EP0731950A1

EP0731950A1 - An apparatus and method for detecting a string of alpha-numeric characters on a surface of a ferro-magnetic component

Info

Publication number: EP0731950A1
Application number: EP95901585A
Authority: EP
Inventors: Vincent Casey; Paul Martin Conheady; Shogo Takayama
Original assignee: BUSICOM Ltd
Current assignee: BUSICOM Ltd
Priority date: 1993-11-24
Filing date: 1994-11-23
Publication date: 1996-09-18
Also published as: JPH09506451A; WO1995014978A1; AU1076495A

Abstract

Apparatus for detecting and recording an engraved character string (3) on a gas cylinder (6) comprises a scanning unit (20) within which is mounted a permanent magnet (33) for generating a magnetic field between the magnet (33) and the surface (5). A plurality of magnetoresistive sensors (34) are arranged in an elongated array (35) and are located in a scanning face (31) in the scanning unit (20) for detecting the magnetic field and variations therein caused by the character string (3). A rotary encoder (40) monitors incremental distances travelled by the scanning unit (20). A control circuit (44) within the scanning unit (20) sequentially reads signals from the magnetoresistive sensors (34) as the scanning unit (20) travels through respective predetermined incremental distances. The distances are stored together with the respective signals from the magnetoresistive sensors (34) and from these stored signals character recognition software can construct and recognise the characters (4) of the character string (3).

Description

"An apparatus and method for detecting and recording a string of alpha-numeric characters on a surface of a ferro-magnetic component"

The present invention relates to apparatus and to a method for detecting and recording a string of alpha-numeric characters formed on a surface of a component of ferro-magnetic material. Typically, the apparatus and method is suitable for detecting a string of alpha-numeric characters engraved on the surface of a cylinder of ferro-magnetic material of the type commonly used for storing gas in compressed or liquid form.

In order to maintain a record of the location of gas cylinders, for example, cylinders containing acetylene, oxygen, propane, butane and other gases, such cylinders are identified by a combination of alpha-numeric characters. Such characters, in general, are engraved by punching or the like into the surface of the cylinder adjacent the neck thereof. As the cylinders are being dispatched to the various destinations, a record is kept of the identity details of the respective cylinders and their respective destinations. This requires a visual inspection of each cylinder and manual recording of the alpha-numeric character reference engraved on each cylinder. It will be appreciated that this is a relatively laborious and a time consuming task and by virtue of the need for human intervention, both in the visual inspection of the alpha-numeric characters and in the manual recording thereof, errors can, and indeed do occur. This is undesirable.

Attempts have been made to overcome these problems, for example, U.S. Patent Specification No. 4,521,676 discloses a protective cap for a pressurised gas cylinder of ferro-magnetic material. Binary encoded data is formed on the protective cap. The binary encoded data is formed by punching a plurality of holes in the cap at predetermined locations. A duel head inductive transducer is moved over the holes for reading the encoded data. However, while this arrangement to some extent alleviates the problems of visually reading strings of alpha-numeric characters on gas cylinders known heretofore, it suffers from a number of disadvantages. Firstly, it is not possible to visually cross check the read encoded data against any visually readable reference on the gas cylinder. To facilitate visual cross checking, it is necessary to provide a visually readable alpha¬ numeric reference as well. Additionally, where the string of alpha-numeric characters on the gas cylinder does not correspond with the encoded identification on the cap, visual cross checking of the code read by the duel head inductive transducer is impossible. Most importantly, the arrangement disclosed in this U.S. Patent Specification does not provide a method or apparatus which is capable of reading the same string of alpha-numeric characters which can be visually read by eye.

PCT Specification No. WO 93/17400 also provides an arrangement of identifying gas cylinders. In this case, a management board of non-magnetic material is secured to the gas cylinder. The board is provided with a plurality of holes, and a number of magnetically permeable pins are inserted in selected holes to provide a unique array of pins in the boards of respective cylinders. A sensor head with magnetic sensors located in position corresponding to each of the holes on the management board is brought into alignment with the management board for detecting the unique array of pins for identifying the board and in turn the gas cylinder. However, this arrangement requires attachment of a management board to each gas cylinder, and also requires the engagement of magnetically permeable pins in selected holes of each board so that the boards of the gas cylinders each have a unique array of magnetic permeable pins. Additionally, it is not possible to visually cross check the identification of the respective management boards made by the sensor head. A further serious disadvantage of the arrangement disclosed in this PCT Specification is the need to provide the management board attached to the gas cylinder. The management -

board is vulnerable to being damaged, and being detached from t gas cylinder.

European Patent Specification No. 0,494,617A discloses a method and apparatus for identifying an object on which a bar code or grid code pattern is provided thereon. The bar code or grid co pattern comprises areas of electrically conductive and non- electrically conductive material. A sensor which comprises an electro-magnetic oscillator coil produces an electro-magnetic alternating field which is damped as the sensor approaches a zon of conducting material. In this way, the bar code or grid pattern is read. However, this method and apparatus requires th provision of a bar code or grid pattern which is formed by zones of electrically conductive and non-electrically conductive material, and thus is relatively expensive to provide. Furthermore, the method and apparatus does not enable visual cross checking of the recorded identification with the bar code or grid pattern, since in general, it is not possible to visuall identify characters from their bar code or grid pattern.

