JP2014186018A - Potential detector and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact potential detector configured to accurately detect a surface potential of a member.SOLUTION: A potential detector for detecting a surface potential of a member includes: at least two cantilevers with piezo-resistor arranged at different distances in a direction substantially perpendicular to the member; measurement means for measuring the surface potential of the member on the basis of deflection of the cantilever with piezo-resistor due to interatomic force acting between the member and the cantilever with piezo-resistor; and holding means for holding the two or more cantilevers with piezo-resistor at a predetermined distance.

Description

  The present invention relates to a potential detection device and an image forming apparatus.

  In recent years, printers using digital photography and digital multifunction peripherals have been improved in image quality and stability. This tendency is particularly noticeable for high-speed machines targeting the production print market represented by copy centers in companies that handle the printing of manuals and proposals. In such a market, products that can stably output high image quality over a long period of time are required more than office products.

  On the other hand, as one of the factors that cause instability of the electrophotographic system, there is performance deterioration of each member over time. There are various types of members that deteriorate, but one that has a large effect on image quality is light fatigue of the photoreceptor. Specifically, when the photosensitive member repeatedly receives the writing light, the residual potential is increased and the toner is hardly developed on the photosensitive member.

  In particular, if the image formation is very fast like products for the production print market, the time from erasure exposure to the next charging will be shortened, and the recovery time of light fatigue cannot be secured sufficiently, Light fatigue is more likely to occur. As a result, the next image formation is performed without recovering the normal state, and the portion where the light fatigue occurs causes the phenomenon of density unevenness and remarkably deteriorates the image quality. In particular, when light fatigue unevenness occurs in the longitudinal direction of the photosensitive member, it is particularly difficult to correct the image density unevenness.

  In order to maintain the initial image quality when light fatigue of the photoconductor progresses, it is necessary to take measures such as adjusting the amount of writing light, maintaining the initial image quality by the control method, or replacing the deteriorated photoconductor It is. In particular, since products for the production print market require stability of image quality, it is necessary to detect the state of deterioration at the earliest possible stage. On the other hand, the progress of light fatigue cannot be detected easily.

  With respect to the above, Patent Document 1 discloses that the surface potential of the photoconductor enables the density adjustment according to the degree of recovery from light fatigue by controlling the charging potential according to the elapsed time after the immediately preceding image forming operation. A control device is disclosed. Patent Document 2 discloses a copy image adjustment method in which an image density on a photoconductor is detected by a photoelectric sensor, and a charge amount and an exposure amount are adjusted based on a comparison result between the detected density and a reference value.

  Further, Patent Document 3 discloses a surface potential detection device that detects and controls the potential after charging and the potential after exposure by mounting a surface potential sensor that detects the surface potential in a non-contact manner. .

  According to the surface potential control device for a photoconductor disclosed in Patent Document 1, it is possible to correct the charging output approximate to the light fatigue characteristics, and it is possible to form an image with a constant density. However, in the surface potential control device of Patent Document 1, the light fatigue unevenness in the longitudinal direction cannot be canceled.

  The copy image adjustment method disclosed in Patent Document 2 is a method that is easy to implement with a simple structure. However, detecting the surface state of the photoconductor based on the detected density of the photoconductor is not an accurate method, and it is difficult to correctly recognize the progress of deterioration in a minute region.

  In addition, the surface potential detection device disclosed in Patent Document 3 can directly detect the potential on the photoconductor, and is therefore an excellent method for correcting density changes due to light fatigue. However, since there is a limit to reducing the potential sensor, it can be arranged only in a limited portion in the longitudinal direction. Therefore, when light fatigue unevenness occurs in the longitudinal direction, the degree of fatigue cannot be detected correctly and corrected.

  Here, the inventor of the present invention has found that the above problem can be solved by applying a cantilever. The knowledge that the applied potential can be evaluated from the mirror image force due to the charge on the surface of the member was obtained because a minute force can be accurately measured by using a silicon probe called a cantilever.

  However, a conventional force measuring method called an optical lever method can be used as a dedicated measuring device because of its cantilever configuration, but cannot be used as a compact sensing device for control. That is, the configuration is such that the back surface of the cantilever is irradiated with laser light and the reflected light is detected by a quadrant detector. Further, the action is to detect the warpage and deflection of the cantilever when a force is applied to the cantilever by the movement of the reflected light on the quadrant detector.

  Therefore, a laser source, a four-divided detector, and an optical system are required, and a compact configuration cannot be achieved, and it is very difficult to install in a copying machine or a printer. In addition, since laser light is used for measurement, sensing light also causes the electrostatic latent image to be disturbed and image quality defects to occur if a part of the leaked or reflected light is applied to the photoconductor. It is difficult to use as a device.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a potential detection device that can be configured compactly and detects the surface potential of a target member with high accuracy.

