JP2011053192A - Device and method for measuring electrostatic latent image, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and method for measuring an electrostatic latent image, capable of measuring charge distribution or potential distribution occurring on the surface of a photoreceptor at high resolution of micron order, and to provide an image forming device using a measured photoreceptor. <P>SOLUTION: A photoreceptor sample 20 is irradiated with an electron beam so as to be charged; an electrostatic latent image is formed by an exposure section 6; an emission electron from the photoreceptor sample 20 is detected by scanning by the electron beam; and the electrostatic latent image distribution of the photoreceptor sample surface is measured, based on the detection signal. The exposure section 6 includes an LD light source 61, a light deflector 65, a synchronous signal-generating means for generating a synchronization signal at an end of a scanning range of the laser beam, and a write-in timing signal generating means for generating an emission timing control signal, when the laser beam scans the photoreceptor sample surface based on the synchronization signal. The distribution of the electrostatic latent image is measured at a predetermined timing, after the end of the exposure by the exposure section 6. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrostatic latent image measuring device, an electrostatic latent image measuring method, and an image forming apparatus. In particular, in an apparatus using a semiconductor laser as a light source, an adverse effect of light emission due to a bias current when the light is turned off is avoided. By doing so, an electrostatic latent image with high accuracy and high quality can be formed.

  An image forming apparatus that forms an image by executing an electrophotographic process includes a photoconductor, and a unit for executing each process of charging, exposure, development, transfer, fixing, and cleaning is provided on the photoconductor. Have. An electrostatic latent image is formed on the photosensitive member by performing a charging process and an exposure process. The accuracy or quality of the electrostatic latent image determines the accuracy or quality of the formed image. The decisive factor of the accuracy or quality of the electrostatic latent image formed on the photoconductor is the surface potential when the electrostatic latent image is formed, and the performance or quality of the photoconductor is measured by measuring this surface potential. Be evaluated.

  Conventionally, as a method for measuring the surface potential of a sample, there is a method in which a sensor head is brought close to a sample having a potential distribution, and electrostatic attraction or induced current that occurs as an interaction at that time is measured and converted into a potential distribution. In this method, the resolution is as low as several millimeters in principle, and a resolution of 1 micron cannot be obtained.

  As a method for observing an electrostatic latent image using an electron beam, there is an invention described in Patent Document 1, but the sample is limited to an LSI chip or a sample that can store and hold an electrostatic latent image. That is, it is not possible to measure a photoreceptor that causes dark decay that is normally used in an image forming apparatus or the like. Since a normal dielectric can hold a charge semipermanently, even if measurement is performed over time after forming a charge distribution, the measurement result is not affected. However, in the case of a photoconductor as an image carrier used in an image forming apparatus, since the resistance value is not infinite, the charge cannot be held for a long time, dark decay occurs, and the surface potential decreases with time. . The time that the photoconductor can hold the charge is at most several tens of seconds even in the dark room. Therefore, even if an attempt is made to observe in an electron microscope (SEM) after charging and exposure, the electrostatic latent image disappears at the preparation stage.

  Further, in the apparatus described in Patent Document 2, the wavelength used is completely different from that of the photoreceptor sample targeted by the present invention, and an arbitrary line pattern and a latent image of a desired beam diameter and beam profile are displayed. It is impossible to form and the object of the present invention cannot be achieved.

  Therefore, we have devised a method capable of measuring an electrostatic latent image even with a photoconductor sample having dark decay (see Patent Document 3, Patent Document 4, and Patent Document 5).

  If there is a charge distribution on the surface of the photoreceptor sample, an electric field distribution corresponding to the surface charge distribution is formed in the space. For this reason, the secondary electrons generated by the incident electrons are pushed back by this electric field, and the amount reaching the detector is reduced. Therefore, a portion where the electric field strength is strong is dark and a weak portion is bright and contrasted, and a contrast image corresponding to the surface charge distribution can be detected. Therefore, when the photosensitive member is exposed, the exposed portion is black and the non-exposed portion is white, and the electrostatic latent image formed thereby can be measured.

  By the way, as an exposure light source for forming an electrostatic latent image, there is a method of forming an electrostatic latent image by using a semiconductor laser whose wavelength is in a visible light region to an infrared light region and turning on and off the laser light.

  In order to reproduce the actual writing process, an electrostatic latent image having a desired pattern is formed by turning on and off at the timing when the light beam scans on the surface of the photoreceptor sample. For this purpose, it is necessary to detect the start position of scanning. Then, in order to form a latent image at a desired position on the photoconductor sample, it is necessary to turn on light at a predetermined position. In addition, the semiconductor laser used as a light source oscillates by giving a drive current above the reference. However, in order to improve the optical response, a constant drive current (bias current) below the reference is also applied at the timing of turning off the light. Always supply. When there is a bias current, LED emission occurs. That is, when a semiconductor laser is used, it means that light is emitted even when the light is turned off.

At this time, that is, when the bias current is flowing, the amount of light is very weak. Therefore, if the irradiation time is short, the electrostatic latent image is not affected. However, even if the amount of light is weak, the integrated amount of light increases when irradiated for a long time, and an electrostatic latent image is formed when the required exposure amount of the photoreceptor is reached. As a result, a desired electrostatic latent image cannot be formed.
Therefore, in order to form a desired electrostatic latent image using a semiconductor laser, it is necessary to minimize the time during which the sample is irradiated with light emitted from the bias current when the light is extinguished.

The present invention is a measurement of an electrostatic latent image that can measure the charge distribution or potential distribution generated on the surface of a photosensitive member made of a dielectric material with high resolution on the order of microns, which has been extremely difficult in the prior art. An object of the present invention is to provide an apparatus and a measuring method, and in particular, to provide an apparatus and a measuring method for measuring an electrostatic latent image on a photoconductor exposed by an exposure unit including a scanning optical system.
Another object of the present invention is to provide an image forming apparatus provided with a photoconductor measured by the above measuring method using the above apparatus.

The surface charge described here is defined. Strictly speaking, it is well known that the electric charges are spatially scattered in the sample. For this reason, the surface charge refers to a state in which the charge distribution state is largely distributed in the in-plane direction compared to the thickness direction. Further, the charge includes not only electrons but also ions.
Further, there may be a state in which there is a conductive portion on the surface and a voltage is applied to the conductive portion, thereby causing a potential distribution on the surface of the sample or in the vicinity thereof.

  The present invention relates to an electron beam irradiation apparatus for generating a charged charge on a photosensitive member sample by irradiating the photosensitive member sample with an electron beam, an exposure unit for forming an electrostatic latent image on the charged photosensitive member sample surface, A detector for detecting electrons emitted from the photosensitive member sample by scanning the photosensitive member sample surface with an electron beam, and an electrostatic latent image on the photosensitive member sample surface by a detection signal obtained by the detector. In the apparatus for measuring an electrostatic latent image for measuring an image distribution, the exposure unit includes a light source composed of a semiconductor laser, an optical deflector that scans the surface of the photosensitive member sample with the laser light from the light source, and the laser light. Synchronization signal generating means for detecting the laser beam at the end of the scanning range to generate a synchronization signal, and controlling the emission timing when the laser beam scans the photoconductor sample surface based on the synchronization signal Comprising a write timing signal generating means for generating an order of the write timing signal, and the most important features to measure the distribution of the electrostatic latent image at a predetermined timing from the end of exposure by the exposure unit.

The present invention also uses a semiconductor laser having a plurality of light emitting portions as a light source of the exposure portion, and emits light by a light emitting portion that emits light by a synchronizing signal from the synchronizing signal generating means and a writing timing signal from the writing timing signal generating means It is good also as a structure from which a light emission part differs.
In the present invention, the light emitting unit that emits light in response to the write timing signal from the synchronization timing signal generating unit may be a plurality of light emitting units.
In the present invention, the light source of the exposure unit is a semiconductor laser, and includes a pixel clock generation unit that generates a pixel clock from a reference clock and a synchronization signal, and a pixel pattern generation unit that generates a pixel pattern from pixel information. Also good.