PCT Patent Specification No. WO 93/13494 discloses a system for identifying gas cylinders which requires an electro-magnetic wav transmitting device to be secured to the cylinder. A read/writ head is provided for reading the signal transmitted by the transmitting device for analysis and storing in a computer. Thi arrangement requires the provision of an electro-magnetic wave transmitting device to be attached to each cylinder, which is relatively expensive. Furthermore, the transmitting device is vulnerable to damage and being detached from the cylinder. Additionally, it is not possible to visually cross check the da read from the transmission device.

European Patent Specification No. 0,586,083A discloses a magneti transponder for securing around the neck of a gas cylinder. Th transponder comprises a flat annular electrically conductive ai core coil connected to an integrated circuit. On bringing a reader/exciter adjacent the coil, the integrated circuit is activated and transmits encoded data contained therein through the coil which also acts as an antenna. The transmitted data is read by the reader/exciter and can thus be stored. This arrangement requires the provision of a relatively expensive magnetic transponder which must be attached to the gas cylinder, and which is vulnerable to damage, and furthermore, does not provide for ready visual cross checking of data read from the cylinder.

Thus, none of the prior art arrangements provide for direct reading of the string of alpha-numeric characters provided on th surface of a gas cylinder, and furthermore, in general, visual cross checking of the data read from the gas cylinders in general, is not possible.

There is therefore a need for an apparatus and a method for detecting and recording a string of alpha-numeric characters formed on the surface of a gas cylinder, or indeed, any other component of ferro-magnetic material.

The present invention is directed towards providing such an apparatus and method.

According to the invention there is provided apparatus for detecting and recording a string of alpha-numeric characters formed on a surface of a component of ferro-magnetic material, the apparatus comprising a detector head for moving over the surface for scanning thereof, a distance monitoring means for detecting the distance moved by the head, a magnetic field generating means located in the head for generating a magnetic field between the magnetic field generating means and the surface, a plurality of magnetic sensors forming an elongated array located in the head for detecting the magnetic field strength adjacent the surface for detecting the characters as th detector head is moved over the string of characters, and a storing means for storing signals received from the magnetic sensors in respect of each character and the distance monitoring means, and a control means for controlling the writing of signals from the magnetic sensors and the distance monitoring means to the storing means for enabling recognition of each character by a character recognition means.

The advantages of the invention are many. In particular, the apparatus according to the invention provides for direct reading of the string of alpha-numeric characters on a component, for example, a gas cylinder or the like. Thus, by writing the read signals of the characters to suitable character recognition hardware and software, the read characters can readily easily be displayed to facilitate visual cross checking with the character string on the gas cylinder. Of particular importance is the fact that this can be achieved without the need for any additional identification characters or encoded data on the gas cylinder or on any part of the gas cylinder. Furthermore, there is no need for the provision of a management board, a transmitter, or a transponder or any other such device to be secured to the gas cylinder. This is a particularly important advantage in that it enables cylinders to be readily identified without the need for any additional item, be it costly or otherwise to be added to the cylinder. Additionally, the apparatus provides a relatively accurate apparatus for detecting and recording the string of characters. The provision of the magnetic sensors in an elongated array provides for relatively accurate detection and recording of the string of characters.

Ideally, the head defines a scanning face which, in use, is adjacent the surface being scanned, the magnetic sensors being located in the head adjacent the scanning face intermediate the magnetic field generating means and the scanning face. This facilitates in relatively accurate detection and recording of the characters. It is preferable that each magnetic sensor is a thin film type magnetic sensor or a semi-conductor type magnetic sensor. It has been found that the use of thin film type magnetic sensors provides particularly accurate results due to their magnetic sensitivity and small size. It is believed that similar advantages would be achieved by the use of semi-conductor type magnetic sensors for similar reasons.

In one aspect of the invention each magnetic sensor is a magnetoresistive sensor. It has been found that particularly good results can be achieved by using magnetoresistive sensors, and where the magnetoresistive sensors are thin film magnetoresistive sensors, particularly, accurate results can be achieved due to the magnetic sensitivity and relatively small size of the sensors.

Advantageously, the magnetic sensors are elongated sensors and are arranged end to end and spaced apart from each other, and are aligned longitudinally to form the elongated array, and preferably, the length of each magnetic sensor is not greater than the minimum dimension of the characters to be detected at the surface of the component. In general, it has been found that subject to practical limitations, the shorter the length of each magnetic sensor is, the more accurate will be the results achieved by the apparatus. Preferably, the length of each magnetic sensor is not greater than half the minimum dimension of the characters to be detected at the surface of the component, and advantageously, the length of each magnetic sansor is not greater than one third of the minimum dimension of the characters to be detected at the surface of the component. Where possible the length of each magnetic sensor is not greater than one fifth of the minimum dimension of the characters to be detected at the surface of the component.

