JP2006201259A - Image forming apparatus having fixing temperature analysis means - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve productivity and achieve energy saving by monitoring a fixing temperature state by using wevelet transformation to predict a kind of paper, and altering process control. <P>SOLUTION: The image forming means comprises a wevelet transformation means for finding frequency characteristics in a length (time) x direction of an original signal waveform by making a basic waveform a small waveform to the length (time) x direction of a signal waveform as compared with the original signal waveform, and calculating cross-correlation relationship of the basic waveform and the original signal waveform to find the degree of similarity between the original signal waveform and the basic waveform and a means for reading temperature characteristics of a fixing heater. The image forming apparatus comprises a statistic processing means for statistically processing the transformation result by carrying out wevelet transformation regarding secular change of read temperature information as the original signal waveform. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus characterized by grasping a temperature change of a fixing heater by transfer paper and changing the control based on a temperature change state for the purpose of image guarantee corresponding thereto.

  FIG. 6 is a block diagram for explaining conventional fixing heater temperature control, and FIG. 7 is a flowchart of simple temperature control. FIG. 8 is a diagram showing a state in which the fixing heater is controlled to the target temperature.

  In general, a heater used for a fixing device uses a commercial power source as a power source, and adjusts temperature by turning on / off power by a switching element such as a triac. The temperature of the fixing heater is detected directly or indirectly using a contact-type or non-contact-type temperature detection thermistor, etc., and if this detection result is lower than the target temperature, the switch element is turned on and energized. When the temperature exceeds the target temperature, the switch element is turned off to stop energization to adjust the temperature so that the fixing device temperature does not deviate from the target temperature range, thereby realizing fixing control.

As another conventional example, for example, Patent Document 1 and Patent Document 2 can be cited.
Japanese Patent Laid-Open No. 11-143290 JP 2002-182525 A

  However, the control method according to the prior art is not necessarily optimal control.

  The temperature control by the fixing heater has a problem that the follow-up of the correction control with respect to the temperature change is not good because there is always a time delay from the start of power supply control to the actual target temperature.

  In such a case, it is necessary to increase the power supply to the heater in order to recover the temperature once lowered, which can be said to be a wasteful power consumption that occurs due to a time delay.

  FIG. 9 is a diagram showing the state of the fixing heater temperature change when the cardboard flows continuously.

  As shown in this figure, for example, when thick paper that is completely cooled in the paper feed cassette is continuously passed, the temperature is taken away from the fixing device at the instant of passing, so this appears as a temperature ripple. . This temperature ripple tends to appear larger as the paper becomes thicker, and does not appear so prominently in thin paper where heat is not easily removed. If no special temperature control is performed, the overall temperature gradually decreases as shown in this figure.

  As a judgment means for recognizing such a state, a method of obtaining a Fourier coefficient of a detection pattern in order to detect a temporal ripple of the fixing heater temperature as a pattern is conceivable. Although a certain amount of results can be obtained if the change is periodic with the temperature level maintained, a temperature vs. time curve in which ripples are superimposed on the down slope as the temperature actually decreases as shown in the figure Therefore, the correct discrimination method cannot be realized. The essential feature of the Fourier transform is that the Fourier transform is handled as a collection of waves that are repeated infinitely with respect to the position or time axis compared to the original signal waveform.

  Therefore, although such a characteristic state can be observed, the follow-up correction is performed such that the control is performed when the fixing temperature is likely to deviate from the target range as described in the related art, resulting in a decrease in productivity. Not only was it wasted power.

In order to solve the above problems and achieve the object, an image forming apparatus according to claim 1 of the present invention provides:
Compared to the original signal waveform, the length (time) of the signal waveform is smaller in the x-direction, and a basic waveform is calculated by calculating the cross-correlation between the basic waveform and the original signal waveform. And a wavelet transform means for obtaining a frequency signal characteristic in the x direction of the length (time) of the original signal waveform, and a means for reading the temperature characteristic of the fixing heater. In the image forming apparatus, the time-dependent change of the read temperature information is used as an original signal waveform, wavelet transform is executed by the wavelet transform unit, and a statistical processing unit for statistically processing the conversion result is provided. It is characterized by judging.