The present invention may also be configured to include a shutter that shields light from entering the photoconductor sample surface except during measurement, and a shutter control unit that controls opening and closing of the shutter in conjunction with exposure timing.
The shutter control unit may include a unit that opens the shutter using a synchronization signal of the scanning optical system as a trigger signal and closes the shutter in conjunction with the data valid period signal after forming the electrostatic latent image.
The shutter means may be a mechanical shutter.
The present invention may also be configured to measure under conditions where there is a region where the velocity vector in the sample vertical direction of incident charged particles is inverted.

  The present invention also irradiates a photoconductor sample with an electron beam to generate a charged charge on the photoconductor sample, exposes the charged photoconductor sample surface to form an electrostatic latent image, and the photoconductor sample surface In the method for measuring an electrostatic latent image, the electron beam emitted from the photosensitive member sample is detected by scanning the electron beam, and the electrostatic latent image distribution on the surface of the photosensitive member sample is measured by the detection signal. Is performed by scanning a laser beam of a light source composed of a semiconductor laser on the surface of the photoconductor sample in the exposure unit, and detecting the laser beam by a synchronization signal generating means at the end of the scanning range of the laser beam. And generating a write timing signal for controlling the light emission timing when the laser beam scans the surface of the photoconductor sample based on the synchronization signal, and whether the exposure is completed. At a predetermined timing and measuring the distribution of the electrostatic latent image.

  The present invention also irradiates a photoconductor sample with an electron beam to generate a charged charge on the photoconductor sample, exposes the charged photoconductor sample surface to form an electrostatic latent image, and the photoconductor sample surface In the method for measuring an electrostatic latent image, the electron beam emitted from the photosensitive member sample is detected by scanning the electron beam, and the electrostatic latent image distribution on the surface of the photosensitive member sample is measured by the detection signal. Is performed by scanning the surface of the photoconductor sample with laser light from a light source composed of a semiconductor laser in the exposure unit, and before and after the time for forming the electrostatic latent image, the laser light from the light source is observed in the observation area of the photoconductor sample. It is characterized in that the influence of offset light emission due to the bias current of the semiconductor laser is suppressed by shielding so as not to reach.

  An image forming apparatus according to the present invention is an image forming apparatus for forming an image by performing an electrophotographic process on a surface of a photoconductor, wherein the photoconductor is a static image according to any one of claims 1 to 9. It is a photosensitive member measured by a measuring device for an electrostatic latent image.

In the image forming apparatus, the wavelength of the laser light emitted from the writing light source is 780 nm or less, the beam spot diameter in the sub-scanning direction on the photosensitive member surface is 60 μm or less, and the beam in the sub-scanning direction on the photosensitive member surface. If the spot diameter is A and the formed latent image diameter in the sub-scanning direction is B,
1.0 <B / A <2.0
It is recommended that the configuration satisfies the above.

  According to the apparatus for measuring an electrostatic latent image according to the present invention, a semiconductor laser is used as a light source of the exposure unit, a synchronization signal generating means, and a write timing signal generating means for controlling the light emission timing when the light beam scans the sample surface. Since the influence of the heat generated by the synchronous light emission on the write light emission can be reduced, writing with uniform optical power can be performed, and highly accurate measurement can be performed.

  A semiconductor laser having a plurality of light emitting parts is used as the light source of the exposure part, and the light emitting part that emits light by the synchronization timing signal generating means and the light emitting part that emits light by the write timing signal generating means are different from each other. For example, the influence of the synchronization light emission due to the write light emission can be reduced, and highly accurate measurement can be performed.

  According to what obtains a synchronizing signal by emitting light from a plurality of light emitting parts, it is possible to form an electrostatic latent image with high positional accuracy even with a light source having a light emitting part with low light emission power, and to measure with high resolution. Is possible.

  According to the invention, a semiconductor laser is used as the light source of the exposure unit and includes a pixel clock generation unit that generates a pixel clock from a reference clock and a synchronization signal, and a pixel pattern generation unit that generates a pixel pattern from pixel information. An electrostatic latent image can be formed, and as a result, the electrostatic latent image can be measured with high resolution on the order of microns.

  Since the shutter is opened using the synchronization detection signal of the scanning optical system as a trigger signal and the shutter is closed after the electrostatic latent image is formed, the shutter opening time can be suppressed to the minimum necessary. A few clear electrostatic latent images can be formed. As a result, it is possible to measure an electrostatic ray image with a high resolution on the order of microns.

  When the shutter control means has means for opening the shutter using the synchronization detection signal of the scanning optical system as a trigger signal and closing the shutter after forming the electrostatic latent image, the shutter opening time can be minimized. Therefore, a clear electrostatic latent image with less noise can be formed, and as a result, the electrostatic ray image can be measured with a high resolution on the order of microns.

  According to the one using a mechanical shutter as the shutter means, the offset emission can be shielded at high speed without deteriorating the transmission wavefront of the laser light, and a highly accurate electrostatic latent image can be formed. As a result, an electrostatic ray image can be measured with high resolution on the order of microns.

  According to one having a means for measuring under conditions where there is a region where the velocity vector of the incident charged particles in the vertical direction of the sample is reversed, the potential depth can be measured quantitatively and the potential distribution can be increased. It becomes possible to measure with high accuracy.

  According to the semiconductor laser used as the light source of the exposure unit and having the shutter means for shielding the offset emission due to the bias current, a desired electrostatic latent image can be formed. An image can be measured with a high resolution on the order of microns.

According to the image forming apparatus of the present invention, it is possible to evaluate the electrostatic latent image formed on the photoconductor using the measuring device and feed it back to the design. Therefore, the quality of each process for forming an image is improved, a high-quality image can be obtained, and a latent image carrier having high durability, high stability, and excellent energy saving is used. The image forming apparatus can be provided.
In particular, an image forming apparatus equipped with a multi-beam scanning optical system such as a VCSEL that tends to cause uneven image density can obtain the above-described effect, and is therefore suitable for an image forming apparatus equipped with a multi-beam scanning optical system. .

It is a front view which shows typically the Example of the measuring apparatus of the electrostatic latent image which concerns on this invention. It is sectional drawing which shows the structure of the vacuum chamber and exposure part of the said Example. The potential distribution in the space between a charged particle trap and a sample is shown, (a) is explanatory drawing by a contour line display, (b) is a schematic diagram which shows the hole of the potential in the said contour line. It is a perspective view which shows the example of the optical scanning device applicable as an exposure part to this invention. It is an array diagram showing an example of a two-dimensional array of vertical cavity surface emitting semiconductor lasers applicable as a light source of the exposure unit. It is an arrangement | sequence diagram which shows the specific example of each light emission point which makes the two-dimensional array of the said semiconductor laser. It is an arrangement | sequence diagram which shows the example divided into the light emission part for making the light emission part of a light source emit a synchronous beam, and the light emission part for light-emitting a writing beam. It is a block diagram which shows the example of the light source drive circuit of the said exposure part. It is a block diagram which shows the example of the control apparatus of the said light source drive circuit. It is a timing chart which shows operation | movement of each circuit part of the said control apparatus. It is a graph which shows the relationship between the drive current of a semiconductor laser, and optical output. The difference in exposure depending on the presence / absence of a laser beam shielding means is shown in comparison. (A) is a graph showing a case where the shielding means is not provided, and (b) is a graph showing a case where the shielding means is provided. It is a timing chart between signals in the embodiment of the present invention. It is a block diagram which shows the structure of the control system in the Example of the said invention. It is a flowchart which shows operation | movement of the said control system. It is a schematic diagram which shows the function of the mechanical shutter used for the Example of this invention. It is a schematic diagram which shows the various examples of a latent image pattern. It is a front view which shows typically the principal part of another Example of the measuring apparatus of the electrostatic latent image which concerns on this invention. The relationship between the incident electrons and the photoconductor sample is shown. (A) is a schematic diagram showing a case where the acceleration voltage is larger than the surface potential potential, and (b) is a schematic diagram showing a case where the acceleration voltage is smaller than the surface potential potential. It is a graph which shows an example of the depth measurement result of a latent image. It is a conceptual diagram which shows a beam spot diameter and a latent image diameter. 1 is a front view schematically showing an embodiment of an image forming apparatus according to the present invention.

