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For industrial applications, wherein for instance objects provided with bar codes which are passing on a conveyer belt must be recognized, little space is usually available for arrangement of such a scanning device. In practice recourse is made to a scanning device wherein the decoding part for receiving the laser radiation reflected by the bar code is situated outside the housing of the device transmitting the laser scan lines. This makes a separate housing for the decoding part necessary, which is laborious and expensive.
In the French patent specification 2.401.438 a scanner with a polygonal rotatable mirror is described. In this scanner the source of laser light is formed by a gas laser, which makes this device bulky and not suitable for use in an industrial environment where little space is usually available.
Nor is the scanning device described in the international patent application PCT/US86/00370 suitable for application in an industrial environment, inter alia because of its size. In this known scanner a scanning unit is mounted in a pair of scales for simultaneous weighing and scanning of objects, for instance in a supermarket .
The present invention provides a device for scanning one or more bar codes on an object in an industrial environment, comprising;
- a housing provided with a window for passage of one or more scanning radiation beams and of radiation induced by a bar code ;
- one or more plate-like components on which are arranged a radiation source, a sensor sensitive to the radiation and further electronic, optical and mechanical components ;
- a polygonal rotatable mirror for generating scan lines from the radiation beams and drive means therefor; and - placing means for placing the plate-like components and the optical, mechanical and electronic components arranged thereon in the housing in fitting manner. The present invention provides an extremely compact device in which both the laser light transmitting parts and the laser light receiving parts are incorporated in the same housing.
Because the components are preferably arranged close to the outer walls of the housing, the optical path of the laser scan lines is as large as possible, which provides a sufficient length of scan lines with relatively compact dimensions of the housing. Because the mirror surfaces of the rotatable -polygonal mirror have angles close to 45", the optical path of the laser beam is further enlarged internally, whereby the effective scan line length is also further increased. In the embodiment to be further described hereinbelow, a line length of 60 mm is obtained at the location of the window, while 1200 lines per second are generated by the scanning device, which is made possible by the high processing speed of the electronics and a high rotation speed of the polygonal mirror.
In a preferred embodiment the device according to the present invention has dimensions (1 x w x h) in the order of magnitude of 12 cm x 9 cm x 4.5 cm. Little space is hereby taken up by the device according to the present invention which, as stated above, is of importance in most industrial embodiments .
Since the line length preferably amounts to about 60 mm, the device according to the present invention can be mounted for instance close to a conveyer belt, which results in space-saving. It will be apparent that the focussing area of the scan lines can be adjusted as desired, depending on the application, whereby at a somewhat greater distance from a conveyer belt, for instance 10 mm, a greater line length, for instance 70 mm, is available for scanning an object passing on the conveyer belt .
Since preferably about 1200 lines per second are written, a conveyer belt on which objects with a bar code are placed can be driven at relatively great speed. There is in any case, due to the great number of lines, an increased chance of a bar code being read properly. In this industrial environment there is often only one possibility available for correct recognition of the bar code on a passing object. Because the lines are written at great speed, it becomes possible to apply a so-called grid whereby, in addition to the above mentioned advantages, good recognition of a bar code can still be achieved when it is positioned less precisely in relation to the device according to the present invention.
Spring-mounted feet preferably form part of the fitting means, whereby the internal unit is little subject to vibrations possibly occurring in an industrial environment.
A thermally conductive and electrically insulating mat is preferably arranged between the cover of the housing and the part of the internal unit dissipating much heat in order to draw off the heat to the (metal) housing.
Further advantages, features and details of the present invention will be elucidated on the basis of the following description of a preferred embodiment thereof with reference to the annexed drawings, in which:
Fig. 1 shows an exploded perspective view of a device according to the present invention which can be placed in a housing in the assembled state;
fig. 2 shows a view in perspective of the assembled part of fig. 1 for placing in a housing which has been disassembled; and
fig. 3 shows a schematic top view in cross section of the device of fig. 1 and 2 with several laser beams indicated therein in order to elucidate the operation thereof .
Internal unit 1 (fig. 1) for an industrial scanning device comprises a number of boards 3, 4 and 47 with printed circuitry (not shown) in addition to a plastic plate 2 on which the optical and electronic components for a scanning device according to the present invention are arranged. Arranged on board 3 is a laser light trans- mitting unit 4, for instance a laser diode, as well as a sensor or detector 5 for receiving the radiation induced or scattered by a bar code. Electronics (not shown) connected to the detector 5 are situated behind a metal screening plate 6 of board 3. Because the laser source 4 and the detector 5 are arranged on the same board, few problems occur in respect of adjustments of the various optical components, since possible slight variations in the arrangement thereof influence both the outgoing and the returning laser beam.
Fixed by means of snap connections to the board 3 is component 7 which is manufactured from injection-moulded plastic and on which a lens 9 for the detector is also arranged. Lens 9 is preferably of injection-moulded plastic and is provided with two leg parts, whereof leg part 10 is visible in figure 1, which leg parts are preferably formed integrally with the lens. The leg parts fit into openings or recesses 11, 12 of the screening plate 6 and can be snapped fixedly therein for easy and correct positioning of the lens and to facilitate the assembly. Also arranged on the plastic component 7 is a flat mirror 13 which casts the light received from a bar code via lens 9 onto the detector 5.
The components from injection-moulded plastic reduce the weight and can be manufactured in large numbers at little expense, while the snap connections reduce the labour involved in assembly.
Also arranged on board 3 is a second detector circuit 14 which receives light reflected from a preferably cylindrical mirror 15, the function of which will be described below.
