Scanning arrangement and method

Abstract: A scanning arrangement located within a scanning device which is operative for repetitively scanning indicia having parts of different light reflectivity, for example, bar code symbols, and more particularly, pertains to a novel scanning motor of the arrangement for enabling a scan element which is supported by a holder structure mounted on a mylar motor to implement angular oscillatory movements in a linear scan direction between a pair of scan end positions. Hereby, pursuant to the structure of the scanning device, the scanning arrangement is preferably mounted on a single printed circuit board located within a lightweight scanning device of a hand-held housing of gun-shaped configuration which may be readily held and manipulated by a user of the scanning device. The structure of the scanning motor and of the scanning arrangement which are mounted on a printed circuit board is considerably simplified through the construction of the various components being essentially of molded plastic material, and through the utilization of a mylar leaf spring which limits the end scan positions of a scan element or mirror which is oscillated by a read-start device including a permanent magnet mounted on an arm of the holder for the scan mirror.

Description: Generally, the present invention relates to a scanning arrangement located within a scanning device which is operative (for example) for repetitively scanning indicia having parts of different light reflectivity such as bar code symbols. The utilization of laser scanning devices for the scanning and reading of information provided on a target; such as a package or sale item, is well known in this particular technology and has found wide acceptance in commerce. In this connection, various types of laser scanning devices incorporate scanning heads which house optical reading systems, such as bar code readers, for the reading of information or bar code symbols on targets which are scanned by a laser beam projected from the bar code reader. In general, such laser scanning devices; especially those in the type of bar code readers, are widely employed in industry, such as manufacturing, shipping, and in retail commerce and; for example, may be permanently incorporated in the structures of check-out counters of supermarkets, whereby the items of merchandise having the bar code symbols imprinted thereon or applied thereto are passed over a fixed bar code reader located beneath the counter surface so as to provide a record for the merchant of the merchandise being purchased by a consumer, and concurrently a readout (and possibly a printed record) for the consumer. Alternatively, the bar code reader or laser scanning device may also be constituted of an optical scanner unit which is fixedly mounted on a stand extending above a support platform or countertop on which the merchandise may be arranged; or in many instances of utilization, pursuant to a preferred embodiment of the invention, may be in the form of a miniature, lightweight and gun-shaped device having a pistol grip, and which the activated device is normally passed over the bar code symbol which is imprinted on a sale item or target at some short distance therefrom so as to enable scanning of the information provided by the bar code symbols. Discussion of the Prior Art Various optical readers and optical scanning systems have been developed heretofore for reading bar code symbols appearing on a label or on the surface of an article. The bar code symbol itself is a coded pattern of indicia comprises of a series of bars of various widths spaced apart from one another to bound spaces of various widths, the bars and spaces having different light-reflecting characteristics. The readers and scanning systems electro-optically transform the graphic indicia into electrical signals, which are decoded into alphanumerical characters that are intended to be descriptive of the article or some characteristic thereof. Such characters are typically represented in digital form and utilized as an input to a data processing system for applications, in point-of-sale processing, inventory control, and the like. Scanning systems of this general type have been disclosed, for example, in U. S. Patent Nos. 4,251,798; 4,369,361; 4,387,297; 4,409,470; 4,760,248; and 4,896,026, all of which have been assigned to the same assignee as the instant application. Among the foregoing, and in addition thereto, of particularly advantageous construction is a scan board module for laser scanners as illustrated and claimed in U. S. Patent No. 5,015,833, which has also been assigned to the same assignee as the instant application. In this connection, U. S. Patent 5,015,833 discloses a scan board module contained in a generally lightweight hand-held gun-shaped housing which includes a printed circuit board on which optical and scanning components are mounted in an optically-aligned operative relationship. The printed circuit board is mounted in a manner within the housing, and the operative scanner components thereon are fastened thereto such that they are protected from damage caused by impacts or shocks sustained during rough handling or possible dropping of the scanning device. Moreover, the modular mounting of the various operative components on a single printed circuit board as disclosed and shown in this patent, as well as that elucidated particularly with regard to the embodiment of Fig. 2 of the co-pending U. S. Patent 5 168 149 (Appln. 