In a preferred aspect of the invention the magnetic field generating means comprises a permanent magnet. 7

Ideally, the distance monitoring means monitors the distance moved by the head over the surface in a direction transversely o the elongated array of magnetic sensors. Preferably, the distance monitoring means comprises a rotary encoder mounted in the head.

In general, it is preferable that the rotary encoder comprises a wheel for engaging the surface of the component with rolling engagement for measuring and recording the distance travelled by the detector head along the character string.

In one aspect of the invention the control means comprises a multiplex means for sequentially writing signals from the magnetic sensors to the storing means at predetermined intervals in response to the distance monitoring means detecting the head having moved respective predetermined distances.

Preferably, the control means comprises a microcontroller for writing the signals from the magnetic sensors to the storing means, and an analog to digital converter for converting analog signals from the magnetic sensors to digital signals for deliver to the microcontroller.

In another aspect of the invention an amplifying means is provided for amplifying analog signals from the magnetic sensors

It is preferable that a compensating means is provided for temperature compensating for compensating for changes of temperature of the magnetic sensors. Preferably, the temperatur compensating means comprises an additional magnetic sensor connected into a circuit containing the magnetic sensors, the additional magnetic sensor being connected into the said circuit by a Wheatstone bridge circuit.

In one aspect of the invention the apparatus is for detecting alpha-numeric characters engraved into the surface of the component.

In another aspect of the invention the apparatus is for detecting a string of alpha-numeric characters formed on the surface of a cylinder of the type suitable for containing a gas in compressed or liquified form.

Additionally, the invention provides a method for recording a string of alpha-numeric characters formed on a surface of a component of ferro-magnetic material using the apparatus according to the invention, the method comprising the steps of scanning the surface of the component by moving the head over an area of the surface containing the string of alpha-numeric characters, reading and storing signals from the magnetic sensors at predetermined intervals, and storing details of the intervals against the respective sets of signals stored from the magnetic sensors.

Preferably, each predetermined interval corresponds to the head having moved over the surface through a predetermined distance. Advantageously, the signals from the magnetic sensors are sequentially read at the end of each predetermined interval.

It is preferable that the signals from the magnetic sensors are converted from analog to digital form, and ideally, the signals from the magnetic sensors are stored in digital form.

The invention will be more clearly understood fro.n following description of a preferred embodiment thereof given by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a perspective view of apparatus according to the invention for detecting and recording a string of alpha¬ numeric characters engraved into a surface of a ferro- magnetic gas cylinder, Fig. 2 is a perspective view of portion of the gas cylind illustrating the string of alpha-numeric characters,

Fig. 3 is schematic view of a portion of the apparatus of Fig. 1 and of a portion of the gas cylinder of Fig. 2 showing the string of alpha-numeric characters enlarged,

Figs. 4a and 4b are respectively side and end sectional views of portion of the gas cylinder on the lines A-A and B-B, respectively of Fig. 3,

Fig. 5 is a block representation of a circuit diagram of the apparatus of Fig. 1,

Fig. 6 is a detail of the circuit diagram of Fig. 5,

Fig. 7 is a cross-sectional view of a portion of the apparatus of Fig. 1 in use,

Fig. 8 is a graph illustrating the profile of a magnetic field generated across a portion of a character being detected by the apparatus of Fig. 7, and

Fig. 9 is a perspective view of a detail of a portion of the apparatus of Fig. 1.

Referring to the drawings there is illustrated apparatus according to the invention indicated generally by the reference numeral 1 for detecting and recording a string of alpha-numeric characters formed on a surface of a component of ferro-magnetic material, in this case, the apparatus is particularly suitable for detecting and recording a string 3 of alpha-numeric characters 4 engraved into a surface 5 of a steel gas cylinder adjacent a neck 7 thereof. Before describing the apparatus 1 i detail, the string 3 of characters 4 will first be described. -

10

In this case, six alpha-numeric characters 4 are provided, namely, three letters and three numerals. The string 3 is read from the left side 9 to the right side 10. Each character 4 is formed by engraving into the surface 5 of the steel gas cylinder 6, typically by punching. The characters 4 are formed by groove 11 engraved into the surface 5 of the gas cylinder 6. Transvers cross-sectional views of the grooves 11 forming the first of the characters 4 in the string 3, namely, the letter "T" are illustrated in Figs. 4a and 4b. Each groove 11 extends into the gas cylinder 6 to a base 12 which is joined by side walls 14 to the surface 5 of the cylinder 6 along edges 15.

