Image forming apparatus, control method, and program

Abstract

To enable appropriately detecting kinds of sheets without largely reducing through-put when a plurality of sheets is continuously conveyed.SOLUTION: An image formation device 1 comprises: an environment sensor 19 that acquires environment information; a storage unit 41 that stores the environment information the environment sensor 19 acquires; a conveyance unit 2 that conveys a sheet; a detection sensor 30 that detects a physical property value of the sheet conveyed by the conveyance unit 2; and a control unit 5 that, when a plurality of sheets is continuously conveyed by the conveyance unit 2, can implement calibration of the detection sensor 30 in between the sheets until a next sheet arrives at a detection position by the detection sensor 30 since a previous sheet passes the detection position thereby. The control unit 5 is configured to determine whether to implement the calibration in between next sheets on the basis of the environment information to be acquired by the environment sensor 19, and past environment information stored in the storage unit 41.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to an image forming apparatus, a control method, and a program.

Background Art

[0002] An image forming apparatus such as an MFP (Multifunction Peripherals) includes a sheet storage unit capable of storing a plurality of sheets such as printing paper, conveys the sheets one by one from the sheet storage unit, and forms an image on the conveyed sheet and outputs it. In this type of image forming apparatus, the types of sheets used for image formation are various. The image forming apparatus can form a high-quality image on the sheet by performing an operation suitable for the type of the sheet.

[0003] Conventionally, in an image forming apparatus as described above, there is known one provided with an optical sensor for detecting the type of sheet stored in the sheet storage unit (for example, Patent Document 1). In this conventional technique, light is irradiated onto the sheet stored in the sheet storage unit, the reflected light is detected, and calculations are performed to determine the type of the sheet.

[0004] By the way, it is known that the sensitivity of a sensor such as an optical sensor changes depending on temperature, humidity, etc. Therefore, in order to accurately determine the type of sheet using a sensor such as an optical sensor, it is necessary to perform calibration (calibration process) of the sensor regularly or irregularly. However, in the case immediately after power-on, since the temperature inside the apparatus is low, if the sensor calibration is performed at that timing, when the temperature inside the apparatus rises due to subsequent warm-up or the like, the type of sheet cannot be accurately determined. To prevent this, the image forming apparatus of Patent Document 1 is configured not to perform sensor calibration when the temperature inside the apparatus is low, and to perform sensor calibration when the temperature inside the apparatus rises and is within a predetermined temperature range.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2007-223740 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Different types of sheets may be mixed together in the sheet storage section of an image forming apparatus. For example, if a user replenishes the sheet storage section while there are still sheets remaining, and the type of the replenished sheet differs from the type of the previous sheet, then multiple types of sheets will be mixed in the sheet storage section. Assuming that multiple types of sheets are mixed in the sheet storage section, it is desirable to install a sensor for detecting the type of sheet along the sheet transport path and detect the type of each sheet as it is transported along the path. By adopting such a configuration, it is possible to detect the type of each sheet individually even when multiple sheets are transported continuously, and changes in sheet type can be detected in real time.

[0007] Even when multiple sheets are continuously transported in an image forming apparatus, the environmental conditions inside the apparatus (such as temperature and humidity) may change sequentially. To compensate for changes in sensor sensitivity due to such environmental changes, it is preferable to perform sensor calibration immediately before detecting the type of sheet. In other words, when multiple sheets are continuously transported, it is preferable to perform sensor calibration during the period between when the previous sheet passes the detection position and when the next sheet reaches the detection position.

[0008] When multiple sheets are transported continuously, the image forming apparatus sets a short interval between sheets to improve throughput. For example, when outputting 75 sheets per minute, the sheet interval is approximately 160 ms. When outputting 20 sheets per minute, the sheet interval is approximately 1550 ms.

[0009] In contrast, sensor calibration requires a certain amount of time. For example, sensor calibration takes about 1.8 seconds. Therefore, when multiple sheets are being transported continuously, it is not possible to perform calibration properly at the interval between the previous sheet and the next sheet.

[0010] Therefore, in order to properly calibrate the sensors when multiple sheets are transported in succession, it is necessary to widen the gap between the previous sheet and the next sheet. However, if the sensor calibration is performed every time with the gap between the previous and next sheets widened, there is a problem in that the throughput of the image forming apparatus is significantly reduced.

[0011] The present invention was made to solve the above problems and aims to provide an image forming apparatus, control method, and program that can appropriately detect the type of sheet without significantly reducing throughput. [Means for solving the problem]

[0012] To achieve the above objective, the invention according to claim 1 is an image forming apparatus comprising: an environmental sensor for acquiring environmental information; a storage unit for storing the environmental information acquired by the environmental sensor; a transport unit for transporting sheets; a detection sensor for detecting the physical properties of the sheets transported by the transport unit; and a control unit capable of performing calibration of the detection sensor between sheets when a plurality of sheets are transported continuously by the transport unit, from the time the previous sheet passes the detection position by the detection sensor until the next sheet reaches the detection position, wherein the control unit determines whether or not to perform the calibration between the next sheets based on the environmental information acquired by the environmental sensor and past environmental information stored in the storage unit.

[0013] The invention according to claim 2 is an image forming apparatus according to claim 1, wherein the storage unit stores environmental information acquired by the environmental sensor during the previous calibration execution, and the control unit determines whether or not to perform the calibration based on the environmental information acquired by the environmental sensor after the previous calibration execution and the past environmental information stored in the storage unit, in order to determine the environmental changes since the previous calibration execution.

[0014] The invention according to claim 3 is an image forming apparatus according to claim 2, characterized in that the control unit determines that there has been no change in the environment since the previous calibration was performed, and decides not to perform the calibration between sheets.

[0015] The invention according to claim 4 is an image forming apparatus according to claim 2, characterized in that the control unit determines that there has been a change in the environment since the last calibration was performed, and decides to perform the calibration between the next sheets.

[0016] The invention according to claim 5 is an image forming apparatus according to claim 3 or 4, characterized in that the control unit determines that there is an environmental change when the difference between the first environmental information acquired by the environmental sensor at the time of the previous calibration and the second environmental information acquired by the environmental sensor after the previous calibration has been performed exceeds a predetermined range.

[0017] The invention according to claim 6 is an image forming apparatus according to claim 5, characterized in that the control unit corrects the physical property values ​​of the sheet detected by the detection sensor based on the difference if the difference does not exceed the predetermined range.

[0018] The invention according to claim 7 is an image forming apparatus according to claim 1, characterized in that the environmental sensor includes a temperature sensor and detects the temperature of the transport section.

[0019] The invention according to claim 8 is an image forming apparatus according to claim 1, characterized in that when the control unit decides to perform the calibration between the next sheets, it temporarily suspends the transport operation of the transport unit for the next sheet.

[0020] The invention according to claim 9 is an image forming apparatus according to claim 8, characterized in that the control unit performs the calibration while temporarily suspending the transport operation of the transport unit for the next sheet, and resumes the transport operation of the transport unit for the next sheet after the calibration is completed.

[0021] The invention according to claim 10 is an image forming apparatus according to claim 1, wherein the control unit, in the calibration, causes the detection sensor to perform a detection operation when there is no sheet at the detection position, and corrects the output of the detection sensor based on the result of the detection operation.

[0022] The invention according to claim 11 is an image forming apparatus according to claim 1, characterized in that the control unit determines the conveying speed of the sheet by the conveying unit based on the physical property values ​​of the sheet detected by the detection sensor.

[0023] The invention according to claim 12 is an image forming apparatus according to claim 1, further comprising an image forming unit that forms an image on a sheet conveyed by the conveying unit, wherein the control unit determines image forming parameters to be set in the image forming unit based on the physical property values ​​of the sheet detected by the detection sensor.

[0024] The invention according to claim 13 is an image forming apparatus according to claim 1, wherein when a plurality of sheets are continuously conveyed by the conveying unit, the control unit causes the detection sensor to detect the physical property value of the sheet each time the sheet passes through the detection position.

[0025] The invention according to claim 14 is an image forming apparatus according to claim 13, wherein when the physical property value of the sheet detected by the detection sensor changes, the control unit sets the conveyance speed of the first sheet conveyed by the conveyance unit at the start of the next job to the first speed, and when the sheet conveyed at the first speed passes through the detection position, causes the detection sensor to detect the physical property value of the sheet a predetermined number of times, and sets the conveyance speed of the sheets conveyed thereafter to the second speed higher than the first speed based on the physical property values of the sheets detected a predetermined number of times.

