JP3866321B2 - Optical scanner - Google Patents

Description

直流電流によるフォトダイオード散弾雑音のような相互に関連しない雑音に対しては、雑音は、通常のシングルフォトダイオード前端よりも√２大きくなる。この場合、総雑音は、
Ｉt＝√Ｉ＾n12＋Ｉ＾n22
により得られる。
【００４４】
この雑音は相互に関連しないため、
Ｉn1＝Ｉn2＝Ｉ＾であり、
したがって、
Ｉt＝√２Ｉ＾である。
背景証明からの雑音は、このように散弾雑音が増加しても通常、非再帰システムにおいて優勢である。人工光の雑音源が存在しない場合に第２の検出器が適応してオフの状態になれば、信号対雑音比は改善されるだろう。
【００４５】
再帰反射性システム（図１３（ｄ））と非反射性システム（図１３（ｅ））の双方における代替手段も、比較のために示されている。図１３（ｅ）の手段では、光検出器Ｄ１とＤ２の前に、フレネルレンズ、ホログラフィー格子、または他の光学要素が使用され得る。
図６と図７に示されている分離された集光ミラーは、分離された集光ミラーが使用される上記の他の実施の形態のいずれとも結合して使用され得る。走査ミラーが集光ミラーとしての働きもするスキャナにこの種の分割されたミラーを使用することも可能だろう。他のスキャナの実施の形態は、図８に示されている。この実施の形態では、レーザ５１０からのビームは、読み取る記号へ導かれる前に円筒形の走査ミラー５１２により整形される。走査ミラー５１２の円筒形の表面は、要求されるように、Ｘ方向においてビームを整形する。
他の実施の形態は、図９に示されている。ここで、レーザ６１０からの光は、第１の走査ミラー６１２と第２の走査ミラー６１４に当たる。双方のミラーは、円筒形の表面を有し、そのためにビームを、要求されるようにＸ方向とＹ方向に整形する。
【００４６】
図８と図９に示されたとおりのミラー断面は、要求されるビーム整形に応じて選択され得る。例えば、ある場合には、円筒状の面よりも環状の面を有する方が便利だろう。さらに、その整形は、光が走査要素に当った後または当たる前に、１つ以上の固定されたミラーから光ビームを反射することにより行われてもよい。最も一般的な形としては、ビームの整形は、ビームを１つ以上の非平面から反射することにより実行される。
【００４７】
上記の、図８と図９に関して説明され図示された実施の形態は、他の実施の形態のいずれとも結合して使用され得る。
図１０は、一例として、前述したいずれの実施の形態の一部ともなれる適切な型のハンドヘルド型レーザスキャナを示している。図１０のスキャナに含まれた特定の特徴は、図１から図９までに関して既に述べた特徴とは細かい部分で異なるが、図９に関連して述べたいずれの実施の形態も、図１０に示された種類のハンドヘルド型スキャナの一部とすることができることは当然理解されるだろう。
【００４８】
図１０のスキャナは、引き金７３９を備えた、握ることのできるハンド部７３６を有する本体７３５を含む。本体７３５内にはレーザモジュール７１５がある。レーザモジュール７１５からの光は、例えば図２、図３または図５に示された形のミラーであり得る、振動するミラー７１０を照射するようになっている。その結果生じるビーム７３７は、窓７３８を通ってハウジングを出ていく。ミラー７１０は、記録される記号７１４を横切って走査線７１３を描くように振動するように配置される。記号から反射された光は、窓７３８を通り、集光ミラー７２６によって集められ、光検出器７２５に反射される。次いで光学信号が、電気信号に変換され、記号７１４の特徴が決定される。
【００４９】
この発明は多数の特定の実施の形態に関連して図示され説明されたが、この発明の精神から逸脱することなく、様々な修正や構造の変更が行われ得るため、示されたどの細部にも限定する意図はない。
さらに分析しなくても、上記事項はこの発明の要点を十分に開示しているので、他人は現在の知識を応用することによって、先行技術の観点からこの発明の包括的または特定的側面の本質的な特徴を公正に構成する要素を除外することなく、それを様々な利用法に直ちに応用することができる。したがって、これらの応用は以下の請求項の意味および均等物の範囲に含まれるべきであり、また含まれることが意図されている。
【図面の簡単な説明】
【図１】図１は、多面折り曲げミラーを利用した、本発明の１つの実施の形態による多レンジレーザスキャナを示す。
【図２】図２は、他の実施の形態、つまり走査集光体を備えた２レンジスキャナを示す。
【図３】図３は、他の実施の形態、つまり別個の集光体を有する２レンジスキャナを示す。
【図４】図４は、他の実施の形態、つまり２つのレーザビームを使用する２レンジのスキャナを示す。
【図５】図５は、図４の実施形態で使用された、分離された走査ミラーをさらに詳しく示す。
【図６】図６は、他の実施の形態、つまり光を２つの分離された光検出器へ導く分離された集光ミラーを有するスキャナを示す。
【図７】図７は、図６の分離された集光ミラーの中心断面図である。
