GB2354361A - Method of reading data - Google Patents

Abstract

A method of data reading comprising the steps of generating an optical beam and directing the optical beam along an outgoing path, scanning the beam over a scan angle and directing the scanned beam toward the object (eg bar code) to be read, focussing the incoming light from the object toward a scanning mirror 54, pivoting the scanning mirror and reflecting the incoming light from the scanning mirror 54 onto a detector 64. Preferably the components are arranged such that a collection spot remains generally stationary on the detector 64. The scanning mirror may have a scan section and a collection section. An arrangement in which there are two mirrors, one scanning mirror and one collection mirror is also described.

Description

2354361 RETRO -DIRECTIONAL COLLECTION SYSTEM FOR DATA READING The field of

the present invention relates to optical systems for data reading and particularly to a scanning system having an improved retro-directional collection system. Data reading devices, such as bar code scanners, read symbols such as those found on consumer and industrial products, including one-dimensional codes such as UPC code, EAN/JAN, Code 39 or two-dimensional codes such as PDF-417.

Scanners may be stationary, handheld or combination stationary/handheld scanners.

Bar code scanners, as any optical system, require incoming light which has reflected off the target to be focused and sensed by a suitable detector. Typically, the incoming light is collected by a collection mirror or a focusing lens and directed to the detector. Particularly in longer range scanning applications, such as greater than six feet (more or less depending on the scanner), the collecting proficiency of the optical system becomes more critical in order to achieve ef f ective' detection. Put simply, light reaching the detector must have adequate intensity for effective detection. The intensity of light reaching the detector is dependent in part on the size of the collection mirror or the focusing lens.

A retro- directional collection system is an optical system where the image of the detector follows the illumination spot on the target. Current retro-direction systems fall into two categories: flat scan mirror or curved scan mirror.

2 Fig. 1 illustrates a flat scan mirror configuration wherein all the optical elements that effect focus on the system along the scanning direction are placed between the source 12 and the scanning mirror 16. A laser source 12 directs a beam off fold mirror 14 which reflects the beam onto a f lat scan mirror 16. The scan mirror 16 is oscillated to scan the beam over a desired scan angle to produce a scan line. Return light which is reflected and/or refracted off the target reflects off the scan mirror 16 and is then passed through the collection optics 17 which focus the light onto the detector 18. The collection optics 17 disposed along the scanning axis 15 are all between the scan mirror 26 and the detector 18. The present inventor has recognized that one disadvantage of this system is that the collection aperture limit is the size of the scanning mirror 16. In order to collect more light, the scanning mirror 16 must be made larger. A larger scanning mirror requires the scanning- motor and/or flexure to move more mass which may result in reliability concerns, greater power consumption, and larger volume displacement in the scanner.

Fig. 2 illustrates another scan system 20 in which curvature is added to the scanning mirror 26. The laser source 22 directs a beam off fold mirror 24 which reflects the beam onto a flat scan mirror insert 27 on the mirror 26.

The scan. mirror 26 and the flat scan mirror insert 27 are oscillated to scan the beam over a desired scan angle to produce a scan line. Return light which is reflected and/or refracted off the target reflects off the curved scan mirror 26 which focuses the light onto the detector 28. This curved scan mirror system has the advantage of reducing the internal path length of the collection system so the volume of the packaging can be smaller, but it retains the disadvantage of having the scan mirror be the collection limiting aperture.

3 The present inventor has recognized that in either system, a pivoting scan mirror operates both as a fold mirror for outgoing light and as a collection 'mirror for incoming light. Such a system may also require a beam splitter which may further reduce intensity of incoming light. Though it is desirable to have a large size collection mirror, the larger the collection mirror, the more massive pivoting mechanism required to accommodate the larger mirror mass thereby further increasing the overall size and weight of the system. The size of the collection mirror is somewhat limited by the load which may be applied to the pivoting mechanism. Moreover, a larger mirror also increases power consumption of the pivoting mechanism. By contrast, a smaller mirror requires a smaller pivoting mechanism and reduces power consumption and by reducing the load on the pivoting mechanism may also enhance the mechanism's reliability.

Non-retrodirectional systems which do not have the outgoing beam and the incoming beam reflecting off the same mirror typically have their collection system mounted off axis which may result in much larger size systems. The detection spot translates across the detector. This translation requires increased detector area which results in greater susceptibility to ambient light and electronic noise.

Summary of the Invention

The present invention is directed to a scan module and scanning assemblies therefore. In a first preferred construction, the scan assembly seeks to address one or more of the disadvantages discussed above and optionally also to reduce the internal path length requirement of the collection system. In a preferred construction, the collection lens is positioned to focus light from the target onto the scanning mirror with the geometry arranged so that 4 the dither mirror angle compensates for the collection field angle caused by the angular movement of the outgoing beam.

