Patent Description:
To determine whether an image defect has occurred, an image forming apparatus that optically reads an image formed on a recording material has been proposed. <CIT> discloses a configuration in which the periodicity of an image defect is determined by reading an image formed on a plurality of recording materials, and a rotating member that generates the image defect is identified based on the determined periodicity. <CIT> discloses a configuration in which an image formed on a recording material based on image data is read, and an image indicated by the image data is compared to the image formed on the recording material to recognize a state of consumable items or the like.

For example, when an image formed on a recording material is read to determine a type of an image defect, and an image forming operation is changed so as to suppress the image defect of the determined type, another image defect may occur.

<CIT> shows a generic image forming apparatus according to the preamble of claim <NUM>, comprising image forming means arranged to form an image on a recording material based on first image data, control means arranged to control an image forming operation by the image forming means, acquisition means arranged to acquire property information related to a property of the recording material, setting means configured to set a control value to be used in the image forming operation to a base value based on the property information acquired by the acquisition means, reading means arranged to read an image formed on the recording material by the image forming means, and to output second image data, and comparison means configured to compare the first image data to the second image data, wherein the setting means is further configured to determine a correction value based on a comparison result.

It is the object of the present invention to further develop an image forming apparatus according to the preamble of claim <NUM> such that adverse image effects, for example, a so-called "hot offset" as explained below, caused by changing a fixing temperature can be suitably suppressed.

The object of the present invention is achieved by an image forming apparatus having the features of claim <NUM>.

Further features, advantage and effects of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

<FIG> is a configuration diagram of an image forming apparatus according to the present embodiment. Note that the characters Y, M, C, and K at the end of the reference signs in <FIG> indicate that the colors of the toner images, formed by participation of the members indicated by the reference signs, are yellow, magenta, cyan, and black, respectively. However, in the following description, when it is not necessary to distinguish colors, reference signs in which the last character is omitted are used. Each of photoconductors <NUM> is rotationally driven in a clockwise direction in the figure when forming an image. A charging roller <NUM> charges the surface of the corresponding photoconductor <NUM> to a uniform potential by outputting a charging bias voltage. An exposing device <NUM> forms an electrostatic latent image on the photoconductor <NUM> by exposing the corresponding photoconductor <NUM> based on image data. A developing roller <NUM> outputs a developing bias voltage to thereby cause toner to adhere onto the electrostatic latent image on the corresponding photoconductor <NUM>, and thus forms a toner image on the photoconductor <NUM>. A primary transfer roller <NUM> outputs a primary transfer bias voltage to transfer the toner image formed on the corresponding photoconductor <NUM> to an intermediate transfer belt <NUM>. Here, it is possible to form a full-color toner image on the intermediate transfer belt <NUM> by transferring the toner images formed on the respective photoconductors <NUM> to the intermediate transfer belt <NUM> in an overlapping manner.

The intermediate transfer belt <NUM> is rotationally driven in a counterclockwise direction in the figure during image forming. Thus, the toner image transferred onto the intermediate transfer belt <NUM> is conveyed to a position facing a secondary transfer roller <NUM>. On the other hand, a recording material Pin a cassette <NUM> is fed to a conveyance path <NUM>, and is then conveyed to the position facing the secondary transfer roller <NUM> by a plurality of rollers including registration rollers <NUM>. The secondary transfer roller <NUM> outputs a secondary transfer bias voltage to transfer the toner image on the intermediate transfer belt <NUM> to the recording material P. After the transfer of the toner image, the recording material P is conveyed to a fixing device <NUM>. The fixing device <NUM> includes a fixing film <NUM>, and a pressure roller <NUM> that is pressed against the fixing film <NUM>. Further, a fixing heater <NUM> that is a heating member configured to heat the fixing device <NUM>, and a thermistor <NUM> that measures the temperature of the fixing heater <NUM> are provided in the fixing film <NUM>. The fixing device <NUM> fixes the toner image onto the recording material P by pressurizing the recording material P by using the fixing film <NUM> and the pressure roller <NUM> and heating the recording material P by using the fixing heater <NUM>. The recording material P on which the toner image has been fixed is discharged to the outside of the image forming apparatus by discharge rollers <NUM>.

