Patent Grant
9250591
1. Field of the Invention
The present invention relates to a technology for detecting the state of a recording medium.
2. Description of the Related Art
Conventionally, there are image forming apparatuses such as copying machines, printers, and so forth, which have sensors to detect the state of recording media, inside of the image forming apparatus. These apparatuses automatically detect the state of a recording medium, and control transfer conditions (e.g., transfer voltage, conveyance speed of the recording medium at the time of transfer) and fixing conditions (e.g., fixing temperature, conveyance speed of the recording medium at the time of fixing), according to the detection results.
One example of a state of the recording medium to be detected is the moisture included in the recording medium. Different moisture amounts included in the recording medium changes the resistance value and heat capacity of the recording medium, so image quality may deteriorate of images are recorded on recording media under the same transfer conditions and fixing conditions. Accordingly, these apparatuses detect the amount of moisture included in the recording medium, and control the transfer conditions and fixing conditions according to the results of detection.
Japanese Patent Laid-Open No. 2008-145514 describes an image forming apparatus where a lever to detect the thickness of the recording medium is provided in a conveyance path. When the recording medium is conveyed, the lever is pressed upwards by an amount equivalent to the thickness of the recording medium, and the thickness of the recording medium can be detected by the amount of displacement of the lever. This image forming apparatus detects the amount of moisture included in the recording medium by comparing the thickness of the recording medium before passing through a fixing unit and after having passed through the fixing unit. The transfer conditions and the like are controlled according to the moisture amount detection results, thereby improving image quality.
However, the configuration described in Japanese Patent Laid-Open No. 2008-145514 is a configuration to detect thickness by the lever coming into direct contact with the recording medium, there are cases where the precision of thickness detection, and accordingly the precision of moisture amount detection, deteriorates due to the effects of flapping of the recording medium being conveyed. Also, in a case where the recording medium is thin paper, change in the amount of moisture hardly changes the thickness at all, so accurately detecting the amount of moisture has been difficult. Accordingly, while the configuration described in Japanese Patent Laid-Open No. 2008-145514 could obtain moisture amount detection precision sufficient for satisfying the image quality desired at that time, there has been demand in recent years for improved moisture amount detection precision, to satisfy the image quality demanded nowadays.
A sensor is attached to an apparatus having a fixing unit which fixes an image on a recording medium by heating the recording medium. The sensor includes: a transmission unit configured to transmit an ultrasonic wave to the recording medium; a reception unit configured to receive the ultrasonic wave via the recording medium, and output a signal corresponding to the received ultrasonic wave; and a detecting unit. The detecting unit is configured to detect information relating to a state of the recording medium which has changed by passing through the fixing unit, based on a first signal which the reception unit has output upon having received the ultrasonic wave before the recording medium has passed through the fixing unit, and a second signal which the reception unit has output upon having received the ultrasonic wave after the recording medium has passed through the fixing unit.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Embodiments of the present invention will be described with reference to the drawings. It should be noted that the following embodiments are only exemplary, and do not restrict the scope of the present invention thereby.
An ultrasonic wave sensor according to the present embodiment can be used in an image forming apparatus such as a copying machine or printer or the like, for example.
