JP4407922B2 - Image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus (printer, copier, facsimile, etc.) that scans a light beam on a photoreceptor to generate an electrostatic latent image and forms an image on a sheet or the like. In particular, the present invention relates to an auto power control technique for the light emitting element.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus generates an electrostatic latent image by raster scanning a light beam on a charged photosensitive member, and transfers a toner image attached to the electrostatic latent image onto a sheet or the like. Thus, an image is formed.

  Further, as shown in FIG. 4A, the conventional image forming apparatus has a non-image forming period in which the image data signal VIDEO is not input (the non-image forming period between the recording materials or the same as shown in FIG. 4A). During the non-image formation period between the lines in the recording material), the light emitting element is forced to emit light, and the monitor voltage corresponding to the intensity of the light beam at that time is charged in the capacitor, and the subsequent image formation start timing In (trigger timing of the light beam detection signal BD), the light beam intensity feedback control based on the sample hold voltage SH charged in the capacitor, that is, a structure having a so-called auto power control function (for example, , See Patent Document 1).

As another conventional technique related to light beam emission control, a technique for optimizing the horizontal synchronization signal timing in an image forming apparatus using a plurality of light emitting elements has been disclosed and proposed (for example, Patent Documents). 2).
Japanese Patent Laid-Open No. 11-311881 JP 2000-2014 Gazette

  Certainly, if the image forming apparatus has the above auto power control function, it is possible to prevent fluctuations in the intensity of the output light beam, so that it is always desired regardless of variations in light emitting elements, thermal characteristics, etc. It is possible to perform image formation.

  However, in the conventional image forming apparatus, as shown in FIG. 4A, the sample hold voltage SH reaches the desired value VH in order to avoid the discharge of the sample hold voltage SH during the auto power control. Thereafter, the forced light emission of the light beam is continued until the non-image forming period ends. Therefore, there has been a problem that the lighting time of the light emitting element is unnecessarily long, the power consumption is increased, and the heat generation of the light emitting element is a factor for shortening the lifetime.

  As the simplest means for solving the above problem, as shown in FIG. 4B, a configuration in which the start of charging the monitor voltage is delayed to shorten the sampling period can be considered. However, in such a configuration, it is difficult to optimize the sampling period. If the period is too short, the sample hold voltage SH does not reach the desired value VH at the image formation start timing, and the intensity of the light beam is low. There is a problem that there is a possibility that the level does not reach a level sufficient to detect the light beam detection signal BD.

  Further, in Patent Document 2, no consideration or mention is made regarding forcible lighting time reduction of the light emitting element during auto power control.

  SUMMARY OF THE INVENTION In view of the above-described problems, an object of the present invention is to provide an image forming apparatus capable of shortening the forced lighting time of a light emitting element without hindering the operation during auto power control of the light emitting element. .

In order to achieve the above object, an image forming apparatus according to the present invention includes a light emitting means for outputting a light beam, a monitor voltage generating means for generating a monitor voltage corresponding to the intensity of the light beam, and sampling the monitor voltage. A sample hold means for holding; a light emission drive means for driving the light emission means in accordance with a sample hold voltage obtained by the sample hold means; a timing generation means for controlling the drive timing of the light emission means and the sample hold means; A comparison means for comparing the sample and hold voltage with a predetermined reference voltage, and a required charging time from the start of sampling of the monitor voltage until the sample and hold voltage reaches the reference voltage. become further comprises a timer means for measuring, and the non-image forming period, the Timing generating means, to said light emission driving means and said sample-hold means, after instructing the start of sampling driving start and the monitor voltage of the light emitting means, the first time when the sample and hold voltage reaches the reference voltage After instructing the temporary stop of the operation of the light emission driving means and the sample hold means, the time decreases from the first time point to the second time point when the operation of the light emission driving means and the sample hold means is resumed. Calculating the second time point at which the sample and hold voltage reaches the reference voltage between the second time point and the third time point when the end of the non-image forming period is recognized, At the second time point, the configuration is such that the restart of the operation of the light emission drive means and the sample hold means is instructed.

  In the image forming apparatus according to the present invention, the forced lighting time of the light emitting element can be shortened without hindering the operation when the automatic power control of the light emitting element is performed. It is possible to improve the service life.