  In order to solve the above problems, the potential detection device of the present invention is a potential detection device for detecting the surface potential of a target member, and is at least arranged at different distances in a substantially vertical direction with respect to the target member. Two piezo built-in cantilevers, measurement means for measuring the surface potential of the piezo built-in cantilever by an atomic force acting between the target member and the piezo-built cantilever, and at least two piezos And holding means for holding the built-in cantilevers at a predetermined distance from each other.

  According to this invention, it can comprise compactly and it becomes possible to detect the surface potential of an object member accurately.

1 is a schematic configuration diagram of an image forming apparatus including a potential detection device according to a first embodiment of the present invention. It is a schematic block diagram of the other image forming apparatus to which the electric potential detection apparatus of 1st Embodiment in this invention is applied. It is a schematic block diagram of the electric potential detection apparatus of 1st Embodiment in this invention. 5 is a graph showing the relationship between the surface potential of the photoconductor and the acting force acting on the piezoelectric built-in cantilever in the first embodiment of the present invention. It is a graph which shows adjusting exposure amount based on surface potential in 1st Embodiment in this invention. The potential detection device according to the first embodiment of the present invention has an array structure. It is explanatory drawing which showed the positional relationship with respect to the photoreceptor of two piezoelectric built-in type cantilevers in the electric potential detection apparatus of 1st Embodiment in this invention. It is a graph explaining the advantage at the time of making constant the distance between two piezo built-in type cantilevers in 1st Embodiment in this invention. It is a schematic block diagram of the image forming apparatus provided with the electric potential detection apparatus of 2nd Embodiment in this invention. It is a schematic block diagram of the electric potential detection apparatus of 2nd Embodiment in this invention. It is the schematic diagram which showed the phase of the alternating voltage applied between each cantilever in 2nd Embodiment in this invention. It is a schematic diagram which shows operation | movement of the electric potential detection apparatus of 2nd Embodiment in this invention. It is the schematic which made the electric potential detection apparatus of 2nd Embodiment in this invention the array structure. FIG. 5 is a diagram in which the potential detection device according to the embodiment of the present invention is applied to potential unevenness detection of a transfer belt. FIG. 5 is a diagram in which the potential detection device according to the embodiment of the present invention is applied to potential unevenness detection of a charging roller. It is a top view of the self-detection type SPM probe provided with a cantilever.

[First Embodiment]
The potential detection apparatus according to the first embodiment of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the present embodiment as long as the gist of the present invention is not exceeded. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified thru | or abbreviate | omitted suitably.

  The outline of this embodiment will be described below. The inventor has found that a cantilever equipped with a piezoresistor is applied in order to provide a potential detecting device that can be compactly configured and accurately detects the surface potential of a photoconductor as an example of a target member.

  In recent years, a cantilever with a built-in piezo or a self-detecting cantilever has been put into practical use. In this method, the amount of deflection of the cantilever is detected by using a cantilever having a piezoresistor formed on the surface and detecting a change in the resistance value of the piezoresistor. If this type of cantilever is used, an optical system is not required, so a compact configuration can be achieved. Further, it is not necessary to consider that the leaked light reaches the photosensitive member as in the optical lever system.

  More importantly, the dimensions of the cantilever are microscale and can be designed very compactly, including other wiring and installation mechanisms. For this reason, a plurality of sensing units can be arranged in the longitudinal direction of the photoreceptor. Therefore, it is possible to detect unevenness of light fatigue in the longitudinal direction due to the output image pattern or the material bias.

  The present embodiment proposes a potential detection device that accurately detects light fatigue on the surface of a photoconductor using the piezo built-in cantilever. As a result, the image forming apparatus can control the image density with higher accuracy. The present embodiment also proposes a potential detection device that replaces the photoconductor at a more appropriate timing. As a result, a more stable image density can be output.

  A schematic configuration of an image forming apparatus including the potential detection device of the present embodiment will be described with reference to FIG. In the image forming apparatus 1 of the present embodiment, a photoconductor 20 as an image carrier that is driven to rotate clockwise is housed in a main body casing. Around the photosensitive member 20, the charging unit 30, the exposure unit 40, the potential detection device 10 of the present embodiment, the developing unit 50, the transfer unit 60, the cleaning brush 70, the blade 80, and the photosensitive member. A static eliminating unit 90 is disposed.

  The image forming apparatus 1 includes a paper feed cassette that stores a plurality of recording sheets. The recording paper in the paper feed cassette is sent out one by one to the registration roller pair by the paper feed roller. Then, after the timing of the recording paper is adjusted by the registration roller pair, the recording paper is sent out between the transfer unit 60 and the photoconductor 20.

