JP4886496B2 - Surface potential measuring device - Google Patents

Description

  The present invention relates to a measurement technique for measuring a surface potential of a photoreceptor or the like.

  In an electrophotographic image forming apparatus using a photoconductor, it is necessary to always control the charged potential on the surface of the photoconductor to a target potential in order to stably obtain high image quality regardless of the use environment. Conventionally, in order to control the charged potential on the surface of the photoreceptor to the target potential, a surface potential measuring device for measuring the potential on the surface of the photoreceptor has been realized (see Patent Document 1).

  In general, this type of surface potential measuring apparatus uses a tuning fork vibrator incorporating a measurement electrode. At the time of measurement, the tuning fork vibrator is vibrated at a predetermined position near the photoconductor to be measured. At this time, the capacitance between the measurement object and the measurement electrode changes due to the vibration of the tuning fork vibrator, and an AC signal corresponding to the capacitance change is obtained from the measurement electrode.

  The AC signal obtained from the measurement electrode is detected and amplified by a predetermined detection circuit. The detected AC signal is clamped at a predetermined reference potential and then converted into a DC voltage. Next, the AC signal converted to DC is compared with the reference potential. Then, by changing the power supply voltage of the detection circuit in accordance with the difference value, feedback control is performed so that the AC signal converted to DC becomes equal to the reference voltage, that is, the difference becomes zero. This method is called a so-called zero method.

  FIG. 10 shows an example of a response waveform of the surface potential measuring apparatus when the above operation is performed. FIG. 10A shows the potential to be measured. FIG. 10B shows an AC signal obtained from the measurement electrode as the capacitance changes between the measurement object and the measurement electrode. Note that the AC signal in FIG. 10B is actually amplified after extracting only a predetermined frequency band. FIG.10 (c) has shown the measurement result of the surface potential measuring apparatus. In addition, the measurement result of FIG.10 (c) has shown the output value of the variable power supply circuit for changing the power supply voltage of the above-mentioned detection circuit in fact.

That is, by changing the output voltage of the variable power supply circuit in accordance with the detected AC signal, and the output voltage approaches the potential to be measured, the signal amount of the detected AC signal decreases. The output voltage of the variable power supply circuit when the detected AC signal becomes “0” becomes the potential to be measured. In this case, in order to obtain the potential of the measurement object, it is necessary to wait until the detected AC signal becomes “0”, that is, until the response time elapses.
JP-A-2004-61282

  Incidentally, in recent years, in an image forming apparatus, an image forming process has been accelerated. Therefore, also in the surface potential measuring device, it is desired to reduce the time required for measurement in order to follow the high-speed operation of the image forming process.

  In the surface potential measuring device, the response time, that is, the required measurement time is determined by the resonance period of the tuning fork vibrator and the gain of the measurement circuit. Therefore, in order to shorten the time required for measurement by the surface potential measuring device, it is conceivable to use a tuning fork vibrator having a short resonance period.

  However, in this case, it becomes difficult to increase the vibration amplitude of the tuning fork vibrator, and the measurement accuracy is lowered. In order to deal with this problem, if the gain of the measurement circuit is increased too much, the operation becomes unstable, and eventually the measurement accuracy remains lowered.

  The present invention has been made under such a background, and an object thereof is to make it possible to shorten the time required for measurement without degrading measurement accuracy.

In order to achieve the above object, a surface potential measuring device according to the present invention responds to fluctuations in capacitance between a measuring electrode provided opposite to a potential measuring object and the measuring object and the measuring electrode. Te a detection circuit for detecting the potential of the measuring electrodes varying, said a difference detecting means for detecting a difference between the detected potential and the reference potential, which is detected by the detection circuit, for feedback control of the power supply voltage of the detecting circuit variable and power source means, the first control means and, before Symbol detection voltage detected by the detection circuit and the variable power supply means for controlling the output voltage of the variable power supply means in response to a difference detected by said difference detecting means the prediction means for predicting the potential of the measurement object based on the output voltage, the output voltage of the variable power supply means so that the output voltage is predicted potential predicted by the predicting means of the variable power supply means Has a second control means for controlling, the.

  In the present invention, in order to shorten the time required for measurement, the feedback control amount is increased based on the predicted potential, and the circuit gain is not changed. Therefore, according to the present invention, it is possible to shorten the time required for measurement without reducing the measurement accuracy.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus to which a surface potential measuring apparatus according to the first and second embodiments of the present invention is applied. This image forming apparatus is configured as an electrophotographic color image forming apparatus.

  In FIG. 1, photosensitive drums 1001a to 1001d carry images of C (cyan), M (magenta), Y (yellow), and K (black), respectively. The surfaces of the photosensitive drums 1001a to 1001d are charged by the chargers 1002a to 1002d. The charging high voltage for the chargers 1002a to 1002d is supplied by the charging high voltage substrates 1003a to 1003d.