In this case, the collection spot remains sta'tionary on a small detector and the system is retro-directive.

Brief Description of the Drawings:

Fig. I is a diagrammatic view of a retro-directional scanner configuration with a flat scan mirror; Fig. 2 is a diagrammatic view of a retro-directional scanner configuration with a curved scan mirror; Fig. 3 is a top diagrammatic view of a retro-directional scanner configuration according to a preferred embodiment of the invention Fig. 4 is a side diagrammatic view of configuration ot Fig. 3; Figs. 5 and 6 are top diagrammatic view of simulations illustrating how the system of Figs. 3-4 maintains position of the light in the scanning plane focused by collection lens and reflected off the scan mirror; Figs. 7 and 8 are side diagrammatic view of simulations illustrating how the system of Figs. 3-4 maintains position of the light focused in the non-scanning plane by collection lens and reflected off the scan mirror; Fig. 9 is a side diagrammatic view of an alternate embodiment in which the light source is pivoted to produce the scan line; -Fig. 10 is a top diagrammatic view of the scanner configuration of Fig. 9; Fig. 11 is a front perspective view of a scan module employing a dithering light source and a curved scanning/collection mirror; Fig. 12 is a side diagrammatic view of the scanning systems of either of the embodiments of Figs. 9-11; Fig. 13 is a side diagrammatic view of the scanning system of Figs. 3-4; Fig. 14 is a top view thereof; Fig. 15 is a perspective view thereof; Fig. 16 is a side diagrammatic view of an alternate embodiment, the focusing system comprising a mirror.

Detailed Descriiption of Preferred Embodiments Preferred embodiments will now be described with reference to the drawings. For clarity of description, any element numeral in one figure will represent the same element if used in any other figure.

Figs. 3-4 illustrate a scan assembly 50 according to a first preferred embodiment of the present invention. The scan assembly 50 includes a light source 52 (for example a laser diode as shown), a scanning element 54 (shown as a dithering mirror), a collection lens 60 which focuses return light from the target onto the dithering mirror 54 which in turn reflects the return light onto fold mirror 62 and then onto detector 64. The reading beam 51 is directed onto the end portion 56 of the scan mirror 54. The end portion 56 is arranged at 450 to the central portion 55 of the scan mirror 54. The mirror 54 is oscillated or rotated over an angle to produce a scan beam along an outward optical path.

Return light which is reflected and/or refracted off the target is focused by collection lens 60.

In this embodiment, the outgoing beam 51 intersects the scan element 56 parallel to the axis of rotation and is folded 900 into the scan plane. This configuration results in an outgoing beam angle which is equal to the mirror scan angle (0,,i,). The collected light enters the collection lens 60 with a chief ray angle equal to minus the outgoing beam angle (-0,). Since the scan mirror 54 is rotated by (0,,,), the net result is that the chief ray terminates at the same location, namely the stationary detector 64 having been reflected downwardly by fold mirror 62. Since the light is being focused on the detector, the spot on the scan mirror 6 is almost half the size of the lens clear aperture. This relationship results in the stationary lens 60 being the limiting aperture and not the scan mirror 54. Collected power may be increased in a smaller mechanical volume which is particularly desirable for handheld scanners where compactness is desirable. The location of the scan mirror 54 and the detector 64 may be optimized for mechanical placement considerations. The ray angle vs. mirror angle ratios may be changed with scan geometry to optimize the scan mirror size and/or internal path length.

Figs. 5-8 show the results from a computer simulation where the lens 60 is offset to move the detection spot to a location below the lens 60 (onto a circuit board 66). As shown in the figures, the collected spot in the top view remains at the same location even though the outgoing beam has been scanned up to +80 in one direction.

A mock-up of the above described system was constructed in the laboratory modifying the scan assembly of a PSC Inc.

Magellan@ scanner, with a focusing lens and a laser module attached to a flat scan mirror. The laser/scan mirror was rotated by 10 degrees and it was observed that the focused collection spot did not move across a target surface. A Pro-E model has been designed and the ray trace showed similar '.results.

The scanning mechanism may comprise a mirror 54 which is dithered or oscillated as described in the previous embodiment, but may alternately comprise a rotating mirror polygon, a rotating or oscillating prism, or a dithering light source such as described in U.S. Patent No. 5,629,510 herein incorporated by reference.

