GB2163584A

GB2163584A - Bar-code reader

Info

Publication number: GB2163584A
Application number: GB08520933A
Authority: GB
Inventors: Paul Fuller
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-08-21
Filing date: 1985-08-21
Publication date: 1986-02-26
Also published as: GB8520933D0

Abstract

A bar code reader uses fibre optic guides (4,5) to transmit light to and from the reading head (7). The fibre optic guides terminate in a plane polished surface (6) which is set back a specified distance from the lowermost part of the reader. Also included is amplification circuitry, a voltage generator chip and a peak detector circuit. <IMAGE>

Description

SPECIFICATION Bar-code reader The present invention concerns bar code readers. Bar code readers enable data to be entered into computers or micro-processors in a rapid and simple way without the need for a keyboard.

At present, most bar code readers have an optical sensor head which incorporates a lightemitting diode, a sensor in the form of a photodiode and a bifurcated aspheric lens to focus the transmitted and received light from and onto the respective diodes.

A bar code reader of a type which does not have a focussing lens is described in GB 1579111. This reader has a metal cap resiliently mounted in a casing and housing fibreoptic light guides. The cap has a slit at its tip through which light can pass to and from the guides. The cap walls are about 0.010" thick and therefore produce a gap of this magnitude between the polished tips of the light guides and the label being scanned. Since there is no provision for securely mounting the fibres within the cap-in fact the fibres provide spring loading for the cap-the distance between the tips of the light guides and the label being scanned will not be kept constant.

Further, this distance is not accurately determined at the manufacturing stage, being dependent on the thickness of the cap, and also on the quantity of a transparent resin filling the slit.

The prior art arrangements tend to have limited resolution, and are complex in their construction.

The present invention has for an object to provide a bar code reader which is simple, robust and capable of a high degree of resolution.

Accordingly to one aspect of the present invention there is provided a bar code reader comprising a head providing a surface contacting portion which is to contact the surface carrying the bar code to be read by the reader, a light-emitting element, a fibre-optic light guide coupling the iight-emitting element to the head of the reader, a light-detecting element, and a return fibre-optic light guide extending from said head to the light detecting element, the light guides terminating within the head of the reader at a plane face which is spaced by a predetermined distance from and fixed with respect to the surface contacting portion.

According to another aspect of the present invention there is provided a method of manufacturing a bar-code reader as defined in the preceding paragraph, in which the distance by which the plane face is spaced is adjusted for maximum output of the light-detecting element before said distance is fixed.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a section through a bar code reader; Figure 2 is a more detailed section through the optical components of the bar code reader of Fig. 1; Figure 3 is a cross-section showing the head of the reader in more detail; Figure 4 shows on a larger scale a clamp bar for the head of Fig. 3; Figure 5 is a circuit diagram of the signal processing circuit of the bar code reader of Fig. 1; Figure 6 is a diagram of a power supply chip for the circuit of Fig. 5; Figure 7 shows detail of another form of optical component of the bar code reader; and Figures 8a and 8b illustrate the technique used to couple the fibres to the light-emitting and light detecting elements.

Referring now to the drawings, Fig. 1 shows a bar code reader comprising a casing 1 which is a two-part plastics moulding.

The casing 1 ends in a receiver/transmitter head generally indicated at 2. When the reader is used to read a bar code the head 2 is wiped over the code and both illuminates the code and collects light reflected from the code. As can be seen from Fig. 2 the head 2 includes a steel cylinder 3 through which pass two 0.005" (0.12mum) diameter optic fibres (e.g. CROFON fibres) 4 and 5. The fibres terminate at a plane polished face 6 which is recessed into the head 2 so that when the head is wiped over a bar code the face 6 is parallel to and lies an accurately predetermined distance from the surface bearing the code.It has been discovered that the resolution of the reader is very dependent on this distance and for the reader to achieve a resolution of .005" (0. 12mum) the face 6 should be spaced at a distance of 0.002" (0.05mm) from the lower rim 7 of the head 2. Naturally, small variations in this spacing will still give adequate performance. The tip of the moulding is made from a phenolic resin which gives hard wearing properties. The tip is also radiused to allow some deviation from the vertical when the reader is in use.

As shown in more detail in Fig. 3, the fibres 4 and 5 are bonded in the thin walled steel cylindrical tube 3. To set the distance between the optical fibres and the rim 7 the tube housing the fibres can be moved in a channel 53 along an axis of the reader. When the correct position is attained, the tube 3 is clamped at that position in the groove, using a clamp bar 54 (Fig. 4). The bar 54 has screw holes 55 corresponding to screw holes 56 on the reader and a central portion 57 for being received by the channel 53, the central portion having a groove 58 for accommodat ing the tube 3.

The main part 8 of the casing acts as a handle and is provided with a ribbon cable 9 leading, for example, to a microprocessor (not shown).

The optical fibre 4 is connected to a lightemitting diode 11, e.g. type OP290 so as to transmit light from diode 11 to head 2. Fibre 5 is coupled to a light detecting arrangement 12. The casing 1 also houses a regulated power supply circuit 13 and a signal processing circuit 14. These circuits will be described in greater detail hereinafter.

Referring now to Fig. 2 of the drawings it will be seen that fibre 4 enters a case 16 housing the diode. The light receiving end of fibre 4 is polished.

Fibre 5 is connected to a moulded case 18 which is sealed so that there is zero ambient effect. Case 18 houses the light detector 12 which may be a phototransistor of the type Optron OPSOOSLA.