  When image light reflecting each color image is exposed to the charged photosensitive drums 1001a to 1001d by the exposure devices 1004a to 1004d, electrostatic latent images are formed on the surfaces of the photosensitive drums 1001a to 1001d. At this time, the exposure operation of the exposure apparatuses 1004a to 1004d is controlled by a drive control circuit on the exposure apparatus drive substrates 1005a to 1005d.

  The electrostatic latent images formed on the photosensitive drums 1001a to 1001d are developed as visible toner images by the developing devices 1006a to 1006d. This development processing is performed by applying a high voltage to the developing devices 1006a to 1006d by the high-voltage substrates 1007a to 1007d.

  The toner images on the photosensitive drums 1001a to 1001d are primarily transferred to a belt-like intermediate transfer member 1010 by primary transfer devices 1008a to 1008d. When performing primary transfer, the primary transfer devices 1008a to 1008d are charged by a high voltage supplied from the high voltage substrates 1009a to 1009d. In addition, the toner images (single color images) of the respective colors are superimposed on the intermediate transfer member 1010 in the process of performing the primary transfer to become a full color image. Further, when performing primary transfer, the intermediate transfer member 1010 is rotated clockwise by the DC controller 1016.

  The toner image primary-transferred to the intermediate transfer member 1010 is made uniform by the post charger 1011 in the process in which the intermediate transfer member 1010 further rotates in the clockwise direction in the drawing. The toner image on the intermediate transfer member 1010 is secondarily transferred onto the recording paper by the secondary transfer device 1012. This secondary transfer process is performed by applying a high voltage to the secondary transfer device 1012 by the secondary transfer high-pressure substrate 1013.

  The toner image secondarily transferred onto the recording paper is fixed to the recording paper by the fixing device 1014.

  The fixing device 1014 has a pressure roller and a fixing roller, and the fixing roller has a built-in heater. When performing the fixing process, the temperature of the heater in the fixing roller is controlled by a drive circuit on the heater drive substrate 1015.

  The DC controller 1016 controls the rotation operation of the photosensitive drums 1001a to 1001, the toner stirring operation of the developing devices 1006a to 1006d, and the like in addition to the rotation operation of the intermediate transfer member 1010.

  The series of image forming processes is controlled by the main controller 1017.

  Next, the image forming process will be described in more detail with reference to FIG. Although not shown in FIG. 1, as shown in FIG. 2, the image forming apparatus is provided with primary charging grids 1101a to 1101d and surface potential measuring devices 1102a to 1102d. The subscripts a to d are considered in consideration of the case where there are four image forming stations for four colors C, M, Y, and K.

  Between the primary chargers 1002a to 1002d and the photosensitive drums 1001a to 1001d, primary charging grids 1101a to 1101d are arranged in parallel with the primary chargers 1002a to 1002d. The primary charging grids 1101a to 1101d are electrodes that can be adjusted to a predetermined voltage. By controlling the voltages of the primary charging grids 1101a to 1101d, the amount of current flowing from the primary chargers 1002a to 1002d into the photosensitive drums 1001a to 1001d can be adjusted to control the surface charge amount of the photosensitive drums 1001a to 1001d.

  The surface potential measuring devices 1102a to 1102d are disposed between the exposure devices 1004a to 1004d and the developing devices 1006a to 1006d so as to face the photosensitive drums 1001a to 1001d. These surface potential measuring devices 1102a to 1102d are intended to stabilize the image density and image quality by measuring the surface charging potential of the photosensitive drums 1001a to 1001d and adjusting the primary charging grids 1001a to 1001d.

  The measurement / adjustment processing of the charged potential on the surfaces of the photosensitive drums 1001a to 1001d is performed between the image formation process of one image and the image formation process of the next image (that is, between sheets). It is desirable not to reduce the speed.

  FIG. 3 is a diagram illustrating charging characteristics of the photosensitive drums 1001a to 1001d. The charging characteristics in FIG. 3 indicate the relationship between the surface potential of the photosensitive drums 1001a to 1001d, which is a factor that determines the image quality, and the developing bias potential applied to the developing devices 1004a to 1004d.

3, the horizontal axis represents the primary charging grid 1101a~1101d the set potential (grid potential) _{V g,} the vertical axis represents the surface potential (potential value) V of the photosensitive drum 1001A～1001d. The sign _{V D} in FIG. 3, dark potential, that is, the potential at the time of non-exposure of the charged surface of the photosensitive drum 1001A～1001d. Reference sign _VL indicates the bright portion potential, that is, the surface potential of the photosensitive drums 1001a to 1001d when the exposure is maximized. _Reference sign V _dc indicates a developing bias potential.

As shown in FIG. 3, the light portion potential V _L tends to increase as the dark portion potential V _D increases. The developing bias potential V _dc is determined by an allowable value of the ground cover amount in a portion where no image is formed. This ground fog is sufficient for the toners having different charge amounts (for example, toner having an exceptionally high charge amount) existing in the developing devices 1006a to 1006d to develop with respect to the light portion potential V _D. Generated by having a potential. Therefore, the developing bias potential V _dc is set to a level that slightly attracts the exceptional toner with respect to the dark portion potential V _D so that the ground fogging by the exceptional toner does not occur. Further, a potential difference between the developing bias potential V _dc and the dark portion potential V _D for preventing the exceptional toner from being attracted is referred to as a fog removal potential V _back . This fog removal potential V _back is normally set to about 100 to 200V.