  The image forming apparatus 1 rotates the photoconductor 20 clockwise and charges the photoconductor 20 uniformly by the charging unit 30. Thereafter, the exposure unit 40 irradiates a laser modulated with image data to form an electrostatic latent image on the photoconductor 20, and the developing unit 50 attaches toner to the photoconductor 20 on which the electrostatic latent image is formed. develop.

  The image forming apparatus 1 causes the transfer unit 60 to transfer the photoreceptor 20 on which the toner image is formed by adhering the toner in the developing unit 50 onto the recording paper conveyed between the photoreceptor 20 and the transfer unit 60. The recording sheet on which the toner image is transferred is conveyed to the fixing unit.

  The fixing unit includes a fixing roller heated to a predetermined fixing temperature by a built-in heater and a pressure roller pressed against the fixing roller with a predetermined pressure, and heats and pressurizes the recording paper conveyed from the transfer unit 60. The toner image on the recording paper is fixed on the recording paper and then discharged onto the paper discharge tray.

  On the other hand, the image forming apparatus 1 further rotates the photosensitive member 20 having the toner image transferred to the recording paper by the transfer unit 60, and removes the toner remaining on the surface of the photosensitive member by the blade 80 with the cleaning brush 70. Thereafter, the image forming apparatus 1 neutralizes the charge with the photoreceptor neutralization unit 90.

  In the image forming apparatus 1, after the photosensitive member 20 that has been neutralized by the photosensitive member neutralizing unit 90 is uniformly charged by the charging unit 30, the next image formation is performed as described above. The cleaning brush 70 is not limited to scraping off the residual toner on the photoconductor 20 with the blade 80. For example, the cleaning brush 70 may scrape off the residual toner on the photoconductor 20 with a fur brush.

  Next, a schematic configuration of another image forming apparatus to which the potential detection apparatus of this embodiment can be applied will be described with reference to FIG. 2A shows a schematic configuration of a tandem type full-color image forming apparatus 100, and FIG. 2B shows a schematic configuration of a revolver type full-color image forming apparatus 200. FIG. The description of the same configuration as that of the image forming apparatus 1 of the present embodiment described above is omitted.

  First, a schematic configuration of the tandem full-color image forming apparatus 100 will be described with reference to FIG. In the image forming apparatus 100, an image carrier 102 that is driven to rotate clockwise in a main body housing (not shown) is provided for each color of C (cyan), M (magenta), Y (yellow), and K (black). A tandem arrangement is provided on the intermediate transfer unit 106. Then, the color image is transferred from the toner image transferred to the intermediate transfer unit 106 to the recording paper in the transfer unit 107.

  Next, a schematic configuration of the revolver type full-color image forming apparatus 200 will be described with reference to FIG. The revolver type full-color image forming apparatus 200 is configured to sequentially develop a plurality of colors of toner on one image carrier by switching the operation of the developing device.

  That is, as illustrated, a developing device 205C that develops a cyan toner image, a developing device 205M that develops a magenta toner image, a developing device 205Y that develops a yellow toner image, and the like. A developing device 205K for developing a black toner image is arranged in a revolver shape.

  An image carrier as one of the members mounted on the image forming apparatus of the present embodiment described above will be described. An electrophotographic photosensitive member can be used as the image carrier used in the present invention. Since the electrophotographic photosensitive member transfers a toner image to a recording paper or an intermediate transfer member, it is not preferable that the electrophotographic photosensitive member has a large adhesive force to the toner. Therefore, the present invention can be preferably used. As the electrophotographic photoreceptor, other layers than the above may be formed as long as at least an intermediate layer and a photosensitive layer are provided on the conductive support.

  Next, a schematic configuration of the potential detection device 10 of the present embodiment will be described with reference to FIGS. 1 and 3. As shown in FIG. 3A, the potential detecting device 10 of the present embodiment is arranged with a predetermined distance (hereinafter referred to as “gap”) in a substantially vertical direction from the surface of the photoconductor 20, and has a built-in piezoelectric cantilever. The cantilever 11 and the piezo 12 that is a drive mechanism. As described above, a piezo built-in cantilever is used for the potential detection device 10 of the present embodiment. As shown in FIG. 1, the surface state of the photoreceptor can be detected without adversely affecting the image forming process by installing the potential detection device 10 on the downstream side of the exposure unit 40.

  Further, as shown in FIG. 3B, the potential detection device 10 of this embodiment is held by a holding member 13 or the like along the longitudinal direction of the photoconductor 20, and is installed at a predetermined interval. It is possible to detect potential unevenness in the longitudinal direction. That is, the interval for detecting the potential unevenness in the longitudinal direction of the photoconductor 20 is related to the interval of this arrangement. By determining whether the predetermined interval is narrowed or widened, the total number of potential detection devices 10 can be controlled. Further, if the predetermined interval is widened, the detection accuracy of the potential unevenness is somewhat lowered, but the number of piezo built-in cantilevers is reduced, so that the cost can be reduced.