In addition, the image forming apparatus includes a reader <NUM> that optically reads a surface of the recording material P between the fixing device <NUM> and the discharge rollers <NUM>. The reader <NUM> has, for example, a light emitting element and a contact image sensor (CIS) (not illustrated). The reader <NUM> outputs the read image data of the surface of the recording material P to an engine control unit <NUM> (<FIG>). Further, the image forming apparatus includes a media sensor <NUM>. The media sensor <NUM> has an LED 40a and a CMOS area sensor 40b that are disposed opposite to each other with respect to the conveyance path <NUM>. In the present embodiment, the media sensor <NUM> is provided on the upstream side from the registration rollers <NUM> in the conveyance direction of the recording material. The CMOS area sensor 40b receives light emitted by the LED 40a through the recording material P being conveyed through the conveyance path <NUM>, and outputs a signal indicating a received light amount to the engine control unit <NUM> (<FIG>). Since a transmitted light amount is different depending on a basis weight of the recording material P, the engine control unit <NUM> can determine the basis weight of the recording material based on the received light amount.

Note that the fixing film <NUM> of the fixing device <NUM> is an endless film-shaped member provided with an elastic layer and a surface layer on an outer circumferential surface of a base layer. The elastic layer is formed from an elastic material having heat resistance such as silicon rubber or the like, in order to improve the fixing properties and to make the glossiness uniform. The surface layer is formed from a material having good releasability, and having heat resistance, such as fluorine resin, for the purpose of improving the separability from the recording material and suppressing an offset of toner. A thickness of the surface layer of the fixing film <NUM> is reduced by use. The pressure roller <NUM> has a core shaft portion, at least one or more elastic layers, and a surface layer. The elastic layer is formed from an elastic material having heat resistance such as silicon rubber or fluororubber. The surface layer is formed from a material having good releasability, and having heat resistance such as fluororesin or the like, in order to prevent contamination by toner or paper powder.

<FIG> is a control block diagram of the image forming apparatus according to the present embodiment. Note that in <FIG>, only the functional blocks necessary for the description of the present embodiment are illustrated. A controller <NUM> receives image information from a host computer via a local area network (LAN). An image processing unit <NUM> converts the image information received from the host computer into image data having a format to be used by the image forming apparatus, and outputs the converted image data to an engine unit <NUM>. The controller <NUM> includes a notification unit <NUM> configured to notify a user of a state and the like of the image forming apparatus.

An engine control unit <NUM> of the engine unit performs image forming control on the printing material P as explained using <FIG> based on the image data received from the controller <NUM>. The engine control unit <NUM> controls the reader <NUM>, the media sensor <NUM>, and the fixing device <NUM>. A hard disk drive (HDD) <NUM> is a storage unit that stores information. For example, the image data received from the controller <NUM> and image data read by the reader <NUM> are stored in the HDD <NUM>. Note that in the following description, the image data read by the reader <NUM> is expressed as "read image data", and is distinguished from the image data received from the controller <NUM>. The HDD <NUM> also stores various types of information that is used in the present embodiment. A comparison unit <NUM> compares the image data with the read image data to determine whether or not an image defect has occurred in the image formed on the recording material P. A setting unit <NUM> sets and updates various control values (set values) related to an image forming operation. For example, the setting unit <NUM> sets a target temperature of the fixing heater <NUM>. Based on a detection result of the thermistor <NUM>, the engine control unit <NUM> controls a temperature of the fixing heater <NUM> such that the temperature of the fixing heater <NUM> becomes the target temperature set by the setting unit <NUM>.

<FIG> is a flowchart related to target temperature setting control. Note that <FIG> illustrates processing in a case where an image defect to be detected is a hot offset. The hot offset is an image defect generated because the toner of the recording material P adheres to the fixing film <NUM> to cause the adhering toner to be transferred again to the recording material P. <FIG> is an image indicated by image data, and <FIG> illustrates a state in which a hot offset has occurred in the image formed based on the image data. The toner indicated by a reference sign of <NUM> in <FIG> is in a state where the toner indicated by a reference sign of <NUM> adheres to the recording material P through the fixing film <NUM>, that is, in a state where the toner indicated by the reference sign of <NUM> adheres to the recording material P due to a hot offset. Note that L1 corresponds to a circumferential length of the fixing film <NUM>. The hot offset occurs because the temperature of the fixing film <NUM> increases due to thinning of the surface layer of the fixing film <NUM>. The engine control unit <NUM> controls the temperature of the fixing heater <NUM> so as to become the target temperature, but when thinning of the surface layer of the fixing film <NUM> occurs, the temperature of the fixing film <NUM> when the fixing heater <NUM> is brought to the target temperature may be higher than the appropriate range. In this case, the hot offset occurs.

When receiving a print job, the engine control unit <NUM> performs the processing in <FIG> each time image data of an image to be formed in one recording material is received from the controller <NUM>. First, the engine control unit <NUM> stores image data received from the controller <NUM> in the HDD <NUM> in S100. In S101, the engine control unit <NUM> determines a basis weight of the recording material P based on a detection result of the recording material P by the media sensor <NUM> when the recording material P reaches a detection region of the media sensor <NUM>. The determined basis weight of the recording material P is stored in the HDD <NUM>.