_Bright and dark gradation (contrast) is expressed by the contrast potential V _cont between the development bias potential V _dc and the bright portion potential _VL determined as described above. In order to maintain the image gradation, the dark potential V _D and the bright potential V _L are measured by the surface potential measuring devices 1102a to 1102d between the sheets. The necessary conditions for the response times of the surface potential measuring devices 1102a to 1102d can be derived from the speed of the image forming process and the distance between sheets. The inter-paper distance corresponds to the distance between the trailing edge of the preceding recording sheet and the leading edge of the succeeding recording sheet. That is, the speed of the image forming process _{v PS,} the inter-paper distance is _{L blank,} sheet interval _{L blank} sheet interval a distance corresponding to the photosensitive drum corresponding to the time required for rotation to the time _{t blank} as schematically ,

と表すことができる。

It can be expressed as.

  For example, if the speed of the image forming process is 500 [mm / s] and the distance between papers is 25 [mm], the time between papers is 50 [ms]. Accordingly, the surface potential measuring devices 1102a to 1102d must respond within this paper interval time of 50 [ms]. That is, the response time of the surface potential measuring devices 1102a to 1102d, that is, the time required for measurement must be at least 50 [ms] or less.

In this case, since the bright portion potential V _L at the maximum exposure can theoretically start changing immediately after the trailing edge of the paper passes, the condition of response within the paper interval time of 50 [ms] is satisfied. . However, the dark potential V _D at the time of non-exposure, after the margin portion of the rear end portion of the paper has passed, takes some response time from the potential at the time of exposure to return to the dark potential V _D at the time of non-exposure. This response time is assumed to be 7.5 [ms]. In this case, considering both ends of the paper, the response time of the surface potential measuring devices 1102a to 1102d needs to be within 35 [ms]. Note that the above response time indicates a time required until the measured potential is completely stabilized, and does not indicate a time defined by 10% to 90% of the output like the response time of a semiconductor or the like.

[First Embodiment]
FIG. 4 is a block diagram showing a schematic configuration of the surface potential measuring devices 1102a to 1102d according to the first embodiment. The configuration of the surface potential measuring apparatus according to the second embodiment is the same as that shown in FIG. The surface potential measuring devices 1102a to 1102d are configured to satisfy the above measurement required time.

  In FIG. 4, the drive unit 101 vibrates the tuning fork vibrator 103 by applying a drive signal to the piezoelectric element 102a on the drive side. The drive unit 101 controls the tuning fork type vibration by controlling the drive frequency applied to the drive side piezoelectric element 102a according to the detection signal from the detection side piezoelectric element 102b, that is, the vibration state of the tuning fork type vibrator 103. The child 103 is vibrated at the resonance frequency.

  The timing circuit 104 generates a timing signal at a predetermined timing of the drive signal in the drive unit 101. The timing circuit 104 supplies the generated timing signal to a clamp circuit 112, a peak detection unit 111, and a calculation unit 114, which will be described later.

  When the tuning fork vibrator 103 vibrates, the position and amount of the tuning fork vibrator 103 blocking between the measurement object 105 and the measurement electrode 106 change. As a result, a change occurs in the capacitance between the measurement target 105 and the measurement electrode 106, that is, a potential difference is generated, and an AC signal corresponding to the potential difference between the measurement target 105 and the measurement electrode 106 is obtained from the measurement electrode 106. . Further, the vibration state of the tuning fork vibrator 103 is detected by the piezoelectric element 102b on the detection side. Here, the measurement target 105 is the charged potential of the surfaces of the photosensitive drums 1001a to 1001d.

  The AC signal obtained from the measurement electrode 106 is detected by the detection circuit 107 and voltage amplified, and then output to the band pass filter 109. The band pass filter 109 removes a noise component by extracting a predetermined frequency component from the AC signal. The AC signal from which noise has been removed is amplified by the amplifier circuit 110 and supplied to the clamp circuit 112 and the peak detector 111.

  In addition to the AC signal, the clamp circuit 112 is supplied with a timing signal from the timing circuit 104 and a reference potential from the reference potential generator 113. Therefore, the clamp circuit 112 clamps the AC signal to the reference potential based on the timing signal. The peak detector 111 detects the peak value of the AC signal from which noise has been removed based on the timing signal, and supplies the peak value to the calculator 114.

  FIG. 5 shows the relationship between the drive signal, the timing signal, the output signal of the amplifier circuit 110, the reference potential, and the output of the clamp circuit 112.

FIG. 5A shows a drive signal supplied to the piezoelectric element 102a. FIG. 5B ₁ shows an output signal of the amplifier circuit 110 when the potential of the measurement target 105 is higher than the potential of the measurement electrode 106. FIG. 5B ₂ shows the output signal of the amplifier circuit 110 when the potential of the measurement target 105 is lower than the potential of the measurement electrode 106. FIG. 5 _(a), in synchronization with (b 1), as shown in _{(b 2),} the peak timing of the output signal of the amplifier circuit 110, the rise of the drive signal, the fall.

