Image forming apparatus

Abstract

To suppress productivity reduction when performing printing according to consecutive print jobs.SOLUTION: An image forming apparatus 100 comprises: a media sensor 280 configured to detect sheet characteristics of sheets conveyed from a manual feed tray; an image forming unit 320 configured to form an image on the sheet on the basis of a print job; and a control unit 300 configured to cause the image forming unit 320 to form an image under operating conditions based on the sheet characteristics detected by the media sensor 280. The control unit 300 performs image formation on both surfaces of the plurality of sheets on the basis of a first print job, and when performing image formation on the sheet on the basis of a second print job following the first print job, if first operating conditions of the first print job differ from second operating conditions of the second print job based on the detection results of the media sensor 280, performs image formation on a first sheet and a second sheet of the first print job, and performs image formation on a third sheet of the second print job after completing the image formation in the first print job.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a printer, a copier, or a multifunction peripheral that is equipped with a media sensor that detects paper characteristics such as the surface texture and thickness of paper being conveyed. [Background technology]

[0002] An electrophotographic image forming device feeds paper one sheet at a time from a paper feed section such as a paper feed cassette or manual feed tray, and prints an image on the fed paper. Each type of paper has different paper characteristics, such as surface texture and thickness. The image forming device determines the operating conditions for image formation control (feeding, development, transfer, fixing control, etc.) according to the paper characteristics, and then prints on the paper. The operating conditions include, for example, the paper transport speed, bias voltage during development, transfer bias during transfer, fixing temperature, and image creation speed.

[0003] In addition to being manually set by the user, paper characteristics can also be automatically set using a media sensor installed on the paper transport path. Image forming devices equipped with a media sensor can use the media sensor to determine the paper characteristics of the paper being transported and automatically determine the operating conditions for image formation control based on the paper characteristics (Patent Document 1). Such image forming devices transport a single sheet of paper to detect the paper characteristics when replacing paper, starting up, or returning from a power-saving mode that reduces standby power consumption, and then determine the operating conditions based on the detected paper characteristics. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-62122 Summary of the Invention [Problem to be solved by the invention]

[0005] When printing using consecutive print jobs, if the paper characteristics of the paper for the preceding print job differ from those of the paper for the following print job, the operating conditions, such as the image creation speed setting, may be switched. Furthermore, if double-sided printing is performed in the preceding print job, alternate paper feeding may be performed, in which imaging on the front side of the paper for the following print job begins before printing on the back side of the paper for the preceding print job is completed. In this case, the image creation speed corresponding to the paper for the preceding print job must be switched to the image creation speed corresponding to the paper for the following print job, and vice versa. This may result in a decrease in productivity.

[0006] SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is a primary object of the present invention to provide an image forming apparatus that suppresses a decrease in productivity when printing in accordance with successive print jobs. [Means for solving the problem]

[0007] The image forming apparatus of the present invention comprises a paper feeding means on which paper is placed, a transporting means for transporting the paper from the paper feeding means, a detection means for detecting paper characteristics of the paper transported by the transporting means, an image forming means for forming an image on the paper, and a control means for causing the image forming means to form an image under operating conditions based on the paper characteristics detected by the detection means, wherein the control means forms images on both sides of a plurality of papers based on a first print job, and when forming images on papers based on a second print job following the first print job, if the first operating conditions of the first print job based on the detection results by the detection means and the second operating conditions of the second print job based on the detection results by the detection means are the same, the control means forms an image on a third paper of the second print job between the image formation on the first paper of the first print job and the image formation on the second paper, and if the first operating conditions and the second operating conditions are different, the control means forms an image on the first paper of the first print job and the image formation on the second paper, and then forms an image on the third paper of the second print job after the image formation in the first print job is completed. [Effects of the Invention]

[0008] According to the present invention, it is possible to suppress a decrease in productivity when printing according to successive print jobs. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Figure 2] FIG. [Figure 3] FIG. 1 is a diagram illustrating the configuration of a media sensor. [Figure 4] FIG. 10 is an explanatory diagram of a result of paper discrimination. [Figure 5] FIG. [Figure 6] FIG. [Figure 7] FIG. 10 is a diagram illustrating an example of a selection screen. [Figure 8] FIG. 10 is a diagram illustrating an automatic setting screen. [Figure 9] FIG. [Figure 10] 10 is a flowchart showing a process for setting paper feed stage information. [Figure 11] An explanatory diagram of the imaging order and paper spacing during double-sided printing. [Figure 12] FIG. 4 is an explanatory diagram of a paper position in an image forming apparatus during double-sided printing. [Figure 13] An explanatory diagram of the imaging order and paper spacing during double-sided printing. [Figure 14] An explanatory diagram of the imaging order and paper spacing during double-sided printing. [Figure 15] An explanatory diagram of the imaging order and paper spacing during double-sided printing. [Figure 16] FIG. 4 is an explanatory diagram of the order of printing processing. [Figure 17] FIG. 4 is an explanatory diagram of the order of printing processing. [Figure 18] 10 is a flowchart showing a printing process. [Figure 19] 10 is a flowchart showing an automatic media detection process. [Figure 20] 10 is a flowchart illustrating a page merging process. [Figure 22] 10 is a flowchart illustrating a page skip process. [Figure 21] FIG. 10 is another configuration diagram of the media sensor. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0011] 1 is a diagram showing the configuration of an image forming apparatus according to this embodiment. The image forming apparatus 100 includes a scanner unit 101 and a UI (User Interface) 330 at its top. Such an image forming apparatus 100 can be realized by, for example, a copier, a multifunction peripheral, or an MFP (Multi Function Peripheral).

[0012] The scanner unit 101 reads an original document, for example, when copying or sending a facsimile. The scanner unit 101 transmits image data indicating the read image (original image) to the image forming apparatus 100. When copying, the image forming apparatus 100 prints an image on paper based on the image data acquired from the scanner unit 101.

[0013] The UI 330 is an operation unit having an input interface and an output interface. The UI 330 includes various key buttons such as a numeric keypad 331, a start key 332, and a stop key 333, as well as a touch panel, etc. as input interfaces. The UI 330 includes a display 334, a speaker, etc. as output interfaces. A user can input various instructions and settings to the image forming apparatus 100 using the UI 330. The UI 330 can display on the display 334 a screen for inputting instructions and settings to the image forming apparatus 100, and a screen showing the status of the image forming apparatus 100.

[0014] Image forming apparatus 100 includes laser scanner unit 110, process unit 120, primary transfer unit 121, transfer belt 130, secondary transfer unit 140, fixing unit 170, paper feed unit, and feed mechanism 1000 that feeds paper. The paper feed unit includes paper feed cassettes 150 and 220 that store paper, and a manual feed tray 210 on which paper is placed. Image forming apparatus 100 transfers an image (toner image) formed by process unit 120 and laser scanner unit 110 onto paper fed by feed mechanism 1000 using primary transfer unit 121, transfer belt 130, and secondary transfer unit 140. Image forming apparatus 100 fixes the toner image to the paper using fixing unit 170. The paper on which the image has been printed in this manner is discharged to paper discharge outlet A200, paper discharge outlet B196, or paper discharge outlet C199.