Each character 4 is of height h of approximately 12 mm, see Fig. 3. The grooves 11 forming respective bars 16 of the characters are of width d of approximately 1.0 mm adjacent the surface 5 of the gas cylinder 6. It is preferable that the minimum width d o each groove 11 of the characters 4 adjacent the surface 5 should not be less than 1.0 mm, although, due to imperfections in the engraving of the characters 4, the minimum width d of portions o the grooves 11 may be less than 1.0 mm. It will be appreciated that the minimum dimension of any bar 16 forming a character 4 adjacent the surface 5 of the cylinder 6 will be the width d across the groove 11 forming the bar 16.

The apparatus 1 comprises a hand-held scanning unit 20 which comprises a hollow housing 21. The housing 21 terminates in a portion 22 which forms a detector head 23 also according to the invention for moving over the surface 5 adjacent the string 3 of characters 4 for scanning and detection thereof. A hand-held mini-computer 25 which will be described in more detail below is connected to the hand-held scanning unit 20 by a serial link cable 27 for receiving stored characters from the hand-held scanning unit 20 after a scan of the characters 4. This is described in more detail below.

The housing 21 of the hand-held scanning unit 20 forms a hollow interior region 30 and defines a scanning face 31 in the portion 22 which in use is adjacent the surface 5 of the cylinder 6 as the scanning unit 20 is being moved over the surface 5 for scanning thereof, see Fig. 7. A magnetic field generating means, namely, a permanent magnet 33 is located in the hollow interior region 30 of the housing 21 towards the scanning face 31 for generating a magnetic field between the magnet 33 and the surface 5 of the cylinder 6.

A plurality of magnetic sensors, namely, elongated magnetoresistive sensors 34 are located in the hollow interior region 30 adjacent the scanning face 31 for detecting the strength of the magnetic field and variations therein at a plurality of spaced apart locations on the surface 5 caused by the characters 4 as the scanning unit 20 is moved over the string 3 of characters 4. The magnetoresistive sensors 34 are spaced apart from each other and aligned end to end in an elongated longitudinal array 35 which is located in the scanning face 17 so that in use the array 35 of magnetoresistive sensors 34 lie intermediate the permanent magnet 33 and the surface 5 of the cylinder 6. In this way the magnetoresistive sensors are cut by the lines of magnetic flux extending between the permanent magnet

33 and the surface 5 of the cylinder 6.

In this embodiment of the invention each magnetoresistive sensor

34 is formed by an elongated thin film magnetoresistive element 36, and the magnetoresistive elements 36 are formed on a substrate 38, typically by a thin film deposition technique, which will be well known to those skilled in the art. One of the characteristics of the magnetoresistive elements 36 is that the electrical resistance of each element 36 is a function of the magnetic field strength which is cutting the magnetoresistive element 36. Thus, by determining the electrical resistance of each magnetoresistive element 36, the value of the magnetic field strength cutting the magnetoresistive element 36 can be relatively accurately determined. In this embodiment of the invention the magnetoresistive elements 36 are magnetoresistive elements sold by MR Sensors Limited of Great Britain. In this embodiment of the invention thirty identical magnetoresistive elements 36 form the longitudinal array 35. For convenience only, five of the magnetoresistive elements 36 are illustrated in Fig. 9 formed on the substrate 38.

Each magnetoresistive element 36 is of length / of approximately 0.4 mm. The magnetoresistive elements 36 are spaced apart from each other a distance s of approximately 0.1 mm. Since the minimum dimension of the characters 4 adjacent the surface 5 of the cylinder 6 is the width d, and this, in general, is not less than 1.0 mm, the length of each magnetoresistive element 36 is not greater than 0.5 times the minimum dimension of each character 2 adjacent the surface 5 of the cylinder 6, and in this embodiment of the invention is approximately 0.4 times the minimum dimension of the characters 4 adjacent the surface 5. In Fig. 7 the magnetoresistive elements 36 are illustrated as being shorter than 0.4 times the minimum dimension d since three magnetoresistive elements 36 are illustrated extending across the surface dimension d of the groove 11 of the top bar at A-A of

Fig. 3. The magnetoresistive elements are illustrated in Fig. 7 largely for the purposes of ease of explanation of the invention. However, in practice, it is conceivable that the length of the magnetoresistive elements 36 could be considerably less than 0.4 times the minimum dimension d of the characters 4, and could be as low as 0.15 times the minimum dimension d of the characters 4 adjacent the surface 5. Needless to say, the shorter the distance of the magnetoresistive elements 36 and the more magnetoresistive elements 36 which extend across a bar of a character, the more accurate will be the result, subject to practical limitations.

A distance monitoring means for monitoring the distance moved by the scanning unit 20 as it scans the surface 5 comprises a rotary encoder 40 which is mounted in the hollow interior region 30 of the housing 21 adjacent the scanning face 31. A rotatable wheel 41 is carried on the encoder 40 and projects through the scanning face 31 of the housing 21 for rollably engaging the surface 5 of the cylinder 6 for determining the distance travelled by the scanning unit 20. The wheel 41 is rotatable about a rotational axis 42, see Fig. 3, 5 and 7, which extends parallel to the longitudinal array 35 of magnetoresistive sensors 34, and thus, the wheel 41 monitors the distance travelled by the scanning unit 20 in a direction which extends transversely of the array 35 of permanent magnets 33, in other words, in the direction of the arrows X and Y, see Fig. 3 as the scanning unit 20 scans along the string 3 of characters 4 from the left hand side 9 to the right hand side 10 in the direction of the arrow Y.