  According to a second aspect of the present invention, in the first aspect of the present invention, the fixing temperature control is changed according to the processing result of the statistical processing means, and optimal fixing control is performed.

  According to a third aspect of the present invention, in the first aspect of the invention, the optimum fixing control is performed by changing the process speed according to the processing result of the statistical processing means.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, the process speed adjustment is characterized in that the fixing temperature adjustment is optimized by controlling the paper interval.

  According to a fifth aspect of the present invention, in the first aspect of the invention, the image forming operation is optimized by performing feedback to the transfer current control based on the processing result of the statistical processing means.

  According to a sixth aspect of the present invention, in the first aspect of the present invention, the statistical processing means obtains at least one of an average value, a maximum value, a gradient, and an average value for the maximum value on the cycle. It is characterized by calculating.

  The image forming apparatus according to claim 7, wherein the number of waves of the basic wavelet used in the wavelet transform is changed in the first aspect of the claim to distinguish between the periodicity and the singleness of the fixing temperature change. It is characterized by.

  The image forming apparatus according to claim 8 is characterized in that, in claim 1, the abnormal state is determined based on the processing result of the statistical processing means, and stop, warning, or feedback control to the image forming apparatus is performed. And

(Function)
According to the present invention, it is possible to predict and control the fixing temperature by statistically processing the temperature change of the fixing device, and it is possible to predict the transfer paper being passed by this information. It is possible to control the time delay to a minimum.

  In the present invention, a change in the temperature of the fixing heater of the image forming apparatus over time is detected, and as a detection pattern analysis means, a wavelet conversion means for wavelet conversion and a statistical processing means for statistically processing the conversion result are provided. It is possible to accurately determine and predict temperature changes such as the temperature ripple and gradient of the fuser, and to make analysis methods that are less susceptible to the presence or absence of periodicity, thereby judging the transfer paper being passed. It is possible to achieve optimum image formation by performing feedback correction on temperature control, process speed, paper interval adjustment, transfer conditions, and the like. Further, since predictive control of the temperature becomes possible, it is possible to reduce unnecessary temperature and to reduce the electric power necessary for recovery from the temperature, which can greatly contribute to the improvement of the productivity and energy saving of the apparatus.

  In addition, when any abnormal condition occurs and the fixing temperature changes suddenly, it is possible to easily determine whether it is an abnormal condition or within the range of normal control, thereby ensuring the safety of the image forming apparatus. Is possible.

Example 1
FIG. 1 is a diagram illustrating an image forming apparatus used in the present invention. The image forming apparatus includes a printer unit 20.

  The digital image signal is converted into an image signal to drive the semiconductor laser 21 in the printer unit 20 through filter processing, density conversion, γ conversion, and the like by an image processing apparatus (not shown). The laser beam generated by the semiconductor laser 21 is irradiated to the photosensitive drum 26 through the lens 24 and the reflection mirror 25 by the rotation of the polygon motor 22 and the polygon mirror 23.

  The photosensitive drum 26 is previously charged with a uniform potential by a primary charger 27 to form an electrostatic latent image corresponding to image information by a laser beam. Whether the potential of the electrostatic latent image is increased or decreased is detected by the potential sensor 28 and can be changed by adjusting the discharge current value in the primary charger 27 and the intensity of the laser beam. The electrostatic latent image on the photosensitive drum 26 is visualized as a toner image by being supplied with toner by a developing device 29. This toner image is subjected to corona discharge from the post charger 30 on the photosensitive drum and the charge amount is adjusted, and then transferred by the transfer charger 31 and the separation charger 32 from the paper feed deck 33. Transferred to the paper 34. Thereafter, the transfer paper 34 moves on the conveying belt 35, and in the fixing device 36, the toner is firmly fixed on the transfer paper, and the image is fixed.

