JPH04220786A - Bar code scanner - Google Patents

Abstract

PURPOSE: To generate light beams for scanning at a high speed with a bar code scanner without a moving part and to improve the read precision and efficiency. CONSTITUTION: Arrangement 10 where laser diodes or LED 11 which are sequentially started one by one are linearly arranged is used. Optical output from the arrangement 10 is image-formed on a line 13 on a focus face by using an appropriate lens system, and the video of the arrangement 10 crosses the focus face and appears as the line 13 for scanning. A bar code mark 14 is scanned by the line 13. Since moving parts do not exist in the scanning device, scanning speed can be speeded up compared to a machine type rocking mirror. Relevance is given to data signals by using appropriate algorithm and the precision of decoding can be improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to bar code reading devices and, more particularly, to devices for generating scanning light beams used to read bar code symbols.

0002

[Prior Art] U.S. Patent No. 4,387,297, U.S. Patent No. 4,409,470, U.S. Patent No. 4,251,798
No. 4,760,248 (both S.
ymbol Technologies, Inc. (proprietary of) discloses a barcode reading device. The barcode reading device described in the above patent document,
Other commercially available readers of the same type typically use an oscillating mirror or similar mechanical means to generate the scanning pattern. This type of reader is
Currently widely used in supermarkets and retail stores, it can fully achieve its respective intentions, while still improving reliability, reducing power consumption, reducing size, weight, and reducing component and manufacturing costs. , improvements in operating speed and accuracy continue to be desired. One of the traditional barcode scanner components most susceptible to improvement along these lines:
One is a mechanical scanning device. A mechanical scanning device can consist of a scanning mirror attached to a stepper motor. The scanning mirror has a flat surface portion for directing the outgoing laser beam and a concave portion for collecting the incident reflected light and imaging it onto a photodetector.

[0003] A barcode reader detects a signal generated by a photodetector in response to light reflected from a barcode symbol.
Interpret using decoding circuitry. Typical decoding methods rely on data collected by a single scanning spot that is moved in a straight line across the field of view in which the barcode symbol is placed. Bar code data is buried in background noise, so if the signal can be improved, the decoding circuitry will work more effectively. For this purpose, higher scanning speeds can enable multiple scans and improve the reliability of the collected data, but traditionally used mechanical scanning beam generators or scanners The limitations of this have hindered the use of multiple scan methods.

0004

SUMMARY OF THE INVENTION It is a principal object of the present invention to provide a bar code reader or similar device that does not require a mechanical scanning device such as an oscillating mirror to scan the symbol to be read with a beam of light. It is to be. A second object is to provide a barcode reading device that is capable of scanning at higher speeds by performing scanning without the use of moving parts. A third objective is to increase the signal recovery capability, ie, the likelihood of recovering correct decoding of the bar code symbol, by performing multiple scans using high speed scanning techniques. In addition, the ability to perform multiple scans using high speed scanning techniques can improve the ability to read two-dimensional bar code symbols in the form of multi-column bar code patterns. Another object of the invention is to reduce the size of a laser scanning type bar code reader;
Reduce weight, save power consumption, lower manufacturing costs,
The goal is to improve reliability and extend service life.

[0005]

SUMMARY OF THE INVENTION In a first embodiment, the present invention provides a bar code scanner that uses electronic means to scan (move across) a bar code symbol with a beam of light. I will provide a. To generate the scan lines, electronic means of scanning the bar code symbol are used instead of traditional mechanical scanning devices. In a first embodiment, a linear array of light sources activated one at a time in an orderly sequence generates a series of single spot beams at high speed. These spot beams are mapped onto the bar code symbol to simulate a scanning beam. Alternatively, a tunable laser and a diffraction grating whose diffraction angle changes depending on the wavelength of the laser output can be used. In this case,
As the frequency of the laser changes in a selected pattern, the diffraction angle changes accordingly, causing the laser beam to scan the symbol. The scanning speed is significantly greater than that possible with mechanical scanning devices, and the scanning pattern can be tailored to specific symbols and locations. Although scanning mirrors have been advantageously used in some of the disclosed embodiments, a scanner without moving parts can improve system reliability. Additionally, improvements in power consumption, size, shape, and weight by using features of various embodiments of the present invention result in a bar code reader that is easier to use.

[0006] The high speed scanning made possible by the generation of scan lines without moving parts allows multiple scans to be performed within the time of a single scan of conventional devices. This ability to perform multiple scans improves the decoding signal, ie the electrical signal from the photodetector. By multiple scans at fixed vertical distances on the barcode symbol and the output of the photodetector being the composite signal returned from all the scans,
Misreadings due to defects in the symbol itself or background noise will be avoided. Alternatively, multiple scan lines can be used to read a two-dimensional barcode symbol with a multi-column barcode pattern. Instead of a scanning device without moving parts as described above, a mechanical scanning device, such as an oscillating mirror, can be used to generate multiple scan lines. In this case, multiple scan lines can be generated using multiple light sources or a single light source and a beam splitter. Liquid crystal devices used as beam splitters are made by changing the magnitude or frequency of the voltage applied to a plate holding the liquid crystal material.
It is possible to dynamically change the number of scan lines.

As another example of using multiple scan lines in a bar code reader or similar device, a mechanical scanning device can be used to scan the viewing field in a raster fashion. Also, since multiple scan lines are generated for each scan, the frequency of the mechanical scanning device can be reduced. The reflected light from multiple simultaneous scan lines is separated by first modulating each scan line with a different frequency and then using a bandpass filter to recover the different signals.