A control means, in this case, a control circuit indicated generally by the reference numeral 44 in Figs. 5 and 7 controls the scanning unit 20, and is located in the hollow interior region 30 of the housing 21 away from the permanent magnet 33. The control circuit comprises a number of individual sub-circuits which are described below. An interface IC circuit 45 of the rotary encoder 40 digitises the output from the encoder 40 for delivery to the control circuit 44. Such rotary encoder circuits and their associated interface IC circuits for producing a digitised signal will be well known to those skilled in the art.

The control circuit 44 comprises a microcontroller 47 which reads signals from the magnetoresistive elements 36, and in turn, in an analog to digital converter in the controller 47, digitises the signals and then writes the signals to a storing means, namely, a random access memory 48. The microcontroller 47 also reads the signals from the rotary encoder 40 from the interface IC circuit 45 and writes these signals to the random access memory 48 in which the signals from the respective magnetoresistive elements 36 are correlated with the corresponding signals from the rotary encoder 40. The magnetoresistive elements 36 are connected in parallel between input terminals 50 and 51 of a Wheatstone bridge circuit 52 for enabling determination of their respective resistance values for in turn determining the strength of the magnetic field to which each element 36 is subjected. Thirty dry reed relays SI to S30 which correspond to the respective thirty magnetoresistive elements 36 are connected with the corresponding magnetoresistive elements 36 in series across the respective input terminals 50 and 51. A multiplex means, namely, a multiplexer 55 under the control of the microcontroller 47 sequentially operates the relays SI to S30 for sequentially connecting the magnetoresistive elements 36 across the input terminals 50 and 51 of the Wheatstone bridge circuit 52 so that the microcontroller 47 can sequentially read the signals from the magnetoresistive elements 36 resulting from the magnetic field to which each magnetoresistive element 36 is subjected and write the signals in digitised form into the random access memory 48. The multiplexer 55 is described in more detail below.

The Wheatstone bridge circuit 52 comprises a pair of resistors Rl and R2. The resistor Rl is connected between one of the input terminals 50 and a terminal 60 and the resistor R2 is connected between the terminal 60 and an output terminal 61, the input terminals 50 form the other output terminal of the Wheatstone bridge circuit 52. A temperature compensating means for compensating for variation in the temperature of the magnetoresistive elements 36 comprises an additional magnetoresistive element R3 which is identical to the magnetoresistive elements 36, and which is connected into the Wheatstone bridge circuit 52 between the terminals 61 and 51. The additional magnetoresistive element R3 is located in the hollow interior region 30 of the housing 21 in the scanning face 31 so that it is adjacent the surface 5 being scanned and is subject to a substantially identical temperature to that which the magnetoresistive elements 36 are subjected. Thus, any change in the resistance of the magnetoresistive elements 36 due to temperature variation is compensated for by the additional magnetoresistive element R3. The values of the resistors Rl and R2 are chosen to set the output voltage levels of the Wheatstone bridge circuit 52 across the terminals 50 and 61 at a desired level. A power supply circuit 63 applies a power supply voltage across the terminals 60 and 51 of the Wheatstone bridge circuit 52. The output voltage from the Wheatstone bridge circuit 52 across the terminals 50 and 61 is delivered through an amplifier 64 to an analog input of the microcontroller 47 which in turn writes the signals in digital form into the random access memory 48.

In this embodiment of the invention the microcontroller 47 activates the multiplexer 55 at predetermined intervals which are a function of the distance moved by the scanning unit 20. The microcontroller 47 reads the output from the interface IC circuit 45 of the rotary encoder 40 and each time the rotary encoder 40 records the scanning unit 20 as having moved through a predetermined distance, which in this embodiment of the invention is 0.5 mm the multiplexer 55 is activated for sequentially switching in the microresistive elements 36 across the input terminals 50 and 51.

The multiplexer 55 comprises a decode logic circuit 67 and thirty relay drivers 68 for driving the respective relay switches SI to S30, only one relay driver 68 is illustrated in Fig. 3. The sequence in which the relay switches SI to S30 are to be switched for respectively and sequentially connecting the magnetoresistive elements 36 into the Wheatstone bridge circuit 52 is determined by the microcontroller 47 which outputs codes, one for each relay switch SI to S30 which are identified by the decode logic circuit 67 which in turn operates the appropriate relay driver 68 for operating the corresponding relay switch SI to S30 according to the code received from the microcontroller 47.

