WO1991017516A1

WO1991017516A1 - Oscillatable holographic optical element for bar code scanning

Info

Publication number: WO1991017516A1
Application number: PCT/US1991/003055
Authority: WO
Inventors: Robert W. Rudeen; George R. Huggett
Original assignee: Intermec Corporation
Priority date: 1990-05-02
Filing date: 1991-04-30
Publication date: 1991-11-14
Also published as: CA2062819A1; EP0481055A1; EP0481055A4; JPH04506880A

Abstract

An oscillating holographic optical element for scanning a light beam across a bar code symbol. The holographic element (36) is mounted on a holding frame which is connected to a stepper motor (38) that is excited by electrical signals to cause the holographic element to oscillate. The holographic element can either transmit light outwardly toward the bar code symbol, or collect light scattered from the bar code symbol, or both. The holographic element can consist of a single hologram, two separate holograms, or two holograms superimposed over one another. The holographic element can also serve to filter received light.

Description

Desαiption

OSCIL ATABLE HOLOGRAPHIC OPΗCAL ELEMENT FOR BAR CODE

SCANNING

Technical Field

This invention relates to a holographic optical element and, more particularly, to a holographic optical element that can be oscillated for use with a bar code scanning reader.

Background Art

A bar code reader typically uses a beam of light to scan across a bar code, which consists of alternating strips (' -jars") of differing reflectivities. The scanner then receives and interprets the fluctuations in the returning light that are caused by the bar code. It is known in the prior art to read bar codes by means of a hand-held wand which makes contact with the surface on which the bar code is printed. However, the need to make contact with the surface is frequently inconvenient and gives uninterpretable readings because the wand is not moved' across the^* bar code with a sufficiently uniform velocity. An alternative to a hand-held wand is a scanning reader which does not require physical contact with the bar code which is to be read. A scanning reader typically produces a beam of light which is repetitively scanned across an area. If the beam of light is incident upon a bar code (or some other symbology), the modulated light which is scattered by the bar code is returned to sensing circuitry in the scanning reader for interpretation. The widths of the alternating areas of different reflectivity are measured on the basis of the relative times required for the beam of light to scan them. This allows the reader to be used with bar codes which have a wide variety of sizes as long as the relative widths of the elements of the bar codes are preserved. Accordingly, it is preferable, although not necessary, that the light beam be scanned across the bar code at a substantially uniform rate in order to ease the task of interpreting the bar code.

In order to insure that the light beam is scanned at a substantially uniform rate, it is typically reflected from a mirror within the scanner that moves repetitively at a uniform rate. The mirror is generally driven by a small electrical motor under the control of electronic control circuitry. The mirror is typically either rotating at a constant speed or oscillating on the end of a shaft attached to a motor which can step between two extreme angular positions. Examples of rotating optical elements are shown in U.S. Patent Nos. 4,025,761, 4,097,729, 4,450,350, 4,575,625, and 4,692,603. Examples of oscillating mirror optical elements are shown in U.S. Patent Nos. 4,593,186, 4,736,095, and 4,808,804. In handheld applications, an oscillating mirror is generally preferable, since it can be made both lighter and more compactly than a rotating optical element. Contained with the mirror is typically a collecting mirror which receives and focuses the light scatter from the bar code symbol which is scanned. In order to reduce power consumption, it is important top keep the oscillating mirror as light as possible.

Disclosure of the Invention It is an object of the present invention to provide a holographic optical element for scanning an oscillating light beam onto a bar code symbol.

It is another object of the present invention to provide an integral optical element including a holographic optical element which transmits an oscillating light beam onto an bar code symbol and focuses the light received from the bar code symbol onto a fixed point with respect to the integral optical element.

It is a further object of the present invention to provide a light weight optical element for scanning a beam of light onto a bar code symbol.

It is still another object of the present invention to provide a light weight optical element which requires reduced power to scan a beam of light onto a bar code symbol.