520,464) of which the present application is a continuation-in-part, allows for a simple and highly efficient construction and functioning of the scanning arrangement. As disclosed in some of the above patents, one embodiment of such a scanning system resides, inter alia, in a hand-held, portable laser scanning head supported by a user, which is configured to allow the user to aim the head, and more particularly, the light beam or laser beam projected therefrom, at a target and a symbol which is to be read. The light source in a laser scanner is typically a gas laser or semiconductor laser. The use of semiconductor devices, such as a laser diode, as the light source in scanning systems is especially desirable because of their small size, low cost and low power requirements. The laser beam is optically modified, typically by a lens, to form a beam spot of a certain size at the target distance. It is preferred that the beam spot size at the target distance be approximately the same as the minimum width between regions of different light reflectivity, i.e., the bars and spaces of the symbol. Bar code symbols are formed from bars or elements that are typically rectangular in shape with a variety of possible widths. The specific arrangement of elements defines the character represented according to a set of rules and definitions specified by the code or "symbology" used. The relative size of the bars and spaces is determined by the type of coding used, as is the actual size of the bars and spaces. The number of characters per inch represented by the bar code symbol is referred to as the density of the symbol. To encode a desired sequence of characters, a collection of element arrangements are concatenated together to form the complete bar code symbol, with each character of the message being represented by its own corresponding group of elements. In some symbologies a unique "start" and "stop" character is used to indicate where the bar code begins and ends. A number of different bar code symbologies exist. These symbologies include UPC/EAN, Code 39, Code 128, Codabar, and Interleaved 2 of 5. For purpose of discussion, characters recognized and defined by a symbology shall be referred to as legitimate characters, while characters not recognized and defined by that symbology are referred to as illegitimate characters. Thus, an arrangement of elements not decodable by a given symbology corresponds to an illegitimate character(s) for that symbology. In order to increase the amount of data that can be represented or stored on a given amount of surface area, several new bar code symbologies have recently been developed. One of these new code standards, Code 49, introduces a "two-dimensional" concept by stacking rows of characters vertically instead of extending the bars horizontally. That is, there are several rows of bar and space patterns, instead of only one row. The structure of Code 49 is described in U. S. Patent No. 4,794,239. A one-dimensional single-line scan, as ordinarily provided by hand-held readers, has disadvantages in reading these two dimensional bar codes; that is, the reader must be aimed at each row, individually. Likewise, the omnidirectional scan-line readers produce a number of scan lines at an angle to one another so these are not suitable for recognizing a Code 49 type of two-dimensional symbols. Moreover, Wells U. S. Patent No. 4,902,083 discloses a low vibration resonance scanning unit for miniature optical display apparatus, in which a resonance scanning unit employs a so-called tuning fork design. A scan mirror is mounted on one arm of a tuning fork, and a counter-balancing mass is mounted on the other arm of the tuning fork. Although this provides for the oscillation of the scan mirror to generate a raster display, the structure is relatively complex in nature and necessitates a plurality of components to produce the scanning operation. In the scanning systems known in the art, the light beam is directed by a lens or similar optical components along a light path toward a target that includes a bar code symbol on the surface. The scanning functions by repetitively scanning the light beam in a line or series of lines across the symbol. The scanning component may incorporate a drive or scanning motor adopted to either sweep the beam spot across the symbol and trace a scan line across and past the symbol in a high-speed repetitive mode, or scan the field of view of the scanner, or do both. Scanning systems also normally include a sensor or photodetector which functions to detect light reflected from the symbol. The photodetector is therefore positioned in the scanner or in an optical path in which it has a field of view which extends across and slightly past the symbol. A portion of the reflected light which is reflected off the symbol is detected and converted into an electrical signal, and electronic circuitry or software decodes the electrical signal into a digital representation of the data represented by the symbol that has been scanned. For example, the analog electrical signal from the photodetector may typically be converted into a pulse width modulated digital signal, with the widths corresponding to the physical widths of the bars and spaces. Such a signal is then decoded according to the specific symbology into a binary representation of the data encoded in the symbol, and to the alphanumeric characters