GB2237886A

GB2237886A - Document size detecting device for image forming equipment

Info

Publication number: GB2237886A
Application number: GB9024090A
Authority: GB
Inventors: Masao Moriyo; Hiroshi Hanzawa; Moriyuki Koike
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1989-11-08
Filing date: 1990-11-06
Publication date: 1991-05-15
Anticipated expiration: 2010-11-06
Also published as: GB2237886B; DE4035568C2; JPH03150550A; DE4035568A1; GB9024090D0

Abstract

A device incorporated in image forming equipment for surely detecting the size of a document 10 laid on a document table 12 with no regard to the kind of the document utilises the open and closed positions of the presser cover plate 14. The device has a plurality of document sensors PD1-7 for sensing a reflection from the document surface and determines the size of the document on the basis of the combination of the outputs of the document sensors. In addition, the document size is determined by referencing document presence/absence data associated with different sensing positions which are derived from correction data which are in turn derived from two consecutive times of detection effected in the open and closed positions of a presser plate 14. <IMAGE>

Description

:2 2 3.7 DOCUMENT SIZE DETECTING DEVICE FOR IMAGE FORMING EQUIPMENT The

present invention relates to a document size detecting device for image forming equipment of the type forming an image by reading a document laid on a document table.

An electrophoto graphic copier, laser beam printer and facsimile transceiver extensively used today belong to a family of image forming equipment of the type described. An electrophotographic copier, for example, has a cover plate or similar presser plate for pressing a document laid on a glass platen or similar document table from above. In a copy mode which uses the cover plate, it is a common practice to prescan the document to determine the size of the document. Therefore, the problem with a copier of the kind needing such prescanning is that the prescanning should be effected document by document even when a single copy is desired with each document, resulting in slow copying operations.

To eliminate the above problem, a document size detecting device having a plurality of reflection type photosensors may he located below the glass platen, as disclosed in Japanese Patent Laid-Open Publication No. 78849/1981. Specifically, before the cover plate is closed to press the document on the glass platen, the outputs of the photosensors sensed the document are picked up and combined to determined the document size. The photosensors are located at different positions each corresponding to a particular regular document size, so that all the documents of regular sizes may be detected. This kind of device is successfully operable so long as the area of the document to be sensed by any one of the sensor is blank, since the associated sensor will receive a reflection from the blank area to produce an output. However, when the area of the document to be sensed is a black image portion, whether it be solid or not, the associated sensor will not produce an output since no reflection is incident thereto, i. e., the result of detection will be the same as in the case wherein a document does not exist. This brings about erroneous size detection.

In the light of the above, the sensors"may sense a document twice, i. e. when the cover plate is open and when the cover plate is closed, as taught in Japanese Patent Laid-Open Publication Nos. 6241/1987 and 8640/1988 by way of example.

This approach will be successful when a document is thin.

However. when use is made of a thick document such as a book, the operator has to press it by hand and. therefore, cannot use the cover plate. As a result, the sensors cannot sense such a document twice, failing to determine the document size with accuracy.

i i It is therefore an object of the present invention to provide a document size detecting device for image forming equipment capable of detecting the size of a document laid on a document table with accuracy with no regard to the kind of the document.

It is another object of the present invention to provide a generally improved document size detecting device for image forming equipment.

In image forming equipment having a document table to be loaded with a document and a document presser movable between an open position and a closed position for pressing the document laid on the document table, a document size detecting device of the present invention comprises a first document presser position detecting member for detecting the open position of the document presser, a second document presser position detecting member for detecting the closed position of the document presser, a plurality of document sensors disposed below the document table and each comprising a light emitting element for emitting light toward the document table and a light-sensitive element for receiving a reflection from the document laid on the document table, and a controller for determining the size of the document laid on the document table on the basis of a combination of presence and absence of the document represented by output values of the individual document sensors. The controller determining that the document exists when the output values of the individual document sensors do not change from the open position to the closed position of the document presser, and that the document does not exist when the output values change.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which:

Fig. 1 is a fragmentary side elevation of an electrophotographic copier representative of image forming apparatus and to which a document size detecting device embodying the present invention is applied; Fig. 2 shows the positions of documents having various sizes on a document table and the positions of document sensors; Fig. 3 is a sectional front view showing the arrangement of the document sensors; Fig. 4 is a schematic diagram showing a specific construction of each of the document sensors; Fig. 5 is a graph indicating a relation between the amount of light incident to each document sensor and the position of a presser plate; Fig. 6 is a block diagram schematically showing a control system included in the illustrative embodiment; and Figs. 7 to 11 are flowcharts demonstrating specific operations of the control system shown in Fig. 6.

Referring to Fig. 1 of the drawings, an electrophotographic copier belonging to a family of image forming equipment and to which an embodiment of the present invention is applied is shown in a fragmentary view. As shown, the copier has a glass platen or similar document table 12 and a cover plate or similar document presser 14. A document 10 is laid on the glass platen 12 and pressed by the cover plate 14 from above. The cover plate 14 is hinged to a body 16 of the copier in such a manner as to be movable up and down, as indicated by an arrow X in the figure. The cover plate 14 has an actuating portion 14b. A first switch 18 and a second switch 20 are mounted on the copier body 16 to serve as switches which are responsive to a first and a second document pressing position, respectively. The switches is 18 and 20 may each be implemented by an interruption type photosensor, while the actuating portion.14b of the cover plate 14 may be implemented by an intercepting plate. The sesors 18 and 20 each is turned on when the optical path thereof is interrupted by the actuating portion 14b. Specifically, the switches 18 and 20 are responsive to, respectively, the open and closed positions of the cover plate 14. In the closed position, the cover plate 14 presses the document 10 against the glass platen 12.

As shown in Fig. 2, documents 10a to 10e having different sizes each is laid on the glass platen 22 and positioned by being 1 i 1 1 abutted against a scale 22 which is located in close proximity to the glass platen 12. To identify the documents having regular sizes such as A and B, document sensors, e. g., seven sensors are arranged at predetermined positions such as positions P1 to P7. Specifically, as shown in Fig. 3, seven document sensors PD1 to PD7 are respectively located at the positions P1 to P7 which do not interfere with a scanner 26 or optics 32. The scanner 26 includes a light source 28 and a mirror 30 for exposing a photoconductive element 24 of the copier imagewise.

The optics 32 includes mirrors 34, 36, 38, 40 and 42, and lenses 44, 46 and 48. In Fig. 3, the document sensors PD5 and PD6 are not shown.

As shown in Figs. 3 and 4, the document sensors PI) each has a single light emitting diode (LED) or similar light emitting is element 50 for emitting light toward the glass platen 12, and a single phototransistor or similar light-sensitive element 52 to which a reflection from the glass platen 12 will be incident. If desired, the light emitting elements 50 each being assigned to respective one of the document sensors PD may be replaced with a single or shared light emitting element which emits light toward the glass platen 12 from below.

Fig. 5 shows a relation between the amount of light incident to each light-sensitive element 52 and the position of the cover plate 14. In the figure, the ordinate and abscissa are representative of the amount of incident light and the position of -B- the cover plate 14. As Fig. 5 indicates, the amount of incident light depends on the position of the cover plate 14, 1. e. the distance between the cover plate 14 and the light-sensitive element 52. Therefore, if a threshold value that allows the light-sensitive element 52 to identify a reflection from the cover plate 12 (and to discriminate characters and solid image portions) is determined beforehand, it will be determined that the cover plate 14 exists when the amount of incident light is greater than the threshold value or that it does not exist when otherwise. It follows that even when the cover plate 14 is not fully closed, the cover plate 14 will be determined to be in the closed position only if it is positioned such that an amount of light greater than the threshold value is incident to the light-sensitive element 52. For this reason, the second switch is 20 is so positioned as to be turned on when the cover plate 14 reaches a half-closed position, as distinguished from the fully closed position, where the amount of incident light is greater than the threshold value. Such a position will hereinafter be referred to as a first light receiving position and is indicated by A in Fig. 5 by way of example. On the other hand, the first switch 18 is so positioned as to be turned on when the cover plate 14 reaches a position, or second position, where the amount of incident light is smaller than the threshold value, as indicated by B in Fig. 5 by way of example.