  The detection of the mirror image force on the surface of the photosensitive member using a piezo built-in cantilever is basically the same as the method using an atomic force microscope. Here, a specific measurement action will be described. First, a certain gap is provided between the piezoelectric built-in cantilever and the surface of the photoreceptor. By doing so, a Coulomb force is generated between the surface charge of the photoconductor and the mirror image charge induced in the cantilever by the surface potential of the photoconductor. At this time, the tip of the piezoelectric built-in cantilever is drawn toward the photosensitive member. By monitoring the amount of deflection of the piezoelectric built-in cantilever at this time, the surface potential of the photoreceptor can be measured.

  Further, since the spring constant of the piezoelectric built-in cantilever is limited to several to several tens N / m, it is important to set an appropriate gap with respect to the surface potential of the detection target. FIG. 4 shows the relationship between the surface potential of the photoreceptor and the force acting on the cantilever. The surface potential of the photoreceptor is several tens to several hundreds V. For example, when using a cantilever with a spring constant of 4 N / m, such as a self-detecting cantilever (width 50 μm, length 400 μm) manufactured by SII Nanotechnology (currently Hitachi High-Tech Science), the detectable force range is several to several hundreds Since it is nN, the gap between the photoreceptor surface and the cantilever is preferably set to 100 to 300 μm.

  For the piezoelectric built-in cantilever constituting the potential detection device 10 of this embodiment, for example, an SPM probe is used. The schematic configuration and operation of the SPM probe will be described with reference to FIG.

  FIG. 16 is a plan view of the self-sensing SPM probe 700. FIG. In FIG. 16, a self-detecting SPM probe 700 has a configuration in which a lever portion provided with a probe 712 at the tip and a support portion are connected by two bent portions. Piezoresistors 722 and 724 are formed on the two bent portions, respectively.

  The piezoresistors 722 and 724 are formed from a part of the lever part to a part of the support part, particularly on the bent part. Further, an insulating layer is formed on the piezoresistors 722 and 724 and the support portion. Note that in FIG. 11, an insulating layer is not illustrated in order to simplify the drawing and facilitate understanding. The two bent portions and the piezoresistors 722 and 724 are formed symmetrically about the line passing through the probe 712 in the longitudinal direction of the cantilever 702 as the central axis.

  On the insulating layer, the conductive layers 726 and 728 serving as wirings are routed from the portion located at the lever portion of the piezoresistors 722 and 724 through the bent portion and the portion located at the support portion of the piezoresistors 722 and 724, The cantilever support portions are formed up to portions where the piezoresistors 722 and 724 are not formed.

  One end of the conductive layer 726 located at the lever portion and the underlying piezoresistor 722 are electrically connected at the metal contact portion 742. Similarly, one end located at the lever portion of the conductive layer 728 and the underlying piezoresistor 724 are electrically connected at the metal contact portion 744.

  Further, on the insulating layer, the conductive layers 732 and 734 serving as wirings extend from a portion where the piezoresistors 722 and 724 are formed to a portion where the piezoresistors 722 and 724 are not formed in the support portion, respectively. Is formed.

  One end of the conductive layer 732 located on the piezoresistor 722 and the lower piezoresistor 722 are electrically connected at a metal contact portion 736. Similarly, one end of the conductive layer 734 located on the piezoresistor 724 and the lower piezoresistor 724 are electrically connected at the metal contact portion 738.

  In this way, the lever portion and the support portion of the cantilever 702 are connected by the two bent portions, and the piezoresistors are linearly formed on the bent portions from the lever portion to the support portion. It can be effectively used as a piezoresistor formation region and can be formed thin. Therefore, a resistance value difference indicating a displacement difference between the two bent portions caused by torsion of the cantilever 702 appears between the two piezoresistors remarkably and accurately.

  Further, in order to read out the resistance value of each piezoresistor, a metal contact portion electrically connected to the piezoresistor from both ends of the piezoresistor is formed, and the support portion of the cantilever 702 is formed from both metal contact portions. A conductive layer serving as a wiring is led to a portion where a piezoresistor is not formed in a state where an oxide layer is disposed in a lower layer.

  That is, the change in resistance value of the piezoresistor at the bent portion can be read out from the two conductive layers guided on the support portion, and the deflection amount and the warpage amount of the cantilever 702 can be detected from these resistance value changes. . For this reason, the signal processing unit collates the resistance value with the reference data of the deflection amount and the warpage amount.

  In this case, the signal processing unit obtains a correspondence relationship between the resistance value of the piezoresistor and the deflection amount and the warpage amount in advance, and obtains the deflection amount and the warpage amount from the input resistance value. it can.