Figs. 9-10 illustrate an alternate configuration comprised of a scan engine 80 in which the light source is dithered to provide the scanning beam. A light source comprising a laser diode 82 is mounted with a scanning mirror 85.The laser diode 82 and scanning mirror 85 may be 7 mounted together or on a common mount/chassis driven by a single motor. The light source may be centrally mounted in the mirror 85 as in Figs. 9-10 or offset such as at the top or bottom of the mirror. The scanned outgoing beam passes through an opening 92 in the center of the focusing lens to scan a bar code 99 in the scan area. Return light reflecting or refracting off the bar code 99 is focused by focusing lens 90 back onto the scanning mirror 85 and to fold mirror 87 which folds the focused light down onto a detector 89 mounted to PCB 95. The various components may be mounted to a chassis and incorporated into a self contained and removable module such as described in U.S.

Patent No. 5,475,206 hereby incorporated by reference.

Further one or more the components including lens 90, detector 89 and scanning elements 82, 85 may be mounted on the printed circuit board 95 which in turn may be directly mounted within the head of a handheld scanner or indirectly mounted via a chassis such as in the 5,475,206 patent.

The central portion 92 of the lens 90 may be a non powered optical portion of the lens or alternately a gap or hole. As shown in the top view of Fig. 10, the hole 92 may be wider in the scan plane (in the view, the horizontal plane) and smaller in the transverse (non-scanning) plane as shown inFig. 9. Alternately, the central section may have optical power providing focusing characteristics to the outgoing beam 83. If optically powered, the central portion 92 will need be designed to compensate for the outgoing beam 83 being scanned therethrough.

Fig. 11 illustrates a detailed perspective view of an alternate configuration scan engine 100, similar to the embodiment disclosed in U.S. Patent No. 5,629,510 in which the light source is dithered to provide the scanning beam.

A light source comprising a laser diode module 102 and a parabolic collection mirror 105 are mounted on a rotor body 103, the diode being positioned above the collection mirror 8 105. The laser diode module 102 and collection mirror 103 may be mounted together on the rotor body, secured by a mounting plate 107. The rotor body 103 is pivotally supported by flexures 110, 112, 114 (the fourth flexure not visible in the figure) and driven by a magnetic drive assembly as described in the 5,629,510 patent. Pivoting of the laser diode 102 scans the outgoing beam which passes over the collection lens to scan a target object in the scan area. Return light reflecting or refracting off the target is focused by collection lens 108 back onto the pivoting collection mirror 105 (shown as curved, parabolic mirror which further focuses the return beam) which reflects the focused light down onto a detector mounted on a printed circuit board (not shown) The collection mirror 105 may be curved or flat depending upon the given application.

Fig. 12 is schematic side view of a scanning system 110 similar to system 100 in Fig. 11 which shall be used to further explain system configuration techniques. The system includes a laser diode 112 which is pivoted over a total scan angle about an axis 113. The collection mirror pivots about a total angle a,,,t., about the axis 113. The collection mirror 115 and the laser diode 112 may be driven by a common drive or may be driven by separately controlled drive mechanisms (such as motors M, and M,) The scanned beam from the diode 112 passes over the collection lens 116 onto a target bar code 119. Return light reflecting off the bar code 119 is focused by lens 116 toward the scan collection mirror 115 which reflects the light to fold mirror 118 which in turn reflects the return light onto detector 120.

The system 110 is constructed and arranged such that the focused spot on the detector remains substantially stationary. The simplest geometry for such a system, for example, is to set at,,,, and arranging the elements such that 9 d f where d = distance from collection lens 116 to scan/ collection mirror 115; f = focal length of collection lens 116; By controlling the pivoting of the laser diode 112 and the collection mirror 115 such that they are pivoted about the same axis 113 and are pivoted at the same period, the relationship Gi.(t) = 20,-(t) should be able to be maintained where 0j,,(t) deviation angle of the collected light reflected off the scan/collection mirror 115 at a given time t; ()Ou,(t) pivot angle of the outgoing scanned beam generated from laser diode 112 at a given time t.

This relationship is determined by the geometry of the optical components, namely distance d and focal length f and the control of the pivot angles a and.

The laser diode 112 and the scan/collection mirror 115 are pivoted about the same axis and are pivoted at the same period and angle, but optical angles 0.,,, and 01. are different. In this system where a,.,,,, and d = %f, the focus spot of the collected light from the bar code 119 is maintained generally stationary on the detector 120. The system 110 illustrated is an example arrangement and configuration. The relative positions of the optical components and the lens focal length may be modified to achieve the stationary spot on the detector 120. This system has the advantage that the outgoing beam angle 0 and the collection mirror pivot angle a may be separately controlled enabling the relationship of d and f be varied to a desired physical geometry according to physical constraints of the scan module.

