JP2007127420A - Potential detection sensor and image forming device equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remove sufficiently toner adhering to a detection window of a potential detection sensor with a simple constitution. <P>SOLUTION: A rocking body 11a is rocked by applying a frequency corresponding to a characteristic frequency to a piezoelectric element 14 relative to the rocking body 11a having electrodes 21, 22 on the surface, to thereby detect the surface potential of a measuring object. A vibration part 12a having the detection window has a characteristic frequency not generating resonance with the rocking body 11a. A frequency corresponding to the characteristic frequency of the vibration part 12a is applied to the piezoelectric element, and thereby the vibration part 12a is vibrated without rocking the rocking body 11a, and the toner adhering to the detection window is shaken off. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a potential detection sensor that detects a potential of a surface to be measured, for example, a photosensitive drum surface, and an image forming apparatus including the same.

  In an electrophotographic image forming apparatus, it is essential to uniformly charge the surface of the photosensitive drum during charging regardless of changes in the environment. For this reason, the charged potential of the photosensitive drum is measured using a potential measuring device (potential detection sensor), and feedback control is performed to keep the potential of the photosensitive drum uniform using the result.

As a conventional potential detection sensor, there is a non-contact potential detection sensor, and here, a method called a mechanical AC electric field induction type is often used. In this method, the potential of the surface of the measurement target is a function of the magnitude of the current extracted from the detection electrode built in the potential detection sensor,
i = dQ / dt = d / dt [C · V] (1)
It is given by the formula. Here, Q is the amount of charge appearing on the detection electrode, C is the coupling capacitance between the detection electrode and the measurement object, and V is the potential of the surface of the measurement object. The capacity C is
C = A / S / X (2)
It is given by the formula. Here, A is a proportional constant related to the dielectric constant of the substance, S is the detection electrode area, and X is the distance between the detection electrode and the measurement object.

  Using these relationships, the potential V of the surface of the measurement object is measured. To accurately measure the charge amount Q appearing on the detection electrode, the size of the capacitance C between the detection electrode and the measurement object is set. It has been found so far that it should be modulated periodically. As a method for modulating the capacitance C, the following method is known.

  The first method is to effectively modulate the area S of the detection electrode. In a typical example of this method, a fork-shaped shutter is inserted between the measurement object and the detection electrode, and the shutter is periodically moved in a direction parallel to the surface of the measurement object. As a result, the degree of shielding of the lines of electric force from the measurement target reaching the detection electrode is changed, and the area of the detection electrode is effectively changed to realize the modulation of the capacitance C between the measurement target and the detection electrode. is doing. In addition, there is one in which a metal shielding member having an opening is arranged at a position facing the measurement object. In this device, a detection electrode is provided at the tip of a fork-shaped vibration element, and the position of the detection electrode is changed in parallel just under the opening, thereby modulating the number of lines of electric force reaching the detection electrode and The capacitance C is modulated.

  The second method is to periodically change the distance X between the detection electrode and the measurement object. In a typical example of this method, the detection electrode is arranged at the tip of a cantilever-shaped vibrator, and the cantilever is vibrated to periodically change the distance X between the measurement target and the detection electrode. There is one that modulates the capacitance C.

  However, when scattered toner or dust adheres to the detection electrode or the opening in the image forming apparatus having the potential detection sensor using these methods, the effective detection electrode area changes and the measurement target There was a drawback that the potential could not be measured accurately.

  As a countermeasure against the adhesion of the toner, dust and the like to the sensor, there is a technique in which a known reference voltage is applied to a conductor at a distance equivalent to the photosensitive member and the potential is measured. It has been proposed to obtain actual sensor detection characteristics, calibrate the detection characteristics immediately after the power is turned on and every predetermined number of copies, and display a message prompting the sensor to be cleaned when the correction amount becomes large (for example, patents) Reference 1).

  Also proposed is a sensor housing configuration that generates an air flow that does not disturb or fly the toner on the surface of the photosensitive drum, and does not enter the area measured by the sensor. (For example, refer to Patent Document 2).

JP-A-5-61304 JP 2000-077554 A

  However, the method disclosed in Patent Document 1 cannot prevent dust and the like from adhering to the detection electrode and the opening of the shielding member. Further, according to the method of Patent Document 2, it is impossible to prevent toner, dust, or the like scattered inside the image forming apparatus from adhering to the detection electrode or the opening of the shielding member when the image forming apparatus is not turned on. .