These and other objects can be provided by an integral optical element for transmitting light in an oscillating manner across a bar code symbol and for focusing light scattered from the bar code symbol, the integral optical element comprising a holographic element.

In addition, these and other objects can be provided by an oscillatory scanner for reading a bar code symbol and for focusing light received from the bar code symbol. The scanner comprises means for producing a coherent beam of light, means for directing the beam of light onto the bar code symbol, a holographic element for focusing the received light, and means for moving the holographic element in an oscillatory manner so that the holographic element is directed to receive the light scattered by the bar code symbol.

Further, these and other objects can be provided by a scanner for reading bar code symbols having distinct areas of contrasting reflectivity. The scanner comprises means for producing a coherent beam of light, means for directing the beam of light onto the bar code symbol, a holographic element for focusing the received light, means for moving the holographic element in an oscillatory manner so that the holographic element is directed to receive the light scattered by the bar code symbol, and transducer means located at the substantially fixed pomt for converting the received light into an electrical signal representative of the distinct areas of contrasting reflectivity.

Brief Description of the Drawings

Figure 1 is a perspective diagram of a scanning laser bar code reader. Figure 2 is an end-on view of the top end of the scanning laser bar code reader shown in Figure 1.

Figure 3 is an exploded perspective view of the optics portion of the scanning laser bar code reader shown in Figure 1.

Figure 4 is a top view of the optics portion of the scanning laser bar code reader shown in Figure 1.

Figure 5 is a schematic diagram of the circuitry of the motor drive electronics of the scanning laser bar code reader shown in Figure 1.

Figure 6A is a top view of a oscillatable holographic optical element for use in the scanning laser bar code reader shown in Figure 1. Figure 6B is a front elevation view of the oscillatable holographic optical element shown in Figure 6A.

Figure 6C is a side elevation view of the oscillatable holographic optical element shown in Figure 6 A Best Modes for Carrying Out the Invention

One embodiment of a laser scanner of the type with which the inventive holographic optical element is intended to operate is shown in Figures 1 and 2. While Figures 1 and 2 show a handheld integral laser scanner, the inventive holographic optical element can also be used with other optical scanning systems, including in-the-counter and desk-top scanners. Further, such optical scanning systems are not necessarily limited to bar code scanning. Figure 1 is a perspective diagram of the laser scanner. Figure 2 is an end-on view of the top end of the laser scanner shown in Figure 1. The laser scanner 10 contains electronic circuitry and optical components contained within a case 12. It includes a keyboard 14 and liquid crystal display (LCD) 16 for the display of bar codes which have been read by the laser scanner 10 as well as for programming a microprocessor (not shown) contained within the laser scanner 10.

Upon actuating a pair of opposed triggers 18 (one shown in Figure 1), the laser scanner 10 is activated, as will be described subsequently, to produce a scanning beam 22 of laser light The scanning beam 22 passes through the window 20 placed in the top end of the laser scanner 10, as shown in Figure 2. The scanning occurs in the plane 24 (shown in Figure 2). The light from the scanning beam 22 is projected forwardly of the laser scanner 10. If it reaches a surface, some of the impinging energy is scattered and returns to the window 20. If the scattering surface happens to contain bar code symbology which the scanning laser beam impinges upon, the returning light will be modulated by the pattern of reflectivities which the bar code symbology contains. The light received by the laser scanner 10, if it is scattered from a bar code symbology, can be amplified and processed by circuitry in accordance with techniques which are conventional to those skilled in the art of bar code reader design.

Figure 3 is an exploded perspective view of the optics portion of the laser scanner 10, shown in Figure 1. Figure 4 is a top view of the optics portion of the scanning laser bar code reader shown in Figure 1. The laser scanner 10 shown in Figures 3 and 4 uses a visible beam to scan the bar code symbology.

