JP4931846B2 - Electrostatic latent image evaluation method and electrostatic latent image evaluation apparatus - Google Patents

Description

  The present invention relates to an electrostatic latent image evaluation method suitable for an electrophotographic image forming apparatus such as a copying machine or a laser printer, an electrostatic latent image evaluation apparatus, and an image forming apparatus incorporating these methods or apparatuses.

In an electrophotographic image forming apparatus such as a copying machine or a laser printer, the following image forming process is usually performed when an image is output.
a. A charging step for uniformly charging the surface of the photoconductive photoreceptor; b. An exposure step of irradiating light on the surface of the charged photoreceptor to form an electrostatic latent image by photoconductivity; c. A developing step of forming a visible image on the photoreceptor using the charged toner particles; d. A transfer step of transferring the developed visible image to a transfer material such as a piece of paper; e. A fixing step of fusing and fixing the transferred image on a transfer material; f. A cleaning step of cleaning residual toner on the photoreceptor after transfer of the visible image; g. Static elimination process to eliminate residual charge on the photoconductor

  The process factor and process quality in each of these processes greatly affect the quality of the final output image. In recent years, in addition to high image quality, there has been a growing demand for environmentally friendly imaging processes such as high durability, high stability, and energy saving, and there is a strong demand for improving the process quality of each process. .

  In the above image forming process, the electrostatic latent image formed on the photoconductor by charging and exposure is a factor that directly affects the behavior of the toner particles, and the quality of the electrostatic latent image on the photoconductor is accurately evaluated. It becomes important. By observing the electrostatic latent image on the photoconductor, evaluating the quality, and feeding back the results to the design, the process quality of the charging and exposure processes can be improved. As a result, image quality, durability, Further improvement in stability and energy saving can be expected.

  As a method for measuring the surface charge distribution or surface potential distribution in a dielectric such as a photoconductive photoconductor with high resolution on the order of microns (μm), the techniques described in Patent Documents 1 and 2 are known. According to the electrostatic latent image measurement method and the electrostatic latent image evaluation method described in these patent documents, the surface of the measurement sample is scanned with a charged particle beam to detect secondary electrons generated on the measurement sample surface. The quality of the electrostatic latent image is evaluated. In these methods, the electric field distribution on the surface of the measurement sample is directly measured, and the surface potential distribution is calculated arithmetically based on this electric field distribution.

JP 2003-295696 A JP 2003-305881 A

  By the way, a semiconductor laser light emitting element is often used as a light source of an optical writing device included in an image forming apparatus. The light generated by the semiconductor laser light-emitting element is transmitted through several lenses and becomes a beam spot condensed to a size of several tens of μm. The position of the beam spot is scanned by an optical deflector represented by a polygon mirror, By controlling the lighting timing of the semiconductor laser light emitting element, a scanning beam spot pattern is formed at the surface position of the photoreceptor.

  The lighting timing control of the semiconductor laser light emitting element is performed by controlling the forward current value injected into the semiconductor laser light emitting element. When driving at high speed, the bias current is flowing even when the lamp is not lit. Therefore, the output is very low (on the order of nW to μW) compared to when the lamp is lit, but it emits weak light. . Hereinafter, this weak issue is referred to as “offset emission”. The photosensitive member is also exposed by offset light emission, and if the offset light emission intensity is high, it also appears as noise in the output image. When setting the bias current, increasing the setting value of the bias current value improves the time response characteristics of the lighting pulse, but at the same time, the offset emission intensity also increases. At present, the bias current level that does not appear in the output image is set by an experiment using an image forming apparatus. However, this setting is based on the result of evaluating the output image, that is, the developed and fixed image. There is a possibility that the adjustment accuracy can be further improved by performing the setting based on the observation result of the electrostatic latent image before outputting the image.

  In order to meet the demands for high image quality and high-speed image output, multi-beams are being developed, including higher light source output and the use of surface-emitting laser light sources (VCSEL). In addition, it is required to achieve both high speed driving of the laser light emitting element and avoidance of influence on the output image by offset light emission. Therefore, the adjustment of the bias current value is required to be more strict than before, and the necessity of directly grasping the influence of offset light emission at the electrostatic latent image level is increasing.

  In view of the above, the present invention provides an electrostatic latent image evaluation method and an electrostatic latent image evaluation apparatus capable of clarifying the influence of offset light emission on electrostatic latent image formation in a semiconductor laser light emitting element. For the purpose.

  The present invention also provides an image forming apparatus capable of obtaining a higher quality image by setting a bias current value in a semiconductor laser light emitting element based on evaluation information grasped by using the evaluation method or the evaluation apparatus. The purpose is to provide.

  The electrostatic latent image evaluation method according to the present invention is a method in which a surface of a photoconductive sample on which an electrostatic latent image pattern is formed by charging and exposure of a light image is charged with a charged particle beam. Scans two-dimensionally, captures charged particles that are electrically affected by the electrostatic latent image pattern, detects the intensity signal corresponding to the position on the electrostatic latent image pattern forming surface, and detects An electrostatic latent image evaluation method for extracting an electrostatic latent image pattern from a measured intensity signal and calculating a width and an area of the electrostatic latent image pattern, wherein the electrostatic latent image pattern is calculated from a time when the exposure of the optical image is started. The most important feature is to measure the time until the image pattern formation start time.

  The electrostatic latent image evaluation method according to the present invention also includes the first exposure by weak light emission caused by the injection current below the emission threshold value in the semiconductor laser light emitting element, and the optional exposure during the first exposure. The electrostatic latent image formed by the second exposure when the exposure time of the first exposure is made variable by performing the second exposure by the current injection exceeding the light emission threshold in the light emitting element at the timing of It is characterized by measuring changes in the width and area of the pattern.