The novel features of the invention are set forth in the claims. These and other features and advantages of the present invention will be better understood from the following detailed description taken in conjunction with the accompanying drawings.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A bar code scanner according to a first embodiment of the invention, shown in FIG. 1, uses a linear array 10 of laser diodes or LEDs 11 that are activated sequentially, one at a time. US Pat. No. 4,445,125 discloses a linear array of laser diodes formed on a common substrate that can be used as linear array 10. The light output from the linear array 10 is imaged by a suitable lens system 12 onto a line 13 in the focal plane. That is, the image of the linear array 10 appears as a line 13 scanning across the focal plane. A target, for example a barcode symbol 14, is scanned by the line 13 mentioned above. The light beam scanning line 13 performs just the same function as the laser scanning used in conventional bar code readers. However, the advantage of the scanning device of FIG.
It is possible to increase the scanning speed considerably. The illustrated spot size of the scan line 13 is merely an example; the actual spot size representing the image of the diode 11 may be as large as the minimum dimensions of the bars and spaces;
It may be larger than that.

The light reflected from the barcode symbol 14 is
A photodetector (photodiode) passes through the lens system 16
15. Photodetector 15 sequentially outputs analog electrical signals on line 17 representing the received reflected light. This sequential output signal is shaped by wave shaping circuitry 18 to produce a square wave signal on line 19. This square wave signal is then decoded in the usual manner to identify the bar code symbol. Microprocessor 20 is used to drive linear array 10 using multiple drive circuits 21, as well as to decode the detected and shaped signals on line 19. The drive circuit 21 is
As shown in FIG. 2, it can be configured with a large number of transistors 22. Each transistor 22 is connected in series with one of the laser diodes 11 of the linear array 10. The base emitter circuit of transistor 22 is driven from a decoder 23 which receives a one-of-N address signal on line 24 from microprocessor 20 to activate a particular laser diode 11. In this way, the laser diodes 11 starting at one end of the linear array and ending at the other end can be turned on one at a time at high speed. The pulse width used to drive the base of transistor 22 to turn on laser diode 11 can be varied by feedback based on reflected light, as described below.

A monitoring photodiode 25 is located within the reader housing to detect any light output from the light emitting diode 11 using suitable optical equipment if necessary. The electrical output from photodiode 25 is applied to the input of microprocessor 20 through line 26 and wave shaper or digitizer 18a. This monitoring photodiode 25 has two
do one job. First, by adjusting the pulse width of the drive current pulse, e.g. by an address strobe applied from the microprocessor 20 to the decoder 23 through line 27, the laser diode or LED 11
can maintain the output power within a suitable range. In this way, feedback is provided to adjust the pulse width used to drive transistor 22. Alternatively, the voltage level of the power supply to laser diode 11 could be varied to adjust the drive current of diode 11. Second, the monitoring photodiode 2
5 sends input to microprocessor 20 for use in fault detection and correction. That is, if one or more laser diodes 11 fail and do not produce light output, the location or spot within the scan line 13 that the laser diode must illuminate will always be dark, even if it is not actually a light output. Even if this position of the code symbol 14 is a white space, it will be interpreted as a black bar in the return signal. To prevent this erroneous interpretation, microprocessor 20 is programmed to ignore all signals on input line 17 during the duration of the failed diode. In FIG. 3(a), the electrical output of the monitoring photodiode 25 on line 26 should be a series of consecutive overlapping pulses 30, but if a faulty laser diode is present, a blank 31 will result. The microprocessor 20, as shown in FIG. 3(b),
A blank period 32 is generated. The barcode symbol 14 shown in FIG. 3(c) is on line 1 as shown in FIG. 3(d).
7, but the blank period 3
Since the return signal between 2 and 2 is false, this input is ignored or assumed to be either black or white. If the code can be decoded with this ambiguity (ambiguity), correct reading is possible. If decoding is not possible, at least erroneous reading can be avoided, and a correct reading result can be obtained by the user operating the switch again or by automatic rescanning without user intervention. In any case, a failure is signaled so that the user can return the reader for repair.

As shown in FIG. 4, the optical system used to image the linear array 10 onto the focal plane of the bar code symbol 14 focuses the light from each laser diode, one for each laser diode 11. A large number of individual lenslets 12a, 12b, 12c, etc. that collimate the beams can be used. Each lenslet 12a, 12b, 12c, etc. is individually positioned to collimate the light of each laser diode into a parallel beam of light, so that the single light spot of each laser diode is aligned with the area where the bar code symbol is expected to be placed. The line 13 consisting of the light spot is imaged onto the focal plane of
Lens 12 is used to generate . The linear array 10 is comprised of a number of laser diodes or LEDs fabricated on a semiconductor chip rather than individual devices as shown.
It can be composed of In that case, although the actual size of the linear array 10 of laser diodes 11 is small, it can be easily enlarged with a lens system 12 to produce a scan line 13 of the desired length. In order to ensure that the light spot in the enlarged view of the scan line 13 in FIG. The image may be formed using

Next, FIG. 5 will be explained. Figures 1 to 4
The barcode scanner can be attached to a gun-type handheld reader 35 having a gun handle 36 that is held by the user. The laser scanning beam 37 generated by the linear array 10 exits through the front window 38 and the light reflected from the barcode symbol 14 passes through this window to the photodetector 15. Microprocessor 20 and other circuitry of FIGS. 1 and 2 are mounted on a circuit board within reader 35. Microprocessor 20 and other circuitry of FIGS. If the reader is self-powered, it is equipped with a battery. Reading device 35
are connected to a central station by an RF link or wire cable. When the user points reader 35 at bar code symbol 14 and operates trigger switch 39, scanning, detection, and decoding functions are activated.