The components of the image forming apparatus 1 illustrated in
Next, the image forming operations of the image forming apparatus 1 will be described. The image forming control unit 3 includes a central processing unit (CPU) 80, which centrally controls the image forming operations of the image forming apparatus 1. Image forming commands and image data are input to the image forming control unit 3 from a host computer or the like, omitted from illustration. The image forming apparatus 1 thereupon starts image forming operations, and a recording medium P is supplied from the sheet feed cassette 2 by the supply roller 4. The recording medium P is conveyed by the conveyance roller 5 and conveyance opposing roller 6, toward the nip portion (omitted from illustration) formed by the secondary transfer roller 19 and secondary transfer opposing roller 20, so as to be timed correctly with the image formed on the intermediate transfer belt 17. Along with the operation of the recording medium P being supplied from the sheet feed cassette 2, the photosensitive drums 11Y, 11M, 11C, and 11K are changed to a constant potential by the charging rollers 12Y, 12M, 12C, and 12K. The optical units 13Y, 13M, 13C, and 13K expose the surfaces of the charged photosensitive drums 11Y, 11M, 11C, and 11K by laser beams to form electrostatic latent images, in accordance with input image data. The formed electrostatic latent images are visualized by developing performed using the developing units 14Y, 14M, 14C, and 14K and the developing agent conveying rollers 15Y, 15M, 15C, and 15K. The electrostatic latent images formed in the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K are developed by the developing units 14Y, 14M, 14C, and 14K in their respective colors. The photosensitive drums 11Y, 11M, 11C, and 11K are each in contact with the intermediate transfer belt 17, and rotate synchronously with the intermediate transfer belt 17. The developed images of the respective colors are transferred onto the intermediate transfer belt 17 in order by the primary transfer rollers 16Y, 16M, 16C, and 16K, so as to form one superimposed image. The image formed on the intermediate transfer belt 17 are secondary-transferred onto the recording medium P by the secondary transfer roller 19 and secondary transfer opposing roller 20. The image transferred onto the recording medium P is fixed by being heated and pressurized by a fixing unit 21 including a fixing roller and so forth. Developing agent remaining on the intermediate transfer belt 17 without being transferred onto the recording medium P is cleaned by a cleaning unit 36.
In a case where no image forming is to be performed on the back face of the recording medium P, the recording medium P upon which the image has been formed is guided to a conveyance path where discharge rollers 22 have been provided, by the flapper 91, and is discharged to a discharge tray 26. This conveyance path is indicated by a solid line in
Next, the ultrasonic wave sensor 90 will be described. The ultrasonic wave sensor 90 (hereinafter also simply “90”) is capable of detecting the grammage of the recording medium P. The term grammage means the mass of the recording medium P per unit area, and is expressed in terms of grams per square meter, or g/m2. The sensor 90 which detects the grammage of the recording medium P is disposed on the upstream side of the secondary transfer roller 19 and secondary transfer opposing roller 20 in the conveyance direction of the recording medium in the image forming apparatus 1 illustrated in
The transmission unit 31 and the reception unit 32 have similar configurations, each being configured including a piezoelectric element (or simply “piezo element”), which is an inter-conversion element of mechanical displacement and electric signals, and electrode terminals. Inputting pulsed voltage of a predetermined frequency to the electrode terminals of the transmission unit 31 causes the piezoelectric element to oscillate and generate a sound wave. When a recording medium P is interposed therebetween, the emitted sound wave is transmitted through the air and reaches the recording medium P. Upon the sound wave reaching the recording medium P, the recording medium P is vibrated by the sound wave. Vibration of the recording medium P transmits the sound wave which further travels through the air and reaches the reception unit 32. The sound wave which has been transmitted from the transmission unit 31 reaches the reception unit 32 in a state of having been attenuated by the recording medium P. The piezoelectric element of the reception unit 32 outputs a voltage value corresponding to the amplitude of the received sound wave to the electrode terminals. This is the operational principle of transmitting and receiving an ultrasonic wave using piezoelectric elements.
Next, the method for detecting the grammage of the recording medium P using the sensor 90 will be described with reference to the block diagram in
A signal indicating starting of measurement is input from the control unit 60 to a drive signal control unit 341. Upon receiving the input signal, the drive signal control unit 341 instructs a drive signal generating unit 331 to generate drive signals. The drive signal generating unit 331 generates and outputs signals having the frequency set beforehand.