  The electrostatic latent image evaluation apparatus according to the present invention includes a charging unit and an optical image exposure unit for forming an electrostatic latent image pattern, and the electrostatic latent image of the photoconductive sample on which the electrostatic latent image pattern is formed. Charged particle beam scanning means for two-dimensionally scanning the pattern formation surface with a charged particle beam, and capturing the charged particles that are electrically influenced by the electrostatic latent image pattern and outputting the intensity signal of the electrostatic latent image pattern An electrostatic latent image evaluation apparatus comprising: an evaluation unit that detects and evaluates a charge distribution state in the electrostatic latent image pattern detected in correspondence with a position on a formation surface, and the optical image exposure unit Is a semiconductor laser light-emitting element, comprising: a light emission time control means for weak light emission caused by current injection below the light emission threshold in the semiconductor laser light-emitting element; and a means for calculating the width or area of the electrostatic latent image pattern. Special To.

  In the above-mentioned electrostatic latent image evaluation apparatus, light emission time control means and output control means by current injection above the light emission threshold in the light emitting element, exposure with weak light emission by current injection below the light emission threshold in the light emitting element, and It is further preferable to include a latent image characteristic change detecting means for detecting an electrostatic latent image pattern formed by exposure in which both exposure by light emission caused by current injection exceeding the light emission threshold is superimposed.

  An image forming apparatus according to the present invention employs the above-described electrostatic latent image evaluation method or electrostatic latent image evaluation apparatus, and sets a bias current value of a semiconductor laser light emitting element.

  According to the electrostatic latent image evaluation method and the electrostatic latent image evaluation apparatus according to the present invention, the degree of influence of offset light emission on an image can be grasped by measuring this at the electrostatic latent image level. It is possible to directly evaluate the degree of influence of the offset light emission on the image by eliminating the influence of conditions other than the exposure process such as the development process. An evaluation method and an evaluation apparatus can be provided.

  In the electrostatic latent image evaluation method and the electrostatic latent image evaluation apparatus according to the present invention, an actual image is configured by measuring the degree of influence on the image by offset light emission superimposed on the exposure by image pattern writing. It can be measured and evaluated under conditions close to the writing conditions of the forming apparatus.

  In the electrostatic latent image evaluation method and the electrostatic latent image evaluation apparatus according to the present invention, the evaluation is performed under the optical writing condition using the system including the optical image exposure means to which the optical scanning means is added and reflecting the conditions of the image forming apparatus. By performing the configuration, it is possible to measure and evaluate under conditions close to the writing conditions of the actual image forming apparatus.

  According to the image forming apparatus of the present invention, a semiconductor mounted in an image forming apparatus is evaluated by evaluating the degree of influence of offset light emission on an image using the electrostatic latent image evaluation method and the electrostatic latent image evaluation apparatus. The adjustment accuracy of the laser light emitting element can be increased, and the adjustment margin of the bias current can be increased. As a result, high image quality and high-speed driving can be achieved at a higher level.

  Embodiments of an electrostatic latent image evaluation method, an electrostatic latent image evaluation apparatus, and an image forming apparatus incorporating these methods or apparatuses according to the present invention will be described below with reference to the drawings.

  First, an outline of the electrostatic latent image evaluation apparatus and an evaluation process based on the electrostatic latent image evaluation method will be described. In FIG. 1 showing an embodiment of an electrostatic latent image observation apparatus, reference numeral 11 denotes a charged particle gun, 12 denotes an aperture, 13 denotes a condenser lens for charged particles, 14 denotes a beam blanker, and 15 denotes a charged particle beam. A scanning lens 16 for deflecting the objective lens 16 is an objective lens for the charged particle beam. These charged particle gun 11, aperture 12, condenser lens 13, beam blanker 14, scanning lens 15, and objective lens 16 constitute a charged particle beam irradiation unit 10. The operation of each component of the charged particle beam irradiation unit 10 is controlled by the charged particle beam control unit 31. The charged particle beam irradiation unit 10 and the charged particle beam control unit 10b constitute a “charged particle beam scanning unit”.

  In FIG. 1, reference numeral 17b denotes a semiconductor laser light emitting element (hereinafter also referred to as "LD") as a light source, 17a denotes an LD control unit for driving the light source, 18 denotes a collimator lens, 19 denotes an aperture, and 20 denotes an imaging lens. Each is shown. Each of these optical components constitutes “optical image exposure means”. By the optical image exposure means, the light beam from the LD 17b is condensed on the surface of the photoconductive sample 00 to form a beam spot. Further, the light emission time and the light beam intensity can be adjusted and set by the LD control unit 17a.

The relationship between the forward current value injected into the LD 17b and the optical output of the LD 17b is a broken line as shown in FIG. As shown in FIG. 2, when the current value during lighting is set to Io and the bias current value during non-lighting (lighting standby state) is set to Ib, light outputs Po and Pb are obtained by the respective current values. The output value Pb is the offset light emission output. The output value Pb is very weak and the output range is 50 μW or less. The “weak light emission” described in the claims means an output in this range. I _OFF is a state in which the power supply to the laser light emitting element 17b is off, and in this state, the light output is also zero. In order to form an electrostatic latent image on the photoconductive sample 00 by offset light emission, the current value is set to Ib and the photoconductive sample 00 is exposed. The current value during non-exposure is set to I _OFF .