[0015] The process unit 120 includes a photosensitive drum, a developing device, a charging roller, a photosensitive drum cleaner, etc. In the process unit 120, the surface of the photosensitive drum is charged by the charging roller, and then irradiated with laser light from the laser scanner unit 110. As a result, a latent image is formed on the surface of the photosensitive drum. The laser scanner unit 110 irradiates the photosensitive drum with laser light modulated based on image data acquired from the scanner unit 101 or an external personal computer, etc. As a result, a latent image based on the image data is formed on the photosensitive drum.

[0016] The latent image formed on the photosensitive drum is developed with toner in a developing unit. By developing, an image (toner image) is formed on the photosensitive drum. The process unit 120 of this embodiment has four photosensitive drums to form a color image. Toner images of different colors are formed on the four photosensitive drums. In this embodiment, toner images of yellow (Y), magenta (M), cyan (C), and black (K) are formed on the four photosensitive drums. When forming a monochrome image, only a black toner image is formed.

[0017] A primary transfer voltage is applied to the toner images on the photosensitive drums in primary transfer section 121, and the toner images are transferred to transfer belt 130. The four photosensitive drums sequentially transfer the toner images onto transfer belt 130. The toner images of each color are superimposed on top of each other on transfer belt 130. The toner images of each color transferred to transfer belt 130 are transported to secondary transfer section 140 by the rotation of transfer belt 130. After the toner remaining on the photosensitive drums after transfer is removed by a photosensitive drum cleaner, the photosensitive drums are used for the next image forming operation.

[0018] When the process unit 120 starts an image forming operation, sheets of paper are set in the paper feed cassettes 150 and 220 and the manual feed tray 210, which are paper feed units, and are then fed. The fed sheets are transported to the secondary transfer unit 140 via a transport path 42. Sheets stored in the paper feed cassette 150 are fed to a transport path 41 by a pickup roller 151. Transport rollers A 153, B 154, and C 155, as well as a pre-registration transport roller 161, are provided on the transport paths 42 and 41 from the paper feed cassette 150 to the secondary transfer unit 140 to transport the fed sheets. Sheets placed on the manual feed tray 210 are fed to a transport path 40 by the pickup roller 211. Transport rollers C 155 and a pre-registration transport roller 161 are provided on the transport paths 40 and 42 from the manual feed tray 210 to the secondary transfer unit 140 to transport the fed sheets. The pre-registration transport rollers 161 transport the paper to the secondary transfer unit 140 in synchronization with the timing at which the toner image carried on the transfer belt 130 is transported to the secondary transfer unit 140 .

[0019] A pickup sensor 152 is provided between the pickup roller 151 and the conveyance roller A 153. A manually fed paper presence / absence detection sensor 214 is provided at the base end of the manual feed tray 210. A media sensor 280 is provided on the conveyance path 40. A first conveyance sensor 160 is provided on the conveyance path 42 between the conveyance roller C 155 and the pre-register conveyance roller 161.

[0020] The secondary transfer unit 140 transfers the toner images of each color onto the paper all at once by applying a secondary transfer voltage to the paper and the toner images. The paper onto which the toner images have been transferred by the secondary transfer unit 140 is transported to the fixing unit 170. A transport belt 190 is provided between the secondary transfer unit 140 and the fixing unit 170, and the paper is transported to the fixing unit 170 by the transport belt 190.

[0021] The fixing unit 170 applies heat and pressure at a predetermined fixing temperature to the paper sheet onto which the toner image has been transferred while sandwiching and transporting the paper sheet, thereby melting and fixing the toner image to the paper sheet. This fixes the image to the paper sheet. The paper sheet with the fixed image is transported to one of transport path C234, transport path B231, or transport path A230. For this purpose, flappers A172 and B182 are provided downstream of the fixing unit 170 in the paper transport direction. Transport roller D162 and second transport sensor 171 are provided between the fixing unit 170 and flappers A172 and B182.

[0022] A paper discharge roller 180 is provided on the conveying path C234. The paper discharge roller 180 discharges the paper to the paper discharge outlet A200. A conveying path D181 is connected to the conveying path B231. The conveying path D181 branches into a paper discharge path A193 to the paper discharge outlet B196 and a paper discharge path B184 to the paper discharge outlet C199. A flapper 183 is provided at the branch point between the paper discharge path A193 and the paper discharge path B184. A conveying roller E232, a paper discharge roller A241, and a paper discharge roller B242 are provided on the conveying path B231 and the conveying path D181.

[0023] Discharge path A193 is provided with discharge rollers C243 and a first discharge sensor 195. The paper transported to discharge path A193 by flapper 183 is discharged to discharge outlet B196 by discharge rollers C243. Discharge path B184 is provided with discharge rollers D244, E245, F246, and a second discharge sensor 197. The paper transported to discharge path B184 by flapper 183 is discharged to discharge outlet C199 by discharge rollers D244, E245, and F246.

[0024] The conveying path A230 is provided with a reversing roller 163, a double-sided conveying roller A164, a double-sided conveying roller B165, a double-sided conveying roller C166, and a double-sided conveying roller D179. A double-sided reversing conveying path 233 is connected to the conveying path A230. The double-sided reversing conveying path 233 is provided with a double-sided conveying roller E168.

[0025] For example, when a sheet is discharged to the sheet discharge port A200 with the print side facing down during single-sided printing, the reversing roller 163 reverses its rotation direction just before the rear end of the sheet guided by the flapper A172 to the conveyance path A230 passes through the reversing roller 163. This causes the sheet to be conveyed toward the sheet discharge roller 180. Also, when a sheet of paper after printing on its first side has been completed during double-sided printing is conveyed to the double-sided reversing conveyance path 233, the reversing roller 163 conveys the sheet without reversing its rotation direction. The sheet is conveyed to the double-sided reversing conveyance path 233 via the reversing roller 163, double-sided conveyance roller A164, double-sided conveyance roller B165, double-sided conveyance roller C166, double-sided conveyance roller D179, and double-sided conveyance roller E168.

[0026] A duplex conveying path 235 for conveying paper to the conveying path 41 is connected to the duplex reversing conveying path 233. After being conveyed to the duplex reversing conveying path 233, the conveying direction of the paper is reversed and the paper is conveyed to the duplex conveying path 235. For this purpose, a flapper 178 is provided at the branching point of the duplex conveying path 235. The duplex conveying path 235 is provided with duplex conveying rollers F169, G175, H176, and I177. The duplex reversing conveying path 233 and the duplex conveying path 235 are also provided with a plurality of sensors for detecting paper.

