Recording media smoothness detector and image forming apparatus incorporating same

A recording media smoothness detector includes a sensor and a calculator. The sensor includes a light source to emit light toward a recording medium and a light detector to detect an amount of light reflected by the recording medium. The calculator includes a first memory to store an initial output value of the sensor and a second memory to store a decreased output percentage of the sensor relative to the initial output value per number of recording media detected. The calculator is configured to calculate a decreased output amount of the sensor from the decreased output percentage of the sensor per number of recording media detected, according to a number of recording media detected by the sensor, to adjust a luminosity of the light source based on the calculated decreased output amount of the sensor and determine a type of the recording medium based on an output of the sensor after the adjustment of the luminosity of the light source and based on the number of recording media detected by the sensor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35 U.S.C. §119(a) to Japanese Patent Application Nos. 2014-053228, filed on Mar. 17, 2014, and 2015-003397, filed on Jan. 9, 2015, in the Japan Patent Office, the entire disclosure of each of which is hereby incorporated by reference herein.

BACKGROUND

Technical Field

Embodiments of the present invention generally relate to a recording media smoothness detector and an image forming apparatus incorporating the recording media smoothness detector.

Background Art

Various types of electrophotographic image forming apparatuses are known, including copiers, printers, facsimile machines, and multifunction machines having two or more of copying, printing, scanning, facsimile, plotter, and other capabilities. Such image forming apparatuses usually form an image on a recording medium according to image data. Specifically, in such image forming apparatuses, for example, a charger uniformly charges a surface of a photoconductor serving as an image carrier. An optical writer irradiates the surface of the photoconductor thus charged with a light beam to form an electrostatic latent image on the surface of the photoconductor according to the image data. A developing device supplies toner to the electrostatic latent image thus formed to render the electrostatic latent image visible as a toner image. The toner image is then transferred onto a recording medium directly, or indirectly via an intermediate transfer belt. Finally, a fixing device applies heat and pressure to the recording medium carrying the toner image to fix the toner image onto the recording medium.

Such image forming apparatuses may incorporate a recording media smoothness detector to detect smoothness of recording media.

SUMMARY

In one embodiment of the present invention, a novel recording media smoothness detector is described that includes a sensor and a calculator. The sensor includes a light source to emit light toward a recording medium and a light-detecting device to detect an amount of light reflected by the recording medium. The calculator includes a first memory to store an initial output value of the sensor and a second memory to store a decreased output percentage of the sensor relative to the initial output value per number of recording media detected. The calculator is configured to calculate a decreased output amount of the sensor from the decreased output percentage of the sensor per number of recording media detected, according to number of recording media detected by the sensor, to adjust a luminosity of the sensor based on the calculated decreased output amount of the sensor and determine smoothness of the recording medium based on an output of the sensor after the adjustment.

In another embodiment of the present invention, a novel recording media smoothness detector is described that includes a sensor and a calculator. The sensor includes a light source to emit light toward a recording medium and a light-detecting device to detect an amount of light reflected by the recording medium. The calculator includes a first memory to store an initial output value of the sensor and a second memory to store a decreased output percentage of the sensor relative to the initial output value per unit length of recording media. The calculator is configured to calculate a decreased output amount of the sensor from the decreased output percentage of the sensor per unit length of recording media, according to a unit length of recording media detected by the sensor, to adjust a luminosity of the sensor based on the calculated decreased output amount of the sensor and determine smoothness of the recording medium based on an output of the sensor after the adjustment.

Also described are image forming apparatuses incorporating the recording media smoothness detectors.

The accompanying drawings are intended to depict embodiments of the present invention and should not be interpreted to limit the scope thereof.

DETAILED DESCRIPTION

Although the embodiments are described with technical limitations with reference to the attached drawings, such description is not intended to limit the scope of the invention and not all of the components or elements described in the embodiments of the present invention are indispensable.

In a later-described comparative example, embodiment, and exemplary variation, for the sake of simplicity like reference numerals are given to identical or corresponding constituent elements such as parts and materials having the same functions, and redundant descriptions thereof are omitted unless otherwise required.

