DE4438613C2 - Imaging device - Google Patents

Description

The invention relates to an image forming device having the features of claims 1 and generally relates to an image forming device for displaying image information on a light sensitive unit with the help of a laser beam.  

As an example of a conventional image forming device, there are for example an image generation device, which image information tion on a light-sensitive unit using a laser beam writes. In recent years, imaging has been used device, as described above, for the purpose of Often, a plastic lens is used to reduce costs or weight det.

Also related to the general distribution of images Generation devices, such as laser printers, laser facsimiles devices or laser copiers as well as in connection with the off stretching the scope of application Ability to change an image size evenly (or in terms of accuracy when changing an image size) higher and stricter been.  

From JP 3-132155 A an imaging device is known in which a light beam in Main scanning direction is moved. A light sensitive material is used Image information shown. This known image generation device has two Sensing devices that the deflected light beam at its respective end or Detect reversal points. The time between those given by the sensing devices Signals elapse with which they indicate that it detects the deflected light beam have is measured. During the measured time, a predetermined number of Pulses that are used as write clocks are generated. The predetermined number of In any case, pulses are generated even if the measured time should vary.

In this prior art, however, there is an offset in the pixels a sheet edge, since phase deviations of the detected pulses are not taken into account can.

It is the object of the present invention to provide an image forming device strike in which an offset of the pixels with respect to a sheet edge avoided can be.

This object is achieved by an image forming device with the in claim 1 listed features solved. Advantageous embodiments of the invention Generation device are defined in the subclaims.  

According to the invention, an image generation device is proposed for writing image information onto a light-sensitive unit using a laser beam, the device according to the invention comprising the following features:
a number of laser beam sensing devices over which the laser beam moves to sense and detect the laser beam in the main scanning direction, a write clock generating device, a constant clock signal source for emitting a clock signal with a constant frequency, a measuring device for a number of clocks of the constant clock signal source from one At a time at which a first of the number of laser beam sensing devices senses a laser beam until a time at which another laser beam sensing device senses the laser beam, a write frequency correction device to count the count value which has been measured by means of the measuring device to compare a previously set reference count value and to correct the write clock frequency so that the measured count value coincides with or substantially with the reference count value, the write clock generating device having a number of write clocks with the same frequency Frequency and different phases to each other, and a phase synchronization circuit selects from the number of write clocks whose phase comes closest to a synchronism detection signal that the first laser beam sensing device emits to the clock with this phase for write synchronization to use.

The invention based on preferred embodiment shape with reference to the accompanying drawings explained. Show it:

FIG. 1 is an explanatory view illustrating a configuration of a writing portion in an image forming apparatus according to a first embodiment of the invention;

Fig. 2 is an illustration for explaining a configuration of a write clocks generating circuit, and

Fig. 3 is a flowchart of operations of the write clock generating circuit according to the first embodiment.

An image forming device according to the invention is described in the order of a (first) embodiment 1 , an embodiment 2 , an embodiment 3 , an embodiment 4 and an embodiment 5 with reference to the corresponding figures in detail. Fig. 1 shows a configuration of a writing portion in an image forming apparatus according to an embodiment 1. In Fig. 1, a laser beam, which has been emitted by a laser diode 101 , reaches a polygonal mirror 102 . The polygon mirror 102 has an accurate polygonal shape and rotates in a constant direction at a constant rotation speed, which is determined by a rotation speed of a photosensitive drum 103 , a writing density and a number of areas of the polygon mirror 102 .

The laser beam is reflected at the polygonal mirror 102 and deflected by it ( 102 ). The deflected laser beam passes onto an fθ lens 104 which has a plastic lens to reduce costs and weight, which converts a scanning beam having a constant angular velocity so that scanning on the light sensitive drum 103 at a constant speed performed, kissing it on the photosensitive drum 103 fo so as to form a very small dot and further has a mechanism for correcting a disturbed image surface.

The laser beam which has passed the fθ lens 104 first reaches a position of a first laser beam detection sensor 105 , which is provided outside an image area, then passes over the light-sensitive drum 103 , also reaches a position of a second laser beam detection sensor 106 , which is provided outside the image area, and is recorded at any point. Here, the first laser beam detection sensor 105 and the second laser beam detection sensor 106 are laser beam sensing devices according to Embodiment 1, and in particular, the first laser beam detection sensor 105 plays the role of a synchronism detecting sensor to a laser beam scanning sync signal (a synchronism detection signal) to feel and determine.

