Automatic duplex recording apparatus

Abstract: In an automatic two-sided copying apparatus, a recording sheet which has a toner image on its one side is reversed by an automatic duplex unit and the recording sheet is fed from the automatic duplex unit to be copied on its second side. The apparatus is provided with a feeding state detector which detects that number of recording sheets set by an operator to be copied have been conveyed from the sheet feeding section in the main body, a refeeding state detector which detects that refeeding of at least one of the stacked recording sheets in the automatic duplex unit is possible, and with a timing controllor which receives detection outputs from both the feeding state detector and the refeeding state detector and initiates the start of refeeding from the automatic duplex unit. The duplex unit comprises an intermediate stacker means (20) provided with aligning means (23A, 23B, 24A, 24B).

Description: BACKGROUND OF THE INVENTION The present invention relates to an improvement in copyproductivity of an automatic duplex recording apparatus which reads both sides of a document and produces copies on both sides of a recording sheet. As a device for reversing a document and thereby copying from both sides of the document, there has been known a reversible automatic document feeder (hereinafter referred to as RADF). When such a device is used, a large number of copies can easily be produced. Further, copies produced are in the same sequence as that of the documents, which eliminates the necessity of changing the sequence of produced copies. Further, when interlocked with a sorter, collating and sorting by page can automatically be made and a large number of copies can be put in order accurately. As a device wherein copies are produced automatically on both sides of a recording sheet through a single operation of a button, there has been known an ADF. When this unit is used, information on both sides of a document are copied onto both sides of a recording sheet, resulting in a saving of cost for recording sheets and easy filing. Further, it can be applied in many ways, including collecting materials in a booklet form for quick view. When two-sided copying is made on a conventional automatic duplex copying apparatus, sheet refeeding from ADU is started only after the detection of the stacked last recording sheet (having a copy only on one side) among the number of sheets set for 1st side copying. The above-mentioned operations will be explained as follows, referring to Fig. 6. When a copy button is pressed (Fig. 6 (a)), sheet feeding for 1st side copying is made (Fig. 6 (b)). As an assumption for the explanation of the operations, a certain number of copies are set (hereinafter the number of copies set is called a set number of copying). When the first sheet of the recording sheets arrives at a photosensitive body, 1st side copying is started and the 1st side copying is continued until the set number of copying is completed. (Fig. 6 (c)) . The recording sheets which have been finished in terms of 1st side copying are stacked in ADU (Fig. 6 (d)). After completion of stacking in ADU, sheet aligning is made in ADU (Fig. 6 (e)). After completion of the sheet aligning, sheet refeeding from ADU is made (Fig. 6 (f)) and then 2nd side copying is made (Fig. 6 (g)). According to the time chart for the foregoing, there is a period of time for the photosensitive body to wait ( non-operation time) between the completion of 1st side copying and the start of 2nd side copying. Due to this standby period for a photoreceptor, it has been difficult to improve the copy-productivity for duplex copying. Incidentally, though the ratio of the standby period to the copying time depends upon the set number of copying, it has been impeding the improvement of copy-productivity. From EP-A-0 221 328 is known an apparatus for producing duplex copy sets from a duplex original set utilizing a reversible automatic document feeder (RADF) and a first-in-first-out duplex tray. Although in this known apparatus there are provided sensors in the tray and the RADF, these sensors merely serve to indicate that the respective unit has been emptied. Moreover, although this known apparatus attempts to maximize the throughput of the apparatus during duplex recording, this is achieved in this prior art apparatus in that upon duplex recording a sheet that has been placed in a stacking means of the duplex tray is staged partially out of the tray towards a paper feed nip which will be controlled as the sheet is needed in the synchronized copy process. The staging out of the leading edge of the sheet in the tray is entirely independent of the copy or feed process but rather only dependent on the presence of the sheet in the tray. Another recording apparatus for duplex recording utilizing a duplex tray for stacking one-sided recorded sheets for reverse side recording is described in US-A-4 858 740. According to this prior art, the sheet re-feeding of the sheets in the duplex tray is conducted at a timing delayed from that of the maximum throughput and the set-up completion stage is latched until the completion of the printing operation. Therefore, this prior art teaches to link the re-feeding of the sheets in the duplex tray with the completion of the printing operation of the first side recording, thus inevitably leading to a time delay between the front and reverse side recording. Therefore, it is desirable to improve copy-productivity in the manner wherein the recording sheets are conveyed so that the recording sheets, each having been copied on its first side and stacked on ADU may pass through the image-transfer section for the start of copying on the second side while the recording sheets, each having