  Next, when the surface potential unevenness is detected by the potential detection device 10 of the present embodiment, the image density unevenness can be kept constant by adjusting the exposure amount based on the result. For example, as shown in FIG. 5, when there is a region where light fatigue occurs locally and the post-exposure potential is high, by increasing the amount of light only in that region and maintaining the target development potential, The occurrence of density unevenness can be suppressed.

  The potential detection device 10 of the present embodiment dynamically oscillates a cantilever having a high spring constant by the piezoelectric element 12 as the driving mechanism described above, and detects a change in amplitude or a change in frequency, thereby detecting the photoconductor. The surface potential of can be detected. Although there is an increase in cost for providing the piezo 12 for causing the cantilever to oscillate, it is possible to increase the detection sensitivity of the surface potential.

  A self-detecting cantilever can be used as the cantilever with a built-in piezo. The cantilever oscillation method is the same as that of a general atomic force microscope, and the cantilever is oscillated by periodically expanding and contracting the piezo 12 installed at the base of the cantilever 11.

  On the other hand, as shown in FIG. 3 (c), a piezo built-in cantilever 11a with a relatively low spring constant and a built-in piezo 12a is used as a built-in piezo cantilever, and the cantilever warpage due to induced charges is statically generated. It is good also as taking the structure to detect. Thereby, it is possible to suppress an increase in cost by separately providing the piezo 12 as a drive mechanism.

  As shown in FIG. 6, it is also effective to use an array structure as a piezo built-in cantilever. Here, as the potential detection device 300 having an array structure, a configuration in which three piezo built-in cantilevers 310 are arranged in an array structure is adopted.

  By using such an array structure, even when the cantilever is damaged or the performance is deteriorated during use, the surface potential of the photoconductor can be continuously monitored by using another cantilever. . As a matter of course, the larger the number of cantilevers constituting the array, the greater the risk tolerance such as breakage. On the other hand, from the viewpoint of reducing the manufacturing cost of the cantilever, it is preferable that the cantilever is composed of about 3 to 10 cantilevers.

  Next, the potential detection apparatus 10 of the present embodiment will be specifically described with reference to FIGS. The inventor of the present invention has found that it is effective to dispose the piezo built-in cantilever at two positions different in distance from the member to be detected.

  Since the detection target member such as the photosensitive member rotates or moves during operation of the apparatus, the shake always occurs. The image force detection detected by the piezo built-in cantilever depends on the distance from the target member. Therefore, when a variation in distance occurs due to a shake, the detected image force and the potential value calculated from the image force also vary. For example, in the case of a photoconductor, a shake of about 10 to 50 μm occurs, but this variation in distance directly affects the detected value of the image force. Here, the charge on the target member such as the photosensitive member induces a charge of opposite polarity to the cantilever with built-in piezo, and a Coulomb force acting between the target member and the cantilever with built-in piezo is generated. This Coulomb force is a mirror image force, and the Coulomb force changes depending on the amount of charge on the target member. Due to the action of the Coulomb force, the piezoelectric built-in cantilever is deformed so as to be pulled toward the target member. This deformation is detected as a deflection amount or a warp amount.

  Therefore, as shown in FIG. 7, the potential detection device 10 of the present embodiment has two different positions 1 and 2 at different distances in the substantially vertical direction with respect to the photosensitive member 20 as a detection target member. There are two piezo built-in cantilevers. Further, two piezo built-in cantilevers are held at a predetermined distance from each other by a predetermined holding member 14. The holding member is not limited to the structure shown in FIG. 7 as long as it can hold the two piezoelectric built-in cantilevers with a certain distance from each other. As a method for fixing the two piezoelectric built-in cantilevers, they may be fixed with a fixing member such as a screw, or may be fixed with an adhesive or the like.

  Here, for example, a cantilever 11x provided with a piezo 12x is disposed approximately 200 μm away from the photoconductor 20, and the cantilever 11y provided with the piezo 12y is disposed with a certain distance of approximately 100 μm between the cantilever 11x with a built-in piezo. Has been.

  In this way, the cantilevers are arranged at two positions that are different from the target member, and these cantilevers are configured so that the distance between the cantilevers does not change even during operation of the device, and the mirror image force is detected. By doing so, it is possible to cope with the above-mentioned shake of the photosensitive member. In any of the cantilevers, the distance from the photoconductor 20 can vary during the operation of the apparatus, but the distance between the cantilevers is always fixed at 100 μm.

