This application is based on Japanese Patent Application No. 2015-095879 filed on May 8, 2015, the contents of which are incorporated herein by reference.
1. Technical Field
The present invention relates to an image forming apparatus.
2. Description of Related Art
In an electrophotographic image forming apparatus, control parameters of a fixing unit for heating and fixing a toner image onto a paper (a sheet of paper) are changed according to the type of a paper on which an image is formed. For example, when a paper is a thick paper, the temperature of a heating roller is set to be high as compared with the case in which a paper is a plain paper.
In relation to this, Japanese Unexamined Patent Publication No. 2008-180947 discloses a technology of measuring the temperature of a heating roller before and after one paper passes through a fixing unit and determining the type of the paper from a temperature gradient. According to this technology, it is possible to automatically determine the type of a paper and determine control parameters of the fixing unit.
However, in this technology, since a small temperature change when one paper passes through the fixing unit is measured, there is a possibility that the type of the paper cannot be determined correctly. On the other hand, a temperature change when a plurality of papers pass through the fixing unit is also considered to be measured, but if a time for determining the type of the paper is too long, since a time until the state of the fixing unit is stabilized also becomes long, it is not preferable.
The present invention has been accomplished in view of the above problem. Accordingly, objectives of the present invention are to provide an image forming apparatus capable of accurately determining the type of the paper in a short time as much as possible by measuring the temperature of a fixing member.
In order to achieve at least one of the abovementioned objects, an image forming apparatus, reflecting one aspect of the present invention, includes: a paper feeding tray configured to store papers; a conveying unit configured to convey a paper stored in the paper feeding tray; an image forming unit configured to form a toner image on the paper conveyed by the conveying unit; a fixing member configured to heat and fix the toner image formed by the image forming unit onto the paper; a temperature sensor configured to detect a temperature of the fixing member; a heater configured to heat the fixing member; a detection unit configured to detect that the temperature of the fixing member reaches a lower limit value at which the temperature once reduced by start of a heating and fixing process to the paper turns to rise, after an image forming operation starts; and a determination unit configured to determine a type of the paper based on at least one of an elapsed time from a predetermined reference time point after the image forming operation starts to a time point at which it is detected that the temperature of the fixing member reaches the lower limit value, and a temperature difference between the temperature of the fixing member at the reference time point and the lower limit value.
Preferably, in the image forming apparatus, the determination unit determines that the paper is thicker as the temperature difference is larger.
Preferably, in the image forming apparatus, the determination unit determines that the paper is thicker as the elapsed time is longer.
Preferably, the image forming apparatus further includes a controller configured to control an operation of the heater by reflecting the type of the paper determined by the determination unit in a control parameter of the heater.
The objects, features, and characteristics of this invention other than those set forth above will become apparent from the description given herein below with reference to preferred embodiments illustrated in the accompanying drawings.
The embodiments of this invention will be described in detail with reference to the accompanying drawings. In addition, in the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Furthermore, dimensional ratios in the drawings are exaggerated and different from actual ratios for convenience of the description.
As shown in
The controller 110 includes CPU (Central Processing Unit), RAM (Random Access Memory), and ROM (Read Only Memory), appropriately reads out various programs stored in the ROM, the storage unit 170 and the like, and develops the read programs on the RAM, wherein the CPU executes the developed programs, thereby performing various functions.
The operating display unit 120, for example, is formed by superposing a touch sensor on a display surface of LCD (Liquid Crystal Display), and displays an operation screen and receives various operations by a user.
The image reading unit 130 includes an optical system configured from a mirror and a lens and an imaging device such as a CCD (Charge Coupled Device) image sensor, and reads a document placed on a platen glass or a document conveyed from ADF (Auto Document Feeder) (not shown), thereby generating image data.
The image forming unit 140 includes developing units 141Y, 141M, 141C, and 141K corresponding to toner of Y, M, C, and K colors. Toner images formed through charging, exposure, and development processes by the developing units 141Y, 141M, 141C, and 141K are sequentially superposed on an intermediate transfer belt 142 and are transferred onto a paper S by a secondary transfer roller 143.