[0026] The invention according to claim 15 is an image forming apparatus according to claim 1, wherein the control unit sets the conveyance speed of the first sheet conveyed by the conveyance unit to the first speed, causes the detection sensor to detect the physical property value of the sheet a predetermined number of times when the sheet conveyed at the first speed passes through the detection position, sets the conveyance speed of the second and subsequent sheets to the second speed higher than the first speed based on the physical property values of the sheets detected a predetermined number of times, and causes the detection sensor to detect the physical property value of the sheet a number of times less than the predetermined number when the sheet conveyed at the second speed passes through the detection position.

[0027] The invention according to claim 16 is an image forming apparatus according to claim 15, wherein the control unit sets the conveyance speed of the first sheet conveyed by the conveyance unit to the first speed when the sheet bundle is replenished or when the execution of the job is started.

[0028] The invention according to claim 17 is an image forming apparatus according to claim 1, wherein the detection sensor is constituted by an optical sensor or an ultrasonic sensor.

[0029] The invention according to claim 18 is a control method for an image forming apparatus comprising: an environmental sensor for acquiring environmental information; a transport unit for transporting sheets; and a detection sensor for detecting the physical properties of sheets transported by the transport unit, wherein, when a plurality of sheets are transported continuously by the transport unit, the control method comprises: a first step of performing calibration of the detection sensor between sheets after the previous sheet has passed the detection position by the detection sensor and until the next sheet reaches the detection position; a second step of storing the environmental information acquired by the environmental sensor in a predetermined storage unit; and a third step of determining, after the second step has been performed, whether or not to perform the calibration between the next sheets based on the environmental information acquired by the environmental sensor and past environmental information stored in the storage unit.

[0030] The invention according to claim 19 is a program to be executed in an image forming apparatus comprising: an environmental sensor for acquiring environmental information; a transport unit for transporting sheets; and a detection sensor for detecting the physical properties of sheets transported by the transport unit, wherein the program is configured to cause the image forming apparatus to perform the following steps: a first step of performing calibration of the detection sensor between sheets when a plurality of sheets are being transported continuously by the transport unit, from the time the previous sheet passes the detection position by the detection sensor until the next sheet reaches the detection position; a second step of storing the environmental information acquired by the environmental sensor in a predetermined storage unit; and a third step of determining, after the second step has been performed, whether or not to perform the calibration between the next sheets based on the environmental information acquired by the environmental sensor and past environmental information stored in the storage unit. [Effects of the Invention]

[0031] According to the present invention, when multiple sheets are being transported continuously, the type of sheet can be appropriately detected without significantly reducing throughput. [Brief explanation of the drawing]

[0032] [Figure 1] This figure shows an example configuration of an image forming apparatus. [Figure 2] This is a diagram showing an example of a detection sensor configuration. [Figure 3] This diagram illustrates the detection sensors used during calibration. [Figure 4] This is a block diagram showing the functional configuration of the control unit. [Figure 5] This figure shows an example of a sheet settings screen. [Figure 6] This figure shows an example of control information. [Figure 7] This flowchart shows an example of a processing procedure performed by an image forming apparatus. [Figure 8] This flowchart shows an example of a detailed processing procedure for printing the first page. [Figure 9] This flowchart shows an example of a detailed processing procedure for printing subsequent pages. [Figure 10] This is a flowchart showing an example of a physical property detection process. [Modes for carrying out the invention]

[0033] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. In the embodiments described below, elements common to all are denoted by the same reference numerals, and redundant explanations of these elements will be omitted.

[0034] Figure 1 shows an example of the internal configuration of an image forming apparatus 1 in one embodiment of the present invention. The image forming apparatus 1 shown in Figure 1 is a device that executes a printing job by forming an image using an electrophotographic method, and is capable of forming a color image in a tandem manner. The image forming apparatus 1 includes, inside the main body 1a, a transport unit 2 that feeds and transports sheets 9 such as printing paper one by one, an image forming unit 3 that forms an image on the sheet 9 transported by the transport unit 2, a fixing unit 4 that fixes the image formed on the sheet 9 by the image forming unit 3, a control unit 5 that controls the operation of the image forming apparatus 1, and an operation panel 6 that can be operated by the user. The image forming apparatus 1 also includes an environmental sensor 19 inside the main body 1a that acquires environmental information inside the device, such as temperature and humidity.

[0035] The transport unit 2 includes a sheet storage unit 10, a pickup roller 11, a paper feed roller 12, a transport path 13, a detection sensor 30, a timing roller (registration roller) 14, a secondary transfer roller 15, and a paper discharge roller 16.

[0036] The sheet storage section 10 is a tray capable of storing multiple sheets 9, and is located at the bottom of the device body 1a. It is detachable from the bottom of the device body 1a. For example, when replenishing the sheet storage section 10 with sheets 9, the sheets 9 can be easily replenished by pulling the sheet storage section 10 out from the bottom of the device body 1a.

[0037] The pickup roller 11 contacts the uppermost sheet 9 among the multiple sheets 9 stored in the sheet storage section 10 and is driven to rotate in a predetermined direction (counterclockwise), thereby feeding at least one sheet 9 downstream. The paper feed roller 12 is located downstream of the pickup roller 11 and supplies the sheets 9 fed from the pickup roller 11 to the transport path 13 further downstream. The paper feed roller 12 comprises a drive roller 12a and a driven roller 12b, and has a sheet separation function that separates the uppermost first sheet 9 from the second and subsequent sheets 9 by gripping the sheet 9 fed from the pickup roller 11 between the nip of the drive roller 12a and the driven roller 12b. Therefore, even if two or more sheets 9 are fed by the pickup roller 11, the paper feed roller 12 can transport only the uppermost first sheet 9 to the transport path 13 downstream.

[0038] The sheets 9 supplied to the transport path 13 by the paper feed roller 12 are transported along the transport path 13 in the direction of arrow F2. A detection sensor 30 is provided at a predetermined position in the transport path 13. The detection sensor 30 is a sensor that detects the physical properties of the sheets 9 transported by the transport unit 2. By detecting the physical properties of the sheets 9 with the detection sensor 30, the type of sheet 9 transported by the transport unit 2 can be identified. For example, an optical sensor or an ultrasonic sensor can be used as the detection sensor 30. In this embodiment, an example in which the detection sensor 30 is configured as an optical sensor will be described.

[0039] Furthermore, a timing roller 14 is provided in the transport path 13 at a predetermined position downstream of the detection sensor 30. The sheet 9 being transported along the transport path 13 stops when its leading edge reaches the nip of the timing roller 14. At this time, the sheet 9 can be corrected for skew by forming a loop in the sheet 9 while pressing its leading edge against the nip of the timing roller 14.

[0040] The timing roller 14 is driven to rotate in accordance with the timing when the image formed by the image forming unit 3 is transported to the position of the secondary transfer roller 15, and transports the sheet 9 toward the secondary transfer roller 15. As the sheet 9 passes the position of the secondary transfer roller 15, the image (toner image) formed by the image forming unit 3 is secondary transferred to the surface of the sheet 9.

[0041] The sheet 9, on which the image has been transferred at the secondary transfer roller 15, then enters the fuser unit 4, where it undergoes heating and pressurizing treatment. This fixes the image (toner image) transferred to the sheet 9. The fuser unit 4 is equipped with a heating roller 27 and a pressurizing roller 28. The heating roller 27 is also provided with a halogen heater 29, which is a heat source. When this halogen heater 29 is lit, the surface of the heating roller 27 is heated to a predetermined fixing temperature. The heating roller 27 and the pressurizing roller 28 then apply heating and pressurizing treatment as the sheet 9, on which the image (toner image) has been transferred, passes through the nip between the heating roller 27 and the pressurizing roller 28, fixing the image (toner image) to the sheet 9. Thus, as the sheet 9 passes through the fuser unit 4, one printed sheet with the image is completed. The sheet 9 with the fixed image is discharged by the paper discharge roller 16 from the discharge port 17 onto the paper discharge tray 18 located on the top of the main body 1a of the device.

[0042] The image forming unit 3 has an intermediate transfer belt 23 made of an endless belt, and a color image is formed on the surface of the intermediate transfer belt 23 by sequentially transferring toner images of four colors, Y (yellow), M (magenta), C (cyan), and K (black), onto the intermediate transfer belt 23. Then, when the color image formed on the intermediate transfer belt 23 passes a position opposite the secondary transfer roller 15, the color image is secondary transferred to the surface of the sheet 9 being transported by the transport unit 2.