The reception unit 32 receives the ultrasonic waves transmitted from the transmission unit 31 or the ultrasonic waves attenuated at the recording medium P, and outputs received signals to a detection circuit 342 of the reception control unit 34. The detection circuit 342 includes an amplifying unit 351 and a half-wave rectifying unit 352, as illustrated in
Next, the results of having detected grammage before the recording medium P passes through the fixing unit 21, and the results of having detected grammage after the recording medium P has passed through the fixing unit 21, are illustrated in
It can be seen from
It can also be seen in
In the present embodiment, a value obtained by multiplying by 1,000 the absolute value of the difference between the calculation coefficient of the recording medium P before passing through the fixing unit 21 the first time, and the calculation coefficient after having passed through the fixing unit 21 once, is defined as the moisture amount included in the recording medium P (information relating to moisture amount), for sake of convenience. For example, in the case of paper A, (0.03903−0.03238)×1000=6.65, so the amount of moisture is 6.65. The amount of moisture continued in paper differs depending on the state in which the paper is stored, and the amount of moisture contained in paper left standing for a long time under an environment of temperature 30° C. and humidity 80% (hereinafter, referred to as “standing paper”) is around 6.65. On the other hand, paper immediately after having been removed from its wrapper (hereinafter referred to as “newly-opened paper”) has less moisture amount. In the present embodiment, paper regarding which the detected amount of moisture is 1.5 or more is defined as standing paper, and paper regarding which the detected amount of moisture is less than 1.5 is defined as newly-opened paper. Note that the method for calculating the amount of moisture is not restricted to this method, and an arrangement may be made where the difference between the computation coefficient of the paper before passing through the fixing unit 21 the first time and the computation coefficient after having passed through the fixing unit 21 once is normalized by the computation coefficient after having passed through the fixing unit 21 once, or the like. The CPU 80 controls various image forming conditions according to the amount of moisture, in the same way as with the case of grammage. For example, with regard to secondary transfer, if the amount of moisture contained in the paper is great, the resistance value of the paper drops, and transfer current readily escapes to the margin portions. As a result, transfer defects readily occur. Therefore, there may be a need to increase the value of voltage applied to the secondary transfer roller 19 (hereinafter, described as “secondary transfer bias”). Also, with regard to fixing, the heat capacity of paper containing a great amount of moisture is also great, so the fixing temperature has to be raised accordingly.
Table 1 illustrates the detection results of the amount of moisture under an environment of temperature 30° C. and humidity 80% in the first embodiment, secondary transfer bias at the time of forming an image on the first face, and fixing temperature settings. There are standing paper and newly-opened paper for each of the three types of paper each with different grammage, for a total of six types of paper in this example. A table is stored in the storage unit 346 storing the moisture amounts and image forming conditions shown in Table 1, from which the CPU 80 reads out data and sets image forming conditions.
Overall, when the amount of moisture is small, the secondary transfer bias and fixing temperature are both set low, and the secondary transfer bias and fixing temperature are both set high for the standing paper of which the amount of moisture is great. While an example of setting the secondary transfer bias and fixing temperature according to the amount of moisture is described in the present embodiment, other image forming conditions may be set, such as charging bias, developing bias, laser beam intensity, conveyance speed of paper, and so forth. Here, the charging bias means the value of voltage to be applied to the charging roller 12, and developing bias means the value of voltage to be applied to the developing agent conveying rollers 15Y, 15M, 15C, and 15K. For example, in a case of standing paper where the secondary transfer bias has to be set high, the charging bias, developing bias, and laser beam intensity are set so that the amount of developing agent in the toner images formed by developing the electrostatic latent images on the photosensitive drums 11Y, 11M, 11C, and 11K is greater. Thus, even if transfer current escapes to the margins as described above, and a greater amount of residual toner remains on the intermediate transfer belt 17 after secondary transfer, an amount of developing agent can be transferred onto the paper.
Next, the timing for setting the image forming conditions and performing image formation based on the results of the detected amount of moisture will be described. The ultrasonic wave sensor 90 according to the present embodiment can detect grammage without temporarily stopping the paper, so even when consecutively forming images on multiple sheets of paper, the grammage of the paper for when printing on the first face and the second face can be detected in real time, without temporarily stopping image formation. Accordingly, optimal image forming conditions can be set based on the amount of moisture calculated from the difference in grammage (or computation coefficient) at the time of forming an image on the first face of a first sheet and at the time of forming an image on the second face thereof, and this can be reflected when forming an image on the first face of a subsequent second sheet.
Next, detection of amount of moisture and control of image forming conditions according to the present embodiment will be described with reference to the flowcharts in
First, operations regarding the first sheet will be described with reference to the flowchart in
In the same way for the second face of the first sheet as with the first face, the sensor control unit 30 calculates the calculation coefficient (S108) from the no-paper measurement (S106) and with-paper measurement (S107), the CPU 80 sets the image forming conditions (S109), and performs image forming (S110). At the same time, the sensor control unit 30 detects the amount of moisture of the first sheet from the results in S103 and S108, and stores this in the storage unit 346. The image forming conditions for the second face may be the same as with the first face, or may be conditions set with the secondary transfer bias and fixing temperature reduced from those of the first face by a predetermined value. If changes can be made right away, image forming conditions may be set reflecting the amount of moisture detected in S108.