  In FIG. 1, reference numeral 24 denotes a charged particle detector, 25a denotes a signal processing unit, 25b denotes an evaluation unit, 26 denotes a monitor, and 27 denotes an output device such as a printer. The charged particle detector 24, the signal processing unit 25a, the latent image characteristic calculation unit 25b, the monitor 26, and the output device 27 constitute “evaluation means”. Reference numeral 28 denotes a sample mounting table, 00 denotes a photoconductive sample, and 29 denotes a light-emitting element for charge removal. The sample mounting table 28 is composed of a grounded metal plate. As shown in FIG. 1, each of the above parts is disposed in a casing 30, and the inside of the casing 30 can be highly decompressed by a vacuum control unit 31. That is, the casing 30 has a function as a “vacuum chamber”.

  The entire electrostatic latent image evaluation apparatus is controlled by a host computer (hereinafter referred to as “PC”) 32. The charged particle beam control unit 10a, the signal processing unit 25a, and the like described above can be set as “part of their functions” in the host PC 32.

In the state shown in FIG. 1, the photoconductive sample 00 whose surface is uniformly charged is placed on the sample placing table 28, and the inside of the casing 30 is highly decompressed. In this state, a light beam spot is formed on the uniformly charged surface of the photoconductive sample 00 according to the light emission of the LD 17b.
The intensity distribution of the light beam spot has a Gaussian profile in the cross section, and the diameter at 1 / e 2 times the intensity peak value is as small as about 50 μm, for example.

  The photoconductive sample 00 is exposed when the light beam spot is formed, and an electrostatic latent image pattern corresponding to the light image irradiated on the photoconductive sample 00 is formed. The surface of the photoconductive sample 00 on which the electrostatic latent image pattern is thus formed is scanned two-dimensionally with a charged particle beam. That is, when a charged particle beam is emitted from the charged particle gun 11, the emitted charged particle beam passes through the aperture 12, the beam diameter is regulated, and then passes through the beam blanker 14 while being focused by the condenser lens 13. . The charged particle beam focused by the condenser lens 13 is focused on the surface of the photoconductive sample 00 by the objective lens 16. At this time, by deflecting the direction of the charged particle beam by the scanning lens 15, the position where the charged particle beam is focused is two-dimensionally on the surface of the photoconductive sample 00, for example, orthogonal to the horizontal direction of the drawing and the drawing. It can be displaced in the direction of

  In this way, the surface of the photoconductive sample 00 on which the electrostatic latent image pattern is formed is two-dimensionally scanned with the charged particle beam. The size of the scanned area can be changed by setting the magnification of the scanning lens. For example, it can be observed at various magnifications such as a low magnification of about 5 mm × 5 mm and a high magnification of about 1 μm × 1 μm.

  A trapping voltage having a predetermined polarity is applied to the charged particle detector 24. By this action of the trapping voltage, “charged particles that are electrically affected by the electrostatic latent image pattern” are captured by the charged particle detector 24, and the intensity, that is, the number of trapped particles per unit time is detected. Converted to a signal. The “region that is two-dimensionally scanned by the charged particle beam: S” of the photoconductive sample 00 is represented by S (X, Y) using two-dimensional coordinates, for example, 0 mm ≦ X ≦ 1 mm, 0 mm ≦ Y ≦ 1 mm. The electrostatic latent image pattern formed in this region: S (X, Y) is defined as its surface potential distribution: V (X, Y).

  Since the two-dimensional scanning of the region by the charged particle beam is performed under a predetermined condition, if the time from the start to the end of the two-dimensional scanning is T0 ≦ T ≦ TF, the scanning is performed. Time: T corresponds to each scanning position in the scanning area: S (X, Y) 1: 1. Since the charged particles captured by the charged particle detector 24 are electrically influenced by the surface potential distribution of the electrostatic latent image pattern: V (X, Y), the intensity of the charged particles captured at time: T: F (T) has a correspondence relationship with surface potential distribution: V {X (T), Y (T)} with time: T as a parameter. This correspondence can be known by observing the intensity of the charged particles affected by the reference potential: VN. Based on this correspondence, the intensity: F of the charged particles is calibrated to become intensity: F. The corresponding potential: V can be known. Therefore, by sampling the detection signal obtained from the charged particle detector 24 at an appropriate interval, the surface potential distribution: V (X, Y) can be specified for each “micro area corresponding to sampling”.

  As described above, the charged particle beam is a particle beam that is affected by an electric field or a magnetic field, such as an electron beam or an ion beam. An “electron gun” is used, and if an ion beam is used, an “ion gun” or the like is used.

  Hereinafter, the case where an electron beam is used as the charged particle beam will be described in detail. At this time, the charged particle gun 11 is an “electron gun”, and the “surface on which the electrostatic latent image pattern is formed” of the photoconductive sample 00 is two-dimensionally scanned with an electron beam. In order to form an electrostatic latent image pattern on the photoconductive sample 00, it is necessary to uniformly charge the surface prior to exposure with a light image. For the uniform charging of the photoconductive sample 00, charging may be performed outside the observation apparatus, and the uniformly charged photoconductive sample 00 may be mounted on the sample mounting table 28. However, as described above, the inside of the casing 30 needs to be highly depressurized. When the inside of the casing 30 is depressurized after setting the photoconductive sample 00, it is charged by dark decay until scanning by the electron beam becomes possible. The potential is attenuated, and in some cases, the electrostatic latent image pattern cannot be observed. From this point of view, it is preferable that uniform charging of the photoconductive sample 00 is performed in the casing 30 “after high pressure reduction is realized”.

  In the embodiment shown in FIG. 1, charging by an electron beam is performed using a charged particle beam scanning means. When the photoconductive sample 00 is irradiated with the electron beam, “secondary electrons” are generated from the photoconductive sample 00 by the impact of the irradiated electrons. In the balance between the amount of electrons irradiated to the photoconductive sample 00 as an electron beam and the amount of secondary electrons generated, the ratio of the amount of irradiated electrons R1 to the amount of emitted secondary electrons R2: R1 / R2 is 1 or more For example, the amount of electrons irradiated by subtraction exceeds the amount of secondary electrons, and the difference between the two accumulates in the photoconductive sample 00 and charges the photoconductive material 00.