【図８】図８は、ビームの整形が円筒形の走査ミラーにより行われる、他の実施の形態である。
【図９】図９は、Ｘ方向とＹ方向の双方でのビーム整形が２つの円筒形のミラーにより行われる、もう１つの実施の形態である。
【図１０】図１０は、前述のどの実施の形態も含み得る、典型的なハンドヘルド型のスキャナを示す。
【図１１】図１１は、本発明による２つの光検出器の配置を示す。
【図１２】図１２は、図１１の２つの光検出器の配置の回路図である。
【図１３】図１３（ａ）は、集光体／反射体の配置の第１の実施の形態を図示する２つの光検出器の配置である。
図１３（ｂ）は、集光体／反射体の配置の第２の実施の形態を図示する２つの光検出器の配置である。
図１３（ｃ）は、集光体／反射体の配置の第３の実施の形態を図示する２つの光検出器の配置である。
【符号の説明】
１０ レーザダイオード
１２ 走査ミラー
１４ 折り曲げミラー
１６ ミラー部（反射部）
１８ ミラー部（反射部）
２０ ミラー部（反射部）
２２ スキャナハウジング
２４ 開口
２６ 記号
２８、３０、３２ 位置
３８ 光学系[0001]
BACKGROUND OF THE INVENTION
The present invention relates generally to an optical scanner, and more particularly to a scanner having two or more operating ranges.
[0002]
[Prior art]
Most scanners, such as bar code scanners, are designed to be used at specific distances or distance ranges from the symbol to be scanned. If the user holds the scanner too close or too far from the symbol, the symbol and / or flying spot beam will not be in focus and decoding will not be possible.
[0003]
Such a scanner is particularly convenient in environments where successive symbols to be read are placed at different distances from the scanner and it is difficult or impossible for the user to change the distance between the scanner and the symbol. That's not true. In order to cope with such a situation, the allowable operation range of the conventional scanner is expanded in order to give the user as much as possible, or the first operation range or according to the user's preference or request, for example, Attempts have been made to provide multi-range scanners that can operate in the second operating range. One possibility is to provide the scanner with a two-position switch so that the scanner operates at a first operating distance at the first position of the switch and at a second operating distance at the second position. The disadvantage of such a scanner is that it requires an additional moving part to operate in two separate operating ranges. Such a system is also not "automatic" because the user must manually select the correct operating range depending on the distance of the current symbol to be read. If an incorrect operating range is selected, no decoding is performed.