[0043] The image forming unit 3 includes a plurality of exposure units 21Y, 21M, 21C, 21K corresponding to the Y, M, C, and K colors, a plurality of image forming units 20Y, 20M, 20C, 20K corresponding to the colors, primary transfer rollers 22Y, 22M, 22C, 22K positioned opposite each image forming unit 20Y, 20M, 20C, 20K, a plurality of toner bottles 26Y, 26M, 26C, 26K corresponding to the colors, the aforementioned intermediate transfer belt 23, a drive roller 25 that circulates and drives the intermediate transfer belt 23, and a driven roller 24 that rotates in response to the circulating movement of the intermediate transfer belt 23. In the following, the exposure units 21Y, 21M, 21C, and 21K of each color will be collectively referred to as the exposure unit 21, the image forming units 20Y, 20M, 20C, and 20K of each color will be collectively referred to as the image forming unit 20, the primary transfer rollers 22Y, 22M, 22C, and 22K of each color will be collectively referred to as the primary transfer rollers 22, and the toner bottles 26Y, 26M, 26C, and 26K of each color will be collectively referred to as the toner bottles 26.

[0044] The exposure unit 21 is positioned near the image forming unit 20 corresponding to each color. In this embodiment, the exposure unit 21 is located below each image forming unit 20. The exposure unit 21 is equipped with a light source such as a semiconductor laser or an LED, and irradiates the surface of the image carrier (photosensitive drum) of the image forming unit 20 corresponding to each color with scanning light based on image data, thereby exposing the surface of the image carrier and forming an electrostatic latent image.

[0045] Each image forming unit 20 corresponding to a color is located below the intermediate transfer belt 23. The toner bottle 26 is positioned above the intermediate transfer belt 23 and supplies a developer containing toner of the color corresponding to each image forming unit 20.

[0046] Each image forming unit 20 is positioned opposite the primary transfer roller 22, with the intermediate transfer belt 23 in between. The image forming unit 20 includes an image carrier positioned opposite the primary transfer roller 22. The image carrier is composed of, for example, a photosensitive drum extending from the front to the back of the image forming apparatus, and has a photosensitive layer on its surface. When image forming is performed in the image forming unit, the image carrier is driven to rotate in a predetermined direction (clockwise). The image forming unit includes a cleaner, a charging unit, and a developer around the image carrier. The charging unit charges the surface of the image carrier to a predetermined charge. Once the surface of the image carrier is charged to the predetermined charge by the charging unit, an electrostatic latent image is formed on the surface of the image carrier by scanning light irradiated from the exposure unit 21. The developer applies a developer consisting of toner and carrier to the surface of the image carrier, thereby revealing the electrostatic latent image with toner and forming a toner image on the surface of the image carrier. The toner image formed on the surface of the image carrier in this manner is first transferred to the intermediate transfer belt 23 by a bias voltage applied from the primary transfer roller 22 when the intermediate transfer belt 23 circulates in the direction of arrow F1.

[0047] Each image forming unit 20 forms a color image on the surface of the intermediate transfer belt 23 by superimposing toner images of each color onto the intermediate transfer belt 23. This color image moves in a circular motion in the direction of arrow F1, integrally with the intermediate transfer belt 23. As the intermediate transfer belt 23 passes between the secondary transfer roller 15 and the drive roller 25, the color image adheres to the surface of the sheet 9 fed out from the timing roller 14 and is then secondaryly transferred to the surface of the sheet 9 by the bias voltage applied from the secondary transfer roller 15.

[0048] The environmental sensor 19 is located near the detection sensor 30 and acquires environmental information inside the device body 1a. The environmental sensor 19 is equipped with a temperature sensor 19a. Therefore, the environmental sensor 19 can acquire at least temperature information inside the device body 1a as environmental information. In addition to the temperature sensor, the environmental sensor 19 may also be equipped with a humidity sensor.

[0049] The image forming apparatus 1 having the above configuration adjusts the transport speed of the sheet 9 and the operating speed of the image forming unit 3 (for example, the circulating movement speed of the intermediate transfer belt 23) according to the type of sheet 9 transported along the transport path 13, and also adjusts the fixing operation in the fixing unit 4 (for example, the fixing temperature). For example, if the sheet 9 is cardboard, the transport speed of the sheet 9 is reduced compared to when it is plain paper, and the fixing temperature in the fixing unit 4 is set to a higher temperature. Conversely, if the sheet 9 is plain paper, the transport speed of the sheet 9 is increased compared to when it is cardboard, and the fixing temperature in the fixing unit 4 is set to a lower temperature. In other words, the image forming apparatus 1 performs optimal control according to the type of sheet 9, thereby ensuring the maximum throughput according to the type of sheet 9 while forming a high-quality image on the sheet 9.

[0050] The type of sheet 9 can be set in the image forming apparatus 1 by the user operating the control panel 6. However, the user may not know the type of sheet 9 stored in the sheet storage unit 10. In this case, the user cannot set the type of sheet 9 appropriately. Therefore, the user should pre-set automatic detection of the type of sheet 9 in the image forming apparatus 1. When automatic detection of the type of sheet 9 is set, the image forming apparatus 1 activates the detection sensor 30 when the sheet 9 being transported along the transport path 13 passes the detection position of the detection sensor 30, and automatically detects the type of sheet 9 based on the detection result of the detection sensor 30.

[0051] Figure 2 shows an example of the configuration of the detection sensor 30. The detection sensor 30 detects the physical properties of the sheet 9 when the sheet 9, which is being transported along the transport path 13, passes a predetermined detection position. The detection sensor 30 comprises a light source unit 31 for transmission, a light source unit 32 for reflection, a light receiving unit 33, and a reflector 35. The light source unit 31 and the reflector 35 are positioned opposite one side of the sheet 9 being transported along the transport path 13, while the light source unit 32 and the light receiving unit 33 are positioned opposite the other side of the sheet 9. That is, the light source unit 31 and the light receiving unit 33 face each other across the transport path 13, and the light source unit 32 and the reflector 35 face each other across the transport path 13.

[0052] The light source unit 31 for transmission is equipped with multiple light sources 31a and 31b, each emitting light of a different wavelength. The light sources 31a and 31b are composed of, for example, LED light sources. Light source 31a is, for example, a light source that emits near-infrared light. Light source 31b is a light source that emits blue light. Both light sources 31a and 31b emit light onto the sheet 9 when the sheet 9 is passing through the detection position of the detection sensor 30. After passing through the sheet 9, the light is received by a light-receiving element 34, such as a photodiode, provided in the light-receiving unit 33, and converted into an electrical signal (for example, voltage).

[0053] The reflective light source unit 32 is equipped with multiple light sources 32a, 32b, and 32c, each emitting light of a different wavelength. The light sources 32a, 32b, and 32c are composed of, for example, LED light sources. The light sources 32a, 32b, and 32c emit R (red), G (green), and B (blue) light, respectively. All of these light sources 32a, 32b, and 32c emit light onto the sheet 9 when the sheet 9 passes the detection position detected by the detection sensor 30. After being reflected from the surface of the sheet 9, the light is received by the light receiving element 34 of the light receiving unit 33 and converted into an electrical signal (for example, voltage).

[0054] The sheet 9 has different transmittances for each wavelength of light depending on its type. Furthermore, the sheet 9 also has different reflectances for each wavelength of light depending on its type. Therefore, the detection sensor 30 measures the amount of transmitted light that passes through the sheet 9 and the amount of reflected light that is reflected from the surface of the sheet 9. Specifically, the detection sensor 30 detects the physical properties of the sheet 9 by emitting light from each light source 31a, 31b, 32a, 32b, and 32c at a predetermined intensity and measuring the amount of transmitted and reflected light. However, since the light-receiving element 34 in the light-receiving unit 33 needs to detect transmitted and reflected light of each wavelength individually, it cannot simultaneously emit light from the multiple light sources 31a, 31b, 32a, 32b, and 32c included in the transmission light source unit 31 and the reflection light source unit 32. Therefore, the detection sensor 30 is configured to sequentially light up multiple light sources 31a, 31b, 32a, 32b, and 32c one by one in a time-division manner when the sheet 9 is passing through the detection position, and to individually detect the transmitted and reflected light of each wavelength. The image forming apparatus 1 can determine the type of sheet 9 being transported along the transport path 13 based on the physical properties of the sheet 9 (amount of transmitted light and amount of reflected light) detected by the detection sensor 30.

[0055] In particular, the detection sensor 30 in this embodiment is installed in the transport path 13 through which each sheet 9 is transported. Therefore, when the image forming apparatus 1 executes a print job in which multiple sheets 9 are transported in succession, it can determine the type of sheet 9 each time a sheet 9 passes the detection position of the detection sensor 30. As a result, if the type of sheet 9 changes during the continuous transport of multiple sheets 9, the image forming apparatus 1 can detect that change in real time.