Referring to Fig. 6, a specific construction of a control 1 j -g- system included in the illustrative embodiment will be described.

In Fig. 6, the light-sensitive elements 52 of individual document sensors PD are connected to a microcomputer (CPU) 54 via an analog- to- digital converter (ADC) 5 6. The light emitting elements 50 of the individual document sensors PD are connected to the CPU 54 via a driver 60 and an input/output Q/0) port 58. The first and second switches 18 and 20 are connected to the I/0 port 58. When the output port of the 1/0 port 58 goes high or M", the light emitting elements 50 (e. g. LEDs 50, Fig.

3) each is turned on to illuminate the document 10 via the glass platen 12. The light emitting elements 50 may be turned on either constantly or only at the time of size detection, as desired. Light reflected from the document 10 is incident to the light-sensitive elements 52 (e. g. phototransistors 52, Fig. 3), so that the outputs of the elements 52 representative of the amounts of light incident thereto are fed to the microcomputer 54 via the ADC.

The ADC 56 converts the outputs of the light-sensitive elements 52 of the individual document sensors PD into digital values. Assume that (logical) ONE and (logical) ZERO are respectively representative of a condition wherein the digial value is greater than a predetermined threshold value and a condition wherein the former is smaller than the latter. Then, the output of the ADC 56 will be ONE when characters printed on the document 10 or the background thereof is read or ZERO when a is solid image portion printed on the document 10 or an area where the document 10 does not exist is read. In the case of a solid image portion, despite that the document 10 exists, the result of detection will be the same as in the case wherein the document 10 does not exist at all. To eliminate such erroneous decisions, the illustrative embodiment corrects data associated with a single document 10 by using two different data, i. e., data resulted from the open and closed positions of the cover plate 14.

Specifically, the data derived from the light-sensitive elements of the individual document sensors PD are corrected on the basis of the ON state of the first switch 18 representative of the open position of the cover plate 14 and the ON state of the second switch 20 representative of the closed position of the cover plate 14, as shown in Table 1 below.

Table 1

SW 18 ON SW 20 ON DOCTYMNT 10 prese nt 0 0 1 absent 0 0 present (sOlid image) In Table 1, ONEs and ZER0s outPutted by each light-sensitive element 52 indicate respectively that the amount of incident light is smaller than the threshold value and that it is 1 i i greater than the threshold value. Assume that the output of the light-sensitive element 52 is ONE when the cover plate 14.is open (switch 18 is ON) and does not change to ZERO when the plate 14 is closed (switch 20 is ON). This indicates that a reflection is sensed in both of the open and closed positions of the cover plate 14, i.e., the document 10 exists. If the output of the light-sensitive element 52 is ZERO when the cover plate 14 is open and does not change to ONE when the plate 14 is closed, it is determined that the amount of incident light is smaller than the threshold value and remains the same with no regard to the position of the cover plate 14, i. e., a solid image portion on the document 14 is sensed. In any case, the document 10 is determined to exist when the output does not change in both of the open and closed positions of the cover plate 14. When the output is ZERO in the open position of the cover plate 14 and changes to ONE on the closing of the plate 14, meaning that a reflection from the plate 14 is not received in the open position of the plate 14 and is received on the closing of the plate 14, it is determined that the document 10 does not exist. The output which is ONE in the closed position of the cover plate 14 and changes to ZERO in the closed position of the same means that a reflection is sensed in the open position, i. e., some reflecting object exists, and that a reflection is not sensed in the closed position, i. e., no reflecting object exists. This is a phenomenon that never occurs in practice.

The size of the document 10 is determined by using the results of detection shown in Table 1 and size determining data or codes which are shown in Table 2 below.