  Embodiments of an electrostatic latent image measuring apparatus, an electrostatic latent image measuring method, and an image forming apparatus according to the present invention will be described below with reference to the drawings.

  FIG. 1 shows an embodiment of an apparatus for measuring an electrostatic latent image according to the present invention. In FIG. 1, an electrostatic latent image measuring device includes a charged particle irradiation unit (electron beam irradiation device) that irradiates a charged particle beam, an exposure unit, a sample placement unit, a detection unit for primary inverted charged particles, secondary electrons, and the like. It has. As used herein, charged particles refer to particles that are affected by an electric or magnetic field, such as an electron beam or an ion beam. In this embodiment, the charged particle irradiation unit is composed of an electron beam irradiation device and irradiates an electron beam. In the following, embodiments of the electrostatic latent image measuring device will be described in detail.

  In FIG. 1, an electron beam irradiation apparatus 4 that is a charged particle beam irradiation apparatus is configured by incorporating each component into a vacuum chamber 40 as follows. An electron gun 41 for irradiating a charged particle beam is attached near the upper end of the vacuum chamber 40, and below it is a suppressor electrode 42, an extractor or extraction electrode 43, an acceleration electrode 44, a condenser lens 45, a beam blanking electrode 46, a partition. A valve 47, a movable diaphragm 48, a stigmeter, that is, a correction electrode 49, a deflection electrode (corresponding to a scanning lens) 50, an electrostatic objective lens 51, and a beam emission opening 52 are arranged in this order.

The suppressor electrode 42 and the extraction electrode 43 control the electron beam, the acceleration electrode 44 controls the energy of the electron beam, and the condenser lens 45 focuses the electron beam generated from the electron gun. The beam blanking electrode 46 turns on / off the electron beam, and the gate valve 47 and the movable diaphragm 48 function as an aperture for controlling the irradiation current of the electron beam. The deflection electrode 50 functions as a scanning lens for scanning the electron beam that has passed through the beam blanker, and the electron beam that has passed through the deflection electrode 50 is again converged on the surface of the photoreceptor sample 20 by the objective lens 51. A driving power source (not shown) is connected to each lens.
When an ion beam is used as the charged particles, a liquid metal ion gun or the like is used instead of the electron gun 41.

  An electron beam is irradiated onto the photoconductor sample 20 mounted on the sample mounting unit 15 by the electron beam irradiation unit including the above lenses. Secondary electrons, primary inversion electrons, and the like are emitted from the photoconductor sample 20, and a detector 8 that detects the emitted electrons is provided. As the detector 8, a scintillator, a photomultiplier tube, or the like is used. Usually, the scintillator is configured to capture charged particles by applying a high voltage of about 8 to 10 kV at the drawing voltage. In order to guide the detected charged particles to the detector 8, an emitted particle generating member that generates emitted particles at the time of charged particle collision is disposed.

The back side of the photoconductor sample 20, that is, the sample mounting table 15 is normally connected to the ground (GND) and used at 0V, but can be configured to apply an appropriate voltage as required.
The emitted particles include electrons and ions, and it is common to detect and measure electrons. However, it is also possible to detect a positive ion by applying a negative pull-in voltage to the detector 8 and observe a contrast image. It is.

  In FIG. 1, reference numeral 6 denotes an exposure portion. The exposure unit 6 is a so-called well-known laser scanner, which is a light source 61 such as a semiconductor laser (LD) that emits light having a sensitivity with respect to the photosensitive sample 20, a collimator lens 62, an aperture 63, a condensing lens 64, An optical deflector 65 including a galvanometer mirror, a polygon mirror, a scanning imaging lens 66, a mirror 67, and the like are provided. The exposure unit 6 can generate a desired beam diameter and beam profile on the photoconductor sample 20, and can scan the surface of the photoconductor sample 20 with the beam. The light source 61 is controlled by the LD control means so that the photoconductor sample 20 can be irradiated with a light beam with an appropriate exposure time and exposure energy.

  The exposure unit 6 includes a scanning mechanism using a galvano mirror or a polygon mirror in the optical system in order to form a line pattern. Further, a multi-beam scanning optical system using a VCSEL or the like as the light source 61 may be configured. Further, in addition to the scanning in the main scanning direction by the optical deflector 65, a system capable of forming a two-dimensional exposure pattern may be provided by providing a mechanism for scanning in the sub scanning direction.

  The exposure unit 6 is arranged outside the vacuum chamber 40 so that the vibration of the optical deflector 65 made of a polygon motor or the like and the influence of the electromagnetic field do not affect the trajectory of the electron beam. By moving the exposure unit 6 away from the orbital position of the electron beam by the electron beam irradiation apparatus, it is possible to suppress the electron beam from being affected by disturbance. The light beam emitted from the exposure unit 6 enters the photosensitive member sample 20 from an optically transparent incident window 68, and the exposure unit 6 is isolated from the space of the vacuum chamber 40.

  FIG. 4 shows an example of an optical scanning device that can be substituted for the exposure unit 6. In this specification, the main scanning direction will be described as the Y-axis direction, the sub-scanning direction as the Z-axis direction, and the direction orthogonal to these will be described as the X-axis direction. In FIG. 4, the optical scanning device controls a light source unit 1011, a cylindrical lens 1012, a polygon mirror 1013 that is an optical deflector, an fθ lens 1014, a toroidal lens 1015, a folding mirror 1016, a synchronization sensor 1017, an area sensor 1018, and the above-described units. A control device 1019 is provided for controlling automatically.

  The light source unit 1011 includes a light source having a plurality of light emitting units (hereinafter referred to as “light source LA”), a light source driving circuit 400 (see FIG. 8) for driving the light source LA, and a coupling lens (hereinafter referred to as “CL”). is doing. Here, for example, as shown in FIG. 5, the light source LA constitutes a two-dimensional array of vertical cavity surface emitting semiconductor lasers (VCSEL) in which 32 light emitting portions are formed on one substrate. is doing. This two-dimensional array is a direction (in the following, also referred to as “M direction” for convenience) inclined by an angle θ from a direction corresponding to the sub-scanning direction (here, Z-axis direction) ( Hereinafter, there are four light emitting section rows in which eight light emitting sections are arranged at equal intervals along the “T direction” for convenience. These four light emitting unit rows are arranged at equal intervals in the Z-axis direction. That is, the 32 light emitting units are two-dimensionally arranged along the T direction and the Z axis direction, respectively. Here, for the sake of convenience, they are referred to as a first light emitting unit row, a second light emitting unit row, a third light emitting unit row, and a fourth light emitting unit row from the top to the bottom in FIG. In the present specification, the “light emitting portion interval” refers to the distance between the centers of two light emitting portions.