In S102, the setting unit <NUM> first determines a base temperature Tb (base value) corresponding to the basis weight determined in S101. <FIG> shows a correspondence relationship between the basis weight and the base temperature Tb. In this example, the basis weight is evaluated by using two threshold values in three levels. In this example, the two respective threshold values are "<NUM>" and "<NUM>". For example, the base temperature Tb corresponding to the basis weight of "<NUM>" in <FIG> is <NUM>. In addition, the setting unit <NUM> manages a correction temperature ΔT (correction value) for each basis weight level (three in this example). An initial value of the correction temperature ΔT for each level is <NUM>. Note that, a configuration in which the correction temperature ΔT for each level is updated to the initial value of <NUM> when one print job is completed, and a configuration in which the correction temperature ΔT at the end of the print job is used in the next print job may be applicable. The setting unit <NUM> sets a target temperature Tg of the fixing heater <NUM> to a value obtained by subtracting the correction temperature ΔT of the level to which the basis weight belongs, from the base temperature Tb corresponding to the basis weight determined in S101.

Thereafter, in S103, the engine control unit <NUM> forms an image on the recording material based on the image data while controlling the temperature of the fixing heater <NUM> so as to become the target temperature Tg. Thereafter, in S104, the engine control unit <NUM> causes the reader <NUM> to read the image on the recording material P, acquires the read image data, and stores the read image data in the HDD <NUM>. In S105, the comparison unit <NUM> compares the image data stored in the HDD <NUM> with the read image data, and determines whether a hot offset has occurred based on the comparison result.

In a case where the engine control unit <NUM> determines that a hot offset has not occurred, the engine control unit <NUM> terminates the processing in <FIG>. In this case, the correction temperature ΔT belonging to the level of the basis weight of the recording material P on which the image has been formed is not changed. On the other hand, in a case where the engine control unit <NUM> determines that a hot offset has occurred, the engine control unit <NUM> provisionally determines, in S106, the correction temperature ΔT that belongs to the level of the basis weight of the recording material P on which the image has been formed. A method of determining the updated correction temperature ΔT will be described below using <FIG>. As illustrated in <FIG>, a surface temperature of the fixing film <NUM> and a density of a hot offset are in a proportional relationship. Additionally, the hot offset does not occur when the surface temperature of the fixing film <NUM> is lower than or equal to a threshold temperature Ts. The engine control unit <NUM> determines a density d1 of toner that has adhered to the recording material P due to the hot offset, and estimates a surface temperature T1 of the fixing film <NUM> from the relationship illustrated in <FIG>. Then, in S <NUM>, the engine control unit <NUM> provisionally determines a difference between the estimated surface temperature T1 and the threshold temperature Ts as the updated corrected temperature ΔT. Note that a configuration may be applicable in which a value obtained by adding a predetermined margin to the difference between the estimated surface temperature T1 and the threshold temperature Ts is provisionally determined as the correction temperature ΔT. In addition, in this example, the correction temperature ΔT has been determined based on the density of the toner that has adhered to the recording material P due to the hot offset, but an area of the toner that has adhered to the recording material P due to the hot offset can be also used.

In the present embodiment, an upper limit is provided for an absolute value of the correction temperature ΔT for each level. <FIG> shows an example of the upper limit value for each level. As shown in <FIG>, the lower the basis weight is, the larger the upper limit value is set. The reason why the lower the basis weight is, the larger the upper limit value is set is that the occurrence of adverse effects according to the correction temperature ΔT varies depending on the basis weight of the recording material P. Specifically, in a case of a relatively thin recording material P having a small basis weight, the fixing margin with respect to the fixing temperature is large, and thus, even when the correction temperature ΔT is made large, the adverse effects are small. On the other hand, in a case of a relatively thick recording material P having a large basis weight, the fixing margin with respect to the fixing temperature is small, and the adverse effects may occur when the correction temperature ΔT is made large.

The engine control unit <NUM> determines, in S107, whether or not the provisionally determined correction temperature ΔT is within the upper limit. When the provisionally determined correction temperature ΔT is within the upper limit value, the engine control unit <NUM> updates, in S108, the correction temperature ΔT to the correction temperature ΔT determined in S <NUM>. On the other hand, when the provisionally determined correction temperature ΔT exceeds the upper limit value, the engine control unit <NUM> notifies the user of the occurrence of the image defect and the replacement of the fixing device <NUM> via the notification unit <NUM> of the controller <NUM>. Note that in this case, the processing in <FIG> is terminated without updating the correction temperature ΔT.