The scanner of FIGS. 1-5 can operate at very high speeds. If there are N laser diodes 11 in a linear array and the pulse width applied to each laser diode 11 via transistor 22 is Tp, then the number of scans per second is given by nscan=1/NTp. Ru. For example, if N=100 and Tp=1 μsec, the scanning rate is 104 scans/sec. By changing the value of Tp in real time, the scanning speed can be changed.

The use of the scanner of FIGS. 1-5 with no moving parts allows the scanning pattern to be flexibly adapted to the symbology. For example, if it is determined that the barcode occupies only a portion of the total scan line 13, power consumption can be saved by applying drive current only to the transistor 22 of the laser diode 11 that actually illuminates the barcode symbol 14. can do. Similarly, if the decoding of the signal on line 17 indicates an ambiguity for a small portion of the bar code symbol, limiting the addressing applied to multiplex drive circuit 15 causes more scanning to be performed on that portion. be able to.

FIG. 6 shows another embodiment of a bar code reader without moving parts. Tunable laser diode 4
0 or the laser beam 41 generated by the laser tube is
It passes through a suitable lens system 42 and hits a diffraction grating 43,
The reflected light beam passes through another lens system 44 and is imaged in the plane of the barcode symbol 45 .

Since the diffraction grating 43 has the property of reflecting light at an angle determined by the wavelength of the light generated by the laser diode 40, by changing the wavelength of the laser diode 40, the light beam 41 can be changed to the bar code symbol 4.
5 can be swept along a line 46 across the plane of the screen. As in the embodiment of FIG. 1, photodiode 47, which detects the light reflected from bar code symbol 45, generates an analog electrical signal on line 48 which is transmitted via a waveform shaping device to a decoder. The scanner shown in FIG. 6 can be mounted in the gun-type hand-held reader 35 shown in FIG. 5 or in the housing of a reader of the type described in the previously cited patent documents. The user's actuation of a trigger switch 39 on the reader activates the laser light source 40, photodetector 47, associated microprocessor, and data transmission circuitry.

Adjusting the wavelength of the laser diode 40 by an amount of Δλ causes a change in the diffraction angle of ΔΘ=(m/α cosΘ)Δλ. Here, m is the diffraction order, α is the line pitch (in the case of a 1200 lines/mm diffraction grating, α=1/120
0 mm, i.e. approximately 0.8 μm), Θ is the incident beam 4
1 and a line perpendicular to the surface of the grid 43.

The angular resolution limited by diffraction is δΘ
It is expressed as = (λ/N・αcos Θ). where N is the total number of lines in the grid. Therefore, the number of resolvable spots nspot is expressed by Equation 1 shown at the end of this description. For a diffraction grating with a linear density of 1200 lines/mm and a length of 1 cm, N = 12,0
It is 00. Also, it is relatively easy to achieve Δλ=50 Å in the tunable laser diode 40. Therefore, the number of resolvable spots is: nspot=12,000・50Å/6,700Å≒
It is 90. m=1, αcos Θ=0.5 μm, Δ
For λ = 50 Å, the resulting angular deviation is
ΔΘ=0.01 rad≈0.6°. The optical magnification required for lens system 44 to obtain a scan angle of ±15° is approximately 50x.

There are several ways to tune the laser diode 40 to obtain the variable wavelength output light beam 41. Semiconductor lasers can have their output wavelength tuned in a variety of ways. There are methods that require mechanical movement and methods that do not require mechanical movement, but in both cases, the laser light source is activated by an electrical input with a sawtooth waveform sent from a sweep signal generator 51 on line 50. 40
, the output wavelength of is changed, resulting in scan line 46.

[0021] Instead of one piece as in the embodiment of FIG.
A further embodiment of the invention using two linear arrays 10a, 10b is shown in FIG. The construction of the remaining parts of the device is the same as the embodiment of FIG. 2 linear arrays 10a, 1
0b results in two scan lines 13a, 13b separated above and below each other by a distance corresponding to the actual spacing of linear arrays 10a and 10b and the magnification of optical system 12. This dual scan line scheme can be used beneficially in several ways. First, if two linear arrays 10a
, 10b are activated in parallel in the same order, the two scanning lines 13a and 13b also have simultaneity. In this case, if the two scan lines cross the same barcode symbol 14, the reflected light received by the photodetector 15 will also have simultaneity based on the two scan lines 13a, 13b. The advantage of having two scan lines is that
This can be understood by referring to FIG. Background area 53
returns an uncorrelated signal 54, whereas the two portions of the symbol 14 scanned by the two scan lines 13a, 13b return correlated waveforms. A single photodetector 15 simultaneously collects the light reflected from the two scan lines and sums the intensity of the reflections so that the total signal 55 detected from the barcode symbol 14 is
The contrast becomes stronger. On the other hand, barcode symbol 14
The other background regions 53 produce different signals, so the overall contrast from these background regions is weaker. The digitizing circuitry for shaping the analog waveform on line 17 to recover the barcode information can easily distinguish between changes in the barcode region of the signal and uncorrelated signals from the background region 53. can. 9 and 10 show that the dual scanning scheme of FIG. 7 can compensate for barcode imperfections as another advantage. As shown in FIG. 9, if barcode symbol 14 has a defect in the form of a cut 57, the signal returned from scan line 13a will have a corresponding false area 58, whereas the signal returned from scan line 13b will have a corresponding false area 58. The signal is correct. However, since the composite signal 59 on line 17 at the output of photodetector 15 is still interpretable, the correct data will be recovered. Similarly, as shown in FIG.
If there is a defect in the form of a 0, the signal returned from one scan line 13a will have a false area 61 as if there were a very wide bar within the symbol, but two scan lines 13a The composite electrical signal 62 representing the sum of lines 13a and 13b shows a distinct change and can be decoded to obtain correct barcode data.