The hand-held mini-computer 25 comprises a housing 70 within which appropriate micro-computer hardware (not shown) is housed. A keypad 71 for inputting data and commands into the mini¬ computer 25 is provided on the housing 70. A display 72 for displaying data is also provided on the housing 70. On the scanning unit 20 having completed a scan across the string 3 of characters 4 data stored in the random access memory 48 relating to the string 3 of characters 4 is downloaded from the random access memory 48 under the control of the microcontroller 47 on a command being inputted into the mini-computer 25 through the keypad 71. Imaging and character recognition software which will be well known to those skilled in the art and which does not form part of the invention is provided in the mini-computer 25 for identifying the characters 4 of the character string 3 from the stored signals downloaded from the random access memory 48. The character string 3 is thus displayed on the display 72. The mini-computer 25 has a memory (not shown) with sufficient capacity to store many character strings 3. Information, for example, the location of each gas cylinder 6 may be inputted against the corresponding character string 3 indicating the location and/or destination of the gas cylinder 6 through the keypad 71, and this is stored in the memory (not shown) in the mini-computer 25. An interface 74 is provided in the mini¬ computer 25 for interfacing with an integrated circuit card 75 to facilitate downloading of stored data in the mini-computer 25 for transfer to a personal computer or a main frame computer for subsequent storing or processing. Additionally, the hardware and software in the mini-computer 25 have provision for enabling one or more missing characters of the character string 3 to be inputted manually through the keypad 71 and subsequently stored in the mini-computer 25 and displayed on the display 72.

Further, provision is made in the mini-computer 25 for enabling one or more of the characters 4 of the string 3 which have been incorrectly identified by the scanning unit 20 to be corrected by inputting the correct character or characters through the keypad 71. In use, the scanning unit 20 is placed on the surface 5 of the gas cylinder 6 with the wheel 41 of the rotary encoder 40 engaging on the surface 5. The scanning unit 20 is placed to the left hand side 9 of the character string 3 and spaced apart from the first of the characters 4, and the scanning unit 20 is oriented so that the scanning unit can be passed along the character string 3 from the left hand side 9 to the right hand side 10 with the longitudinal array 35 of the magnetoresistive sensors 34 extending transversely of the character string 3. Since the direction of motion of the scanning unit 20 will be along the length of the character string 3, namely, parallel to the character string 3, and since the direction of motion of the scanning unit 20 is always transverse of the longitudinal array 35 of the magnetoresistive sensors 34, the array 35 of magnetoresistive sensors 34 extends transversely of the character string 3. The wheel 41 of the rotary encoder 40 extends from the scanning face 17 so that as the scanning unit 20 is being moved over the character string 3 the scanning face 17 and in turn the magnetoresistive sensors 34 and the additional magnetoresistive sensor R3 are just spaced apart from the surface 5 of the cylinder 6.

On the microcontroller 47 detecting a signal from the rotary encoder 41 indicating that movement of the scanning unit 20 has commenced, the microcontroller activates the multiplexer 55 for sequentially operating the relay switches SI to S30 for sequentially switching the microresistive elements 36 across the input terminals 50 and 51 of the Wheatstone bridge circuit 52 for delivery to the amplifier 64. The microcontroller 47 digitises and reads the signals from the respective magnetoresistive elements 36 and writes the signals to the random access memory 48 and also writes the distance travelled by the scanning unit 20 as being zero against the signals read from the microresistive elements 36. The microcontroller 47 continues to scan the interface IC circuit 45. Each time the microcontroller 47 determines from the signals read from the rotary encoder 40 that the scanning unit 20 has travelled an incremental distance corresponding to the predetermined distance of 0.5 mm, the microcontroller 47 reads the output signal from the interface IC circuit 45 and writes this signal which corresponds to the distance travelled by the scanning unit 20 to the random access memory 48. The microcontroller 47 simultaneously activates the multiplexer 55 for sequentially activating the relay switches SI to S30 for, in turn, sequentially switching the magnetoresistive elements 36 across the input terminals 50 and 51 of the Wheatstone bridge circuit 52. The output voltage signals on the terminals 50 and 61 corresponding to the input voltages on the input terminals 50 and 51 as the magnetoresistive elements 36 are being sequentially switched across the terminals 50 and 51 are amplified and in turn sequentially read by the microcontroller 47, digitised and are written to the random access memory 48 and cross referenced with the corresponding distance signal already written by the microcontroller 47. On the scanning unit having scanned the entire character string 3 and has reached the right hand side 10 of the character string 3, an appropriate command is entered through the keypad 71 for downloading the stored signals in the random access memory 48 relating to the character string 3 into the mini-computer 25 through the cable 27. The location and other relevant data relating to the gas cylinder 6 is inputed through the keypad 71 and stored and cross referenced with the data relating to the character string 3 in the mini-computer 25. The character recognition software (not illustrated or described) operates on the stored signals of the character string 3 and converts the stored signals into the corresponding character, namely, letters and numbers which are displayed on the display 72. An operator compares the displayed characters with the actual characters on the gas cylinder 6 to ensure that the displayed characters are correct. If any of the displayed characters is incorrect or is absent due to the inability of the scanning unit 20 to pick up sufficient signals for the character recognition software to identify the character, the operator using the keypad 71 can correct the incorrect character or enter the missing character or characters. The corrected string of characters displayed on the display 72 is then stored by the mini-computer 25 on the integrated circuit card 75 together with the other related data relevant to the gas cylinder, for example, its location, destination and the like. The apparatus 1 is then ready to scan the next cylinder. After each cylinder has been scanned the character strings 3 and the location of the cylinder and other relevant data is inputted and stored on the integrated circuit card 75 as already described.