[0056] Incidentally, the detection sensor 30 described above experiences changes in sensor sensitivity due to changes in the internal environmental conditions (temperature, humidity, etc.) inside the device body 1a. Therefore, the image forming apparatus 1 periodically or irregularly calibrates the detection sensor 30 to correct the sensor sensitivity.

[0057] Figure 3 illustrates the detection sensor 30 during calibration. As shown in Figure 3, the calibration of the detection sensor 30 must be performed when the sheet 9 is not present at the detection position by the detection sensor 30. The calibration of the detection sensor 30 is performed individually for each of the multiple light sources 31a, 31b, 32a, 32b, and 32c. When calibrating the transmission light source unit 31, the image forming apparatus 1 emits light from the multiple light sources 31a and 31b at different timings. The image forming apparatus 1 corrects the sensitivity of the photodetector 34 (gain adjustment) so that the voltage output from the photodetector 34 becomes a predetermined voltage when each of the light sources 31a and 31b emits light at a predetermined intensity. Similarly, when calibrating the reflection light source unit 32, the image forming apparatus 1 emits light from the multiple light sources 32a, 32b, and 32c at different timings. At this time, since the sheet 9 is not interposed between the light sources 32a, 32b, and 32c and the reflector 35, the light emitted from the light sources 32a, 32b, and 32c is reflected by the reflector 35 and incident on the photodetector 34. The image forming apparatus 1 performs sensitivity correction (gain adjustment) of the photodetector 34 so that the voltage output from the photodetector 34 becomes a predetermined voltage when each of the light sources 32a, 32b, and 32c is emitted at a predetermined intensity. In this way, sensitivity correction of the photodetector 34 is performed for each of the light sources 31a, 31b, 32a, 32b, and 32c during the calibration of the detection sensor 30. For this reason, a certain amount of time (for example, about 1.8 seconds) is required from the start to the end of the calibration.

[0058] Figure 4 is a block diagram showing the functional configuration of the control unit 5. The control unit 5 comprises a CPU 40 and a storage unit 41, and controls the operation of each part of the image forming apparatus 1. The CPU 40 is a hardware processor that reads and executes the program 42 stored in the storage unit 41. The storage unit 41 is a non-volatile storage device, such as a hard disk drive (HDD) or a solid-state drive (SSD). The operation panel 6 comprises a display unit 7 and an operation unit 8. The display unit 7 is composed of, for example, a liquid crystal display, and displays an operation screen that can be operated by the user. The operation unit 8 is composed of touch panel keys and push button keys, and accepts user operations. The environmental sensor 19 is equipped with a temperature sensor 19a.

[0059] For example, the control unit 5 displays a sheet setting screen on the display unit 7 of the operation panel 6 and sets whether or not to automatically detect the type of sheet 9 based on the user's operation on the sheet setting screen. Figure 5 shows an example of the sheet setting screen G1. As shown in Figure 5(a), the sheet setting screen G1 displays operation buttons B1 and B2 for setting whether or not to automatically detect the type of sheet 9. Operation button B1 is a button to set whether or not to automatically detect the type of sheet 9. Operation button B2 is a button to set whether or not to automatically detect the type of sheet 9. The user sets whether or not to automatically detect by touching either operation button B1 or B2.

[0060] Figure 5(b) shows an example screen when the user operates operation button B1. If the user sets automatic detection, the sheet settings screen G1 displays the detailed settings screen G2. This detailed settings screen G2 displays operation button B3 to instruct automatic detection normally, and operation button B4 to instruct automatic detection every page.

[0061] Normal automatic detection is a detection method in which the detection sensor 30 detects the physical properties of the first sheet 9 that is fed and transported from the sheet storage unit 10 at the start of execution of a print job, but does not perform physical property detection for the second and subsequent sheets 9. When the first sheet 9 is transported, the control unit 5 sets the transport speed of the sheet 9 to the minimum speed (first speed) and transports the sheet 9. Because the transport speed of the sheet 9 is the minimum speed, the sheet 9 passes slowly through the detection position of the detection sensor 30. Therefore, the detection sensor 30 can detect the physical properties of the sheet 9 multiple times when the first sheet 9 is passing through the detection position, enabling highly accurate detection. When the first sheet 9 is transported, the control unit 5 determines the type of sheet 9 based on the highly accurate detection result from the detection sensor 30, and based on that determination result, determines the transport speed (second speed) when transporting the second and subsequent sheets 9. Then, when it is time to feed the second and subsequent sheets 9, the control unit 5 feeds and transports the sheets 9 at a transport speed (second speed) determined based on the first sheet 9. In this case, the transport speed (second speed) is faster than the minimum speed (first speed). When normal automatic detection is set, the detection sensor 30 does not perform detection when the second and subsequent sheets 9 are transported. In this normal automatic detection case, a certain amount of time is required each time from the start of execution of the print job until the first sheet 9 is ejected.

[0062] Automatic detection per page is a detection method in which the detection sensor 30 detects the physical properties of the first sheet 9 that is fed and transported from the sheet storage unit 10 at the start of execution of a print job, and also detects the physical properties of the second and subsequent sheets 9 using the detection sensor 30. When the first sheet 9 is transported, the control unit 5 sets the transport speed of the sheet 9 based on the sheet information 43 stored in the storage unit 41 and transports the sheet 9. Since the transport speed of the sheet 9 is the transport speed corresponding to the type of sheet 9, the sheet 9 passes the detection position of the detection sensor 30 at a relatively high speed. Therefore, when the first sheet 9 passes the detection position, the detection sensor 30 performs a simplified detection, which means that the number of times it can detect the physical properties of the sheet 9 is less than in the case of normal automatic detection. The detection sensor 30 also performs a simplified detection when the second and subsequent sheets 9 pass the detection position. When the control unit 5 detects that the type of sheet 9 has changed to a type different from the type of sheet recorded in the sheet information 43, based on the simple detection result from the detection sensor 30, it causes the detection sensor 30 to perform a high-precision detection operation at the start of the next print job to accurately determine the type of sheet 9. In this case of automatic detection per page, the time required from the start of the print job until the first sheet 9 is ejected is faster than in the case of normal automatic detection. Thus, the image forming apparatus 1 of this embodiment is configured to detect the type of each sheet 9 when multiple sheets 9 are transported in succession.

[0063] The user can select and set their preferred automatic detection method from normal automatic detection and page-by-page automatic detection by operating the operation buttons B3 and B4 on the detailed settings screen G2. However, if, for example, sheet 9 remains in the sheet storage section 10 and the user replenishes sheet 9, it is preferable for the user to select page-by-page automatic detection.

[0064] Figure 5(c) shows an example screen when the user operates operation button B2. If the user has set it not to automatically detect, the sheet setting screen G1 will display the detailed settings screen G3. This detailed settings screen G3 displays several operation buttons B5, B6, B7, and B8 for selecting one sheet type from several sheet types such as plain paper, thick paper 1, thick paper 2, and thick paper 3. If the user knows the type of sheet 9 that has been replenished in the sheet storage unit 10, they can set the type of sheet 9 by selecting and operating one of the operation buttons B5, B6, B7, and B8.

[0065] Returning to Figure 4, the memory unit 41 stores not only the program 42, but also sheet information 43, control information 44, and environmental information 45. Sheet information 43 is information that records the type of sheet 9. For example, if the type of sheet 9 is manually set by the user, the sheet information 43 records the type of sheet 9 set by the user. Also, if automatic detection of the type of sheet 9 is set, the sheet information 43 records the type of sheet 9 that is automatically determined based on the detection result by the detection sensor 30.

[0066] Control information 44 is information referenced when executing a print job. Figure 6 shows an example of control information 44. Control information 44 assigns a type of sheet 9, such as plain paper, cardboard 1, cardboard 2, and cardboard 3, according to the basis weight of the sheet 9. Control information 44 is information for setting image formation parameters when the image forming unit 3 forms an image on the sheet 9 for each type of sheet 9. For example, as shown in Figure 6, control information 44 specifies the transport speed of the sheet 9 and the fixing temperature in the fixing unit 4 for each type of sheet 9. Therefore, by referring to control information 44, it is possible to determine image formation parameters such as the transport speed and fixing temperature appropriate for the type of sheet 9. Note that the relationship between transport speeds V1, V2, V3, V4 shown in Figure 6 is V1>V2>V3>V4, and these transport speeds are set to maximize throughput according to each type of sheet 9. Also, the relationship between fixing temperatures T1, T2, T3, T4 is T1 <T2<T3<T4である。

[0067] Environmental information 45 is information that records environmental information acquired by the environmental sensor 19. Environmental information 45 includes temperature information detected by at least the temperature sensor 19a included in the environmental sensor 19. Here, the environmental information 45 stored in the storage unit 41 is the environmental information acquired by the environmental sensor 19 when the calibration of the detection sensor 30 was performed. In other words, the environmental information 45 stored in the storage unit 41 is information that indicates the environmental state inside the device at the time of the previous calibration.