  As a result, toner or the like adheres to the open end of the detection electrode or the detection window of the shielding member, and the effective area of the detection electrode changes, so that the surface potential of the object to be measured cannot be accurately measured and the photosensitive drum is appropriately charged. The problem of not being able to obtain a stable image due to the inability to remain was left.

  In recent years, the potential detection sensor is required to be reduced in size and thickness as the diameter of the photosensitive drum is reduced and the density around the drum is increased.

Here, the magnitude of the current taken out as an output signal from the mechanical AC electric field induction type potential detection sensor is based on the above formulas (1) and (2).
i = d / dt [A · V · S / X] (3)
Therefore, with the downsizing of the potential detection sensor as described above, the detection electrode area S becomes smaller, which also reduces the sensor output current i, which is easily affected by toner, dust, and the like. This is disadvantageous in terms of measurement accuracy.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a potential detection sensor and an image forming apparatus that are small in size and can accurately measure the surface potential of an object to be measured.

  The present invention relates to a swingable swinging body disposed opposite to a surface to be measured, a detection electrode disposed on a surface of the swinging body on the surface to be measured, and between the detection electrode and the surface to be measured. A shielding member having a detection window arranged; and a driving means for swinging the swinging body, and based on a change in the distance between the surface to be measured and the detection electrode due to swinging of the swinging body, In the potential detection sensor for detecting a potential, the shielding member includes a vibrating portion that vibrates in a portion including the detection window, and the driving unit vibrates the vibrating portion in accordance with an applied frequency. And a cleaning mode in which the vibration part is vibrated while the rocking body is stopped or rocked.

  The present invention also provides a charging means for charging the surface of the image carrier as the measurement surface, an exposure means for exposing the charged surface of the image carrier to form an electrostatic latent image, and an electrostatic latent image. An image forming apparatus including a developing unit that develops a toner image, the image forming apparatus including a potential detection unit that detects a potential of the surface of the image carrier after charging, and the potential detection unit is the above-described potential detection sensor. It is characterized by.

  According to the present invention, the potential of the surface to be measured can be detected by swinging the swinging body without vibrating the vibrating portion in the detection mode. Further, the vibrating part can be vibrated in a state where the rocking body is stopped or rocked by the cleaning mode. Due to this vibration, the toner or the like adhering to the detection window can be shaken off. Thereby, the area of the detection window, that is, the effective area of the detection electrode does not change, and the potential of the surface to be measured can be accurately measured. In addition, since the oscillating body and the oscillating portion can be driven by a single driving unit, the potential detection sensor and thus the image forming apparatus can be reduced in size accordingly.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, what attached | subjected the same code | symbol in the same drawing or a different drawing performs the same structure or the same effect | action, The duplication description is abbreviate | omitted suitably about these.

<Embodiment 1>
FIG. 10 shows an image forming apparatus to which the present invention can be applied. The image forming apparatus shown in the figure is an electrophotographic printer, and the figure is a schematic view corresponding to a longitudinal sectional view of the printer as viewed from the front side, that is, from the side where the user is located when operating the printer. .

  An outline of the configuration and operation of a printer (hereinafter referred to as “image forming apparatus”) will be described with reference to FIG.

  The image forming apparatus includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 1 as an image carrier. Around the photosensitive drum 1, a primary charger (charging means) 2, a potential detection sensor (potential detection means) 7, an exposure device (exposure means) 3, and a developing device are arranged in that order almost along the rotation direction (arrow R1 direction). An apparatus (developing means) 4 is provided. Further, a transfer roller (transfer means) 5, a cleaning device (cleaning means) 6 and the like are provided.

  During image formation, the photosensitive drum 1 is rotationally driven at a predetermined process speed (circumferential speed) in the direction of arrow R1 by a drum driving unit (not shown). The surface of the photosensitive drum 1 is uniformly (uniformly) charged to a predetermined polarity and potential by the primary charger 2. An electrostatic latent image is formed on the photosensitive drum 1 after charging by the exposure device 3. The exposure device 3 oscillates a laser beam L based on image information. The laser beam L is reflected by the reflection mirror 3a, and the surface of the photosensitive drum 1 is scanned and exposed. On the surface of the photosensitive drum 1, the electrostatic charge image is formed by removing the charge of the exposed portion. The electrostatic latent image is developed as a toner image by attaching toner to the developing sleeve 4a of the developing device 4.