The above configuration maintaining a 2 to 1 ratio provides a simplified construction. Other ratios may be chosen and the system designed accordingly. It may be desirable to place the dither mirror 115 closer to the detector 120. For example setting a,,,al = 2,.t.j by using two motors or a single motor with a suitable gear system, and arranging the elements such that d = (3/4) f where d = distance from collection lens 116 to scan/ collection mirror 115; f = focal length of collection lens 116.

By controlling the pivoting of the laser diode 112 and the collection mirror 115 such that they are pivoted about the same axis 113 and pivoted at the same -period, the relationship 0 j. (t) = 4 0, (t) should be able to be maintained where 0j,,(t) deviation angle of the collected light reflected off the scan/collection mirror 115 at a given time t; 00Ut (t) pivot angle of the outgoing scanned beam generated from laser diode 112 at a given time t.

since the dither mirror is closer to the focal point (than the previous embodiment), the area of the dither mirror 115 is 1/4 the area of the collection lens 116.

Figs. 13-15 schematically illustrate a scanning system similar to system 50 in Figs. 3-4 which shall be used to further explain system configuration techniques. The system includes a collection mirror 135 which is pivoted over a 11 total angle a,.,., about an axis 133 and a laser diode 132 which directs a reading optical beam along a path parallel to the rotational axis 133 of the pivoting collection mirror 135. A scan mirror 136 is mounted to the collection mirror 135 at an angle y of about 1350 from vertical (450 from horizontal). The scan mirror 136 scans the beam from the diode 132 over an angle as shown in Figs. 14-15 through a central portion 141 of lens 140 and toward a target to be scanned. Return light reflecting off the target is focused by lens 140 toward the scan collection mirror 135 which reflects the light to fold mirror 142 which in turn reflects the return light onto detector 144. The system 130 is constructed and arranged such that the focused spot on the detector remains substantially stationary, for example by arranging the elements such that d = (M)f where d = distance from collection lens 140 to scan/ collection mirror 135; f = focal length of collection lens 140; and controlling the pivoting of the scan mirror 136 and the collection mirror 135 such that Oi,,(t) 20,,.,(t) where -Oi.(t) deviation angle of the collected light reflected off the scan/collection mirror 135 at a given time t; outgoing beam angle off of scan mirror 136 at a given time t.

Being attached, the collection mirror 135 and scan mirror 136 are pivoted about the same axis and are pivoted at the same period and by directing the optical beam from the laser diode 132 parallel to the rotational axis 133 and arranging the scan mirror 136 at an angle of 1350 (that is 12 orienting the collection mirror 135 vertical and the scan mirror 450 from horizontal) the ratio Oi,, = 20.,t is maintained. In such a relationship, the focus spot of the collected light from the target is maintained generally stationary on the detector 120. The system 110 illustrated is an example arrangement and configuration. The relative positions of the optical components and the lens focal length may be modified to achieve the stationary spot on the detector 144.

The fixed collection system may comprise any suitable components such as lenses, mirrors or combinations thereof.

Fig. 16 illustrates an alternate system 150 employing a curved (focusing) fixed collection lens 160. In the system 150, an optical beam 151 is produced by a light source 152 such as a laser diode. The light source 152 is mounted with pivoting collection mirror 155, which together are pivoted by a suitable pivot drive mechanism about an axis 153. As the diode 152 is pivoted, the beam 151 is scanned over a scan angle and reflected off a fold mirror 156 and toward the target being scanned. Incoming light reflecting off the target is collected by fixed collection lens 160 which focuses the beam toward the pivoting collection mirror 155 which in turn reflects the incoming light toward a detector 164. The components are constructed and arranged as previously described to maintain a stationary spot on the detector 164 over the scanning of the beam 151.

A suitable compact scan module mounted on a chassis or printed circuit board incorporating the scan engine configurations above may be conveniently disposed within the head of a handheld scanner housing. Alternately, the housing may be mounted into an application device such as, for example, a portable transaction terminal (not shown) Electrical connection to a terminal can be made through suitable means such as electrical leads or connectors (not shown). The housing may be formed of plastic and is 13 preferably plated with metal for reasons of shielding the scan engine from stray electromagnetic radiation which improves the signal-to-noise ratio thereof..

The light source in any of these embodiments may comprise any suitable source such as: lasers, laser diodes, coherent light sources, light emitting diodes, non-coherent light sources, and combinations thereof.

Though the above described dithering assembly provides for a highly compact structure, the dithering assembly may further-include additional drive mechanism(s) to produce multiple scan lines for creating a more complex scan pattern such as for example, an asterisk pattern. Such a complex pattern generation system is described in Rando et al. U.S.