[0004]
One of the difficulties faced by bar code reader designers when trying to expand the operating range is that the larger the operating range and the greater the range of symbols that can be read, the more reflected from the symbol. The resulting light-to-noise ratio tends to be low. One way to address this is to provide a non-conventional optical system in which the optical system associated with either the laser or the photodetector has two separate focal points. An example of this is shown in US Pat. No. 5,332,892, assigned with this application. In the device shown in that document, the two focal points are associated with corresponding circuits to provide two separate channels of data obtained from the scanned barcode. The two channels have different resolutions. Due to the different angles and densities of operation, at least one resolution is suitable for sensing all or most of the barcode data, regardless of the barcode distance to the scanner and / or the code size or density. Let's go. The scanning beam of the bar code reader is typically extracted from the laser diode. Such diodes are robust and relatively inexpensive, but have the disadvantage that the beam generated from the laser diode has astigmatism. A laser diode with astigmatism can be characterized as having two apparent light sources separated from each other along the optical path. One of the light sources lies on a horizontal plane, appears to come out of the laser diode chip, and has a low angular aperture. The other apparent light source lies on a vertical surface, appears to emerge from the chip's facet, and has a high angular aperture. Two apparent light sources, typically about 20 microns apart, form two beam waists in different planes and different directions when measured against the flat joint of the chip.
[0005]
The resulting relatively complex beam profile will require selective shaping before it can be used effectively in an optical scanner. Several means of providing such beam shaping are described in our co-pending application US patent application Ser. No. 08 / 268,982, filed Jun. 30, 1994.
[0006]
[Problems to be solved by the invention]
A further difficulty with current prior art scanners is that the signal can be drowned out by specular reflection from the surface on which the symbol to be read is printed.
It is an object of the present invention to at least alleviate the problems of the prior art.
[0007]
It is another object to provide a simple and inexpensive means of adjusting the beam profile (cross section at a specific distance from the light source) as required in one or both of the X and Y directions.
It is another object to provide a scanner that can be operated at at least two different operating distances so that the user does not have to select an appropriate operating distance in advance.
[0008]
It is another object to provide a simple and inexpensive scanner that can read at least two symbols at different distances.
It is another object to provide a scanner that reduces or eliminates the problems caused by specular reflection.
[0009]
[Means for Solving the Problems]
According to one aspect of the present invention, there is provided an optical scanner for reading a symbol having areas of different light reflectivity, comprising:
A light source that generates a light beam;
A scanning optical element that receives the light beam and generates a scanning exit light beam therefrom;
A polyhedral reflector having a first surface with a first side and a second surface with a second side, the scanner having a first when the beam is reflected from the first surface; Suitable for reading symbols at a distance or range of motion, and for symbols at a second distance or range of motion when the beam is reflected from the second surface.
[0010]
In a preferred embodiment, the polyhedral reflector comprises a split mirror, the first portion of the mirror determining the first surface and the second portion determining the second surface. The mirror may be a scanning mirror of a scanning optical element or a folding mirror. In the latter case, the folding mirror receives the scanning light beam from the scanning optical element and directs it to the symbol to be read.
[0011]
Since the scanning beam is reflected from the first and second surfaces of the reflector, the resulting dynamic focus or multi-focus improves the operating range of the scanner without the need for additional moving parts. Furthermore, no additional lens or aperture is required.
The preferred apparatus of the present invention can obtain an increase in scan rate without changing the scanning element. This increases efficiency (ability to decode in a single scan). This efficiency is lost in conventional means of obtaining dynamic focus using an aperture or lens.
[0012]
By using different cross sections for each reflector, the beam can be shaped as required at a variety of different working distances.
According to another aspect of the invention, there is provided an optical scanner for reading a symbol having regions of different light reflectivity, the scanner having a first side having a first side and a second side. Includes a scanning optical element having a polyhedral reflector having a second different side.
[0013]
According to another aspect of the invention, there is provided an optical scanner for reading a symbol having regions of different light reflectivity, the scanner comprising a first side of a first side and a second different side. And a multi-face folding mirror having a second surface.
According to another aspect of the invention, there is provided an optical scanner for reading a symbol having areas of different light reflectivity, the scanner including a multi-faceted collector mirror for collecting light reflected from the symbol, The condensing mirror has a first surface on a first side and a second surface on a second different side.
[0014]
According to another aspect of the invention, there is provided a multi-range scanner assembly that electro-optically reads a symbol having portions of different light reflectivity on a target disposed at a variable distance from the assembly, comprising:
(A) a first light source for generating a first beam for short range scanning;
(B) a second light source for generating a second beam for long range scanning;
(C) a scanning element including a scanning mirror that causes the first beam and the second beam to alternately scan the field of view;
(D) a condensing optical system for collecting the light reflected from the field of view;
(E) an optical detector for detecting light directed by the condensing optical system and generating an electric signal corresponding to the reflected light.