  In the present embodiment, the advantages obtained by always fixing the distance between the cantilevers to 100 μm as described above will be described with reference to FIG. FIG. 8 is a graph showing the correlation between the horizontal axis with the cantilever distance X [μm] from the surface of the photoconductor 20 and the vertical axis with the mirror image force F [nN] acting on the cantilever. A numerical value obtained when the surface potential of the photoconductor 20 is 100 V is indicated by “♦”, and a numerical value obtained when the surface potential of the photoconductor 20 is 200 V is indicated by “□”. The numerical value obtained when the voltage is 500 V is indicated by “×”.

  FIG. 8A is a graph showing an ideal state in which no vibration is generated in the photoconductor 20, and in this case, the surface potential of the photoconductor 20 can be detected by each cantilever alone. it can. On the other hand, FIG. 8B shows a state in which the photoconductor 20 is shaken and the distance between the cantilever and the photoconductor 20 is narrower than the ideal state. FIG. 8C shows a state in which the photoconductor 20 is shaken and the distance between the cantilever and the photoconductor 20 is wider than the ideal state.

  Here, with respect to the mirror image force F which is a detected value, when the surface potential V of the photoconductor and the distance X between the photoconductor and the cantilever on the photoconductor side, V = k × F / X is established. Note that k is a proportional constant that can be determined in advance. Since X varies during the operation of the apparatus, it becomes an unknown, and when the distance between the cantilever and the photoconductor is one level, the two unknowns of the distance X and the surface potential V of the photoconductor cannot be obtained.

  On the other hand, if the distance from the photoconductor 20 is always changed to two levels as described above, the distance between the cantilevers is fixed to 100 μm, and the mirror image force can be detected, V = k × F / X, V = k × Two unknowns V and X can be obtained from the two equations F / (X + 100). That is, two unknowns can be obtained by making the two cantilevers have different distances from the photoconductor 20 and fixing the distance between the two cantilevers.

  The distance between the cantilevers is preferably set so that the mirror image force can be detected even by the cantilever 11y at the position 2 which is larger than the fluctuation of the target member and is far from the target member. In the example of the present embodiment, the distance is set to 100 μm, but specifically, the distance is preferably set to 50 to 100 μm.

[Second Embodiment]
Next, a potential detection device according to a second embodiment of the present invention will be described with reference to the drawings. In addition, description is abbreviate | omitted about the content which overlaps with 1st Embodiment.

  First, the difference between this embodiment and 1st Embodiment is demonstrated. According to the potential detection device of the first embodiment, it is possible to control the image density with higher accuracy by using a piezo built-in cantilever and accurately detecting light fatigue on the surface of the photoreceptor.

  On the other hand, in the electrophotographic image forming apparatus, there is a problem that a small amount of scattered abnormal toner is generated, such as scumming or defective cleaning. Abnormal toner needs to be detected in order to prevent poor cleaning and the like. However, since the potential generated by the toner charge is even smaller than the potential on the member such as the photoreceptor, a configuration for solving this is added to the first embodiment. There is a need. Therefore, the present inventor has found the configuration of the present embodiment in which the potential detection accuracy is improved by applying a predetermined voltage to the piezoelectric built-in cantilever by the voltage applying means to detect the presence or absence of toner.

  Furthermore, in the present embodiment, the voltage to be applied is set to a predetermined AC voltage, and the maximum applied voltage to the cantilever, that is, the peak-to-peak voltage is increased to increase the potential detection accuracy. Moreover, control which changes a voltage frequency according to the linear velocity of an object member is performed. As a result, when the toner passes under the cantilever, an AC voltage is applied to the cantilever so that the AC cycle is equal to or shorter than the passing time. According to the present embodiment, by applying a voltage to the cantilever, the displacement of the cantilever at the time of potential measurement is amplified and a minute potential at the toner potential level can be measured. It becomes possible to detect accurately, and it is possible to reduce the user load due to the occurrence of an abnormality while the image forming apparatus is operating. Here, the peak-to-peak voltage is a difference between the maximum voltage and the minimum voltage when an AC voltage is applied.

  In the present embodiment, an embodiment in which toner is exclusively detected will be described. However, the present invention is not limited to this, and can be applied to a scene where it is necessary to improve the accuracy of potential detection of a target member.

  A schematic configuration of an image forming apparatus 400 including the potential detection device of the present embodiment will be described with reference to FIG. As shown in FIG. 9, in the present embodiment, a sensing unit 410 using a piezoelectric built-in cantilever as a potential detection device is installed on the downstream side of the blade 80. As shown in FIG. 3B, similarly to the first embodiment, a cantilever is provided in parallel to the longitudinal direction of the photoconductor without a gap, thereby detecting a cleaning failure in the entire longitudinal direction of the photoconductor. can do.