It is to be noted that, in the following description, suffixes “c”, “m”, “y”, and “k” denote colors cyan, magenta, yellow, and black, respectively. To simplify the description, these suffixes are omitted unless necessary.

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, embodiments of the present invention are described below.

Initially with reference toFIG. 1, a description is given of a configuration of an image forming apparatus1000according to an embodiment of the present invention.

FIG. 1is a schematic sectional view of the image forming apparatus1000. In the present embodiment, the image forming apparatus1000is an electrophotographic image forming apparatus.

As illustrated inFIG. 1, the image forming apparatus1000includes, a body100, an image reading device200positioned on the body100, and a duplex unit300positioned on the right side of the body100.

The body100includes an intermediate transfer device10. The intermediate transfer device10includes an endless intermediate transfer belt11entrained around a plurality of rollers and stretched almost horizontally. The intermediate transfer belt11rotates in a counterclockwise direction inFIG. 1.

Image forming devices12c,12m,12y, and12kare arranged side by side parallel to and under the intermediate transfer belt11of the intermediate transfer device10, in that order, in a direction in which the intermediate transfer belt11is rotated. The image forming devices12c,12m,12y, and12kform toner images of cyan, magenta, yellow, and black, respectively. Each of the image forming devices12c,12m,12y, and12kincludes a drum-shaped image bearer rotated in a clockwise direction inFIG. 1and various devices surrounding the image bearer, such as a charging device, a developing device, a transfer device, and a cleaning device. An exposure device13is disposed below the image forming devices12c,12m,12y, and12k.

A sheet feeder14is disposed below the exposure device13. The sheet feeder14includes a plurality of trays15, in this case two trays15, each of which accommodates recording media20. Sheet feeding rollers17are positioned above and to the right of the trays15, respectively. Each of the sheet feeding rollers17picks up the recording media20one at a time from the corresponding tray15to feed the recording medium20thus picked up to a recording medium conveyance passage16.

The recording medium conveyance passage16is disposed on the right inside the body100to convey the recording medium20perpendicularly upward to an internal ejection section18defined between the body100and the image reading device200. A pair of conveyance rollers19, a secondary transfer device21facing the intermediate transfer belt11, a fixing device22, and a pair of ejection rollers23are provided, in that order, along the recording medium conveyance passage16, in a direction in which the recording medium20is conveyed. A sheet feeding passage37is located upstream from the pair of conveyance rollers19in the direction in which the recording medium20is conveyed. The sheet feeding passage37joins the recording medium conveyance passage16to feed the recording medium20coming from the duplex unit300or a recording medium20coming from a bypass tray36crossing the duplex unit300, toward the pair of conveyance rollers19. A re-feed conveyance passage24, which is a branch conveyance passage to the duplex unit300, is located downstream from the fixing device22in the direction in which the recording medium20is conveyed.

To provide a fuller understanding of embodiments of the present invention, a description is now given of an image forming operation of the image forming apparatus1000.

The image reading device200reads a document image, and according to the image data, the exposure device13irradiates the surfaces of the image bearers of the image forming devices12with light to form latent images thereon. The developing devices develop the latent images into visible toner images. Primary transfer devices25c,25m,25y, and25ksequentially transfer the toner images of cyan, magenta, yellow and black, respectively, onto the intermediate transfer belt11so that the toner images are superimposed one atop another on the intermediate transfer belt11. Thus, a color toner image is formed on the intermediate transfer belt11.

In the meantime, one of the sheet feeding rollers17is selectively rotated to pick up a recording medium20from the corresponding tray15to convey the recording medium20to the recording medium conveyance passage16. Alternatively, a recording medium20is sent from the bypass tray36to the recording medium conveyance passage16through the sheet feeding passage37. The pair of conveyance rollers19receives the recording medium20thus conveyed, and feeds the recording medium20to a secondary transfer position between the intermediate transfer belt11and the secondary transfer device21at a predetermined time, so that the secondary transfer device21transfers the color toner image onto the recording medium20from the intermediate transfer belt11at the secondary transfer position. The recording medium20bearing the color toner image is then conveyed to the fixing device22, which fixes the color toner image onto the recording medium20. Then, the recording medium20is conveyed from the fixing device22to the pair of ejection rollers23, which ejects the recording medium20to the internal ejection section18.