  Accordingly, the amount of electrons emitted from the electron gun 11 and its acceleration voltage are adjusted, and the above condition: the condition that R1 / R2 is larger than 1 is set, and the electron beam is scanned two-dimensionally. The property sample 00 can be uniformly charged. Such adjustment of the amount of emitted electrons and the acceleration voltage is performed by the charged particle beam control unit 10a. Further, on / off of the electron beam accompanying the scanning of the electron beam is performed by controlling the beam blanker 14 by the charged particle beam control unit 10a.

  FIG. 3 schematically shows a state in which the surface of the photoconductive sample 00 is charged with an electron beam as described above. An example of the photoconductive sample 00 shown in FIG. 2 is a so-called “function-separated type photoreceptor”, in which a charge generation layer 2 is provided on a conductive layer 1 and a charge transport layer 3 is formed thereon. It is. The electrons irradiated by the electron gun are shot into the surface of the charge transport layer 3 and are captured by the electron orbits of the charge transport layer material molecules on the surface of the charge transport layer 3, and the charge transport layer in a state in which the molecules are negatively ionized. 3 remains on the surface. This state is a state in which the photoconductive sample 00 is charged.

  When the photoconductive sample 00 in such a charged state is irradiated with the light LT, the irradiated light LT passes through the charge transport layer 3 and reaches the charge generation layer 2, and the energy is generated in the charge generation layer 2. To generate positive and negative charge carriers. Among the generated positive and negative charge carriers, the negative carriers move to the conductive layer 1 due to the repulsive force due to the negative charges on the surface of the charge transport layer 3, and the positive carriers are transported through the charge transport layer 3 to the same layer. It counteracts with the negative charges (captured electrons) on the surface portion of 3. In this way, in the portion of the photoconductive sample 00 irradiated with the light LT, the charged charge is attenuated, and a charge distribution according to the intensity distribution of the light LT is formed. This charge distribution pattern is nothing but an electrostatic latent image pattern.

  The photoconductive sample 00 uniformly charged as described above is exposed in accordance with a light image to form an electrostatic latent image pattern. This exposure is performed by the “optical image exposure means” in the embodiment shown in FIG. That is, the light from the semiconductor laser 17 b forms a light beam spot on the surface of the photoconductive sample 00 via the imaging lens 20. In a state where the electrostatic latent image pattern is formed on the photoconductive sample 00 as described above, the scanning region of the photoconductive sample 00 is two-dimensionally scanned with an electron beam. Secondary electrons generated by this scanning are detected by the charged particle detector 24. Since the detection target is a secondary electron and a negative charge, the charged particle detector 24 applies a positive voltage (capture voltage) for capturing the secondary electrons, and positively generates the secondary electrons generated by scanning the electron beam. Capture by aspiration with voltage. The captured electrons are converted into scintillation luminance by a scintillator and further converted into an electric signal.

  In the space between the surface of the photoconductive sample 00 and the charged particle detector 24, the charge on the surface of the photoconductive sample 00 (negative charge forming an electrostatic latent image) and the charged particle detector 24 are applied. A “potential gradient” is formed by the positive trapping voltage. Based on the known principle described in Patent Document 2 described above, an intensity signal corresponding to the distribution of the electrostatic latent image pattern is obtained by the potential gradient. The intensity here is the detected intensity (number of secondary electrons) of secondary electrons, and is a signal having a low intensity at a place where an electrostatic latent image pattern is formed and a high intensity at a place where it is not formed. It becomes.

  If the intensity signal obtained by the charged particle detector 24 is sampled by the signal processing unit 25a at an appropriate sampling time, 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 region corresponding to sampling”, and the surface charge distribution, that is, the potential contrast image: V (X, Y) can be configured as two-dimensional intensity image data by the signal processing unit 25a. The intensity image data obtained as described above includes an electrostatic latent image pattern formed in accordance with the time integration of the light intensity on the surface of the photoconductive sample 00.

  By applying a binarization process to the intensity image data, the latent image characteristics can be calculated. Hereinafter, the latent image characteristics are parameters indicating the distribution state of the electrostatic latent image pattern, such as the area in the electrostatic latent image pattern, the area ratio in the entire image, and the diameter in a specific direction as shown in FIG. It is a general term.

  FIG. 5 shows details of the operation process of the latent image characteristic calculator 25b in FIG. As shown in FIG. 5, the latent image characteristic calculation unit 25 b performs “time-series intensity image data accumulation process” 41 a, time until an electrostatic latent image is formed by offset light emission, that is, “offset exposure allowable time measurement process”. 41b. Each operation is shown below.

Time-series intensity image data accumulation process Prior to the calculation of the latent image characteristics, exposure by offset light emission is performed by the above-described optical image exposure means, and at the same time, time-series intensity image data to be evaluated is acquired. A plurality of pieces of intensity image data are acquired at a constant sampling interval Ts (for example, appropriately selected within a range of 0.25 to 1 ms). The time from the acquisition start time T ₀ to the end time T _END is acquired by a predetermined time setting (for example, appropriately selected in the range of 0.2 to 1 s). However, in this case, when the offset emission intensity is low, the electrostatic latent image pattern may not be formed within a predetermined time. In order to prevent this, an area ratio Ru (an appropriate value larger than 0%, for example, appropriately selected within a range of 10 to 50%) of the electrostatic latent image to be photographed is determined in advance, and FIG. It is desirable that the latent image area ratio is sequentially calculated and compared as in the intensity image acquisition flow shown, and imaging is continued until Ru is reached.

