GB1579111A - Optical code readers - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO OPTICAL CODE READERS (71) We, THE PLESSEY COMPANY LIMITED, a British Company, of Vicarage Lane, Ilford, Essex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to optical code readers.

A number of methods are known to those skilled in the art, whereby digital data appertaining to the identity of objects or of individual people can be represented in the form of a bar-code printed on a package, a form, or a label which can be attached to a package.

Such codes are becoming widely used in such establishments as Libraries for the identification of books and borrowers, in hospitals for the identification of patients, drugs and records, in retail shops and wholesale depots for stock control, and in supermarkets and department stores for Point of Sale Data Capture.

Several types of code are in use, most of which are arranged as a series of parallel lines up to 1" long extending over a lateral distance of up to 4". The best known of these codes is the Universal Product Code adopted by the U.S. Uniform Grocery Product Code Council, in which each numerical character of a 10 digit code is represented by a combination of 2 dark and 2 light bands of various relative widths depending on the digit represented.

Other codes represent the decimal digits in binary coded decimal form, in which binary zeroes are represented by one sub-pattern and binary ones are represented by another.

Such codes and methods of reading and decoding them are well known, and described in prior patents and other publications. In particular, a code and decoding method used by the applicant have been described in U.K. Patent 1, 369, 197 and U.S. Patent 3,783,245.

The essential link between the printed code and the decoding electronics is the device used to scan the label and convert its pattern of dark and light bars into electrical signals which can be decoded electronically.

One common group of devices used for this purpose utilises laser beams scanned across the label and photomultiplier cells to detect the resulting changes in light level as the laser beam passes across the dark and light parts of the code pattern.

Another group of devices are described as light pens or wands, and these are held in the hand. They superficially resemble a ballpoint pen with a flexible cable emerging from its upper end. In some designs this cable may comprise electrical wires exclusively, in other arrangements the signal may be conveyed along the cable through an optical fibre.

At the tip of the pen which passes across the code, some designs employ a small lens system to focus a spot of light on the part of the code immediately underneath the tip, and to produce an image of the code element on a photodiode or phototransistor which converts the variations in light detected as the tip passes across the pattern, into electrical signals.

A preferred design uses short lengths of optical fibre extending from the tip of the pen to a light source and a light detector respectively, so arranged that the only light reaching the detector is that reflected into the relevant optical fibre at the tip of the pen.

In order to make the device substantially independent of ambient light conditions, the source of illumination in the pen and the photodetector may be arranged to operate in the infra-red part of the spectrum.

In the grocery trade however, the specifications adopted for the Universal Product Code include the ability to be read in the light from a Helium Neon Laser, which is of a specific wavelength in the red part of the spectrum. Printing inks are used for this code, which are detcctable in light of this wavelength, but are not always readable in white light or light of other wavelengths. A light pen designed to read such labels may, therefore, advantagcously employ red light of a similar wavelength to that of the Helium Neon Laser.

It has been found in practicc that if the optical fibres employed are glass, the pen tends to be somewhat fragile, and if dropped on its tip the fibres will easily chip or shatter with obvious impairment of their performance. On the other hand, when plastic fibres are used, the abrasive effecf of the paper on which the codes are printed gradually wears the plastic during the life of the pen until its light transmission is seriously impaired. Experience shows that, whereas a very light pressure on the paper is all that is required, most users accustomed to using a ball-point pen with a moderately high pressure exert a similar pressure on the light pen, which greatly accelerates the rate of wear.

Accordingly one of the desirable features of a wand for scanning optically encoded data is to have a resiliently mounted tip which in use is scanned across data to be read.

One design of light pen has provision for ensuring that the pressure on the tip of the plastic light fibres cannot exceed a low pressure of 20 gms or under, however heavily the user presses the wand onto the paper.

Moreover, the electronics integral with the pen, and the light fibre section are both modular and can be changed very quickly, the light fibre section being so simple in design that in the unlikely event of excessive wear, it can readily be replaced.

Several of the existing designs of optical reading wand are designed to read only the particular variety of bar code offered by their manufacturcrs, but it is now clear that in some application areas such as Libraries one type of code is becoming the preferred standard whilst in others such as supermarkets other typcs are preferred. To data no single design of wand has been capable of reading all varieties of code. There are a number of reasons for this.

Some codes are more critical than others in terms of a minimum line width and of discrimination between wide and narrow lines.

Others are printed to less demanding printing standards, allowing random ink splashes or voids which in other codes would be pro hibitivc.

It is an object of this invention to comply with all these various constraints including those concerned with compatibility with He Ne Lasers in a single design of wand which is sturdy and yet can readily be repaired if damaged.

Experience has shown that a wand which superficially resembles a ball point pen tends to be handled by users as if it was one. Often the angle at which a ball point pen is held is not optimum for an optical reading wand, and, therefore, this habit is undesirable.