  The toner image thus formed on the photosensitive drum 1 is transferred by the transfer roller 5 to the recording material P such as paper supplied from the direction of the arrow Kp to the transfer portion between the photosensitive drum 1 and the transfer roller 5. The After the toner image is transferred, the toner (transfer residual toner) remaining on the surface of the photosensitive drum 1 is removed by the cleaning blade 6a of the cleaning device 6 and used for the next image formation. On the other hand, the recording material P after transfer of the toner image is conveyed to a fixing device (not shown), where it is heated and pressurized to fix the toner image on the surface. The recording material P after the toner image is fixed is discharged to the outside of the image forming apparatus main body (not shown). Thus, image formation on one side of one recording material P is completed.

  1, 2 (a), and (b) show a schematic configuration of a potential detection sensor 7 to which the present invention can be applied. Here, FIG. 1 is an exploded perspective view of the potential detection sensor 7. FIG. 2B is a longitudinal sectional view (longitudinal sectional view in a direction perpendicular to the axis of the photosensitive drum 1) of the potential detection sensor 7 viewed from the same direction as FIG. 2A is a longitudinal sectional view (a longitudinal sectional view cut along a plane passing through the axis of the photosensitive drum 1) of the potential detection sensor 7 as viewed from the direction of the arrow Z in FIG. 2B.

  As shown in these drawings, the potential detection sensor 7 includes a support substrate 11, a shielding member 12, a sensor housing 13, and a piezoelectric element 14 as a driving means. The entire potential detection sensor 7 is attached to an image forming apparatus main body (not shown) via a support member 15.

  FIG. 3 shows details of the support substrate 11. The support substrate 11 has a substantially rectangular frame portion 11d, a swinging body 11a, and torsion spring portions 11b and 11b. A rectangular window portion 11c is formed substantially at the center of the frame portion 11d. The window portion 11c is provided with a rectangular rocking body 11a slightly smaller than this. And the rocking | swiveling body 11a and the above-mentioned frame part 11d are connected by the two torsion spring parts 11b and 11b. The frame portion 11d, the window portion 11c, the swinging body 11a, and the torsion spring portions 11b and 11b of b described above are formed symmetrically with respect to one center line XX. The torsion spring portions 11b and 11b described above function as torsion springs. That is, the torsion spring portions 11b and 11b support the swinging body 11a so as to be swingable with respect to the frame portion 11d.

  On one surface of the oscillating body 11a, that is, the surface facing the photosensitive drum 1, two flat detection electrodes 21 and 22 having the same shape are arranged symmetrically with respect to the center line XX. ing. The detection electrodes 21 and 22 are respectively connected to extraction electrodes 25 and 26 formed on the support substrate 11 by electrode wirings 23 and 24 formed on the torsion spring portion 11b. The extraction electrodes 25 and 26 are connected to the inverting input contact 31 and the non-inverting input contact 32 of the differential amplifier 30 installed outside the support substrate 11 by wirings 27 and 28.

  As shown in FIG. 1, the shielding member 12 is provided with a detection window 12a at substantially the center. The detection window 12a is formed in a rectangular shape that is slightly smaller than the rocking body 11a of the support substrate 11, and is disposed at a position corresponding to the rocking body 11a. The shielding member 12 is formed with a “U” -shaped slit 12c so as to surround the detection window 12a. A portion of the shielding member 12 surrounded by the slit 12c is a plate-like vibrating portion 12b.

  The sensor housing 13 is formed in a rectangular parallelepiped box shape and has an opening on the side facing the photosensitive drum 1. As shown in FIGS. 2A and 2B, the above-described shielding member 12 is disposed on the outside, and the above-described support substrate 11 is disposed on the inside via mounting jigs 16 and 16. It is installed. The shielding member 12 and the support substrate 11 are arranged at an interval so that they do not come into contact with each other even when the former vibrating portion 12b and the latter oscillating body 11a vibrate or oscillate. It is installed.

  The piezoelectric element 14 as the driving means is disposed on the opposite side of the sensor housing 13 from the shielding member 12. When the piezoelectric element 14 vibrates, the vibration is transmitted to the shielding member 12 via the housing 13 and to the support substrate 11 via the mounting jigs 16 and 16.