When the first laser beam detection sensor 105 and the second laser beam detection sensor 106 receive a laser beam, the sensors output detection signals DETP1 and DETP2 to a write clock generating circuit 107 . In accordance with the detection signals DETP1 and DETP2, the write clock generating circuit 107 counts a very specific number of clocks from a point in time at which the first sensor 105 detects a laser beam to a point in time at which the second sensor 106 detects the laser beam the measured count value with the standard or reference count value, which will be described later, corrects the write clock frequency, so that the measured count value agrees with the reference count value, and outputs a write clock CLK₀ corresponding to the write clock frequency.

It should be noted here that the write clock generating circuit 107 outputs as a write clock CLK₀ a number of clocks, each having a different phase from one another. Likewise, the write clock generating circuit 107 corrects a write scale factor by generating a write clock, so that it could also be referred to as a scale factor correction circuit.

The write clock CLK₀, which has been output by the circuit 107 , is input to a phase synchronizing circuit 108 . Likewise, in the phase synchronizing circuit 108, the detection signal is inputted DETP1 described above, which each time a sampling is performed by a laser beam detecting sensor laser beam 105 is obtained from the first.

The phase synchronization circuit 108 selects from a number of write clocks CLK₀, each having a different phase to one another, a clock which has the phase closest to the synchronism detection signal, and outputs the clock as a write clock CLK to a laser drive circuit 109 . On the other hand, the laser drive circuit 109 causes the laser diode 101 to emit light corresponding to an image signal (image data) synchronized with the write clock CLK to generate an image and emits a laser beam.

Fig. 2 shows a configuration of the write clock generating circuit 107 , which has a counter 201 , flip-flops 202 to 204 , a control circuit 205 and a clock generating circuit 206 . Here, the counter 201 counts a clock ICLK for an input measurement and is deleted in accordance with the detection signal DETP1 by the first laser beam detection sensor 105 . The flip-flop (DFF1) 202 locks data in the counter 201 in accordance with the detection signal DETP2 from the second laser beam detection sensor 106 . Here, the locked data (the count value) indicate a time between scanning by means of the first laser beam detection sensor 105 and scanning by means of the second laser beam detection sensor 106 . Likewise, the flip-flop (DFF2) 203 and the flip-flop (DFF3) 204 are circuits, each of which synchronizes a timing control for locking the detection signal DETP2 from the second laser beam detection sensor 106 into an input clock at the counter 201 .

The control circuit 205 sets an on / OC signal from the flip-flop 202 from "H" (high) to "L" (low), reads a locked count, compares a measured count with the standard or reference count, and corrects it a write clock frequency, so that the measured count value coincides with the standard or reference count value.

It should be noted here that the clock generating circuit (PLL) 206 generates a number of clocks CLK₀, each having a different phase to one another, with a frequency which corresponds to data which have been output by the control circuit 205 .

Next, referring to the configuration as described above, referring to the configuration of the write clock generating circuit 107 shown in FIG. 2 and referring to the operation of the write clock generating circuit 107 shown in FIG. 1 described.

First, the counter 201 is cleared in accordance with the detection signal DETP1 from the first laser beam detection sensor 105 ; the clock ICLk for a measurement is counted by means of the counter 201 ; Data in the counter 201 is latched by the flip-flop (DFF1) 202 in accordance with the detection signal DETP2 from the second laser beam detection sensor 106 , and a measurement is made for a time (count) between scanning by the first laser beam detection Setting sensor 105 and the scanning by means of the second laser beam detection sensor 106 performed (S301).

Then, the control circuit 205 sets an / OC signal from the flip-flop 205 from "H" to "L", reads a locked count, makes a determination as to whether any error was made during an operation to correct the scaling factor (S302) , performs error correcting processing when any error (such as an abnormal count) is detected, displays the content of the generated error as a message from a higher level controller (S303), and sets a write clock frequency to a specific write clock frequency (a predetermined standard or reference write clock frequency, or a write clock frequency if an adjustment of the initial clock has been made, or a write clock frequency corrected immediately before the error is generated) (S304) to close the process break up.

On the other hand, if it is determined that no error has been generated (that the count is normal), the control circuit 205 compares the measured count T1 with the standard or reference count T0 (S305) and makes a determination as to whether the measured count T1 is actual or does not agree with the standard count value T0 (S306). If T1 is substantially the same as T0 (T1 substantially coincides with T0), the process is ended.