For convenience, each light emitting unit is specified as shown in FIG. That is, from the upper left to the lower right in FIG. 5, the eight light emitting units constituting the first light emitting unit row are v1-v8, the eight light emitting units constituting the second light emitting unit row are v9-v16, the first. The eight light emitting units constituting the three light emitting unit rows are denoted by v17 to v24, and the eight light emitting units constituting the fourth light emitting unit row are denoted by v25 to v32.
As illustrated in FIG. 8, the light source driving circuit 400 individually drives the 32 light emitting units based on various driving information from the control device 1019.
The coupling lens CL makes light from the light source LA substantially parallel light. Accordingly, substantially parallel light is output from the light source unit 1011 shown in FIG.

  In FIG. 4, a cylindrical lens 1012 condenses the light from the light source unit 1011 near the deflection surface of the polygon mirror 1013 in the sub-scanning direction, and forms a long line image in the main scanning direction. The polygon mirror 1013 is a regular hexagonal columnar member having a low height (flat), and six deflecting reflection surfaces are formed on the side surface. And it is rotationally driven at a fixed angular velocity in the direction of the arrow shown in FIG. 4 by a rotating mechanism mainly composed of a motor (not shown). Therefore, the light emitted from the light source unit 1011 and condensed near the deflection reflection surface of the polygon mirror 1013 by the cylindrical lens 1012 is deflected at a constant angular velocity by the rotation of the polygon mirror 1013.

  The fθ lens 1014 has an image height proportional to the incident angle of light from the polygon mirror 1013, and deflects light with a constant angular velocity by the polygon mirror 1013 (hereinafter, this deflected light is also referred to as “scanning light”). It is moved at a constant speed in the main scanning direction on the surface to be scanned. The light transmitted through the fθ lens 1014 forms an image on the surface of the photosensitive drum 1030 that is the surface to be scanned through the toroidal lens 1015 and the folding mirror 1016.

  Incidentally, the image surface of the scanning light on the surface to be scanned moves from the scanning start end toward the scanning end as the polygon mirror 1013 rotates. The effective scanning area is an area where writing is performed according to image data. When the image plane of the scanning light reaches the scanning end, it returns to the scanning start end for the next scanning.

  A synchronization sensor 1017 is disposed outside the effective scanning area at a position equivalent to the image plane. The synchronization sensor 1017 is disposed at a position where light before the start of scanning reflected by the folding mirror 1016 enters, and outputs a signal (photoelectric conversion signal) corresponding to the amount of received light. Therefore, the start of scanning on the photosensitive drum 1030 can be detected from the output signal of the synchronization sensor 1017.

  As shown in FIG. 9, the control device 1019 includes a reference clock generation circuit 402, a pixel clock generation circuit 405, an image processing circuit 407, a light source selection circuit 414, a write timing signal generation circuit 415, and a synchronization timing signal generation circuit 417. ing. Note that the arrows used in FIG. 9 indicate the flow of typical signals and information, and do not represent the entire connection relationship of each block.

  FIG. 10 is a timing chart showing the operation of each circuit. 10, s19 is an output signal (synchronization signal) from the synchronization sensor 1017, s15 is an output signal (LGATE signal) of the write timing signal generation circuit 415, s14 is an output signal of the light source selection circuit 414, and s16 is an image processing circuit 407. The write data which is the output of is shown. Hereinafter, the operation of each part of the control device 1019 shown in FIG. 9 will be described with reference to FIG.

  The image processing circuit 407 creates write data s16 for each light emitting unit based on image information from the host device. The write data s16 is supplied to the light source drive circuit 400 as one of the drive information at the timing of the pixel clock signal. The reference clock generation circuit 402 generates a high-frequency clock signal that serves as a reference for the entire control device 1019. The pixel clock generation circuit 405 mainly includes a PLL circuit, and generates a pixel clock signal based on the synchronization signal s19 and the high frequency clock signal from the reference clock generation circuit 402. The frequency of the pixel clock signal is the same as the frequency of the high frequency clock signal, and the phase of the pixel clock signal matches the phase of the synchronization signal s19. Therefore, by synchronizing the image data with the pixel clock signal, it is possible to align the writing position for each scan. The pixel clock signal is supplied to the light source driving circuit 400 as one of the driving information and to the image processing circuit 407, and is used as a clock signal for the write data s16.

  The write timing signal generation circuit 415 changes the LGATE signal (data valid period signal) s15 from the low level to the high level after elapse of t1 after the light beam passes through the light receiving element 1018 after the rising of the synchronization signal s19. When the preset time t2 further elapses, the LGATE signal s15 is changed from the high level to the low level. The LGATE signal s15 is supplied to the light source driving circuit 400 as one of the driving information. The time t1 corresponds to a scanning (hereinafter also referred to as “writing” for convenience) start time by light modulated according to image information. The time t2 corresponds to the writing scan time. By synchronizing the LGATE signal s15 with the rising timing of the synchronization signal s19, the write start timing can be aligned.

  When the image surface of the scanning light reaches the scanning end, the light source selection circuit 414 selects a light emitting unit used to detect the start of the next scan from the 32 light emitting units, and designates the selected light emitting unit. Output a signal. When the light source is a VCSEL, since it is difficult to detect with a synchronous sensor with one light emitting unit, a plurality of light emitting units are selected from the arrangement in the Z direction to emit light. For example, as shown in FIG. 7, the light emitting unit is divided into a light emitting unit for emitting a synchronizing beam and a light emitting unit for emitting a writing beam in the scanning direction. By separating the light emitting portions in this manner, the influence of heat generated by synchronous light emission on the write light emission can be reduced, so that writing with uniform optical power can be performed. The output signal s14 of the light source selection circuit 414 is supplied to the light source drive circuit 400 as one of the drive information. The shape of the sample to be scanned with the light beam is arbitrary. In the example shown in FIG. 1, a flat surface is assumed, and in the example shown in FIG. 4, a curved surface is assumed.

  The scanning optical system is preferably arranged outside the vacuum chamber 40 so that the influence of the vibration of the polygon motor that drives the optical deflector 65 such as a polygon mirror or the influence of the electromagnetic field does not affect the trajectory of the electron beam. By moving the vibration source and electromagnetic field away from the electron beam trajectory position, it is possible to suppress the influence of disturbance. The light beam from the scanning optical system is preferably incident into the vacuum chamber 40 through an optically transparent incident window. A shutter capable of temporally blocking the light beam from the semiconductor laser is disposed between the photoconductor sample 20 and the light source.

  FIG. 2 is a cross-sectional view showing the structure of the vacuum chamber 40 and the exposure unit 6 of the above embodiment. As shown in FIG. 2, an incident window 68 through which light can be incident from the outside is disposed inside the vacuum chamber 40 at an angle of 45 ° with respect to the vertical axis of the vacuum chamber 40. An exposure apparatus 6 that causes the scanning beam 77 to enter the chamber 40 is disposed outside the vacuum chamber 40. As described above, the exposure unit 6 includes a scanning optical system, and includes a light source unit, a scanning lens, synchronization detecting means, an optical deflector 65 including a polygon mirror, a mirror 72 for bending an optical path, and the like. The main part of the exposure unit 6 is disposed on the optical housing 69, and the upper part is covered with a cover 71 and shielded from light.

  The optical housing 69 is mounted on a horizontal translation table 83, and the translation table 83 is mounted on the vibration isolation table 81 via a plurality of columnar structures 82. The path of the scanning beam 77 bent obliquely downward at an angle of approximately 45 ° by the mirror 72 is shielded by an external light shielding cylinder 73, an internal light shielding cylinder 75, and a labyrinth portion 74 interposed between the inner and outer light shielding cylinders. Has been. The scanning lens 66 has an fθ characteristic, and the light beam moves at a substantially constant speed with respect to the image plane when the light polarizer 65 rotates at a constant speed. Further, the beam spot diameter can be scanned substantially uniformly.

  Since the scanning optical system is disposed separately from the vacuum chamber 40, the vibration generated when the optical deflector 65 such as a polygon scanner is driven is not directly propagated to the vacuum chamber 40, and the vibration described above. Is less affected. Further, although not shown in FIG. 2, if a damper is inserted between the structure 82 and the vibration isolation table 83, a more effective vibration isolation effect can be obtained.