Note that although the processing in <FIG> suppresses the hot offset that occurs by an increase in the fixing temperature, the present invention can be similarly applied to an image defect generated by a decrease in the fixing temperature. For example, when the fixing temperature becomes too low, an image defect (void image) may occur in which toner does not adhere to a high-density region to which the toner is to adhere. In this case, in S102 in <FIG>, the target temperature Tg is determined by adding the correction temperature ΔT to the base temperature Tb. Furthermore, the correction temperature ΔT for each level is provided with an upper limit value as illustrated in <FIG>. In <FIG>, the larger the basis weight is, the larger the upper limit value of the correction temperature ΔT is set. Note that the reason why the larger the basis weight is, the larger the upper limit value of the correction temperature ΔT is set is that, as the basis weight is small, the resistance to thermal stress deteriorates, so that increasing the correction temperature ΔT increases the possibility of the occurrence of adverse effects such as curling or winding around the fixing device <NUM>.

In the present embodiment, the base temperature Tb corresponding to the basis weight of the recording material P is corrected by the correction temperature ΔT to be set as the target temperature Tg of the fixing heater <NUM>. Note that, in a case where an image defect has occurred in the image formed on the recording material P, the correction temperature ΔT is set based on the degree of the image defect. The image defect is determined by reading the image formed on the recording material P. Note that the upper limit value of the correction temperature ΔT is provided corresponding to the basis weight. By providing the upper limit value of the correction temperature ΔT based on the basis weight, it is possible to suppress adverse effects caused by changing the fixing temperature.

Note that the determination and update of the correction temperature ΔT may be performed each time an image is formed on the predetermined number of recording materials P. Additionally, the occurrence of an image defect is determined each time an image is formed on the recording material P, and the correction temperature ΔT is determined, but a configuration may be applicable in which each time an image is successively formed on the predetermined number of recording materials P, the correction temperature ΔT is updated to an average value of the correction temperature ΔT determined each time. As a result, the frequency of changing the image forming conditions can be made moderate.

Additionally, in the present embodiment, the basis weight of the recording material P is used as property information related to the properties of the recording material P, but a configuration may be applicable in which the roughness and glossiness of the surface of the recording material P are used as the property information. In addition, in the present embodiment, the target temperature of the fixing heater <NUM> is controlled, but the present invention can also be applied to setting of other control values such as the secondary transfer bias voltage. That is, the control value related to the image forming operation is not limited to the target temperature of the fixing heater <NUM> described in the present embodiment, and can be, for example, a target value of the secondary transfer bias voltage. The present invention can also be applied not only to the color image forming apparatus illustrated in <FIG>, but also to a monochrome image forming apparatus. Furthermore, the present invention is applicable not only to an electrophotographic image forming apparatus, but also to ink ejection control and the like of an ink-jet image forming apparatus.

Next, the second embodiment will be described focusing on differences from the first embodiment. In the first embodiment, description has been made focusing on the control of the fixing temperature in a case where a hot offset has occurred as an image defect. In the present embodiment, the type of an image defect is determined by comparing image data to read image data, and a control target is selected based on the determined type of the image defect and the basis weight. An example is shown in <FIG>. As shown in <FIG>, for example, in a case where an image defect is generated in which toner adheres to a region to which the toner is not to adhere (non-normal toner adherence), the fixing temperature is controlled when the basis weight of the recording material P is smaller than <NUM>. In other words, this is similar to the first embodiment. On the other hand, in a case where the non-normal toner adherence occurs, when the basis weight of the recording material P is equal to or larger than <NUM>, control of a developing bias voltage is performed under the estimation that so-called development fog has occurred, rather than a hot offset. As described in the first embodiment, adverse effects due to the fact that the larger the basis weight is, the lower the fixing temperature is made are likely to occur. Therefore, when the basis weight is large, identification of the cause and control correction can be quickly performed by controlling the developing bias voltage in advance.

In addition, as shown in <FIG>, for example, in a case where an image defect (void image) has occurred in which toner does not adhere to a high-density region to which the toner is to adhere, the fixing temperature is controlled when the basis weight of the recording material P is equal to or larger than <NUM>. In other words, it is determined that a fixing failure has occurred, similarly to the first embodiment. On the other hand, in a case where a void image has occurred, when the basis weight of the recording material P is smaller than <NUM>, control of the secondary transfer bias voltage is performed under estimation that a so-called secondary transfer defect has occurred, rather than the fixing failure. As described in the first embodiment, as the basis weight is small, adverse effects due to increasing the fixing temperature are likely to occur. Thus, when the basis weight is small, the secondary transfer bias voltage can be controlled in advance to quickly identify the cause and to correct the control.