  FIG. 4, which is a view taken along the line YY in FIG. 3, shows the surface S of the measuring object (hereinafter simply referred to as “measuring object S”) using the potential detection sensor 7 shown in FIGS. The state arrange | positioned facing is shown. The measurement object S is, for example, the surface of the photosensitive drum 1 in the present embodiment, and the photosensitive drum 1 rotates around an axis extending in the horizontal direction in the drawing or an axis extending in the direction perpendicular to the paper surface. When the measuring object S opposed to the oscillating body 11a is substantially planar, the oscillating body 11a is disposed so as to be substantially parallel to the neutral position (a position shown in FIG. 5A described later). ing. In FIG. 4, the support substrate 11a, the detection electrodes 21, 22 and the like are accommodated in the aforementioned sensor housing 13 provided to shield unnecessary lines of electric force. The sensor housing 13 is formed of a conductive material and is grounded. The support substrate 11 that supports the oscillator 11a is fixed to the sensor housing 13 by appropriate mounting jigs 16 and 16. Due to the presence of the grounded sensor housing 13, the electric lines of force pass through the detection window 12 a of the shielding member 12 and reach the detection electrodes 21 and 22 only from the measurement object S that faces the oscillator 11 a almost directly in front. That is, the noise component can be suppressed. For this reason, it is possible to measure the potential with high accuracy.

  The potential detection sensor 7 appropriately selects the shape, material, and the like of the oscillating body 11a and the torsion spring portions 11b and 11b, and applies vibration by the piezoelectric element 14, thereby causing the oscillating body 11a to be twisted to the torsion spring portion 11b, The central axis C of 11b can be periodically swung around the rocking center.

  FIGS. 5A, 5B, and 5C are views of the oscillating body 11a as seen from the direction of arrows YY in FIG. FIG. 5 (a) shows a state (hereinafter, this state is referred to as a "neutral state") when the oscillating body 11a reaches the same position as the resting state during the resting state or during the swinging. Here, the distance between the detection electrodes 21 and 22 and the measuring object S is X0, from the center axis C of the oscillator 11a to the center points E and F of the length of the detection electrodes 21 and 22 in the direction orthogonal to the center axis C. Are the distances L1 and L2, respectively.

FIG. 5B shows a state in which the oscillating body 11a oscillates and the distance between the detection electrode 21 and the measuring object S is the longest. At this time, the oscillating body 11a is inclined counterclockwise by an angle θ1 from the neutral state of FIG. In the state of FIG. 5B, the distance X1max between the center point E of the detection electrode 21 and the measuring object S is
X1max = X0 + L1 · sin (θ1) (4)
Indicated by

In this state, the smallest distance X2min between the center point F of the detection electrode 22 and the measurement object S is
X2min = X0−L2 · sin (θ1) (5)
Indicated by

On the other hand, FIG. 5C shows a state in which the swinging state of the swinging body 11a is changed and the distance between the detection electrode 21 and the measuring object S is the smallest. At this time, if the oscillator 11a is inclined clockwise by an angle θ2 from the neutral state in FIG. 5A, the distance X1min between the measuring object S and the center point E of the detection electrode 21 is
X1min = X0−L1 · sin (θ2) (6)
Indicated by

In this state, the largest distance X2max between the center point F of the detection electrode 22 and the measuring object S is:
X2max = X0 + L2 · sin (θ2) (7)
Indicated by

In the present embodiment, the oscillating body 11a and the detection electrodes 21 and 22 have a symmetric structure with respect to the central axis C, and therefore L1 = L2 and θ1 = θ2. Therefore,
X1max = X2max, X1min = X2min (8)
Holds.

The oscillating body 11a can oscillate sinusoidally, and at this time, oscillating at an angular frequency ω,
When ΔX = L1 · sin (θ1), the distance X1 (t) between the center point E of the detection electrode 21 and the measurement target surface S at an arbitrary time t is
X1 (t) = X0 + ΔX · sin (ω · t) (9)
Indicated by

On the other hand, the distance X2 (t) at an arbitrary time t between the center point F of the detection electrode 22 and the measurement object S is
X2 (t) = X0 + ΔX · sin (ω · t + π)
= X0−ΔX · sin (ω · t) (10)
Indicated by Here, π represents the phase delay in radians and is equivalent to 180 °.

  Next, a potential measurement method using the potential detection sensor 7 described above, that is, an operation of the potential detection sensor 7 in the detection mode will be described.