Operations regarding the second sheet will be described with reference to the flowchart in
In the same way for the second face of the second sheet as with the second face of the first sheet, the sensor control unit 30 calculates the calculation coefficient (S120) from the no-paper measurement (S118) and with-paper measurement (S119), the CPU 80 sets the image forming conditions (S121), and performs image forming (S122). At the same time, the sensor control unit 30 calculates the amount of moisture of the second sheet from the results in S113 and S120, and stores this in the storage unit 346, to be reference at the time of setting the image forming conditions for the first face of the third sheet. This amount of moisture detection and control of image forming conditions is performed in the same way for the third and subsequent jobs. Alternatively, the CPU 80 may directly control the image forming conditions of the image forming apparatus 1 from the values of the calculation coefficient for the first face and second face, without the sensor control unit 30 detecting the amount of moisture.
Note that while the validity of the amount of moisture detected the previous time has been described as being determined based on the elapsed time from the previous detection of amount of moisture in the present embodiment, the present invention is not restricted to this. An arrangement may be made where an environment sensor (omitted from illustration) is used, and the value of the environment sensor at the time of detecting the amount of moisture the previous time is compared with the value of the environment sensor at the time of detecting the amount of moisture this time, and the validity of the amount of moisture detected the previous time is determined depending on the magnitude of the change in values. In other words, in a case where the ambient environment (temperature, humidity, etc.) has changed greatly, the amount of moisture contained in the recording medium P also has changed, so the amount of moisture is to be detected again. On the other hand, in a case where the ambient environment has not changed much, the amount of moisture contained in the recording medium P has not changed much either, so the amount of moisture is not to be detected again. Also, an arrangement may be made where detection results of a sensor (omitted from illustration) which detects opening/closing of the cassette 2 are used to determine validity of the amount of moisture detected the previous time. In other words, the sensor detects whether or not the cassette 2 has been opened somewhere between the previous moisture amount detection and the moisture amount detection this time. In a case where the cassette 2 has been opened, the likelihood that the recording medium P accommodated in the cassette 2 has been replaced or added is high, so the amount of moisture is to be detected again. There are also cases where the amount of moisture differs between paper which has been stacked at the bottom of the cassette 2 and left standing for a long period of time, paper on the top, and paper in between. The paper on the top within the cassette 2 is in contact with the atmosphere, and is readily affected thereby. On the other hand, the paper at the middle is protected by the paper above, and is not readily affected by the atmosphere. In an environment where the humidity is high, for example, the sheets paper on the top will have a greater amount of moisture than the sheets of paper at the middle or below. In such a case, optimal image forming conditions can be set by reflecting the newest detection results of the amount of moisture at the next sheet of paper. For example, in a case of forming images on 100 sheets at once, the detection results of the amount of moisture of the first sheet is reflected in the image forming conditions of the first face of the second sheet, and the detection results of the amount of moisture of the 99'th sheet is reflected in the image forming conditions of the first face of the 100'th sheet.
As described above, the amount of moisture contained in a recording medium can be detected in the present embodiment, by obtaining the difference between grammage before the recording medium passes through the fixing unit and after having passed through the fixing unit. Accordingly, the amount of moisture contained in the recording medium can be accurately detected.
A second embodiment will be described. A feature of this embodiment is that image forming conditions are set from the detected amount of moisture and the calculation coefficients of the second face. The primary portions are the same as with the first embodiment, so only portions which are different from the first embodiment will be described here.
In the first embodiment, the calculation coefficient of the first face of the second sheet, and the amount of moisture of the first sheet, were used to set image forming conditions for the first face of the second sheet. However, there are cases where sheets with little difference in grammage, such as 75 g paper and 80 g paper for example, are not readily determined regarding which is which by the calculation coefficient of the first face of the second sheet. Table 2 shows the calculation coefficients of the second face of the first sheet of 75 g paper and 80 g paper, the calculation coefficient of the first face of the second sheet, the amount of moisture of the first sheet, and image forming conditions.