Although a range in which it is determined that T1 is substantially the same as T0 depends on the resolving power of the clock generating circuit 206 which generates a write clock in accordance with corrected data for the write clock frequency output from the control circuit 205 when the Write clock for a count timing signal is used to measure a count between scanning by the laser beam detection sensor 105 and scanning by the laser beam detection sensor 106 , it is possible to control a write clock frequency with an accuracy that corresponds to a clock of the Write clock corresponds, so that a range of ± 1 to about ± 5 should be set taking into consideration such restrictions as a time required for the processing. Of course, if the condition T1 = T0 (the measured counter T1 completely matches the standard reference value T0 (error = 0)) is used instead of the condition T1 ≒ T0, the accuracy in correcting the write clock frequency becomes higher.

Conversely, if T1 is not substantially equal to T0, it is determined whether the measured count T1 is larger or smaller than the standard or reference count T (S 307), and if T1 is smaller than T0, the write clock frequency is decreased so that T1 becomes greater than T0 (S308); then control returns to step S301, and again a time (a count) is measured between scanning by the first laser beam detection sensor 105 and scanning by the second laser beam detection sensor 106 . If T1 is not less than T0, the write clock frequency is increased so that the count T1 becomes less than T0 (S308); then control returns to step 301, and again a time (a count) between a scan by the first laser beam detection sensor 105 and the scan by the second laser beam detection sensor 106 is measured.

As described above, in Embodiment 1, a scaling factor can be automatically corrected in accordance with changes in the optical characteristics of a scanning optical system to focus a laser beam used for scanning on an image recording surface of the photosensitive drum 103 to an image in view to produce changes in peripheral conditions or with regard to other causes. Also, as shown in the flowchart in Fig. 3, the write clock frequency control sequence includes a feedback loop (a loop to return from steps S308 and S309 to step S301) so that precise control over frequency can be performed. By storing correction data in the initial scale factor setting in the device, it is also possible to perform an initial scale factor setting and a time-series correction of the scale factor with the same configuration.

If a time between a scan using a laser beam detection sensor and a scan using another laser beam detection sensor or other sensors is measured by counting a number of clocks with a counter, processing of the count value (a determination of whether the count value is normal or is abnormal, or computing for correction) is generally very complicated when a frequency of the input clock changes; however, in Embodiment 1, the count processing can be simplified and the workload on the control circuit 205 can be substantially reduced by setting a clock for measuring the standard count (namely, a clock ICLK for a measurement) to a specific one constant frequency is set.

When a case occurs in which a measurement of a sampling time is unusable due to some error while correcting a scaling factor, such as an error exceeding a certain correction range, or a breakage of a laser beam detection sensor, or even when a correction of a scaling factor is unnecessary bar, the control circuit 205 detects the error, interrupts the correction process and sets a specific write clock (the previously set standard or reference write clock frequency or a write clock frequency if the write clock setting was carried out initially, or a write clock frequency which occurs immediately before has been corrected to generate the error) at step 5304 described above. In the configuration as described above, a state in which an image forming device cannot form an image is prevented, and the operation of the device can even be maintained, b an error has occurred. However, this does not apply to such errors as an interruption in a synchronism sensing signal emitter since it becomes impossible to form an image. In other words, even if an error that does not cause much disturbance in image formation occurs while correcting a scaling factor, the error can be temporarily bypassed.

On the other hand, when such an error occurs as described above and the error is processed in the write clock generating circuit 107 , control sections at a higher level control the image forming device from this control circuit without recognizing this error and assume that the Imaging device is in the normal state. For this reason, when such an error occurs, in the error processing at step S303 as described above, the content of the generated error is reported as a message to a control section at a higher level from this operation when the higher control sections receive a warning hand over to an operator or higher systems according to the error message so that the error is quickly avoided or circumvented. Also, as described above, an operation of the image forming device can be continued without an image quality being significantly deteriorated even during a waiting time in the event of an error bypass.

Also, with the aid of a laser beam detection sensor which has been used to measure a scanning time when the laser is turned on in a certain position of the laser beam sensing sensor, a detection signal for a light source can be obtained when main scanning is performed. For this reason, by using a detection signal from the first laser beam detection sensor 105 as a synchronism detection signal to generate a control signal for a write clock phase synchronism or image recording, a laser beam detection device can be used for both measuring a sampling time and for sensing and detecting a synchronism detection signal can be used, so that the system configuration can be simplified and the number of components required can be reduced, so that the effect of a cost reduction is achieved.