been copied on its first side, are being fed to ADU from the image-transfer section. However, the distance between the recording sheets adjoining each other for refeeding is changed by adjusting and controlling so that both sheet alignment and sheet refeeding may be conducted separately, because sheet refeeding and sheet alignment can not be made concurrently as disclosed in Japanese Patent O.P.I. Publication No. 161641/1987. Thus, the change of distance between recording sheets adjoining each other has required a period of time and thereby the copy-productivity has been low. SUMMARY OF THE INVENTION An object of the present invention is to realize an automatic duplex recording apparatus wherein it is possible to improve copy-productivity for two-sided copying by shortening a period of time needed between the completion of copying on the first side of the recording sheet and the start of copying on the second side thereof. According to the present invention there is provided an automatic duplex recording apparatus comprising: (a) processing means for forming a toner image on a recording sheet, (b) feed means for feeding the recording sheet to said processing means for forming the toner image on a first side of said recording sheet, (c) first detection means for detecting the completion of feeding of the recording sheet from said feed means, (d) duplex means including stacking means for receiving and reversing the recording sheet on which a toner image has been formed on a first side thereof, said duplex means refeeding the recording sheet to the processing means for forming a toner image on a second side of the recording sheet, (e) second detection means for detecting that at least one recording sheet stacked on said stacking means included in said duplex means is ready to be fed, and (f) control means for generating a start timing signal for starting refeeding of the recording sheet stacked on said stacking means when the first detection means detects that the feeding means has completed feeding a preset quantity of recording sheets and the second detection means detects that the recording sheet stacked on said stacking means is ready to be fed, said duplex means starting refeeding in response to the thus generated start timing signal. In an automatic duplex recording apparatus of the invention, the detection output by means of the feeding state detection means is generated when it is detected that the recording sheets in the number of copies set have been conveyed from the sheet feeding section in a main body, and the detection output by means of the refeeding state detection means is generated when refeeding of at least one of the recording sheets stacked on the automatic duplex unit is possible. The timing control means, after receiving both detection output, gives instructions for the start of refeeding to the automatic duplex unit. In this case, since the detection output is generated before all of the recording sheets in the number of copies set have been stacked on the automatic duplex unit, generation of standby time between copying on the first side of the recording sheet and copying on the second side thereof can be limited to the minimum. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 represents a block diagram showing the electric constitution of an automatic duplex recording apparatus that is an example of the invention, Fig. 2 is a structural diagram illustrating the state of operations in the apparatus of the example, Fig. 3 is a time chart illustrating the state of operations in the apparatus of the example, Fig. 4 is a time chart illustrating the state of other operations in the apparatus of the example, Fig. 5 is a flow chart showing the operations in an automatic duplex recording apparatus of the example shown in Fig. 1, and Fig. 6 is a time chart illustrating the copy-productivity of a conventional automatic duplex copying apparatus. DESCRIPTION OF THE PREFERRED EMBODIMENT Examples of the invention will be explained in detail as follows, referring to the drawings. First, the outline of the operations in an electrophotographic copying recording apparatus to which the invention is applied will be explained, referring to Fig. 2. In Fig. 2, document 1 placed on reversible automatic document feeder (hereinafter referred to as RADF) 10 is moved onto platen glass 2 by RADF 10 at the start of copying. Document 1 placed on platen glass 2 is exposed to light by means of scanning exposure optics unit 20, and thereby a latent image corresponding to document 1 is formed on photoreceptor 30. This latent image is converted to a toner image on the surface of photoreceptor 30 by photoreceptor image forming section 3. The toner image is transferred onto recording sheet 41 supplied from sheet feeding unit 40 which will be described later, and transferred toner image is heated and fixed by fixing unit 50. The recording sheet thus copied on its first side is led to automatic duplex unit (hereinafter referred to as ADU) 80 by sheet ejection switching section 70. Then, the second side of the recording sheet reversed by ADU 80 and conveyed to photoreceptor 30 again, is subjected to copying (formation of toner image). After the toner image is fixed, the recording sheet is ejected to the outside of the apparatus by means of sheet ejection switching section 70. Next, referring to Fig. 1 showing the electrical structure of the apparatus in the present example, aforesaid Fig. 2 and Figs. 3 - 5 showing the flow of operations in the apparatus in the present example, the sequence of operations along the flow of sheet feeding in the present example will be explained successively. First, setting of mode such as the number of copies, recording sheet size, magnification and final ejection position are made