  The potential detection using the piezo built-in cantilever is to detect the Coulomb force acting between the charge of the cantilever induced by voltage application and the charge of the photoconductor surface and toner as the deflection and warpage amount of the cantilever. Do by. Specifically, an AC voltage having a peak-to-peak voltage of 1 to 500 V and a frequency of 1 to 100 kHz is applied to the piezoelectric built-in cantilever 411 by the voltage applying unit 414, and the deflection and warpage of the cantilever at the time of the peak voltage are measured. By detecting, the potential is estimated.

  If there is an electric charge in the vicinity of the cantilever, it is possible to detect the potential by detecting its mirror image force. However, as in this embodiment, when detecting a very small potential like toner, the cantilever It is effective to increase the amount of deformation of the cantilever by applying a voltage. Thus, the application of the AC voltage to the piezoelectric built-in cantilever is to increase the amount of deformation of the cantilever and increase the detection SN ratio. As a result, a charge larger than that due to the charge on the target member such as the photoconductor is present in the piezoelectric built-in cantilever, and the image power due to the charge on the target member and the charge on the piezoelectric built-in cantilever increases.

  The amount of deformation of the cantilever to be detected can also be amplified by applying a DC voltage to the cantilever. However, since the AC voltage has a smaller load on the cantilever due to voltage application, it is better to use the AC voltage in order to keep applying the voltage stably for a long time. In this case, since the peak-to-peak signal of the cantilever displacement is important, it is sufficient to apply a high-pass filter to the obtained displacement signal. In addition, since alternating current voltage has better stability at the time of voltage application than direct current voltage, in this embodiment, although alternating current voltage is illustrated, it cannot be overemphasized that direct current voltage may be sufficient.

  Furthermore, more specific values of the voltage and frequency applied to the cantilever should be optimized by the cantilever, the gap between the photoconductors, the linear velocity of the photoconductor, etc. In recent years, the speed of each part related to the image forming apparatus has been increased. Since this is advancing, the frequency must be set to reflect this point.

  For example, if the image forming apparatus is currently commercialized, the photosensitive member linear velocity is 100 mm / s to 1000 mm / s. In order to detect a toner layer of about one dot level, that is, about 30 μm square on a photosensitive member driven at a linear speed of 1000 mm / s, an alternating voltage of two or three cycles with a time width of 30 usec. Must be applied. For this reason, it is necessary to set the frequency to about 100 kHz.

  Here, when a voltage is applied to two cantilevers as in the present embodiment, a configuration in consideration of the influence of an electric field acting on the cantilevers is necessary. This will be described with reference to FIG.

  That is, it is necessary to consider the influence on the detection accuracy due to the electric field acting between two cantilevers having different distances from the target member and the deformation amount of each cantilever changing. For example, when an electric field is generated by the voltage applied to the cantilever 411x at position 1, and the cantilever 411y at position 2 is deformed by the electric field, the detection accuracy of the deformation amount of the cantilever due to the potential of the photosensitive member and the toner on the photosensitive member is lowered.

  Therefore, as shown in FIG. 10, by arranging a sheet 413 as an electric field blocking means for blocking an electric field between two cantilevers, the electric field generated from each cantilever is blocked. This makes it possible to detect the potential of the photoconductor and the toner with high accuracy. The sheet 413 is made of a conductive member and is grounded. For example, a 1 mm thick sheet of Al (Aluminum) or SUS (Steel Use Stainless) is disposed between the cantilevers, so that detection with higher accuracy is possible. For the sake of illustration, the holding member 14 shown in the first embodiment is omitted.

  By the way, as described above, when the sheet 413 is disposed between the cantilevers, when an AC voltage having the same phase is applied to each of the cantilevers 411x and 411y of the position 1, the position where the potential on the photoconductor 20 is monitored is the same. It will not be.

  Therefore, in this embodiment, as shown in FIG. 11, the potential is sensed in a state where the phase of the AC voltage applied between the cantilevers is shifted. As a result, as shown in FIG. 12, it is possible to monitor the same position on the photoreceptor 20, for example, the toner T. An arrow R indicates the direction in which the photoconductor 20 rotates. The specific phase shift amount is determined by the photosensitive member linear velocity and the distance between the cantilever arrays in the circumferential direction. For example, when the photosensitive drum linear velocity is 400 mm / s and the distance between the arrays of piezo built-in cantilevers is 1 mm, the time difference when detecting the same photoconductor position between different cantilever arrays is 2. 5 msec. If the AC voltage frequency to be applied is 1 kHz [period 1 msec], the time difference 2.5 msec corresponds to a phase shift of 2.5 periods between the cantilevers, and the phase difference between the cantilevers may be set to 180 °.

  Next, as shown in FIG. 13A, it is necessary to consider the influence on the potential detection in the potential detection device of this embodiment having an array structure in which a plurality of cantilevers are arranged along the longitudinal direction of the photoconductor 20, for example. There is. The influence is that, as one of the detection noise factors in the present method, noise is generated when the potential is detected by the cantilever being deformed by the air flow generated by the rotation of the photoconductor 20.