  The transfer residual toner remaining without being transferred onto the transfer paper at the transfer charger position is peeled off from the photosensitive drum by the cleaner 37, and the residual potential on the photosensitive drum is leveled by the static eliminator 38 for the next image output. Prepare.

  The transfer paper 34 passed from the paper feed deck 33 is transported to the transfer charger 31 by a paper feed roller 40, a retard roller pair 41, and a transport roller pair 42.

  FIG. 2 is a block diagram for explaining the control of the image forming apparatus according to the present invention.

  The temperature information from the temperature detection element described in the conventional example is captured by time change, and the relationship between this temperature and time is processed by the wavelet transform unit. The wavelet transform is a signal processing method for calculating how much basic waveform signals called mother wavelets are included in data. In the present invention, a general Morlet mother wavelet is used, and the mother wavelet Ψ (x) is given by the following calculation formula.

ここで、ｘはマザーウェーブレットの位置を示し、aは波形の周期を示し、σは波の数を示している。本実施例ではσ＝1.0としており、最もシンプルなマザーウェブレットとなっている。マザーウェーブレットΨ（ｘ）にはガウス関数exp（ｘ²）が含まれるため、位置（時間）ｘを変化させても、事実上有限な関数である。位置（時間）ｘが十分大きければ、マザーウェーブレットΨ（ｘ）がほぼ０となるためである。このマザーウェーブレットが元信号にどれだけ含まれるかを示すもの、言い換えれば、マザーウェーブレットとの相互相関関係を演算するものがウェーブレット変換の結果であり、以下の計算式で与えられる。

Here, x represents the position of the mother wavelet, a represents the waveform period, and σ represents the number of waves. In this embodiment, σ = 1.0, which is the simplest mother weblet. Since the mother wavelet Ψ (x) includes a Gaussian function exp (x ² ), even if the position (time) x is changed, the mother wavelet Ψ (x) is effectively a finite function. This is because if the position (time) x is sufficiently large, the mother wavelet Ψ (x) becomes almost zero. What indicates how much the mother wavelet is included in the original signal, in other words, what calculates the cross-correlation with the mother wavelet is the result of the wavelet transform, and is given by the following calculation formula.

ここで、ｆ（ｘ）は元信号情報で、本実施例では温度変化情報であり、ｂは具体的な信号内位置を示す。ここで得られた二次元のウェーブレット変換後信号Ｗ（ａ，ｂ）を、統計処理により、フィルタリング処理されたフィルタ変換後信号ＷF（ａ，ｂ）から固有の数値を導き出す。本実施例では、最大値Ｗmaxと、平均値Ｗave、温度勾配Ｗslopeを求めている。

Here, f (x) is original signal information, which is temperature change information in this embodiment, and b indicates a specific signal position. The two-dimensional wavelet transformed signal W (a, b) obtained here is subjected to statistical processing to derive a unique numerical value from the filtered signal WF (a, b) after filtering. In this embodiment, the maximum value Wmax, the average value Wave, and the temperature gradient Wslope are obtained.

From the filter-converted signal WF (cycle a, time b), the maximum peak value seen in the cycle a at each time b is searched and converted into one-dimensional W _1D (time b). The value Wm having a peak is searched. The number m is a collection of data indicating 1 to m peaks. The peak satisfies W _1D (b−1) ≦ W _1D (b) <W _1D (b + 1) or W _1D (b−1) <W _1D (b) ≦ W _1D (b + 1). Calculation is performed by defining W _1D (b) as Wm (number m). An average is obtained for the aggregate of data of Wm (number m), and the average value WM is obtained. According to such an averaging process, it is possible to grasp a rapid temperature change as a ripple while grasping a temperature gradient from the most rapid temperature change to several conspicuous temperature changes.