Correction of a write clock frequency in the write clocks generated by the circuit 107 can in principle be carried out with a time control which excludes the time for image generation. However, a correction of a write clock (a correction of a scaling factor) is carried out in the present invention in order to obtain excellent image quality even with changes in the environmental conditions of the image forming device, so that it is desirable to adjust the timing to correct (set) keep a write clock frequency as close as possible to the timing controller for imaging. For example, if a timing for correcting a write clock frequency is set to a time when a start key is pressed, image formation is carried out only after correction of a scaling factor, so that outputting high quality images can be maintained without successive changes in the images peripheral conditions. Or in a case where a number of frames (fields) are generated by pressing the start key once and a time for correcting a write clock frequency in a clock zone in a continuous recording operation from a point in time when a field is recorded until is set at a time when the next field is recorded, image quality can be prevented from deteriorating due to such causes as an increase in the ambient temperature in continuous operation, and thus outputting a high quality image can be maintained.

Configuration and operations in Embodiment 2 are the same as those in Embodiment 1 except that when a clock frequency ICLK for measuring the standard / reference count is set to a constant value, the constant value is used as a certain constant write clock frequency; with this configuration, the workload on the control circuit 105 can be significantly reduced.

A number of clocks CLK₀, each having different phases, and which have been output by the write clock generating circuit 107 are input into the phase synchronization circuit 108 . In the phase synchronizing circuit 108 , a synchronism detection signal is input, which is obtained every time a scanning is performed by means of a laser beam (a detection signal DETP1 from the first laser beam detection sensor 105 ); the phase synchronizing circuit 108 selects from a number of clocks CLK₀, each having a different phase and output from the clock signal generating circuit 107 , a clock having a phase closest to that of the synchronism detection signal and outputs the clock as a write clock CLK. For this reason, a write clock with a small phase error can be obtained every time a scanning is performed by a laser beam (the laser scanning direction is referred to as the main scanning direction and the direction perpendicular to the laser scanning direction is called the sub-scanning direction).

As described above, operations such as a counter reset or a data hold are performed in accordance with a signal that is synchronized with respect to a main scanning cycle in measuring a time period between scanning by means of a laser beam detection sensor and scanning by means of another laser beam detection sensor to correct a scaling factor so that in Fig. 2, using a constant write clock which is substantially synchronized with a synchronism detection signal for a main scan as an input clock (ICLK) for the counter 201 , a count error due to a phase shift between a detection signal from a laser beam detection sensor and a clock is closed, and a time measurement between scanning by means of a laser beam detection sensor and scanning by means of another laser beam detection sensor can be performed with high accuracy. Also, when timing between scanning by laser detection sensors using a write clock is performed when conditions for recording using an image forming device change, a write clock according to the new recording condition can be used, so that the need for the control circuit 205 change, can be reduced, and a very versatile imaging device can be created.

Configuration and operations in Embodiment 3 are the same as those in Embodiment 1 except that a frequency of a clock ICLK for measuring the standard or reference count is used as a basic write clock frequency before correction. It should be noted that the basic write clock frequency is set according to conditions for recording by an image forming device.

In the embodiment 3 , in addition to the effects realized in the embodiment 1 , it is not necessary to add a number of data types for a frequency (such as data for the basic write clock frequency, data for a write clock frequency when a correction is initially made) in the control circuit 205 manage. For this reason, even if an initial correction for temporally successive changes in an image forming device is required, it is only necessary to set a frequency of the clock ICLK for measuring the standard or reference count value at the standard write clock frequency so that the operation is not affected by previous correction data and it is possible to perform a reset using a relatively simple configuration.

Configuration and operations in Embodiment 4 are the same as those in Fig. 1, except that a count value measured by the counter 201 when a clock setting was initially made is used as the standard count value.

The standard count value, which is used as a reference value for frequency control in the write clock generating circuit 107 , need not be set for each image forming device if a spread in the time between scanning by a number of laser beam detection sensors or in optical characteristics of an optical one Scanning systems such as the polygon mirror 102 , the fθ lens 104 and the like, or a change in the time interval due to deformation or other temporal changes is so small that it can be ignored; in practice, however, it is difficult to suppress scattering between imaging devices, and it is known that the optical characteristics change in connection with a temperature fluctuation in each imaging device, and the change can have some influence on the output image quality.

In contrast, in Embodiment 4, a count value measured when an initial correction has been made is used as the standard or reference count value so that the reference count value can be set for each imaging device and an influence by scattering optical ones Characteristics between different devices can be suppressed. As a result, a highly accurate correction of a scaling factor is realized.

Configuration and operations in Embodiment 5 are the same as those in Embodiment 1 except that unless the clock generating circuit 107 does not measure a time or a number of clocks between scans by means of laser beam detection sensors, no light from one laser to one position is emitted, which corresponds to one or more units (here the second laser beam detection device 106 ) corresponds to a number of laser beam detection sensors (here two units).