so represented. The decoding process in known scanning systems usually work in the following way. The decoder receives the pulse width modulated digital signal from the scanner, and an algorithm implemented in software attempts to decode the scan. If the start and stop characters and the characters between them in the scan were decoded successfully and completely, the decoding process terminates and an indicator of a successful read (such as a green light and/or an audible beep) is provided to the user. Otherwise, the decoder receives the next scan, performs another decode attempt on that scan, and so on, until a completely decoded scan is achieved or no more scans are available. Laser scanners are not the only type of optical instrument capable of reading bar code symbols. Another type of bar code reader is one which incorporates detectors based upon charge coupled device (CCD) technology. In such readers, the size of the detector is larger than or substantially the same as the symbol which is to be read. The entire symbol is flooded with light from the reader, and each CCD cell is sequentially read out to determine the presence of a bar or a space. Such readers are lightweight and easy to use, but require substantially direct contact or placement of the reader on the symbol to enable the symbol to properly read. Such physical contact of the reader with the symbol is a preferred mode of operation for some applications, or as a matter of personal preference by the user. The closest prior art to the present invention is represented by EP-A-425844. A similar device is shown in EP-A-456095. The device shown in EP-A-425844 incorporates those features set out in the introductory portion of Claim 1. Although such devices do have distinct advantages over other state-of-the-art scanners, the arrangement shown could still perhaps be improved both in the protection of the system from accidental damage (for example if the scanner is dropped) and in the ease of adjustment and maintenance. It is an object of the present invention to improve the robustness of such prior art scanners, and to make them even easier and more convenient to maintain. According to the present invention an optical scanner is characterised by those features set out in the characterising portion of Claim 1. With the introduction of an intermediate support means for mounting the sean mirror, said means having separate arms to which the ends of the leaf spring are attached, the applicants have found that the leaf spring can be better protected against accidental shocks. It also provides for more modularity, in that the entire unit, including the attachments for holding the ends of the leaf spring, can be removed and if necessary replaced. Preferably, the intermediate mounting means comprises a bracket having first and second arms, all of which are unitary and manufactured from a moulded plastics material. This provides an inexpensive yet efficiently constructed device, which is easily assembled onto a printed circuit board. It is highly shock and damage resistant, while being readily exchangeable with similar components during servicing of the scanning device. The leaf spring is preferably Mylar. The reason Mylar is preferred instead of metal spring material is that its very low modulus of elasticity permits relatively low resonant frequencies without the strip getting impractically thin. It is also more difficult to accidentally damage Mylar than thin metal springs during assembly. Mylar can be deformed more than metal during drop or shock without being permanently deformed. The arms are preferably resiliantly flexible, which provides additional cushioning and support for the Mylar spring. Preferably, the device is electrically activated by an electromagnetic coil which is adapted to alternately attract and repel a permanent magnet, mounted to the oscillating means, so as to impart oscillatory motion to the post and hence to the optical element (for example a scan mirror). The force applied by the electromagnetic coil is counterbalanced by the milar spring, which provides a restoring force. As a consequence, the scan mirror moves between predetermined positions while tending to return normally, in the absence of any electromagnetic force, to a central position intermediate the two end positions. The arrangement is preferably operated at its own natural frequency. This frequency is determined by the stiffness of the spring and the inertia of the moving parts. A drive circuit may be provides that symchronises itself to this natural frequency. The circuitry may also control the scan angle by monitoring the voltage generated in a secondary winding in the drive coil. Drive current may be adjusted automatically to maintain a preset scan angle. Stops may be provided to limit the range of travel of the oscillating member. Preferably, a scan element is supported by a holder structure mounted on the motor to implement angular oscillatory movements in a single scan direction between a pair of scan end positions. The scaning arrangement is preferably mounted on a single printed circuit board located within a small, lightweight scanning device, which is to be implemented either as a fixed mount scanner or in a hand-held configuration which may be readily held and manipulated by a user of the scanning device. The invention may be carried into practice in a number of ways and one specific embodiment will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 