FIG. 5C shows a timing signal supplied from the timing circuit 104 to the clamp circuit 112. This timing signal is a signal synchronized with the fall of the drive signal. FIG. 5D shows a reference potential supplied from the reference potential generation unit 113 to the clamp circuit 112. FIG. 5 (e ₁ ) shows an output signal of the clamp circuit 112 when the potential of the measurement target 105 is higher than the potential of the measurement electrode 106. FIG. 5D shows a reference potential supplied from the reference potential generation unit 113 to the clamp circuit 112. FIG. 5E ₂ shows an output signal of the clamp circuit 112 when the potential of the measurement target 105 is lower than the potential of the measurement electrode 106. Figure _{5 (d), (e 1} ), as shown in _{(e 2),} the output signal of the clamp circuit 112 is clamped to the reference potential in synchronism with the timing signal.

  The integrating circuit 115 integrates the output signal of the clamp circuit 112 to convert the alternating current signal related to noise removal into direct current as much as possible. The output value of the integration circuit 115 is larger than the reference potential when the potential of the measurement target 105 is higher than the potential of the measurement electrode 106. In this case, the output value of the integration circuit 115 increases as the potential difference between the measurement electrode 106 and the measurement target 105 increases. Further, the output value of the integrating circuit 115 is smaller than the reference potential when the potential of the measuring object 105 is lower than the potential of the measuring electrode 106. In this case, the output value of the integration circuit 115 decreases as the potential difference between the measurement electrode 106 and the measurement target 105 increases. In other words, when the difference between the output value of the integration circuit 115 and the reference potential is “0”, the potential of the measurement electrode 106 indicates the potential of the measurement target 105.

  The error amplifier circuit 116 outputs a difference signal between the output value of the integration circuit 115 and the reference potential. The output signal of the error amplification circuit 116 rises when the output value of the integration circuit 115 is larger than the reference potential. On the other hand, when the output value of the integrating circuit 115 is smaller than the reference potential, the output signal of the error amplifying circuit 116 falls.

The variable power supply circuit 117 outputs a low-level power supply voltage (VFL) corresponding to the output value of the error amplification circuit 116 to the detection circuit 107. Then, feedback control is performed so that the output value of the integration circuit 115 is always equal to the reference potential, that is, the potential difference between the measurement target 105 and the measurement electrode 106 becomes zero. By this feedback control, the current flowing through the detection resistor _RS of the detection circuit 107 becomes “0”, and in this state, the output value of the variable power supply circuit 117 indicates the voltage of the measurement target 105. The output value of the variable power supply circuit 117 is divided by the voltage dividing circuit 118 at a predetermined voltage dividing ratio and output. That is, the voltage dividing circuit 118 outputs a potential corresponding to the voltage division ratio of the potential to be measured. This partial pressure is performed so that it can be digitally captured via an ADC or the like.

  In accordance with the timing signal, the calculation unit 114 performs twice the peak value of the AC signal detected by the peak detection unit 111 and the value obtained by dividing the output voltage value of the variable power supply circuit 117 by the voltage dividing circuit 118 twice. take in. Next, the calculation unit 114 predicts the potential of the measurement target 105 based on the acquired values. Then, the calculation unit 114 controls the variable power supply circuit 117 by interrupt control so that the output voltage of the variable power supply circuit 117 becomes the predicted potential. This interrupt control is released when the output voltage value of the variable power supply circuit 117 reaches the predicted potential. Strictly speaking, interrupt control is canceled when the output of the error amplification circuit 116 reaches a value corresponding to the predicted potential.

  That is, the feedback control by the variable power supply circuit 117 includes normal control based on the output of the error amplifier circuit 116 and interrupt control based on the predicted potential calculated by the calculation unit 114. Then, normal feedback control is performed until a timing signal for two pulses is output after the measurement is started. After the timing signals for the two pulses are output, the potential of the measurement target 105 is predicted by calculation, and feedback control based on the predicted potential is performed by interruption. In the feedback control based on the predicted potential, the feedback control amount is larger than in normal feedback control, and the speed at which the output of the integrating circuit 115 approaches the reference potential is increased.

Then, after the output voltage of the variable power supply circuit 117 reaches the predicted potential by feedback control based on the predicted potential, the normal feedback control is resumed. By this normal feedback control, the output of the integration circuit 115 further approaches the reference potential. When the difference between the output of the integrating circuit 115 and the reference potential becomes “0”, the potential of the measurement electrode 106 and the potential of the measurement target 105 become equal, and as a result, the current flowing through the detection resistor R _S. Becomes “0”. In this state, the output value of the variable power supply circuit 117 indicates the voltage of the measurement target 105.

  Next, the flow of operations of the surface potential measuring devices 1102a to 1102d will be described with reference to FIG.

  Since FIG. 6 shows a flow related to the operation of the circuit, each step in FIG. 6 does not follow a strict time series (the same applies to FIG. 8 described later).