The optics portion of the internal components of the laser scanner

10 is preferably included on a two-piece support frame 30. Support frame 30 include parts 30a and 30b which snap together to form a unitary support for the optical and associated components. The components in the support frame 30 can be separated into two categories. One category includes the components which deal with generating and transmitting the scanning beam 22. The other category includes the components which deal with receiving any light which may be returning as a result of transmitting the scanning beam 22.

Those components in the first category include a laser diode 32, a turning mirror 34, a holographic element 36, and a motor 38. The laser diode 32 is supplied with electrical power through electrical leads 40 by electronic circuitry contained elsewhere in the laser scanner 10. Associated with the laser diode 32 is a holder 42 which contains and holds, as a fixed assembly, lenses and other optical elements which are required to form the scanning beam 22 into the desired form. For example, the scanning beam 22 may be generated from the beam of laser light produced by the laser diode 32 by passing the beam from the laser diode 32 through one or more lenses to aid in focussing the scanning beam 22 at a particular plane exterior to the laser scanner 10 and/or through an aperture stop to reshape the beam to have a desired cross-section.

After the scanning light beam 22 passes through the optical elements held by the holder 42, it passes through a hole 44 in the turning mirror 34 to the holographic element 36. The holographic element 36 is attached to the motor 38 by the shaft 46, which causes the holographic element 36 to oscillate with the motor 38 about the axis aligned with the shaft 46. Plane 24 (see Figure 2) is perpendicular to the axis aligned with the shaft 46. The scanning beam 22 is diffracted from the holographic element 36 and is directed through the window 20 within the plane 24 in accordance with the position of the holographic element 36.

Any light that is received due to scattering from an object, such as a bar code, which is exterior to the laser scanner 10 is transmitted through the window 20. The window 20 protects the interior of the laser scanner 10 from contaminants outside the laser scanner 10. The returning light is diffracted by the holographic element 36 onto the turning mirror 34, which directs the light to the photodiode 60 after the light passes through a filter 62. The holographic element 36 is at least as large as the window 20, so that essentially all of the received light energy is directed to photodiode 60. This maximizes the strength of the signal produced by the photodiode 60, thereby improving the performance of the electronic circuitry which processes the signals produced by the photodiode 60.

Figure 5 is a schematic diagram of the circuitiy of the motor drive electronics of the ____πi_g laser bar code reader shown in Figure 1. The motor 38 is a stepper motor having, for example, the capability of producing steps which are eighteen degrees wide. The motor 38 includes two windings 80A and 80B. Each of the windings 80A and 80B is center-tapped, dividing the winding into two legs. The center of each of the windings is held at a substantially fixed first voltage, such as the supply voltage for the electronic circuit of the laser scanner 10. Typically, the supply voltage is five volts. Each of the legs of the two windings 80A and 80B can be excited separately. To accomplish this, the end of each of the legs is capable of being grounded (or held at some other voltage, if appropriate) respectively through a circuit including one of the transistors 82χ, ... , 824. For example, if an appropriate signal is applied at point A, the gate of the transistor 821 will cause current to pass through the upper leg of the winding 80A. This will cause the motor 38 to rotate slightly. If signals are applied to points A, Abar, B, and Bbar in the correct order, the motor 38, and consequently, the oscillating holographic element 36, can be caused to oscillate. This, in turn, will cause the light beam 22 to be scanned through the window 20. It will also cause the light received from the direction in which the light beam 22 is being transmitted to be focused on the photodiode 60. If the signals are applied properly to the points A, Abar, B, and Bbar, the light beam 22 can be caused to move in successive passes within an angular range having two angular extremes. If desired, the motion of the light beam 22 between extremes can be made to have a substantially constant angular velocity.

The signals applied to the points A, Abar, B, and Bbar can be generated by an electronic logic device 84. Device 84 also receives a pulse train, or other appropriate signal, from an oscillator 86, as well as a motor motion detect signal on line 88.