Upon duplex printing, the recording medium20is conveyed to the duplex unit300through the re-feed conveyance passage24after an image is formed on a front side of the recording medium20. In the duplex unit300, the recording medium20is turned over and conveyed to the pair of registration rollers19through the sheet feeding passage37. The pair of registration rollers19feeds the recording medium20toward the secondary transfer position where another color toner image is transferred onto a back side of the recording medium20from on the intermediate transfer belt11. The recording medium20is then conveyed to the fixing device22, which fixes the unfixed color toner image onto the back side of the recording medium20. Then, the recording medium20is conveyed from the fixing device to the pair of ejection rollers23, which ejects the recording medium20to the internal ejection section18.

Usually, in image forming apparatuses, fixing conditions including heat and pressure are taken into account to appropriately fix the toner image onto the recording medium. In particular, such fixing conditions are determined specifically for each type of recording medium to form a high-quality image on the recording medium because the image quality is significantly influenced by such factors as the material, thickness, humidity, smoothness, and coating (if any) of the recording medium. The smoothness is, e.g., a surface smoothness of the recording medium, and can be ascertained by the time (in seconds) it takes for a certain amount of air to flow between the surface of the recording medium and a testing board adhering to the surface of the recording medium. The smoothness and fixability of recording medium are correlated because the fixing rate of toner in the recessed portions of the recording medium depends on the roughness thereof. Accordingly, if an image is fixed onto the recording medium under fixing conditions neglecting the smoothness, a high-quality image may not be obtained and, in some cases, fixing errors may occur, generating an unacceptable image on the recording medium.

Meanwhile, as image forming apparatuses have become more sophisticated and modes of expression have become more diverse, there are now hundreds of different types of recording media. Each type of recording media has a variety of brands with, e.g., different basis weights and thicknesses. Therefore, to form a high-quality image, fixing conditions are determined precisely according to, e.g., the types and brands of recording media.

There are increasing numbers of types of recording media, such as plain paper, coated paper such as gloss coated paper, mat coated paper, and art paper, overhead projector (OHP) sheets, and special paper that is embossed.

In the image forming apparatuses, generally, the fixing conditions are determined according to the basis weight of the recording medium by which the recording medium is classified. For example, paper having a basis weight of about 60 g/m2to about 90 g/m2is classified as plain paper. Paper having a basis weight of about 91 g/m2to about 105 g/m2is classified as medium thick paper. Paper having a basis weight of about 106 g/m2to about 200 g/m2is classified as thick paper. The fixing temperature, the conveying speed of the recording medium, and the like are determined according to these classifications.

Generally, the basis weight of recording media is listed on the package so that the basis weight is easily ascertained. The basis weight information is selected on an operation panel of a copier or on a printer driver displayed on a printer.

Thus, generally, the basis weight is set manually, which may be troublesome. In addition, if the wrong basis weight is set, an intended high-quality image may not be obtained.

Accordingly, some image forming apparatuses incorporate a sensor to detect the thickness of recording media to automatically sort the recording media to form images thereon.

On the other hand, the smoothness of recording media is not usually listed on the package, which makes it difficult to ascertain. For this reason, a sensor may be used to obtain the smoothness of recording media, since, as described above, smoothness and fixability are correlated.

The image forming apparatus1000includes a smoothness sensor40(hereinafter simply referred to as a sensor40) constituting a recording media smoothness detector1that detects smoothness of the recording medium20. The sensor40is provided on a conveyance passage through which the recording medium20is conveyed.

