Device for Detecting the Position of Web Side Edge

1. Field of the Invention

This invention relates to a system for detecting the position of the side edge of a web, and more particularly for constantly detecting the position of the side edge of a travelling web and correcting the lateral deviation of the travelling web by controlling a web feeding means based on the result of the detection.

2. Description of the Prior Art

On a rotary press, it is normally required to keep the roll of printing paper running at a fixed position without lateral deviation with respect to the rotary press. This is done by holding the roll of printing paper to run at a correct position, for example, by adjusting the position of a feeding means such as guide rollers of the travelling web. One end being fixed and the other end being free to move horizintally based on the result of the detection of the position of the side edge of the roll of printing paper using the side edge itself as the detecting point.

Conventionally, such a system is already known which comprises 2 units of photoelectric devices. One unit is so installed as to emit light on a designated position referred as the first position and which is located slightly inward of the datum side edge of a travelling roll of paper. The datum side edge being defined as the position of the side edge of a web while it is run at a correct position. This unit detects whether the light passes through said first position or not. The other unit is installed so as to emit light to another designated position referred as second position which is located slightly away from the datum side edge in the direction contrary to the web side. The second unit detects whether the light passes through the second position or not. The position of the side edge of the web is detected based on the results of the detection by both photoelectric devices. The two units of photoelectric device are in many cases intalled side by side in a plane parallel to the surface of the travelling roll of paper and in a direction perpendicular to the direction of travel of the paper. However, with this arrangement, it is difficult to obtain accurate detection due to the fact that the setting of the units at the first position and second positions is dependent on the size of the photoelectric device itself.

It is an object of the present invention to provide a device for detecting the position of the side edge of a web which is designed so as to solve the above problems.

An object of the present invention is to provide a device for detecting the position of the side edge of a web comprising a detector unit which is designed so as to emit light onto the position of the side edge of a web and detect the brightness of the lighted position by the light reflected from said lighted position, whereby the condition for installation can be sufficiently improved.

Another object of the present invention is to provide a device for detecting the position of the side edge of a web which is designed to divide the lighted position into three areas and to be capable of comparing the brightness of each of said areas with each other, whereby the accuracy of detecting the position of the side edge of a web can be adequately improved.

FIG. 1 illustrates an embodiment of the device for detecting the position of the side edge of a web of the present invention;

FIG. 2 is a schematic illustration of the relationship between the position of the beam of light and that of the side edge of travelling paper shown in FIG. 1 and

FIG. 3 shows an embodiment of the electric circuit components in the embodiment of the device for detecting the position of side edge of a web as is illustrated in FIG. 1.

In FIG. 1, reference numeral 1 indicates a web e.g. a travelling roll of paper such as a printing paper. Numeral 2 shows the side edge of the web 1. Numeral 3 shows a feeding means e.g. a guide roller whose surface is treated so as not to easily reflect light as compared with web 1. Numeral 4 indicates a device for detecting the position of the side edge of the web. Numeral 5 shows a light emitting source. Numerals 6 and 7 show small lenses respectively. Numeral 8 shows a large lens Numeral 9 shows a beam of light. Numeral 10 shows an optical fiber. Numeral 11 shows a photoelectric conversion circuit. Numeral 12 shows a connector for an outgoing line Numerals 13-1, 13-2 and 13-3 indicate amplifier circuits respectively, and numerals 14-1 and 14-2 show comparison circuits respectively.

The light emitted from the light emitting source 5 is made to pass through the small lens 6 and the large lens 8 to form a light beam 9 in the vicinity of the side edge 2 of the web 1. The reflected light from the light beam 9 enters the optical fiber 10 after passing through the large lens 8 and the small lens 7. At this point, the optical fiber 10 introduces light corresponding to the brightness of each of three areas of the light beam 9. Namely, first area 15, second area 16 and third area 17 as shown in FIG. 2. Code 1a shown in FIG. 2 indicates the condition of the travelling paper 1 when it is fed in a correct condition without being laterally deviated. Numeral 2a shows the side edge of a travelling paper 1a and this location defines the datum position. Numerals 1b and 1c respectively show the travelling paper when it is deviated laterally to the right or left, and numerals 2b and 2c show respectively the side edges of the travelling paper at their respective conditions.