  FIG. 3 shows a graph (left) showing the change over time of the detected fixing heater temperature and a graph (right) after the graph is subjected to wavelet transform and statistical processing.

  The temperature ripple component generated when the paper passes through the fixing device at a certain timing and the temperature is taken away appears as a periodic temperature change by the statistical processing after the wavelet transform. If the paper is thick and the amount of temperature ripple increases, the amount of periodic temperature change increases, so that the level after statistical processing appears greatly. The lower graph shows a case where a single temperature change occurs.

  FIG. 4 is a flowchart of a routine for controlling the image forming apparatus by analyzing the change with time of the fixing temperature in this embodiment. It is determined whether or not the fixing heater temperature detected by the temperature detecting element is within the target fixing temperature range. If the fixing heater temperature is out of this range at the initial stage, the temperature is controlled so that it naturally falls within the initial target range. When it is confirmed that the temperature is within the temperature range where paper feeding can be started, paper feeding is started. The temperature detection is performed in parallel while passing the paper, and this is stored as data. Next, the stored temperature change with time is wavelet transformed, and statistical processing is performed to obtain the maximum ripple value Wmax and the average value Wave and store them. Further, the gradient is calculated from the change amount of the average value of the temperature, and this is also stored.

  After that, if the temperature ripple is more than a certain value and the temperature gradient is lower than a certain value by each value obtained, it is determined that the card is continuously passed through the thick paper from the balance with the input image forming mode, and the image The forming apparatus is switched from normal control to cardboard dedicated control.

  If cardboard is continuously fed at high speed, the heat of the fixing unit will continue to be taken away, so the temperature drop is predicted based on the data after this statistical processing, and the fixing temperature is raised so that no more heat is taken away The temperature control may be changed in the direction. In this case, not only can the speed decrease be minimized by preventing unnecessary temperature decrease, but also the power required to increase the temperature once decreased can be reduced, greatly contributing to energy saving control. it can.

  In addition, if the temperature decrease gradient is steep and cannot be covered only by temperature control, it is possible to control the temperature decrease gradient of the fixing device gently by reducing the sheet passing speed to the minimum necessary. In such a case, the same effect can be obtained by waiting for the temperature decreased by increasing the sheet passing interval to return to the specified value.

  In addition, since the transfer conditions tend to be stricter for thick paper, if this process determines that continuous paper is used for thick paper, correction feedback is provided to the high-voltage power supply control to increase the transfer current, and optimal transfer conditions are set. Also good.

(Example 2)
In this embodiment, whether or not a periodic temperature change occurs when a cardboard is continuously fed as shown in the first embodiment from the result of statistical processing of the fixing temperature over time by wavelet transformation, or A method for determining whether or not a temperature change occurs once will be described.

  FIG. 5 is a flowchart of a routine for performing temperature change statistical processing in this embodiment. As shown in FIG. 2, the analysis range is stored from the time-dependent change information of the temperature detected by the temperature detection thermistor. Next, the wavelet transformation is performed by the wavelet transformation unit with the number of waves σ of the mother wavelet represented by Equation 1 being 1.0. Then, the statistical processing unit obtains the maximum value Wmax1 and stores the maximum value period amax1. Further, a higher peak value is obtained as an average value Wz1 of several pieces from the top.

  Furthermore, in this embodiment, the wavelet transform is performed by the wavelet transform unit with the number of waves of the mother wavelet σ shown in Equation 1 being 4.0. Then, the statistical processing unit obtains the maximum value Wmax2 and stores the maximum value period amax2. Further, a higher peak value is obtained as an average value Wz2 of several pieces from the top.

  Thereafter, the two maximum values Wmax1 and Wmax2 obtained are compared with the respective periods amax1 and amax2 and two average values Wz1 and Wz2 corresponding to several high peaks.