[0015]
According to another aspect of the invention, there is provided a multi-range scanner assembly that electro-optically reads a symbol having portions of different light reflectivity on a target disposed at a variable distance from the assembly, comprising:
(A) a light source for selectively generating a first beam for short range scanning and a second beam for long range scanning;
(B) a scanning element that causes the first beam and the second beam to scan over the field of view;
(C) a condensing optical system for collecting the light reflected from the field of view;
(D) An optical detector for detecting light directed by the condensing optical system and generating an electrical signal corresponding to the reflected light.
[0016]
According to another aspect of the present invention, an optical scanner is provided for reading a symbol having regions of different light reflectivity, the scanner including a plurality of reflective surfaces for receiving light reflected from the symbol. The first reflective surface guides the reflected light to the first photodetector and the second surface guides the reflected light to the second photodetector.
Such an arrangement that focuses the reflected light onto two different, distant photodetectors can cause one of the photodetectors to fail, while the other photodetector does not. Try to avoid.
[0017]
According to another aspect of the present invention, there is provided an optical scanner for scanning symbols having regions of different light reflectance,
A light source for generating a light beam;
A scanning optical element for receiving a light beam and generating a scanning light beam therefrom;
A beam shaping reflector including a non-planar mirror for shaping the beam.
[0018]
Any beam shape can be obtained by reflection from a non-planar surface. If the reflector is shaped in both the X and Y directions, beam shaping in both directions can be obtained. On the other hand, if a cylindrical mirror is used, the beam is shaped only in one direction. The non-planar may be a scanning mirror or a stationary folding mirror.
[0019]
Appropriate beam shaping using cylindrical mirrors in this way can allow the designer to reduce the spot size in the vertical (Y) direction at large scan distances. This improves visibility. In addition, the spot size for short distances (0 to 30 inches) is increased, improving the performance of the dot matrix.
[0020]
In any of the above inventive concepts, the light source is preferably a laser beam. The laser light source is preferably a VLD (visible laser diode). The VLD may have a lens, possibly a cylindrical lens, in front of it to shape some of the beam initially.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a multi-range laser scanner, for example for a barcode reader, comprising a first embodiment of the invention. In the illustrated embodiment, the laser diode 10 generates a light beam that is directed to the scanning mirror 12 through a small central hole 13 in the bending mirror 14. The folding mirror 14 is a segmented or multiple mirror that includes three separate mirror sections 16, 18, 20. The mirror part 16 is convex, the mirror part 18 is flat, and the mirror part 20 is concave. When the scanning light beam generated by the scanning mirror 12 moves across the bending mirror 14, it strikes each mirror section 16, 18, 20 in order. Light reflected from the folding mirror exits the scanner housing 22 through a window or opening 24 and strikes a reading symbol 26.
[0022]
Symbol 26 is shown in three places. That is, a near position 28 corresponding to the operating distance of the mirror unit 20, an intermediate distance 30 corresponding to the operating distance of the mirror unit 18, and a far distance 32 corresponding to the operating unit of the mirror unit 16. Of course, in an actual embodiment, it will be appreciated that there is a fairly large spacing between 28 and 30 and 32. In the figure, the space is shown narrower than actual for simplicity.
[0023]
The effect of the three mirrors is that three separate scan lines are generated, first at 28 positions, second at 30 positions and third at 32 positions. The purpose is therefore very likely to be read by at least one scan line therein, whatever the distance of the symbol 26 from the scanner. Of course, the symbol does not have to be exactly 28, 30, or 32 in order to be decoded. There is a considerable depth of field in each case, and depending on the actual distance, these depths of field may overlap. In this case, the depth of field allows the barcode symbols to be decoded almost reliably. Effectively merge into one complete “operating area”.
[0024]
Each mirror section is arranged at an appropriate angle so that the scanning lines overlap each other and are focused at different distances.