Note that, for example, when the roughness of the surface of the recording material P is large, a risk that a secondary transfer failure occurs increases, so the surface properties of the recording material P are detected to prioritize control in which the secondary transfer bias is made high. In this way, an item for which control is to be changed can be set according to the properties of the recording material P to be detected.

As described above, the control target is changed based on a combination of the type of the image defect, that is, a comparison result by the comparison unit <NUM>, and the property information of the recording material. According to this configuration, it is possible to quickly perform the identification of the cause of the image defect and the correction control.

Next, a third embodiment will be described focusing on differences from the first embodiment and the second embodiment. As illustrated in <FIG>, in the present embodiment, a plurality of image forming apparatuses <NUM>, and <NUM> to <NUM>, and an HDD apparatus <NUM> are connected to a LAN <NUM>. Note that, in the present embodiment, the image forming apparatus <NUM> is similar to the image forming apparatus described in the first embodiment and the second embodiment. In contrast, the image forming apparatuses <NUM> to <NUM> have differences from the image forming apparatus <NUM>.

<FIG> indicates differences between the image forming apparatus <NUM> and each of the image forming apparatuses <NUM> to <NUM>. As indicated in <FIG>, the image forming apparatus <NUM> differs from the image forming apparatus <NUM> in that the image forming apparatus <NUM> does not have the reader <NUM>. The image forming apparatus <NUM> differs from the image forming apparatus <NUM> in that the image forming apparatus <NUM> does not have the reader <NUM> and the media sensor <NUM>. Furthermore, the image forming apparatus <NUM> has a different image forming configuration from the image forming apparatus <NUM>, and differs from the image forming apparatus <NUM> in that the image forming apparatus <NUM> does not include the reader <NUM>. Furthermore, the image forming apparatus <NUM> has a different image forming configuration from the image forming apparatus <NUM>, and differs from the image forming apparatus <NUM> in that the image forming apparatus <NUM> does not include the reader <NUM> and the media sensor <NUM>. Note that the different image forming configuration means that, for example, the configuration itself related to image forming, such as transferring a toner image directly from each of the photoconductors <NUM> to the recording material P without using the intermediate transfer belt <NUM>, is different. Additionally, the different image forming configuration also means that the configuration itself is basically similar to that in <FIG>, but the configurations and materials of the respective members are different.

The image forming apparatus <NUM> stores, in the HDD apparatus <NUM> via the LAN <NUM>, history data indicating a relationship between the correction temperature ΔT associated with the level of the basis weight and the number of recording materials P (hereinafter, the cumulative number) on which an image has been formed. Each of the image forming apparatuses <NUM> to <NUM> can acquire the history data indicating the relationship between the cumulative number stored in the HDD apparatus <NUM> and the correction temperature ΔT via the LAN <NUM>. Note that, as described in the first embodiment, the correction temperature ΔT varies according to the level of the basis weight.

Since the image forming apparatus <NUM> does not have the reader <NUM>, the image forming apparatus <NUM> cannot determine an image defect by using read image data. However, since the image forming apparatus <NUM> includes the media sensor <NUM>, the image forming apparatus <NUM> can acquire the basis weight of the recording material P. Accordingly, the image forming apparatus <NUM> can determine the correction temperature ΔT according to the basis weight based on the history data acquired from the HDD apparatus <NUM>. Note that the correction temperature ΔT to be used is a value corresponding to the cumulative number in the image forming apparatus <NUM>.

Since the image forming apparatus <NUM> does not have the media sensor <NUM>, the image forming apparatus <NUM> cannot detect the basis weight of the recording material P. However, a managed print service (hereinafter, abbreviated as MPS) that performs centralized management of a plurality of image forming apparatuses placed in an office has recently been provided. In the MPS environment, management may be performed by a "management user" providing the service, together with the management of recording mediums. Thus, when the type of the recording material P to be used in the office is assumed to be the same, the image forming apparatus <NUM> can determine the correction temperature ΔT based on the history data stored in the HDD apparatus <NUM>. Furthermore, when the user sets the type of the recording material P, the correction temperature ΔT can be determined based on the history data stored in the HDD apparatus <NUM> and the basis weight corresponding to the type.