As described in relation to Embodiment 1 , when a time between a scan by means of a laser beam detection sensor and a scan by another laser beam detection sensor is measured to correct a write clock, the correction accuracy can be increased by one Sampling time is measured during the correction in order to correct a scaling factor. In Fig. 2, a time between scanning by means of two laser beam detection sensor units (a count value measured by means of the counter 201 ) by resetting the counter 201 in accordance with the detection signal DETP1 from the second laser beam detection sensor 106 and in accordance with holding dates in the counter the detection signal DETP2 measured by the second laser beam detection device 106 , so that it is no longer necessary to enter a detection signal in the circuit shown in FIG. 2, if it is not necessary, the sampling time in a time zone and not in a time period to measure for a scaling factor correction. For this reason, an image forming device is designed and arranged such that when a measurement of a time between scans by means of laser beam detection sensors or a count value is not carried out, no light is emitted from a laser to a position which corresponds to at least one or more laser beams -Detach sensor units that are required to measure sampling time. Therefore, the life of a laser or a photoelectric converter or that of light-sensitive material and the like which has been used for recording images can be extended.

In the configuration shown in FIG. 2, when the detection signal DETP2 is always output from the second laser beam detection sensor 106 (by emitting light from a laser to a position corresponding to a laser beam detection sensor), if a time to one Retrieve measurement result in a control circuit when a write clock is corrected, coincides with a time to output the signal DETP2, the measurement result is normally not fetched and queried. In a similar case, it becomes necessary to perform such processing as controlling the time to fetch and retrieve the measurement result in order to synchronize it with a time to output the signal DETP2. Therefore, in Embodiment 5 , if light is not emitted from a laser to a position corresponding to the second laser beam detection sensor 106 , time control can be omitted, and the measurement result can be called up asynchronously, so that a control circuit is simplified can be.

It should be noted that although a plastic lens such as the fθ lens 104 is used in the above-described Embodiments 1 to 5 , high image quality can be obtained while maintaining the ability to smoothly change the size of images ; the same effect can be achieved without being affected by changing the scanning speed even when a conventional glass lens is used. Likewise, the number of laser beam detection sensors is not always limited to two (2) units, and of course the same effect can be achieved with the help of two or more laser beam detection sensors.

Claims (7)

1. An image forming device for writing image information onto a light-sensitive unit using a laser beam, having the following features:

• - A number of laser beam sensing devices ( 105 , 106 ) over which the laser beam moves in each case for sensing and detecting the laser beam in the main scanning direction;
• - a write clock generator;
• - a constant clock signal source for delivering a clock signal (ICLK) with constant frequency;
• - a measuring device ( 201 ) for counting a number of cycles of the constant clock signal source from a point in time at which a first of the number of laser beam sensing devices ( 105 ) senses the laser beam to a point in time at which another laser beam sensing device ( 106 ) feels the laser beam;
• - A write frequency correction device ( 107 ) to compare the count value, which has been measured by means of the measuring device ( 201 ), with a previously set reference count value and to correct the write clock frequency, so that the measured count value with or essentially with the reference count value coincides, wherein the write clock generation device ( 107 ) generates a number of write clocks (CLK₀) with the same frequency and different phases to each other; and
• - A phase synchronization circuit ( 108 ) selects from the number of write clocks (CUK₀) whose phase comes closest to a synchronism detection signal (DETP1), which the first laser beam sensing device emits to write the clock with this phase Synchronization to use.

2. Imaging device according to claim 1, characterized in that the certain constant clock frequency is a basic write clock frequency before one Correction is carried out. 3. Imaging device according to claim 1, characterized in that the Write frequency correction device is activated only at predetermined times. 4. Imaging device according to claim 3, characterized in that the predeterminable time is the pressing of a start button. 5. Imaging device according to one of claims 3 or 4, characterized records that the specifiable time between two fields in a continuous Is recording mode. 6. Imaging device according to one of claims 3 to 5, characterized in that when the write frequency correction device ( 107 ) is out of operation, a laser beam is emitted only at positions which are within the number of laser beam sensing devices ( 105 , 106 ). 7. Imaging device according to one of claims 1 to 6, characterized in that the write frequency correction means ( 107 ), if a too large error occurs to correct the write clock frequency, a write clock frequency to a predetermined reference write clock frequency, to a write clock frequency that has been previously set when a write clock setting has been made at a designated time or sets to a write clock frequency that has been corrected immediately before the error occurs, and ends the correction process.