APPARATUS FOR MONITORING FOR FAULTS IN TRANSLUCENT STRIP MATERIAL

Abstract: Apparatus for monitoring for faults in translucent strip material, such as photographic film, comprises a transport device 16, 12, 13, 22 for continuously moving the film 11 in its longitudinal direction and an optical scanning device 23 including a beam divider 21 which divides a single series of scanned light beams 14 into first and second sets of scanned light beams 14a 14b. The first set of light beams 14a is used to carry out transmission measurements on the film as it passes in tensioned condition between two spaced apart rollers 12, 13 and the second set 14b is used to carry out measurements in remission or reflection as the film passes around the sur­ face of a roller 16. The roller 16 has an air permeable surface and air is blown through this surface from the inside of the roller to form an air cushion between the film and the roller. Faults are detected by the electronic processing circuitry 18 in response to variations in the transmission and remission measurements carried out by the light detectors 15 and 17.

Description: The invention relates to an apparatus for monitoring for faults in transparent strip-like material and has particular reference to the detection of faults in photographic film. A monitoring apparatus is already known for this purpose and generally comprises a transport device for continuously moving a film in its longitudinal direction, an optical scanning device which generates a scanning light bead for scanning the film line by line point by point transversely of its direction of movement and a photoelectric light detecting arrangement including at least one light conducting rod for receiving light from the scanning light-bead as modified by the film. In apparatus of this kind it is necessary to monitor the film for faults both in transmission and also in remission or reflection. This can for example be achieved by guiding the film over a glass roller or a section of a glass cylinder and by projecting a scanning light beam which moves periodically to and fro onto the film in this region. A first light receiver arranged behind the scanning region can receive the transmitted light and a second light receiver arranged in front of the film can receive the remitted or reflected light and can detect faults which influence or affect the tranmitL-:d rc mitted or reflected light. An arrangement of this kind is, however, disadvantageous beczwse faults, which are not truly present, can be simulated if the glass roller or the section of a glass cylinder are dirty, by the formation of air bubbles between the film and the glass surface and if scratches are present on the glass surface. The principal object underlying the present invention is thus to provide a monitoring apparatus for monitoring for faults in film material which enables measurements to be taken both in transmission and also in remission or reflection without the two measurements mutually and unfavourably influencing one another. A further object of the.present invention is to keep the trouble and expense required to generate the scanning light bead at a very low level. Further objects and aims of the present invention will become clear from the subsequent description and include the provision of'a simple and compact apparatus. For accomplishing the above objects the invention envisages apparatus for monitoring for faults in translucent strip material such as photographic film, the apparatus comprising a transport device for continuously moving the strip material in its longitudinal direction, an optical scanning device for projecting a series of light beams at the strip for line by line point by point scanning thereof in a direction transverse to its direction of movement and photoelectric detector means with at least one light con ducting rod for receiving light from said light beams after impingement of the light from said light beams.on the film and characterized in that the strip is forwarded in tensioned condition between two spaced apart rollers, that a first set of the light beams impinge on the strip substantially at right angles thereto in the region between said two rollers, that a first photoelectric detector arrangement is arranged behind the strip to receive light from said first set of light beams, that the strip either before or.after both of the said rollers is fed around a further roller and that a second set of light beams is directed onto the strip in this region and that a second photoelectric detector arrangement is provided for light reflected from the strip at said further roller. Thus, in accordance with the invention,the transmission measurement and the reflection or remission measurement take place at two respective points spaced apart in the longitudinal direction of the strip or film material. For this reason the two light detectors are usefully connected to an electronic processing circuit which contains a store.or memory and which coordinates the two spacially separated detection points. The spacial separation of the two detection points which is actually present can thus be. cancelled by electronic means. In practice a fault in the film material will generally affect both the transmission and the reflection or remission measurements and the electronic processing circuit can simply consist of a device for delaying the signal from the first measurement for a period of time corresponding to the movement of the film from the point of the first measurement to the point of the second measurement and an and gate which passes an error signal when the measurement at the @@@@d measurement point also indicates that a fa@@t is p@@@@@t. Bexause the