GB1579578A

GB1579578A - Film scanning apparatus

Info

Publication number: GB1579578A
Application number: GB1744077A
Authority: GB
Original assignee: MAN Maschinenfabrik Augsburg Nuernberg AG
Current assignee: MAN AG
Priority date: 1976-04-27
Filing date: 1977-04-26
Publication date: 1980-11-19
Also published as: IT1073201B; DE2618387A1; FR2349860B1; BE854019A; FR2349860A1; CH630184A5

Abstract

The film assemblies intended for producing offset printing plates are electrooptically scanned for their area coverage, i.e. the ratio of bright to dark areas. For this purpose, the film assembly (1) is fed through a measuring chamber (6) between a light source (2) and a pickup (3). Pairs of rollers (7, 8) are used to convey the film assembly (1). While the film assembly (1) is being conveyed, it is conveyed in a stretched state through a loading slot (4) and an unloading slot (5) of the stationary measuring chamber (6). <IMAGE>

Description

(54) FILM SCANNING APPARATUS (71) We, MASCHINENFABRIK AUGSBURG -NÜRNBERG AKTIENGESELLSCHAFT, a German company, of 8900 Augsburg, Stadtbach strasse 1, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to scanning apparatus for scanning a coating on a length of film, the apparatus having a light source for transmitting light through the film over its entire width and a receiver, aligned with the light source and separated from it, in use of the apparatus, by the film, which receiver is subdivided into several zones and connected to an arrangement for analysing the measured values.

The appaatus of the invention is particularly, although not exclusively, suitable for scanning a mounting film for the operation of a rotary offset printing machine. Such a film comprises a copy of the printing plate and as can be inferred from German Offenlegungsschrift 1 761 333, an accurate measurement for adjusting the inking zone may be achieved in a simple manner by measuring the brightness distribution of the transparent printing copy, i.e. the mounting film.

From the M.A.N. publication "Research, Engineering, Manufacturing", No. 6 there is known an arrangement of the type mentioned above with a rotating drum of transparent material for stretching the film to be scanned.

The light flux produced by a light source disposed within the drum and passing through the drum and the film is registered by a receiver disposed outside the drum. Stretching the film to be scanned on a rotatable drum can be very time consuming, however, and requires a very high degree of care and experience on the part of the operating personnel. Furthermore, using a drum as the carrier for the film to be scanned, particularly with a large film length, necessitates a large diameter of the drum and thus a considerable size in the structural size of the whole arrangement. However, quite apart from this, the stretching apparatus on the drum which is required in the known apparatus necessitates a considerable outlay in terms of construction, technical manufacture and materials. A further drawback of the known apparatus in which the entire interior chamber of the drum is illuminated, lies in the fact that it can lead to the occurrence of stray light and thus not inconsiderable adulteration of the measurement results.

A further proposed arrangement is shown in German Auslegeschrift 22 29 500 but that is both uneconomic and impractical.

According to the present invention there is provided scanning apparatus for scanning a film coating on a length of film, comprising a stationary chamber having an entry slot and an exit slot for the film, means for transporting the film in a taut state through the chamber, a light source disposed in the chamber for transmitting light through the film over its entire width and a receiver, aligned with the light source and located so as to be separated from it by the film in use of the apparatus, which receiver is subdivided across the width of the film into a plurality of zones each of which is connected with a respective means for averaging output signal values from that zone.

Thus, the film may be transported in a taut condition through the stationary chamber containing the light source and the receiver.

Owing to the fact that a stretching drum and stretching devices of the known arrangements are not required, a simple, space-saving and easily operable apparatus may be provided.

For the light source and the receiver, which in apparatus of the present invention may extend over the film width merely in the form of a narrow strip which is subdivided into zones and does not cover the entire film surface, commerical structural parts, favourable there fore in view of their production costs, may advantageously be used.

Preferably the chamber is defined between two roller pairs disposed adjacently to one another, between whose rollers the film may be passed through the chamber. Insertion of the film to be scanned into the entry slot afforded by the nip of one pair of cooperating rollers is easy and effortless to perform. The rollers undertaking the infeed and the passing on of the film which lie fully against one another simultaneously represent a reliable screening of the chamber against light penetrating from outside.

Expediently, the roller pairs each comprise a driven transport roller and an entrained contact roller. A simple drive is thereby obtained. Moreover, it is ensured, in a simple manner, that despite large diameter tolerances, the peripheral speeds of the transport roller and the coordinated contact roller of each pair can atuomatically adjust themselves to one another.

Advantageously, a constant speed motor is provided to drive the transport rollers. In addition to providing a speed which remains constant over an entire measuring operation, this may also enable a simple construction of apparatus for analysing measured data.