FIG. 2is a schematic view of the sensor40. As illustrated inFIG. 2, the sensor40includes a light-emitting device41serving as a light source and a light-receiving device42serving as a light-detecting device. The light-emitting device41emits light45toward the recording medium20. The light45is reflected by the recording medium20in a first reflection region46, becoming reflected light47that is received by the light-receiving device42. The light-emitting device41is a laser or a light-emitting diode (LED) provided with a drive source43for emitting light. The light-receiving device42is, e.g., a photodiode or a phototransistor, provided with a detecting circuit44that amplifies a detected current and converts the detected current from analog to digital data. The light reflected by the recording medium20includes regular reflection light and scattering light. By providing a plurality of light-emitting devices41and drive sources43or a plurality of light-receiving devices42and detecting circuits44, the scattering light can be used for detection of surface nature. It is to be noted that, inFIG. 2, the recording medium20is conveyed in a horizontal direction or to the back of the sheet face. In addition, a condenser lens is provided on an optical axis.

FIG. 3is a diagram illustrating relative positions of the sensor40and the recording medium20. Specifically, the light-emitting device41and the light-receiving device42of the sensor40are disposed in a direction perpendicular to the recording medium20that is conveyed in a direction indicated by arrow Z, to the back of the sheet face. The following description is given with reference to the drawings viewed in a direction indicated by arrow A inFIG. 3.

FIG. 4is a diagram of the sensor40and the recording medium20, illustrating voltage detected by the sensor40for a prescribed distance. InFIG. 4, the sensor40and the recording medium20face each other.

In the present embodiment, the sensor40is disposed inside the image forming apparatus1000to scan a prescribed position or section on the recording medium20and equalize detected voltage. Specifically, the sensor40equalizes the detected voltage that fluctuates due to slight roughness in the surface of the recording medium20, thereby obtaining an average smoothness of the recording medium20.

To ensure a sufficient length of the prescribed section for accurate equalization of detected voltage, the prescribed section preferably has a length of at least about 40 mm. In addition, an appropriate trigger such as rotation of a registration motor that drives the pair of conveyance rollers19is used so that the sensor40detects one recording medium20at an appropriate time inside the image forming apparatus1000.

Referring now toFIG. 5, a description is given of calculation of smoothness for using the average voltage obtained by the sensor40for, e.g., fixing temperature control.FIG. 5is diagram illustrating detection of recording media, with a graph of a function for calculating smoothness.

As illustrated in the graph ofFIG. 5, the average voltage is converted to smoothness that can be processed more efficiently using a polynomial equation such as “y=ax+b”. Alternatively, the average voltage may be used as is with the coefficients of the polynomial equation being zero.

When the average voltage is converted to smoothness, coefficients “a” and “b” are obtained in advance by, e.g., measuring smoothness of a specific part of a recording medium20using a method stipulated by Japanese Industrial Standards, JISP8155 (as indicated by D inFIG. 5), and scanning the specific part of the recording medium20with the sensor40in an ideal sensor environment to measure output voltage of the sensor40(as indicated by E inFIG. 5). Thus, the smoothness and the sensor output value of the specific part of the recording medium20are obtained. The number of sample recording media is increased (as indicated by sample 1 to sample “N”) to obtain data on a number of correlations between smoothness and sensor output value. A regression analysis is conducted on the data to obtain the coefficients “a” and “b” of the polynomial equation.

Referring now toFIG. 6, a description is given of a position of the sensor40.FIG. 6is a schematic diagram illustrating an exemplary position of the sensor40.

For example, a medium-sized image forming apparatus typically used in an office has a plurality of trays, and providing a dedicated sensor for each tray is expensive. Therefore, the sensor40is preferably disposed to detect a recording medium20where a plurality of conveyance passages converge, as illustrated inFIG. 6. However, paper dust from the recording media20may adhere to the sensor40while the recording media20pass through the conveyance passage on which the sensor40is disposed, resulting in decreased output of the sensor40.

