirable to have a narrow beam width  25  in order to read barcodes that are very small. Small barcodes are often used to reduce the cosmetic impact of the barcode or to allow the barcode to be placed in compact or unobtrusive locations. In such applications, a large scanning beam size would result in bringing in false reads or interference from the area surrounding the barcode, causing a decrease in the performance of the scanner and an increase in the incidence of false-reads and no-reads. 
     Accordingly, in a scanner  20 , the micro-lens  10  is configured on a longitudinally adjustable base portion  30  which allows micro-adjustments of the micro-lens  10  in order to vary the beam size  25  in order to optimize the performance of the scanner. As shown in FIGS. 4A and 4B, the scanning beam width  25  will increase proportionally the farther downstream the scanning beam one moves (see, e.g., W 1 &gt;W 2 &gt;W 3  in FIG.  4 A). However, the beam size may also be adjusted by changing the positioning of the micro-lens  10  relative to the light source  15 . In FIG. 4B, the micro-lens  10  has been moved closer to light source  15  relative to its position in FIG.  4 A. By moving the micro-lens  10  closer to the light source  15 , the waist size is decreased for the same distance L 1  as between the configurations shown in FIGS. 4A and 4B. Specifically, the waist W 4  at length L 1  in FIG. 4B is narrower than waist W 1  also at length L 1  in FIG.  4 A. 
     In a scanner  20 , the micro-lens  10  may be configured and operatively positioned such that very small movements of the micro-lens  10  are required to adjust the resultant beam width  25 . Specifically, in order to produce a scanner system suitable for use in extremely compact applications (e.g., pen scanner; wrist-mounted scanning devices) a micro-lens  10  may be configured and positioned such that an adjustment of &lt;10 microns is required to alter the resultant beam width  25 . As shown in FIG. 1, the micro-lens  10  is mounted extremely close to light source  15  such that the focus of the beam may be adjusted extremely quickly with very small movements of the longitudinally adjustable base portion  30 . Accordingly, a scanner  20  may be made extremely compact while having a very fast focusing reaction time. 
     As shown in FIG. 5, in an alternative embodiment, the light source  15  may be mounted to a longitudinally adjustable base portion  30   b  while the lens  10  remains fixed relative to the light source  15 . In this manner, a scanner system  70   b  may be customized for alternative applications and configurations. Furthermore, both the light source  15  and the micro-lens  10  may be mounted to separate longitudinally adjustable base portions  30   b  and  30 , respectively, in order cut the response time of the focusing system in half while doubling the length that the micro-lens  10  and light source  15  may be adjusted relative to each other. 
     In a preferred embodiment, the light source  15  and micro-lens  10  are mounted to a common substrate  40  such as a silicon wafer. As described above, a comb-drive mechanism or other micro-actuator can be integrated directly into the substrate to allow relative adjustment of the micro-lens  10 , the light source  15 , or both. A single substrate provides a compact and robust design which is shock and impact resistant and which can be integrated into the design of a chip for use with an electronic device. Alternatively, a device may utilize both first and second base substrates (not shown) where, for example, the micro-lens  10  is mounted to the first substrate while the light source  15  is mounted to the second substrate. In this embodiment, fabrication of the device is facilitated since the comb-drive or other micro-actuator, micro-lens  10 , and first substrate are fabricated by a first process while the light source  15  and second substrate are fabricated by a second process. 
     The width  25  of the scan beam may also be altered with an adjustable aperture configured to shape the scan: beam emitted from the light source  15 . FIG. 2A shows such a configuration including first and second linearly adjustable walls  42 ,  44  that widen and narrow the aperture  46 . In this manner, the waist  25  of the scan beam is consequently widened or narrowed by the mechanical operation of the first and second walls  42 ,  44 . Alternatively, as shown FIG. 2B, the aperture  46  may be widened or narrowed by rotating the first and second walls  42 ,  44 , relative to each other. 
     In order to optimize the performance of a scanner system  70   b  such as described above in connection with FIG. 5, a comb-drive  80  or other micro-actuator may be used to vary the relative spacing of the light source  15  and the micro-lens  10 . Alternatively or additionally, the waist  25  of the scan beam may be controlled through linear or rotational manipulation of first and second walls  42 ,  44 . However, in order to determine the appropriate waist size  25  desired for a specific application, in a preferred embodiment, the operation of which is graphically illustrated in FIG. 6A, a detector  110  is included for enabling the detection of the location and orientation of an object to be scanned. 
     In the scanning operation shown in FIG. 6A, a scanner device  20  is triggered which activates a detector  10  configured to collect detection information based on the location and orientation of an object to be scanned. For example, a proximity detector may be used to determine the distances and orientation of the object to be scanned. One such proximity detector is described in U.S. Pat. No. 5,495,077, issued to Miller, et. al., the disclosure of which is incorporated by reference in its entirety. Alternatively, an aiming beam may be employed to facilitate the proper aiming of the scanner relative to the object to be scanned. This aiming beam typically comprises a quick burst of visible light that indicates to the operator whether the scanner is correctly positioned to read the appropriate location (e.g., the barcode) on an object to be scanned. One such laser light transmitter and proximity detector is described in U.S. Pat. No. 5,424,717, issued to Platt, et. al., the disclosure of which is incorporated by reference in its entirety. In a preferred application, an aiming beam may be configured such that reflected light from the aiming beam may be detected and utilized for determining the distance and orientation of the object to be scanned. In any event, one skilled in the art can practice the disclosed systems with a variety of detectors that are suited for this function. 