  If the number of waves σ is 1.0 and 4.0, the meaning of the results is different even if the other analysis conditions are the same. When σ is 1.0, it is suitable for detection of cardboard with a little periodicity, for example, single-sheet cardboard and hardware failure detection, but when σ is 4.0, continuous cardboard with relatively periodic cycles, etc. From the difference of σ, it can be seen whether it occurs periodically. Therefore, the maximum values Wmax1 and Wmax2 are checked to determine whether they are periodic. If Wmax1 is larger, it can be seen that the maximum value is a cardboard single-passage paper with less periodicity or, in some cases, a rapid change in temperature due to a malfunction.

  Also, the average values Wz1 and Wz2 are checked to determine whether they are periodic. The periodicity may be determined not by the maximum value but by the average value. If Wz1 is larger, it can be seen that the average value is a temperature change with less periodicity.

If it is determined that there is periodicity, the control is changed by determining the paper type and predicting the temperature ahead as in the first embodiment in accordance with the state of the command input to the image forming apparatus.
If it is determined that a temperature change with low periodicity has occurred, and if the maximum value Wmax1 exceeds that value using a certain threshold value, feedback is given to the control of the image forming apparatus as an error. It can be used as a means for detecting the occurrence of a temperature change that is not possible with normal control. This can also be determined based on the average value Wz1, and in this case, it may be considered that the determination is in a time range slightly longer than the determination based on the maximum value Wmax1.

  That is, some sudden and abnormal temperature change is detected by the maximum value Wmax1, and when there is a slight shift in control, it can be detected by the average value Wz1.

FIG. 3 illustrates an image forming apparatus used in the present invention. FIG. 3 is a block diagram illustrating control of the image forming apparatus according to the first exemplary embodiment. The figure which shows the raw data of the temperature change in Example 1, and the data after a process. 3 is a flowchart illustrating a routine for controlling the image forming apparatus according to the first exemplary embodiment. 9 is a flowchart illustrating a routine for controlling the image forming apparatus according to the second exemplary embodiment. FIG. 10 is a block diagram illustrating control of an image forming apparatus in a conventional example. 10 is a flowchart of a routine for controlling the image forming apparatus in the conventional example. The figure explaining the temperature adjustment control in a prior art example. The figure which shows the fixing temperature change at the time of continuous thick paper passing in a prior art example.

Explanation of symbols

31 Transfer Charging Device 36 Fixing Device

Claims (8)

Compared to the original signal waveform, the length (time) of the signal waveform is smaller in the x-direction, and a basic waveform is calculated by calculating the cross-correlation between the basic waveform and the original signal waveform. And wavelet transform means for obtaining the frequency characteristics in the x direction of the length (time) of the original signal waveform,
And in the image forming apparatus provided with means for reading the temperature characteristics of the fixing heater,
The wavelet transform is executed by the wavelet transform means using the time-dependent change of the read temperature information as the original signal waveform, and the operation state is judged by having a statistical processing means for statistically processing the conversion result. Image forming apparatus.   2. The image forming apparatus according to claim 1, wherein the fixing temperature control is changed according to a processing result of the statistical processing means, and optimal fixing control is performed.   The image forming apparatus according to claim 1, wherein optimum fixing control is performed by changing a process speed according to a processing result of the statistical processing unit.   According to a first aspect of the present invention, the process speed adjustment is characterized in that the fixing temperature adjustment is optimized by controlling the paper interval.   The image forming operation is optimized by performing feedback to the transfer current control based on the processing result of the statistical processing means.   According to a first aspect of the present invention, the statistical processing means calculates at least one of an average value, a maximum value, a gradient, and an average value for a maximum value on a cycle.   2. The image forming apparatus according to claim 1, wherein the number of waves of the basic wavelet used in the wavelet transform is changed to discriminate and discriminate between periodicity and single occurrence of fixing temperature change.   According to a first aspect of the present invention, the abnormal state is determined based on the processing result of the statistical processing means, and stop, warning, or feedback control to the image forming apparatus is performed.

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