As described above, the smoothness of a recording medium20is obtained using an output value of the sensor40. Paper dust may decrease output values of the sensor40, that is, smoothness detectability, and may make it difficult to distinguish between recording media20. For example, if no paper dust adheres to the sensor40, a recording medium20having a high smoothness (voltage: 2.9 V and smoothness: 200 seconds) can be distinguished from a recording medium20having a low smoothness (voltage: 2.3 V and smoothness: 20 seconds). By contrast, if paper dust adheres to the sensor40, the recording medium20having a high smoothness may be detected with a voltage of 2.3 V and a smoothness of 20 seconds. As a result, the recording medium20having a high smoothness may be erroneously identified as a recording medium having a low smoothness.

FIG. 7is a diagram illustrating adjustment of an amount of light to be emitted by the light-emitting device41, hereinafter referred to as an LED, according to an embodiment of the present invention.

FIG. 7illustrates a case in which three trays (first through third trays) are provided. The first through third trays may include a bypass tray36in addition to trays15. An initial output value of the sensor40for each tray is stored in memory and a decreased output amount from the initial output value is calculated for each tray. Then, a sum unit94sums the decreased output amount thus calculated for each tray. An LED luminosity adjuster95adjusts a luminosity of the LED (i.e., an amount of light to be emitted by the light source) according to the decreased output amount thus summed.

Referring now toFIGS. 8 and 9, a description is given of correction and update of sensor output according to embodiments of the present invention.

FIG. 8is a block diagram of a recording media smoothness detector1A according to a first embodiment.

As illustrated inFIG. 8, the recording media smoothness detector1A includes a calculator70that includes an initial value calculator80and an LED luminosity calculator90. The LED luminosity calculator90includes first through n tray calculators96. Each of the tray calculators96includes a first memory91, a second memory92, and a third memory93. The first memory91stores an initial output value of the sensor40. The second memory92stores a table or regression equation of a decreased output percentage of the sensor40determined for each initial output value of the sensor40per number of recording media20conveyed. It is to be noted that the number of recording media20conveyed is the number of recording media20detected by the sensor40while passing through a conveyance passage on which the sensor40is disposed. The third memory93accumulates and stores a decreased output amount of the sensor40that is calculated based on the number of recording media20detected and a decreased output percentage per number of recording media20, which is obtained using the table or regression equation stored in the second memory92from the initial output value stored in the first memory91. The LED luminosity calculator90also includes the sum unit94and the LED luminosity adjuster95. The sum unit94adds the decreased output amount stored in the third memory93to another to calculate a total decreased output amount. The LED luminosity adjuster95calculates an LED luminosity of the sensor40based on the total decreased output amount to adjust the LED luminosity at a predetermined time. The initial value calculator80calculates an initial output value of the sensor40to rewrite the initial output value stored in the first memory91. According to the first embodiment, decreased paper dust-generated sensor output can be more accurately predicted and updated.

FIG. 9is a block diagram of a recording media smoothness detector1B according to a second embodiment.

As illustrated inFIG. 9, the recording media smoothness detector1B includes a calculator70that includes an initial value calculator80and an LED luminosity calculator90. The LED luminosity calculator90includes first through n tray calculators96. Each of the tray calculators96includes a first memory91, a second memory92, and a third memory93. The first memory91stores an initial output value of the sensor40. The second memory92stores a table or regression equation of a decreased output percentage of the sensor40determined for each initial output value of the sensor40per distance of recording media20conveyed, that is, a unit length of recording media20that pass through the conveyance passage on which the sensor40is disposed. The third memory93accumulates and stores a decreased output amount of the sensor40that is calculated based on a distance of a recording medium20detected and a decreased output percentage per unit length of recording media20, which is obtained using the table or regression equation stored in the second memory92from the initial output value stored in the first memory91. The LED luminosity calculator90also includes a sum unit94and an LED luminosity adjuster95. The sum unit94adds the decreased output amount stored in the third memory93to another to calculate a total decreased output amount. The LED luminosity adjuster95calculates an LED luminosity of the sensor40based on the total decreased output amount to adjust the LED luminosity at a predetermined time. The initial value calculator80calculates an initial output value of the sensor40to rewrite the initial output value stored in the first memory91. According to the second embodiment, decreased paper dust-generated sensor output can be more accurately predicted and updated.