In the time-series intensity image acquisition flow shown in FIG. 6, first, the LD controller 17a shown in FIG. 1 sets the current value to Ib and starts exposure by offset light emission (S1). At the same time, the acquisition of the intensity image is started, the image acquisition time is managed by the time counter 33 shown in FIG. 1, and the loop processing is rotated at a constant sampling interval Ts to continue the image acquisition (S3, S4, S5). . As described above, when the area ratio reaches a predetermined Ru, the image acquisition loop processing is terminated (YES in S3), and the LD controller 17a sets the current value to I _OFF and stops offset light emission. (S6). The time at this time is _TEND (S7). By the above, from the offset light emission start time T0, up to the T _END the image acquisition is completed through the time the electrostatic latent image pattern by the offset light emission is formed, intensity image data of "time series corresponding to each of the time Can be acquired.

Offset exposure permissible time measurement process For each image of “time series intensity image data” acquired in the above time series intensity image data accumulation process, the latent image area value is calculated and plotted in time series, as shown in FIG. This is a graph of “related data of offset light emission time and latent image area”. In addition to the graph, FIG. 7 shows a schematic diagram of intensity image data and a graph of “relationship data between offset light emission time and integrated exposure energy” for three typical latent image formation states in the graph. . As can be seen from the graph of “Relation data between offset light emission time and integrated exposure energy”, when offset light emission is started, the integrated exposure energy increases in proportion to the elapsed time. On the other hand, in the graph of “Relation data between offset light emission time and latent image area”, an electrostatic latent image pattern is not formed for a while after the start of offset light emission. This state is represented as “state (1)” in FIG. The formation of the electrostatic latent image pattern can be confirmed at a certain time. The state at the time when the formation of the electrostatic latent image pattern can be confirmed is shown as “state (2)” in FIG. Thereafter, the area of the latent image increases in proportion to the passage of time. This state is represented as “state (3)” in FIG. The time range in which the offset light emission does not affect the electrostatic latent image formation, that is, the “offset exposure allowable time” is the time immediately before the transition from the offset light emission start time to “state (2)” where the latent image area is larger than zero. Time to time. The time just before the was claim "electrostatic latent image pattern formation start time" (the symbol T _SG), to move to the "state (2)" The latent image area is greater than zero state It is synonymous with.

The “offset light emission time and latent image area relation data” and “offset exposure allowable time” as shown in FIG. 7 can be calculated by following the flowchart of FIG. First, “time-series intensity image data” is prepared (S11), the time scale T is set to T0 (= 0) (S12), and the latent image area is calculated from the intensity image data at time T (S13). . Next, it is determined whether or not the latent image area at time T is 0 or more (S14). If it is 0 or less, the process proceeds to S15. If it is 0 or more, T is recorded as offset exposure allowable time data _TSG. (S16), and then the process proceeds to S15. In S15, replacing T in T + Ts, then T is determined whether reaches _{T END} (S17). If T does not reach _TEND , the latent image area is calculated from the intensity image data at time T, and the latent image area data corresponding to time T is recorded (S18), and the process returns to step S14. If in step S17 T reaches T _END, recording a latent image area data corresponding to the time T that has been recorded, and outputs the offset exposure allowable time data T _SG (S19), a series of operations finish.

  In the above example, as a condition for determining whether or not the “electrostatic latent image pattern formation start time” is set, “latent image area is greater than 0”, and the time until the time immediately before this is established is the “offset exposure allowable time”. However, the criterion value should be selected according to the situation. For example, considering the toner adhesion capability in the development process, it is effective to set the area and diameter that affect the toner adhesion as the condition values. In this case, it is desirable to set the latent image area condition in the range of 0 to 40 μm ^ 2 or less and the latent image diameter condition in the range of 0 to 10 μm or less.

  In addition, depending on the imaging conditions of the intensity image to be acquired and the state of the photoconductive sample, an electrostatic latent image pattern may be formed in an area other than the exposure area due to offset light emission due to the occurrence of charge leakage. There is also. In consideration of this, it is also effective to extract only a relative change before and after the offset light emission when evaluating the latent image area.

  By measuring the “offset exposure allowable time” based on the above method, the influence of offset light emission in the semiconductor laser light emitting device can be grasped.

  The above-mentioned “time-series intensity image data”, “offset emission time and latent image area relation data”, and “offset exposure allowable time” measurement results are displayed on the display unit 26 in FIG. By outputting, it can be obtained visually or as data as a quantitative evaluation result.

  In the case where the surface of the photoconductive sample 00 set in the casing 30 shown in FIG. 1 is initially charged unevenly for some reason, such a charged state is considered to be an observation noise. Therefore, before carrying out the charging step for observation, it is preferable to perform photo-discharge of the photoconductive sample 00 by irradiating light with light from the light-emitting element 29 (for example, light-emitting diode) for discharging. . In addition, the light neutralization by the light emitting element 29 is performed prior to each observation when the same photoconductive sample 00 is observed a plurality of times while changing the formation conditions of the electrostatic latent image pattern. The light emitting element 29 for light neutralization may be omitted depending on circumstances.

  As described above, the embodiment shown in FIG. 1 is configured as an electrostatic latent image evaluation method and an electrostatic latent image evaluation apparatus using a system in which the exposure spot position with respect to the photoconductive sample 00 does not change. May be changed to evaluate the electrostatic latent image. The embodiment shown in FIG. 9 is the optical writing that reflects the configuration of the image forming apparatus by using a system including the optical image exposure means 50 to which the optical scanning means is added and measuring under conditions close to the image forming apparatus. Evaluation can be performed under conditions. Thereby, it becomes possible to grasp the influence of offset light emission in the image forming apparatus more directly.