  As an exposure light source for forming an electrostatic latent image on the photoreceptor sample 20, an LD that emits light in the infrared region from visible light is used, and the laser light is scanned by a deflector composed of a polygon mirror. An optical scanning apparatus that blinks to form an electrostatic latent image requires a time of several seconds until the polygon mirror rotates at a constant speed after startup. In addition, in order to flash the laser beam at the desired position and write it to the desired position, writing is started after a predetermined time from the output point of this detection signal, based on the output timing of the detection signal from the synchronous detector. ing.

  When a latent image pattern is formed by flashing light, it is necessary to increase the light responsiveness of a light source composed of a semiconductor laser with respect to an image pattern signal. For example, in the case of modulating at 1 μs or less, it is necessary to always allow a bias current to flow through the semiconductor laser even when the image data for improving the pattern light pulse reproducibility and droop characteristics is turned off. A semiconductor laser oscillates by applying a driving current that exceeds a reference. However, in order to improve photoresponsiveness, LED emission occurs when a bias current is applied. That is, when a semiconductor laser (LD) is used as the light source, light is emitted even when the light is off.

  FIG. 11 shows the relationship between the LD drive current IF and the optical output. In FIG. 1, a on the horizontal axis indicating the LD drive current is a drive current when the light is turned off, b is a reference current IF for laser oscillation, and c is a drive current for LD lighting. The relationship of a <b <c is established. Pon is the light output when the LD is turned on, and Poff is the light output when the LD is turned off. When the drive current IF is small, the light output is weak due to LED emission, and laser oscillation occurs when the drive current IF reaches the reference current. Compared to the normal laser oscillation output of about 1 to 10 mW, the bias current when extinguished is several tens of microwatts, which is about 1/100 or less that during normal oscillation. Never become. For this reason, the bias current is kept flowing even when the LD is extinguished, with an emphasis on enhancing the light response.

  However, even with a minute amount of light, the integrated amount of light increases when irradiated for a long time, and an electrostatic latent image is formed when the required exposure amount of the photoreceptor is reached. As a result, a desired electrostatic latent image cannot be formed.

  Therefore, in the present invention, when forming a desired electrostatic latent image using a semiconductor laser, the luminous flux is an electron beam of the photoconductor sample so as to minimize the time during which the sample is irradiated with LED light emission due to the bias current when the light is extinguished. The structure is devised so that it is irradiated outside the scanning region. For example, offset light emission due to the LD bias current is shielded. Alternatively, a shutter may be disposed between the LD light source and the photoconductor sample, and this may be used as the offset light emission shielding unit. That is, the offset light emission can be blocked by closing the shutter before exposure so that the light beam does not pass and opening the shutter so that the light beam passes during the exposure.

  FIG. 12 shows a comparison of exposure states when the shielding means is not provided and when it is provided. FIG. 12A shows a case where the shielding means is not provided, and FIG. 12B shows a case where the shielding means is provided. When the shielding means is not provided as shown in FIG. 12 (a), the irradiation time of the offset light before exposure is long, and a latent image is formed by offset exposure when the integrated light quantity reaches the necessary exposure energy. On the other hand, if a shielding means is provided, as shown in FIG. 12B, before the exposure, the shutter is closed to shield the offset light emission, and during the exposure, the shutter is opened so that the offset light before the exposure is used. Exposure can be avoided and latent image formation can be prevented. Therefore, the photoconductor sample can be measured with high accuracy. After exposure, if necessary, an exposure end detection signal can be given to close the shutter.

  Next, means for forming an electrostatic latent image on the photoreceptor sample will be described. First, the photosensitive member sample 20 is irradiated with an electron beam by the above-described electron beam irradiation apparatus. The acceleration voltage | Vacc | is set to an acceleration voltage higher than the acceleration voltage at which the secondary electron emission ratio is 1, so that the amount of incident electrons exceeds the amount of emitted electrons, so that electrons are accumulated in the photoreceptor sample 20 and charged. Raise up. As a result, the photoconductor sample 20 is uniformly charged with a negative charge. A desired charging potential can be formed by appropriately setting the acceleration voltage and the irradiation time.

Next, the photosensitive sample 20 is exposed by the exposure optical system, that is, the exposure unit 6. The optical system is adjusted to form a desired beam diameter and beam profile. The required exposure energy is a factor determined by the characteristics of the photoreceptor sample 20, but is usually about ² to 6 mJ / m ² . For a photoreceptor sample with low sensitivity, ten or more mJ / m ² may be required. The charging potential and the required exposure energy are preferably set according to the characteristics of the photoreceptor sample and the process conditions.

  Then, the above-described shutter mechanism is arranged to cut off the offset light due to the LD bias current. In this way, an electrostatic latent image having a desired pattern can be formed. FIG. 17 shows various examples of the latent image pattern. FIG. 17A shows an example of isolated one dot, FIG. 17B shows 2by2, and FIG. 17C shows each pattern of a grid with one dot.

  If there is a charge distribution on the surface of the photoreceptor sample 20, an electric field distribution corresponding to the surface charge distribution is formed in the space. For this reason, the secondary electrons generated by the incident electrons are pushed back by the electric field, and the amount of secondary electrons reaching the detector 8 is reduced. Accordingly, at the charge leak portion, the exposed portion is black and the non-exposed portion is white, and a contrast image corresponding to the surface charge distribution can be measured.

  FIG. 3A is an explanatory diagram showing the potential distribution in the space between the charged particle trap and the sample in contour lines. The surface of the sample is uniformly charged negatively except for the portion where the potential is attenuated due to light attenuation, and the charged particle trap is given a positive potential. In the “potential contour line group”, the “potential increases” as it approaches the charged particle trap from the surface of the sample. Accordingly, the secondary electrons el1 and el2 generated at the points Q1 and Q2 in the figure, which are “negatively charged portions” in the sample, are drawn to the positive potential of the charged particle trap, and the arrows G1 and It is displaced as indicated by G2 and is captured by the charged particle trap.

  On the other hand, in FIG. 3A, the point Q3 is “a portion where the negative potential has been attenuated by light irradiation”, and in the vicinity of the point Q3, the potential contours are arranged as shown by broken lines. Then, “the closer to Q3 point, the higher the potential”. In other words, the secondary electron el3 generated in the vicinity of the point Q3 is subjected to an electric force restrained on the sample side as indicated by an arrow G3. For this reason, the secondary electron el3 is captured in the “potential hole” indicated by the broken line potential contour and does not move toward the charged particle trap. FIG. 3B schematically shows the “potential hole”.

  As described above, the intensity of secondary electrons (number of secondary electrons) detected by the charged particle trap is such that the portion having a large intensity is “the ground portion of the electrostatic latent image (a portion that is uniformly negatively charged, FIG. 3 (a), which is a portion represented by points Q1 and Q2 ”, and a portion with a low intensity is represented by“ an electrostatic latent image portion (a portion irradiated with light, represented by point Q3 in FIG. 3A). Part) ”.

  Therefore, if the electrical signal obtained by the secondary electron detection unit is sampled at an appropriate sampling time by the signal processing unit, the surface potential distribution: V (X, Y) is obtained using the sampling time: T as a parameter as described above. It can be specified for each “small area corresponding to sampling”, and the surface potential distribution (potential contrast image): V (X, Y) is configured as two-dimensional image data by a signal processing unit, and this is output by an output device. If output, an electrostatic latent image can be obtained as a visible image signal.

  For example, if the intensity of secondary electrons to be captured is expressed as “brightness or weakness”, the image portion of the electrostatic latent image is dark, the ground portion is bright and contrasted, and a bright and dark image corresponding to the surface charge distribution is obtained. It can be expressed (output). Of course, if the surface potential distribution can be known, the surface charge distribution can also be known.