  Upon receiving the measurement start signal from the main controller 1017 (see FIG. 1), the surface potential measuring devices 1102a to 1102d vibrate the tuning fork type driver 103 by drive control by the drive unit 101 (step S601). The timing circuit 104 generates a timing signal according to the drive control by the drive unit 101, and supplies the timing signal to the clamp circuit 112, the peak detection unit 111, and the calculation unit 114 (step S602).

  Further, the capacitance between the measurement object 105 and the measurement electrode 106 is changed by the vibration of the tuning fork type driver 103, and an AC signal corresponding to the capacitance change is output from the measurement electrode 106. Here, the measurement object 105 is the surface potential of the photosensitive drums 1001a to 1001d as shown in FIG. The AC signal output from the measurement electrode 106 is detected by the detection circuit 107 (step S603). The detected AC signal has a noise component removed by a BPF (band pass filter) 109 and further amplified by an amplifier circuit 110. Peak detector 111 detects the peak value (Vppx) of the AC signal amplified by amplifier circuit 110. The calculation unit 114 stores the peak value (Vppx: x = 1, 2) in a memory (not shown) built in the calculation unit 114 in preparation for the prediction calculation of the potential of the measurement target 105 (step S604). In this case, the calculation unit 114 stores only the peak values (Vpp1, Vpp2) obtained based on the first two timing signals from the start of measurement.

  As described above, the AC signal amplified by the amplification circuit 110 is output to the error amplification circuit 116 via the clamp circuit 112 and the integration circuit 115. Then, the error amplifier circuit 116 outputs a value corresponding to the error between the input AC signal and the reference potential to the variable power supply circuit 117. The variable power supply circuit 117 outputs a voltage corresponding to the value from the error amplifier circuit 116. The output voltage of the variable power supply circuit 117 is divided by the voltage dividing circuit 118, and is output as a potential (Vox) corresponding to the current detection potential of the measurement target 105 (step S605). At this time, the calculation unit 114 stores the partial pressure value (Vox: x = 1, 2) in a memory (not shown) built in the calculation unit 114 in preparation for the prediction calculation of the potential of the measurement target 105 ( Step S606). In this case, the calculation unit 114 stores only the partial pressure values (Vo1, Vo2) obtained based on the first two timing signals from the start of measurement.

  The AC signal clamped by the clamp circuit 112 and further integrated by the integration circuit 115 is compared with a reference potential by the error amplification circuit 116 (step S607). As a result of the comparison, if the error between the AC signal and the reference potential is not “0” (step S608), the main controller 1017 determines whether the timing signal output count, that is, the potential detection count of the measurement target 105 is the second count. It is determined whether or not (step S609). As a result, if it is not the second time but the first time or the third time or more, the main controller 1017 changes the output voltage of the variable power supply circuit 117 based on the output of the error amplifier circuit 116 as usual.

  On the other hand, if the number of detections of the potential of the measurement target 105 is the second time, the main controller 1017 causes the calculation unit 114 to predict the potential of the measurement target 105 using the four values stored in the memory (step S611). Then, the main controller 1017 controls the output voltage of the variable power supply circuit 117 to be the potential predicted by the calculation unit 114 by interrupt control (step S610).

  When the error between the AC signal and the reference potential is “0” (step S608), the main controller 1017 outputs the output voltage of the variable power supply circuit 117 (strictly, the output voltage of the voltage dividing circuit 118) at that time. The measurement result is output (step S612), and the measurement is terminated.

  FIG. 7 shows an example of a response waveform in the above measurement operation. FIG. 7A shows the charged potential of the surface of the measurement object 105, that is, the photosensitive drums 1001a to 1001d. FIG. 7B shows a measurement start command signal. In this figure, the measurement start command signal is related to positive logic and the High level is in a commanded state, but a measurement start command signal based on negative logic may be used. FIG. 7C shows a detected AC signal obtained by amplifying the AC current flowing through the detection resistor Rs by the amplifier circuit 110 due to a change in capacitance between the measurement target 105 and the measurement electrode 106. FIG. 7D shows the surface potential of the photosensitive drums 1001a to 1001d, that is, the output voltage of the variable power supply circuit 117, by outputting two timing pulses from the start of measurement measured by the surface potential measuring device.

  As shown in FIG. 7C, feedback control based on the output of the normal error amplifier circuit 116 is performed until the peak values (Vpp1, Vpp2) of the first two detected AC signals are obtained from the start of measurement. Done. In other words, in the first and second feedback control, the output voltage of the variable power supply circuit 117 is changed based on the output of the error amplifier circuit 116 as usual. Therefore, the response time in this period is the same as the conventional one.

  Based on the peak values of the first two detection AC signals, the surface potentials of the photosensitive drums 1001a to 1001d are predicted. The third and subsequent feedback control is performed based on the predicted potential. In this case, the predicted potential is smaller than the output value of the error amplifier circuit 116, as will be described later. Therefore, in the third and subsequent feedback control based on the predicted potential, the degree of change in the output voltage of the variable power supply circuit 117 (feedback control amount) increases, so that the measurement result rapidly approaches the actual potential of the measurement target, The response time is shorter than the feedback control (see FIG. 7D).