Moreover, customers in a library or shop thinking that the wand is in fact a pen may damage it by trying to use it as such. Also it has been found that intruders breaking into premises equipped with light pens will take away the pens, probably under this same mistaken impression. It is, therefore, considered preferable that the wand, while being of a convenient shape for holding in the hand should not be readily mistaken for a conventional ball point pen.

It is known that users of ball point pens commonly hold them at an angle of about 60 from the plane of the paper on which they write. Some users may hold the pen as low as 45" from the plane of the paper. It is found that a pen-shaped code-reading wand using optical fibres as in our co-pending British Patent 1,504,869 gives less than optimum performance when inclined obliquely to this extent from the perpendicular. An ideal arrangement would constrain the tip of the pen to be normal to the paper on which a bar code label is printed. However, in theory a code printed on an opaque surface should give very little response from a wand whose flat tip rested close to the paper because little light from the illuminating fibres could enter the sense fibre.The fact that such a pen does work is attributed to the fact that the paper on which labels are printed is usually to some degree translucent and light from the source fibres penetrates the paper before illuminating the ink of the bar code from the rear.

Operation in this mode can lead to loss of definition and consequent difficulty in reading some codes.

These last two difficulties and others are mitigated in the preferred embodiment of this invention by raising the tips of the optical fibres a small distance above the surface of the label, and by placing a fine slit across the tip of the reading head to limit the spread of illumination and also to restrict the field of view of the sense fibre. The problem of optimum reading angle is solved by constructing the wand in such a manner that the reading head is inclined by about 30 from the axis of the wand, so that when a user holds the wand at a comfortable angle of about 60 from the plane of the label, the read head is approximately normal thereto.

According to the invention there is, therefore. provided a wand for scanning optically encoded data including a pen shaped structure. an optical fibre arrangement mounted within said pen shaped structure, in which said optical fibre arrangement comprises a first optical fibre, for transmission of light from a light source to the tip of said pen shaped structure, and a second optical fibre, for transmission of light from said first optical fibre, after reflection from an object, from said tip to a light detecting arrangement, in which the tip of said pen shaped structure includes a tubular cap of relatively hard material in which the first and second optical fibres are terminated within said tubular cap for protection of said optical fibre ends against abrasive wear.

The tubular cap is preferably provided with a slit, the fibres being mounted alongside one another such that the field of view from each fibre is restricted by said slit.

The pen shaped structure is constructed to co-operate with positioning means on said tubular cap to ensure that said slit is held in a predetermined alignment with respect to the body of the pen shaped structure.

The tubular cap is preferably mounted within the body of the pin shaped structure at an angle of 30 with respect to the longitudinal axis of the pen shaped structure.

The tubular cap is preferably resiliently mounted within the body of the pen shaped structure for movement into said structure when pressure is applied to the end of said cap.

The volume within the tubular cap not occupied by said fibres is preferably filled with a light transmitting plastics compound to prevent egress of foreign matter into said cap.

Other advantages of the new design of wand will be apparent from the following description which relates to the drawings accompanying the provisional specification in which: Figure 1 is a cross-sectional side elevation of the wand showing the principal components of which it is composed.

Figure 2 is a cross sectional plan view of the wand showing other constructional details.

Figure 3 illustrates the construction of the replacable optical fibre subassembly, and the housing which accommodates it at the tip of the wand.

Figure 4 illustrates on a large scale the optical design of the pen tip.

Figure 5 is a Circuit diagram of the complete unit. Illumination of the label to be read is provided by light emitting diode (2). This diode comprises a chip with a closely controlled emitting area, encapsulated in a plastic moulding with a minimum of encapsulating resin interposed between the 0.015" square chip and the 0.020" diameter plastic optical fibre (3) into which most of its light output is transmitted.

In a preferred embodiment, the chip may be of such a light emitting material as to emit red light similar in wavelength to a heliumneon laser, but for some applications where the colour of the light is not critical, the chip may alternatively be of a composition suitable for emitting light of other colours, or infra red. Infra red has two advantages which in some applications may overshadow the disadvantage of being unable to meet the UPC specification on colour range of readable labels. In the first place an infra red emitter is expected on theoretical grounds to be some 50 times as efficient as a red one, while in the second place when infra red light is used, a colour filter can be used to exclude ambient visible light from the light detector in order to improve the immunity of the wand to extraneous illumination.

The l.e.d. chip is accurately located on the axis of its plastic moulding and this in turn is inserted from one side of a cylindrical hole (6), the ferrule (7) carrying the plastic optical fibre (3) being located in the same cylindrical hole by an annular plastic bush (9) to ensure accurate alignment between the optical fibre and the l.e.d. when they are brought into contact during assembly.