The plastic component 7 is also fixed to plastic chassis part 2 onto which is arranged a rotatably driv-able polygonal mirror 20, the mirror surfaces of which extend as far as the plate-like part 2 itself and beneath which an electric drive motor 21 of small dimensions is placed. Also arranged on component 2 is a second flat mirror 22 for allowing the laser light from the laser source 4 to pass through a window via mirror unit 19 and further mirror parts 60 and 13 and polygonal mirror 20 to an object with bar code. Further fixed to component 2 is a part 8 on which is arranged the electric power supply source for power supply to the internal unit.
Because of the limited space usually available in industrial environments, the scanner according to the present invention has in the shown preferred embodiment (fig. 2) a length 1 of about 12 cm, a width w of about 9 cm and a height h of about 4.5 cm. Since with these compact dimensions the heat dissipation of the scanning device could represent a problem, components with the most dissipation, such as the laser source, the power supply source and the integrated circuits of the control are placed partly for this reason as far as possible to the outside of the boards, and the electric power supply source is situated as remotely as possible from and opposite the laser source, since for safety purposes the latter is automatically switched off at a determined temperature of for instance 50 *C.
It is further endeavoured in the scanning device according to the present invention to restrict to a minimum the amount of wiring between the various boards close to the metal walls.
In the shown and described preferred embodiment the only wiring is formed by a flat cable leading to the stator part of the electric motor.
After the internal unit shown in fig. 1 is assembled it can be placed as a whole in a lower housing part 30 (fig. 2) , for which purpose the internal unit is provided with a rod-like protrusion 31 on which the internal unit can be gripped. The lower housing part is preferably provided on two standing side walls with dovetail fastening parts 33 respectively 34 for rapid and simple mounting in this environment, such as sliding and clamping onto a frame part of a conveyor bel . The bottom of the lower housing part 30 is provided with fitting parts 35, 36 and 37, of which the fitting part 37 is open on one side, while corresponding rubber foot parts 38, 39 and 40 are arranged on the internal unit for absorbing vibrations which occur in the industrial environment. The rubber foot parts 38 and 39 are arranged on the plate 2, while foot part 40 is arranged on the component 7 placed thereon, whereby this component is likewise well supported in spring-mounted manner. Because the fitting part 37 is open on one side it is easy to place the internal unit in the housing part 30 in rapid manner. Further arranged in one of the standing walls of housing part 30 is a connector 42 for electric power supply and data communication with the internal unit.
After the internal unit 1 has been placed in the lower part 30 of the housing a mat-like element 44 is placed thereon, which is preferably of electrically insulating and heat conducting silicone material, which comes into contact with a. cover 45 which is placed on the lower part 30 of the housing. The cover 45 is provided with a laser light-transmitting window 46 of scratch-resistant material which is glued against the cover on the outside thereof.
A board 47 provides the electrical connection between the part 8 with the power supply and the board 3 on which (most) electronic components are situated.
A peripheral cord seal is preferably situated between the cover and the lower part of the housing in order to make the housing leak water-tight.
The mirror surfaces 51, 52, 53, 54, 55, 56, 57 and 58 (fig. 3) of polygon 21 have in each case a slightly different position relative to the vertical and in the present embodiment have successive angles of 46.60*;
46.14'; 45.68*; 44.77*; 44.32'; 45.23'; 43.43*; and
43.87* relative to the central axis of the rotor of the motor. Due to these angles differing slightly in each case, eight parallel scan lines with a length of 6 cm are generated through the window in this embodiment to scan bar codes on objects present in front of that window. Due to the above-mentioned sequence of the angles, mutually adjacent scan lines are not of course written successively. The polygon is preferably manufactured from injection moulded plastic with vapour-deposited mirror material, whereby the weight can become extremely low and amount for instance to 2.7 gram. The angles of the mirror sur-faces have the above-mentioned successive values in order to keep the imbalance as small as possible during driving at high speed, for instance 9000 rpm, and to limit it for instance to a value of about 5 rrtgmm, while it is ensured that the mutual distance between successive scan lines does not become large such that at a determined speed of forward movement of the objects with bar code, a bar code can pass unscanned between mutually adjacent visible lines .
All options for the sequence of the above-mentioned angles of the polygon were calculated using a computer. While the finally chosen sequence does not have the very smallest imbalance of the polygon, it does ensure that the distance between two successively written parallel scan lines comprises no more than five times the distance between two such successive lines, thus preventing a bar code "slipping through" .
It has been found in practice that assembly of a polygon on the rotor of the motor can take place rapidly, sufficiently accurately and securely with double-sided adhesive tape.
In fig. 3 can also be seen that a beam B coming from laser source 4 falls onto the polygon via adjustable mirror 19, a fixedly disposed further mirror 60 and mirror 13, and falls onto the concave mirror 15 close to the transition between two mirror surfaces, in the figure between mirror surface 54 and 55, which mirror 15 is situated adjacently of mirror 22. Using the concave mirror 15 and the detector 14 arranged on board 3 the end of a scan line is then recorded each time and passed on to the control electronics of the scanner. More position information hereby becomes available for decoding bar codes and more accurate recognition can take place, for instance if two codes are located in one scan line or a code extends over two scan lines.
After assembly of the internal unit of a scanning device according to the present invention only the adjustable mirror 19 has to be adjusted for correct operation of the scanning device, while all other components are fixedly positioned relative to each other.

The above described embodiment should not be interpreted as limitative; the rights requested are defined by the following claims, within the scope of which many modifications can be envisaged.