The light corresponding to the brightness of first area 15, that corresponding to the brightness of second area 16 and that corresponding to the brightness of third area 17, which introduced by the optical fiber 10 are respectively converted into electric signals by the photoelectric conversion circuit 11. The converted electric signals are then respectively inputted into the amplifier circuits 13-1, 13-2 and 13-3 through the connector for the outgoing line 12. The comparison circuit 14-1 compares the output of the amplifier circuit 13-1 amplifying the electric signal corresponding to said first area 15, with the output of the amplifier circuit 13-2 amplifying the electric signal corresponding to said second area 16. The comparison circuit 14-2 compares the output of the amplifier circuit 13-2 with that of the amplifier circuit 13-3 amplifying the electric signal corresponding to said third area 17. The travelling paper 1 is returned to its correct position by driving and controlling a feeding means, e.g. one end of a guide roller 3 in the direction to the left or right based on the output of the comparison circuit 14-1 and comparison circuit 14-2. FIG. 3 in which the electric circuit illustrating the photoelectric conversion circuit 11 and circuits following it, will now be described.

In FIG. 3 reference numeral 11 shows a photoelectric conversion circuit. Numerals 13-1, 13-2 and 13-3 show amplifier circuits respectively. Numerals 14-1, and 14-2 show comparison circuits, e.g. differential amplifiers. Numerals 18-1, 18-2 and 18-3 show light receiving diodes respectively. Numerals 19-1, 19-2 and 19-3 show transistors respectively, wherein each flows a collector current proportionally corresponding to the amount of light received by each of said light receiving diodes 18-1, 18-2 and 18-3, respectively. Numerals 20-1 and 20-2 show transistors which drive and control relay windings 21-1 and 21-2, to be described later, and form together with the relay windings 21-1 and 21-2 a roller drive and control circuit of the present invention. Numeral 21-1 shows a relay winding which when energized, drives a feeding means 3 so as to have the travelling paper (1a, 1b, 1c) shown in FIG. 2, move to the right in the direction of arrow a shown in FIG. 2. Numeral 21-2 shows a relay winding which, when energized, drives the feeding means 3 so as to have the travelling paper (1a, 1b, 1c) shown in FIG. 2 move to the left in the direction of arrow b shown in FIG. 2.

In the photoelectric conversion circuit 11, the light receiving diodes 18-1, 18-2 and 18-3, as well as the transistors 19-1, 19-2 and 19-3 are all formed on the same printed circuit board. The light receiving diode 18-1 and transistor 19-1 located in the upper portion convert the brightness of the first area 15 into an electric signal. The light receiving diode 18-2 and transistor 19-2 located in the lower portion convert the brightness of the second area 16 into an electric signal, and the light receiving diode 18-3 and transistor 19-3 located in the intermediate portion convert the brightness of the third area 17 into an electric signal.