  As described so far, the oscillating body 11a oscillates in a sinusoidal manner, so that the center points E and F of the detection electrodes 21 and 22 installed on the oscillating body 11a are opposed to the oscillating body 11a. The distance to the measuring object S changes periodically as shown by the equations (9) and (10). In the present embodiment, the oscillating body 11a and the detection electrodes 21 and 22 have a symmetric structure with respect to the central axis C. Therefore, the distance between the measurement target S and the detection electrode 21 is represented by the distance X1 (t) from the measurement target S to the center point E, and similarly, the distance between the measurement target S and the detection electrode 22 is pointed from the measurement target S. It can be represented by the distance X2 (t) to F.

  The capacitance formed between the detection electrode 21 and the measurement target S is C1 (t). Similarly, the capacitance formed between the detection electrode 22 and the measurement target S is C2 (t). . According to this, from the two detection electrodes 21 and 22 provided in the potential detection sensor 7 shown in FIGS. 3 and 4, the following expression is obtained from the expressions (3), (9), and (10). Two output signals i1 (t) and i2 (t) that can be extracted.

i1 (t) = d / dt (C1 (t) / V)
= D / dt [A · V · S / X1 (t)]
= D / dt [A · V · S / (X0 + ΔX · sin (ω · t))] (11)
i2 (t) = d / dt (C2 (t) / V)
= D / dt [A · V · S / X2 (t)]
= D / dt [A · V · S / (X0 + ΔX · sin (ω · t + π))]
= D / dt [A · V · S / (X0−ΔX · sin (ω · t))]
= I1 (t + π / ω) (12)

  Here, i1 (t) is an output signal current generated by the time change of the charge generated by the capacitance formed between the detection electrode 21 and the measuring object S. Further, i2 (t) is an output signal current generated by the time change of the charge generated by the capacitance formed between the detection electrode 22 and the measurement target S. Further, S is the area V of the detection electrodes 21 and 22, the potential of the measuring object S, and A is a proportionality constant, which is the same as the proportionality constant A used in the equation (2).

  Therefore, by oscillating the oscillator 11a sinusoidally at the angular frequency ω, the capacitances C1 and C2 between the measuring object S and the detection electrodes 21 and 22 on the oscillator 11a are changed sinusoidally. In this way, signal currents i1 (t) and i2 (t) including information on the surface potential V of the measuring object S and having a phase difference of π (= 180 °) can be taken out independently, and the surface potential V can be detected. Can do.

  A method for processing the signal currents i1 (t) and i2 (t) extracted from the above-described potential detection sensor will be described.

  From the equations (11) and (12), by oscillating the oscillating body 11a at the frequency f (ω = 2 · π · f), i1ω (t) and i2ω (t) = The signal current of i1ω (t + π / ω) can be taken out independently. The amount of charge Q shown in the above equation (1) is generally a very small physical quantity, and the output signal current i expressed by its time derivative is also very small.

  Therefore, the signal currents i1ω (t) and i2ω (t) are also minute signals. However, these signals are in the above relationship, and the signal current i2ω (t) has a phase of i1ω (t) of 180 ° (π) (this is π / ω = 1 / (2f) in terms of time). It is equivalent to one that is shifted by a half of the period as represented by In order to process such a signal, a detection circuit called a differential amplifier is suitable. By processing i1ω (t) and i2ω (t) with a differential amplifier, the magnitude of the output signal is doubled. In addition, noise that affects both detection electrodes 21 and 22 can be removed.

  Next, a method for driving the oscillating body 11a in the potential detection sensor 7 will be described.

  FIG. 6 illustrates a mechanism for oscillating the oscillating body 11 a in the potential detection sensor 7. The support substrate 11 having the oscillating body 11 a is attached to the piezoelectric element 14 via mounting jigs 16 and 16. Electrodes 41 and 42 for driving power supply are formed on the piezoelectric element 14, and these are connected to the driving power supply 43.

  When the oscillating body 11a moves as shown in FIG. 5, the oscillating body 11a is oscillated (vibrated) at a frequency called a resonance frequency fc corresponding to the structure. This is generally called a natural mode of vibration of the oscillator 11a. The drive power supply 43 gives a drive signal having a frequency equal to fc to the piezoelectric element 14 via the electrodes 41 and 42, so that the oscillation body 11 a and the support substrate 11 housed in the sensor housing 13 on the piezoelectric element 14 have a frequency. The vibration of fc can be given. At this time, the natural vibration mode of the oscillator 11a is coupled with the vibration of the frequency fc by the piezoelectric element 14 and vibrates at the resonance frequency fc. As a result, it becomes possible to oscillate the oscillator 11a at its resonance frequency fc using the drive mechanism shown in FIG.