The light, having been efficiently coupled into the fibre at the source end is conducted down the fibre to the tip (10) where it is refracted at the inclined polished end face (1lot) of the fibre to illuminate a small area 20 of the label (21).

The area of the label illuminated is limited in the direction of scan by means of a tubular metal cap (11) with a diametrical slit (31) 0.040" long x 0.004" wide arranged to extend across diameters of the two 0.020" fibres (1) and (3). Some of the light diffusely reflected from the illuminated area of the label enters the end surface (22) of the second plastic optical fibre (1) where it is refracted in the same manner as for the incident light at surface (14) of fibre (3). The reflected light is conducted down the fibre (1) to a photodiode (23) which is capable of sensing the changes in light intensity reflected from dark or light areas of the label.

It is preferable to use a photodiode rather than a phototransistor as the light detector because at the low levels of illumination resulting from the use of a red l.e.d. as the light source, the speed of response of a phototransistor would not be adequate to facilitate the use of a convenient scanning speed. A photodiode suffers from the disadvantage compared with a phototransistor of a low signal level, and therefore, it is necessary to use an integrated circuit operational amp lifier ( 16) to boost this signal to an acceptable level for subsequent transmission along the umbilical cable (19) to the associated electronic circuit modules (26). The cable is anchored in the wand moulding by clamp (15).

The active components of an effective operational amplifier are provided on commercially available integrated circuit chips, but the use of discrete capacitors and resistors to define the amplifier characteristics and for decoupling is precluded by the very limited space available in a compact handheld wand. Consequently, a hybrid thick film circuit has been adopted to combine the passive components and the operational amplifier chip into a physically compact assembly capable of being accommodated within the body of the wand.

The body of the wand comprises a plastic moulding preferably of polycarbonate composition made in two halves for ease of assembly. The two halves (4, 5) are held together by small nuts (35) and bolts (32) or self-tapping screws, and these fixings are conccaled by adhesive plastic labels (13) applied to the recessed flat surfaces (24) on each side of the wand. It will be impossible for a user to opcn up the wand without disfiguring the label, and this will ensure that any such tampering will be revealed to service engineers when they carry out legitimate repairs to the wand.

The shape of the wand body (4, 5) has been so designed that the axis of the optical components is inclined at 30 to the general axis of the wand. This ensures that when the wand is held at an angle of about 60 from the plane of the label, the tip will be substantially normal thereto.

The body of the wand is provided with a rectangular aperture (27) in its upper end in which a rectangular encapsulated l.e.d. (25) can be located for use as an indicator. This may have various uses. including an indication that an iten of data input by the wand has been correctly acccpted by the electronics module.

At a convenient level about one inih above the tip of the wand are provided two plastics press button keytops (8) giving access to miniature switch cartridges (17) of a type commonly used on pocket calculators. These may be connected electrically in parallel so that they are equally convenient to use for left handed or right handed users. or to minimise fatigue when the wand is being used for long continuous periods, they may be operated interchangeably by the user's thumb or indcx finger.Normally the buttons are used to enter data to the associated electronic module after vcrification on a visual display, or alternativcly they may be used to cancel erroncous cntries. As a further option, the two buttons may be connected independently so that these two functions (or any other two as may be required) can both be carried out from the wand. This option may be implemented by changing the circuit connections (44 and 47).

It has been found in practice that the tip of a hand-held wand. when used extensively for reading data from relatively abrasive paper labels, can, after a few hundred thousand entries of data. become abraded to an extent sufficient to impair its optical properties.

Three separate design features in the preferred embodiment are all designed in part to minimise this problem.

The springiness of the plastics optical fibres can be used as described in our British patent No. 1,504,869 to absorb most of any mechanical loading applied to the tip of the pen when it is stroked across a label. The 30 angle between the axis of the optical tip of the wand and the axis of the main body of the wand facilitates control of the flexing which occurs in the fibres when pressure is applied to the tip.

The tubular metal cap (11) which also contains the 0.004" x 0.040" slit (31) is about 0.010" thick and therefore introduces a gap of this magnitude between the polished tips of the optical fibres and the label being scanned. The actual friction between the wand tip and the label is, therefore, taken, not on the ends of the optical fibres but partly by this metal cap itself. Since cap (11) is lightly spring loaded by the fibres the major part of any frictional abrasion on the tip of the wand is taken by the tubular metal insert (12) which is held captive between the two halves (4 and 5) of the plastic body, and in the bore of which the metal cap (11) is slidably located.To prevent dust, dirt, paper scrapings or any other foreign matter obscuring the 0.004" wide slit in the metal cap (11), this slit is filled with a small quantity of highly transparent optical resin of selected refractive index. When it is desirable to constrain the use of the pen to certain colours of label this resin may be loaded with dye to produce a colour filter as appropriate.