  As described above, when the output value of the error amplifying circuit 116 becomes a value corresponding to the predicted potential, switching to normal feedback control is performed.

Next, a method for calculating the predicted potential will be described. The amplitude of the detection AC signal from the detection circuit 107 changes over time due to the distance between the measurement electrode 106 and the measurement target 105, the deterioration of the tuning fork vibrator 103, the environmental change, and the like. Accordingly, the amplitude of the detected AC signal is defined as a variable α. Further, the output obtained by amplifying the detection AC signal from the detection circuit 107 by the amplifier circuit 110 is Vpp, the output of the current voltage dividing circuit 118 is V _O , and the voltage dividing ratio is β. Further, the potential of the measuring object 105 is Vx. In this case, the following relational expression holds.

また、検出交流信号の増幅後の１番目と２番目のピーク値をそれぞれＶ_ＰＰ１及びＶ_ＰＰ２とし、その時点での可変電源の出力値をそれぞれＶ_Ｏ１及びＶ_Ｏ２とする。この場合、Ｖ_ＰＰ１及びＶ_ＰＰ２は、上記の数式２より、

Further, the first and second peak values after amplification of the detected AC signal are V _PP1 and V _PP2 , respectively, and the output values of the variable power supply at that time are V _O1 and V _O2 , respectively. In this case, V _PP1 and V _PP2 are obtained from Equation 2 above.

となる。ここで、分圧回路１１８の分圧比βは、既知の値であり、定数として扱うことができる。また、検出交流信号の振幅αは、次式で計算することができる。

It becomes. Here, the voltage dividing ratio β of the voltage dividing circuit 118 is a known value and can be treated as a constant. The amplitude α of the detected AC signal can be calculated by the following equation.

測定対象１０５の電位Ｖｘは、数式４で計算した検出交流信号の振幅αを用いて、

The potential Vx of the measurement target 105 is obtained by using the amplitude α of the detected alternating current signal calculated by Equation 4.

と予測することができる。

Can be predicted.

The calculation unit 114 predicts the potential of the measurement target 105 by such calculation. The arithmetic unit 114 under the control of the main controller 1017, bring the output voltage of the variable power supply circuit 117 to the prediction potential V _X point in the interrupt control. Thereby, the feedback control amount becomes larger than in the case of normal feedback control, and the response speed of the surface potential measuring devices 1102a to 1102d is increased.

  Moreover, sufficient measurement accuracy can be ensured by returning to the normal feedback control after the feedback control by this interruption.

  For example, it is assumed that the frequency of the tuning fork vibrator 103 is 500 Hz and the response speed of the variable power supply circuit 117 is 4 ms. In this case, the response speed of the surface potential measuring devices 1102a to 1102d is (500 Hz for two cycles: two timing signal pulses) + (4 ms) + (about 500 Hz for about one cycle: stability of the device operation after feedback control. The required time) is about 10 ms. On the other hand, the conventional response speed is about several tens of ms to 100 ms. Therefore, although it depends on the response speed of the variable power supply circuit 117, in this embodiment, there is no doubt that the time required for measurement can be shortened as compared with the prior art.

[Second Embodiment]
In the first embodiment, the potential of the measurement target 105 is predicted only once. On the other hand, in the second embodiment, the potential is predicted a plurality of times. That is, the second embodiment is different from the first embodiment in that feedback control of the power supply voltage of the detection circuit 107 based on the predicted potential is performed a plurality of times.

  In the second embodiment, the calculation unit 114 uses the latest two values for the peak value of the output of the amplifier circuit 110 and the value obtained by dividing the output voltage value of the variable power supply circuit 117 by the voltage dividing circuit 118. Are sequentially updated and recorded in the memory. Here, the latest two values are values obtained based on the latest two timing signals.

  Then, the calculation unit 114 predicts the potential of the measurement target 105 based on the latest two peak values and partial pressure values. Furthermore, the arithmetic unit 114 controls the variable power supply circuit 117 by interrupt control so that the output voltage of the variable power supply circuit 117 becomes the predicted potential.

  The calculation unit 114 repeats the output control of the variable power supply circuit 117 based on such a predicted potential under the control of the main controller 1017. Then, the main controller 1017 determines the output voltage of the variable power supply circuit 117 when the peak value becomes a predetermined value or less as the potential of the measurement target 105.

  Next, the flow of operation of the surface potential measuring devices 1102a to 1102d in the second embodiment will be described with reference to FIG. In FIG. 8, the same steps as those in FIG. 6 are given the same step numbers.

  Upon receiving the measurement start signal from the main controller 1017 (see FIG. 1), the surface potential measuring devices 1102a to 1102d vibrate the tuning fork type driver 103 by drive control by the drive unit 101 (step S601). The timing circuit 104 generates a timing signal according to the drive control by the drive unit 101, and supplies the timing signal to the clamp circuit 112, the peak detection unit 111, and the calculation unit 114 (step S602).