A description is now given of updating sensor output in an image forming process.

In the present embodiment, the initial output value is an output value of the sensor40at a time when the output value of the sensor40is not affected by paper dust. Alternatively, the initial output value is an output value of the sensor40to which paper dust adheres, at a time immediately after being corrected by an LED luminosity calculation. When the time has come, the initial value calculator80obtains a sensor output while identifying a tray from which the recording medium20is conveyed. The initial value calculator80registers the sensor output thus obtained as an initial output value in the first memory91of the tray thus identified. It is to be noted that the sensor40provides different output values depending on the smoothness of recording media20. Accordingly, the initial output value varies depending on the type of recording media20. If the smoothness of recording media20differs between the trays, the initial output value registered in the first memory differs between the trays.

The first memory91through the third memory93are provided for each tray, and identical calculation is performed for each tray. When the image forming apparatus1000identifies changes of the trays, the tray subjected to the calculation is also changed.

The sum unit94sums the values stored in the third memories93as a total decreased output amount. In other words, the values accumulated in the third memories93indicate contribution of the trays to the decreased output percentage of the sensor40. Specifically, for example, the first tray accommodates recording media20that easily generate paper dust whereas the second tray accommodates recording media20that hardly generate paper dust. When the same number of recording media20are conveyed from the first and second trays, passing before the sensor40, the first tray has a greater contribution to contamination of the sensor40than the second tray. When the recording media20are conveyed as described above, the total decreased output amount is calculated by the sum unit94and an output value of the sensor40affected by paper dust is predicted from the total decreased output amount. Based on the total decreased output amount, the LED luminosity adjuster95calculates and adjusts an LED current to obtain an output value of the sensor40that is not affected by an accumulation of paper dust on the sensor40.

A description is now given of an operation when the type of recording media20may be changed.

If a tray (e.g., first tray) accommodates a different type of recording media20from the previous one, the recording media20may have different smoothness from the smoothness of recording media20previously placed on the tray. In addition, the decreased paper dust-generated output percentage with respect to the number of recording media20may change. Accordingly, the initial output value is measured again for the recording media20currently placed on the tray. To ensure correction of sensor output for the re-measurement, firstly, the LED luminosity adjuster95calculates and updates an LED current. The change of recording media20placed on the tray is identified by opening/closing of the tray.

Data used for detecting the opening/closing of each tray include, e.g., readings of an opening/closing sensor151generally incorporated in image forming apparatuses, when the software of the image forming apparatuses is activated. On the other hand, when the software of the image forming apparatuses is not activated because, e.g., the power is turned off or the image forming apparatuses are in energy saving mode, the opening/closing of each tray is identified by the position of a bottom board of each tray because the position of the bottom board moves when the tray is opened or closed. Accordingly, upon the next activation of software, the position of the bottom board is identified by a blocked/unblocked state of an upper-limit sensor, to detect the opening/closing of each tray.

By repeating the above-described operation, the sensor output is corrected by increasing the luminosity even if the sensor40provides a decreased paper dust-generated output.

An image forming condition calculator60uses such corrected sensor output to constantly set appropriate image forming conditions including a fixing temperature.

Referring now toFIGS. 10A and 10B, a description is given of a process of updating output of the sensor40.FIG. 10Ais a flowchart of the process of updating the sensor output.FIG. 10Bis a continuation of the flowchart of the process of updating the sensor output inFIG. 10A.

In step S1, an image forming process is started. In step S2, it is determined whether the recording medium20conveyed from the tray is the first one in the current image forming process. If so (Yes in step S2), in step S3, it is determined whether the tray is opened/closed after the previous image forming process. If so (Yes in step S3), in step S4, it is determined that new recording media20are placed on the tray, and therefore, the LED luminosity adjuster95adjusts an LED luminosity based on the total decreased output amount in the previous image forming processes. In step S5, a recording medium20is conveyed. In step S6, the initial value calculator80calculates an initial output value for the tray, to store the calculated initial output value in the first memory91. Then, the process returns to step S2for the next recording medium20.