Fig. 7 illustrates another form of optical component which allows the setting of the distance between the face 6' and the lower rim 7 to be attained even more simply. In this form the optical fibres 4', 5' are bonded onto a flat plate 50. At manufacture, the optical fibres can extend beyond the end of the casing so that they can be cut in a single "constant velocity" action, preventing the formation of inclusions on the end face of the fibre, using the end of the plate as a guide. With this arrangement, it is not necessary to carry out the expensive polishing of the fibre tips.

To set the distance between the plane face 6' and rim 7 in this arrangement the plate has an adjustment slot 61 and guide slots 59, 60.

The latter receive screws 62,63 which are tightened when adjustment has been effected to secure the plate 50 to the casing 1 of the reader. For adjustment purposes, the casing has a hole 64 and the adjustment slot 61 on the plate is provided eccentrically of the hole 64. An adjustment tool (not shown) has an eccentrically mounted pin for engaging the hole 64 and can be inserted into the slot 64 so that rotation of the tool causes the position of the plate to be adjusted relative to the casing.

The fibres are connected to the diode 11 as shown in Figs. 8a and 8b. The lens face is cut off along line x-x and polished to within 0.3 mm of the sensitive surface 51 of the diode chip. This enables the fibre 4' to be placed adjacent the sensitive chip to permit transmission of the largest possible signal. A similar technique is carried out to connect the detector 12 (a phototransistor) to the other fibre 5. The cases 16,18 may be secured to the casing 1 using epoxy resin or the light emitter and light detector may be clamped to permit ease of assembly, adjustment and replacement.

At manufacture, the positions of the light emitter 11 and light detector 12 are adjusted independently relative to the end of the fibre 4 or 5 to achieve a maximum output from the light detector. During set up, a spacer (not shown) is provided in the space 65 to avoid scratching of the fibre end or chip face while adjustment of the chip in all directions relative to the fibre is made.

Referring to Figs. 5 and 6, the output of detector 12 is taken to a two-stage amplifier arrangement consisting of amplifiers 28 and 29 connected in series. The output of amplifier 29 is taken to one input of a peak detector circuit generally indicated at 30. This peak detector circuit includes an operational amplifier 31 the negative input of which is connected directly to the output of amplifier 29.

The positive input of amplifier 31 is connected to the junction between two resistors 32 and 33 which form part of a feed-back loop. Resistor 33 is a 1MQ resistor and resistor 32 is 10KQ. The latter resistor is connected to a circuit containing two diodes 34 and 35 connected in parallel but of opposite poiarity. One junction of the two diodes is connected to the output line from amplifier 29 and the other junction to a capacitor 36. The peak detector circuit 30 is thus a negative and positive gain detector operating on both the 0 volt line and +volts.

In this signal processing circuit a single phototransistor is used for speed. To provide the required accuracy of reading it is necessary for the peak detector circuit to produce a significant swing at all times even when the output efficiency of detector 12 has varied because of ambient temperature conditions. In order to achieve this the reader also includes a power supply chip which is shown in greater detail in Fig. 6. This chip has the type No. 7660 and takes a +5 volt input from, for example, a microcomputer's own power supply and provides an output of +9 volts. The two points at which this +9 volt supply is used are shown in Fig. 5.

The usable output of the signal processing circuit just described appears as a series of pulses at output point 40 which indicate the passage of the reader over the alternate black and white portions of a bar code. To indicate that the reader is operational these output pulses are used to switch off and on a LED 41. LED 41 fiashes on when the reader passes over a bar.

It will be seen that in order to compensate for variations in the detector 12 and other circuit components amplifier 29 is provided with a feed-back loop including a variable resistor 44.

At the manufacturing stage of the reader, the distance between the plane face 6 and rim 7 is adjusted to give a maximum output from the phototransistor, and is then fixed. It has been found that this condition gives the optimum sensitivity point for the reader.

In addition as described above the LED 11 and phototransistor 12 are independently adjusted for maximum output.

Claims

1. A bar code reader comprising a head providing a surface contacting portion which is to contact the surface carrying the bar code to be read by the reader, a light-emitting element, a fibre-optic light guide coupling the light-emitting element to the head of the reader, a light-detecting element, and a return fibre-optic light guide extending from said head to the light detecting element, the light guides terminating within the head of the reader at a plane face which is spaced by a predetermined distance from and fixed with respect to the surface contacting portion.

2. A bar code reader as claimed in claim 1, wherein said distance is approximately 0.002" (.05 mm) from the surface contacting portion.

3. A bar code reader as claimed in claim 1 or 2, wherein each fibre optic light guide has a diameter of 0.005" (.12 mm).

4. A bar code reader as claimed in any one of the preceding claims, wherein the light detector element is a single phototransistor.

5. A bar code reader as claimed in any one of the preceding claims, wherein the output of the light detector is coupled to two series-connected amplification stages, the output of the second stage being connected to a peak detector circuit.

6. A bar code reader as claimed in any one of the preceding claims and including a regulated power supply housed within a casing of the reader.

7. A bar code reader as claimed in claim 6, wherein the regulated power supply comprises a voltage generator chip giving an output of +9 volts.

8. A bar code reader according to any preceding claim in which the light guides are carried by a plate providing with the light guides said plane face.

9. A bar code reader substantially as hereinbefore described with reference to Figs.

1,2,5 and 6 or Figs. 7 and 8 of the accompanying drawings.

10. A method of manufacturing a bar-code reader according to any preceding claim, in which method the distance by which the plane face is spaced is adjusted for maximum output of the light-detecting element before said distance is fixed.

11. A bar code reader manufactured by the method of claim 10, substantially as hereinbefore described with reference to Figs. 3 and 4 of the accompanying drawings.