In a case of determining between the 75 g standing paper and the 80 g newly-opened paper, referencing the amount of moisture and calculation coefficients of the first face of the second sheet as with the first embodiment yields moisture amount of 4.63 and 0.71 respectively, as shown in Table 2, so the difference between standing paper and newly-opened paper can be easily detected. Next, the calculation coefficients of the first face of the second sheet are 0.04426 and 0.04384, with the 75 g standing paper being slightly greater than the 80 g newly-opened paper. Accordingly, the 80 g newly-opened paper and the 75 g standing paper can be determined from the amount of moisture of the first sheet and the calculation coefficients of the first face of the second sheet, by providing a threshold value between 0.04426 and 0.04384. However, the difference in calculation coefficients of the first face of the second sheet is small, so in a case where there is a certain amount of change in the calculation coefficients due to manufacturing variance of the paper, there is a high likelihood that wrong detection will be made. Therefore, at the time of setting the image forming conditions of the first face of the second sheet in the present embodiment, the precision of determination is improved by referencing the amount of moisture of the first sheet and the calculation coefficient of the second face of the first sheet. Description regarding the amount of moisture will be omitted, since this is the same as described above. From Table 2, it can be seen that the calculation coefficients of the second face of the first sheet is 0.04889 for the 75 g standing paper and 0.04455 for the 80 g newly-opened paper, which is a difference greater than that of the first face of the second sheet. As a result, the precision of determining between the 80 g newly-opened paper and the 75 g standing paper is improved, so it can be said that this is may be a configuration regarding setting optimal image forming conditions for each paper.
The flow for detection of the amount of moisture and control of image forming conditions is almost the same as with that in the first embodiment, illustrated in
As described above, image forming conditions are set based on the amount of moisture of the first sheet and the calculation coefficient of the second face of the first sheet in the present embodiment, so more optimal image forming conditions can be set.
Relationship Between Temperature Change and Grammage Detection Results
Next, a third embodiment will be described. A configuration will be described in the present embodiment which detects information relating to change in temperature of the recording medium, as information relating to change in the state of the recording medium. The relationship between temperature of recording medium and calculation coefficients, actually obtained by the present embodiment, is illustrated in
It can be seen from
In the present embodiment, dividing the absolute value of the difference in calculation coefficients between the first face and the second face by 0.01 yields the temperature change of the recording paper, for convenience sake. For example, in the case in
(0.99−0.83)/0.01=16
which means the temperature change is 16° C. The temperature of the recording medium rises by passing through the fixing unit 21, though the magnitude of temperature change differs depending on the fixing temperature at the time of fixing an image to the first face of the recording medium, the heat capacity of the recording medium, and so forth. Note that description is made in the present embodiment with regard to a case where the relationship between the difference of calculation coefficients and the change in temperature is fixed at 1:100 regardless of the temperature value. However, the relationship between the difference of calculation coefficients and the change in temperature may be different from this example in some situations. Even so, the method for obtaining temperature change from calculation coefficients can be set according to that situation, and thus various situations can be handled.
Setting Image Forming Conditions
The CPU 80 sets the optimal image forming conditions with regard to temperature change obtained as described above in the present embodiment. More specifically, in a case where the temperature of the recording medium at the time of fixing an image on the second face is higher than at the time of fixing an image on the first face, the fixing temperature for the second face is set to be lower than the fixing temperature for the first face. The easiest way to do this is to set a value obtained by subtracting the temperature change from the fixing temperature of the first face as the fixing temperature of the second face. Thus, overheating by the fixing unit 21 can be prevented in a case where the temperature of the recording medium is high, and consequently image deterioration such as hot offset and so forth can be suppressed. Hot offset is a phenomenon where toner on the recording medium adheres to a fixing roller in the fixing unit 21, and after one rotation of the roller, the toner is fixed at a different location on the recording medium.
Next, the timing for setting image forming conditions and performing image forming based on the obtained temperature change will be described. The ultrasonic wave sensor 90 according to the present embodiment can detect the grammage of recording paper without temporarily stopping the recording paper. Accordingly, even when consecutively forming images on multiple sheets of recording paper, the grammage of the all sheets of recording paper can be detected in real time, without temporarily stopping image formation. Thus, optimal image forming conditions can be set from the temperature change obtained from the difference in calculation coefficients between the first face and second face for example, and reflected when forming an image on the second face.