  In this way, a bright and dark contrast image with a large secondary electron detection amount at the charging portion and a small secondary electron detection amount at the exposure portion is generated, and the dark portion can be regarded as a latent image portion by exposure. The boundary between light and dark can be the diameter of the latent image. In this way, it is possible to measure the electrostatic latent image on the photoreceptor with high resolution on the order of microns.

  In order to reduce the influence of offset light emission due to the LD bias current, the shutter is in the open state for the exposure time for forming the electrostatic latent image, and the shutter is closed before and after that. Ideally. In order to realize this, it is desirable to link the exposure timing and the shutter opening / closing timing. The timing of exposure is determined by the synchronization signal of the scanning optical system. Therefore, it is desirable to open the shutter in conjunction with the synchronization signal of the scanning optical system. In addition, it is desirable to close the shutter in conjunction with the time when the level of the FGATE signal, which is a data valid period signal, becomes low (low). As means for realizing this, if the synchronization signal of the scanning optical system is a trigger signal for opening the shutter, the timing of writing can be made uniform.

  The configuration of the control system is shown in FIG. In FIG. 14, an electron beam control device is a control device for an electron beam irradiated by the charged particle beam irradiation device 4 and is controlled by a host computer. The host computer controls the optical unit via the control board, and controls the shutter controller by controlling the shutter control controller according to the trigger signal from the control board.

  FIG. 15 shows the operation of this control system. After a control command for measurement is executed (S1), a synchronization signal of the scanning optical system is detected (S2), and the detected signal is used as a trigger signal for opening the shutter (S3). Then, the laser is turned on at the timing when the shutter is opened to the effective diameter of the exposure optical system (S4, S5). As a result, an electrostatic latent image is formed on the photosensitive member sample. This electrostatic latent image is measured (S6), and the shutter is closed after the exposure is completed (S7). After exposure, in addition to closing the shutter, the LD bias current may be set to 0 to stop the light emission itself.

  By the way, the shutter is not limited to an electronic shutter or a mechanical shutter, and there is a time lag between when an instruction is given and when the shutter is actually opened. If the time from when the trigger signal is detected until the shutter starts to open is Td, and the time from when the shutter starts to open until the equivalent of the effective diameter of the laser beam is opened is Tr, The shutter opens with a delay of Td + Tr. Therefore, the LD must be turned on in consideration of that amount. That is, it is desirable to turn on the LD with a delay of Td + Tr after receiving a synchronization signal serving as a trigger output. As a method of delaying the time, assuming that one scanning time by the scanning optical system is Tf, a latent image is generated by turning on the LD when a natural number n satisfying Td + Tr <n × Tf from a synchronization signal serving as a trigger output. There is a method of forming.

  FIG. 13 shows a timing chart of the above signals. In FIG. 13, after the execution command input signal from the PC is asserted, after the data valid period signal (FGATE) becomes high (asserted), the first trigger signal is output by the input of the first synchronization signal, The shutter opens. After writing the image pattern, when FGATE becomes low (negated), the second trigger signal is output and the shutter is closed.

  As the shutter, there is a method using an element that changes the optical transmittance, such as a liquid crystal modulation element. In this case, there is an advantage that no mechanical movable part is required. However, there is a possibility that the optical response and the transmitted wavefront will be affected. Therefore, a mechanical shutter may be used as the shutter. The mechanical shutter described here creates a state where an object is present (FIG. 16A) and a state where no object is present (FIG. 16B) with respect to the optical path traveling direction as shown in FIG. Thus, it refers to a means capable of creating a state where the light beam reaches the measurement sample and a light shielding state by changing the traveling direction of the optical path.

  The mechanical shutter mechanically controls the opening / closing operation and speed of the shutter by a governor, a spring, or the like. Examples of the mechanical shutter include a structure that opens from the center to the periphery and closes from the periphery toward the center using a guillotine shutter and a plurality of shutter blades. The guillotine shutter has holes in each of the two plates, the plate corresponding to the front curtain travels, the plate corresponding to the rear curtain travels, and the shutter speed changes due to the change in the overlapping state of the holes It can be made to be. Moreover, although it is mechanical, the thing of the structure which controls opening and closing with an electrical signal may be sufficient. As a result, it can be opened and closed at an appropriate timing that is accurately adjusted by the synchronization signal. By using a mechanical shutter as the shutter means, offset light emission can be shielded at high speed without deteriorating the transmitted wavefront of the laser light.

  The position of the shutter is preferably arranged outside the vacuum chamber 40. This is because, if it is disposed in the vacuum chamber 40, the surrounding electromagnetic field fluctuates when the mechanical shutter is opened and closed and before and after that, which may cause the trajectory of the scanning electron beam to be bent. By disposing the mechanical shutter outside the vacuum chamber 40, it is possible to suppress the above problems.

  By measuring the profile of the surface charge distribution and the surface potential distribution, it is possible to measure with higher accuracy. FIG. 18 is a diagram showing another embodiment of the surface potential distribution measuring apparatus of the present invention. In FIG. 18, a sample application unit 213 on the lower side of the photoconductor sample 20 is connected to a voltage application unit that can apply a voltage ± Vsub. Further, a grid 90 is arranged above the sample 20 in order to suppress the incident electron beam from being affected by the sample charge. The sample placement portion 213 is made of a conductive material, an insulator 212 is disposed below it, and a conductor 211 is disposed below it, and the conductor 211 is grounded (dropped to GND).

  FIG. 19 shows the relationship between incident electrons and a photoreceptor sample. FIG. 4A shows the case where the acceleration voltage is larger than the surface potential potential, and FIG. 4B shows the case where the acceleration voltage is smaller than the surface potential potential. There is a region where the velocity vector of the charged particles incident in the vertical direction of the sample is reversed before reaching the sample, and the primary incident charged particles are detected. Although the acceleration voltage is generally expressed as positive, the applied voltage Vacc of the acceleration voltage is negative, and in order to give a physical meaning as a potential potential, it is easier to describe it as negative. Therefore, the acceleration voltage is expressed as negative (Vacc <0) here. The acceleration potential of the electron beam is Vacc (<0), and the potential potential of the sample is Vp (<0).

A potential is the electrical potential energy of a unit charge. Therefore, the incident electrons move at a speed corresponding to the acceleration voltage Vacc at the potential 0 (V). That is, assuming that the charge amount of electrons is e and the mass of electrons is m, the initial velocity of electrons v0 is
mv02 / 2 = e × | Vacc |
It is represented by In vacuum, due to the law of conservation of energy, it moves at a constant speed in the region where the acceleration voltage does not work, the potential increases as it approaches the sample surface, and the velocity decreases due to the influence of Coulomb repulsion of the sample charge. Therefore, the following phenomenon generally occurs.

In the case of the state shown in FIG. 19A, since | Vacc | ≧ | Vp |, the electron reaches the sample although its speed is reduced.
As shown in FIG. 19B, in the case of | Vacc | <| Vp |, the velocity of incident electrons is gradually decelerated under the influence of the potential potential of the sample, and the velocity reaches zero before reaching the sample. And go in the opposite direction.

  In a vacuum with no air resistance, the energy conservation law is almost completely established. Therefore, the potential on the surface of the photoconductor sample can be measured by measuring the conditions under which the energy on the sample surface, that is, the landing energy, becomes almost zero when the energy of the incident electrons is changed. Here, primary inversion charged particles, particularly electrons, are referred to as primary inversion electrons. The secondary electrons generated when reaching the sample and the primary inversion charged particles differ greatly in the amount reaching the detector, so that they can be distinguished from the border of contrast between light and dark.