When two scan lines 13a, 13b are used as shown in FIG. 7, the scan lines should be perpendicular to the individual bars of symbol 14. The permissible misalignment depends on the density of the barcode and the actual spacing value between the two scan lines 13a, 13b. Assuming in FIG. 11 that the diameter of the spot in scan line 13a or 13b is greater than the minimum width D of the bar (or space), the maximum allowable tilt angle α is expressed as tan α≈(0.5 D)/L. be done. Here, L is the two scanning lines 13a, 13b
The interval between

The embodiment shown in FIG.
two linear arrays 10a, 10b to give rise to a, 13b;
10b, but the number of arrays can be increased to two or more. Using more than two scan lines provides benefits similar to those discussed above, but to a greater extent. Additionally, you get the ability to scan multiple rows of barcode patterns simultaneously. FIG. 12 shows a barcode symbol 1 consisting of a three-column barcode pattern, as described in U.S. Pat. No. 4,794,239.
Three scanning lines 13a, 13b, 1 imaged on 4a
3c is shown. The symbol shown is a Code-49 format symbol that can have up to eight columns of bar code patterns. In FIG. 12, as an example, three scanning lines 13a are shown.
, 13b, 13c are shown, it should be noted that even more scan lines could be beneficially used in this embodiment of the multiple scan scheme of the present invention. Code-49 format symbols have traditionally been scanned repeatedly using single-scan readers until an indicator light or buzzer indicates to the user that a complete correct decoding has been obtained. Also, pending U.S. Patent Application No. 317,533 (198
The photodetector was a vidicon-type image tube, and the entire symbol was illuminated rather than being scanned. In contrast, the scanning speed provided by the present invention allows multiple scans of multiple columns to be easily identified by sequentially activating one column at a time. That is, the laser diodes 11 of the linear array 10a for the scanning line 13a are activated one after another (
During this time, all other linear arrays are not activated), followed by linear arrays 10b, 10c, and so on. Therefore, at any given moment the laser diode 1
1 is activated and only one spot on the barcode symbol 14 is illuminated, only one photodetector 15 is needed. Another method of simultaneously generating two or more scan lines and identifying their reflected light is to generate light spots modulated at different wavelengths or frequencies and separate the reflected light with optical or electrical filters. It is. For example, as shown in FIG. 13, the individual laser diodes in the first row are activated with a constant frequency burst, as shown by waveform 64, rather than a rectangular pulse at a constant voltage level, while the laser diodes 11 in the second row are activated. Can be activated with similar bursts of different frequencies. A bandpass filter 65 placed in the path from photodetector 15 is then responsive to these frequencies and generates separate simultaneous inputs representing returns from the bar code symbol for two different scan lines to microprocessor 20. send. Similarly,
Instead of frequency division multiplexing as shown in FIG. 13, time division multiplexing can be used. In this case, array 10a
, 10b are activated alternately, one at a time, and the return signal on line 17 is then switched in synchronization with the alternate activation to create two separate data streams. This switching is done by the microprocessor 20.
Or it can be done in circuitry in front of the microprocessor input.

In another embodiment of the concept of generating scan lines without moving parts and using multiple scan lines, a complete raster scan scanner can be created by increasing the number of columns in the array. . That is, as shown in Figure 14, for example, 25 columns by 100 rows of laser diodes or light emitting diodes (2500 diodes in this example, although more diodes are needed to obtain sufficient resolution). The array 10 can be made up of semiconductor chips consisting of a matrix of diodes, one at a time, to activate the diodes. This scanner is similar to the two-dimensional scanning described in the previously cited pending U.S. patent application Ser.
Create a two-dimensional viewing zone at the focal plane where 4 is expected to be. The scanner of FIG. 14 is particularly suited for use with multi-row bar code symbols, such as Code-49, where the rows of bar codes are stacked one above the other. First, scan field 66 at high speed and incompletely (perhaps activating diodes 11 every 1 in 5 or 1 in 10) and simply scan the barcode symbol without attempting to decode it. By looking at the number of changes per unit length, for example, the visual field 6
The position and orientation of the barcode characters within 6 can be found. Each diode is then activated in turn to scan only the local area of the viewing field 66 where the bar code symbol 14 is located, producing a set of scan lines that intersect the column of bar code symbols 14. Note that the angular orientation of the scan lines 13a, 13b, etc. need not be parallel to the row of diodes 11, but may be oblique to match the orientation of the symbol 14 within the viewing field 66. If we activate a series of diodes forming a straight line (not necessarily in the same column) within a matrix of diodes, the scan line will be diagonal.