The fixing unit 150 includes a heating roller 151 acting as a fixing member and a pressure roller 152, heats and presses the paper S conveyed to a fixing nip between both these rollers 151 and 152, and melts and fixes the toner images on the paper S to the surface of the paper S. In the vicinity of the heating roller 151, temperature sensors 153 to 155 are provided.
As shown in
The pressure roller 152 includes, in the order from the inner side, a core metal 152a composed of a cylindrical metal, an elastic layer 152b which is formed on the core metal 152a and composed of a material such as silicone rubber and foamed silicone rubber, and a releasing layer 152c such as fluororesin. The outer diameter and axial length of the pressure roller 152 are equal to those of the heating roller 151. In addition, a heater may also be disposed inside of the core metal 152a of the pressure roller 152.
The temperature sensors 153 to 155 detect the surface temperature of the heating roller 151. The temperature sensors 153 to 155 are respectively disposed at a center part, a back side, and a front side which are different positions in a width direction, and measure an axial temperature distribution of the heating roller 151. As the temperature sensors 153 to 155, for example, thermistors disposed in a non-contact state for the heating roller 151 are used.
The fixing driving unit 160 includes a driving motor, thereby rotationally driving the heating roller 151 or both of the heating roller 151 and the pressure roller 152. Furthermore, the fixing driving unit 160 includes a contacting/separating mechanism 161 configured from a cam mechanism and a driving source, thereby moving the pressure roller 152 between a “contacting position” and a “separating position”. As shown in
The storage unit 170 is an auxiliary storage device configured with HDD (Hard Disk Drive) or a semiconductor memory such as SSD (Solid State Drive). The storage unit 170 stores a plurality of types of control parameters for calculating a duty ratio from the detection temperatures of the temperature sensors 153 to 155.
The power supply unit 180 includes a plurality of switching elements 181 and 182 and a zero cross detection section 183. As shown in
The controller 110 performs duty control, in which a predetermined period corresponding to an integral multiple of a half wave of the commercial alternating current power supply 185 is employed as a control cycle, by using the zero cross signal. This control cycle, for example, is fifteen half-wave lengths. The control cycle of the fifteen half-wave lengths corresponds to 300 msec in the case of a commercial power supply of 50 Hz. The controller 110 controls the switching elements 181 and 182 in synchronization with the zero cross signal and performs on/off control of the heaters 156 and 157 in a half-wave unit. In the fifteen half-waves of the control cycle, for example, if the heaters 156 and 157 are turned on during the period of 1 half-wave, the duty ratio becomes 6.7%, and if the heaters 156 and 157 are turned on during the periods (all the periods) of the fifteen half-waves, the duty ratio becomes 100%.
The paper feeding conveyance unit 190 includes a plurality of paper feeding trays 191 and 192 and a plurality of pairs of conveying rollers driven by a conveying motor (not shown). The paper feeding trays 191 and 192 store a number of papers S therein. The papers S stored in the paper feeding trays 191 and 192 are fed to a downstream conveyance path one by one.
In addition, the image forming apparatus 100 may also include elements other than the above-described elements, or may not include a part of the above-described elements.
In the image forming apparatus 100 configured as described above, a temperature transition of the heating roller 151 is measured after the start of an image forming operation, so that the type of the paper S is determined. Hereinafter, with reference to
When a copy start instruction is received from a user, the image forming apparatus 100 starts on/off control (step S101). In more detail, firstly, the pressure roller 152 moves to the “contacting position” and rotates together with the heating roller 151. Then, the controller 110 of the image forming apparatus 100 starts on/off control for turning off the heaters 156 and 157 in the heating roller 151 when the temperature of the heating roller 151 is higher than a target temperature, and turning on the heaters 156 and 157 at fixed duty ratios (for example, 100% for both) when the temperature of the heating roller 151 is lower than the target temperature.
Next, the image forming apparatus 100 starts an on/off control timer (step S102). In more detail, the controller 110 of the image forming apparatus 100 starts a timer for measuring an elapsed time from a start time point of the on/off control.
Next, the image forming apparatus 100 stores a present temperature (step S103). In more detail, the controller 110 of the image forming apparatus 100, for example, stores the present temperature of the heating roller 151, which is detected by the temperature sensor 153 of the center part, in the RAM as the temperature of the heating roller 151 at the start time point of the on/off control.