Application Serial No. 08/662,514 herein incorporated by reference. Depending upon the application, other scan mechanisms may be used in the module such as for example the other dithering mechanisms disclosed in Rando et al. U.S.

Application Serial No. 08/662,S14, and rotating polygon mirrors or holographic elements, particularly for generating multiple scan lines.

Thus while embodiments and applications of the present invention have been shown and described, it would be apparent to one skilled in the art that other modifications are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the claims that follow.

14

Claims (20)

1 A method of data reading comprising the steps of generating an optical beam and directing the optical beam along an outgoing path at an outgoing angle; scanning the optical beam over a scan angle and directing the scanned optical beam toward an object to be read; focusing incoming light from the object toward a scanning mirror; pivoting the scanning mirror corresponding to the scanning of the optical beam; reflecting the incoming light from the scanning mirror onto the detector.

2. A method according to Claim 1 further comprising arranging scanning and collection optics to maintain position of the incoming light generally stationary on the detector.

3. A method according to Claim I or 2 wherein the step of focusing. incoming light from the object toward a scanning mirror comprises passing the incoming light through a focusing lens.

4. A method according to Claim 3 further comprising passing the scanned outgoing beam around the focusing lens toward the toward an object to be read.

S. A method according to Claim 3 further comprising passing the scanned outgoing beam through the focusing lens toward the toward an object to be read.

6. A method according to Claim 3 wherein the step of scanning the optical beam over a scan angle comprises reflecting the optical beam with a pivoting scan mirror, wherein the scan mirror, light source and collection lens are constructed and arranged such that a collection spot remains generally stationary on the detector.

7. A method of data reading comprising the steps of pivoting a scan mirror, the scan mirror having a collection section and a scan section arranged at.an angle to the collection section; generating an optical beam and.directing the optical beam onto the scan section of the scan mirror; scanning the optical beam with the scan mirror to produce a scanned beam over a scan angle; collecting return light which is reflected and/or refracted off a target through a collection lens and onto the collection section of the scan mirror and then onto a detector.

B. A method according to Claim 7 wherein the scan section of the scan mirror is arranged at 1350 to the collection section.

9. A method according to Claim 7 or 8 further comprising passing the scanned beam over the collection lens toward the target.

10. A method according to Claim 7 or 8 further comprising passing the scanned beam through the collection lens toward the target.

11. A method according to Claim 7 further comprising arranging the scan section of the scan mirror at 450 to the collection section; 16 constructing and arranging the collection lens and scan mirror wherein d (M)f where d = distance from collection lens to the scan mirror, f = focal length of the collection lens.

12. A system for data reading comprising pivoting collection mirror; pivoting scan mirror; a light source for directing an optical beam onto the scan mirror, the scan mirror scanning the optical beam to produce a scanned beam toward a target; a collection lens for focusing light reflected and/or refracted off the target toward the collection mirror; a detector for sensing light focused by the collection lens and reflected by the collection mirror.

13. A system according to Claim 12 further comprising a scan drive motor, wherein the scan mirror and collection mirror are mounted together and driven by the scan drive motor..

14. A system according to Claim 12 or 13 wherein the light source is selected from the group consising of: lasers, laser diodes, coherent light sources, light emitting diodes, non-coherent light sources, and combinations thereof.

15. A system according to claim 12,13 or 14 wherein the scan mirror is selected from the group consisting of: a flat mirror, a curved mirror, a parabolic mirror, a dithering mirror, a rotating polygon mirror, a rotating single facet mirror, a pivoting or rotating holographic element.

17

16. A system according to Claim 12,13, 14 or 15 further comprising a fold mirror positioned between the collection lens and the collection mirror for directing light along a light path from the collection mirror to the detector.

17. A system according to any one of Claims 12 to 16 wherein the scan mirror, collection lens, light source and collection lens are constructed and arranged such that a collection spot remains generally stationary on the detector.

18. An optical scanning system, comprising:

a light source generating an optical beam along an outgoing optical path toward an object to be scanned; a detector for detecting return light from the object; a scan mirror in the outgoing optical path for scanning the optical beam over a scan angle toward the object; a scan/collection mirror for directing the return light toward the detector; a stationary focusing element for-focusing and collecting the return light and for directing the return light toward the scan/collection mirror.

19. A method of data reading substantially as hereinbefore described with reference to and as illustrated in Figures 3 to 16 of the accompanying drawings.

20. A system for data reading, or an optical scanning system, constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in Figures 3 to 16 of the accompanying drawings.