  An example of the component arrangement of the optical image exposure means 50 in FIG. 9 is shown in FIG. In FIG. 10, the optical image exposure means 50 includes a semiconductor laser light emitting element 51b, a collimating lens 52, an aperture 53, a cylinder lens 54 having power only in the sub-scanning direction, a polygon mirror 55 as a deflector, an fθ lens 56, and synchronization detection. The light receiving element 58 is provided. The light beam 57 is deflected in the main scanning direction by the polygon mirror 55 to form a scanning beam spot on the surface of the photoconductive sample 00. The embodiment shown in FIG. 9 is the same as the system configuration shown in FIG. 1 except that the optical image exposure means 50 to which the optical scanning means described above is added is provided.

  The details of the latent image characteristic calculation unit 25b in FIG. 9 are also configured in the same manner as shown in FIG. As shown in FIG. 5, the latent image characteristic calculation unit 25b includes a “time-series intensity image data accumulation process” 41a, a time until an electrostatic latent image is formed by offset light emission, and an “offset exposure allowable time measurement process” 41b. The “relationship data between the offset light emission time and the latent image area” is a graph as shown in FIG. 11 corresponding to FIG. In the intensity image data for the three typical latent image forming states in the graph shown in FIG. 11, a linear latent image scanned in the main scanning direction is formed as shown in the schematic diagram of FIG. The

  The time range in which the offset light emission does not affect the formation of the electrostatic latent image, that is, the “offset exposure allowable time” is also in a state where the latent image area is larger than 0 from the offset light emission start time, as in the embodiment described above. It can be measured as the time until the time immediately before shifting to a certain “state (2)”.

  As in the above-described embodiment, the latent image formation determination condition is “the latent image area is greater than 0” in the above-described embodiment. However, this is not necessarily limited, and the determination condition value is appropriately set according to the situation. Should be selected. As described above, the setting is effective in the range of 0 to 40 μm 2 or less as the latent image area condition and the range of 0 to 10 μm or less as the latent image diameter condition.

  The numerical example about the result measured as mentioned above is shown. As measurement conditions, when the pixel density is 600 dpi, the image frequency is 40 MHz, the rotation speed of the polygon mirror is 40,000 rpm, and the latent image formation determination condition is “the latent image area is greater than 0”, the “offset exposure allowable time” is 8.0 ms. Met.

  In the above description, the evaluation method and apparatus for the presence / absence of electrostatic latent image formation by exposure only by offset light emission have been described. However, in image forming apparatuses, exposure by image pattern writing is performed in addition to exposure by offset light emission. Is performed in a superimposed manner. Due to differences in exposure intensity and time due to offset light emission, a difference may appear in the electrostatic latent image pattern formed after image pattern writing. In the following, an evaluation method and apparatus for this pattern difference will be described.

  First, a phenomenon in which the electrostatic latent image pattern formed after image pattern writing differs depending on the difference in exposure intensity and time due to offset light emission will be described with reference to the schematic diagrams of FIGS. First, as shown in FIG. 12, an intensity image is acquired by setting an exposure time by three types of offset light emission. The acquired intensity image is as shown in FIG. 13, and no electrostatic latent image pattern is formed. FIG. 14 shows an intensity image in a case where 1 dot (dot) image pattern writing is performed in addition to exposure by offset light emission. In FIG. 14, an electrostatic latent image pattern corresponding to a difference in exposure time setting due to offset light emission is formed. The latent image in the case of “offset exposure time (a)” is a pattern which is not affected by offset light emission at all. On the other hand, the latent images of “offset exposure time (b)” and “offset exposure time (c)” are affected by offset light emission, and a linear latent image pattern in the main scanning direction is generated. The occurrence of pattern fatness can be confirmed.

  FIG. 15 shows an embodiment of an evaluation apparatus that can evaluate this pattern difference. The embodiment shown in FIG. 15 differs from the above-described embodiment shown in FIG. 9 in the configuration of the latent image characteristic calculation unit. In the embodiment shown in FIG. 15, the latent image characteristic calculation unit is denoted by reference numeral 25c. Details of the latent image characteristic calculation unit 25c are shown in FIG. In FIG. 16, the latent image characteristic calculation unit 25 c includes a “time-series intensity image data accumulation process” 41 a, a time until an electrostatic latent image is formed by offset light emission “offset exposure allowable time measurement process” 41 b, “offset Intensity image acquisition process by exposure, image pattern exposure, and superposition exposure "41c" and "offset exposure allowable time measurement process at the time of image pattern writing" 41d. Of these, the first two steps are the same as the operations described with reference to FIG. Through these processes, information on the allowable offset exposure time is acquired. The operation of the second half is shown below.

  In the “intensity image acquisition process by offset exposure, image pattern exposure, and superposition exposure” 41c, the offset light emission in the time shorter than the offset exposure allowable time obtained in the previous process, and the image pattern during the offset light emission (for example, 1 dot pattern) To obtain an intensity image. The image pattern exposure conditions, for example, pattern, power, duty, light emission timing, etc. are aligned, and only the offset light emission time condition is made variable, and a plurality of intensity images are acquired. Thereby, as shown in the schematic diagram of FIG. 14, intensity images having different electrostatic latent image patterns can be obtained according to the offset light emission time condition. When acquiring images with variable offset emission time conditions, always include the condition that the offset emission time is zero.