The image forming apparatus <NUM> has the media sensor <NUM>, and thus, can acquire the basis weight of the recording material P. However, since the image forming configuration of the image forming apparatus <NUM> is different from that of the image forming apparatus <NUM>, the correction temperature ΔT used by the image forming apparatus <NUM> cannot be used as it is. However, by previously determining a conversion method from the correction temperature ΔT in the image forming apparatus <NUM> to the correction temperature ΔT in the image forming apparatus <NUM> while considering differences in image forming configuration between the image forming apparatus <NUM> and the image forming apparatus <NUM>, the image forming apparatus <NUM> can determine the correction temperature ΔT.

Since the image forming apparatus <NUM> does not have the media sensor <NUM>, the image forming apparatus <NUM> cannot detect the basis weight of the recording material P, and has a different image forming configuration from that of the image forming apparatus <NUM>, similarly to the image forming apparatus <NUM>. However, similarly to the image forming apparatus <NUM>, when the type of the recording material P to be used in the office is assumed to be the same, the image forming apparatus <NUM> can determine the basis weight. Additionally, similarly to the image forming apparatus <NUM>, the correction temperature ΔT stored in the HDD apparatus <NUM> can be converted and used.

As described above, according to the present embodiment, a first image forming apparatus stores, in the HDD apparatus <NUM>, the history data indicating the relationship among the cumulative number, the correction temperature ΔT, and the basis weight (properties) of the recording material. According to this configuration, even in a case of a second image forming apparatus that does not have the reader <NUM>, the correction temperature ΔT can be determined based on the basis weight of the recording material on which an image is formed and the cumulative number. Furthermore, even in a case of a third image forming apparatus that does not have the reader <NUM> and in which image forming is different from that of the first image forming apparatus, the correction temperature ΔT can be determined based on the basis weight of the recording materials on which an image is formed and the cumulative number. Note that the third image forming apparatus converts the correction temperature ΔT stored in the HDD apparatus <NUM> in accordance with a predetermined conversion method. Note that the conversion method is predetermined based on differences in image forming configuration between the first image forming apparatus and the third image forming apparatus. Furthermore, even in a case of a fourth image forming apparatus that does not have the media sensor <NUM>, when a recording material having similar properties is assumed to be used, the correction temperature ΔT can be determined based on the cumulative number.

Note that instead of providing the HDD apparatus <NUM>, a configuration may be applicable in which the history data is stored in the image forming apparatus <NUM>. In this case, the image forming apparatuses <NUM> to <NUM> acquire the correction temperature ΔT by accessing the image forming apparatus <NUM>. In other words, the image forming apparatus <NUM> provides the history data to the image forming apparatuses <NUM> to <NUM>.

Next, a fourth embodiment will be described, focusing on differences from the first embodiment to the third embodiment. <FIG> illustrates a portion from the registration rollers <NUM> to the fixing device <NUM>. In the image forming apparatus, in order to stabilize the conveyance of the recording material P, the recording material P is deflected between the secondary transfer roller <NUM> and the fixing device <NUM> as illustrated by a reference sign P1 (an arching state P1) in <FIG> (hereinafter, referred to as arching control). The arching control is performed by adjusting a rotational speed of the pressure roller <NUM>. However, the pressure roller <NUM> that has exceeded an expected lifetime may reduce the rubber hardness, and reduce the outer diameter. As a result, the conveying speed of the recording material by the pressure roller <NUM> is reduced, and the desired amount of arching cannot be maintained. As a result, as illustrated by a reference sign P2 (arching state P2) and a reference sign P3 (arching state P3) in <FIG>, an arch having a desired amount of arching or larger can be formed.

In the configuration of the image forming apparatus, the pinching and conveying force of the recording material caused by the secondary transfer roller <NUM> and the intermediate transfer belt <NUM> is smaller than that of the registration rollers <NUM> and the fixing device <NUM>. Thus, the stress stored in the recording material P in the arching state is released at the moment when the rear end of the recording material P passes through the registration rollers <NUM>. As in the arching states P2 and P3, when the amount of arching is large, the stress to be released also increases, and at the moment when the rear end of the recording material P passes through the registration rollers <NUM>, the conveying speed of the recording material may change. At this time, transfer blur may occur. <FIG> is an image that is indicated by image data, and <FIG> illustrates a state in which transfer blur occurs in the image that is indicated by the image data illustrated in <FIG>. In <FIG>, expansion and contraction of the image occur at a position at a distance L2 from the rear end of the recording material P. Note that the distance L2 is a distance between the registration rollers <NUM> and the secondary transfer roller <NUM>. As a result, a stripe-like density difference <NUM> occurs in a direction orthogonal to the conveyance direction of the recording material.