[0027] When a sheet of paper is transported to the duplex reversing transport path 233 during double-sided printing, its transport is temporarily stopped when its trailing edge passes through the duplex transport rollers D179. The duplex transport rollers E168 reverse their rotation direction and transport the sheet in the opposite direction. The flapper 178 guides the sheet to the duplex transport path 235. The sheet guided to the duplex transport path 235 is transported to the transport path 41 by the duplex transport rollers F169, G175, H176, and I177. This series of operations turns the print side of the sheet of paper over, and the second side, opposite to the first side, becomes the print side. The sheet transported to the transport path 41 is then transported to the secondary transfer unit 140, where an image is printed on the second side in the same way as on the first side.

[0028] 2 is an explanatory diagram of a control unit that controls the operation of the image forming apparatus 100 configured as described above. The control unit 300 is built into the image forming apparatus 100. The control unit 300 is an information processing device including a central processing unit (CPU) 301, a read-only memory (ROM) 302, a random access memory (RAM) 303, and a non-volatile memory 304. The control unit 300 also includes a recovery factor monitoring unit 305, a network interface (I / F) 314, a fax interface (I / F) 315, and an image processing unit 316. The image forming unit 320, the UI 330, and the I / O 307 are connected to the control unit 300. The recovery factor monitoring unit 305 monitors factors that cause a print job to return to normal operation, for example, when the print job is interrupted before completion.

[0029] The I / O 307 is connected to various sensors provided in the image forming apparatus 100 and various motors that serve as drive sources for the feed mechanism 1000. The various motors include, for example, a pre-fixing conveyance motor 145, a fixing motor 173, a post-fixing conveyance motor 146, a manual feed conveyance motor 147, a first paper discharge conveyance motor 148, and a second paper discharge conveyance motor 149. The various sensors include, for example, the first conveyance sensor 160, the second conveyance sensor 171, the pickup sensor 152, the first paper discharge sensor 195, the second paper discharge sensor 197, the manual feed paper presence / absence detection sensor 214, and the media sensor 280. The I / O 307 is also connected to various other sensors, such as a fixing motor stable rotation detection sensor 174, a first paper length detection sensor 218, a second paper length detection sensor 219, and a manual feed paper width volume sensor 217.

[0030] The CPU 301 controls the operation of the image forming apparatus 100 by executing a computer program stored in the ROM 302. The RAM 303 provides a work area for the CPU 301 when it executes processing. The CPU 301 acquires detection results from various sensors via the I / O 307, and controls the operation of various motors via the I / O 307 based on the acquired detection results. In this way, the CPU 301 controls paper feeding and the fixing unit 170.

[0031] The CPU 301 of the control unit 300 starts a print operation when, for example, an instruction to start a print operation (hereinafter referred to as a "print job") is input from the UI 330. The CPU 301 can also acquire a print job via the network I / F 314 or the fax I / F 315. The network I / F 314 acquires a print job from an external device such as a personal computer via a network, for example. The fax I / F 315 acquires a print job via facsimile communication.

[0032] The CPU 301 uses an image processing unit 316 to perform image processing on an image to be printed in accordance with a print job. The image processing unit 316 performs image processing such as image expansion and rotation. The CPU 301 uses an image forming unit 320 to control the operation of each component in the image forming apparatus 100, thereby printing the image on paper. The image forming unit 320 can control the application and drive of high voltages to the process unit 120, transfer belt 130, secondary transfer unit 140, etc. shown in FIG. 1, and can also control the laser scanner unit 110. The image forming unit 320 can also control the heater of the fixing unit 170 shown in FIG. 1.

[0033] Upon receiving the print job, the CPU 301 interprets the print job and starts the printing operation. After starting the printing operation, the CPU 301 performs a paper feeding operation.

[0034] When feeding paper from paper feed cassette 150, CPU 301 drives pre-fixing conveyance motor 145 via I / O 307 to rotate pickup roller 151. As pickup roller 151 rotates, paper sheets in paper feed cassette 150 are fed one by one. At this time, CPU 301 determines whether the paper feeding operation was successful or not based on the detection result of pickup sensor 152. When feeding paper from manual feed tray 210, with paper placed on manual feed tray 210, an instruction to transport paper on manual feed tray 210 is input via UI 330. CPU 301 determines whether paper is placed on the manual feed tray based on the detection result of manual feed paper presence / absence detection sensor 214. CPU 301 drives manual feed motor 147 via I / O 307 to rotate pickup roller 211. As pickup roller 211 rotates, paper on manual feed tray 210 is fed one sheet at a time.

[0035] The surface properties, thickness, etc. of the paper fed from manual feed tray 210 are detected by media sensor 280. CPU 301 detects the paper characteristics based on the detection results of media sensor 280, and sets operating conditions for image formation control, such as fixing temperature, transfer voltage, paper conveyance speed, and image creation speed, according to the detected paper characteristics, and performs image formation.

[0036] In parallel with the paper feeding operation, CPU 301 starts the image forming operation by process unit 120 so as to be in time for the paper to arrive at secondary transfer unit 140. The image forming operation by process unit 120 is as described above.

[0037] CPU 301 detects the position of the paper being transported by transport rollers A 153, B 154, and C 155 based on the detection result of first transport sensor 160. Based on the timing at which first transport sensor 160 detects the leading edge of the paper, CPU 301 controls the transport of the paper so that the leading edge of the paper and the leading edge of the toner image on transfer belt 130 coincide at secondary transfer unit 140. For example, if first transport sensor 160 detects the paper earlier than the toner image, CPU 301 stops the paper at the position of pre-registration transport rollers 161 for a predetermined time and then resumes transport.

[0038] CPU 301 transfers the toner image onto the paper by applying a secondary transfer voltage to the paper and toner image that have reached secondary transfer unit 140. The paper onto which the toner image has been transferred is transported to fixing unit 170 via transport belt 190. CPU 301 drives the fixing roller of fixing unit 170 using fixing motor 173 to heat and fix the toner image onto the paper. The paper onto which the image has been fixed is then transported further downstream in the paper transport direction.

[0039] When the second conveyance sensor 171 detects the leading edge of the paper after the image has been fixed, the CPU 301 determines whether to convey the paper to conveyance path A230, conveyance path B231, or conveyance path C234, according to the contents of the print job specified in advance via the UI 330. The CPU 301 controls the flappers A172 and B182 depending on the determination result to switch the paper's guide destination. Specifically, in the case of double-sided printing or when the paper is to be discharged print-side down to the paper discharge outlet A200, the CPU 301 switches the flapper A to guide the paper to conveyance path A230. When single-sided printing or double-sided printing is completed, the CPU 301 guides the paper to either conveyance path B231 or conveyance path C234. When the paper is to be discharged to the paper discharge outlet B196 or paper discharge outlet C199, the CPU 301 switches the flapper B182 to guide the paper to conveyance path B231. When the paper is discharged to the paper discharge port A200, the CPU 301 switches between the flapper A172 and the flapper B182 to guide the paper to the transport path C234.