  Further, the capacitance between the measurement object 105 and the measurement electrode 106 is changed by the vibration of the tuning fork type driver 103, and an AC signal corresponding to the capacitance change is output from the measurement electrode 106. Here, the measurement object 105 is the surface potential of the photosensitive drums 1001a to 1001d as shown in FIG. The AC signal output from the measurement electrode 106 is detected by the detection circuit 107 (step S603). The detected AC signal has a noise component removed by a BPF (band pass filter) 109 and further amplified by an amplifier circuit 110. Peak detector 111 detects the peak value (Vppx) of the AC signal amplified by amplifier circuit 110. The calculation unit 114 stores the peak value (Vppx: x = 1, 2, 3,...) In a memory (not shown) built in the calculation unit 114 in preparation for the prediction calculation of the potential of the measurement target 105. (Step S604). In this case, the calculation unit 114 sequentially stores only two peak values obtained based on the latest two timing signals, and deletes the other peak values.

  As described above, the AC signal amplified by the amplification circuit 110 is output to the error amplification circuit 116 via the clamp circuit 112 and the integration circuit 115. Then, the error amplifier circuit 116 outputs a value corresponding to the error between the input AC signal and the reference potential to the variable power supply circuit 117. The variable power supply circuit 117 outputs a voltage corresponding to the value from the error amplifier circuit 116. The output voltage of the variable power supply circuit 117 is divided by the voltage dividing circuit 118, and is output as a potential (Vox) corresponding to the current detection potential of the measurement target 105 (step S605). At this time, the calculation unit 114 prepares for the prediction calculation of the potential of the measurement target 105, and a memory (not shown) in which the partial pressure value (Vox: x = 1, 2, 3,...) Is built in the calculation unit 114. (Step S606). In this case, the calculation unit 114 sequentially stores only two partial pressure values obtained based on the latest two timing signals, and deletes the other partial pressure values.

  The AC signal clamped by the clamp circuit 112 and further integrated by the integration circuit 115 is compared with a reference potential by the error amplification circuit 116 (step S607). Then, the main controller 1017 determines whether or not the number of detections of the potential of the measurement target 105, that is, the number of feedback control operations is the second or more from the start of measurement (step S801). As a result, if the number of times of feedback control is less than 2, the main controller 1017 determines whether or not the difference between the AC signal and the reference potential is “0” as a result of the comparison in step S607 (step S608). ).

  As a result, if the difference between the AC signal and the reference potential is not “0”, the main controller 1017 performs control so as to vary the output of the variable power supply circuit 117 based on the output of the error amplification circuit 116 corresponding to the difference. (Step S610). On the other hand, if the difference between the AC signal and the reference potential is “0”, the main controller 1017 measures the output voltage (strictly speaking, the output voltage of the voltage dividing circuit 118) of the variable power supply circuit 117 at that time. (Step S612) and the measurement is terminated.

  If it is determined in step S801 that the number of times of feedback control is two or more, the main controller 1017 determines whether or not the latest peak value has become a predetermined value or less (step S802). As a result, if the latest peak value is not less than or equal to the predetermined value, the main controller 1017 causes the calculation unit 114 to predict the potential of the measurement target 105 using the four values stored in the memory (step S611). Then, the main controller 1017 performs control so that the output voltage of the variable power supply circuit 117 becomes the potential predicted by the calculation unit 114 (step S610).

  On the other hand, when the latest peak value is equal to or lower than the predetermined value, the main controller 1017 proceeds to step S612, and the output voltage of the variable power supply circuit 117 at that time (strictly, the output voltage of the voltage dividing circuit 118). Is output as a measurement result, and the measurement is terminated.

FIG. 9 shows an example of a response waveform in the measurement operation in the second embodiment. FIG. 9A shows the charging potential of the surface of the measurement object 105, that is, the photosensitive drums 1001a to 1001d. FIG. 9B shows a measurement start designation signal. In this figure, the measurement start command signal is related to positive logic and the High level is in a commanded state, but a measurement start command signal based on negative logic may be used. FIG. 9C shows a detected AC signal obtained by amplifying the AC current flowing through the detection resistor Rs by the amplifier circuit 110 due to the capacitance change between the measurement target 105 and the measurement electrode 106. Note that V _PP1 , V _PP2 ,... V _PPn shown in FIG.

  FIG. 9D shows the surface potential of the photosensitive drums 1001a to 10001d, that is, the output voltage of the variable power supply circuit 117, from which two timing pulses are output from the measurement start measured by the surface potential measuring device.

The calculation unit 114 holds the latest two peak values and the latest two partial pressure values from the start of measurement, and until the next peak value is obtained, the latest two peak values and the latest two partial pressures. Based on the value, the charged potential of the surface of the photosensitive drums 1001a to 1001d is predicted. That is, the calculation unit 114 first performs potential prediction using V _PP1 and V _PP2 , then performs potential prediction using V _PP2 and V _PP3, and uses the V _PPn and V _{PPn + 1} to predict potential in the nth time. I do. Then, the main controller 1017 performs control so that the output voltage of the variable power supply circuit 117 becomes the potential predicted by the calculation unit 114.