On the other hand, if it is determined that the recording medium20is not the first one in the current image forming process (No in step S2), or if it is determined that the tray is not opened or closed after the previous image forming process (No in step S3), then, the LED luminosity is not adjusted and a recording medium20is conveyed in step S7. In step S8, from the decreased output percentage per recording medium20, decreased output amounts are accumulated and summed by the sum unit94to obtain a total decreased output amount. In short, when an image forming process is started, the image forming apparatus1000identifies a tray from which a recording medium20subjected to the image forming process is conveyed, and causes a tray calculator96corresponding to the tray thus identified to calculate a decreased output percentage per recording medium20as a conveyance trigger. With the conveyance trigger, according to the first embodiment, a decreased output percentage per number of recording media20is obtained from the initial output value and the decreased output percentage calculation table for the tray. On the other hand, according to the second embodiment, a decreased output percentage per unit length of recording medium20is obtained from the initial output value and the decreased output percentage calculation table for the tray. In the second embodiment, the decreased output percentage per unit length of recording media20is multiplied by a length of a recording medium20in the direction in which the recording medium20is conveyed from the tray, thereby obtaining a decreased output percentage for each recording medium20conveyed. The length of the recording medium20is obtained by an automatic size detecting function typically used in image forming apparatuses. For example, readings of a size sensor152provided for each tray are used.

In step S9, it is determined whether a prescribed time for updating the LED luminosity has come. As described above, based on the total decreased output amount, the LED luminosity adjuster95calculates and adjusts an LED current to obtain an output value of the sensor40that is not affected by an accumulation of paper dust on the sensor40. Ideally, the LED luminosity is calculated and adjusted per recording medium20. However, the decreased output percentage per recording medium20is extremely small, specifically, at most about 0.3% for each thousand sheets of recording media20conveyed. Therefore, in actuality, the LED luminosity is calculated and adjusted after an image forming process is performed for a predetermined number of recording media20, taking into account the computation load of a central processing unit (CPU) of the image forming apparatus. Accordingly, in the present embodiment, the total decreased output amount is compared with a predetermined threshold. The prescribed time for updating the LED luminosity is when the total decreased output amount exceeds the threshold.

If it is determined that the prescribed time for updating the LED luminosity has come (Yes in step S9), the LED luminosity is adjusted in step S10. In step S11, it is determined whether the image forming process is completed. If so (Yes in step S11), the image forming process ends in step S12. By contrast, if it is determined that the prescribed time for updating the LED luminosity has not come (No in step S9), or if it is determined that the image forming process is not completed (No in step S11), then, the process returns to step S2for the next recording medium20.

By repeating the above-described operation, the sensor output is corrected by increasing the luminosity even if the sensor40provides a decreased paper dust-generated output.

The image forming condition calculator60uses such corrected sensor output to constantly set appropriate image forming conditions, including a fixing temperature.

A description is now given of creating a decreased output percentage calculation table that is stored in the second memory92. The table is created off-line in advance.

A sensor that is not affected by paper dust is disposed in an image forming apparatus. In other words, the sensor does not provide a paper dust-generated decreased output value. Recording media are conveyed for measurement of sensor outputs. After completing the measurement for one type of recording media, the sensor is cleaned up so that the sensor does not provide a decreased output value. Next, another type of recording media are conveyed for measurement of sensor outputs. The above-described operation is performed for recording media having different smoothness degrees to obtain a relation between the number of printouts and absolute sensor output value.

FIG. 11is a graph illustrating a relation between sensor output and the number of printouts. The absolute sensor output value depends on the reflection rate (i.e., smoothness) of the recording media. Since differences in decreased paper dust-generated output percentages due to the smoothness of the recording media cannot be evaluated, the sensor output is normalized to 100 when the number of printouts is zero. It is to be noted that, inFIG. 11, an arrow F indicates that the sensor outputs decrease due to paper dust.