  Note that a scanning electron microscope or the like includes a backscattered electron detector. In this case, the backscattered electrons are generally reflected (scattered) on the rear back surface by the interaction with the sample material, This refers to electrons that jump out of the surface of the sample. The energy of the reflected electrons is comparable to the energy of the incident electrons. The intensity of the reflected electrons is said to increase as the atomic number of the sample increases, and this is a detection method that is effective for observing differences in the composition of the sample and irregularities. In contrast, primary inversion electrons are electrons that are inverted before reaching the sample surface under the influence of the potential distribution on the sample surface, and are completely different from reflected electrons.

FIG. 20 is a diagram illustrating an example of the depth measurement result of the latent image. At each scanning position (x, y), the difference between the acceleration voltage Vacc and the applied voltage Vsub under the sample is Vth (= Vacc−Vsub).
Then, the potential distribution V (x, y) can be measured by measuring Vth (x, y) when the landing energy is almost zero. Vth (x, y) has a unique correspondence with the potential distribution V (x, y). If Vth (x, y) is a gentle charge distribution or the like, the potential distribution V (x, y) is approximated. equivalent to y).

  The curve shown in the upper part of FIG. 20 shows an example of the surface potential distribution generated by the charge distribution on the sample surface. The acceleration voltage of the electron gun for two-dimensional scanning was set to −1800V. The potential at the center (horizontal axis coordinate = 0) is about -600V, the potential increases in the negative direction as it goes from the center to the outside, and the potential in the peripheral region whose radius exceeds 75 μm from the center is about -850V. ing. The oval in the middle of the figure is an image of the detector output when the back surface of the sample is set to Vsub = −1150V. At this time, Vth = Vacc−Vsub = −650V. The oval in the lower part of the figure is an image of the detector output obtained under the same conditions as above except that Vsub = −1100V. At this time, Vth is -700V.

  As can be seen from the results shown in FIG. 20, it is possible to measure the surface potential information of the sample by scanning the sample surface with electrons while changing the acceleration voltage Vacc or the applied voltage Vsub and measuring the Vth distribution. . By using this method, it is possible to visualize the latent image profile on the micron order, which has been difficult in the past.

  In the method of measuring a latent image profile with primary inverted electrons, the energy of incident electrons changes drastically, and the trajectory of incident electrons may shift, resulting in a change in scanning magnification or distortion. Will be. In that case, the electrostatic field environment and the electron trajectory can be calculated in advance, and correction can be performed based on the calculation, thereby making it possible to measure with higher accuracy.

  The photosensitive member has a reciprocity failure phenomenon in which the latent image formation state is different when the relationship between the light amount and the exposure time is different even though the total exposure energy density given to the photosensitive member is the same. In general, when the exposure energy is constant, the stronger the amount of light, the lower the sensitivity (latent image depth), causing a change in the toner adhesion amount, resulting in a difference in image density. It is considered that when the amount of light is strong, the amount of recombination of carriers increases and the amount of carriers reaching the surface decreases. In the case of a multi-beam scanning optical system such as a VCSEL, image density unevenness appears remarkably.

  By evaluating the electrostatic latent image on the surface of the photoreceptor sample with the electrostatic latent image measuring apparatus according to the present embodiment, it is possible to measure with a resolution of the order of 1 micron. Quantitative details can be analyzed at the dot level. Therefore, the exposure amount can be optimized, charging and exposure conditions that do not impose a burden on the photoreceptor sample can be known, and a photoreceptor having energy saving and high durability can be obtained.

  In order to improve the image quality of output images, attempts have been made to optimize the optical system, shorten the light source wavelength to 780 nm or less, and reduce the beam spot diameter in the sub-scanning direction to 60 μm or less. However, current photoconductors are less sensitive to short-wavelength light, and a small-diameter beam is strongly affected by light scattering and charge diffusion within the photoconductor, resulting in a larger latent image diameter. The depth of the image also becomes shallow, and the final output image has a problem that gradation and sharpness cannot be stably obtained at a high level.

FIG. 21 shows a conceptual diagram of the beam spot diameter and the latent image diameter. Here, the beam spot diameter is defined as a diameter in a range where the beam spot light quantity distribution is ^{equal to} or ^larger than e ^{−2 of the} maximum light quantity. The diameter of the latent image is a diameter of a circle or an ellipse drawn at the light / dark boundary of the contrast image. It is known that the composition and thickness of the charge transport layer affect the degree of light scattering and charge diffusion, and the composition of the charge generation layer affects the sensitivity, but no clear correlation is known.

Therefore, in the electrostatic latent image measurement method performed by using the electrostatic latent image measurement device of this embodiment, a photoconductor is produced by changing the composition and thickness of the charge transport layer and the composition of the charge generation layer. The latent image is measured by exposing under the same conditions as used in the above, for example, with a charging potential of 800 V, exposure energy of 4 mJ / m ² and a light source wavelength of 780 nm or less and a beam spot diameter in the sub-scanning direction of 60 μm or less. As shown in FIGS. 21A and 21B, when the beam spot diameter in the sub-scanning direction on the photosensitive member surface is A and the latent image diameter in the sub-scanning direction to be formed is B,
1.0 <B / A <2.0
If a photoconductor that satisfies the above is selected, a photoconductor that is stable at a high level of gradation and sharpness in the final output image can be obtained. In the above conditional expression, the lower limit of 1.0 is a theoretical limit that light scattering and charge diffusion always occur in any photoconductor and cannot be less than this, and the upper limit of 2.0 is the final output image. Therefore, this is the limit necessary to ensure the stability of gradation and sharpness.

  Next, an embodiment of the image forming apparatus according to the present invention using the photoconductor measured using the electrostatic latent image measuring apparatus according to the present invention described above will be described. FIG. 22 shows a schematic configuration of a laser printer 1000 which is one form of the image forming apparatus. In FIG. 22, the laser printer includes an optical scanning device 1010, a photosensitive drum 1030, a charging charger 1031, a developing roller 1032, a transfer charger 1033, a charge eliminating unit 1034, a cleaning blade 1035, a toner cartridge 1036, a paper feeding roller 1037, and a paper feeding tray. 1038, a registration roller pair 1039, a fixing roller 1041, a paper discharge roller 1042, a paper discharge tray 1043, and the like.

  The charging charger 1031, the developing roller 1032, the transfer charger 1033, the charge removal unit 1034, and the cleaning blade 1035 are each arranged in the vicinity of the surface of the photosensitive drum 1030. Then, with respect to the rotation direction of the photosensitive drum 1030, the charging charger 1031 → the developing roller 1032 → the transfer charger 1033 → the charge eliminating unit 1034 → the cleaning blade 1035 are arranged in this order.

  A photosensitive layer is formed on the surface of the photosensitive drum 1030. Here, the photosensitive drum 1030 rotates clockwise (in the direction of the arrow) within the plane of FIG. The charging charger 1031 uniformly charges the surface of the photosensitive drum 1030. The optical scanning device 1010 irradiates the surface of the photosensitive drum 1030 charged by the charging charger 1031 with light modulated based on image information from a host device (for example, a personal computer). As a result, a latent image corresponding to the image information is formed on the surface of the photosensitive drum 1030 on the surface of the photosensitive drum 1030. The latent image formed here moves in the direction of the developing roller 1032 as the photosensitive drum 1030 rotates. The configuration of the optical scanning device 1010 will be described later. Toner cartridge 1036 stores toner, and this toner is supplied to developing roller 1032. The developing roller 1032 causes the toner supplied from the toner cartridge 1036 to adhere to the latent image formed on the surface of the photosensitive drum 1030 to visualize the image information. The latent image to which the toner is attached (hereinafter also referred to as “toner image” for convenience) moves in the direction of the transfer charger 1033 as the photosensitive drum 1030 rotates.