transmission measurement is carried out from that part of the strip of maQ0ri-- wb5ch i s supported in tensioned condition between the two spaced apart rollers optimum conditions are present for effecting this kind of measurement. A certain degree of fluttering of the strip material does not disadvantageously affect the transmission measurement. The reflection measurement would however be considerably disadvantageously influenced by fluttering of the strip material. For this reason tb reflection, or remission measurement is carried out on the film which is fed around the third or further roller. A particularly favourable and undisturbed movement of the film around this roller is brought about by providing the roller with an air permeable peripheral wall through which air is blown from the inside of the roller towards the outside in order to maintain an air cushion between the strip and the roller. In this way optimum conditions are provided for carrying out the reflection measurement. A transmission measurement would,however,not be possible at this position because of the special construction of the third roller. The generation of the series of light beams for projection onto the strip material is ensured in particularly simple fashion by arranging for the light beams, which are preferably produced by a single scanning -device which -for example incorporates a laser and a mirror wheel, to be divided into first and second sets of light beams by a beam divider and for the distances traversed by the first and second sets of light beams from the beam divider to the strip material to be equal. in this way the scanning light beads,which are projected onto the strip mterial at two points which are spaced apart in the longitudinal direction of the strip material, have the same form and intensity. A particularly straightfdrward spacial construction is achieved if the planes of the film at the two scanning points are inclined at an angle one to the other such that one of the sets of light beams lies in the extension of the undivided series of light beams and the other set of light beams is reflected out of the series of light beams by the beam divider. ThUSs for generating two scBnnin6 light beads only a simple beam divider is required in addition to a single device for generating a scanning light bead. The invention will now be described in further detail and by way of example only with reference to the accompanying drawing, the single figure of which shows a schematic side view of an apparatus for monitoring for faults in translucent strip material'. As seen in the drawing continuously moving film material 11 is drawn in the direction illustrated by the arrows by means of a film transport device which is not illustrated in detail but which includes in customary fashion and in addition to the rollers 16, 12,13 and 22 a film winding device which--draws film via a film tensioner from a spool of film material. The film 11 is led from a generally horizontal direction around an apertured roller 16 and pressurized air is supplied to the interior of the apertured roller 16;in order to form a defined air cushion between the surface of the roller and the film. This is useful, apart from other reasons, in order to avoid draw and ing in air bubbles/disturbing the optical measurement pro- cedure. In addition travelling waves in the longitudinal direction of the film are avoided by the presence of the air cushion. After the film 11 has passed around the roller 16 by somewhat more than 1800 so that it is now moving in approximately the opposite direction it reaches a guide roller 12 and is guided around this roller into the vertical direction. After traversing a predetermined path the film is once more turned around a.further guide roller 13 through an angle of approximately 90 from whence it is guided in the opposite direction to the incoming film around another guide roller 22. The film then leaves this further roller 22 in an approximately vertical direction and is passed on for a subsequent treatment or use and eventual winding by the winding roller (not shown) of the transport device. An optical scanning device 23 is located generally above the aperturedroller 16 and generates a series of scanning light beams 14 in a manner known per se by means of a laser and a mirror wheel and also lenses anda strip-like concave mirror (not shown). The series of light beams 14 carry out a continuous and periodic scanning movement at right angles to the plane of the drawing, i.e. -the beams 14 can be regarded as moving vertically downwardly through a vertically directed plane arranged at right angles to the plane of the drawing. A beam divider 21 is provided at the -lower end of the scanning device 23 and is inclined at an angle of 450 to the vertical direction. The beam divider, which can be a half-silvered mirror thus divides the series of light beams 14 into first and second sets of light beams 14a, 14b. The first set of light beams 14a are reflected at right angles to the right out of the series of light beams 14 and the second set of light beams 14b are directed vertically downwardly as an extension T the series of light beams 14 and impinge on the fiîm at the point 20 at an angle or to the surface of the roller 16. Light specularly reflected from the point 20 at the angle of reflection ok reaches the centre of a light detector ion device 17 which can contain one or more light conducting rods and cylindrical lenses which extend parallel td the scanning direction, i.e. at right angles to the plane of the drawing. Light remitted in the regions 24 25 can, if required, be detected separately from the specularly reflected light and can be processed in the electronic