FIG. 12is a graph illustrating a relation between normalized sensor output and the number of printouts. As illustrated inFIG. 12, the recording media having the lowest smoothness shows the greatest decreased output percentage per recording medium. When adhering to the sensor, paper dust coats a lens of the sensor and decreases the amount of light passing through the lens. The recording media having a relatively low smoothness generate a relatively large amount of paper dust. Accordingly, the paper dust coats the lens of the sensor in large amounts, thereby decreasing the amount of light passing through the lens and thus adversely affecting sensor precision.

Since the decreased output percentage depends on the smoothness of recording media, it can be expressed as a gradient of the decrease. For example,FIG. 12illustrates a regression equation of “Y=100×R^Number of recording media”, where R represents a rate of decrease with respect to the number of recording media. The rate of decrease depends on the recording media, in a range of about 0.9985±0.001. To use the relation for an update, gradients of the decreased percentage of the normalized sensor output are obtained with respect to a plurality of recording media.

FIG. 13is a graph of a table or regression equation, illustrating a relation between gradients of decreased output percentage and initial sensor output. Specifically, the horizontal axis indicates absolute sensor output values when the number of printouts is zero. The vertical axis indicates the inclination. From the data, a regression equation or a look-up table is created as a decreased output percentage calculation table with respect to initial output values. For example, an equation of “R=A×sensor output when the number of printouts is zero+B” may be stored as a look-up table.

If an image forming apparatus in use has conveyance conditions widely differing between trays, generating different amounts of paper dust, a table or regression equation may be created and stored for each tray.

A description is now given of calculation performed by the LED luminosity adjuster95.

The amount of light to be emitted by the LED is obtained from the decreased output amount, using the table or regression equation as illustrated inFIG. 13. The table or regression equation is created off-line in advance.

Firstly, absolute sensor output values are obtained with different LED currents, by changing the amount of paper dust adhering to a sensor. From the absolute sensor output values thus obtained, a decreased output percentage from a sensor output provided when no paper dust adheres to the sensor is obtained. In addition, an LED current (a2, a3. . . ) to correct the decreased sensor output to the sensor output provided when no paper dust adheres to the sensor is obtained.

Thus, a graph illustrated inFIG. 14is created.FIG. 14shows a relation between absolute output value of the sensor and LED current.

A regression equation of, e.g., “LED current=a1+A×decreased output percentage” may be created from the graph.

FIG. 15is a graph of such a regression equation. The LED luminosity adjuster95calculates and determines an LED current based on the total decreased output amount, using the regression equation or a table of the regression equation.

Referring now toFIG. 16, a description is given of a sensor maintenance process.FIG. 16is a flowchart of the sensor maintenance process.

Usually, maintenance of image forming apparatuses, such as replacement of deteriorating parts and cleaning of sensors, is performed periodically. In step S21, the sensor40is cleaned. For example, paper dust is removed from the sensor40. By cleaning the sensor40, the total decreased output amount used to predict a sensor output value by the above-described calculation becomes zero. Accordingly, the predicted sensor output value is also reset.

In the present embodiment, a cumulative value reset button (or execution button) is provided on a control panel400of the image forming apparatus1000. After the cleaning of the sensor40is completed, the execution button is pressed in step S22. In step S23, initialization starts. In step S24, the values accumulated in the third memories93and the LED luminosity are reset to their respective initial values. In step S25, the initialization is completed.

FIG. 17is a diagram illustrating an example of sensor output in the sensor maintenance process. In this example, the LED current is updated when the decreased output percentage for each tray does not reach a predetermined threshold.

As described above, according to at least one embodiment of the present invention, a decreased paper dust-generated output amount of a smoothness sensor is accurately predicted to adjust a luminosity of the smoothness sensor without additional production costs, to appropriately detect the output of the smoothness sensor.

Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.

For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention and appended claims.

Further, any of the above-described devices or units can be implemented as a hardware apparatus, such as a special-purpose circuit or device, or as a hardware/software combination, such as a processor executing a software program.