  Next, the manufacturing method of the support substrate 11 in this Embodiment is demonstrated.

  The structure of the potential detection sensor 7 shown in FIG. 3 can be batch-molded in large quantities by processing a silicon substrate using micromachine technology. Specifically, the slits 11c1 and 11c2 penetrating the substrate can be easily formed in the silicon substrate using a processing technique such as a dry etching technique. At this time, the portions left after the processing become the frame portion 11d, the torsion spring portion 11b, and the swinging body 11a of the support substrate 11.

  Further, by using a film forming technique generally used in the semiconductor processing technique, an insulating thin film is formed on the surfaces of the support substrate 11, the torsion spring portion 11b, and the oscillator 11a, and the detection electrodes 21, 22; Electrode wirings 23 and 24 can also be formed.

  As a result, the frame portion 11d, the torsion spring portion 11b, the oscillating body 11a, the detection electrodes 21, 22 and the electrode wirings 23, 24 of the substrate 11 constituting each of the above-described portions can be easily assembled without going through an assembly process. It can be formed on one substrate. Furthermore, it is possible to manufacture a large number of potential detection sensors 7 in a lump using a silicon substrate having a size capable of forming a plurality of structures of the potential detection sensor 7 of the present embodiment.

  In the present embodiment, the shielding member 12 described above has a vibration mode in which the frequency of the vibration part 12 b is different from the resonance frequency fc of the oscillator 11. As already described, the oscillator 11 is coupled with the vibration of the frequency fc by the piezoelectric element 14 and vibrates at the resonance frequency fc. The resonance frequency fc can be set to an appropriate value by changing the shape of the torsion spring portion 11b. In the present embodiment, the case where the resonance frequency fc is about 20 kHz will be described as an example.

  In general, in order to generate resonance in the natural vibration mode, it is only necessary to give a vibration having a frequency equal to the natural frequency. If the frequency of the given vibration is within about 5% of the natural frequency, the resonance state Become. In order for the vibration part 12b of the shielding member 12 not to resonate due to the vibration of the oscillator 11a or the vibration of the piezoelectric element 14, the natural frequency of the vibration part 22a may not be in the range of 19 to 21 kHz.

  FIGS. 11A, 11B, and 11C show the operation of the shielding member 12 in the vibration mode (cleaning mode) of the shielding member 12. FIG.

  As the material of the shielding member 12, a stainless spring material having a thickness of 0.3 mm was used. The shielding member 12 has an outer shape of 8 mm wide × 15 mm long, and the size of the detection window 12a is 1.5 mm × 1.5 mm. The shape of the vibration part 12b defined by the slit 12c is a rectangular shape having a width of 4 mm (width) x a length of 11.5 mm.

  In this case, the primary vibration mode is a bending mode of 1500 Hz as shown in FIG. 11A, the secondary vibration mode is a bending mode of 9000 Hz as shown in FIG. 11B, and the third vibration mode is a figure. As shown in Fig. 11 (c), the torsional mode is 9750 Hz. The fourth vibration mode (not shown) is a bending mode of 17.9 kHz, and the fifth vibration mode (not shown) is a bending mode of 25.8 kHz. Thus, since there is no vibration mode of the vibration part 12b of the shielding member 12 at 19 to 21 kHz, the vibration part 12b of the shielding member 12 does not resonate even when the piezoelectric element 14 or the oscillator 11a vibrates at 20 kHz during measurement. Absent. On the contrary, if the piezoelectric element 14 which is a driving means is driven at 1500 Hz, 9000 Hz, and 9750 Hz, the vibration portion 12b of the shielding member 12 resonates at each frequency, and bending vibration and torsional vibration are excited. At this time, the oscillating body 11a does not oscillate because it does not enter the resonance state. By driving the piezoelectric element 14 at these frequencies during non-measurement, the vibration member 12b having the detection window 12a of the shielding member 12 can be vibrated, and the toner or the like adhering to the detection window 12a can be removed. At this time, if the vibration part 12b is vibrated at a plurality of frequencies having different vibration modes such as a bending mode and a torsion mode, it is possible to effectively screen those that are difficult to screen in one vibration mode.