[0040] The CPU 301 drives the conveying rollers D162 and E232 using the post-fixing conveying motor 146 to convey the paper that has been conveyed to the conveying path B231 to the conveying path D181. The CPU 301 drives the paper discharge rollers A241 and B242 using the first paper discharge conveying motor 148 to convey the paper in the direction of the paper discharge outlet B196 and paper discharge outlet C199.

[0041] When discharging the paper to paper discharge port B196, CPU 301 switches flapper 183 to guide the paper to paper discharge path A193, and drives paper discharge rollers C243 with first paper discharge conveyance motor 148 to discharge the paper to paper discharge port B196. When discharging the paper to paper discharge port C199, CPU 301 switches flapper 183 to guide the paper to paper discharge path B184, and drives paper discharge rollers D244, E245, and F246 with second paper discharge conveyance motor 149 to discharge the paper to paper discharge port C199.

[0042] When printing on one side and discharging the paper to the paper outlet A200 with the print side facing downwards, the CPU 301 switches the flapper A172 and controls the rotation of the reversing roller 163 to transport the paper as described above. When printing on the first side of a double-sided print job is complete, CPU 301 switches flapper A172 and guides the paper to double-sided reversing conveyance path 233. To transport the paper to double-sided reversing conveyance path 233, CPU 301 controls the rotation of reversing roller 163, double-sided conveyance roller A164, double-sided conveyance roller B165, double-sided conveyance roller C166, double-sided conveyance roller D179, and double-sided conveyance roller E168. Then, as described above, CPU 301 reverses the rotation of double-sided conveyance roller E168 and controls the rotation of double-sided conveyance roller G175, double-sided conveyance roller H176, and double-sided conveyance roller I177 to transport the paper to conveyance path 41.

[0043] The image specified in the print job is printed on the specified number of sheets of paper. When all the sheets of paper with the printed image have been ejected, the printing operation for the print job is completed. When the entire print job is completed, the CPU 301 displays the completion of the print job on the UI 330.

[0044] (Media Sensor) FIG. 3 is a configuration diagram of the media sensor 280. The media sensor 280 in FIG. 3 is an optical sensor used to detect the surface texture and thickness of paper as paper characteristics. The media sensor 280 includes a media sensor unit 54, an external LED (Light Emitting Diode) 55b as an external light source, a light collecting guide 57d, and an arithmetic and control unit 58. The media sensor unit 54 includes an LED 55a as a light source, phototransistors 56a and 56b as light receiving units, and slits 57a, 57b, and 57c. The arithmetic and control unit 58 controls the operation of the media sensor 280 and performs calculations according to the output values of the phototransistors 56a and 56b.

[0045] When detecting the surface property of the paper S, the media sensor 280 operates as follows. Light emitted from the LED 55a is irradiated through the slit 57a onto the surface of the paper S being transported along the transport path 40. The phototransistor 56a receives the reflected light that is reflected by the surface of the paper S and collected through the slit 57b. The phototransistor 56b receives the reflected light that is reflected by the surface of the paper S and collected through the slit 57c.

[0046] The surface quality of the paper S is determined as follows. Phototransistor 56a receives light diffusely reflected by paper S from light source LED 55a and outputs a diffuse reflection output value corresponding to the amount of diffusely reflected light received. Phototransistor 56b receives light specularly reflected by paper S from light source LED 55a and outputs a specular reflection output value corresponding to the amount of specularly reflected light received. The surface roughness x of paper S is expressed by the following equation using the output values of phototransistors 56a and 56b. Surface roughness x = specular reflection output value / diffuse reflection output value ... (Equation 1)

[0047] Equation 1 utilizes the characteristic that the amount of specularly reflected light increases when the surface property of the paper S is "smooth" and "fine." The calculation control unit 58 performs calculation processing of Equation 1 and transmits a numerical value (surface property x) that quantifies the surface property of the paper S to the CPU 301. The CPU 301 determines the surface property of the paper S using the acquired surface property x and a threshold value for determining surface property. If the surface property x is greater than the threshold value, the surface property is determined to be "smooth" and "fine." If the surface property x is smaller than the threshold value, the surface property is determined to be "rough" and "coarse." Note that, although one threshold value is used in this embodiment, the CPU 301 may use multiple threshold values to determine the surface property in a more detailed manner.

[0048] The thickness of the sheet S is determined as follows: An opening is provided in the transport path 40 for irradiating the sheet S with light from the external LED 55b. Light emitted from the external LED 55b as a light source passes through the light collecting guide 57d and is irradiated onto the back surface of the paper S. At least a portion of this light is transmitted through the paper S. The transmitted light that has passed through the paper S is received by the phototransistor 56a via the slit 57b. The phototransistor 56a outputs a specular transmission output value corresponding to the amount of transmitted light received. The calculation control unit 58 detects the transmittance of the paper S from the specular transmission output value. The calculation control unit 58 sends the detected transmittance to the CPU 301. The thicker the paper S, the lower the transmittance value, and the thinner the paper S, the higher the transmittance value. The thickness of the paper S is determined by this transmittance characteristic.

[0049] The CPU 301 determines the thickness of the sheet S using the acquired transmittance and a threshold value for determining thickness. In this embodiment, the thickness of the sheet S is classified into three types: "thick," "normal," and "thin." To do this, the CPU 301 uses a thickness / thinness discrimination threshold value A and a thickness / thinness discrimination threshold value B as threshold values for determining the thickness. Here, the thickness / thinness discrimination threshold value A is a larger value than the thickness / thinness discrimination threshold value B.

[0050] The CPU 301 determines that the thickness of the sheet S is "thin" if the transmittance is higher than the thickness discrimination threshold A, and determines that the thickness of the sheet S is "thick" if the transmittance is lower than the thickness discrimination threshold B. The CPU 301 determines that the thickness of the sheet S is "normal" if the transmittance is lower than the thickness discrimination threshold A and higher than the thickness discrimination threshold B. Note that, although two thickness discrimination thresholds are used in this embodiment, the CPU 301 may use one thickness discrimination threshold, or may use three or more thickness discrimination thresholds to more finely classify the thickness of the sheet S.

[0051] In this embodiment, the media sensor 280 has been described using an optical sensor as an example, but the sensor is not limited to this as long as it can detect paper characteristics such as the surface texture and thickness of the paper S. For example, the media sensor 280 may be another type of sensor, such as an ultrasonic sensor that uses the reflection or transmission of ultrasonic waves. The surface texture and thickness of the paper S can also be set manually by the user using the UI 330, without using the media sensor 280. For example, the paper characteristics such as the surface texture and thickness of the paper stored in the paper feed cassettes 150 and 220 are set by the UI 330 when the paper is stored. Furthermore, the paper characteristics detected by the media sensor 280 may be at least one of the surface texture and thickness, or a characteristic other than the surface texture and thickness.