There need not be exactly three mirrors, but may be two, or more than three, depending on the requirements of a particular application. The exact mirror profile can also be selected for specific applications. The longitudinal section selected depends on the required operating range and the longitudinal section of the scanning mirror 12. The scanning mirror 12 is preferably a flat surface, but may be non-planar, for example, a cylindrical shape or a spherical shape in some cases. Instead of mirror 12, a rotating prism, polygon, hologram, lens, zone plate or other convenient optical scanning element could be used. If the scanning element includes a polygon, each face of the polygon may have a different curvature. In that case, the mirror parts 16, 18 and 20 may all have the same longitudinal section (although not necessarily so). This is because in that case a plurality of operating distances can be determined by the curvature of the polygonal surface. A typical polygon suitable for use with three planar folding mirror sections is shown at 36.
[0025]
Further shaping of the beam can be accomplished by use of optics 38 in front of laser 10.
In the embodiment of FIG. 1, the light reflected from symbol 26 may follow approximately the same path in the opposite direction toward the photodetector (not shown), or alternatively, for that purpose. There may be separate focusing optics (not shown).
[0026]
Now, an embodiment including a two-range scanner with a scan detector is shown in FIG. Laser diode 110 directs the beam to a scanning mirror, shown generally at 112, arranged to oscillate about axis 114. The mirror has four separate mirror sections, of which the outer two 116, 118 have a spherical longitudinal section and the inner two 120, 122 are planar. The laser light reflected from the mirror 112 forms two separate scan lines with different operating ranges from a barcode reader or other optical scanner due to the beam contour.
[0027]
In this embodiment, light reflected from a symbol (not shown) strikes the scanning mirror again and is reflected from there to a photodetector such as photodiode 124. The photodiode should of course not interfere with the laser 110 and be placed out of the page or on one side as indicated by the dotted line 126.
The mirror 112 can have as many faces as required, each having a different longitudinal section. The required number of planes and their longitudinal sections are in accordance with the application and the details are within the expertise of the person skilled in the art.
[0028]
Another embodiment is shown in FIG. This shows a two-range scanner with a separate collector mirror.
The laser 210 generates a light beam that passes through a small aperture 211 in the collector mirror 214. The beam strikes a scanning mirror 212 having two separate surfaces, the first surface 216 being a plane and the second surface 218 being a cylindrical surface. The light is reflected from the mirror 212 to the condensing mirror 214 and from there to a reading symbol (not shown) that protrudes to the right of the drawing. The light reflected from the symbol is collected on a collecting mirror 214 and directed to a photodiode or other photodetector 220. This would be placed under the mirror 212 or offset to one side as indicated by the dotted line 222.
[0029]
The two mirror parts 216 and 218 generate alternating scans with different operating ranges.
Referring now to FIG. 4, an embodiment incorporating two laser assemblies 310 and 311 that emit parallel beams is shown. The laser assembly 310 is focused for short range operation. For simplicity, this is called a “short range laser”. Similarly, the laser assembly 311 is focused for long range operation. This is referred to as a “long range laser” for simplicity. Appropriate optics 312 and 314 determine the operating range of the laser and different beam profile characteristics. Alternatively, the short range laser and its optical system may be the same as the long range laser and its optical system.
[0030]
In other embodiments, laser assemblies 310 and 311 have different frequency lasers. Visible laser diodes are currently available at two different wavelengths, 635 nm and 670 nm. Short wavelength elements (635 nm) look better and are preferably used for high ambient light conditions or aiming. Thus, in the preferred method, the brightest beam in the long range is desired for visibility and aiming, so the 670 nm laser diode is focused as a “short range laser” and the 635 nm laser diode as a “long range laser”. Can be focused. In high ambient light conditions, it is possible to turn both lasers on and use them, rather than alternately using the lasers. Even if there are two beams, the barcode symbol can be read effectively if the beams are correctly focused on the target surface so that the spots overlap or are very close together.