<FIG> shows a relationship between a plain paper sheet having a basis weight w = <NUM> and transfer blur, and <FIG> shows a relationship between a cardboard sheet having a basis weight w = <NUM> and transfer blur. As shown in <FIG>, in the plain paper, no transfer blur occurs in the arching states P1 and P2. However, in a case of the arching state P3, negligible transfer blur may infrequently occur. However, the transfer blur infrequently occurs in the arching state P3 when the image forming apparatus is unexpectedly used, such as when the image forming apparatus continues to be used over its expected lifetime. That is, unless the image forming apparatus is unexpectedly used, the transfer blur does not occur in a case where the basis weight w is equal to or smaller than <NUM>. On the other hand, as indicated in <FIG>, in a case of the cardboard sheet, transfer blur does not occur in the arching state P1, but transfer blur occurs in the arching states P2 and P3. In this way, whether or not transfer blur occurs depends on, in addition to the degree of arching state, the basis weight of the recording material. This is because the stress stored in the recording material in the arching state increases as the basis weight increases.

In the present embodiment, the correction control in which the rotational speed of the pressure roller <NUM> is made larger than the reference rotational speed is performed to suppress the transfer blur. First, as indicated in <FIG>, in the arching states P2 and P3 in the case of the cardboard sheet, the rotational speed of the pressure roller <NUM> is corrected. Note that, in the case of the arching state P2, the rotational speed of the pressure roller <NUM> is made <NUM>% faster than the reference rotational speed. On the other hand, in the case of the arching state P3, the rotational speed of the pressure roller <NUM> is made <NUM>% faster than the reference rotational speed. Note that, in the case of the arching state P1, the correction is not performed because transfer blur does not occur.

On the other hand, as illustrated in <FIG>, in the case of the plain paper sheet, the correction control of the rotational speed of the pressure roller <NUM> is not performed regardless of the arching state. As described above, transfer blur infrequently occurs in the arching state P3, but this is only a case when the image forming apparatus is unexpectedly used. This is also because other adverse effects may occur when the correction control is performed in order to suppress transfer blur caused by such unexpected use. Specifically, this is because, when the correction control is performed in order to reduce the amount of arching, adverse effects such as image rubbing due to excessive pulling of the recording material may easily occur.

<FIG> is a flow chart related to rotational speed setting control of the pressure roller <NUM>. The engine control unit <NUM> performs processing in <FIG> each time image data is received from the controller <NUM>. First, the engine control unit <NUM> stores the image data received from the controller <NUM> in the HDD <NUM>, in S200. The engine control unit <NUM> determines the basis weight of the recording material P based on the detection result of the recording material P by the media sensor <NUM> when the recording material P reaches the detection region of the media sensor <NUM> in S201, and determines whether the recording medium P is a plain paper sheet or a cardboard sheet in S202. When the plain paper sheet is used, the setting unit <NUM> sets a target rotational speed Sg to a base rotational speed Sb (base value) in S211. On the other hand, when the cardboard sheet is used, the setting unit <NUM> sets the target rotational speed Sg to a speed obtained by adding a correction value ΔS to the base rotational speed Sb in S203. The correction value ΔS is a value indicating an increasing amount of the base rotational speed Sb, and its initial value is <NUM>.

Thereafter, the engine control unit <NUM>, in S204, forms an image on the recording material based on the image data while controlling the rotational speed of the pressure roller <NUM> so as to become the target rotational speed Sg. Thereafter, in S205, the engine control unit <NUM> causes the reader <NUM> to read the image on the recording material P, acquires the read image data, and stores the read image data in the HDD <NUM>. In S206, the comparison unit <NUM> compares the image data stored in the HDD <NUM> with the read image data to determine whether transfer blur has occurred or not. For example, the comparison unit <NUM> can determine that the transfer blur has occurred when a density difference, which is not present in the image based on the original image data, occurs in the image based on the read image data in a width direction orthogonal to the conveyance direction. Note that the density difference in the width direction occurs at around the distance L2 from the rear end of the recording material, so the comparison unit <NUM> can determine whether or not the transfer blur has occurred by determining whether or not the density difference occurs at around the distance L2 from the rear end of the recording material.

In a case where the engine control unit <NUM> determines that the transfer blur has not occurred, the engine control unit <NUM> terminates the processing in <FIG>. In this case, the correction value ΔS is not changed. On the other hand, in a case where the engine control unit <NUM> determines that the transfer blur has occurred, the engine control unit <NUM> determines whether the recording material being conveyed in S207 is the cardboard sheet or the plain paper sheet. Since the correction value ΔS is for the cardboard sheet, when the recording material is the plain paper sheet, the engine control unit <NUM> terminates the processing in <FIG>. Note that, in this case, the engine control unit <NUM> stores, in the HDD <NUM>, the fact that the transfer blur has occurred in the plain paper sheet.