  FIG. 1 is a block diagram showing a main configuration of the image forming apparatus according to the present invention (around the light emitting unit of the image forming unit). As shown in the figure, the image forming apparatus according to the present embodiment includes a laser diode 1, a photodiode 2, and a current / voltage conversion unit 3 (hereinafter referred to as an I / V conversion unit 3) as the main components. ), A sample hold processing unit 4, a drive current generation unit 5, a laser diode drive unit 6 (hereinafter referred to as an LD driver 6), a beam detector 7, and a timing generation unit 8, An electron that forms an image by raster scanning a light beam on a charged photoreceptor (not shown) to generate an electrostatic latent image, and transferring a toner image attached to the electrostatic latent image onto a sheet or the like. This is a photographic image forming apparatus. Of the above-described main components, the laser diode 1, the photodiode 2, the I / V conversion unit 3, the drive current generation unit 5, and the LD driver 6 are packaged in the same semiconductor chip.

  The laser diode 1 is a light emitting means for outputting a light beam. From both ends of the light emitting surface, the front light beam LF for raster scanning the photoconductor to generate an electrostatic latent image, and its auto power control. Two necessary rear light beams LB are output.

  The photodiode 2 receives the rear light beam LB and outputs a current signal whose current level varies according to the intensity thereof. The I / V converter 3 converts the current signal into a voltage and outputs a monitor voltage MON whose voltage level varies according to the current signal.

  The sample hold processing unit 4 samples and holds the monitor voltage MON based on the auto power control signal APC from the timing generation unit 8 and outputs the obtained sample hold voltage SH. The configuration and operation of the sample hold processing unit 4 will be described in detail later.

  The drive current generation unit 5 generates a drive current for the laser diode 1 based on the sample hold voltage SH. The LD driver 6 performs drive control (light on / off switching control) of the laser diode 1 based on the image data signal VIDEO from the image data generation unit (not shown) and the auto power control signal APC from the timing generation unit 8. At that time, the LD driver 6 performs drive control of the laser diode 1 in accordance with the drive current set by the drive current generator 5.

  The beam detector 7 receives a front light beam LF reflected by a polygon mirror (not shown), and generates a light beam detection signal BD for detecting the scanning position (scanning timing). The polygon mirror described above is a polygon mirror that rotates at a predetermined rotational speed, is provided in the light guide path of the front light beam LF, and reflects the incident front light beam LF in a predetermined angular range, An optical member that repeatedly scans the photosensitive member.

  The timing generation unit 8 controls the turn-on / off timing of the laser diode 1 and the sample hold timing of the sample hold processing unit 4 based on the above-described light beam detection signal BD in the auto power control of the laser diode 1. Auto power control signal APC is generated, and the signal is output to the sample hold processing unit 4 and the LD driver 6, respectively. In addition to the auto power control signal APC, the timing generator 8 also generates a clock signal that serves as an operation reference for each part of the apparatus and a horizontal synchronization signal (not shown) for instructing the scan start timing. Output. The configuration and operation of the timing generation unit 8 will be described in detail later.

  Although not shown in the figure, the image forming apparatus according to the present embodiment is formed on a sheet, a display unit for displaying various information, an operation unit for receiving user operations, in addition to the above components. A fixing unit that heats and fixes an image, a paper feeding unit that serves as a paper supply source to the image forming unit, a memory unit that is used as a storage area for control programs and a development area for image data, and information that is connected via a network Various circuit elements such as a communication unit that communicates with the processing device, a modem that converts image data into a facsimile signal, and a network control unit that establishes a connection with a public telephone line are provided.

  Next, the internal configuration and operation of the sample hold processing unit 4 and the timing generation unit 8 will be described in more detail with reference to FIG. FIG. 2 is a block diagram (including a partial circuit diagram) illustrating a configuration example of the sample hold processing unit 4 and the timing generation unit 8.

  As shown in the figure, the sample hold processing unit 4 of the present embodiment includes a switch 41 and a capacitor 42. One end of the switch 41 is connected to the output end of the I / V conversion unit 3, and the monitor voltage MON is applied to the one end. The other end of the switch 41 is grounded via the capacitor 42 and is also connected to the input end of the drive current generator 5 and one input end of a comparator 82 described later. The open / close control end of the switch 42 is connected to an output end of an auto power control signal generation unit 83 described later, and the auto power control signal APC is applied to the one end.

  In the sample hold processing unit 4 configured as described above, the switch 42 is closed in response to the assertion (for example, high level) of the auto power control signal APC, and is opened in response to the negation (for example, low level). Therefore, the assertion period of the auto power control signal APC is a period in which the capacitor 42 is charged by the monitor voltage MON, and the negation period is a period in which the charge voltage is held. In other words, the assertion period of the auto power control signal APC is a sampling period of the monitor voltage MON, and the negation period is a holding period of the monitor voltage MON.