<Embodiment 2>
The potential detection sensor of the present embodiment will be described with reference to FIGS. Here, FIG. 7 is an exploded perspective view for explaining a mechanism for swinging the support substrate 11 and the swinging body 11 a of the support substrate 11. FIG. 8 is a view showing a cross section in a direction perpendicular to the central axis C. FIG.

  In the above-described first embodiment, the piezoelectric element 14 is used as a driving unit for driving the oscillator 14, but a different configuration is employed in the present embodiment.

  In the present embodiment, the hard magnetic film 51 is formed on the surface of the two surfaces of the oscillator 11a where the detection electrodes 21 and 22 are not formed. The hard magnetic film 51 is formed so that different magnetic poles N and S are located at both ends of the oscillating body 11a sandwiching the central axis C of the torsion spring portions 11b and 11b. In addition, a flat substrate 50 is disposed substantially in parallel with the support portion 11d that supports the oscillating body 11a on the side opposite to the surface to be measured S (not shown). In the substrate 50, an opening 52 having substantially the same shape as the opening 11c provided in the support substrate 11 is also provided in the substrate 50, and a planar coil 53 wound in a planar shape is formed around the opening 52. Yes. The support substrate 11 is bonded to the substrate 50 via the spacer 54. In the present embodiment, the hard magnetic film 51, the planar coil 53, the spacer 54, etc. constitute driving means.

  In this structure, a magnetic field is generated in the opening 52 by supplying an appropriate current to the planar coil 53. By using the attractive force and the repulsive force generated between this magnetic field and the magnetic poles N and S of the hard magnetic film 51 formed on the oscillating body 11a, a couple force in the driving direction of the oscillating body 11a can be generated. it can.

  At this time, by periodically changing the direction of the current flowing in the planar coil 53, the direction of the magnetic field generated by the coil 53 is reversed, and the direction of the couple generated in the oscillator 11a is changed. As a result, the oscillator 11a can be swung. At this time, if the direction of the current flowing through the planar coil 53 is changed at the same frequency as the resonance frequency fc of the vibrating body 12b (see FIG. 1), the rocking body 11a is swung at the resonance frequency fc, and this rocking is further performed. Thus, the vibrating body 12b can resonate at the frequency fc. It is also possible to cause the oscillating body 11a to oscillate by changing the direction of the current flowing through the planar coil 53 at an arbitrary frequency other than the resonance frequency fc. The other points are the same as those in the embodiment using the piezoelectric element described above.

  As for the support substrate 11 of the present embodiment, the manufacturing method can form a structure including the oscillator 11a from a single silicon substrate using micromachine technology, as in the first embodiment. . In addition, a plurality of elements can be collectively formed on a single silicon substrate.

  Furthermore, the substrate 50 including the planar coil 53 can also form a plurality of elements at once on a single silicon substrate. Of course, the method of manufacturing the potential detection sensor according to the present invention is not limited to such a micromachine semiconductor processing technique.

  FIGS. 12A, 12B, and 12C show other configurations of the shielding member. The shielding member 61 is provided with slits 21c and 21d so as to surround the detection window 21a. The slit 21c is linearly formed in the vertical direction on the left side of the shielding member 61 in FIG. The slit 21d is formed in a “U” shape on the left side of the slit 21c. The inside of these slits 21c and 21d is a vibration part 21b. The vibrating part 21b is connected to the other part of the shielding member 61 at the upper and lower ends of the slit 21c.

  FIGS. 12A, 12B, and 12C show vibration modes of the shielding member 61, respectively. The primary vibration mode is a 1.6 kHz bending mode as shown in FIG. 12A, the second vibration mode is a 10.1 kHz bending mode and the third vibration mode is as shown in FIG. 12B. As shown in FIG. 12C, the 10.5 kHz twist mode is set. The fourth order is a bending mode of 18.7 kHz, and the fifth order is a bending mode of 29.3 kHz bending. The frequency of these vibration modes can be set to an appropriate frequency depending on the shape of the vibrating portion 12a of the shielding member 12 (see FIG. 1) and the connection shape with other portions of the shielding member 61.

  FIGS. 13A, 13B, and 13C show another example of the shielding member.