Control of image forming conditions according to the present embodiment will be described with reference to the flowchart in
As described above, the ultrasonic wave sensor 90 according to the present embodiment can calculate the change in temperature of the recording medium from having passed through the fixing unit 21, from the difference in the calculation coefficient before fixing an image on the first face and the calculation coefficient before fixing an image on the second face. Also, the image forming apparatus 1 according to the present embodiment can control the image forming conditions based on the change in temperature of the recording medium, so high-quality images can be obtained.
While an example of setting the fixing temperature in accordance with change in temperature has been described in the present embodiment, this is not restrictive. For example, the electric resistance of the recording medium also changes due to change in temperature thereof, so the voltage value applied to the primary transfer roller 16 and secondary transfer roller 19 may be controlled. Further, other image forming conditions described above may be controlled. Also, the CPU 80 may directly control the image forming conditions of the image forming apparatus 1 from the difference in value between calculation coefficients, without obtaining the change in temperature of the recording medium. The present embodiment has also been described as calculating calculation coefficients from the results of with-paper measurement and no-paper measurement. However, a configuration may be made where calculation coefficients are calculated from the results of with-paper measurement, and change in temperature of the recording medium is obtained therefrom.
A fourth embodiment will be described. A feature of the present embodiment is that the image forming conditions of the second face are set based on the time elapsed from performing detection by an ultrasonic wave up to fixing the image on the second face. Accordingly, optimal image forming conditions can be set for the timing at which the recording medium actually passes through the fixing unit 21, and consequently a high-quality image can be obtained. The primary portions are the same as with the third embodiment, so only portions which are different from the third embodiment will be described here.
In the third embodiment, change in temperature of the recording medium is obtained based on difference in calculation coefficients between the first face and second face, as described earlier. However, there is difference in time from the point of having performed detection by an ultrasonic wave (after having calculated the calculation coefficient for the second face) up to the point where the image is fixed on the recording medium, and there are cases where further change in temperature may occur in that time. The reason is that the temperature of the recording medium which has risen due to having formed the image on the first face converges on (falls to) the temperature before having formed the image on the first face, as time passes.
In the present embodiment, optimal image forming conditions at the timing at which the recording medium actually passes through the fixing unit 21 are set based on the time from having performed detection by an ultrasonic wave until fixing the image on the second face, in light of the above-described nature. Specifically, the amount of change of calculation coefficient over the time elapsed from fixing an image on the first face is measured beforehand, and stored in an unshown storage unit in the image forming control unit 3 as a profile such as illustrated in Table 3. The amount of change in the calculation coefficient from having performed detection by an ultrasonic wave up to fixing an image on the second face is calculated at the time of calculating temperature change in S209 in the third embodiment, and thus temperature change is calculated. For example,
As described above, higher image quality can be obtained by the image forming apparatus according to the present embodiment, by controlling image forming conditions based on the time up to fixing an image on the second face of the recording medium.
The information shown in Table 3 does not have to be measured beforehand as in the present embodiment. For example, an arrangement may be made where the recording medium is stopped at the detection position 200 after fixing an image on the first face of the first sheet of the job, and detection by ultrasonic waves is performed consecutively until temperature change converges, thereby calculating a calculation coefficient. The result may then be stored in an unshown storage unit, and image forming conditions of the second and subsequent sheets may be controlled according to this information. Further, the amount of change of the calculation coefficient may be approximated by interpolation according to time. Alternatively, multiple profiles depending on the environment may be stored in the storage unit, so that a particular profile can be selected therefrom according to the environment where the image forming apparatus 1 is situated. Note that the term “environment” here includes the temperature and humidity around the image forming apparatus 1, which can be detected by an environment sensor provided to the image forming apparatus 1.
A fifth embodiment will be described. A feature of the present embodiment is setting optimal image forming conditions according to the amount of moisture included in the recording medium, in addition to change in temperature of the recording medium. The primary portions are the same as with the third embodiment, so only portions which are different from the third embodiment will be described here.