on the operation setting section (not shown) (step (1)). After documents are set on RADF 10 and a copy button is pressed, copying is started. As stated above, recording sheet 41 is fed to photoreceptor 30 from sheet feeding unit 40 (step (3)). On the sheet feeding unit 40, there are provided three sheet cassettes 42a - 42c capable of holding three types of recording sheets 41a - 41c in different sizes, for example. Recording sheets 41a - 41c are fed out from sheet cassettes 42a - 42c by feed-out rollers 43a - 43c and feed-out belts 44a - 44c. Feed-out belts 44a - 44c are spread over feed-out rollers 43a - 43c respectively, and when feed-out rollers 43a - 43c rotate clockwise (Fig. 2) under the condition that recording sheets 41a - 41c are in contact with feed-out belts 44a - 44c respectively, the recording sheets 41a - 41c each positioned on the top is fed out leftward in Fig. 2 sheet by sheet. Recording sheets 41a - 41c fed out by feed-out belts 44a - 44c are conveyed to the position P2 (Fig. 2) by means of sheet feeding roller 61 and registration roller 62. From the position P2, the recording sheet is fed out by registration roller 62 after being synchronized with photoreceptor 30, and then a toner image is transferred onto the recording sheet from the surface of photoreceptor 30 (copying on the first side: step (4)). After the aforesaid step, in the case of one-side copying, the recording sheet is subjected to heating and fixing in fixing unit 50 and then ejected to the outside of the apparatus from sheet ejection switching section 70, thus, copying is completed. In the case of duplex copying, refeeding (step (7)) of recording sheets stacked in ADU 80 is carried out as stated below. Downstream the fixing unit 50, there is provided sheet ejection switching section 70 which has a function for switching to sheet ejection path 76 that leads recording sheet 41 after fixing straight to the outside of the apparatus or to introduction path 77 for guiding the recording sheet to guide plate 71 for duplex copying. The sheet ejection switching means 70 is composed of guide plate 71, upstream roller 72, downstream roller 73, movable separating body 75 which is of an inverse triangle shape in its section and swivels with shaft 74 as a fulcrum, and an electromagnetic solenoid (not shown). Due to the movable separating body 75 whose section is an inverse triangle, sheet ejection path 76, introduction path 77 connected to guide plate 71 along the right side, and reversing sheet ejection path 78 which connects guide plate 71 to downstream roller 73 along the left side are formed. The movable separating body 75, being driven by a driving unit such as an electromagnetic solenoid (not shown), moves its right tip up and down and switches by opening introduction path 77 and closing sheet ejection path 76 or by closing introduction path 77 and opening sheet ejection path 76. The recording sheet 41 fed down to the lower portion (Fig. 2) through sheet ejection switching section 70 is fed into ADU 80 (loading in ADU; step (5)). The recording sheet 41 conveyed to automatic duplex unit 80 is reversed against stacker 83 and ejected. In this case, the trailing edge of the recording sheet is detected by stack sensor 84 composed of a photosensor or the like. Incidentally, the stack sensor 84 forms a refeeding state detection means. Ejected recording sheet 41 slides on the surface of stacker 83 and stops when it hits a stopper plane. Successive recording sheets 41 fed into in succession are stacked on stacker 83 one after another and hit the stopper plane, thus the leading edges of recording sheets 41 are aligned. Under the condition mentioned above, when the signals for the start of refeeding are generated at ADU controlling unit 114, roller 85 is driven by ADU driving section 123 for rotation and multi-feed prevention roller 86 rotates counterclockwise. Thereby, a plurality of recording sheets 41 stacked on stacker 83 are fed out successively sheet by sheet beginning with the lowermost sheet. The recording sheet 41 is further conveyed by sheet feeding roller 87 and sheet feeding roller 87' both of which are in pressure-contact with each other and rotate, and passage of the leading edge of recording sheet 41 is detected by ADU passage sensor 88 composed of a photosensor. The recording sheet 41 is further conveyed and fed into registration roller 62 (step (7)). After that, the recording sheet is subjected to copying on its second side (reverse side) at photoreceptor 30 (step (8)), and after being processed for fixing by fixing unit 50, passes through reversing sheet ejection processing section 76 of sheet ejection switching section 70 and then is ejected to the outside of the apparatus. In the manner mentioned above, first recording sheet 41, after sheet refeeding, is copied on its reverse side. After that, the signals for the start of refeeding are inputted and thereby refeeding for the next recording sheet 41 that is on standby on stacker 83 is started. After that, aforesaid refeeding action and reverse side copying action are repeated for the number of N which is the number of copies set. Incidentally, when stack sensor 84 detects the passage of N sheets and ADU passage sensor 88 does not count N sheets, jam-clearing (step (11)) is to be conducted because an occurrence of jamming is considered. When documents exist in RADF 10, actions mentioned above are to be repeated (step (13) - step (4)). Now, the specific features of the present example will be explained as follows, referring to Fig. 3. When the stack of the first document is detected by stack sensor 84 (first ready condition; Fig. 3 (f)), and passage sensor 63 (63a - 63c in Fig. 2) detects the passage of N sheets that is the number of copies set (second ready