illustrates a front view of a scanning device in the form of a hand-held, gun-shaped laser scanning head constructed pursuant to the invention; Figure 2 illustrates a front perspective view of the scanning device of Fig. 1 during operation thereof, schematically connected to other components of a laser scanning system; Figure 3 illustrates a sectional view taken along line 3 - 3 in Fig. 1; Figure 4 illustrates, on an enlarged scale, a sectional view through a portion of a printed circuit board having the scanning arrangement with a scanning motor constructed pursuant to the invention mounted thereon, taken along line 4 - 4 in Fig. 3; Figure 5 illustrates a sectional view taken along line 5 - 5 in Fig. 4; Figure 6 illustrates a top plan view of the support member for mounting the scan mirror and the scanning motor components including a Mylar leaf spring; Figure 7 illustrates an elevational end view of the support structure of Fig. 6; Figure 8 illustrates a plan view of a trunnion for mounting the support structure of Fig. 7 on a printed circuit board; Figure 9 illustrates an end view of the trunnion of Fig. 8; Figure 10 illustrates an elevational view of a post and bracket structure for attaching the scan mirror and portion of the scanning motor to the support bracket; Figure 10a illustrates a cross-sectional view through the post of Fig. 10; Figure 11 illustrates an elevational side view of the arm and bracket for attaching the magnet component of the scanning motor to the attaching post for the scan mirror; Figure 12 illustrates a top plan view of the scan motor attachment shown in Fig. 11; Figure 13 illustrates a top plan view of the post and bracket arrangement for mounting the scan mirror fastening the scanning motor; and Figure 14 illustrates a front view of the mylar leaf spring. DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Referring now more specifically to the drawings, and particularly Figs. 1 to 3, the invention relates to a laser scanning device of which is readily adapted for reading, scanning and/or analyzing symbols, for example, bar code symbols or any of the symbols as detailed hereinbefore. Turning now to Fig. 1, there is illustrated one embodiment of the present invention in the form of a generally hand-held reading head 10 that includes a generally gun-shaped housing having a handle portion 12 of generally rectangular cross-section and generally elongated along a handle axis, and a generally horizontally-elongated barrel or body portion 11. The cross-sectional dimension and overall size of the handle portion 12 is cut that the head 10 conveniently can fit and be held in a user's hand. The body and handle portions are constituted of a lightweight, resilient, shock-resistant, self-supporting material, such as a synthetic plastic material. The plastic housing preferably is injection-molded, but can be vacuum-formed or blow-molded to form a thin, hollow shell which bounds an interior space whose volume measures less than a value on the order of 50 cubic inches and, in some applications, the volume is on the order of 25 cubic inches or less. Such specific values are not intended to be self-limiting, but to provide a general approximation of the overall maximum size and volume of the head 10. The shell is formed of two housing parts 12a, 12b meeting along a generally vertical joining line 12c. As considered in an intended position of use as shown in Fig. 2, the body portion 11 has a front prow region or nose having an inclined front wall 11a. The body portion 11 also has a rear region or stern having a rear wall 11b spaced rearwardly of the inclined front wall 11a. The body portion 11 also has a top wall 11c, and a pair of opposed side walls 11e, 11f between the top and bottom walls. The front wall 11a is sloped relative to the top and bottom walls. A manually-actuatable, and preferably depressible, trigger 13 is mounted for movement relative to the head in a forwardly-facing region where the handle and body portions meet and where the user's forefinger normally lies when the user grips the handle portion in the intended position of use. A window 14 is stationarily mounted at the nose and is light-transmissive to allow laser light to pass from the interior to the exterior of the head, and vice versa. A flexible, non-bulky, coil-type electrical cable 15 with multiple freedoms of movement interconnects the head 10 to the remainder of the components of the laser scanning system, such as a decode module and host device, as is known in the art. A plurality of components are mounted in the head and, as explained below, at least some of them are actuated by the trigger 13, either directly or indirectly, by means of a control microprocessor. One of the head components may be an actuatable laser light course (see Fig. 3). e.g. such as a semiconductor laser diode, operative, when actuated by the trigger 13, for propagating and generating an incident laser beam whose light, as explained above, is at least marginally visible to the human eye. The emitted laser diode beam is highly divergent; diverges differently in different planes parallel and perpendicular to the longitudinal direction of beam propagation; is non-radially symmetrical, i.e. anamorphic; and has a beam cross-section resembling an oval. The diode may be of the continuous wave or pulse type. The diode requires a low voltage (e.g. 12 v DC or less) supplied by a power regulator and a battery (DC) source which may be provided within the head, or by a rechargeable battery pack accessory detachably mounted on the head, or by a power conductor in the cable 15 connected to the head from an external power supply (e.g. DC source). Diodes which emit laser light or different wavelengths are also within the scope of this invention. Although the embodiment illustrated in Figures 1 and 2 is a hand-held one, the present invention may also be implemented in a fixed mount, tabletop, or other configurations. Having reference to the cross-sectional view shown in Fig. 3, an optical assembly 30 is mounted in the device on a thin-flexible printed circuit board 20, and is adjustably positioned relative to the board for optically modifying and directing the emitted light or laser beam along a specified optical path towards a reference plane which is located exteriorly of the device. A symbol to be read may be arranged in the vicinity of the reference plane, at the reference plane, or towards one side or at an opposite side thereof, in essence, anywhere within the depth of field of the applicably modified laser beam and within a range of working distances as measured relative to the laser device. Hereby, the light or laser beam reflects off the symbol as a specular component in one direction and as a scattered component in many directions, and that portion of the scattered laser light which travels along a second optical path away from the symbol back towards the scanning device is referred to as the returning light portion and is employed for providing the information relative to that provided on the symbol. As shown in Fig. 3, the optical assembly 30 may be similar to or identical with that disclosed in U. S. Patent 5,015,833, which is commonly assigned to the assignee of the present application and is incorporated herein by reference. Consequently, with the exception of relatively general comments, it is not considered to be necessary to repeat all of the information and details concerning the optical assembly. However, as is well known in this technology, the optical assembly may be constituted of a focusing lens, probably in the configuration of a plano-convex lens, and cooperating with an aperture for focusing the emitted laser or light beam at a reference plane. Suitable springs for adjusting the lens and other components may be incorporated in the optical assembly, including a light generating source, such as a laser diode for producing the required light to be projected against a scanning arrangement 36, pursuant to the present invention described in detail hereinbelow. Referring now more specifically to the assembled components of the scanning arrangement as shown in Figs. 4 and 5 of the drawings, the arrangement 36 includes an upstanding support member 40, as shown in Figs. 6 and 7, having a central portion in the shape of an elongate bracket 42 with extending generally L-shaped bent arms 44, 46 projecting from its opposite ends, each of the arm subtending an acute angle α . The elongate generally rectangular bracket 42 is mounted on the printed circuit board 20 through the intermediary of suitable fasteners (not shown) extending through holes 47 formed in the ends of the bracket and engaging into threaded bores 58 of a trunnion 60 and includes an apertured central portion 48 for the swivable support of a post 50, as illustrated in Fig. 10, having a lower end extending through the board 20, as shown in Figs. 8 and 9, positioned to extend across the lower surface of the printed circuit board 20. The post 50 includes a bracket member 52 to which there is fastened a suitable scan element 54, such as a flat scan mirror through fastener elements extending so as to be oscillatable about an axis y extending coaxially through the post. Fastened to the post 50 is a projecting arm member 70 having a magnet 72 mounted on the outer distal end 74 of the arm member, which magnet is adapted to be electrically alternatingly attracted to or repelled from the interior of an electrically energized and electromagnetic coil structure 76 mounted on the printed circuit board 20 by being movable into and out of an aperture in the coil, thereby resultingly oscillating the arm member 70 and post 50 and imparting a reciprocating oscillatory movement to the scan mirror 54. In order to properly position the scan mirror 54, and to essentially restore or bias the scan mirror towards its centered position, the distal ends 44, 46 of each of the bent arm members 42 of the structure bracket 42 are provided with clamping components, such as in the shape of in cross-section hemispherical cylindrical extensions 60, 62 having projecting dowels 64 cooperating with complementary clamping members 66, 68 adapted to be fastened thereon. Extending through a notch portion 80 formed in the post 50, and also in engagement with the arm supporting the magnet, is a flat leaf spring 80 constituted from a sheet of Mylar, as shown in Fig. 14 of the drawings, whereby the central portion of the mylar leaf spring 80 has holes 82 therein adapted to be engaged by fasteners or dowels extending from the arm mounting the magnet so as to clamp the spring to the rotatable post 50 supporting the scan mirror 54, while the opposite ends 84, 86 of the Mylar spring each include holes 88, 90 adapted to engage over the dowels 64 extending between the respective hemispherically cross-sectional clamping elements 60, 66; 62, 68 at the outer ends of the