[0031]
In yet another embodiment, one of the laser assemblies 310 and 311 is a visible laser and the other assembly is an infrared laser whose beam is generally not visible. Infrared lasers are suitable for use in applications such as reading safety badges that require an infrared reading beam, reading direct thermal printed barcodes, reading specific color barcodes, etc. ing. A device similar to that shown in FIG. 4 may be used, but there is no restriction that the optical system must be in the “short range” or “long range”. As in the previous embodiment, scanning with two lasers can be performed alternately, or both lasers can be turned on for use.
[0032]
The beam from the long range laser 311 is reflected by a pair of parallel placed mirrors (or appropriately shaped prisms) so that the resulting two laser beams are parallel and adjacent to each other. The beam hits the scanning mirror 322 and reflects off the symbol read from it (not shown, but protrudes to the left in FIG. 4).
[0033]
Instead of separate long and short range lasers, a single laser can be used with appropriate optics (eg, a beam splitter).
The light reflected from the symbol is condensed by a mirror 322 (which also serves as a condensing mirror in the same manner as a scanning mirror) and guided to a photodetector 324.
Details of the mirror 322 are shown in FIG. The mirror is generally curved and includes a large area of light collection surface 325 with a central portion that is separated into two. The central left side 326 has a cylindrical surface, and the right side 328 has a flat surface. The light beam from the short range laser 310 strikes 326 and the light from the long range laser 310 strikes 328.
[0034]
In use, the laser controller operates the laser so that the laser is alternately turned on and off. The system seems to perform two scans (left to right and right to left) with the long range laser on, and then two scans with the short range laser on. Controlled. The alternation continues until decoding is successful.
[0035]
The system also provides an aiming mode that is initiated by the user selecting a first position of the trigger 328 on the scanner housing 330. In this mode, the controller 326 blinks the long range laser 311 while moving the mirror 322. In this mode, the user can easily see the scanning beam and align the symbols accordingly. As soon as the symbols are correctly aligned with the scanner, the user moves the trigger 328 to the second position to initiate an appropriate scan.
[0036]
6 and 7 show another embodiment in which the scanner includes a split collector mirror 410. The mirror has a first position 412 that directs light 416 coming from a symbol (not shown) to a first photodetector 418. The second position 414 receives the reflected light 416 and guides it to the second photodetector 420.
The portions 412 and 414 are of any convenient cross-section (eg, planar or cylindrical) and are preferably inclined by a common angle α from the general direction of incoming reflected light 416.
[0037]
Providing two separate photodetectors would allow the system to prevent flooding due to mirror reflection from the symbol or specular reflection from the surface on which the symbol was printed. Specular reflection may disable one of the photodetectors, while the other does not.
An embodiment of spaced photodetectors D1 and D2 is shown in FIG. 11, and a circuit for processing the signal is shown in FIG.
[0038]
Systems with a wide optical field of view (such as non-retroreflective optics) are generally disturbed by background noise generated by ambient and artificial light sources. The front detector is filled with signal power due to background noise and renders the system inoperable. Background noise from artificial light sources will become more pronounced as the trend for high performance light sources continues. One common technique is to reduce the optical field of view by using retroreflective optics. However, non-retroreflective optics are usually required for small scan engines. A technique for solving the problem of detector background noise malfunction for an ID scanning system will be described with reference to FIGS.
[0039]
FIG. 11 shows a general arrangement of a system that provides a photoelectric converter front end that obtains a desired signal plus noise power from a first detector and only obtains noise power from a second detector. The present invention provides the circuit of FIG. 12 that reduces these signals to produce only the required signal power. The field of view of both concentrators is set as narrow as possible to keep the same background surface to be rectangular and for noise matching. Optical filter and electronic gain matching may be used for each detector to match the background noise level of each detector closer.
[0040]
Several arrangements have been proposed to ensure that the laser source path is on the axis of the field of view of the first collector. The reflector (which may be scanning means) may be disposed behind the light collector as shown in FIG. However, the collector must have a narrow slit (or be divided in two) to allow the passage of the laser light.