At the end of each day, or at any other convenient and appropriate time the integrated circuit card 75 may be removed from the mini-computer 25 for transferring the data into a personal computer or a main framework computer.

Referring to Fig. 7 the detector head 23 of the scanning unit 20 is illustrated in position over the first character 4 of the character string 3, namely, the letter "T". The array 35 of magnetoresistive sensors 34 are aligned along the line A-A of the top cross bar 16 of the first character 4. Magnetic flux lines extending between the permanent magnet 33 and the surface 5 of the gas cylinder 6 are illustrated by broken lines 76. The magnetic flux lines are only illustrated adjacent the groove 11 forming the top cross bar 16 of the first character 4 and the distortion of the magnetic flux lines caused by the groove 11 can clearly be seen. Fig. 8 illustrates graphically by the curve H the varying strength in the magnetic field across the groove 11, which is detected by seven of the magnetoresistive elements 34. The magnetic field strength of the magnetic field is at a minimum adjacent the centre of the groove 11. The strength of the magnetic field adjacent the edges 15 of the groove 11 is highest due to bunching of the lines of magnetic flux. The varying strengths of the magnetic field across the groove 11 along the line A-A are determined by the respective resistances of magnetoresistive sensors 34, and from the signals received from the magnetoresistive sensors 34, the profile H of the groove 11 can be constructed. It is from the series of these profiles which are stored in the random access memory 48 against the respective distances at which the profiles were recorded, that the character recognition software determines the shape of the characters, and in turn, recognises and identifies the characters.

While the means for switching the magnetoresistive elements 36 across the input terminals 50 and 51 of the Wheatstone bridge circuit 52 have been described as being dried reed relay switches, any other suitable switch means may be provided, and it is envisaged that in practise high speed MOSFETS may be used. Dry reed relays SI to S30 are used because of their relatively low and stable "on" resistance which is in general less than or equal to 0.1 Ohms, and also, because of their relatively negligible resistance temperature co-efficient and their relatively high switching speeds.

Additionally, while the magnetic sensors have been described as being elongated film type magnetoresistive sensors, other suitable magnetic sensors may be used. In general, it is preferable that the magnetic sensors should be sensitive and of relatively small size to facilitate accurate detection of the profile of the magnetic field across the bars of the respective characters. Thin film type magnetic sensors are, in general, of sufficiently small size. It is also envisaged that semi¬ conductor type magnetic sensors may be used, for example, magnetodiode and magnetotransistor magnetic sensors. Hall effect sensors may also be used.

It is envisaged that the magnetic field generating means may be provided by any other suitable magnetic field generating means other than a permanent magnet. It is also envisaged that other suitable distance monitoring means besides a rotary encoder may be used. In certain cases, it is envisaged that the distance monitoring may be provided in software, or in other hardware form.

While the apparatus according to the invention has been described for detecting and recording a character string on a surface of a gas cylinder, it will be readily apparent to those skilled in the art that the apparatus may be used for scanning any character string on any other article, component or object, provided the character string is formed on a surface of ferro-magnetic material. Additionally, it will be appreciated that it is not necessary that the character string be engraved into the surface, the character string may be embossed on the surface. However, it is important that the character string should be formed on the surface in such a way that the characters of the character string cause deformation of the magnetic flux lines between the magnetic field generating means and the surface, which can in turn be detected by the magnetoresistive sensors.

Claims

1. Apparatus for detecting and recording a string (3) of alpha¬ numeric characters (4) formed on a surface (5) of a component (6) of ferro-magnetic material, characterised in that the apparatus (1) comprises a detector head (23) for moving over the surface (5) for scanning thereof, a distance monitoring means (40) for detecting the distance moved by the head (23), a magnetic field generating means (33) located in the head (23) for generating a magnetic field between the magnetic field generating means (9) and the surface (5), a plurality of magnetic sensors (34,36) forming an elongated array (35) located in the head (23) for detecting the magnetic field strength adjacent the surface (5) for detecting the characters (4) as the detector head (23) is moved over the string (3) of characters (4), and a storing means (48) for storing signals received from the magnetic sensors (34,36) in respect of each character (4) and the distance monitoring means (40), and a control means (44) for controlling the writing of signals from the magnetic sensors (34,36) and the distance monitoring means (40) to the storing means (48) for enabling recognition of each character (4) by a character recognition means (25).