  In the "offset exposure allowable time measurement process at the time of image pattern writing" 41d, the latent image area in the image pattern latent image is enlarged for different intensity images of the electrostatic latent image pattern according to the offset emission time condition obtained in the previous process. Find the rate. Based on the area of the electrostatic latent image pattern of the intensity image obtained in the previous process under the condition that the offset light emission time is zero, the enlargement ratio of the latent image area in each intensity image is obtained. An example of the result of obtaining the enlargement ratio is shown in FIG. As can be seen from FIG. 17, the change in the schematic diagram in FIG. 14 is reflected, and it can be seen that the latent image enlargement ratio changes as the offset light emission time increases.

From the graph shown in FIG. 17, the offset light emission time to reach a predetermined latent image area variation rate allowable value S _Limit is calculated, and with this time, the measurement result of “offset exposure allowable time at the time of image pattern writing” and To do. S _Limit is a value determined on the basis of the image quality specification value. As a setting example, if the image pattern to be written is a 1 dot pattern, it is desirable to use about + 10% of the reference pattern as a guide. By measuring the allowable offset exposure time, it is possible to grasp the influence of offset light emission at the time of image writing by the scanning beam.
Further, instead of the “area” described as the evaluation index of the above-described electrostatic latent image pattern, “circle equivalent diameter” may be used. The equivalent circle diameter D is the area of the latent image,
D = (S / π) ^ 0.5 * 2
It is represented by The evaluation index based on the equivalent circle diameter is effective because it can be introduced as an evaluation index based on the diameter similar to the line image diameter, particularly in a latent image having a complicated shape as shown in FIG.

Next, it is preferable to mount the semiconductor laser light emitting element, which has been evaluated using the above-described electrostatic latent image evaluation apparatus and whose bias current is adjusted based on the evaluation, in the image forming apparatus. An embodiment of such an image forming apparatus will be described. FIG. 18 shows an example of a general image forming apparatus. In the example of the image forming apparatus shown in the figure, a unit for executing an image forming process as described below is arranged around and around a drum-shaped photoconductor as an image carrier. .
a. Charging unit: charging step for uniformly charging the photoconductive photosensitive member b. Exposure unit: an exposure process in which an electrostatic latent image is formed by photoconductivity by irradiating light to a photoreceptor c. Development unit: Development step of forming a visible image on the photoreceptor using charged toner particles d. Transfer unit: Transfer step for transferring the developed visible image to a transfer material such as a piece of paper e. Fixing unit: a fixing step of fusing and fixing the transferred image on a transfer material; f. Cleaning unit: a cleaning step for cleaning residual toner on the photoreceptor after transfer of the visible image g. Static elimination unit: Static elimination process to eliminate residual charge on the photoconductor

  In the image forming apparatus, it is desired that a high-quality image can be obtained, and that a high-speed optical writing semiconductor laser light-emitting element is mounted in order to form an image with a light beam. Hereinafter, an image forming apparatus with high image quality and high speed driving will be described. As a light source of an optical writing device included in an image forming apparatus, when a semiconductor laser light emitting device is driven at high speed, even when it is not lit (lighting standby state) in order to improve the rising characteristics of the lighting pulse. It is desirable to pass a bias current. However, offset light emission occurs at a very low output (nW to μW order) compared to when the light is on, and the photosensitive member is exposed. If the offset light emission intensity is high, it appears as noise in the output image. End up. In setting the bias current, the time response characteristic of the lighting pulse is improved by increasing the set value of the bias current value, but at the same time, there is a trade-off relationship in which the offset emission intensity also increases.

When setting the bias current, the previously obtained “offset exposure allowable time at the time of image pattern writing” is used. Based on this time and the offset emission output value (known light source characteristics (see Fig. 2), measured in advance) used in the measurement experiment for this time, the integrated exposure energy density range where no latent image is formed is calculated can do. When the semiconductor laser light emitting element is mounted on the image forming apparatus, the bias current is adjusted so that the integrated exposure energy density due to the offset light emission becomes the upper limit of the above range in consideration of the optical writing conditions. By grasping the influence of offset light emission based on the electrostatic latent image observation result, the upper limit value is driven more strictly than before, so that the adjustment accuracy is improved and the adjustment margin of the bias current is generated. As a result, the image forming apparatus can achieve high image quality and high-speed driving at a higher level, which can contribute to higher quality.
By adjusting the semiconductor laser light emitting element by the above adjustment method, the bias current (“Ib” in FIG. 2) is in the range of 5 to 70 mA.
By introducing the technique of the present invention, the ability to adjust the bias current value for improving the drive speed of the element and avoiding the influence on the output image due to offset light emission is improved.

  The present invention is a technology that can be applied to a high-power, multi-beam light source such as a surface-emitting laser light source (VCSEL) that is expected to be put into practical use in the future in order to achieve high image quality and high speed requirements in image forming apparatuses. .