Next, FIG. 15 will be explained. As shown in FIG. 7, this barcode scanner has two scanning lines 13a,
13b can be generated. However, these two scan lines are produced from a single light source 68 that emits a light beam 69 in accordance with yet another embodiment of the invention. The light beam 69 passes through a beam splitter 70 and is split into two individual beams 71,72. The two beams are directed to a scanning mirror 73 driven by a motor 74, from where they pass through a suitable lens system 75 to form two scanning lines 13a,
13b corresponds to barcode symbol 14. The scanner of FIG. 15 can be mounted on a hand-held gun reader or a stationary reader as shown in FIG. The embodiment of FIG. 15 provides improved resolution and decoding as described with respect to FIGS. 8, 9, and 10.

The number of scanning lines used in the embodiment of FIG. 15 is not limited to the two shown scanning lines 13a, 13b as described in connection with FIG. It is possible to use two or more scanning lines such as scanning lines 13a, 13b, and 13c. Alternatively, as shown in FIG. 16, multiple scan lines 13a, 13b, 13c can be advantageously used to scan a conventional bar code symbol 14 to further increase resolution or correct errors. These three scanning lines 13a, 13b
, 13c are generated using a single light source 68, a beam splitter 70, and a mechanical scanning mirror 73, as shown in FIG.

Next, a plurality of simultaneous scanning lines 13a, 13b,
A barcode scanner that generates scan lines in raster format by repeatedly using 13c is shown in FIG. In this case, to generate scanlines in raster format,
Mechanical means are used in the form of a mirror 76 that oscillates about a vertical axis 77 to generate the horizontal trace and about a horizontal axis 78 to move the three scan lines vertically. . For example, there may be 20 horizontal traces (3 scan lines per trace for a total of 60 scan lines) for each vertical frame. Although three scanning lines 13a, 13b, and 13c are shown in FIG. 17, it should be noted that any number n of scanning lines may be used; however, the scanning frequency of the mechanical beam deflection means is reduced to 1/n. Please understand that this will decrease. The ability to generate multiple scan lines during each rocking cycle of mirror 76 reduces the structural requirements of the mirror drive mechanism. In other words, the mirror drive mechanism is 1
/3 speed allows for smaller, lighter, cheaper structures and lower power consumption. Also, the dwell time of the light spot of the scan line 13a, 13b or 13c can be made longer, the resolution can be increased, and/or the power consumption of the light source can be reduced. Three individual light emitting diodes or laser diodes 81, 82, 83 are activated successively at three individual frequencies f1, f2, f3 while scanning the viewing field 79. That is, three laser diodes are applied with current pulses at three different frequencies in the same manner as in FIG. As can be seen in FIG. 18, three scan lines 13a, 13b, 13c trace from one edge of viewing zone 79 to the other, and then trace axes 77 and 78.
The trace returns to the vertically shifted position determined by the indexing of the scanning mirror 76 around the , and begins tracing again. The three individual light spots producing the scan lines 13a, 13b, 13c have the same frequencies f1, f2 as the light source that produced them.
, f3, of course the reflected light from the spot is also modulated in the same way. A single photodetector 15 is responsive to the light reflected from field 79 for all three scan lines to recover the individual returns from three scan lines 13a, 13b, 13c, and on line 17. Analog electrical signals are generated and applied to three bandpass filters 84, 85, and 86 adjusted to f1, f2, and f3, respectively. 3 to remove the modulation frequency and recover the envelope.
Outputs 87, 8 from bandpass filters 84, 85, 86
8 and 89 are demodulated by a demodulator. The three demodulated signals are applied to three wave shaping or digitizing circuits 18, and the shaped output 19 is sent to the microprocessor 2.
0 as input and decoded. As described in the previously cited U.S. patent application Ser. Therefore, if bar code symbol 14 is placed in viewing field 79 at an angle, the effective scan lines can be at the same angle when interpreting the data in memory. That is, scan lines 13a, 13b, 13c do not necessarily need to be parallel to the pattern of bar code symbol 14 to obtain correct reading and decoding. Because the housing 35 of the reading device of FIG. 5 with the scanner of FIG. 17 attached thereto is not aligned perpendicularly to the bar code symbol, a bitmap image of the viewing zone 79 is stored in memory 90, as shown in FIG. 79' may include an image 14' of bar code symbol 14 that is tilted and distorted. Therefore, even if the data obtained from line 17 is stored by microprocessor 20 in this memory in column 1
Even if it is loaded with a normal pattern such as 3a', 13b', the scanning line defines the pattern, so when accessing for decoding, a signal for decoding is generated that is aligned with the column of barcode pattern 14. Therefore, it is necessary to appropriately address the memory to generate pseudo scanning lines 91, 92, etc. Further, in FIGS. 17 and 18, scanning lines 13a, 1
Note that although 3b and 13c are shown adjacent to each other, an interleaved scanning pattern may alternatively be used for raster scanning in this example.

The embodiment of FIG. 17 includes three individual light sources 81,
82 and 83, a single light source and beam splitter 70 can also be used as shown in FIG. Furthermore, downstream of the beam splitter, in the path of each beam,
An electro-optic light modulator is arranged. The optical modulator applies an identification signal to each beam that can be recovered by bandpass filters 84, 85, 86, as previously described. The light modulator may be, for example, a ferroelectric liquid crystal, an electro-optic or an acousto-optic crystal gate.