Logic device 84 may be produced as a gate array. In response to a signal generated when the user simultaneously activates both of the triggers 18, the logic device 84 generates a number of signals. Among the signals it generates are the signals required to drive the motor 38 at points A, Abar, B, and Bbar, a "Start of Scan" signal, and a "Motion OK" signal. The "Start of Scan" signal is directed to other electronic circuitry in the laser scanner 10 to initialize signal processing which reads the bar code symbology (if any) as represented by the signal produced by the photodiode 60. If the "Motion OK" signal indicates that the motor 38 is not working, other circuitry connected to logic device 84 within the laser scanner 10 can cause the laser diode 32 to be deactivated.

Figures 6A, 6B, and 6C are respectively top, front elevation, and side elevation views of the holographic optical element 36. The holographic optical element 36 can be oscillated for use in the scanning laser bar code reader shown in Figure 1. The oscillation can be accomplished by means of the shaft 46 which is attached to the holographic optical element 36 through a holding means (not shown). The holding means can be a fixture for holding the holographic optical element 36 (which can be substantially flat) in a fixed position with respect to the shaft 46. The holographic optical element 36 can be glued, or otherwise semipermanently fixed, to the shaft 46. Accordingly, the holographic optical element 36 oscillates when the shaft oscillates with the motor 38 (see Figure 3). The oscillation can occur about a fixed axis relative to the integral optical element 36. If desired, the holographic optical element 36 can be made on a light-weight plastic substrate by conventional processes well known to those skilled in the art In one embodiment, the surface 120 of the holographic optical element 36 can be segmented into two separate optical elements, elements 122 and 124. Optical element 122 is shown surrounding optical element 124 in Figure 6, although this configuration is not necessary to the invention. At least one of the optical elements 122 and 124 should be a holographic optical element Both can be holographic if desired. If one of the optical elements, say element 124, is not holographic, it can be a mirror. Such a mirror can be useful for transmitting the light beam 22 onto the bar code symbol. In this configuration, the other optical element (say, element 122), which is holographic, can be used to collect light reflected from the bar code symbol and focused to a substantially fixed point with respect to the holographic optical element 36. The optical element 122 can be made to focus by proper development in accordance with well-known holographic principles. If it is desired that both optical elements 122 and 124 be holographic optical elements, the optical element which transmits the light onto the bar code symbol can also be made holographically to perform as a mirror.

In another embodiment the two optical elements 122 and 124 can effectively be made with the holograms superimposed over one another. This can be accomplished by successively exposing the medium from which the holographic optical element 36 is made to two separate sets of light beams. One set of light beams forms the outgoing holographic optical element and the other set of light beams forms the receiving holographic optical element One set of light beams will match the entry and exit beams that form the scanning beam. The other set of light beams will match the entry and exit beams that are formed by the collecting mirror. In both cases, the holographic optical element is defined by the interference pattern produced by each set of beams.

The holographic optical element 36 can exhibit further advantageous features over the osculating mirror assembly now known in the art Since the optical efficiency is wavelength selective, the holographic optical element 36 can also serve as a filter, capable of filtering out all light except that having the wavelength of the laser light with which the scanner is to be used. This may eliminate the need for use of a separate filter 62 (see Figure 3).

While the detailed description above has been expressed in terms of a specific example, those skilled in the art will appreciate that many other circuits could be used to accomplish the purpose of the disclosed inventive apparatus. Accordingly, it can be appreciated that various modifications of the above-described embodiments may be made without departing from the spirit and the scope of the invention. Therefore, the spirit and the scope of the present invention are to be limited only by the following claims.

Claims

1. An integral optical element for transmitting light in an oscillating manner across a bar code symbol and for focusing light reflected from the bar code symbol, comprising a holographic element

2. The integral optical element of claim 1, further comprising a holder means attached to the holographic element.

3. The integral optical element of claim 2, further comprising means for moving the holder means in an oscillatory manner so that the light reflected by the optical element scans across an area.

4. The integral optical element of claim 1 wherein the holographic element focuses light reflected from the bar code symbol.