In a case where an image is fixed on a recording medium containing a great amount of moisture (hereinafter, “absorbent material”), the moisture contained in the recording medium evaporated due to the recording medium being heated and pressurized, so the grammage of the recording medium is reduced. Accordingly, the calculation coefficient at the time of the temperature change having converged after fixing an image on the second face is a greater value than the calculation coefficient for the first face. Accordingly, in order to take into consideration the effects of the amount of moisture, control has to be performed based on the calculation coefficient at the time of temperature change having converged.
In the present embodiment, in a case where the calculation coefficient at the point of the temperature change having converged after fixing an image on the second face is greater than the calculation coefficient for the first face, the difference is deemed to be due to the amount of moisture in light of the above-described nature, and this is reflected in the image forming conditions. The heat capacity of a recording medium which does not contain very much moisture in comparison with an absorbent material (hereinafter, “non-absorbent material”) is smaller than that of an absorbent material, so the temperature of the recording medium changes greatly due to passing through the fixing unit 21. Accordingly, the fixing temperature at the time of fixing an image on the second face of a non-absorbent material is to be lower than the fixing temperature at the time of fixing an image on the second face of an absorbent material. Specifically, the fixing temperature is set to be around 5° C. lower for a non-absorbent material, as compared with an absorbent material, as shown in Table 4. In the present embodiment, the fixing temperature of the second face is set to be lower than the calculated value in the third and fourth embodiments by a range of 0° C. to 5° C., depending on the amount of moisture. Also in the present embodiment, a recording medium regarding which the difference in calculation coefficients is 0.05 is more is regarded to be an absorbent material, and a recording medium regarding which the difference is less than 0.05 is regarded to be a non-absorbent material. While an example of setting the fixing temperature in accordance with amount of moisture contained in the recording medium has been described in the present embodiment, this is not restrictive. For example, the electric resistance of the recording medium also changes due to the amount of moisture contained therein, so the voltage value applied to the primary transfer roller 16 and secondary transfer roller 19 may be controlled. Further, the above-described other image forming conditions may be controlled.
The method for obtaining the calculation coefficient at the point that temperature change has converted after having fixed an image on the second face will be described. The recording medium is stopped at the detection position 200 after fixing an image on the first face of the first sheet of the recording medium, detection by ultrasonic waves is consecutively performed, and the calculation coefficient is calculated. The amount of change of the calculation coefficient decrease as time elapses as illustrated in
As described above, the ultrasonic wave sensor 90 according to the present embodiment can obtain the amount of moisture contained in the recording medium before passing through the fixing unit 21, by the difference between the calculation coefficient before fixing an image on the first face and the calculation coefficient at the time of temperature change of the recording medium having converged. The image forming apparatus 1 according to the present embodiment can also control image forming conditions based on the amount of moisture contained in the recording medium, so high-quality images can be obtained.
Note that while determination is made in the present embodiment whether an absorbent material or a non-absorbent material, in accordance with the amount of moisture, and image forming conditions are controlled accordingly, but the state of the recording medium may be determined in further detail, and the image forming conditions may be controlled base thereupon. Also, optimal image forming conditions may be controlled according to the amount of moisture on a case-by-case basis.
While the ultrasonic wave sensor 90 has been described as being fixed to the image forming apparatus 1 in the above-described embodiments, the ultrasonic wave sensor 90 may be configured to be detachable from the image forming apparatus 1. A configuration where the ultrasonic wave sensor 90 is detachable allows the user to easily replace a malfunctioning ultrasonic wave sensor 90, for example.
Also, the ultrasonic wave sensor 90 and sensor control unit 30, CPU 80, and other like control units in the above-described embodiments may be integrally configured and formed to be detachable from the image forming apparatus 1. Integrally forming the ultrasonic wave sensor 90 and control unit so as to be detachable allows the user to easily replace the ultrasonic wave sensor 90 with a new ultrasonic wave sensor 90 having updated or added functions.
While the embodiments have been described by way of an example of a laser beam printer, image forming apparatuses to which the present invention is applicable are not restricted thusly. Any apparatus which fix an image formed on a recording medium by heating the recording medium is applicable, including printers and copying machines using other recording methods, such as ink-jet printers and the like.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2013-255668, filed Dec. 11, 2013, and Japanese Patent Application No. 2013-272034, filed Dec. 27, 2013 which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | Kind |
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| 2013-272034 | Dec 2013 | JP | national |
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