FIG. 20 shows yet another embodiment of the present invention. The plurality of scanning lines 13a, 13b, 13c, 13d are
It is generated from a single laser light source 68 by a liquid crystal device 94. As shown in FIG. 15, a beam 69 generated by a laser light source 68 is divided into a plurality of beams 95 by a liquid crystal device 94. As shown in FIG. Mechanical device such as swinging mirror 73
simultaneously sweeps these beams across the area of the bar code symbol as multiple scan lines 13a, 13b, etc. A voltage is applied to the liquid crystal device 94 from lines 96 and 97. The number of beams 95, or scan lines, produced depends on the magnitude and frequency of the voltage. Thus, by varying the magnitude and frequency of the voltage of voltage source 98, beam 95 can be dynamically changed from a single beam to multiple segmented beams. For example, if one scanning line is used, the quality of the signal output from photodetector 15 to line 17 may be poor, but as described in FIGS. 8, 9, and 10, Decoding may be possible using multiple scan lines. Therefore, if correct decoding is not obtained on one scan line, the control program executed by microprocessor 20 can switch voltage source 98 to a multi-scan line state. Also, since the beam splitter will reduce the illumination level of the constant power laser light source 68, the control program may switch from a multiple scan line condition to a single scan line condition if more intense illumination is required. can.

As shown in FIG. 21, a liquid crystal device 94 can be constructed of two glass plates 69 coated with a conductive thin film and a liquid crystal material 100 sandwiched between the glass plates. Liquid crystal material 100 may be, for example, p-methoxy-benzylidene or p-n-butyl-aniline.

Liquid crystal device 94 of FIG.
can be split into two or more beams, so that depending on the detected condition, several levels of voltage can be applied to voltage source 98 to generate the required number of scan lines.

[0032]

Although in various embodiments of the present invention the scan line generating device can also use an oscillating mirror, as previously mentioned, bar code scanner embodiments with no moving parts are electrically Compared to scanners that use mechanical parts,
It has several advantages for certain problems. First, the scanning speed can be very high, reducing the time the laser is on and thus saving power consumption. The higher scanning speed also allows multiple scans to be performed in one read operation, so that appropriate algorithms can be used to correlate the data signals to increase the accuracy of decoding. Second, the scanning pattern can be flexibly adapted to the symbol. That is, the scan can be tailored to fit a particular barcode symbol and location. For example, after an initial scan, the position and width of the barcode symbol within the viewing zone is known to be at a particular location, so the viewing zone is rescanned only at that location. This saves power. Third, after the first scan, only the small portion that showed ambiguous decoding can be rescanned and a correct decoding of only that problematic portion can be obtained. Fourth, improved reliability is obtained with scanners without moving parts, but could alternatively be achieved using only electronics and fixed optics.

A bar code scanning method using multiple scan lines disclosed as yet another embodiment of the present invention has important features. By generating a composite signal from multiple simultaneous scans, the effects of noise or defects can be minimized and the reliability of the decoding process can be increased. Additionally, the high scanning speed made possible by the lack of moving parts allows multiple scan lines to be generated sequentially, one line at a time. This allows the reflected light from multiple scanning lines to be separated when only one photodetector is used. That is, multi-column bar code symbols and the like can be scanned using this method.

Although the invention has been described in terms of specific embodiments, the above description is not to be construed in a limiting sense. Various modifications of the disclosed embodiments, other embodiments of the invention, and changes in the features of the disclosed or other embodiments will readily occur to those skilled in the art after reading the above description. It will be. It is therefore intended that the appended claims cover all modifications, alternative embodiments, or changes falling within the true scope of the invention.

[0035]

[Math 1]

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a barcode scanner that uses a linear array of light sources instead of a single light source and mechanical scanning means, according to one embodiment of the invention.

FIG. 2 is a partial electrical circuit diagram of the barcode scanner of FIG. 1;

FIG. 3 is a timing diagram showing events versus time for various events (voltages) in the barcode scanner of FIGS. 1 and 2;

4 is an enlarged partial view of the linear array of light sources of FIG. 1 according to another embodiment of the invention; FIG.

[Figure 5] Figure 1 attached to a handheld barcode reader
- Figure 5 is a partially cut away perspective view of the scanner of Figure 4;

FIG. 6 is a schematic illustration of a barcode scanner that uses a diffraction grating without moving parts, in accordance with yet another embodiment of the invention.

FIG. 7 is a schematic diagram of a barcode scanner using a dual linear array of light sources in place of the single linear array of FIG. 1, according to yet another embodiment of the invention.

8 is a timing diagram showing events (voltages) versus time that may occur in the scanner of FIG. 7 to illustrate background noise removal; FIG.

FIG. 9 is a timing diagram showing possible events (voltages) versus time in the scanner of FIG. 7 to illustrate compensation for barcode defects (cuts);

10 is a timing diagram showing possible events (voltages) versus time in the scanner of FIG. 7 to illustrate compensation for barcode defects (black spots); FIG.

FIG. 11 is an enlarged view of a barcode symbol scanned with two light beams to illustrate the allowed tilts.

FIG. 12 is a top view of a multi-column barcode symbol scanned with multiple scan lines, in accordance with yet another embodiment of the invention.

13 is a perspective view of a barcode scanner corresponding to FIG. 7 with two rows of light sources activated with signals of different frequencies, according to yet another embodiment of the invention; FIG.

FIG. 14 is a perspective view of a barcode scanner corresponding to FIG. 7 using a two-dimensional array of light sources in accordance with yet another embodiment of the invention.