2. Apparatus as claimed in Claim 1 characterised in that the head (23) defines a scanning face (31) which, in use, is adjacent the surface (5) being scanned, the magnetic sensors (34,36) being located in the head (23) adjacent the scanning face (31) intermediate the magnetic field generating means (33) and the scanning face (31) .

3. Apparatus as claimed in Claim 1 or 2 characterised in that each magnetic sensor (34,36) is a thin film type magnetic sensor (36).

4. Apparatus as claimed in any preceding claim characterised in that each magnetic sensor (34,36) is a magnetoresistive sensor (34,36).

5. Apparatus as claimed in any preceding claim characterised in that the magnetic sensors (34,36) are elongated sensors (34,36) and are arranged end to end and spaced apart from each other, and are aligned longitudinally to form the elongated array (35).

6. Apparatus as claimed in Claim 5 characterised in that the length (1) of each magnetic sensor (34,36) is not greater than the minimum dimension (d) of the characters (4) to be detected at the surface (5) of the component (6) .

7. Apparatus as claimed in Claim 6 characterised in that the length (1) of each magnetic sensor (34,36) is not greater than half the minimum dimension (d) of the characters (4) to be detected at the surface (5) of the component (6) .

8. Apparatus as claimed in Claim 7 characterised in that the length (1) of each magnetic sensor (34,36) is not greater than one third of the minimum dimension (d) of the characters (4) to be detected at the surface (5) of the component (6) .

9. Apparatus as claimed in Claim 8 characterised in that the length (1) of each magnetic sensor (34,36) is not greater than one fifth of the minimum dimension (d) of the characters (4) to be detected at the surface (5) of the component (6) .

10. Apparatus as claimed in any preceding claim characterised in that the magnetic field generating means (33) comprises a permanent magnet (33) .

11. Apparatus as claimed in any preceding claim characterised in that the distance monitoring means (40) monitors the distance moved by the head over the surface in a direction transversely of the elongated array (35) of magnetic sensors (34,36).

12. Apparatus as claimed in any preceding claim characterised in that the distance monitoring means (40) comprises a rotary encoder (40,41) mounted in the head (23).

13. Apparatus as claimed in Claim 12 characterised in that the rotary encoder (40,41) comprises a wheel (41) for engaging the surface (5) of the component (6) with rolling engagement.

14. Apparatus as claimed in any preceding claim characterised in that the control means (44) comprises a multiplex means (55) for sequentially writing signals from the magnetic sensors (34,36) to the storing means (48) at predetermined intervals in response to the distance monitoring means (40) detecting the head (23) having moved respective predetermined distances.

15. Apparatus as claimed in Claim 14 characterised in that the control means (44) comprises a microcontroller (47) for writing the signals from the magnetic sensors (34,36) to the storing means (48), and an analog to digital converter for converting analog signals from the magnetic sensors (34,36) to digital signals for delivery to the microcontroller (47).

16. Apparatus as claimed in any preceding claim characterised in that an amplifying means (64) is provided for amplifying analog signals from the magnetic sensors (34,36).

17. Apparatus as claimed in any preceding claim characterised in that a compensating means (R3) is provided for temperature compensating for compensating for changes of temperature of the magnetic sensors (34,36).

18. Apparatus as claimed in Claim 17 characterised in that the temperature compensating means (R3) comprises an additional magnetic sensor (R3) connected into a circuit containing the magnetic sensors (34,36), the additional magnetic sensor (R3) being connected into the said circuit by a Wheatstone bridge circuit (52).

19. Apparatus as claimed in any preceding claim characterised in that the apparatus (1) is for detecting alpha-numeric characters (4) engraved into the surface (5) of the component (6).

20. Apparatus as claimed in any preceding claim characterised in that the apparatus (1) is for detecting a string (3) of alpha¬ numeric characters (4) formed on the surface (5) of a cylinder (6) of the type suitable for containing a gas in compressed or liquified form.

21. A method for detecting and recording a string (3) of alpha- numeric characters (4) formed on a surface (5) of a component (6) of ferro-magnetic material using the apparatus (1) according to any preceding claim, the method comprising the steps of scanning the surface (5) of the component (6) by moving the head (23) over an area of the surface (5) containing the string (3) of alpha- numeric characters (4), reading and storing signals from the magnetic sensors (34,36) at predetermined intervals, and storing details of the intervals against the respective sets of signals stored from the magnetic sensors (34,36).

22. A method as claimed in Claim 21 characterised in that each predetermined interval corresponds to the head (23) having moved over the surface through a predetermined distance.

23. A method as claimed in Claim 21 or 22 characterised in that the signals from the magnetic sensors (34,36) are sequentially read at the end of each predetermined interval.

24. Apparatus as claimed in any of Claims 21 to 23 characterised in that the signals from the magnetic sensors (34,36) are converted from analog to digital form.

25. Apparatus as claimed in any of Claims 21 to 24 characterised in that the signals from the magnetic sensors (34,36) are stored in digital form.