On the other hand, when the recording material is determined to be the cardboard sheet in S207, the engine control unit <NUM> provisionally determines the correction value ΔS in S208. Note that, in S206, the engine control unit <NUM> can determine only whether or not the transfer blur has occurred, and cannot determine whether the arching state is P2 or P3. Thus, in the present embodiment, whether the arching state is P2 or P3 is determined depending on whether or not the transfer blur has occurred in the plain paper sheet. Specifically, when information about the fact that the transfer blur has occurred in the plain paper sheet is stored in the HDD <NUM>, the engine control unit <NUM> determines that the arching state is P3. That is, the engine control unit <NUM> determines that the arching state is P3 in a case where the transfer blur has occurred in both the plain paper sheet and the cardboard sheet. Thus, as shown in <FIG>, the correction value ΔS is increased by <NUM>%. On the other hand, when the information about the fact that the transfer blur has occurred in the plain paper sheet is not stored in the HDD <NUM>, the engine control unit <NUM> determines that the arching state is P2. Thus, the correction value ΔS is increased by <NUM>% as shown in <FIG>.

As with the first embodiment, the upper limit value of the correction value ΔS is also provided in the present embodiment. This is because, when the rotational speed of the pressure roller <NUM> is too high, adverse effects such as image rubbing due to excessive pulling of the recording material may easily occur. The engine control unit <NUM> determines whether or not the provisionally determined correction value ΔS is within the upper limit value in S209. When the provisionally determined correction value ΔS is within the upper limit value, the engine control unit <NUM>, in S210, updates the correction value ΔS to the correction value ΔS determined in S208. On the other hand, when the provisionally determined correction value ΔS exceeds the upper limit value, the user is notified of the occurrence of the image defect and the replacement of the fixing device <NUM> and/or each of the conveyance rollers, via the notification unit <NUM> of the controller <NUM>. Note that, in this case, the processing in <FIG> is terminated without updating the correction value ΔS.

As described above, when the image defect is determined, the correction value for the control value related to the image forming is determined based on the basis weight of the recording material. According to this configuration, the occurrence of an image defect different from the determined image defect can be suppressed.

Note that in the present embodiment, setting of the rotational speed of the pressure roller <NUM> for the two basis weights of the plain paper sheet and the cardboard sheet has been described, but the levels of the basis weight can be any two or more levels. In addition, in the present embodiment, the basis weight of the recording material is used as property information, but the thickness or stiffness of the recording material may also be used as the property information. For example, even when the basis weight is the same, since there is a recording material having different stiffness because of the material and the method, any number of combinations among the basis weight, thickness, and stiffness of the recording material can be used as the property information.

Furthermore, a configuration is possible in which a detection image for detecting an image defect is used instead of an image to be formed by the user on the recording material. <FIG> illustrates an example of the detection image. The detection image has an image C1 for detecting a hot offset and a halftone image C2 for detecting transfer blur. In <FIG>, a reference sign of <NUM> denotes toner that has adhered to the recording material due to a hot offset, and a reference sign of <NUM> denotes a region where a density difference occurs due to transfer blur. By using the detection image as illustrated in <FIG>, the occurrence of a plurality of image defects can be detected.

Claim 1:
An image forming apparatus (<NUM>), comprising:
image forming means arranged to form an image on a recording material (P) based on first image data;
control means (<NUM>) arranged to control an image forming operation by the image forming means;
acquisition means (<NUM>) arranged to acquire property information related to a property of the recording material (P);
setting means (<NUM>) configured to set a control value to be used in the image forming operation to a base value based on the property information acquired by the acquisition means (<NUM>);
reading means (<NUM>) arranged to read an image formed on the recording material (P) by the image forming means, and to output second image data; and
comparison means (<NUM>) configured to compare the first image data to the second image data,
wherein the setting means (<NUM>) is further configured to determine a correction value based on a comparison result,
wherein
the setting means (<NUM>) is further configured to change the control value based on the base value and the correction value,
the image forming apparatus (<NUM>) further comprises notification means (<NUM>),
an upper limit value corresponding to the property information is set for the correction value,
in a case where the correction value exceeds the upper limit value, the setting means (<NUM>) is configured not to change the control value and the notification means (<NUM>) is configured to notify a user of information related to the comparison result, and in a case where the correction value does not exceed the upper limit value, the setting means (<NUM>) is configured to change the control value based on the base value and the correction value.