Table 2

P7 P6 P5 P4 P3 P2 P, DOCU] 1 SENSE DOCUMENT 10 POSIT:: SIZE A3 lateral B4 lateral A4 longitudinal B5 longitudinal 0 0 0 0 A4 lateral 0 0 0 AS longitudinal 0 0 0 0 0 B5 lateral 0 0 0 0 0 0 AS lateral In Table 2, the positions of the document sensors PD1 to PD7 are respectively represented by positions P1 to P7, and ONEs and ZER0s are indicative of positions where the document 10 is determined to be present and positions where it is determined to he absent. For example, when all the document sensors PD1 to PD7 located at the positions P1 to P7 sense the document 10, it is is determined that the document 10 has size A3 and positioned laterally with respect to the scanning direction. When the document 10 is sensed only at the positions PS to P7, the document 10 is determined to have size A4 and also positioned laterally with respect to the scanning direction. Further, when the document is sensed only at the positions PS and P7, the document 10 is determined to have size A5 and positioned longitudinally with respect to the scanning direction. A reference will be made to Figs. 7 to 11 for describing the control particular to the illustrative embodiment. In the flow I shown in Fig. 7, whether or not the actuating or interrupting member 14b of the cover plate 14 has turned on the first switch 18 while the plate 14 is moved toward the closed position is determined (STEP 1). If the answer of the STEP 1 is YES, the outputs of the light-sensitive elements 52 of the individual document sensors PD1 to PD7 are evaluated according to a flow shown in Fig. 9 (STEP 2). The results of evaluation are written to a sensor buffer 1 as data associated with the open position of the cover plate 14 (STEP 3). These steps are 20 repeated until data associated with all the sensors PD1 to PD7 have been written to the sensor buffer 1 (STEP 4). In a flow II shown in Fig. 8, assume that the second switch 20 has been turned on (Yes, STEP 11). Then, the outputs of the sensors PD1 to PD7 are evaluated according to the procedure of Fig. 9, and the results of evaluation are written to a sensor buffer 2 as data associated with the closed position of the cover plate 14 (STEP 13). This is also repeated until data associated-with all the sensors PD1 to PD7 have been written to the sensor buffer 2 (STEP 14). Then, the data is corrected by using the data written to the sensor buffers 1 and 2 and Table 1 and according to a flow shown in Fig. 10 (STEP 15). Subsequently, a flow shown in Fig. 11 is executed to determine the size of the document (STEP 16) on the basis of the corrected data and by using Table 2.

In Fig. 9, the outputs of the sensors PD1 to PD7 each is converted into a digital value (STEP 31) and determined whether or not it is greater than the threshold value (STEP 32).

Specifically, the sensor output is converted into ONE if it is greater than the threshold value (STEP 33) or into ZERO if is otherwise (STEP 34). The sensor output ONE indicates that the characters or the background of the ordinary document 10 is being read, while the sensor output ZERO indicates that the solid image portion of the document 10 or the area where the document 10 does not exist, i. e.. the area where no reflection occurs due to the cover plate 14 being open is read.

In Fig. 10, the data correction begins with a STEP 41 for determining whether or not the sensor buffer 1 is ONE. If the answer of the STEP 41 is YES, whether or not the sensor buffer 2 is ONE is determined (STEP 42). If the answer of the STEP 42 is YES, it is determined that the document 10 exists (STEP 43).

i 1 i i 4 i k If the answer of the STEP 41 is NO, whether or not the sensor buffer 2 is ZERO is determined (STEP 44). If the answer of the STEP 44 is YES, it is determined that the document 10 exists; if otherwise, it is determined that the document does not exist.

The size determining flow shown in Fig. 11 is executed when the document 10 exists as determined by the procedure of Fig. 10. First, the corrected data is compared with the codes shown in Table 2 (STEP 5 1) to see if it is identical with any one of the codes (STEP 52). If the answer of the STEP 52 is YES, the size is determined on the basis of the identical code and the size detection is ended (STEP 53). If otherwise, a detection error is indicated (STEP 54).