  On the other hand, the timing generation unit 8 of the present embodiment includes a reference voltage generation unit 81, a comparison unit 82, an auto power control signal generation unit 83, and a reference data storage unit 84.

  The reference voltage generation unit 81 generates a reference voltage VH used for comparison reference with the sample hold voltage SH. The comparison unit 82 compares the sample and hold voltage SH with the reference voltage VH to generate a comparison signal D1. The auto power control signal generation unit 83 controls assertion / negation of the auto power control signal APC based on the light beam detection signal BD, the comparison signal D1, and the reference data D2. The auto power control signal generator 83 includes a timer 83a that measures the required charging time from the start of sampling of the monitor voltage MON until the sample hold voltage SH reaches the reference voltage VH. The reference data storage unit 84 stores reference data D2 necessary for assertion / negate control of the auto power control signal APC. The contents of the reference data D2 will be described in detail later.

  Hereinafter, with respect to the operations of the sample hold processing unit 4 and the timing generation unit 8 having the above-described configuration, an example in which auto power control is performed during a non-image forming period between lines in the same recording material will be described with reference to FIG. Specific explanation will be given. FIG. 3 is a diagram for explaining an example of auto power control in the present embodiment. FIGS. 3A and 3B show a light beam detection signal BD, an auto power control signal APC, and a sample hold voltage SH. The transition state of the image data signal VIDEO over time is shown.

  In the timing generation unit 8 configured as described above, the auto power control signal generation unit 83 asserts the auto power control signal APC when it recognizes the end of the image formation period (that is, the start of the non-image formation period). Thereby, the LD driver 6 is instructed to forcibly emit light from the laser diode 1, and the sample hold processing unit 4 is instructed to start sampling of the monitor voltage MON.

  In this figure, the voltage is already charged in the capacitor 42 at the start of the non-image forming period, and the sample hold voltage SH is not zero level. However, this was sampled and held before the start of the previous line scan. This is because the voltage remains without being discharged.

  Thereafter, the auto power control signal generator 83 monitors the comparison signal D1, and once the sample hold voltage SH reaches the reference voltage VH, the auto power control signal APC is once negated. As a result, the LD driver 6 is instructed to turn off the laser diode 1, and the sample hold processing unit 4 is instructed to stop sampling (holding start) of the monitor voltage MON.

  On the other hand, the auto power control signal generator 83 uses the built-in timer 83a to temporarily calculate the required charging time T1 from the start of the previous sampling until the sample hold voltage SH reaches the reference voltage VH when the sampling period is suspended. measure.

  Then, the auto power control signal generation unit 83 considers that the total time T of the non-image forming period is a fixed value determined according to the scanning speed of the laser diode 1 and the paper size, based on the required charging time T1. The remaining time (T-T1) of the non-image forming period is recognized.

  Further, the auto power control signal generation unit 83 uses the above remaining in order to make the sample hold voltage SH reach the reference voltage VH at the end of the non-image forming period based on the measured required charging time T1 and the reference data D2. Of the time (T-T1), how many light emission stop periods can be recognized, in other words, how many re-sampling periods are required before the end of the non-image forming period is calculated.

  More specifically, the auto power control signal generator 83 charges the amount of charge discharged from the capacitor 42 during the light emission stop period and recharges during the re-sampling period in the remaining time (T-T1). Sampling restart timing is calculated so that the charge amount matches. The auto power control signal APC is continuously negated until the sampling resumption timing obtained by the calculation process is reached.

  For example, when the required charging time T1 is relatively long as shown in FIG. 9A, the auto power control signal generator 83 has a short remaining time (T-T1) and is discharged during the subsequent light emission stop period. In view of the small amount of charge to be recharged, the recharge time T2 assigned to the re-sampling period is set to be relatively short. On the other hand, when the required charging time T1 is relatively short as shown in FIG. 5B, the recharging time T2 is set relatively long. Although not shown in the figure, if the required charging time T1 is longer than a predetermined value, the light emission is forcibly turned on without terminating the sampling period in view of the fact that the light emission must be resumed immediately after the light emission is stopped. It does not matter as a configuration to continue

  The reference data D2 includes the light emission performance of the laser diode 1, the light reception performance of the photodiode 2, the conversion performance of the I / V conversion section 3, the charge / discharge performance of the capacitor 42, the reference voltage VH, and the non-image forming period. In consideration of the total time T and the like, a data table or the like associated with the required charging times T1 and T2 may be provided based on considerations obtained from various experimental results, simulation results, and empirical rules.