  Therefore, in the present embodiment, as shown in FIG. 13B in which the Z portion in FIG. 13A is enlarged and displayed, the fulcrum of adjacent cantilevers is alternately reversed and arranged in the cantilever array continuous in the longitudinal direction. . Thereby, it is possible to reduce the detection noise due to the airflow by obtaining the average of the respective signals.

  The airflow generated in the vicinity of the photoconductor varies in a complicated manner depending on the linear velocity of the photoconductor, the arrangement of the sensing unit including the cantilever itself, fluctuations in rotational shake with time, and the like. In contrast, with the arrangement shown in FIG. 13B, the cantilever fulcrum and the lever itself are arranged symmetrically with respect to the rotation direction of the photoconductor between adjacent cantilevers. Therefore, it is possible to cancel the influence of the random airflow generated by the rotation of the photoconductor and the arrangement of the sensing unit including the cantilever itself.

  Each of the above-described embodiments is a preferred embodiment of the present invention, and various modifications can be made without departing from the scope of the present invention. For example, the potential detection apparatus 10 of the present embodiment can be applied not only to image density correction by performing exposure amount control from detected potential unevenness but also to presenting a photoreceptor replacement message to the user. it can. For example, if the light fatigue has progressed so much that the development potential cannot be adjusted by the exposure amount, it is possible to prevent the occurrence of abnormal images such as streak images by notifying the user of a message for replacing the photoreceptor. it can.

  Further, the potential detection apparatus of the present embodiment can be applied to state detection of other electrophotographic members as shown in FIGS. FIG. 14 shows the configuration of another image forming apparatus provided with a potential detection device 501 for detecting the surface potential of the transfer belt 502, and FIG. 15 shows the potential detection device 601 for detecting the surface potential of the charging roller 603. This is a configuration of another image forming apparatus provided with.

  As described above, the potential detection apparatus of the present embodiment can also be applied to detect the occurrence of potential unevenness in the transfer belt and the charging roller due to surface contamination over time. In the case of a transfer belt or charging roller, the electric potential is uniformly applied in the longitudinal direction by using electric discharge. Therefore, the potential in the longitudinal direction cannot be corrected. A message can be presented to exchange. In addition, it is possible to detect a toner on the transfer belt or the charging roller to prevent a cleaning failure or the like.

DESCRIPTION OF SYMBOLS 1,400 Image forming apparatus 10, 300, 501, 601 Potential detection apparatus 11, 310, 411 Cantilever 11a Built-in piezo cantilever 12 Piezo (drive mechanism)
13, 14 Holding member 20 Photoconductor 300 Array unit 502 Intermediate transfer belt 603 Charging roller 700 Self-sensing SPM probe

Japanese Patent Laid-Open No. 02-163771 JP-A-57-76564 Japanese Patent No. 4076063

Claims (11)

A potential detection device for detecting a potential of a target member,
At least two piezo built-in cantilevers arranged at different distances in a substantially vertical direction with respect to the target member;
Measuring means for measuring the potential of the target member based on the amount of deflection of the piezoelectric built-in cantilever due to an atomic force acting between the target member and the piezoelectric built-in cantilever;
A potential detecting device comprising: holding means for holding the at least two piezo-embedded cantilevers at a predetermined distance from each other.   2. The potential detecting device according to claim 1, further comprising voltage applying means for applying a predetermined voltage to the piezoelectric built-in cantilever.   3. The potential detecting device according to claim 1, wherein a predetermined AC voltage is applied to the piezoelectric built-in cantilever by the voltage applying means.   4. The potential detecting device according to claim 3, wherein the voltage applying unit controls the frequency of the alternating voltage applied to the piezoelectric built-in cantilever according to the linear velocity of the target member.   5. The electric potential detection device according to claim 1, further comprising an electric field interrupting unit configured to interrupt an electric field between the two piezoelectric built-in cantilevers.   6. The potential detecting device according to claim 5, wherein the voltage applying means performs control to shift the phase of the AC voltage applied to each of the two piezoelectric built-in cantilevers by a predetermined phase according to the linear velocity of the target member. .   The potential detecting device according to claim 1, wherein a plurality of the piezoelectric built-in cantilevers are arranged in an array structure.   8. The potential detecting device according to claim 7, wherein fulcrum points of the plurality of piezo built-in cantilevers are alternately inverted and arranged.   9. An image forming apparatus comprising the potential detecting device according to claim 1 on a photosensitive member.   An image forming apparatus comprising the potential detecting device according to claim 1 on a charging roller.   An image forming apparatus comprising the potential detecting device according to claim 1 on a transfer belt.

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