[0068] The CPU 40 of the control unit 5 executes the program 42, thereby causing the control unit 5 to function as a job control unit 50, a sheet determination unit 51, an environmental change detection unit 52, and a calibration execution unit 53.

[0069] The job control unit 50 comprehensively controls the execution of a print job by controlling the operation of the transport unit 2, the image forming unit 3, and the fixing unit 4. When the job control unit 50 receives a print job via a communication interface (not shown), it determines whether automatic detection of the sheet type 9 is set. If automatic detection is set, the job control unit 50 further determines whether it is normal automatic detection or automatic detection per page. Based on this determination, the job control unit 50 controls the execution of the print job.

[0070] For example, if automatic detection is disabled, the storage unit 41 stores sheet information 43 indicating the sheet type specified by the user. Therefore, the job control unit 50 reads the sheet information 43 to identify the sheet type and reads the control information 44 to determine the transport speed of the sheet 9 and the fixing temperature of the fixing unit 4. After that, the job control unit 50 drives the transport unit 2, the image forming unit 3 and the fixing unit 4 based on the determined transport speed and fixing temperature to execute the print job.

[0071] Furthermore, if automatic detection is normally set, the job control unit 50 sets the transport speed of the first sheet 9 to the lowest speed and drives the transport unit 2 to start the transport operation of the sheet 9. Subsequently, as the sheet information 43 in the storage unit 41 is updated, the job control unit 50 refers to the control information 44 based on the updated sheet information 43 to determine the transport speed and fixing temperature of subsequent sheets 9. Then, when it is time to feed the second and subsequent sheets 9, the job control unit 50 drives the transport unit 2, the image forming unit 3 and the fixing unit 4 based on the determined transport speed and fixing temperature to execute the job for the second and subsequent sheets.

[0072] Furthermore, if automatic detection is set for each page, the storage unit 41 stores sheet information 43 indicating the sheet type automatically detected by the high-precision detection operation of the detection sensor 30. Therefore, the job control unit 50 reads the sheet information 43 to identify the sheet type and reads the control information 44 to determine the transport speed of the sheet 9 and the fixing temperature of the fixing unit 4. After that, the job control unit 50 drives the transport unit 2, the image forming unit 3 and the fixing unit 4 based on the determined transport speed and fixing temperature to execute the print job.

[0073] The sheet determination unit 51 functions when automatic detection of the sheet type 9 is set. The sheet determination unit 51 drives the detection sensor 30 during the transport of the sheet 9 to cause the detection sensor 30 to perform an operation to detect the physical properties of the sheet 9 and determines the type of sheet 9. Based on the physical properties of the sheet 9 (transmitted light amount and reflected light amount) output from the detection sensor 30, the sheet determination unit 51 identifies the transmittance and reflectance of light at each wavelength and calculates the basis weight of the sheet 9. Then, by referring to the control information 44, the sheet determination unit 51 identifies whether the type of sheet 9 is plain paper, cardboard 1, cardboard 2, or cardboard 3.

[0074] The sheet determination unit 51 switches the number of times it causes the detection sensor 30 to perform a detection operation according to the transport speed of the sheet 9. For example, when automatic detection is normally set, the sheet determination unit 51 causes the detection sensor 30 to perform a detection operation when the first sheet 9 is being transported. At this time, since the sheet 9 is being transported at the lowest speed, the sheet determination unit 51 causes the detection sensor 30 to perform multiple detection operations. In other words, the sheet determination unit 51 causes the detection sensor 30 to perform high-precision detection with a large number of samples. Based on the results of multiple detections by the detection sensor 30, the sheet determination unit 51 calculates the basis weight of the sheet 9. This reduces the influence of noise and other factors, and allows for high-precision identification of the type of sheet 9. The sheet determination unit 51 then writes the identified type of sheet to the sheet information 43 and updates the sheet information 43.

[0075] In contrast, for example, when automatic detection is set for each page, the sheet determination unit 51 performs a detection operation at least once when the sheet 9 passes the detection position, because the transport speed of the sheet 9 is relatively high. Based on the detection result, the sheet determination unit 51 calculates the basis weight of the sheet 9. In the case of automatic detection for each page, the number of detections (samplings) by the detection sensor 30 is less than in normal automatic detection, so it is more susceptible to noise, and the accuracy of the calculated basis weight is relatively low. Therefore, the sheet determination unit 51 compares the identified sheet type with the sheet type recorded in the sheet information 43 to determine whether the sheet type has changed. If a change in sheet type is detected, the sheet determination unit 51 sets a sheet change detection flag and instructs the system to perform a high-precision detection operation when the next job starts. However, even if the sheet determination unit 51 detects a change in sheet type when the sheet 9 is being transported at high speed, the sheet information 43 in the storage unit 41 is not rewritten because the detection accuracy is low.

[0076] The environmental change detection unit 52 functions when automatic detection of the sheet type 9 is set. The environmental change detection unit 52 also functions immediately before the sheet determination unit 51 performs sheet determination, determining whether calibration of the detection sensor 30 is required. The environmental change detection unit 52 detects environmental changes when the environmental conditions have changed since the last calibration of the detection sensor 30. Before the sheet 9 is fed, the environmental change detection unit 52 acquires environmental information output from the environmental sensor 19 and compares it with environmental information 45 stored in the storage unit 41. The environmental change detection unit 52 then extracts the difference between these two sets of environmental information and determines whether the difference exceeds a predetermined range. If the difference exceeds the predetermined range, the environmental change detection unit 52 detects that the environmental conditions have changed since the last calibration. Here, the predetermined range is the limit range within which the reliability of the physical property values ​​of the sheet 9 detected by the detection sensor 30 is ensured. This predetermined range can be changed as appropriate by, for example, the user or the administrator of the image forming apparatus 1.

[0077] For example, the environmental change detection unit 52 extracts the difference between the temperature information acquired by the temperature sensor 19a and the temperature information contained in the environmental information 45, and determines whether the temperature change since the last calibration has exceeded a predetermined range (for example, a range of ±5°C). If the temperature change since the last calibration has exceeded the predetermined range, the environmental change detection unit 52 detects that the environmental conditions have changed since the last calibration.

[0078] Furthermore, if the environmental sensor 19 includes a humidity sensor, the environmental change detection unit 52 can also detect environmental changes based on humidity changes. For example, the environmental change detection unit 52 extracts the difference between the humidity information acquired by the humidity sensor and the humidity information included in the environmental information 45, and determines whether the humidity change since the last calibration execution exceeds a predetermined range (for example, a range of ±5%). If the humidity change since the last calibration execution exceeds the predetermined range, the environmental change detection unit 52 detects that the environmental conditions have changed since the last calibration execution.

[0079] If the environmental conditions have changed since the last calibration, the sensor sensitivity of the detection sensor 30 may have changed. In other words, the physical properties of the sheet 9 detected by the detection sensor 30 may no longer be accurate. Therefore, when the environmental change detection unit 52 detects that the environmental conditions have changed, it activates the calibration execution unit 53. The environmental change detection unit 52 then causes the calibration execution unit 53 to perform calibration of the detection sensor 30. Conversely, if the environmental change detection unit 52 does not detect that the environmental conditions have changed, it does not perform calibration of the detection sensor 30.

[0080] Furthermore, when the environmental change detection unit 52 detects that the environmental conditions are changing, it rewrites the environmental information 45 stored in the storage unit 41 based on the environmental information acquired by the environmental sensor 19, thereby updating the environmental information 45.

[0081] The calibration execution unit 53 is a processing unit that performs calibration of the detection sensor 30 and corrects the sensitivity of the light-receiving element 34 provided on the detection sensor 30. For example, when automatic detection is set, the calibration execution unit 53 performs calibration of the detection sensor 30 after the start of the print job but before the first sheet 9 reaches the detection position of the detection sensor 30. In automatic detection, the first sheet 9 in the print job is transported at the lowest speed, so there is sufficient time for the first sheet 9 to reach the detection position. Therefore, when automatic detection is set, the calibration execution unit 53 starts performing calibration immediately after the start of the print job and finishes performing calibration before the first sheet 9 reaches the detection position of the detection sensor 30.

[0082] In contrast, if automatic detection is set for each page, the calibration by the calibration execution unit 53 is performed as follows.

[0083] First, in a printing job in which multiple sheets 9 are transported in succession, if the environmental change detection unit 52 detects an environmental change before the feeding of the first sheet 9 begins, the calibration execution unit 53 performs calibration of the detection sensor 30 before the feeding of the first sheet 9 begins.