5. The integral optical element of claim 4 wherein the holographic means focuses the received light onto a substantially fixed point relative to the integral optical element

6. The integral optical element of claim 4, further comprising a holder means attached to the holographic element

7. The integral optical element of claim 6, further comprising means for moving the holder means in an oscillatory manner so that the light reflected by the optical element scans across an area.

8. The integral optical element of claim 4, further comprising a mirror for directing light onto the bar code symbol.

9. The integral optical element of claim 8, further comprising a holder means attached to the holographic element

10. The integral optical element of claim 9, further comprising means for moving the holder means in an oscillatory manner so that the light reflected by the mirror means scans across an area.

11. The integral optical element of claim 10 wherein the holographic element focuses the received light onto a substantially fixed point relative to the integral optical element.

12. The integral optical element of claim 11 wherein the movement of the holder means occurs about a fixed axis relative to the integral optical element.

13. The integral optical element of claim 4, further comprising a holographic optical element for directing light onto the bar code symbol.

14. The integral optical element of claim 13, further comprising a holder means attached to the holographic element

15. The integral optical element of claim 14, further comprising means for moving the holder means in an oscillatory manner so that the light reflected by the mirror means scans across an area.

16. The integral optical element of claim 15 wherein the holographic element focuses the received light onto a substantially fixed point relative to the integral optical element

17. The integral optical element of claim 16 wherein the movement of the holder means occurs about a fixed axis relative to the integral optical element.

18. The integral optical element of claim 4, further comprising means for filtering the wavelength of the light reflected from the bar code symbol.

19. The integral optical element of claim 1 wherein the holographic means focuses the received light onto a point

20. The integral optical element of claim 1 wherein the holographic element directs light onto the bar code symbol.

21. The integral optical element of claim 20, further comprising a holder means attached to the holographic element

22. The integral optical element of claim 21, further comprising means for moving the holder means in an oscillatory manner so that the light reflected by the optical element scans across an area.

23. The integral optical element of claim 22 wherein the holographic element focuses the received light .onto a substantially fixed point relative to the integral optical element.

24. The integral optical element of claim 23 wherein the movement of the holder means occurs about a fixed axis relative to the integral optical element.

25. An oscillatory scanner for reading a bar code symbol and for focusing light received from the bar code symbol, comprising: means for producing a coherent beam of light; means for directing the beam of light onto the bar code symbol; a holographic element for focusing the received light; and means for moving the holographic element in an oscillatory manner so that the holographic element is directed to receive the light reflected by the bar code symbol.

26. The integral optical element of claim 25 wherein the holographic means focuses the received light onto a substantially fixed point relative to the integral optical element

27. The integral optical element of claim 25 wherein the means for moving the holographic element comprises a holder means attached to the holographic element

28. The integral optical element of claim 27 wherein the holographic element focuses the received light onto a substantially fixed point relative to the integral optical element

29. The integral optical element of claim 27 wherein the movement of the holder means occurs about a fixed axis relative to the integral optical element.

30. A scanner for reading a bar code symbol having distinct areas of contrasting reflectivity, comprising: means for producing a coherent beam of light; means for directing the beam of light onto the bar code symbol; a holographic element for focusing the received light; means for moving the holographic element in an oscillatory manner so that the holographic element is directed to receive the hght reflected by the bar code symbol; and transducer means located at the substantially fixed point for converting the received light into an electrical signal representative of the distinct areas of contrasting reflectivity.

31. The integral optical element of claim 30 wherein the holographic means focuses the received light onto a substantially fixed point relative to the integral optical element

32. The integral optical element of claim 30 wherein the means for moving the holographic element comprises a holder means attached to the holographic element

33. The integral optical element of claim 32 wherein the holographic element focuses the received light onto a substantially fixed point relative to the integral optical element

34. The integral optical element of claim 32 wherein the movement of the holder means occurs about a fixed axis relative to the integral optical element