[0052] (Media sensor detection result) FIG. 4 is an explanatory diagram of the paper discrimination results obtained by the media sensor 280. In this embodiment, the surface texture 11 has three detection patterns ("fine (smooth)," "standard," and "rough (rough)"), and the paper thickness 12 has three detection patterns ("thin," "normal," and "thick"). The paper type 13 is automatically discriminated from nine types. In this embodiment, the paper types 13 are nine types: "high-quality thin paper," "high-quality plain paper," "high-quality thick paper," "thin paper," "plain paper," "thick paper," "recycled thin paper," "recycled plain paper," and "recycled thick paper." Operating conditions such as the paper transport speed during image formation, bias voltage during development, transfer bias during transfer, fixing temperature, and image creation speed are set corresponding to the paper type 13. In this embodiment, an image creation speed 14 is set as an operating condition. In the example of FIG. 4, there are two types of image creation speed 14 (160 [mm / s] and 320 [mm / s]). The CPU 301 detects the paper characteristics based on the detection results (surface property x, transmittance) obtained from the media sensor 280, and can determine the paper type and image formation speed based on the detected paper characteristics.

[0053] FIG. 5 is an explanatory diagram of paper feed stage information indicating the paper type placed in each paper feed stage of the paper feed unit. The paper feed stages in this embodiment include paper feed cassettes 150 and 220, and manual feed tray 210. Here, paper feed cassette 150 is the first paper feed cassette, and paper feed cassette 220 is the second paper feed cassette. Paper feed stage information indicating the paper type for each paper feed stage is stored in RAM 303. In FIG. 5, paper type 131 for the first paper feed cassette is "high-quality thin paper," and paper type 132 for the second paper feed cassette is "high-quality plain paper." Paper type 133 for paper placed in manual feed tray 210 is not set, and is automatically determined using media sensor 280 ("automatic").

[0054] The procedure for setting the paper type for manual feed tray 210 will be described. The user places paper on manual feed tray 210 and sets the paper type for manual feed tray 210. The user first operates UI 330 to display a setting screen for the paper type for manual feed tray 210 on display 334. Figure 6 is a view showing an example of such a setting screen.

[0055] This setting screen displays a fixed mode selection button 501, a specified each time mode selection button 502, and an OK button 505. The fixed mode selection button 501 is a button for fixing and setting the paper type of paper placed on the manual feed tray 210. The specified each time mode selection button 502 is a button for setting the paper type of paper placed on the manual feed tray 210 every time paper is placed. In the example of FIG. 6, the fixed mode selection button 501 is selected, and a paper type selection button 503 for selecting a fixed paper type and an automatic media selection button 504 for selecting "automatic" as the paper type are selectable. When the paper type selection button 503 is selected via the UI 330, a paper type selection screen is displayed on the display 334. FIG. 7 is a diagram showing an example of such a selection screen.

[0056] This selection screen displays a paper type selection button group 601, an automatic setting button 602, and an OK button 605. The user selects the paper type from the paper type selection button group 601 and the automatic setting button 602 using the UI 330, and presses the OK button 605 to select the paper type. When a selection is made from the paper type selection button group 601, the paper type of the manual feed tray 210 is set to the selected paper type. When the automatic setting button 602 is selected, the paper type of the manual feed tray 210 is set to "automatic." By setting "automatic," the paper type of the paper placed on the manual feed tray 210 is automatically determined using the media sensor 280.

[0057] When OK button 605 on the selection screen in FIG. 7 is pressed, the display on display 334 returns to the setting screen in FIG. 6. The display on paper type selection button 503 shows the content selected on the selection screen in FIG. 7. In this case, "plain paper" is selected on the selection screen, and "plain paper" is displayed on paper type selection button 503. Note that when automatic media selection button 504 is selected on the setting screen in FIG. 6, the paper type for manual tray 210 is set to "automatic" without going through the selection screen in FIG. 7.

[0058] When the automatic media selection button 504 is selected on the setting screen of FIG. 6, the display 334 displays the automatic setting screen shown in FIG. 8. On the automatic setting screen, the conditions for detecting paper by the media sensor 280 can be set. On the automatic setting screen, an "ON every time" button 401, an "Auto" button 402, an "OFF every time" button 403, and an OK button 404 are displayed. The user can set the conditions for detecting paper by selecting either the "ON every time" button 401, the "Auto" button 402, or the "OFF every time" button 403 on the UI 330 and then pressing the OK button 404.

[0059] The "ON every time" button 401 is a button for setting the media sensor 280 to always detect the first sheet of paper fed from the manual feed tray 210 when a print job starts or is resumed after being interrupted. By selecting the "ON every time" button 401, the paper type is always automatically determined when a print job starts or is resumed after being interrupted. "Auto" button 402 is a button for setting the media sensor 280 to detect the first sheet of paper fed from manual feed tray 210 when a print job is executed. When "Auto" is set as the paper detection condition using "Auto" with "Auto" button 402, the first sheet of paper fed from manual feed tray 210 in a print job after paper has been placed on manual feed tray 210 is detected by media sensor 280. Whether paper is placed on manual feed tray 210 is determined based on the detection result of manual feed paper presence / absence detection sensor 214. The "OFF every time" button 403 is a button for setting the media sensor 280 not to detect the first sheet of paper when a print job is started or resumed after being interrupted.

[0060] Fig. 9 is a view showing an example of the setting screen when each time specification mode selection button 502 is selected in Fig. 6. When each time specification mode selection button 502 is selected, the selection screen of Fig. 7 is displayed on display 334 when paper is placed on manual feed tray 210. The user selects the paper type from this selection screen when placing paper on manual feed tray 210. The information set on each of the screens of Figs. 6 to 9 is stored in RAM 303.

[0061] Fig. 10 is a flowchart showing the process of setting the paper feed stage information in Fig. 5. This process shows the process from when paper is placed on manual feed tray 210 to when paper feed stage information is stored in RAM 303.

[0062] CPU 301 waits until paper is placed on manual tray 210 (S201: N). CPU 301 can determine whether paper is placed on manual tray 210 based on the detection result of manual paper presence / absence detection sensor 214. When paper is placed on manual tray 210 (S201: Y), CPU 301 refers to RAM 303 and determines whether the specified mode is set every time (S202). If the "Every Time OFF" button 403 is set on the automatic setting screen of FIG. 8 and the paper type selection button 503 is not set on the setting screen of FIG. 6, CPU 301 determines that the specified mode is set every time because the paper type cannot be identified. The setting of paper type selection button 503 is saved in non-volatile memory 304.

[0063] If the specified mode every time is not set (S202: N), CPU 301 updates paper type 133 of manual tray 210 in the paper feed stage information (S203) based on the settings on the setting screen in Fig. 6. If the paper type is set to "automatic," the paper feed stage information is updated based on the type of paper identified from the detection result of media sensor 280.