[0041]
In order to avoid a split collector or a collector with a slit, the reflector may be placed in front of it as shown in FIG. 13 (b). The reflector is designed to disturb only a portion of the collected signal.
As another method, as shown in FIG. 13C, there is a method in which a reflector is disposed in a collector mirror. The reflector is designed long enough to receive a standard single-line scanning pattern.
[0042]
FIG. 12 shows an example of a photoelectric receiving circuit optimized for this noise cancellation technique. The two photodiode power supplies may have respective preamplifiers, each of which is then sent to a subtractor. However, the arrangement shown avoids premature saturation of the pre-circuit with a separate amplifier.
When the sensitivity of each detector is represented by S, the photodiode current is
Isn = S (Ps + Pn1)
In = S (Pn2)
Is obtained. Here, Ps and Pn1 are the signal power and noise power seen by the first detector, respectively, and Pn2 is the noise power seen by the second detector. The resulting signal that is amplified is
Ig = Isn-In = S (Ps + Pn1) -S (Pn2) = S (Ps + Pn1-Pn2 = Is + (In1-In2) = Is + It
Is obtained. Here, In1 and In2 are noise currents in the photodiode due to the background noise power viewed by the first and second detectors, respectively.
[0043]
If the two noise sources are very interrelated (true or artificial background noise), It = 0 and all the resulting voltages generated by the pre-receiver are The signal follows the frequency transfer function.

For non-correlated noise such as photodiode shot noise due to direct current, the noise is √2 larger than the front end of a normal single photodiode. In this case, the total noise is
It = √I ^ n12 + I ^ n22
Is obtained.
[0044]
Because this noise is not correlated,
In1 = In2 = I ^,
Therefore,
It = √2I ^.
Noise from background proofs is usually dominant in non-recursive systems even with this increased shot noise. If the second detector is adaptively turned off when no artificial light noise source is present, the signal to noise ratio will be improved.
[0045]
Alternatives in both the retroreflective system (FIG. 13 (d)) and the non-reflective system (FIG. 13 (e)) are also shown for comparison. In the means of FIG. 13 (e), a Fresnel lens, holographic grating, or other optical element may be used in front of the photodetectors D1 and D2.
6 and 7 can be used in conjunction with any of the other embodiments described above in which a separate collector mirror is used. It would be possible to use this kind of split mirror in a scanner where the scanning mirror also acts as a collector mirror. Another scanner embodiment is shown in FIG. In this embodiment, the beam from the laser 510 is shaped by the cylindrical scanning mirror 512 before being directed to the reading symbol. The cylindrical surface of the scanning mirror 512 shapes the beam in the X direction as required.
Another embodiment is shown in FIG. Here, the light from the laser 610 strikes the first scanning mirror 612 and the second scanning mirror 614. Both mirrors have a cylindrical surface so that the beam is shaped in the X and Y directions as required.
[0046]
The mirror cross section as shown in FIGS. 8 and 9 can be selected depending on the required beam shaping. For example, in some cases it may be more convenient to have an annular surface than a cylindrical surface. Further, the shaping may be performed by reflecting the light beam from one or more fixed mirrors after or before the light hits the scanning element. In the most common form, beam shaping is performed by reflecting the beam from one or more non-planar surfaces.
[0047]
The embodiment described and illustrated above with respect to FIGS. 8 and 9 can be used in conjunction with any of the other embodiments.
FIG. 10 shows, by way of example, a suitable type of handheld laser scanner that can be part of any of the previously described embodiments. Although the particular features included in the scanner of FIG. 10 differ in detail from the features already described with respect to FIGS. 1-9, any of the embodiments described in connection with FIG. It will be appreciated that it can be part of a handheld scanner of the type shown.
[0048]
The scanner of FIG. 10 includes a body 735 having a hand portion 736 that can be gripped with a trigger 739. Within the body 735 is a laser module 715. The light from the laser module 715 illuminates a vibrating mirror 710, which can be, for example, a mirror of the shape shown in FIG. 2, FIG. 3 or FIG. The resulting beam 737 exits the housing through window 738. The mirror 710 is arranged to oscillate to draw a scan line 713 across the recorded symbol 714. Light reflected from the symbol passes through window 738 and is collected by collector mirror 726 and reflected to photodetector 725. The optical signal is then converted to an electrical signal and the characteristics of symbol 714 are determined.