processing circuit 18. An aperture stop 26 arranged on both sides ofthe regions 24, 25 prevents stray light from reaching the light detector 17. The first set of beams 14a which is reflected sideways out of th, sexes of light beams 14 impinges at right angles on the film 11 at the point 19. It is important that the distances of the impingement points 19, 20 from the beam divider 21 are the same. Directly behind the impingement point 19 there is located a further light detector -15 which preferably operates only with a single light conducting rod and, if required, a cylindrical lens arranged in front of the light conducting rod. A photodetector is provided at at least one end face of each of the light conducting rods for converting the light which enters the light conducting rod into an electrical signal. An aperture stop 27 is arranged between the film 11 and the light receiver 15 and once more reduces the amount of any light which can reach the light detector. Whereas the light detector 17 responds to specularly re elected and remitted light the light detector 15 detects pertureg in the film, or variations in the transparency or trans at , i. The Particularly advantageous illumination of the two detection points 19 and 20 by one and the same scanning device is achieved by virtue of the fact that the film is guided through an angle of approximately 900 between the Scanning point 20, the roller 12 and the scanning point -19. The film 11 which extends between the scanning points 19 and 20 and also the first and second sets of beams 14a, 14b thus together form an approximately quadrangular figure. Zt desired, transmission on the one hand and remission and also reflection on the other hand can be separately de ticked rather than by combining the two error signals in the electronic processing circuit.18. The precise layout of the electronic processing circuit 18 will depend on the nature of the faults which it is desired to detect. As a general rule faults in the film material will influence both the transmitted and the remitted or reflected light and the electronic processing circuit -can conveniently include delay circuitry such as a store for storing the signal from the first light detector 17 for a period equal to the movement of the film from the scanning point 20 to the scanning point 19 and this signal together with the signal from the light detector 15 can then be subsequently be applied to the two inputs of an And-gate or other desired logic element It will be appreciated that the present invention is primarily concerned with the overall layout of the fault monitoring apparatus and not with the processing of the individual fault signals which will be readily understood by those skilled in the art.

Claims: WE CLAIM: 1. Apparatus for monitor-ing for faults in translucent strip material (11) such as photographic film, the apparatus comprising a transport device (12, 13,22) for continuously moving the strip material (11) in its longitudinal direction, an optical scanning de vice (23) for projecting a series of light beams (14a, 14b) at the strip (11) for line by line point by point scanning thereof in a direction transverse to its direction of movement and photoelectric de tector means '(15, 17, 18) with at least one light conducting rod (17') for receiving light from said light beams after impingement of the light from said light beams (14a, -14b) on the film and charac terized in that the strip (11) is forwarded in tensioned condition between two spaced apart rollers (12, 13), that a first.set (14a) of the light beams (14) impinge on the strip (11) substantially at right angles there to in the region between said two rollers (i2, ), that a first photoelectric detector arrangement (15) is arranged behind the strip (11) -to -receive light from said first set of light beams (14a), that the strip (11) either before or after both of the said rollers (12, 13) is fed around a further roller 16 and that a second set of light beams (lAb) is directed onto the strip in this region and that a second photoelectric detector arrangement (17) is provided .for light re flected from the strip at said further roller. 2. Apparatus according to claim 1 and characterized in that both said first and second photoelectric detection means (15, 17) are connected to an electronic process ing circuit t18) which contains a store which Co- ordinates the two spatiallyseparated detection points (19, 2C. 3. Apparatus according to claim 1 or claim 2 and charac terized in that the light beams (14) are utvi ed into first and second sets of light beams (14a, 14b) and that the distances traversed by said fist and second sets of light beams (14a, 14b) from the beam divider (21).to the scanning points (19, 20) are equal. 4. Apparatus in accordance with one of the preceding claims and characterized in that the planes of the strip (11) at the two scanning points (19, 20) subtend an angle one with the other such that one set of beams (14b) lies in the extension of the undivided beam (14) and the other set of beams (14a) is reflected out of the undivided beam {14)by the beam divider (21). 5. Apparatus according to any one of the preceding claims and characterized in that the further roller (16) has an air permeable peripheralwall through which air is blown from the inside to the outside of.the roller to maintain an air cushion between the strip (11) and the further rdller (16). 6. Apparatus according to any one of the preceding claims and characterized in that said strip material comprises photographiclfilm- material-.

Inventors: OSTERTAG, KLAUS, SICK, ERWIN
Applicants: ERWIN SICK GMBH OPTIK-ELEKTRONIK
Application year: 1980
Main classification: G01N21
IPC codes: G01N21