[0064] If the specifying mode every time is set (S202: Y), CPU 301 displays the selection screen of FIG. 7 on display 334 (S204). This allows CPU 301 to prompt the user to select the paper type. CPU 301 waits until the paper type is selected from the selection screen and OK button 603 is pressed (S205: N). When OK button 603 is pressed (S205: Y), CPU 301 updates paper type 133 for manual tray 210 in the paper feed stage information based on the paper type selected on the selection screen (S206). This completes the paper feed stage information setting process.

[0065] (Double-sided printing control) 11 to 15 are explanatory diagrams of double-sided printing control according to this embodiment. Here, two print jobs (first print job, second print job) that instruct double-sided printing of multiple pages (multiple sheets of paper) will be described. Note that while the first print job instructs double-sided printing, the second print job may be a job that instructs single-sided printing.

[0066] Figure 11 is an explanatory diagram of the imaging order and paper spacing during double-sided printing. "P*" indicates the paper with page number "*," and "front" and "back" indicate the printing side. For example, "P1 front" indicates that printing will be done on the front side of the paper with page number "1."

[0067] The reason why there is a gap between the "P1 face up" and the "P2 face up" is that the motors used to transport paper to the duplex reversing transport path 233 and the duplex transport path 235 are inexpensive and paper transport cannot be performed at 100% productivity. Also, during double-sided printing, a predetermined number of sheets of paper whose front side has been printed are kept waiting in the duplex transport path 235, and 100% productivity is achieved by alternately feeding paper from the paper feed unit and re-feeding paper from the duplex transport path 235. For this reason, the transport of the first (first page) paper to the duplex reversing transport path 233 and the duplex transport path 235 is performed with a gap between the sheets. There is also a gap between the sheets when paper is re-fed from the duplex transport path 235.

[0068] FIG. 11 illustrates duplex printing using two types of print jobs: a first print job that prints on both sides of sheets P1 to P4, and a second print job that prints on both sides of sheets P5 to P6. When printing on both sides, the first print job is executed first, and the second print job starts while the first print job is executing. As a result, the papers used for the first print job and the second print job are mixed between the front side of P5 and the back side of P4 in the double-sided alternating paper feed section. In the double-sided alternating paper feed section, the first print job that is executed first and the second print job that is executed afterwards are mixed, but if the operating conditions (imaging speed) are the same for both print jobs, 100% productivity can be achieved.

[0069] FIG. 12 is an explanatory diagram of the paper positions within image forming apparatus 100 during double-sided printing for the first and second print jobs. P1 paper is located at (1), P4 paper at (2), P2 paper at (3), P5 paper at (4), and P3 paper at (5). During double-sided printing, paper is alternately fed from the paper feed unit and re-fed from double-sided conveying path 235. At the paper discharge port, flappers A172 and B182 are used to alternately discharge paper to the paper discharge port and convey paper to conveying path A230. In FIG. 12, the paper at (1) is discharged, the paper at (2) is conveyed to double-sided conveying path 235 (double-sided paper re-feeding unit) via conveying path A230, the paper at (3) is discharged, the paper at (4) is placed on manual tray 210 (double-sided paper re-feeding unit), and the paper at (5) is discharged.

[0070] FIG. 13 is an explanatory diagram of the imaging order and paper spacing during double-sided printing when the paper characteristics and operating conditions (imaging speed) of the paper used for the first and second print jobs in FIG. 11 are the same. FIG. 13 shows the imaging order after the double-sided alternating paper feed section. In the case of FIG. 13, printing is performed without reducing productivity while maintaining a constant imaging speed. Each sheet is located at positions (1) to (6) within image forming apparatus 100. Position (6) is the same manual feed tray 210 as position (4), but indicates that the sheet will be placed on manual feed tray 210 next. Positions (1), (2), (3), and (5) contain sheets (P1 to P4) for the first print job, and positions (4) and (6) contain sheets (P5 and P6) for the second print job. In FIG. 13, the shaded areas indicate sheets for the second print job.

[0071] Figure 14 is an explanatory diagram of the imaging order and paper spacing during double-sided printing when the paper characteristics and operating conditions (imaging speeds) of the paper used for the first and second print jobs in Figure 11 are different. (1), (2), and (3) contain the paper (P1, P2, P4) for the first print job, and printing is being performed at 100% productivity. However, while the first print job is being executed, the paper characteristics of the paper (P5) for the first page of the second print job are detected, and the imaging speeds of the first and second print jobs are compared. This reveals that the imaging speeds are different.

[0072] In this case, the paper characteristics of P5 front (4), P3 back (5), P6 front (6), P4 back (2), P5 back, and (4) back are different from those of the previous paper. For this reason, the image creation speed is switched before printing on each paper. As a result, image creation on the next paper is stopped until the previous paper passes through the secondary transfer unit 140 in order to switch the image creation speed (operating conditions). This results in a large gap between papers, resulting in a significant drop in productivity.

[0073] FIG. 15 is an explanatory diagram of the image formation order and paper spacing during double-sided printing when the number of image formation speed changes is reduced compared to FIG. 14. In this embodiment, the preceding print job (in this case, the first print job) is given priority, and the subsequent print job (in this case, the second print job) is postponed. Compared to FIG. 14, the image formation operations for the P5 front and P6 front have been postponed. In other words, the image formation operations, which were previously performed in the order of P2 back side → P5 front side → P3 back side → P6 front side → P4 back side → P5 back side, have been changed to the order of P2 back side → P3 back side → P4 back side → P5 front side → P6 front side → P5 back side, resulting in the second print job being postponed. In this case, the first page of the second print job (P5) stops and waits at the detection position of the media sensor 280.

[0074] 16 and 17 are explanatory diagrams of the order of printing processes for each page of multiple print jobs. In FIG. 16, acquired print jobs are registered in a job management database called submitted job T10. When page data indicating the content of the printing process for each page from the print jobs registered in submitted job T10 is determined, the page data is registered in a job management database called execution job T11. If page data is already registered in execution job T11, the registration is performed by adding it after the last page. Therefore, page data is registered in execution job T11 in the order of printing. The page data includes information indicating the paper feed source (paper feed cassettes 150, 220, manual feed tray 210).

[0075] In Figure 16, the page data (P1 to P4) of the first print job has already been registered in the running job T11, and the page data (P5, P6) of the second print job is added after the page data of the last page (P4) of the first print job. The page data registered in the running job T11 is processed in order from the page data registered first. For this reason, the running job T11 is FIFO (First In First Out).

[0076] In Figure 17, when a change in imaging speed occurs between the previous page and the current job T11 due to differences in paper characteristics, page data for P5 and P6 registered in the current job T11 is moved to the pending job T12. Also, if page data is registered in the pending job T12, new page data for P7 registered in the submitted job T10 is moved to the pending job T12. In this case, the page data for P7 may be for the second print job or another print job. This is a necessary process because if the page data registered in the pending job T12 and deferred processing were to be swapped with the submitted order, the order of the deliverables could not be guaranteed.