[0049]
Although the invention has been illustrated and described in connection with a number of specific embodiments, various modifications and structural changes may be made without departing from the spirit of the invention, so that any details shown may be used. There is no intention of limiting.
Without further analysis, the above matter fully discloses the gist of the present invention, so that others can apply the current knowledge to the essence of the comprehensive or specific aspects of the present invention from the perspective of the prior art. It can be immediately applied to various usages without excluding the elements that make up the characteristic features fairly. Accordingly, these applications should be, and are intended to be, included within the meaning and equivalent scope of the following claims.
[Brief description of the drawings]
FIG. 1 illustrates a multi-range laser scanner according to one embodiment of the present invention that utilizes a multi-surface folding mirror.
FIG. 2 shows another embodiment, ie a two-range scanner with a scanning collector.
FIG. 3 shows another embodiment, a two-range scanner with a separate collector.
FIG. 4 shows another embodiment, a two-range scanner using two laser beams.
FIG. 5 shows in more detail the isolated scanning mirror used in the embodiment of FIG.
FIG. 6 shows another embodiment, a scanner having separated collector mirrors that direct light to two separated photodetectors.
FIG. 7 is a central cross-sectional view of the separated condenser mirror of FIG. 6;
FIG. 8 is another embodiment in which beam shaping is performed by a cylindrical scanning mirror.
FIG. 9 is another embodiment in which beam shaping in both the X and Y directions is performed by two cylindrical mirrors.
FIG. 10 illustrates an exemplary handheld scanner that may include any of the embodiments described above.
FIG. 11 shows an arrangement of two photodetectors according to the invention.
FIG. 12 is a circuit diagram of the arrangement of the two photodetectors of FIG.
FIG. 13 (a) is an arrangement of two photodetectors illustrating a first embodiment of a collector / reflector arrangement.
FIG. 13B is an arrangement of two photodetectors illustrating a second embodiment of the collector / reflector arrangement.
FIG. 13C is an arrangement of two photodetectors illustrating a third embodiment of the collector / reflector arrangement.
[Explanation of symbols]
10 Laser diode
12 Scanning mirror
14 Bending mirror
16 Mirror part (reflection part)
18 Mirror part (reflection part)
20 Mirror part (reflection part)
22 Scanner housing
24 opening
26 symbol
28, 30, 32 positions
38 Optical system

Claims (5)

Read a symbol (26) having a light source (10) for generating a light beam and a movable scanning optical element (12) for reflecting the light beam as a scanning beam and having regions of different light reflectivity An optical scanner for
A fixed polyhedral reflector (14) is provided that functions as a folding mirror for receiving the scanning beam from the movable scanning optical element (12) and directing the scanning beam to a readable symbol (26);
The fixed polyhedral reflector (14) has a first surface (16, 20) having a first shape and a second surface (18) having a second shape different from the first shape,
The first shape cooperates with the movable scanning optical element (12) to shape the scanning beam to allow reading of the symbol (26) at a first distance from the scanner;
The second shape cooperates with the movable scanning optical element (12) to allow reading of a symbol (26) at a second distance different from the first distance from the scanner. Shaping the scanning beam;
An optical scanner characterized by that. 2. The optical scanner according to claim 1, wherein the reflector (14) functioning as a bending mirror collects the light reflected by the symbol (26) to be read and guides the reflected light to a photodetector. An optical scanner characterized by that. 2. The optical scanner according to claim 1, wherein the first surface (16, 20) is convex or concave and the second surface (18) is planar. 3. The optical scanner according to claim 1, wherein the movable scanning optical element (12) has a non-planar reflective surface. The optical scanner according to any one of claims 1 to 4, wherein the light source (10) is a laser light source, and beam shaping optics is provided in an optical path of a light beam emitted from the laser light source. An optical scanner provided with a system (38).

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