  When such control is repeated, the potential of the measurement electrode 106 approaches the potential of the measurement target 105, and the peak value of the detected AC signal decreases. Therefore, the main controller 1017 determines the output voltage of the variable power supply circuit 117 when the peak value becomes a predetermined value or less as a final measurement result.

According to this control, if the frequency of the tuning fork vibrator 103 is f _C , the measurement response time t _R is expressed by the following equation.

予測電位の算出方法は、第１の実施の形態と同様である。

The calculation method of the predicted potential is the same as that in the first embodiment.

  In such a second embodiment as well, as in the first embodiment, the time required for measurement can be greatly shortened compared to the prior art.

  The present invention is not limited to the first and second embodiments described above. For example, instead of the peak value of the detected AC signal, the effective value of the detected AC signal, that is, the amplifier circuit 110, the error amplification, and the like. It is also possible to calculate the predicted potential using an effective value such as an output signal of the circuit 116.

  Further, the present invention is limited to a mode in which the measurement result is determined when the peak value of the detected AC signal becomes a predetermined value or less by feedback control based on a plurality of predicted potentials, as in the second embodiment. It will never be done. In other words, after performing feedback control based on a plurality of predicted potentials, it is possible to return to normal feedback control based on the output of the error amplification circuit, and to confirm the measurement result when the error becomes “0”. .

It is a figure which shows schematic structure of the image forming apparatus to which the surface potential measuring apparatus which concerns on the 1st, 2nd embodiment of this invention is applied. It is a figure which shows the deployment position of the said surface potential measuring apparatus in the said image forming apparatus. FIG. 3 is a diagram illustrating a relationship between a grid potential of a primary charger of the image forming apparatus and a surface potential of a photosensitive drum. It is a block diagram which shows schematic structure of the surface potential measuring apparatus which concerns on 1st, 2nd embodiment. It is a figure which shows the output signal etc. of each part of the surface potential measuring apparatus of FIG. It is a flowchart which shows the measurement operation | movement of the surface potential measuring apparatus which concerns on 1st Embodiment. It is a figure which shows the response at the time of the measurement of the surface potential measuring apparatus which concerns on 1st Embodiment. It is a flowchart which shows the measurement operation | movement of the surface potential measuring apparatus which concerns on 2nd Embodiment. It is a figure which shows the response at the time of the measurement of the surface potential measuring apparatus which concerns on 2nd Embodiment. It is a figure which shows the response at the time of the measurement of the conventional surface potential measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Tuning fork type vibrator drive unit 103 ... Tuning fork type vibrator 104 ... Timing circuit 105 ... Measurement object 106 ... Measurement electrode 107 ... Detection circuit 111 ... Peak detection unit 113 ... Reference potential generation circuit 114 ... Calculation unit 116 ... Error Amplifier circuit 117... Variable power supply circuits 1001 a to 1001 d... Photosensitive drums 1102 a to 1102 d.

Claims (7)

A measuring electrode provided opposite to a potential measurement object;
A detection circuit that detects a potential of the measurement electrode that varies in accordance with a variation in capacitance between the measurement object and the measurement electrode;
A difference detecting means for detecting a difference between the detected potential and the reference potential, which is detected by the detection circuit,
Variable power supply means for feedback control of the power supply voltage of the detection circuit;
First control means for controlling the output voltage of the variable power supply means according to the difference detected by the difference detection means;
Prediction means for predicting the potential of the measurement object based on the detection potential detected by the detection circuit and the output voltage of the variable power supply means;
And second control means for controlling the output voltage of the variable power supply means so as to predict the potential predicted by the output voltage said predicting means of the variable power supply means,
A surface potential measuring device comprising:   Timing signal generation means, and the prediction means predicts the potential of the measurement object once based on the detection potential and the output voltage obtained based on the first and second timing signals after the start of measurement. The surface potential measuring device according to claim 1. It said first control means, in response to the measurement start first and second timing signal after, and timing signal after the detected difference in the difference detecting means becomes a value corresponding to the predicted potential 3. The surface potential measuring apparatus according to claim 2, wherein an output voltage of the variable power source means is controlled.   A timing signal generation unit is provided, and the prediction unit predicts the potential of the measurement object a plurality of times based on the detection potential obtained based on the latest two timing signals and the output voltage. 2. The surface potential measuring apparatus according to 1.   5. The surface potential measuring apparatus according to claim 4, wherein the first control means controls the output voltage of the variable power supply means according to the first and second timing signals after the start of measurement. The detection potential is detected as an AC signal, said difference detecting means, the surface potential measurement according to any one of claims 1 to 5, characterized in that detecting the difference between the peak value and the reference potential of the AC signal apparatus. The detection potential is detected as an AC signal, said difference detecting means, the surface potential measurement according to any one of claims 1 to 5, characterized in that detecting the difference between the actual values and the reference potential of the AC signal apparatus.

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