A transport speed of the rollers of approximately two metres per second has proved particularly expedient as in this way sufficiently brief measurement periods are achieved on the one hand, and the traction forces exerted on the film to be scanned, on the other hand, remain so far within the limits that even mounting films which include glued joints can be measured. Through this, preparatory operations can be simplified considerably when small variations occur subsequently.

To exclude possible sources of error, according to a further optional feature of the invention, the interior space of the chamber, i.e. particularly the rollers, can be coated with a non-reflecting material. Furthermore, the chamber can be provided in the area between the roller pairs with an at least unilaterally removable cover. Through this, the occurrence of stray light can effectively be prevented and yet optimum accessibility is ensured.

Furthermore, a guide plate may advantageously be disposed in the area between the entry and exit slots, on which plate the film rests and which plate has a slot-shaped recess for the receiver extending transversely to the film travel direction. These provisions result in reliable guiding of the film to be measured.

In addition, despite the fact that the receiver has an extremely narrow construction, a reliable seal against stray light penetrating from outside is ensured.

The invention may be carried into practice in a number of ways but one specific embodiment will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows diagrammatically in longitudinal section film scanning apparatus in accordance with the invention, Figure 2 shows a front elevation of the embodiment of Figure 1; and Figure 3 shows a block circuit diagram of a computer connected to the apparatus of Figures 1 and 2 for analysing the signals from the scanning apparatus.

Figure 1 shows a mounting film 1 destined for the production of an offset printing plate, whose surface covering, i.e. the ratio of light to dark areas, can advantageously be employed, in operation of the offset printing machine, to adjust automatically the inking duct adjustment screws in the area of the colorimeter of the printing machine thereby to vary automatically the ink flow according to the subject matter to be printed. For this purpose, the mounting film 1 is passed through between a light source 2 and a receiver 3 disposed in a measurement chamber 6 provided with an entry slot 4 and an exit slot 5.

Two roller pairs 7 and 8, disposed at a small space apart, are provided to define ends of the measurement chamber 6. The roller pairs 7 and 8 each comprise a driven transport roller 9 and an entrained contact roller 10, between which the mounting film 1 is passed; the nips between the rollers 9 and 10 of the roller pairs 7 and 8 form respectively the entry slot 4 and the exit slot 5 for the film 1 to enter and leave the chamber 6. Advantageously, the roller pairs 7 and 8 simultaneously undertake the infeed and forwarding of the mounting film 1 and screening of the chamber 6 against stray light.

A regulated speed motor 11 may be used to drive the transport rollers 9 to ensure constant transport speed. However, the cost of the control involved in this can be avoided by providing a load independent motor. In the embodiment illustrated there is provided for the transport rollers 9 of both roller pairs 7 and 8 a common motor 11 which is connected to the driven transport rollers 9 of both roller pairs 7 and 8 by means of a belt 12. A chain drive or toothed wheel gearing, however, would also be feasible, using a common drive motor ensures the same transport speeds of the two roller pairs 7 and 8 and thus advantageously tightened guiding of the mounting film 1. The non-driven rollers 10 of the roller pairs 7 and 8 automatically adjust themselves to the set transport speed, so there is no danger of slippage arising as a result of speed differences. A transport speed of from one to three, preferably two, metres per second has proved particularly expedient.

Between the transport rollers 9 of the roller pairs 7 and 8, a guide plate 13 is expediently disposed which extends to the surfaces of the.

rollers 9. This ensures in a simple manner.

safe guiding of the mounting film 1, particularly the leading and trailing ends of the film, from the entry slot 4 to the exit slot 5 and, in addition, screening of the measurement chamber 6 against dirt penetrating from the drive or light penetrating. To screen the measurement chamber 6 further against undesired stray light, there can be provided in the region of the contact rollers 10 a cover or hood 14 preferably capable of being removed or pivoted open, which expediently rests with its edges against the surfaces of the rollers 10 or against the lateral frame walls.

In Figure 2 the hood 14 is shown in the position where it is pivoted away. The light source 2, for which a commercial tubular lamp may advantageously be used, may be mounted on the hood 14 by means of supports 15 disposed on both sides. When the hood 14 is pivoted to an open position, the tubular lamp is therefore pivoted away from the receiver at the same time, so that unobstructed access to the receiver 3 and to the light source 2 is readily provided. However, it is alternatively possible to mount the tubular lamp in the lateral frame walls of the apparatus so as to be capable of easy removal.

The receiver 3, which, as Figure 2 shows, is subdivided over its length (which corresponds to the film width) into zones, may comprise several receiving elements 16 disposed adjacently, whose length exactly corresponds to the width of a zone. The width, i.e. the dimension in the web travel direction, of the receiving elements 16 and thus of the receiver 3 may be small in proportion to the length of the receiver 3. The small light sensitive receiving surface thus achieved may advantageously be illuminated evenly. Advantageously, commercial optic converters, for example so-called fibre optics, may be used to form the receiving elements 16. The receiving elements 16 are expediently let into a slot-shaped narrow recess 17, extending over the whole film wdith, of the guide plate 13.