The collector voltage of the upper transistor 19-1 is amplified by the amplifier circuit 13-1 and inputted into the positive input terminal of the comparison circuit 14-1. The collector voltage of the intermediate transistor 19-3 is amplified by the amplifier circuit 13-3 and inputted into the negative input terminal of the comparison circuit 14-2. The collector voltage of the lower transistor 19-2 is amplified by the amplifier circuit 13-2 and outputted to a series circuit composed of diode D.sub.1 and resistor R.sub.1, and a series circuit composed of diode D.sub.2 and resistor R.sub.2. The split voltage of the resistor R.sub.1 is inputted into the positive input terminal of the comparison circuit 14-2, while the split voltage of the resistor R.sub.2 is inputted into the negative input terminal of the other comparison circuit 14-1. Comparison circuit 14-1 controls the base current of transistor 20-1 by comparing an input voltage level from the amplifier circuit 13-3 with an input voltage level from resistor R.sub.1. Comparison circuit 14-2 controls the base current of transistor 20-2 by comparing an input voltage level from the amplifier circuit 13-3 with an input voltage level from the resistor R.sub.1. Comparison circuit 14-1 is arranged so as to make the input voltage level being inputted into its positive input terminal equal to the input voltage level being inputted into its negative input terminal when the travelling paper is located at its correct position, that is, the condition of the travelling paper shown by solid lines (1a, 2a) in FIG. 2. The same arrangement is made with comparison circuit 14-2. Description of the cases in which (1) the traveling paper 1 is running at its correct position as shown by solid lines (1a, 2a) in FIG. 2, (2) travelling paper 1 is running at a position as shown by broken lines (1b, 2b) in FIG. 2 and (3) the travelling paper 1 is running at a position deviated tothe left from its correct position as shown by point and chain lines (1c, 2c) in FIG. 2, will now be given below.

In the case of (1), as aforementioned the difference between each input voltage level in the comparison circuit 14-1 and comparison circuit 14-2 is zero. Consequently, both transistors 20-1 and 20-2 are not supplied with the base current, and both transistor 20-1 and 20-2 are maintained in off condition. Due to this, no current is supplied to the relay windings 21-1 and 21-2, and the feeding means 3 (FIG. 1) is not driven. In other words the travelling paper is kept running at its correct position.

In the case of (2), the brightness of third area 17 (FIG. 2) becomes larger compared with the brightness of this area in the case of the above example (1). Because of this, the collector current of transistor 19-3 corresponding to said third area 17 is increased and subsequently the collector output voltage is increased. On the other hand, the brightness at first area 15 and the brightness at second area are maintained at the same level as that of the above example (1). Due to this, only the negative input terminal voltage of the comparison circuit 14-2 is increased compared with the case of the above example (1). The transistor 20-2 is therefore turned on as the output voltage of the comparison circuit 14-2 is increased, and the feeding means 3 is driven as a current flows through the relay winding 21-2. At this time, the transistor 20-1 is still in an off condition, and a current does not flow in the relay winding 21-1. Consequently, the travelling paper 1 is moved to the left, that is, in the direction of an arrow b from its condition shown by broken lines (1b, 2b) in FIG. 2. In other words, the travelling paper 1 is made to return to its correct position.

In the case of example (3), the brightness at first area 15 (FIG. 2) becomes smaller compared with the case of example (1) above.Because of this, the collector current of the transistor 19-1 corresponding to first area 15 is decreased, and subsequently the collector voltage is decreased. On the other hand, the brightness at second area 16 and third area 17 is maintained at the same level as that of the case of example (1) above. Due to this, only the positive input terminal voltage of the comparison circuit 14-1 is decreased compared with the case of example (1) above. The transistor 20-1 is therefore turned on as the output voltage of the comparison circuit 14-1 is increased, and a current flows through the relay winding 21-1. Consequently, the travelling paper 1 is moved to the right, that is, in the direction of an arrow a from its condition shown by lines (1c, 2c) in FIG. 2. In other words, the travelling paper 1 is made to return to its correct position.

As aforementioned, in the case of the present invention, it is possible to accommodate the light emitting source 5, lenses 6, 7 and 8, optical fiber 10 and photoelectric conversion circuit 11 in one case, whereby the installation condition, which has so far been regarded as a problem, can be sufficiently improved. Also, by the provision of an optical fiber 10, it has become possible to detect the brightness of each of areas 15, 16 and 17 which are very closely located to each other at the side edge of a web, whereby the accuracy of detecting the side edge of a web can be improved.

In the case of the present invention, a description has been given about the case in which third area 17 in the aforementioned embodiment is located to the right of the datum side edge 2a as illustrated in FIG. 2. It is needless to say that a similar effect can be obtained by making such an arrangement in which third area 17 is placed at a designated position located to the left of the datum side edge 2a and between first area 15 and second area 16.