arms 42 so as to be fixedly engaged therebetween. Hereby, the spring is bent into two arm segments, for example, at a right angle or 90° to each other extending from the attachment to the post 50 towards each end 84, 86, while positioned by the flexible arm members 42. This will provide a resilient biasing restoring action on the scan mirror 54 opposite the oscillatory movement imparted to the scan mirror by the energizing effect imposed on the magnet, thereby reciprocating the mirror between its end positions. In effect, during the operation of the scanning arrangement, each time an energizing pulse is applied to the coil, the magnet is drawn into the central opening or aperture into the coil, thereby pulling all of the oscillatable components therewith, and concurrently bending the leaf spring. As illustrated in Fig. 4 of the drawings, each of the arms of the leaf spring is generally planar, while upon being displaced responsive to the oscillation of the magnet, each arm of the leaf spring is bent so as to store energy therein. Upon being bent, the leaf spring then releases its stored energy, thereby displacing the magnet and the scan mirror back into and past its centered normal at rest position, with the entire assembly oscillating in a damp manner. This particular structure thus ensures a controlled oscillation of the scan mirror between the two end positions thereof so as to afford a uniform scan operation for reading information on a target object. With the exception of the construction of the leaf spring 80 being constituted from Mylar, the remaining components of the scanning arrangement 36 as set forth hereinabove, with the exception of the scan mirror, may consist of a molded plastic material; for example, such as lexan or the like, and in the simplicity of construction by modularly mounting the entire scanning arrangement on the printed circuit board 20 effectively protects the arrangement against externally produced shocks and impacts encountered during any possible dropping or rough handling of the scanning device while concurrently rendering the construction thereof inexpensive in nature and easily and quickly capable of being serviced.

Claims: An optical scanner comprising a base member (20), an oscillating member (50) mounted for oscillatory motion about an axis, an optical element (54) fixedly secured to the oscillating member (50), and a leaf spring (80) having its ends secured to respective first and second spring holding means (62,64,66,68), a portion of the spring between the said ends being secured to the oscillating member (50), and means (72,76) for providing a cyclical force to the oscillating member (50) whereby the oscillating member and hence the optical element (54) undergoes oscillatory motion about the axis, with the leaf spring (80) providing a restoring biassing force as the oscillating member moves away from a central, neutral position; characterised by intermediate mounting means (40) secured to the base member (20), the intermediate mounting means (40) having a central portion (42) adjacent the oscillating member and first and second arms (44,46) extending outwardly therefrom, the first (60,64,66) and second (62,64,68) spring holding means being attached to or comprising part of the first (44) and second (46) arms, respectively. An optical scanner as claimed in Claim 1 in which the leaf spring (80) is of Mylar. An optical scanner as claimed in Claim 1 or Claim 2 in which the central portion (42) and the first and second arms (44,46) of the intermediate mounting means (40) form a unitary whole. An optical scanner as claimed in any one of Claims 1 to 3 in which the intermediate mounting means (40) is moulded of a plastics material. An optical scanner as claimed in any one of Claims 1 to 4 in which the first and second arms (44,46) are flexible. An optical scanner as claimed in any one of the preceding claims in which the distal ends of the arms (44,46) comprise clamping means (60,62,64,68) for grippingly engaging the ends of the leaf spring (80). An optical scanner as claimed in any one of the preceding claims in which the optical element is a scan mirror (54). An optical scanner as claimed in any one of the preceding claims in which the means for providing a cyclical force comprises a permanent magnet (72) mounted to one of the oscillating member (50) or the base member (20) and an electromagnet (76) mounted to the other of the oscillating member (50) or the base member (20). An optical scanner as claimed in any one of the preceding claims in which the first and second arms (44,46) are bent such that the distal ends extend towards one another. An optical scanner as claimed in any one of the preceding claims in which the base member (20) is a printed circuit board. An optical scanner as claimed in Claim 10 in which the intermediate mounting means (40) is secured in place by securing means which pass through the printed circuit board and are attached to a trunnion (60) below the board. An optical scanner as claimed in Claim 10 or Claim 11 in which the oscillating member (50) includes a post which extends through an aperture in the printed circuit board (20). An optical scanner as claimed in Claim 12 when dependent upon Claim 11 in which the post engages with the trunnion (60).

Inventors: SHEPARD HOWARD, SHEPARD, HOWARD
Applicants: SYMBOL TECHNOLOGIES INC, SYMBOL TECHNOLOGIES, INC.
Application year: 1992
Main classification: G06K7
IPC codes: G06K7