Perfect seating is thereby assured and by lateral displacement of the guide plate 13, simple adjustability is ensured.

To exclude a disruptive reflection during the measuring operation, the interior elements of the chamber, i.e. the guide plate 13, the interior of the hood 14 and the contact rollers 10, disposed in the area of the light source 2 may be coated with a non-reflecting material, for instance they may be lacquered matt black.

The light flux emitted by the light source 2, passing through the film 1 and received by the receiving elements 16 of the receiver 3, is, as Figure 3 shows, conveyed from the individual receiving elements 16 to photocells 18; this is expediently accomplished by using so-called fibre optics. The photocells 18 emit electrical signals corresponding to the incident light intensity which signals can be integrated over the whole film length in integrators-19 disposed respectively sequentially after the photocells 18. The offset voltage or sensitivity of the integrators may advantageously be adapted to the conditions of the individual case, so that films of differing width of length or different white values may readily be measured. A further advantage of the apparatus in accordance with the invention lies in the fact that when a white film is illuminated, i.e. with full light penetration, no integration takes place. A measurement signal and via the integration a measured value only arise with surface covering of the film so that some light gets absorbed. This means a start-stop pulse for the measurement and monitoring of the measuring operation may be omitted. Furthermore, the length of the film to be measured in front of and behind the actual subject being illuminated by the light source is not of importance and cutting of the film is not necessary.

Morover, the sensitivity of response may easily be adapted to all commercial film materials. This can be accomplished in a simple manner because the output signal of the photocells 18 at maximum light penetration is a zero value. Since the standard photocells at maximum impingement yield a maximum voltage, this may here be achieved by a voltage reversal, for instance. It would also be conceivable, for instance, to set the subsequent integrators 19 such that they are at zero on maximum impingement and vice versa. The output signal of each integrator 19 thus exactly corresponds to the surface covering of the illuminated zone of the film 1.

This output signal may, if necessary, be made visually perceptible on an indicator screen 21, with previous storing in a register 20 and/ or be fed into a computer 22 for direct accommodating of the values obtained to the data of a printing machine. A further register 23 may similarly be connected on the output side to the computer 22.

WHAT WE CLAIM IS: 1. Scanning apparatus for scanning a film coating on a length of film, comprising a stationary chamber having an entry slot and an exit slot for the film, means for transporting the film in a taut state through the chamber, a light source disposed in the chamber for transmitting light through the film over its entire width and a receiver, aligned with the light source and located so as to be separated from it by the film in use of the apparatus, which receiver is subdivided across the width of the film into a plurality of zones each of which is connected with a respective means for averaging output signal values from that zone.

2. Scanning apparatus as claimed in claim 1, in which the chamber is defined between two roller pairs disposed adjacent to

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

safe guiding of the mounting film 1, particularly the leading and trailing ends of the film, from the entry slot 4 to the exit slot 5 and, in addition, screening of the measurement chamber 6 against dirt penetrating from the drive or light penetrating. To screen the measurement chamber 6 further against undesired stray light, there can be provided in the region of the contact rollers 10 a cover or hood 14 preferably capable of being removed or pivoted open, which expediently rests with its edges against the surfaces of the rollers 10 or against the lateral frame walls.

In Figure 2 the hood 14 is shown in the position where it is pivoted away. The light source 2, for which a commercial tubular lamp may advantageously be used, may be mounted on the hood 14 by means of supports 15 disposed on both sides. When the hood 14 is pivoted to an open position, the tubular lamp is therefore pivoted away from the receiver at the same time, so that unobstructed access to the receiver 3 and to the light source 2 is readily provided. However, it is alternatively possible to mount the tubular lamp in the lateral frame walls of the apparatus so as to be capable of easy removal.

The receiver 3, which, as Figure 2 shows, is subdivided over its length (which corresponds to the film width) into zones, may comprise several receiving elements 16 disposed adjacently, whose length exactly corresponds to the width of a zone. The width, i.e. the dimension in the web travel direction, of the receiving elements 16 and thus of the receiver 3 may be small in proportion to the length of the receiver 3. The small light sensitive receiving surface thus achieved may advantageously be illuminated evenly. Advantageously, commercial optic converters, for example so-called fibre optics, may be used to form the receiving elements 16. The receiving elements 16 are expediently let into a slot-shaped narrow recess 17, extending over the whole film wdith, of the guide plate 13.

Perfect seating is thereby assured and by lateral displacement of the guide plate 13, simple adjustability is ensured.