     As shown in the embodiment of FIG. 6A, this detection information collected by the detector  110  is sent to a processor  120  (for example, a microprocessor) which calculates actuation information based at least in part on the detection information received, which the processor  120  then sends to micro-actuators  130  in order to adjust the relative spacing of the micro-lens  10  and the light source  15 . For example, the processor  120  may translate the detection information into a voltage signal, wherein the voltage signal will be sent to the micro-actuator  130  which then activates to the corresponding position. In a preferred application, a scanner device  20  may be constructed without a processor  120  wherein the detector  110  is configured such that detection information may be sent directly to the micro-actuator(s)  130  to be used as actuation information. For example, the detection information can be configured as a voltage signal that is read by the micro-actuator(s)  130  as actuation information. 
     Once the micro-actuator(s)  130  receive the actuation information from the processor  120 , they are actuated to adjust the relative spacing of the micro-lens  10  and the light source  15  in order to appropriately adjust the beam width of the scanning beam for the particular location and orientation of the object to be scanned. In the example discussed in the paragraph above, the magnitude of the voltage received from either the processor  120  or, in the case wherein the scanner  20  does not include a processor  120 , from the detector  110  would be proportional to the resultant change in separation between the micro-lens  10  and light source  15 . 
     After the micro-actuator(s)  130  have optimized the beam width of the scan beam for the particular location and orientation of the object to be scanned, the scanner  20  then scans the object to be scanned and creates a unique scan signal based on the reflected light from the scanned object. This scan signal may then be used, for example, to access previously stored information regarding the scanned object. 
     The flow chart FIG. 6B shows an alternate embodiment wherein the scanner  20  is configured with an optimization feedback loop. Specifically, the object is scanned with a scanning beam as herein described and a scan signal is created based on light reflected from the scanned object. This signal is sent to a processor  120  wherein the processor  120  compares the scan signal to a set value or to a previously obtained and stored scan signal to determine whether the signal is of sufficient quality to produce an optimum result. If the signal is of appropriate quality, the scan signal may then be used as an “optimum” scan signal, for example, to access previously stored information regarding the scanned object. Alternatively, it may be necessary for the scanner  20  to repeat the scan of the object with the relative spacing of the micro-lens  10  and the light source  15  set at the spacing corresponding to the optimum scan signal. 
     Moreover, the processor  120  may be programmed so that if the scan signal does not meet a “minimum” scan signal standard programmed into the processor  120  (e.g., has too much signal “noise”) then the processor creates new actuation information which is sent to the micro-actuator(s)  130 , as discussed above. Following actuation of the micro-actuator(s)  130  to alter the waist size of the scan beam, the object is scanned again and a second scan signal is created. The above process is repeated with the second scan signal, and so on, until a final scan signal of the appropriate quality is created which may then be used to access information regarding the scanned object. 
     Alternatively, signal scan values may be obtained for the whole range of relative spacings between the micro-lens  10  and the light source  15 . The processor  120  can be programmed to either choose the optimum scan signal from the signal values obtained over the range of waist sizes sampled (1) and either use the optimum scan signal to access information regarding the scanned object or (2) choose the relative spacing between the micro-lens  10  and the light source  15  corresponding to the optimal scan signal value and scan the object at that optimized setting. For alternative (2), the resultant scan signal would then be used to access information regarding the scanned object. 
     In an alternative embodiment, the operator may manually set the relative spacing between the micro-lens  10  and the light source  15 . In such a configuration, the relative spacing may be adjusted manually, either by the OEM when the scanner device  20  is manufactured or by a user in the field. For example, the OEM or the user may alter the focus parameters of the scanner device  20  for variously sized and positioned objects to be scanned. In such case, as shown in FIG. 6A, the “detector”  110  is actually the user or OEM who inputs the detection information in the form of the focus parameters input into the scanner device  20 . This alternative embodiment offers a relatively simple and robust design that can be modified for a variety of applications in order to tailor the performance of the scanner  20  to the particularities of the application for which it is intended. 
     A user- or OEM-adjustable configuration is particularly useful in that it allows a single scanner configuration to be tailored for specific applications. For example, the scanner may be programmed by either the user or the OEM to transmit a small waist scanning beam which is appropriate for reading small barcode labels. Alternatively, if the device is to be used on larger applications wherein the print quality of the barcode to be read is low, the device may be configured to have a large waist size which integrates over voids, blurring, and other defects in the barcode label. 
     A micro-optical system for use with a scanner system having an adjustable-waist scanning beam has been herein shown and described. From the foregoing, it will be appreciated that although preferred embodiments have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit of the invention. Thus, the present invention is not limited to the embodiments described herein, but rather is defined by the claims that follow.