It is an optical arrangement | positioning figure which shows one Embodiment of the electrostatic latent image observation apparatus concerning this invention. It is a graph which shows the relationship between the forward current value inject | poured into a semiconductor laser light emitting element, and the optical output of a semiconductor laser light emitting element. It is a model figure which shows a mode when the surface of a photoconductive sample is charged with the electron beam. It is a model figure which shows an example of the electrostatic latent image pattern formed according to a latent image characteristic. It is a flowchart which shows the operation | movement process of the latent image characteristic calculating part in one Embodiment of the said electrostatic latent image observation apparatus. It is a flowchart which shows the intensity | strength image acquisition operation | movement in one Embodiment of the said electrostatic latent image observation apparatus. In one embodiment of the electrostatic latent image observation apparatus, graphs showing relationship data between offset light emission time and latent image area, graphs showing relationship data between offset light emission time and accumulated exposure energy, and typical latent image formation states in these graphs It is a model figure which shows intensity | strength image data. It is a flowchart which shows the calculation operation | movement of the relationship data of offset light emission time and a latent image area, and offset exposure permissible time in one Embodiment of the said electrostatic latent image observation apparatus. It is an optical arrangement | positioning figure which shows 2nd Embodiment of the electrostatic latent image observation apparatus concerning this invention. It is a component arrangement | positioning figure which shows the example of the optical image exposure means in the said 2nd Embodiment. It is a model figure which shows the intensity | strength image data in the typical latent image formation state in the graph which shows the relationship data of the offset light emission time in the said 2nd Embodiment, and a latent image area. It is a graph for demonstrating the phenomenon in which the electrostatic latent image pattern formed after image pattern writing changes with the difference in exposure intensity and time by offset light emission. It is a model figure which shows the example of the intensity | strength image data in the case of only the exposure by offset light emission for every difference in exposure time. It is a model figure which shows the example of the intensity | strength image data at the time of performing 1 dot image pattern exposure in addition to the exposure by offset light emission for every difference in exposure time. It is an optical arrangement | positioning figure which shows 3rd Embodiment of the electrostatic latent image observation apparatus concerning this invention. It is a flowchart which shows the operation | movement process of the latent image characteristic calculating part in 3rd Embodiment of the said electrostatic latent image observation apparatus. It is a graph which shows the relationship of the latent image area with respect to the offset light emission time of a photoconductive sample, and the area expansion rate of an image pattern latent image. It is a model figure which shows the example of the image forming apparatus which can apply the electrostatic latent image observation method and electrostatic latent image observation apparatus concerning this invention.

Explanation of symbols

00 photoconductive sample 10a charged particle beam control unit 10b charged particle beam irradiation unit 11 charged particle gun 12 aperture 13 condenser lens 14 beam blanker 15 scanning lens 16 objective lens 17a LD control unit 18 collimating lens 19 aperture 20 imaging lens 24 charging Particle detector 25a Signal processing unit 25b Latent image characteristic calculation unit (evaluation unit)

Claims (9)

A surface of the photoconductive sample on which the electrostatic latent image pattern is formed by charging and light image exposure is two-dimensionally scanned with a charged particle beam to form the electrostatic latent image. Captures charged particles that are electrically affected by the pattern, detects the intensity signal corresponding to the position on the electrostatic latent image pattern forming surface, and extracts the electrostatic latent image pattern from the detected intensity signal. , An electrostatic latent image evaluation method for calculating the width and area of an electrostatic latent image pattern,
An electrostatic latent image evaluation method, comprising: measuring a time from a start time of exposure of the optical image to an electrostatic latent image pattern formation start time.   2. The electrostatic latent image evaluation method according to claim 1, wherein the exposure of the optical image is performed by weak light emission caused by an injection current less than a light emission threshold value in the semiconductor laser light emitting element. Evaluation methods. A surface of the photoconductive sample on which the electrostatic latent image pattern is formed by charging and light image exposure is two-dimensionally scanned with a charged particle beam to form the electrostatic latent image. Captures charged particles that are electrically affected by the pattern, detects the intensity signal corresponding to the position on the surface where the electrostatic latent image pattern is formed, and extracts the electrostatic latent image pattern from the detected intensity signal An electrostatic latent image evaluation method for calculating the width and area of an electrostatic latent image pattern,
The exposure of the optical image includes a first exposure by weak light emission caused by an injection current less than a light emission threshold value in the semiconductor laser light emitting element, and a light emission threshold value in the light emitting element at an arbitrary timing during the first exposure. Second exposure by current injection of
An electrostatic latent image evaluation method, comprising: measuring a change in width and area of an electrostatic latent image pattern formed by second exposure when the exposure time of the first exposure is variable.   4. The electrostatic latent image evaluation method according to claim 3, wherein a change in width and area of the electrostatic latent image pattern formed by the second exposure is within a time range in which the change is equal to or less than a predetermined value. A method for evaluating an electrostatic latent image, comprising: obtaining a maximum value of an exposure time in the exposure. Charging means and optical image exposure means for forming an electrostatic latent image pattern;
Charged particle beam scanning means for two-dimensionally scanning the electrostatic latent image pattern forming surface of the photoconductive sample on which the electrostatic latent image pattern is formed with a charged particle beam;
Charge particles in the electrostatic latent image pattern are detected by capturing charged particles that are electrically affected by the electrostatic latent image pattern and detecting the intensity signal corresponding to the position on the electrostatic latent image pattern forming surface. An electrostatic latent image evaluation device comprising an evaluation means for observing and evaluating a state,
The optical image exposure means is a semiconductor laser light emitting element,
An electrostatic latent image evaluation comprising: a light emission time control means for weak light emission caused by current injection below a light emission threshold in the semiconductor laser light emitting element; and a means for calculating the width or area of the electrostatic latent image pattern apparatus.   6. The electrostatic latent image evaluation apparatus according to claim 5, wherein the light emission time control means and the output control means by current injection above the light emission threshold in the light emitting element, and the weakness by current injection below the light emission threshold in the light emitting element. A latent image characteristic change detecting means for detecting an electrostatic latent image pattern formed by exposure in which both exposure by light emission and exposure by light emission by current injection exceeding the light emission threshold value are superimposed. An electrostatic latent image evaluation device.   7. The electrostatic latent image evaluation apparatus according to claim 5, wherein the optical image exposure unit includes an optical scanning unit.   An image forming apparatus, wherein the bias current value of the semiconductor laser light emitting element is set using the electrostatic latent image evaluation method according to claim 1.   An image forming apparatus, wherein the bias current value of the semiconductor laser light emitting element is set using the electrostatic latent image evaluation apparatus according to claim 5.

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