Since it is expected that eventually even this metal tip could become worn, it has been designed so that once the body of the wand is opened up, this tip as well as the optical fibre assembly and the tubular insert (12) may readily be replaced.

To ensure that the slit in th tip of cap (11) remains at all time aligned in a direction parallel to the plane of FIGURE 1, its rear end is provided with a circular flange (28), part of which is cut away to align with a corresponding flat in the moulding, thus preventing rotation of the cap (11) on its axis.

To minimise reflection of light from the inner surface of the slit (31) the inside of the metal cap (11) is coated with matt black paint. This improves the signal/noise ratio when reading labels.

Seven conductors are required to interconnect the wand to the associated electronics, these provide the following signals.

1. Supply voltages to operational 2. Supply voltage ) amplifier 2. ) amplifier 3. Supply voltage to l.e.d.

4. Return earth for l.e.d.'s and the switchcs 5. Common earth for operational amplifier and output signal.

6. Output signal from the amplifier.

7. Input to indicator lamp and also sensing circuit for press buttons.

In the preferred embodiment, these seven conductors are accommodated in a flexible self-coiling umbilical cable (19) terminated at the far end in a 7-way connector (27) mating with a corresponding socket on the parent electronic module (26).

WHAT WE CLAIM IS: 1. A wand for scanning optically encoded data including a pen shaped structure, an optical fibre arrangement mounted within said pen shaped structure, in which said optical fibre arrangement comprises a first optical fibre, for transmission of light from a light source to the tip of said pen shaped structure, and a second optical fibre, for transmission of light from said first optical fibre, after reflection from an object, from said tip to a light detecting arrangement, in which the tip of the pen shaped structure includes a tubular cap of relatively hard material, in which the first and second optical fibres are terminated within said tubular cap for protection of said otpical fibre ends against abrasive wear.

2. A wand as claimed in claim 1 in which the tubular cap is provided with a slit, the fibres being mounted alongside one another such that the field of view from each fibre is restricted by said slit.

3. A wand as claimed in any one of claims 1 or 2 in which the pen shaped structure is constricted to co-operate with positioning means on said tubular cap to ensure that said slit is held in a predetermined alignment with respect to the body of the pen shaped structure.

4. A wand as claimed in any one of claims 1 to 3 in which the tubular cap is mounted within the body of the pen shaped structure at an angle of 30 with respect to the longitudinal axis of the pen shaped structure.

5. A wand as claimed in any one of claims 1 to 4 in which the tubular cap is resiliently mounted within the body of the pen shaped structure for movement into said structure when pressure is applied to the end of said cap.

6. A wand as claimed in any one of claims 1 to 5 in which the volume within the tubular cap not occupied by said fibres is filled with a light transmitting plastics compound to prevent egress of foreign matter into said cap.

7. A wand substantially as described with reference to Figures 1 to 4 of the drawings accompanying the provisional specification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (1)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   5. Common earth for operational amplifier and output signal.

   6. Output signal from the amplifier.

   7. Input to indicator lamp and also sensing circuit for press buttons.

   In the preferred embodiment, these seven conductors are accommodated in a flexible self-coiling umbilical cable (19) terminated at the far end in a 7-way connector (27) mating with a corresponding socket on the parent electronic module (26).

   WHAT WE CLAIM IS:

   1. A wand for scanning optically encoded data including a pen shaped structure, an optical fibre arrangement mounted within said pen shaped structure, in which said optical fibre arrangement comprises a first optical fibre, for transmission of light from a light source to the tip of said pen shaped structure, and a second optical fibre, for transmission of light from said first optical fibre, after reflection from an object, from said tip to a light detecting arrangement, in which the tip of the pen shaped structure includes a tubular cap of relatively hard material, in which the first and second optical fibres are terminated within said tubular cap for protection of said otpical fibre ends against abrasive wear.

   2. A wand as claimed in claim 1 in which the tubular cap is provided with a slit, the fibres being mounted alongside one another such that the field of view from each fibre is restricted by said slit.

   3. A wand as claimed in any one of claims 1 or 2 in which the pen shaped structure is constricted to co-operate with positioning means on said tubular cap to ensure that said slit is held in a predetermined alignment with respect to the body of the pen shaped structure.

   4. A wand as claimed in any one of claims 1 to 3 in which the tubular cap is mounted within the body of the pen shaped structure at an angle of 30 with respect to the longitudinal axis of the pen shaped structure.

   5. A wand as claimed in any one of claims 1 to 4 in which the tubular cap is resiliently mounted within the body of the pen shaped structure for movement into said structure when pressure is applied to the end of said cap.

   6. A wand as claimed in any one of claims 1 to 5 in which the volume within the tubular cap not occupied by said fibres is filled with a light transmitting plastics compound to prevent egress of foreign matter into said cap.

   7. A wand substantially as described with reference to Figures 1 to 4 of the drawings accompanying the provisional specification.