To exclude a disruptive reflection during the measuring operation, the interior elements of the chamber, i.e. the guide plate 13, the interior of the hood 14 and the contact rollers 10, disposed in the area of the light source 2 may be coated with a non-reflecting material, for instance they may be lacquered matt black.

The light flux emitted by the light source 2, passing through the film 1 and received by the receiving elements 16 of the receiver 3, is, as Figure 3 shows, conveyed from the individual receiving elements 16 to photocells 18; this is expediently accomplished by using so-called fibre optics. The photocells 18 emit electrical signals corresponding to the incident light intensity which signals can be integrated over the whole film length in integrators-19 disposed respectively sequentially after the photocells

18. The offset voltage or sensitivity of the integrators may advantageously be adapted to the conditions of the individual case, so that films of differing width of length or different white values may readily be measured. A further advantage of the apparatus in accordance with the invention lies in the fact that when a white film is illuminated, i.e. with full light penetration, no integration takes place. A measurement signal and via the integration a measured value only arise with surface covering of the film so that some light gets absorbed. This means a start-stop pulse for the measurement and monitoring of the measuring operation may be omitted. Furthermore, the length of the film to be measured in front of and behind the actual subject being illuminated by the light source is not of importance and cutting of the film is not necessary.

Morover, the sensitivity of response may easily be adapted to all commercial film materials. This can be accomplished in a simple manner because the output signal of the photocells 18 at maximum light penetration is a zero value. Since the standard photocells at maximum impingement yield a maximum voltage, this may here be achieved by a voltage reversal, for instance. It would also be conceivable, for instance, to set the subsequent integrators 19 such that they are at zero on maximum impingement and vice versa. The output signal of each integrator 19 thus exactly corresponds to the surface covering of the illuminated zone of the film 1.

This output signal may, if necessary, be made visually perceptible on an indicator screen 21, with previous storing in a register 20 and/ or be fed into a computer 22 for direct accommodating of the values obtained to the data of a printing machine. A further register 23 may similarly be connected on the output side to the computer 22.

WHAT WE CLAIM IS:

1. Scanning apparatus for scanning a film coating on a length of film, comprising a stationary chamber having an entry slot and an exit slot for the film, means for transporting the film in a taut state through the chamber, a light source disposed in the chamber for transmitting light through the film over its entire width and a receiver, aligned with the light source and located so as to be separated from it by the film in use of the apparatus, which receiver is subdivided across the width of the film into a plurality of zones each of which is connected with a respective means for averaging output signal values from that zone.

2. Scanning apparatus as claimed in claim 1, in which the chamber is defined between two roller pairs disposed adjacent to

one another, between whose rollers the film may be passed, one pair affording the entry slot and the other pair the exit slot.

3. Scanning apparatus as claimed in claim 2, in which the roller pairs each comprise a driven roller and an entrained contact roller.

4. Scanning apparatus as claimed in claim 3, in which a constant speed motor is provided for driving the driven roller off each pair.

5. Scanning apparatus as claimed in any one of the preceding claims, in which the means for transporting the film through the chamber is adapted to transport the film at approximately two metres per second.

6. Scanning apparatus as claimed in any one of the preceding claims, in which the interior space of the chamber is coated or otherwise provided with a non-reflecting material.

7. Scanning apparatus as claimed in any one of the preceding claims in which the chamber is provided with an at least unilaterally removable cover.

8. Scanning apparatus as claimed in claim 6, in which the light source is mounted on the cover.

9. Scanning apparatus as claimed in any one of the preceding claims, in which there is disposed in the area between the entry and exit slots a guide plate on which the film can rest, which guide plate has a slot-shaped recess running transversely to the intended film travel direction, in which the receiver is set.

10. Scanning apparatus as claimed in any one of the preceding claims, in which the receiver is a narrow light conductor corresponding in length to approximately the maximum film width and comprises a plurality of receiving elements affording the receiver zones, each individual element being connected to one photocell.

11. Scanning apparatus as claimed in claim 10 in which each receiving element comprises a fibre optic.

12. Scanning apparatus as claimed in claim 10 or claim 11, in which the output signal of the photocells or of the receiver at full light penetration of the film is a zero value.

13. Scanning apparatus as claimed in any one of claims 10 to 12, in which disposed sequentially after each photocell is an integrator whose offset voltage and sensitivity are adjustable.

14. Scanning apparatus as claimed in claim 13, in which the integrator is linked to a computer and/or an indicator.

15. Scanning apparatus as claimed in claim 14, in which the integrator is linked to a computer which is connected to an indicator.

16. Scanning apparatus as claimed in any one of claims 13 to 15, in which a register is provided for storing the output values of the integrator or of the computer.

17. Scanning apparatus substantially as specifically described herein with reference to the accompanying drawings.

18. An offset printing machine including scanning apparatus as claimed in any one of the preceding claims, wherein the ink supply is controlled as a function of the output signal values of the receiver.