condition; Fig. 3 (c)), timing control means 111 gives instructions for sheet refeeding to ADU 80 (Fig. 3 (g)). Under the constitution mentioned above, the timing of refeeding from ADU 80 is advanced and consequently, no waiting time between the first side copying and the second side copying is created as shown in Fig. 3 (i). Incidentally, in Fig. 3, the number of copies set is large to some extent and the stack detection is ahead of the completion of the first side sheet feeding. When the number of copies set is small, the completion of the first side sheet feeding is ahead of the stack detection as shown in Fig. 4. In any case, it is possible to limit useless waiting time to the minimum because the start of copying on the second side is instructed when both conditions become ready. As a result, it is possible to improve the copy-productivity in duplex copying. Incidentally, useless waiting time is actually limited to the minimum in the occasion wherein the recording sheet coming from ADU 80 through refeeding arrives at registration roller 62 immediately after the last recording sheet in the number of copies set for the first side copying passes through the registration roller 62 under aforesaid instruction of timing. In that occasion, it is possible to adjust positions of sensors and to adjust timing by means of a timer. As stated above in detail, an automatic duplex recording apparatus of the invention wherein the recording sheet copied on its one side is reversed by an automatic duplex unit and the recording sheet fed out from the automatic duplex unit is copied on its second side is provided with; a feeding state detection means which detects that recording sheets in the number of copies set have been conveyed from the sheet feeding section in a main body, a refeeding state detection means which detects that refeeding of at least one of stacked recording sheets in the automatic duplex unit is possible, and a timing control means which receives detection output from both a feeding state detection means and a refeeding state detection means and gives instructions for the start of refeeding to the automatic duplex unit. Due to the foregoing, the detection output by means of the feeding state detection means is generated when it is detected that the recording sheets in the number of copies set have been conveyed from the sheet feeding section in a main body, and the detection output by means of the refeeding state detection means is generated when refeeding of at least one of the recording sheets stacked on the automatic duplex unit is possible. The timing control means, after receiving both detection output, gives instructions for the start of refeeding to the automatic duplex unit. In this case, since the detection output is generated before all of the recording sheets in the number of copies set have been stacked on the automatic duplex unit, generation of standby time between copying on the first side of the recording sheet and copying on the second side thereof can be limited to the minimum. Therefore, it is possible to realize an automatic duplex recording apparatus wherein a period of time from completion of copying on the first side of a recording sheet to the start of copying on the second side thereof is shortened, and thereby copy-productivity can be improved.

Claims: An automatic duplex recording apparatus comprising: (a) processing means (3) for forming a toner image on a recording sheet (41), (b) feed means (40) for feeding the recording sheet (41) to said processing means (3) for forming the toner image on a first side of said recording sheet (41), (c) first detection means (63) for detecting the completion of feeding of the recording sheet (41) from said feed means (40), (d) duplex means (80) including stacking means (83) for receiving and reversing the recording sheet (41) on which a toner image has been formed on a first side thereof, said duplex means (80) refeeding the recording sheet (41) to the processing means (3) for forming a toner image on a second side of the recording sheet (41), (e) second detection means (84) for detecting that at least one recording sheet (41) stacked on said stacking means (83) included in said duplex means (80) is ready to be fed, and (f) control means (111) for generating a start timing signal for starting refeeding of the recording sheet (41) stacked on said stacking means (83) when the first detection means (63) detects that the feeding means (40) has completed feeding a preset quantity of recording sheets (41) and the second detection means (84) detects that the recording sheet (41) stacked on said stacking means (83) is ready to be fed, said duplex means (80) starting refeeding in response to the thus generated start timing signal. The apparatus of claim 1, wherein said duplex means (80) begins refeeding a previously stacked recording sheet while the toner image is being formed on the first side of another recording sheet. The apparatus of claim 1, further comprising an automatic document feeder (10) being capable of reversing a document therein. The apparatus of claim 1, wherein two-sided recording is conducted such that a preset quantity of recording corresponding to a second side of a document are made on the second side of each recording sheet after the preset quantity of recording corresponding to a first side of a document are made on the first side of said each recording sheet.

Inventors: MIZUBATA TSUYOSHI, NISHIKI AKIHIKO, YAMADA YASUSHI, MIZUBATA, TSUYOSHI,, NISHIKI, AKIHIKO,, YAMADA, YASUSHI,, MIZUBATA, TSUYOSHI,C/O KONICA CORPORATION, NISHIKI, AKIHIKO,C/O KONICA CORPORATION, YAMADA, YASUSHI, C/O KONICA CORPORATION
Applicants: KONISHIROKU PHOTO IND, KONICA CORPORATION
Application year: 1991
Main classification: G03G15
IPC codes: G03G15