FIG. 15 is a perspective view of a barcode scanner corresponding to FIG. 7 using a beam splitter and a single light source to generate two scan lines.

FIG. 16 is a top view of a barcode symbol scanned with three scan lines.

FIG. 17 is a perspective view of a barcode scanner similar to FIG. 7 that scans a two-dimensional viewing field using multiple simultaneous scan lines, in accordance with yet another embodiment of the present invention.

FIG. 18 is an illustration of a field of view including a barcode symbol scanned by the scanner of FIG. 17;

19 is a diagram of a bitmap memory containing data recovered from scanning a field of view such as that of FIG. 18 using the scanner of FIG. 17;

FIG. 20 is a perspective view of a barcode scanner corresponding to FIG. 7 or FIG. 15 using a liquid crystal device as a beam splitter and a single light source to generate multiple scan lines, according to yet another embodiment of the invention; be. and

21 is a cross-sectional view of the liquid crystal device of FIG. 20. FIG.

[Explanation of symbols] 10 Linear array of light sources 11 Laser diode or LED 12 Lens systems 12a, 12b, 12c Small lenses 13 Scanning line 14 Barcode symbol 14' Image of barcode symbol 15 Photodetector 16 Lens system 17 Lines 18, 18a Wave shaping circuit 19 Line 20 Microprocessor 21 Multiplex drive circuit 22 Transistor 23 Decoder 24 Line 25 Monitoring photodiodes 26, 27 Line 30 Successive series of parallel pulses 31 Blank 32 Blank period 34 Return signal 35 Handheld reader 36 Gun Grip 37 Laser scanning beam 38 Window 39 Trigger switch 40 Laser 41 Laser beam 42 Lens system 43 Diffraction grating 44 Further lens system 45 Barcode symbol 46 Scanning line 47 Photodiode 48, 50 Line 51 Sweeping signal generator 53 Background area 54 Decorrelation signal 55 Total signal 57 Cut 58 Corresponding false region 59 Composite signal 60 Black spot 61 false region 62 Composite signal 64 Waveform 65 Bandpass filter 66 Viewing zone 68 Single light source 69 Beam 70 Beam splitter 71, 72 Individual beam 73 Scanning Mirror 74 Motor 75 Lens system 76 Mirror 77 Vertical axis 78 Horizontal axis 79 Viewing zone 79' Bitmap image 81, 82, 83 Laser diode or LED
84, 85, 86 Bandpass filter 87, 88, 89 Output 90 Memory 91, 92 Pseudo scanning line 94 Liquid crystal device 95 Multiple beams 96, 97 Line 98 Voltage source 99 Glass plate 100 Liquid crystal material

Claims (55)