  On the other hand, if the recharge time T2 is set uniformly without measuring the required charge time T1, the recharge time T2 with respect to the remaining time (T-T1) is too long as in the prior art, and the laser diode 1 When the forced lighting time becomes unnecessarily long, or conversely, the recharge time T2 with respect to the remaining time (T-T1) is too short, and the sample hold voltage SH may not reach the reference voltage VH. Care must be taken because it may cause problems.

  Thereafter, the auto power control signal generator 83 asserts the auto power control signal APC again when it is recognized that the sampling resumption timing has arrived based on the recharge time T2. As a result, the LD driver 6 is instructed to re-emit the laser diode 1, and the sample hold processing unit 4 is instructed to resume sampling of the monitor voltage MON.

  After resuming the sampling, the auto power control signal generator 83 negates the auto power control signal APC when it recognizes the end of the non-image forming period (that is, the start of the image forming period) based on the light beam detection signal BD. To do. As a result, the LD driver 6 is instructed to turn off the laser diode 1, and the sample hold processing unit 4 is instructed to stop sampling (holding start) of the monitor voltage MON. At this time, since the sample hold voltage SH has reached the reference voltage VH, the detection of the light beam detection signal BD is normally performed, and thereafter, the light beam intensity is based on the sample hold voltage SH charged in the capacitor 42. The feedback control is performed. Therefore, fluctuations in the intensity of the output light beam can be prevented, and desired image formation can always be performed without depending on variations in the laser diode 1, thermal characteristics, or the like.

  As described above, in the image forming apparatus according to the present embodiment, the timing generation unit 8 instructs the LD driver 6 and the sample hold processing unit 4 to start driving the laser diode 1 and start sampling the monitor voltage MON. When the sample and hold voltage SH reaches the reference voltage VH, a temporary stop of the both operations is instructed, and then a restart of the both operations is instructed at a timing corresponding to the required charging time T1. By adopting such a configuration, when the auto power control of the laser diode 1 is performed, the forced lighting time of the laser diode 1 can be shortened without hindering the operation thereof. It is possible to improve the service life of.

  In the above embodiment, the operations of the sample hold processing unit 4 and the timing generation unit 8 will be described by taking as an example a case where auto power control is performed during a non-image forming period between lines in the same recording material. However, the application target of the present invention is not limited to this, and can naturally be applied to the case where auto power control is performed during the non-image forming period between the recording materials.

  The configuration of the present invention can be variously modified within the scope of the present invention in addition to the above embodiment.

  The present invention is a useful technique for reducing power consumption and extending the life of a light emitting element mounted on an electrophotographic image forming apparatus.

FIG. 2 is a block diagram showing a main configuration of an image forming apparatus according to the present invention. FIG. 3 is a block diagram (including a partial circuit diagram) illustrating a configuration example of a sample hold processing unit 4 and a timing generation unit 8. These are the figures for demonstrating an example of the auto power control in this embodiment. These are figures for demonstrating one prior art example of auto power control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser diode 2 Photodiode 3 Current / voltage conversion part (I / V conversion part)
4 Sample hold processing unit 41 Switch 42 Capacitor 5 Drive current generation unit 6 Laser diode drive unit (LD driver)
7 Beam Detector 8 Timing Generation Unit 81 Reference Voltage Generation Unit 82 Comparison Unit 83 Auto Power Control Signal Generation Unit 83a Timer 84 Reference Data Storage Unit

Claims (1)

A light emitting means for outputting a light beam;
Monitor voltage generating means for generating a monitor voltage according to the intensity of the light beam;
Sample-hold means for sample-holding the monitor voltage;
A light emission drive means for driving the light emission means in accordance with a sample hold voltage obtained by the sample hold means;
Timing generation means for controlling drive timing of the light emitting means and the sample hold means;
In an image forming apparatus comprising:
A comparison means for comparing the sample and hold voltage with a predetermined reference voltage;
Timer means for measuring a required charging time from the start of sampling of the monitor voltage until the sample and hold voltage reaches the reference voltage;
And further comprising
In the non-image forming period,
The timing generation means includes
After instructing the light emission drive means and the sample hold means to start driving the light emission means and start sampling the monitor voltage, the light emission drive means at a first time when the sample hold voltage reaches the reference voltage. and after instructing to suspend the operation of the sample hold means,
The sample hold voltage, which decreases from the first time point to the second time point when the operation of the light emission driving unit and the sample hold unit is resumed, is the end of the non-image forming period from the second time point. Calculating the second time point such that the reference voltage is reached by a recognized third time point;
An image forming apparatus characterized by instructing to restart the operation of the light emission driving unit and the sample hold unit at the second time point .

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