[0077] In Figure 17, the paper for the second print job has different paper characteristics from the paper for the first print job, resulting in different operating conditions. To prioritize processing of the first print job, page data for P5 and P6 of the second print job is moved from the running job T11 to the pending job T12. After confirmation, page data for P7 is saved in the pending job T12 without going through the running job T11. The submitted job T10, the running job T11, and the pending job T12 are saved in RAM 303, for example.

[0078] 18 is a flowchart showing the printing process for continuously printing images on both sides of paper. This process starts by acquiring a print job via the UI 330, the network I / F 314, or the fax I / F 315. The acquired print job is registered as an input job T10.

[0079] The control unit 300 waits until the page data of the print job registered in the input job T10 is confirmed (S801: N). When the page data of the print job registered in the input job T10 is confirmed (S801: Y), the control unit 300 registers the confirmed page data in the execution job T11 and starts processing using the page data. First, the control unit 300 determines whether the confirmed page data instructs paper feeding from the manual feed tray 210 (manual paper feed) (S802).

[0080] If paper feed was not performed manually (S802: N), the control unit 300 performs the printing process using the page data while executing the page merging process described below (S803). When the page merging process is completed, the control unit 300 determines whether or not there are subsequent pages (S804). The presence or absence of subsequent pages is determined, for example, by a flag (not shown) indicating that the page data of the print job registered in the input job T10 is the final page. If there are subsequent pages (S804: Y), the control unit 300 repeats the process from S801 onwards. If there are no subsequent pages (S804: N), the control unit 300 ends the process.

[0081] If manual paper feed is selected (S802: Y), the control unit 300 executes the automatic media detection process described below (S805). When the automatic media detection process is completed, the control unit 300 determines whether there is any page data for which printing has been previously performed (S806). The presence or absence of such page data is determined, for example, by whether the preceding page data is registered in the execution job T11. If there is no such page data (S806: N), the control unit 300 performs printing processing using the page data while determining whether there are any subsequent pages (S804). If there are subsequent pages (S804: Y), the control unit 300 repeats the processes from S801 onwards. If there are no subsequent pages (S804: N), the control unit 300 ends the process.

[0082] If there is preceding page data (S806: Y), the control unit 300 determines whether or not it is necessary to change the image creation speed (S807). The control unit 300 detects the paper characteristics based on the detection results of the media sensor 280 and determines the image creation speed according to the paper characteristics. The control unit 300 compares the determined image creation speed with the image creation speed in the print process of the preceding page data. If the comparison shows that the image creation speeds are different, the control unit 300 determines that it is necessary to change the image creation speed.

[0083] If it is determined that a change in the imaging speed is necessary (S807: Y), the control unit 300 executes a page skip process (S808), which will be described later. After the page skip process is completed, the control unit 300 determines whether or not there is a subsequent page (S804). If there is a subsequent page (S804: Y), the control unit 300 repeats the processes from S801 onwards. If there is no subsequent page (S804: N), the control unit 300 ends the process. If it is determined that a change in the imaging speed is not necessary (S807: N), the control unit 300 performs printing processing using the page data, while determining whether or not there is a subsequent page without performing page skip processing (S804). If there is a subsequent page (S804: Y), the control unit 300 repeats the processes from S801 onwards. If there is no subsequent page (S804: N), the control unit 300 ends the process.

[0084] 19 is a flowchart showing the automatic media detection process of S805. The automatic media detection process is a process in which the media sensor 280 detects the characteristics of the paper by detecting the paper.

[0085] The control unit 300 determines whether "OFF every time" is set as the condition for detecting paper by the media sensor 280 (S821). "OFF every time" is set by selecting the "OFF every time" button 403 on the automatic setting screen in Fig. 8. If "OFF every time" is set (S821: Y), the control unit 300 ends the automatic media detection process.

[0086] If "OFF every time" is not set (S821: N), the control unit 300 determines whether "Auto" is set as the condition for detecting paper by the media sensor 280 (S822). "Auto" is set by selecting the "Auto" button 402 on the automatic setting screen in FIG. 8. If "Auto" is set (S822: Y), the control unit 300 determines whether there has been a change in the detection result of the manual paper presence / absence detection sensor 214 since the previous print job was executed (S823). The history of the detection result of the manual paper presence / absence detection sensor 214 is saved in, for example, the RAM 303 or the nonvolatile memory 304. The control unit 300 can determine whether there has been a change in the detection result of the manual paper presence / absence detection sensor 214 based on the execution time of the previous print job and the history of the detection result of the manual paper presence / absence detection sensor 214.

[0087] If there is a change in the detection result of the manual paper presence / absence detection sensor 214 (S823: Y), the control unit 300 feeds one sheet of paper placed on the manual tray 210 (S824). The control unit 300 transports the paper to the detection position of the media sensor 280 and acquires the detection result of the paper by the media sensor 280 (S825). At this time, the paper stops and waits at the detection position of the media sensor 280. Upon acquiring the detection result, the control unit 300 ends the automatic media detection process. The control unit 300 detects the paper characteristics of the paper based on the detection result of the media sensor 280. Note that if there is no change in the detection result of the manual paper presence / absence detection sensor 214 (S823: N), the control unit 300 simply ends the automatic media detection process.

[0088] If "automatic" is not set as the paper detection condition for the media sensor 280 (S822: N), the control unit 300 executes the print job and determines whether or not this is the first manually fed page (S826). If this is the first manually fed page (S826: Y), the control unit 300 feeds one sheet of paper from the manual feed tray 210 (S824), obtains the paper detection result from the media sensor 280 (S825), and ends the automatic media detection process. The control unit 300 detects the paper characteristics of the paper based on the paper detection result from the media sensor 280. If this is not the first manually fed page (S826: N), the control unit 300 ends the automatic media detection process.

[0089] 20 is a flowchart showing the page merging process in S803, which is a process for returning the page data saved in the pending job T12 to the running job T11.

[0090] The control unit 300 determines whether page data is registered in the pending job T12 (S841). If page data is not registered in the pending job T12 (S841: N), the control unit 300 moves the page data registered in the input job T10 to the running job T11 and combines it with the end of the running job T11b (S842), and ends the page combining process. If page data is registered in the pending job T12 (S841: Y), the control unit 300 executes a page skip process (S843), which will be described later, and ends the page combining process.

[0091] Fig. 21 is a flowchart showing the page skip processing of S808 in Fig. 18 and S843 in Fig. 20. As described in Fig. 17, the control unit 300 transfers the page data of the pages after the target page to the pending job T12, combines them at the end of the pending job T12 (S851), and ends the page skip processing.