As described above, according to the processes shown in steps S101 to S103 of
Next, the image forming apparatus 100 resets a temperature detection timer (step S104). In more detail, the controller 110 of the image forming apparatus 100 resets a timer for measuring the temperature of the heating roller 151 at a predetermined cycle (for example, 600 msec).
Next, the image forming apparatus 100 determines whether a predetermined time has passed (step S105). In more detail, the controller 110 of the image forming apparatus 100 determines whether a predetermined time (for example, 600 msec) has passed after the timer is reset in the process shown in step S104.
When it is determined that the predetermined time has not passed (step S105: NO), the image forming apparatus 100 waits until the predetermined time passes. On the other hand, when it is determined that the predetermined time has passed (step S105: YES), the image forming apparatus 100 acquires a present temperature (step S106). In more detail, the controller 110 of the image forming apparatus 100 acquires the present temperature of the heating roller 151, which is detected by the temperature sensor 153 of the center part.
Next, the image forming apparatus 100 compares a previous temperature with the present temperature (step S107). In more detail, the controller 110 of the image forming apparatus 100 subtracts a temperature acquired immediately before (for example, before 600 msec) from the temperature acquired in the process shown in step S106, thereby calculating a temperature difference between the previous temperature and the present temperature.
Then, the image forming apparatus 100 determines whether a temperature gradient is equal to or more than 0 (step S108). In more detail, the controller 110 of the image forming apparatus 100 determines whether the temperature difference calculated in the process shown in step S107 is equal to or more than 0. In other words, the controller 110 determines whether the surface temperature of the heating roller 151, which has been reduced once by the start of the heating and fixing process, has turned to rise.
When it is determined that the temperature gradient is smaller than 0 (step S108: NO), the image forming apparatus 100 returns to the process of step S104. Then, the image forming apparatus 100 repeats the processes after step S104 until the temperature gradient is equal to or more than 0.
On the other hand, when it is determined that the temperature gradient is equal to or more than 0 (step S108: YES), the image forming apparatus 100 stops the on/off control timer (step S109). In more detail, since the temperature of the heating roller 151 has turned to rise, the controller 110 of the image forming apparatus 100 stops the on/off control timer started in the process shown in step S102.
Next, the image forming apparatus 100 stores the present temperature (step S110). In more detail, the controller 110 of the image forming apparatus 100 stores the temperature acquired in the process shown in step S106 in the RAM as a lower limit value of the temperature of the heating roller 151.
As described above, according to the processes shown in steps S104 to S110 of
Next, the image forming apparatus 100 determines PID control parameters (step S111). In more detail, the controller 110 of the image forming apparatus 100 firstly acquires the elapsed time measured by the on/off control timer as an arrival time Tx until the temperature of the heating roller 151 reaches the aforementioned lower limit value from the start time point of the on/off control. Furthermore, the controller 110 calculates a temperature difference between the temperature stored in the process shown in step S103 and the temperature stored in the process shown in step S110 as a temperature difference Td between the temperature of the heating roller 151 at the start time point of the on/off control and the aforementioned lower limit value. Then, with reference to predetermined conversion tables 210 and 220 (see
As shown in
In the process shown in step S111, the conversion tables 210 and 220 are referred to and the control parameters of the heaters 156 and 157 are determined from the arrival time Tx and the temperature difference Td. For example, when the arrival time Tx is 4 sec and the temperature difference Td is 7° C., the target temperature and the P constant are determined to 170° C. and 5, respectively. In addition, also in the I constant and the D constant, as the arrival time Tx is longer and the temperature difference Td is larger, a higher value is determined in a similar manner.
Then, the image forming apparatus 100 proceeds to the PID control (step S112) and ends the procedure. In more detail, the controller 110 of the image forming apparatus 100 stops the on/off control of the heating roller 151 and starts the PID control by applying the control parameters determined in the process shown in step S111. In addition, since the technology itself of calculating the duty ratio by the PID control and controlling the heaters 156 and 157 is a well-known technology, a detailed description thereof will be omitted.