[0084] Next, in a printing job in which multiple sheets 9 are transported continuously, if the environmental change detection unit 52 detects an environmental change after the feeding of the first sheet 9 has started, the calibration execution unit 53 performs calibration of the detection sensor 30 after the trailing edge of the previous sheet 9 has passed the detection position of the detection sensor 30, but before the leading edge of the next sheet 9 reaches the detection position of the detection sensor 30. In a printing job in which multiple sheets 9 are transported continuously, the transport speed of the sheets 9 is set not to the minimum speed, but to a transport speed appropriate to the type of sheet 9, and the sheet spacing between the previous and next sheets is also shortened. Therefore, the calibration execution unit 53 temporarily stops the transport operation (paper feeding operation) of the next sheet 9 and performs calibration of the detection sensor 30 with the sheet spacing between the previous and next sheets 9 widened. After the calibration is completed, the calibration execution unit 53 resumes the transport operation (paper feeding operation) of the next sheet 9. As a result, when the detection sensor 30 detects the physical properties of the next sheet 9, it can perform the detection operation with sensitivity correction applied, making it possible to accurately detect the physical properties of the sheet 9.

[0085] As described above, the image forming apparatus 1 of this embodiment includes a control unit 5 that, when multiple sheets 9 are continuously transported by the transport unit 2, can perform calibration of the detection sensor 30 between sheets, from the time the previous sheet 9 passes the detection position of the detection sensor 30 until the next sheet 9 reaches its detection position. The control unit 5 is configured to detect whether or not there has been an environmental change since the last calibration based on environmental information acquired by the environmental sensor 19, and to decide whether or not to perform calibration of the detection sensor 30 between the next sheets.

[0086] If the control unit 5 determines that there has been no change in the environment since the last calibration, it decides not to perform calibration of the detection sensor 30 between sheets, as the reliability of the physical properties of the sheet 9 detected by the detection sensor 30 has not decreased significantly. This allows multiple sheets 9 to be transported continuously at a transport speed appropriate to the type of sheet 9, thus enabling the print job to continue without reducing throughput.

[0087] In response, if the control unit 5 determines that there has been an environmental change since the last calibration, it decides to perform calibration between the next sheets. When the control unit 5 decides to perform calibration between the next sheets, it temporarily stops the transport operation of the transport unit 2 to transport the next sheet 9, widens the gap between the previous sheet 9 and the next sheet 9, and performs calibration of the detection sensor 30. As a result, the control unit 5 can reliably perform calibration of the detection sensor 30 between sheets when multiple sheets 9 are being transported in succession, and can then detect the physical properties of the sheets 9 with high reliability in subsequent detection operations of the detection sensor 30.

[0088] In particular, when multiple sheets 9 are continuously transported in a printing job, the heating roller 27 of the fixing unit 4 remains heated to a predetermined fixing temperature for a long period of time, causing the ambient temperature near the detection sensor 30 inside the main body 1a of the device to gradually rise. Therefore, the control unit 5 monitors whether or not an environmental change has occurred based on the environmental information acquired by the environmental sensor 19, and performs calibration of the detection sensor 30 when it detects that an environmental change has occurred, thereby minimizing the number of calibrations performed during the continuous transport of multiple sheets 9. Consequently, the type of sheet 9 can be appropriately detected during the continuous transport of multiple sheets 9 without significantly reducing throughput.

[0089] Next, the operation of the image forming apparatus 1 will be described. Figures 7 to 9 are flowcharts illustrating an example of a processing procedure performed by the image forming apparatus 1. Figures 7 to 9 illustrate the processing procedure when automatic detection is set for each page. This process is performed by the control unit 5 when the CPU 40 executes program 42.

[0090] When the control unit 5 starts this process, it determines whether or not a print job has been received (step S10). If a print job has been received (YES in step S10), the control unit 5 starts warming up the image forming apparatus 1 (step S11). At this time, the control unit 5 lights up the halogen heater 29 of the fuser unit 4 and heats the surface of the heating roller 27 until it reaches a predetermined target temperature. Next, the control unit 5 analyzes the received print job and confirms the number of prints (N sheets) for the print job (step S12). Next, the control unit 5 initializes the number of output sheets i to 0 sheets (step S13).

[0091] Next, the control unit 5 determines whether the number of output sheets i is 0 (step S14). If it is 0 (YES in step S14), it executes the first sheet printing process (step S15). If the number of output sheets i is not 0 (NO in step S14), the control unit 5 executes the second and subsequent sheet printing processes (step S16). After executing the first sheet printing process or the second and subsequent sheet printing process, the control unit 5 adds 1 to the number of output sheets i (step S17). Next, the control unit 5 determines whether the number of output sheets i has reached N sheets (step S18). If the number of output sheets i has not reached N sheets (NO in step S18), the control unit 5 returns to step S14 and repeats the process from step S14 onwards. If the number of output sheets i has reached N sheets (YES in step S18), the control unit 5 terminates the execution of the print job (step S19). This completes the process by the control unit 5.

[0092] Figure 8 is a flowchart showing an example of a detailed processing procedure for the first print operation (step S15). When the control unit 5 starts the first print operation, it acquires environmental information from the environmental sensor 19 (step S20). Next, the control unit 5 reads the environmental information 45 from the storage unit 41 from the previous calibration operation (step S21) and extracts the difference between it and the environmental information acquired from the environmental sensor 19 (step S22). The control unit 5 then determines whether or not there has been an environmental change since the previous calibration operation based on the extracted difference (step S23). In other words, the control unit 5 determines whether or not the extracted difference exceeds a predetermined range. If the difference exceeds the predetermined range, it determines that there has been an environmental change; if the difference is within the predetermined range, it determines that there has been no environmental change.

[0093] If the control unit 5 determines that there has been an environmental change since the last calibration (YES in step S23), it starts the calibration of the detection sensor 30 (step S24). Specifically, the control unit 5 sequentially emits light from multiple light sources 31a, 31b, 32a, 32b, and 32c at predetermined intensities while the sheet 9 is not present at the detection position of the detection sensor 30, and corrects the sensitivity of the light receiving element 34 so that the voltage output from the light receiving element 34 becomes a predetermined voltage. This calibrates the sensitivity change of the detection sensor 30 due to the environmental change. When the calibration of the detection sensor 30 is completed (YES in step S25), the control unit 5 saves the environmental information acquired in step S20 to the storage unit 41 (step S26). This updates the environmental information 45 in the storage unit 41. If the control unit 5 determines that there has been no environmental change since the last calibration (NO in step S23), it does not perform the processing in steps S24 to S26.

[0094] Next, the control unit 5 determines whether or not the warm-up is complete (step S27). If the warm-up is complete (YES in step S27), it determines whether or not the sheet change detection flag is set (step S28). If the sheet change detection flag is set, it means that a change in the type of sheet 9 was detected during the execution of the previous job.

[0095] If the sheet change detection flag is set (YES in step S28), the control unit 5 sets the transport speed of the sheet 9 to the lowest speed (step S29) and starts the paper feeding operation of the first sheet 9 (step S30). When the control unit 5 starts feeding the first sheet 9, it performs physical property detection processing using the detection sensor 30 (step S31). That is, when the sheet 9 being transported at the lowest speed passes the detection position of the detection sensor 30, the control unit 5 sequentially causes the multiple light sources 31a, 31b, 32a, 32b, and 32c of the detection sensor 30 to emit light at a predetermined intensity, and detects the physical properties of the sheet 9 based on the electrical signal output from the light receiving element 34. At this time, the control unit 5 performs high-precision detection processing by sampling multiple locations in the transport direction of the sheet 9.

[0096] The control unit 5 calculates the basis weight of the sheet 9 based on the physical property values ​​obtained by the physical property detection process (step S31), and performs a sheet determination process to identify the type of sheet 9 based on the basis weight (step S32). Once the type of sheet 9 is identified, the control unit 5 records the type of sheet 9 in the sheet information 43 and updates the sheet information 43. Then, the control unit 5 sets the transport speed of the sheet 9 and the fixing temperature of the fixing unit 4 based on the sheet type recorded in the sheet information 43 (step S34). This determines the transport speed and fixing temperature when the second and subsequent sheets 9 are transported.