[0092] When performing another print job consecutively after a print job that instructs double-sided printing, the image forming apparatus 100 of this embodiment performs printing by alternately switching between paper refed from the double-sided conveying path 235 and paper fed from the paper feed unit. This achieves high productivity. If the operating conditions, such as image creation speed, differ between the paper used in the preceding print job and the paper used in the subsequent print job, the print processing of the preceding print job is executed with priority. Therefore, the image forming apparatus 100 can prevent a decrease in productivity even if the operating conditions, such as image creation speed, differ between the paper refed in the preceding print job and the paper fed from the paper feed unit in the subsequent print job.

[0093] The media sensor 280 may be disposed on the transport path 41. In this case, it is possible to detect the characteristics of paper fed from the paper feed cassettes 150 and 220. When paper is waiting for a subsequent print job, the paper will wait on the transport path 41.

[0094] (Another example of a media sensor) FIG. 22 is another configuration diagram of the media sensor 280. The control unit 300 can detect paper characteristics using this media sensor 280. FIG. 22 is a diagram seen from the transport direction of the paper S (the transport roller C155 side). This media sensor 280 has an ultrasonic sensor 281 and an optical sensor 282, and detects the paper characteristics (e.g., surface texture and basis weight) of the paper S. The ultrasonic sensor 281 is made up of an ultrasonic transmitter 2811 and an ultrasonic receiver 2812. The optical sensor 282 is configured as a CIS (Contact Image Sensor) having, for example, a light source 1501 and a line sensor 1502. The light source 1501 uses, for example, an LED.

[0095] When detecting brightness values using the optical sensor 282, it is necessary to hold the paper at the optical focal position. Furthermore, when detecting the paper S using ultrasound, it is necessary to reduce the effect of flapping of the paper S as it is being transported. In order to stabilize the posture of the paper S, a media sensor opposing roller 260 and a paper pressure roller 261 are provided between the pickup roller 211 and the transport roller C155. The media sensor opposing roller 260 is provided opposite the optical sensor 282 and is configured to press the paper S against the optical sensor 282. This reduces variations in the position and posture of the paper S when the media sensor 280 measures the surface of the paper S. Therefore, the media sensor 280 can stably measure the surface properties and basis weight of the paper S.

[0096] 22, the ultrasonic transmitter 2811 is arranged on the upper block 4011 side, and the ultrasonic receiver 2812 is arranged on the lower block 4012 side, with the transport path 40 of the paper sheet S sandwiched between them. The ultrasonic sensor 281 is configured to output information (output voltage) for determining the basis weight of the paper sheet S by transmitting and receiving ultrasonic waves via the paper sheet S. The basis weight here is the mass per unit area of the paper sheet S, and is expressed in [gsm].

[0097] Both the ultrasonic transmitter 2811 and the ultrasonic receiver 2812 are composed of a piezoelectric element (also called a piezo element), which is an element for converting mechanical displacement into an electrical signal, and an electrode terminal. When a pulse voltage of a predetermined frequency is input to the electrode terminal of the ultrasonic transmitter 2811, the piezoelectric element of the ultrasonic transmitter 2811 oscillates, generating ultrasonic waves. The generated ultrasonic waves propagate through the air. When the ultrasonic waves reach the paper S, the paper S vibrates due to the ultrasonic waves. In this way, the ultrasonic waves generated by the ultrasonic transmitter 2811 propagate to the ultrasonic receiver 2812 via the paper S. The piezoelectric element of the ultrasonic receiver 2812 receives the ultrasonic waves propagated via the paper S, and generates an output voltage at the electrode terminal of the ultrasonic receiver 2812 according to the amplitude of the received ultrasonic waves. The ratio of the output voltage when there is no paper S between the ultrasonic transmitter 2811 and the ultrasonic receiver 2812 to the output voltage when there is paper S is the transmittance. Since the ultrasonic transmittance changes depending on the basis weight (area density) of the paper S, the basis weight of the paper S can be estimated using the ultrasonic transmission coefficient-paper basis weight conversion formula.

Claims

1. a paper feed means on which paper is placed; a conveying means for conveying the paper from the paper feeding means; a detection means for detecting paper characteristics of the paper conveyed by the conveyance means; an image forming means for forming an image on a sheet; a control unit that causes the image forming unit to form an image under operating conditions based on the paper characteristics detected by the detection unit, The control means forms images on both sides of a plurality of sheets of paper based on a first print job, and when forming images on sheets of paper based on a second print job following the first print job, if a first operating condition of the first print job based on the detection result by the detection means and a second operating condition of the second print job based on the detection result by the detection means are the same, the control means forms an image on a third sheet of the second print job between the image formation on the first sheet of the first print job and the image formation on the second sheet of the second print job, and if the first operating condition and the second operating condition are different, the control means forms an image on the first sheet of the first print job and the image formation on the second sheet of the first print job, and then forms an image on the third sheet of the second print job after the image formation in the first print job is completed. Image forming device.

2. a first transport path for transporting the paper from the paper feeding means to the image forming means; a second transport path for re-feeding the paper sheet, on which an image has been formed on a first side by the image forming means, to the image forming means by inverting the print surface to a second side opposite to the first side, The detecting means is provided on the first transport path.

2. The image forming apparatus according to claim 1.

3. When an image is formed on the second side of the first sheet by the image forming means, the second sheet is positioned on the second transport path, and the sheet characteristics of the third sheet are detected by the detection means.

3. The image forming apparatus according to claim 2.

4. The control means causes the third sheet to wait at a detection position of the detection means when the first operating condition and the second operating condition are different.

3. The image forming apparatus according to claim 2.

5. The control means when the first operating condition and the second operating condition are the same, the conveying means conveys the third sheet from the detection position of the detection means to the image forming means, and then conveys the second sheet from the second conveying path to the image forming means; When the first operating condition and the second operating condition are different, the conveying means conveys the second sheet from the second conveying path to the image forming means, and then conveys the third sheet from the detection position of the detection means to the image forming means.

3. The image forming apparatus according to claim 2.

6. when the first operating condition and the second operating condition are different, the control means, after having conveyed the second sheet of paper from the second conveying path to the image forming means by the conveying means, changes the operating condition from the first operating condition to the second operating condition, and conveys the third sheet of paper from the detection position of the detection means to the image forming means by the conveying means.

6. The image forming apparatus according to claim 5.

7. When the first operating condition and the second operating condition are different, after image formation on both sides of the plurality of sheets of paper by the first print job is completed, the control means changes the operating condition from the first operating condition to the second operating condition and starts feeding of sheets by the second print job.

2. The image forming apparatus according to claim 1.

8. the control means causes the image forming means to form an image of the first print job under operating conditions based on the paper characteristics of the first paper of the first print job, and acquires the paper characteristics of the first paper of the second print job from the detection means during execution of the first print job, and compares the operating conditions of the first print job and the second print job.

2. The image forming apparatus according to claim 1.

9. The operating condition is an image forming speed.

2. The image forming apparatus according to claim 1.

Images