As described above, according to the procedure of the flowchart shown in
In addition, in the flowchart shown in
As shown in
In the paper type determination process of the present embodiment, the temperature transition of the heating roller 151 is measured and the lower limit value (a minimum point) of the temperature of the heating roller 151 is detected as a feature point at which the difference of temperature characteristics corresponding to the type of papers is initially noticeable. Then, the type of the paper is determined from the arrival time Tx until the temperature of the heating roller 151 reaches the lower limit value and the temperature difference Td between the temperature of the heating roller 151 at the start time point of the on/off control and the lower limit value. According to such a configuration, the temperature of the heating roller 151 is measured, so that it is possible to accurately determine the type of the paper in a short time as much as possible.
As shown in
On the other hand, in the paper type determination process of the present embodiment, the lower limit value of the temperature is detected as the feature point at which the difference of the temperature characteristics corresponding to the type of papers is initially noticeable and the type of the paper is determined, so that it is possible to accurately determine the type of the paper in a short time as much as possible.
In addition, in the present embodiment, the thickness of a paper can be classified on the basis of a basis weight of the paper. In detail, when the basis weight of the paper is smaller than a first value (for example, 50 g/m2), the paper type is classified into a “thin paper”, and when the basis weight of the paper is equal to or more than a second value (for example, 128 g/m2), the paper type is classified into a “thick paper”. Furthermore, when the basis weight of the paper is equal to or more than the first value and smaller than the second value, the paper type is classified into a “plain paper”.
Furthermore, the controller 110 of the image forming apparatus 100 allows the CPU to execute corresponding programs, thereby serving as a detection unit configured to detect that the temperature of the heating roller 151 has reached the lower limit value and a paper type determination unit (a determination unit) configured to determine the type of the paper.
The present invention shall not be limited to the aforementioned embodiment, and hence it can be variously modified within the scope of the appended claims.
For example, in the above-described embodiment, on the basis of both of the arrival time Tx until the temperature of the heating roller 151 reaches the lower limit value and the temperature difference Td between the temperature of the heating roller 151 at the start time point of the on/off control and the lower limit value, the type of the paper is determined. However, the type of the paper may also be determined on the basis of any one of the arrival time Tx and the temperature difference Td.
In addition, when the temperature of the heating roller 151 reaches the lower limit value, the temperature of the heating roller 151 rises and the temperature difference with the temperature of the heating roller 151 at the start time point of the on/off control is reduced. Consequently, the type of the paper is determined using a lower limit value at which the temperature difference with the temperature of the heating roller 151 at the start time point of the on/off control is maximum, so that the determination accuracy of the type of the paper is highest as compared with the case of determining the type of the paper by using a temperature difference at other time points.
Furthermore, in the above-described embodiment, by employing the start time point of the on/off control as a reference, the arrival time Tx until the temperature of the heating roller 151 reaches the lower limit value and the temperature difference Td with the lower limit value are obtained. However, a reference time point serving as a reference when obtaining the arrival time and the temperature difference is not limited to the start time point of the on/off control and can be set to an arbitrary time point after the start of the image forming operation. For example, after the start of the image forming operation, a time point at which an initial paper makes contact with the heating roller 151 may also be estimated and the estimated time point may also be set as the reference time point.
Furthermore, in the above-described embodiment, the case in which the image forming apparatus performs the copy process has been described as an example. However, the present invention, for example, can also be applied to a case in which the image forming apparatus receives print data and performs a print process.
Units and a method for performing various processes in the image forming apparatus according to the above-described embodiments can also be realized by any one of a dedicated hardware circuit and a programmed computer. The aforementioned program, for example, may also be provided by a computer readable recording medium such as a flexible disk and CD-ROM (Compact Disc Read Only Memory), or may also be provided on-line via a network such as the Internet. In this case, the program recorded in the computer readable recording medium is normally transmitted to and stored in a storage unit such as a hard disk. Furthermore, the aforementioned program may also be provided as single application software or may also be incorporated in software of an image forming apparatus as one function of the apparatus.
Number | Date | Country | Kind |
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2015-095879 | May 2015 | JP | national |