[0097] On the other hand, if the sheet change detection flag is not set (NO in step S28), the control unit 5 reads sheet information 43 from the storage unit 41 (step S35), sets the transport speed of the sheet 9 based on the sheet type recorded in the sheet information 43 (step S36), and starts the paper feeding operation of the first sheet 9 (step S37). When the control unit 5 starts feeding the first sheet 9, it executes the physical property detection process using the detection sensor 30 (step S38). That is, when the sheet 9, which is being transported at a transport speed corresponding to the sheet type, passes the detection position of the detection sensor 30, the control unit 5 sequentially causes the multiple light sources 31a, 31b, 32a, 32b, 32c of the detection sensor 30 to emit light at a predetermined intensity, and detects the physical properties of the sheet 9 based on the electrical signal output from the light receiving element 34. At this time, the number of samples taken by the detection sensor 30 is less than in step S31. Therefore, the physical property detection process in step S38 is a simpler detection process.

[0098] The control unit 5 calculates the basis weight of the sheet 9 based on the physical property values ​​obtained by the physical property detection process (step S38), and performs a sheet determination process to identify the type of sheet 9 based on the basis weight (step S39). Once the type of sheet 9 is identified, the control unit 5 determines whether it is a different type from the sheet type recorded in the sheet information 43, and determines whether the type of sheet 9 has changed (step S40). If it detects that the type of sheet 9 has changed (YES in step S40), the control unit 5 sets a sheet change detection flag (step S41). Conversely, if it does not detect a change in the type of sheet 9 (NO in step S40), the process in step S41 is skipped.

[0099] Next, the control unit 5 performs image formation operation control (step S42). Specifically, the control unit 5 synchronizes the transport operation of the sheet 9 with the image formation operation in the image formation unit 3, and drives the heating roller 27 and pressure roller 28 of the fixing unit 4. As a result, a toner image is transferred to the surface of the sheet 9, and heating and pressure treatments are applied as the sheet 9 with the transferred toner image passes through the fixing unit 4. The sheet 9 with the fixed image is then discharged onto the output tray 18. This completes the first print process (step S15).

[0100] Next, Figure 9 is a flowchart showing an example of a detailed processing procedure for printing the second and subsequent sheets (step S16). When the control unit 5 starts printing the second and subsequent sheets, it waits until it is time to feed the next sheet 9 (step S50). When it is time to feed the paper (YES in step S50), the control unit 5 acquires environmental information from the environmental sensor 19 (step S51). Next, the control unit 5 reads the environmental information 45 from the storage unit 41 from the time of the previous calibration (step S52) and extracts the difference between it and the environmental information acquired from the environmental sensor 19 (step S53). Then, the control unit 5 determines whether or not there has been an environmental change since the previous calibration based on the extracted difference (step S54). That is, the control unit 5 determines whether or not the extracted difference exceeds a predetermined range, and if the difference exceeds the predetermined range, it determines that there has been an environmental change. On the other hand, if the difference is within the predetermined range, the control unit 5 determines that there has been no environmental change.

[0101] If the control unit 5 determines that there have been no environmental changes since the last calibration (NO in step S54), it starts feeding the next sheet 9 (step S55).

[0102] In contrast, if the control unit 5 determines that there has been an environmental change since the last calibration (NO in step S54), it temporarily suspends the paper feeding operation for the next sheet 9 (step S56). The control unit 5 then waits until the trailing edge of the previous sheet 9 passes the detection position of the detection sensor 30 (step S57). Once the trailing edge of the previous sheet 9 passes the detection position of the detection sensor 30 (YES in step S57), the control unit 5 starts the calibration of the detection sensor 30 (step S58). That is, the control unit 5 sequentially emits light from multiple light sources 31a, 31b, 32a, 32b, and 32c at predetermined intensities while the sheet 9 is not present at the detection position of the detection sensor 30, and corrects the sensitivity of the light receiving element 34 so that the voltage output from the light receiving element 34 becomes a predetermined voltage. This calibrates the sensitivity change of the detection sensor 30 due to environmental changes. Here, since the paper feeding operation for the next sheet 9 is temporarily suspended, the next sheet 9 will not reach the detection position of the detection sensor 30 while the calibration is being performed. Therefore, the calibration of the detection sensor 30 can be completed successfully. When the calibration of the detection sensor 30 is completed (YES in step S59), the control unit 5 saves the environmental information acquired in step S51 to the storage unit 41 (step S60). As a result, the environmental information 45 in the storage unit 41 is updated. Then, the control unit 5 resumes the paper feeding operation for the next sheet 9 (step S61).

[0103] When the control unit 5 starts feeding the second and subsequent sheets 9, it executes a physical property detection process using the detection sensor 30 (step S62). That is, when the second and subsequent sheets 9 pass the detection position of the detection sensor 30, the control unit 5 sequentially causes the multiple light sources 31a, 31b, 32a, 32b, and 32c of the detection sensor 30 to emit light at a predetermined intensity, and detects the physical properties of the sheet 9 based on the electrical signal output from the light receiving element 34. At this time, the second and subsequent sheets 9 are transported at a transport speed corresponding to the type of sheet 9. Therefore, the number of samples taken by the detection sensor 30 is reduced.

[0104] The control unit 5 calculates the basis weight of the sheet 9 based on the physical property values ​​obtained by the physical property detection process (step S62), and performs a sheet determination process to identify the type of sheet 9 based on the basis weight (step S63). Once the type of sheet 9 is identified, the control unit 5 determines whether it is a different type from the sheet type recorded in the sheet information 43, and determines whether the type of sheet 9 has changed (step S64). If it is detected that the type of sheet 9 has changed (YES in step S64), the control unit 5 sets a sheet change detection flag (step S65). Conversely, if it is not detected that the type of sheet 9 has changed (NO in step S64), the process in step S65 is skipped.

[0105] Next, the control unit 5 performs image formation operation control (step S66). Specifically, the control unit 5 synchronizes the transport operation of the sheet 9 with the image formation operation in the image formation unit 3, and drives the heating roller 27 and pressure roller 28 of the fixing unit 4. As a result, a toner image is transferred to the surface of the sheet 9, and heating and pressure treatments are applied as the sheet 9 with the transferred toner image passes through the fixing unit 4. The sheet 9 with the fixed image is then discharged onto the output tray 18. This completes the printing process for the second and subsequent sheets (step S16).

[0106] Incidentally, in the above, an example was described in which, if the difference between the environmental information acquired from the detection sensor 30 and the environmental information 45 stored in the storage unit 41 does not exceed a predetermined range, the control unit 5 determines the type of sheet 9 in the subsequent physical property detection process (steps S31, S38, S62) by using the physical property values ​​of sheet 9 detected by the detection sensor 30 as they are. However, even if the difference does not exceed a predetermined range, as long as a difference exists, the sensitivity of the detection sensor 30 may change slightly. Therefore, when the control unit 5 performs the physical property detection process (steps S31, S38, S62), it may correct the physical property values ​​of sheet 9 detected by the detection sensor 30 according to the difference in environmental information.

[0107] Figure 10 is a flowchart showing an example of such a physical property detection process. When the control unit 5 starts the processing procedure in Figure 10, it waits until the sheet 9 being transported by the transport unit 2 reaches the detection position of the detection sensor 30 (step S70). When the sheet 9 reaches the detection position (YES in step S70), the control unit 5 drives the detection sensor 30 and acquires the physical property values ​​of the sheet 9 based on the transmitted light amount and reflected light amount detected by the light receiving element 34 (step S72).

[0108] Next, the control unit 5 determines whether the detection sensor 30 has been calibrated immediately prior to this (step S73). If the detection sensor 30 has been calibrated immediately prior to this (YES in step S73), the physical properties of the sheet 9 obtained from the detection sensor 30 are highly reliable. Therefore, the control unit 5 does not correct the physical properties of the sheet 9.

[0109] In contrast, if the detection sensor 30 has not been calibrated immediately prior to this (NO in step S73), the control unit 5 obtains the difference between the environmental information obtained from the detection sensor 30 and the environmental information 45 stored in the storage unit 41 (step S74). Then, the control unit 5 corrects the physical properties of the sheet 9 obtained from the detection sensor 30 based on this difference (step S75). This correction can compensate for slight changes in the sensitivity of the detection sensor 30 that may occur if the difference does not exceed a predetermined range. Therefore, in the subsequent sheet determination, it is possible to perform sheet determination that takes slight environmental changes into account, and there is an advantage in that the type of sheet 9 can be accurately identified.

[0110] A preferred embodiment of the present invention has been described above. However, the present invention is not limited to what has been described in the above embodiment, and various modifications are applicable.