  The shielding member 62 is provided with slits 22c and 22d so as to surround the detection window 22a, and the inside of the slits 22c and 22d is a vibrating portion 22b. The slit 22c is formed in the left-right direction above and below the vibrating portion 22b. The vibrating part 22b is connected to the other part of the shielding member 62 at the upper and lower ends of the slit 22d.

  FIGS. 13A, 13B, and 13C show vibration modes of the shielding member 62. FIG.

  The primary vibration mode is a bending mode of 1000 Hz as shown in FIG. 13A, the secondary vibration mode is a bending mode of 7500 Hz as shown in FIG. 13B, and the third vibration mode is FIG. ) Is a torsional mode of 8200 Hz. The fourth order is a 10.6 kHz bending mode, and the fifth order is a 22.5 kHz bending mode.

  As shown in FIGS. 11, 12, and 13, the resonance frequency can be easily changed by changing the shapes of the vibrating portions 12b, 21b, and 22b.

It is a disassembled perspective view of an electric potential detection sensor. (A) is a longitudinal cross-sectional view from the arrow Z direction in FIG.2 (b). (B) is the longitudinal cross-sectional view which looked at the electric potential detection sensor from the direction along the axis | shaft of the photosensitive drum. It is a figure explaining the structure of a support substrate. It is a longitudinal cross-sectional view which shows the positional relationship of an electric potential detection sensor and a to-be-measured object. (A), (b), (c) is a figure explaining the positional relationship of each part and measurement object when a rocking | fluctuation body is rock | fluctuating. It is a figure explaining the piezoelectric element as a drive means for driving a rocking body. FIG. 10 is a perspective view showing a driving unit in the second embodiment. FIG. 6 is a longitudinal sectional view for explaining a driving unit according to a second embodiment. It is a perspective view explaining the rocking body swinging. FIG. 2 is a diagram schematically illustrating a configuration around a photosensitive drum of an image forming apparatus. (A), (b), (c) is a figure explaining how the vibration part of a shielding member vibrates. (A), (b), (c) is a figure explaining how the vibration part of another shielding member vibrates. (A), (b), (c) is a figure explaining how the vibration part of another shielding member vibrates.

Explanation of symbols

1 Photosensitive drum (image carrier)
2 Primary charger (charging means)
3 Exposure equipment (exposure means)
4 Developing device (Developing means)
7 Potential detection sensor 11 Support substrate 11a Oscillator 12 Shield member 12a Detection window 12b Vibrating portion 14 Piezoelectric element (drive means)
21, 22 Detection electrode S Surface to be measured (surface to be measured, image carrier surface, photosensitive drum surface)

Claims (6)

A swingable swinging body disposed opposite to the surface to be measured, a detection electrode disposed on the surface of the swinging body on the surface to be measured, and a detection disposed between the detection electrode and the surface to be measured A shielding member having a window; and a driving unit configured to swing the rocking body, and detects a potential of the surface to be measured based on a change in a distance between the surface to be measured and the detection electrode due to rocking of the rocking body. In the potential detection sensor,
The shielding member has a vibrating portion that vibrates in a portion including the detection window;
The driving means vibrates the vibration part in a state where the rocking body is stopped or rocked in a detection mode in which the rocking body is swung without vibrating the vibration part in accordance with an applied frequency. Having a cleaning mode,
A potential detection sensor characterized by that. The oscillating body and the vibrating section have natural frequencies that do not cause resonance with each other,
The drive means is applied with a frequency capable of oscillating the oscillating body in the detection mode, and is applied with a frequency capable of operating the oscillating unit in the cleaning mode.
The potential detection sensor according to claim 1. The driving means is a piezoelectric element that vibrates in accordance with an applied frequency;
The potential detection sensor according to claim 2. The drive means swings the swinging body at a frequency at which the vibrating part resonates due to swinging of the swinging body in the cleaning mode, and the vibrating part resonates even if the swinging body swings in the detection mode. Rock the rocking body at a frequency that does not
The potential detection sensor according to claim 1. The driving means is a driving means for magnetically driving the oscillator;
The potential detection sensor according to claim 4. A charging unit that charges the surface of the image carrier as the measurement surface, an exposure unit that exposes the charged image carrier surface to form an electrostatic latent image, and a development that develops the electrostatic latent image as a toner image An image forming apparatus comprising:
Comprising a potential detecting means for detecting the potential of the surface of the image carrier after charging;
The potential detection means is the potential detection sensor according to any one of claims 1 to 5.
An image forming apparatus.

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