Beam shaping system and diverging laser beam for scanning optical code

• US 6,651,888 B1
• Filed: 11/17/2000
• Issued: 11/25/2003
• Est. Priority Date: 02/02/1999
• Status: Expired due to Term

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Barkan, Edward, Stern, Miklos, Gurevich, Vladimir, Marom, Emanuel, Li, Yajun, Krichever, Mark, Breytman, Alexander
• Primary Examiner(s): Frech, Karl D.
• Assistant Examiner(s): Hess, Daniel A.
• Application Number:
  US09/714,511
• Time in Patent Office: 1,103 Days
• Field of Search: 235/462.01, 235/462.49, 235/472.01, 235/462.22, 235/462.21
• US Class Current: 235/462.21
• CPC Class Codes: G06K 7/10702 Particularities of propagating elements, e.g. lenses, mirrors G06K7/10831 takes precedence
• CPC Class Codes: G06K 7/10801 Multidistance reading

Abstract

An improved optical system for scanning optical codes is disclosed. A laser beam produced thereby is a diverging, nearly diffraction free beam and may be used to produce an elongated scanning spot. A laser assembly which may be used to produce such beams and spots, combines various optical functions in structures which are relatively insensitive to temperature change.

Claims

1. An optical code scanner comprising:

a source for projecting a laser beam from the scanner along a propagation axis to scan optical code symbols and means for optically modifying the laser beam to have

a central peak which diverges from the scanner to the symbols and

a wave front which is generally conical near the propagation axis and flattens at its radial edges with increasing radial distance from the propagation axis.

2. The scanner of claim 1, wherein the laser beam is elongated in a direction perpendicular to the propagation axis.

3. The scanner of claim 1, wherein the central peak diverges linearly from the scanner to the symbols.

4. The scanner of claim 3, wherein the beam produces a spot at a first distance of the scanner which has a dimension d₀ in the direction of scanning less than 13 mils and a dimension d greater than 160 mils at a second distance of the scanner.

5. The scanner of claim 4, wherein the scanner is capable of using the laser beam to read 7.5 mil code at the first distance of less than 9 inches and to read 100 mil code at the second distance greater than 540 inches.

6. A laser beam for use in reading bar codes, the beam having a wave front and a deviation which deviates from a reference plane perpendicular to an axis of propagation, the deviation being characterized by the formula:

7. The laser beam of claim 6, wherein α

is between 0.2·

10<sup>−

3</sup> and 6·

10<sup>−

3</sup> mm<sup>−

1</sup>.

8. The laser beam of claim 7, wherein β

<

2α

/R₀ where R₀ is an aperture.

9. An apparatus for scanning an optical code, comprising:

a source of a scanning laser beam for directing the laser beam along a propagation axis toward the optical code to be scanned and causing the beam to move along a scan line; and

a light detector for receiving light reflected from the optical code, wherein the source of the laser beam includes a laser diode and an optical system positioned with respect to the laser diode and configured to produce a generally conical-shaped wave front in the laser beam and a central spot which increases in area with distance from the scanning apparatus to the code, said wave front flattening at its radial edges with increasing radial distance from the propagation axis.

10. The apparatus of claim 9, wherein the optical system includes at least one element for partially collimating the laser, and imposing a generally conical wave front deformation on the laser beam directed toward the optical cede.

11. The apparatus of claim 10, wherein the optical system includes a plano convex lens for partially collimating the laser beam and an optical element having a substantially flat first surface perpendicular to the optical axis of the system and a second surface defined by a figure of rotation formed by rotating a line about said optical axis at an acute angle with respect thereto, thereby defining an optical element which causes a phase tilt in the beam inward toward the optical axis.

12. The apparatus of claim 10, wherein the optical system includes a collimating lens, a lens providing magnification to cause divergence of the resulting scanning laser beam, a linear axicon lens to produce the conical wave front deformation in the laser beam and an aperture limiting the radial extent of the scanning laser beam.

13. The apparatus of claim 10, wherein the scanning laser beam has a transverse field distribution that can be expressed as a series containing Bessel functions and wherein essentially only a central peak is employed for scanning.

14. A method of producing a laser beam for scanning an optical code comprising the steps of:

(a) providing a diverging laser beam from a laser diode along a propagation axis to the optical code;

(b) reducing the divergence of the laser beam to a predetermined non-zero divergence, and

(c) imposing a generally conical wave front deformation on the beam, said wave front flattening at its radial edges with increasing radial distance from the propagation axis;

wherein the steps (b) and (c) can be performed in any order or simultaneously, and wherein a diverging laser beam is produced from the laser diode to the optical code for scanning the optical code.

15. A method of scanning a symbol comprising the steps of:

(a) generating a beam of laser light;

(b) modifying the beam of light to create a beam which has a generally conical wave front and an intensity profile along a line perpendicular to the axis of propagation characterized by a central peak and a plurality of secondary peaks symmetrically located on either side of the central peak and which central peak has a diameter which increases in area as a function of distance from the scanner to the symbol; and

(c) moving the modified beam across the symbol to be read.

16. The method of claim 15, wherein the central peak has a diameter which increases as a function of distance from the scanner by a factor of between 0.2×

10<sup>−

3</sup> and 6×

10<sup>−

3</sup> per mm of distance projected.

17. Laser scanner apparatus for producing a laser beam with an elongated spot for scanning a symbol, comprising:

a source of a laser beam; and

an optical system for splitting the laser beam from said source and directing circular spot portions of the split beam toward the symbol, centers of said beam circular spot portions being displaced from one another along an axis perpendicular to a direction of scanning of the laser scanner apparatus to produce thereby an elongated region of illumination on a reference plane perpendicular to the beam spot portions in at least part of a working range of the laser scanner apparatus.

18. The apparatus of claim 17, wherein the beam portions are sufficiently displaced so that they have minimum overlap.

19. The laser scanner apparatus of claim 17, wherein the optical system is single period diffraction grating with a cosine-shaped profile.

20. The laser scanner apparatus of claim 17, wherein the grating phase is given by the expression $W$

(y)=W0·

cos

(yA·

2

 



π

)

wherein y is the dimension along the axis perpendicular to the direction of scanning, A is a vertical aperture of the system and W₀ is the amplitude of the grating phase.

21. The apparatus of claim 17, wherein the optical system includes an optical plate having two planar refractive surfaces which are non-parallel and from each of which a portion of the laser beam is propagated.

22. The apparatus of claim 17, wherein the optical system includes a partially reflective plate having two planar reflective surfaces from each of which a portion of the laser beam is propagated.

23. A lens system for an apparatus for providing a laser beam for scanning optical codes, the lens system comprising:

a glass lens with at least one spherical surface; and

a molded plastic element for correcting aberration in the glass lens and for retaining the glass lens in position in the lens system and having a non-planar refractive surface located on an optical axis of the glass lens, which in combination with the glass lens provides an aspherical lens system with greater temperature stability than an optically equivalent aspherical plastic lens.

24. The lens system of claim 23, wherein the plastic element includes at least one surface configured as an axicon.

25. The lens system of claim 23, wherein the molded plastic element provides a phase plate.

26. The lens system of claim 23, wherein the molded plastic element further comprises an integral plastic sleeve for assisting in retaining the glass lens in position in the lens system.