[0111] For example, in the above embodiment, the storage unit 41 stores environmental information 45 from the previous calibration execution, and when multiple sheets 9 are being transported in succession, if the difference between the environmental information acquired by the environmental sensor 19 and the environmental information 45 stored in the storage unit 41 exceeds a predetermined range, the control unit 5 detects an environmental change since the previous calibration execution and performs calibration of the detection sensor 30. However, the control unit 5 is not necessarily limited to detecting environmental changes since the previous calibration execution. For example, the control unit 5 may periodically monitor the environmental information acquired by the environmental sensor 19 when multiple sheets 9 are being transported in succession, and if it detects that an environmental change has occurred during the continuous transport of multiple sheets 9, it may perform calibration of the detection sensor 30. In this case, for example, the control unit 5 is configured to update the environmental information 45 in the storage unit 41 each time environmental information is acquired by the environmental sensor 19. The control unit 5 then determines whether an environmental change has occurred based on the environmental information acquired by the environmental sensor 19 and the past environmental information stored in the storage unit 41, and if it determines that an environmental change has occurred, it performs calibration of the detection sensor 30. Even with this configuration, the same effects and advantages as in the above embodiment remain unchanged.

[0112] Furthermore, in the above embodiment, temperature changes were primarily used as an example of environmental changes. However, the sensitivity of the detection sensor 30 may change not only when the temperature changes, but also when the humidity changes. Therefore, it is preferable that the image forming apparatus 1 be configured to detect environmental changes not only when the temperature changes, but also when the humidity changes.

[0113] Furthermore, in the above embodiment, an example was given in which the detection sensor 30 is composed of an optical sensor. However, even when an ultrasonic sensor is used as the detection sensor 30, a similar change in sensitivity due to environmental changes occurs. Therefore, even when an ultrasonic sensor is used as the detection sensor 30, it is possible to appropriately calibrate the change in sensitivity of the ultrasonic sensor by applying the configuration and operation described in the above embodiment.

[0114] Furthermore, in the above embodiment, an example was described in which, when the sheet change detection flag is set at the start of job execution, the transport speed of sheet 9 is set to the lowest speed (first speed), and the physical properties of sheet 9 are detected with high accuracy when the first sheet 9 is being transported at the lowest speed. However, high-precision detection of the physical properties of sheet 9 is not necessarily limited to when the sheet change detection flag is set at the start of job execution. For example, when the sheet storage unit 10 is pulled out, it is possible that sheet 9 has been replenished by the user. Therefore, the control unit 5 may set the transport speed of sheet 9 to the lowest speed (first speed) and detect the physical properties of sheet 9 with high accuracy when the sheet storage unit 10 is pulled out from the main body 1a and sheet 9 has been replenished.

[0115] Furthermore, the above embodiment illustrates a case where the program 42 executed by the CPU 40 of the control unit 5 is pre-stored in the storage unit 41 of the control unit 5. However, it is not limited to this, and the program 42 described above may be the subject of a transaction on its own. In this case, the program 42 may be provided in a manner that allows it to be downloaded via a network such as the Internet, or it may be provided recorded on a computer-readable recording medium such as a CD-ROM. [Explanation of Symbols]

[0116] 1. Image forming apparatus 2. Conveying section 5. Control Unit 9 sheets 19 Environmental sensors 19a Temperature sensor 30 detection sensors 42 Programs

Claims

1. Environmental sensors that acquire environmental information, A storage unit that stores environmental information acquired by the environmental sensor, A conveying unit that transports the sheets, A detection sensor for detecting the physical properties of the sheet being transported by the transport unit, When multiple sheets are being continuously transported by the transport unit, a control unit is provided that can perform calibration of the detection sensor between sheets, from the time the previous sheet passes the detection position of the detection sensor until the next sheet reaches the detection position. Equipped with, The image forming apparatus is characterized in that the control unit determines whether or not to perform the calibration between the next sheets based on environmental information acquired by the environmental sensor and past environmental information stored in the storage unit.

2. The storage unit stores the environmental information acquired by the environmental sensor during the previous calibration execution. The image forming apparatus according to claim 1, characterized in that the control unit determines whether or not to perform the calibration based on environmental information acquired by the environmental sensor after the previous calibration was performed and past environmental information stored in the storage unit, in order to determine the environmental changes since the previous calibration was performed.

3. The image forming apparatus according to claim 2, characterized in that the control unit determines that there has been no change in the environment since the previous calibration was performed, and decides not to perform the calibration between sheets.

4. The image forming apparatus according to claim 2, characterized in that the control unit determines that there has been a change in the environment since the previous calibration was performed, and decides to perform the calibration between the next sheets.

5. The image forming apparatus according to claim 3 or 4, characterized in that the control unit determines that there is an environmental change when the difference between the first environmental information acquired by the environmental sensor during the previous calibration and the second environmental information acquired by the environmental sensor after the previous calibration has been performed exceeds a predetermined range.

6. The image forming apparatus according to claim 5, characterized in that the control unit corrects the physical property values ​​of the sheet detected by the detection sensor based on the difference if the difference does not exceed the predetermined range.

7. The image forming apparatus according to claim 1, characterized in that the environmental sensor includes a temperature sensor and detects the temperature of the transport section.

8. The image forming apparatus according to claim 1, characterized in that when the control unit decides to perform the calibration between the next sheets, it temporarily suspends the transport operation of the transport unit for the next sheet.

9. The image forming apparatus according to claim 8, characterized in that the control unit performs the calibration while temporarily suspending the transport operation of the transport unit for the next sheet, and resumes the transport operation of the transport unit for the next sheet after the calibration is completed.

10. The image forming apparatus according to claim 1, characterized in that the control unit causes the detection sensor to perform a detection operation when no sheet is present at the detection position during calibration, and corrects the output of the detection sensor based on the result of the detection operation.

11. The image forming apparatus according to claim 1, characterized in that the control unit determines the conveying speed of the sheet by the conveying unit based on the physical properties of the sheet detected by the detection sensor.

12. The system further includes an image forming unit that forms an image on a sheet conveyed by the conveying unit, The image forming apparatus according to claim 1, characterized in that the control unit determines the image forming parameters to be set in the image forming unit based on the physical property values ​​of the sheet detected by the detection sensor.

13. The image forming apparatus according to claim 1, characterized in that the control unit causes the detection sensor to perform an operation to detect the physical properties of a sheet each time a sheet passes the detection position when a plurality of sheets are being continuously transported by the transport unit.

14. The image forming apparatus according to claim 13, characterized in that, when the physical properties of the sheet detected by the detection sensor change, the control unit sets the transport speed of the sheet first transported by the transport unit at the start of the next job to a first speed, causes the detection sensor to detect the physical properties of the sheet a predetermined number of times when the sheet being transported at the first speed passes the detection position, and sets the transport speed of the sheets transported thereafter to a second speed that is faster than the first speed based on the physical properties of the sheet detected a predetermined number of times.

15. The image forming apparatus according to claim 1, characterized in that the control unit sets the transport speed of the sheet first transported by the transport unit to a first speed, causes the detection sensor to detect the physical properties of the sheet a predetermined number of times when the sheet transported at the first speed passes the detection position, sets the transport speed of the second and subsequent sheets to a second speed that is faster than the first speed based on the physical properties of the sheet detected a predetermined number of times, and causes the detection sensor to detect the physical properties of the sheet a fewer number of times than the predetermined number of times when the sheet transported at the second speed passes the detection position.

16. The image forming apparatus according to claim 15, characterized in that the control unit sets the transport speed of the sheet first transported by the transport unit to the first speed when the sheet bundle is replenished or when the execution of a job is started.

17. The image forming apparatus according to claim 1, characterized in that the detection sensor is composed of an optical sensor or an ultrasonic sensor.

18. Environmental sensors that acquire environmental information, A conveying unit that transports the sheets, A detection sensor for detecting the physical properties of the sheet being transported by the transport unit, A control method for an image forming apparatus comprising, When multiple sheets are being continuously transported by the transport unit, the first step is to perform calibration of the detection sensor between sheets after the previous sheet has passed the detection position by the detection sensor and until the next sheet reaches the detection position. The second step involves storing environmental information acquired by the environmental sensor in a predetermined storage unit, After the second step is performed, a third step is taken to determine whether or not to perform the calibration between the next sheets based on the environmental information acquired by the environmental sensor and the past environmental information stored in the storage unit. A control method characterized by having the following features.

19. Environmental sensors that acquire environmental information, A conveying unit that transports the sheets, A detection sensor for detecting the physical properties of the sheet being transported by the transport unit, A program to be executed in an image forming apparatus comprising, When multiple sheets are being continuously transported by the transport unit, the first step is to perform calibration of the detection sensor between sheets after the previous sheet has passed the detection position by the detection sensor and until the next sheet reaches the detection position. The second step involves storing environmental information acquired by the environmental sensor in a predetermined storage unit, After the second step is performed, a third step is taken to determine whether or not to perform the calibration between the next sheets based on the environmental information acquired by the environmental sensor and the past environmental information stored in the storage unit. A program characterized by causing the execution of a specific action.

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