[Claims] 1. A barcode scanner for reading barcode symbols, comprising: (a) an array of light emitting elements; (b) a barcode scanner for reading barcode symbols;
) means for sequentially activating said light emitting elements; (c) optical means for imaging said array of light emitting elements in a viewing zone at a fixed distance from the scanner; a photodetector that generates an electrical signal in response, and (e
) means for decoding said electrical signal to identify a barcode pattern. 2. The barcode scanner according to claim 1, wherein the light emitting element is a laser diode or a light emitting diode. 3. The barcode scanner of claim 1, wherein the array is a linear array and the light emitting elements are activated one at a time. 4. The barcode scanner of claim 1, wherein the activation order starts at one end of the array and continues regularly to the other end. 5. The light emitting device according to claim 1, further comprising: a monitoring light detector responsive to light emitted by the light emitting element; and means for changing the activation means in accordance with the output of the monitoring light detector. Barcode scanner described in. 6. The light emitting device according to claim 1, further comprising: a monitoring light detector that responds to the light emitted by the light emitting element; and means for changing the detection means in accordance with the output of the monitoring light detector. Barcode scanner described in. 7. The barcode scanner of claim 1, wherein the array includes a plurality of the linear arrays. 8. The barcode scanner of claim 7, wherein the light emitting elements are light emitting diodes activated one at a time. 9. The barcode scanner of claim 7, wherein the plurality of linear arrays generate a plurality of scan lines over the barcode symbol. 10. Claim 9, wherein the barcode symbol includes a plurality of columns of barcode patterns.
Barcode scanner described in. 11. A method of reading a barcode symbol, comprising: (a) sequentially activating a plurality of individual light sources into a viewing area in which the barcode symbol can be viewed;
A method comprising the steps of: mapping an ordered series of light spots; and (b) detecting light reflected from the viewing zone to generate an electrical signal. 12. The method of claim 11, wherein the series of light spots starts at one end of the viewing zone and continues in a straight line to the other end. 13. The plurality of individual light sources includes at least one
12. A method according to claim 11, characterized in that the method is arranged in a linear array of . 14. The method of claim 13, wherein a plurality of said linear arrays are stacked one above the other. 15. A method of reading a bar code symbol, comprising: (a) generating a scanning light beam and directing the bar code symbol into a viewing area in which the bar code symbol can be viewed by a light path that does not include a mechanically moving device; A method comprising the steps of: mapping a light beam; and (b) altering the optical path of the light beam by varying an electrical input to generate a scan line across the field of view. 16. The method of claim 15, wherein the optical path is changed by turning on a plurality of light emitting diodes one after another. 17. The method of claim 15, wherein the light beam is a laser beam, and the optical path is changed by changing the wavelength of the laser beam. 18. The method of claim 15, wherein the optical path is varied by sequentially turning on a plurality of linear arrays of light emitting diodes. 19. The barcode symbol includes a plurality of rows of barcode patterns, and the plurality of linear arrays produce a plurality of scan lines that separately scan the barcode pattern. 18. The method described in 18. 20. The method of claim 15, wherein the optical path is varied by varying an electrical signal applied to a liquid crystal device within the optical path. 21. A barcode scanner for scanning barcode symbols, comprising: (a) a light source; (b) means for varying the wavelength of light generated by said light source; and (c) dependent on the wavelength of said light. comprising means for bending the light by an amount;
A barcode scanner comprising: optical means for forming an image of the light source in a viewing zone located a certain distance from the scanner. 22. The barcode scanner according to claim 21, wherein the light source is a laser. 23. Further, (d) a photodetector for generating an electrical signal in response to light reflected from the viewing zone, and (e) means for decoding the electrical signal to identify a barcode pattern. 22. The barcode scanner according to claim 21, further comprising: a barcode scanner. 24. The barcode scanner according to claim 21, wherein the optical path bending means is a diffraction grating. 25. The barcode scanner of claim 24, wherein the diffraction grating has a plurality of lines parallel to the bars of the barcode symbol in the viewing zone. 26. The barcode scanner of claim 25, wherein the light source is a tunable laser that produces a beam of wavelength controlled by an electrical input. 27. A method of reading a bar code symbol, comprising: (a) generating a laser beam of variable wavelength; and (b) providing a viewing area in which the bar code symbol can be viewed by an optical path including a diffraction grating. A method comprising: mapping the laser beam and changing the diffraction angle of the laser beam as the wavelength changes to generate a scan line across the viewing field. 28. The method of claim 27, wherein step (a) uses a laser diode. 29. The method of claim 27, wherein the wavelength is varied linearly to generate a scan line starting at one end of the viewing field and continuing to the other end. 30. Further, (c) detecting light reflected from the viewing zone to generate an electrical signal; and (d) using the electrical signal to identify barcode data corresponding to the symbol. 28. The method of claim 27, comprising the step of decoding. 31. Claim 27, wherein the diffraction grating is composed of a plurality of lines perpendicular to the scanning line.
The method described in. 32. A barcode scanner for scanning a barcode symbol, comprising: (a) a light beam generating device that generates and impinges a plurality of scan lines on the barcode symbol or the like; (c) means for decoding the electrical signals from the plurality of scan lines to identify a bar code pattern; A barcode scanner comprising: 33. The barcode scanner of claim 32, wherein the light beam generating device comprises a single light source, a beam splitter, and a scanning mirror. 34. The barcode scanner according to claim 32, wherein the light beam generating device comprises an array of light emitting elements, and the light emitting elements are activated one after another. 35. The light emitting elements of claim 34, wherein the light emitting elements are arranged in at least one linear array, each linear array being activated in an order starting from one end and continuing regularly to the other end. barcode scanner. 36. The barcode scanner of claim 32, wherein the scan lines are multiplexed. 37. The barcode scanner of claim 36, wherein the scan lines are time division multiplexed. 38. The barcode scanner of claim 36, wherein the scan lines are frequency division multiplexed. 39. The bar code according to claim 36, wherein the decoding means includes demultiplexing means for demultiplexing the electrical signal for each scanning line to recover individual signals. scanner. 40. The barcode scanner of claim 32, wherein the plurality of scan lines correspond to one barcode symbol. 41. Claim 4, wherein the barcode symbol includes a plurality of columns of barcode patterns.
Barcode scanner described in 0. 42. The barcode scanner of claim 40, wherein the plurality of scan lines are repeated in a raster scan pattern. 43. The electrical signal of claim 4, wherein the scan lines are modulated at different frequencies and the electrical signal is filtered to separate responses to the plurality of scan lines.
2. The barcode scanner described in 2. 44. The barcode scanner of claim 42, wherein the plurality of scan lines are generated by different light sources. 45. The barcode scanner of claim 44, wherein the plurality of scan lines are generated by a mechanically scanned light beam. 46. The light beam generating device comprises a single light source, a liquid crystal device functioning as a beam splitter, and a mechanical scanning device.
Barcode scanner described in. 47. The light beam generator selects the number and/or branching of the plurality of light beams,
47. The barcode scanner of claim 46, further comprising a variable voltage and frequency voltage source connected to the liquid crystal device. 48. A method of reading a barcode symbol, comprising: (a) mapping a plurality of light beams to a viewing zone in which the barcode symbol can be viewed; and (b) reflecting a beam of light from the viewing zone. A method comprising: detecting light to generate electrical signals corresponding to the plurality of scan lines. 49. The method of claim 48, comprising generating the plurality of light beams by mechanically scanning the output of a single light source through a beam splitter. 50. The method of claim 48, comprising the step of generating a plurality of light beam scan lines from a plurality of light sources arranged in at least one linear array and activated sequentially. . 51. The method of claim 50, wherein a plurality of said linear arrays are stacked one above the other. 52. The method of claim 48, including the step of generating the plurality of light beam scan lines with a liquid crystal device. 53. The method according to claim 52, further comprising the step of changing the number of the plurality of light beam scanning lines by changing the voltage and/or frequency of the voltage applied to the liquid crystal device. Method described. 54. The method of claim 4 further comprising the step of mapping a single light beam scan line to the viewing zone.
8. The method described in 8. 55. The method of claim 54, including the step of switching between a single scan line state and a multiple scan line state in response to the electrical signal.