  Recording paper 1040 is stored in the paper feed tray 1038. A paper feed roller 1037 is disposed in the vicinity of the paper feed tray 1038, and the paper feed roller 1037 takes out the recording paper 1040 one by one from the paper feed tray 1038 and conveys it to the registration roller pair 1039. The registration roller pair 1039 is disposed in the vicinity of the transfer roller 911, temporarily holds the recording paper 1040 taken out by the paper feeding roller 1037, and the recording paper 1040 and the photosensitive drum 1030 according to the rotation of the photosensitive drum 1030. It is sent out toward the gap with the transfer charger 1033.

  A voltage having a polarity opposite to that of the toner is applied to the transfer charger 1033 in order to electrically attract the toner on the surface of the photosensitive drum 1030 to the recording paper 1040. With this voltage, the toner image on the surface of the photosensitive drum 1030 is transferred to the recording paper 1040. The recording sheet 1040 transferred here is sent to the fixing roller 1041. In the fixing roller 1041, heat and pressure are applied to the recording paper 1040, whereby the toner is fixed on the recording paper 1040. The recording paper 1040 fixed here is sent to the paper discharge tray 1043 via the paper discharge roller 1042 and is sequentially stacked on the paper discharge tray 1043.

  The neutralization unit 1034 neutralizes the surface of the photosensitive drum 1030. The cleaning blade 1035 removes toner (residual toner) remaining on the surface of the photosensitive drum 1030. The removed residual toner is used again. The surface of the photosensitive drum 1030 from which the residual toner has been removed returns to the position of the charging charger 1031 again.

  By using the electrostatic latent image measuring device according to the present invention, a highly desirable photoconductor (latent image carrier) can be obtained, and by using this photoconductor to constitute an image forming apparatus. Thus, it is possible to provide an image forming apparatus capable of obtaining an image with high resolution and high definition and an image with excellent durability.

  By using the electrostatic latent image measuring apparatus according to the present invention, it is possible to evaluate the quality and performance of a photoreceptor used in an image forming apparatus such as a copying machine, a printer, and a facsimile using an electrophotographic process. Then, by designing the image forming apparatus according to the evaluated quality and performance of the photoconductor, a high-quality electrostatic latent image can be formed on the photoconductor, and the electrostatic latent image is developed. Thus, a high quality image can be obtained.

DESCRIPTION OF SYMBOLS 4 Electron beam irradiation apparatus 6 Exposure part 8 Detector 15 Sample mounting part 20 Photoconductor sample 40 Vacuum chamber 61 Light source 65 Optical deflector 1017 Synchronous sensor (synchronization signal production | generation means)

Japanese Patent Laid-Open No. 03-049143 Japanese Patent Laid-Open No. 3-200100 JP 2003-295696 A JP 2004-251800 A JP 2008-233376 A

Claims (12)

An electron beam irradiation apparatus that irradiates an electron beam to a photoconductor sample to generate a charged charge on the photoconductor sample, an exposure unit for forming an electrostatic latent image on the charged photoconductor sample surface, and the photoconductor sample And a detector for detecting electrons emitted from the photoconductor sample by scanning the surface with an electron beam, and measuring an electrostatic latent image distribution on the photoconductor sample surface by a detection signal obtained by the detector In the electrostatic latent image measuring device,
The exposure unit is configured to detect and synchronize the light source composed of a semiconductor laser, the optical deflector that scans the surface of the photosensitive member sample with the laser beam from the light source, and the laser beam at the end of the scanning range of the laser beam. Synchronization signal generation means for generating a signal, and write timing signal generation means for generating a write timing signal for controlling the light emission timing when the laser beam scans the photosensitive member sample surface based on the synchronization signal, Prepared,
An apparatus for measuring an electrostatic latent image, comprising: measuring the distribution of the electrostatic latent image at a predetermined timing from the end of exposure by the exposure unit.   A semiconductor laser having a plurality of light emitting units is used as the light source of the exposure unit, and the light emitting unit that emits light by the synchronization signal from the synchronization signal generating unit is different from the light emitting unit that emits light by the write timing signal from the write timing signal generating unit The apparatus for measuring an electrostatic latent image according to claim 1.   The apparatus for measuring an electrostatic latent image according to claim 1, wherein the light emitting unit that emits light in response to a write timing signal from the synchronization timing signal generating unit is a plurality of light emitting units.   The light source of the exposure unit is a semiconductor laser, and includes a pixel clock generation unit that generates a pixel clock from a reference clock and a synchronization signal, and a pixel pattern generation unit that generates a pixel pattern from pixel information. The apparatus for measuring an electrostatic latent image according to 1, 2 or 3.   5. A shutter according to claim 1, further comprising: a shutter that shields light from entering the surface of the photosensitive member sample other than during measurement; and shutter control means that controls opening and closing of the shutter in conjunction with exposure timing. An apparatus for measuring an electrostatic latent image according to claim 1.   2. The shutter control means according to claim 1, further comprising means for opening the shutter using a synchronizing signal of the scanning optical system as a trigger signal, and closing the shutter in conjunction with a data valid period signal after forming an electrostatic latent image. The apparatus for measuring an electrostatic latent image according to claim 5.   7. The apparatus for measuring an electrostatic latent image according to claim 1, wherein the shutter means is a mechanical shutter.   9. The apparatus for measuring a latent image on a photosensitive member according to claim 1, wherein the measurement is performed under a condition in which a region where a velocity vector in a sample vertical direction of incident charged particles is inverted exists. The photosensitive member sample is irradiated with an electron beam to generate a charged charge on the photosensitive member sample, and an electrostatic latent image is formed by exposing the charged photosensitive member sample surface, and the photosensitive member sample surface is scanned with the electron beam. In the method for measuring an electrostatic latent image, the electrons emitted from the photoreceptor sample are detected, and the electrostatic latent image distribution on the surface of the photoreceptor sample is measured based on the detection signal.
The exposure is performed by scanning the surface of the photoconductor sample with laser light from a light source composed of a semiconductor laser in an exposure unit,
The laser beam is detected by the synchronization signal generating means at the end of the scanning range of the laser beam to generate a synchronization signal,
Based on the synchronization signal, a write timing signal for controlling the light emission timing when the laser beam scans the photoconductor sample surface is generated,
A method for measuring an electrostatic latent image, comprising: measuring the distribution of the electrostatic latent image at a predetermined timing from the end of exposure. The photosensitive member sample is irradiated with an electron beam to generate a charged charge on the photosensitive member sample, an electrostatic latent image is formed by exposing the charged surface of the photosensitive member sample, and the photosensitive member sample surface is scanned with the electron beam. In the method for measuring an electrostatic latent image, the electrons emitted from the photoreceptor sample are detected, and the electrostatic latent image distribution on the surface of the photoreceptor sample is measured based on the detection signal.
The exposure is performed by scanning the surface of the photoconductor sample with a laser beam of a light source composed of a semiconductor laser in an exposure unit,
By blocking the laser light from the light source from reaching the observation area of the photoreceptor sample before and after the time for forming the electrostatic latent image, it is possible to suppress the influence of offset light emission due to the bias current of the semiconductor laser. A method for measuring an electrostatic latent image.   An image forming apparatus for forming an image by executing an electrophotographic process on a surface of a photoconductor, wherein the photoconductor is measured by the electrostatic latent image measuring device according to any one of claims 1 to 9. An image forming apparatus which is a photosensitive member. The wavelength of the laser light emitted from the writing light source is 780 nm or less, the beam spot diameter in the sub-scanning direction on the photoreceptor surface is 60 μm or less, and the beam spot diameter in the sub-scanning direction on the photoreceptor surface is A. When the formed latent image diameter in the sub-scanning direction is B,
1.0 <B / A <2.0
The image forming apparatus according to claim 11, wherein:

Images