Assuming that the document 10 has size A4 and positioned laterally with respect to the scanning direction and is entirely blank, then the sensors will produce outputs shown in Table 3 below.

Table 3

PLATE 14 SENSE P7 1 P6 PS P4 P3 P2 P1 \POSITION POSITION POSITION WHERE 0 0 0 0 SW 18 IS ON POSITION WHERE 1 SW 20 IS ON RESULT OF 0 0 1 0 1 0 CORRECTION 9 When the document 10 having such a size and so positioned has a solid image in a part thereof, c. g., at the position P6, the sensors will produce outputs as shown in Table 4 below.

is 0 -Table 4

PLATE 14 NSE POSITION ION P7 P6 PS P4 P3 P2 P1 POSITION WHERE SW 18 15 ON 0 0 0 POSITION WHERE SW 20 IS ON 0 1 1 1 1 RESULT OF 1 1 1 1.1 1 0 1 0 1 0 1 ORRECTION - Although the output of the sensor located at the position P6 differs from Table 3 to Table 4, the result of correction is identical and, therefore, the results of correction associated with all the sensors are identical. It follows that the document 10 is determined to have size A4 from table 2.

In summary, in accordance with the present invention, a reflection from a document is sensed by a plurality of sensors to determined the size of the document on the basis of the combination of the outputs of the sensors. This, coupled with the fact that whether or not a document exists is determined at the individual sensing positions on the basis of corrected data derived from the open and closed positions of a presser plate, X 1 1 1 1 eliminates detection errors otherwise caused by solid image portions. In addition, even when the presser plate cannot be fully closed due to a thick document, the size of the document is surely determined due to the two consecutive times of detection. Such reliable detection of document size does not is achievable without affecting the copying speed at all.

Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.

4 - 18 CIAIXS 1. A document size detecting device for image forming equipment having a document table to be loaded with a document and a document presser movable between an open position and a closed position for pressing a document laid on said document table, said device comprising:

document presser position detecting means for detecting the position of said document presser; a plurality of document sensing means disposed below maid document table; control means for determining the size of a document laid on said document table on the basis of output values of said individual document sensing means; said control means determining that the document is present at positions for which the output values of corresponding individual document sensing means do not change from said open position to said closed position of said document presser, and that the document is not present at positions for which the output values of corresponding individual document sensing means change from said open position to said closed position of said document presser.

2. A document size detecting device according to claim 1 wherein each document sensing means comprises a light emitting element for emitting light toward said document table and a light-sensitive element for receiving a reflection from the document laid on said document table.

3. A device as claimed in claim 2 wherein a condition where an amount of light incident on said lightsensitive element of each of said document sensing means is k 1 i :1 greater than a predetermined threshold value and a condition wherein said amount of light is smaller than said predetermined threshold value are predetermined to be a first and a second light receiving condition, respectively.

4. A document size detecting device according to claim 1, 2 or 3 wherein the document presser position detecting means comprise first means for detecting the open position of said document presser and second means for detecting said closed position of said document presser.

5. A device as claimed in claim 3. wherein the document presser position detecting means comprise first means for detecting the open position of said document presser and second means for detecting said closed position of said document presser and said first means is set to be operated when the document presser is in such a position that said light- sensitive elements would be in said second light receiving condition in the absence of a document, while said second means is set to be operated when the document presser is in such a position that said light- sensitive elements would be in first light receiving condition in the absence of a document and said document presser is not fully closed.

6. A document size detecting device constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

7. Image forming apparatus including a document size detecting device according to any one of the preceding claims.

Published 1991 at The Patent 01fice, State House. 66/71 High Holborn. London WC I R4T? Further copies may be obtained from Sales Branch, Unit 6. Nine Mile Point. Cwmficlinfach. Cross Keys, Newport. NPI 7RZ. Printed by Multiplex techniques ltd, St Mary Cray, Kent.