Scanning timing detection device and image forming device

Abstract

To prevent timing for starting formation of an electrostatic latent image on a surface of a photoreceptor drum from changing even in a case where one light reception element is used and the light intensity and beam diameter of a light beam change.SOLUTION: A scan timing detection device comprises: an optical detection unit having one light reception element which receives a light beam and a detection signal generation part which generates a light detection signal corresponding to the light reception intensity of the received light beam; and a synchronous signal generation unit which generates a synchronous signal for deciding timing for emitting the light beam to a scam start position of the light beam scanning a scan object body by comparing the light detection signal with prescribed comparison voltage. The light detection signal is made of a detection AC signal being the AC component of the detection signal that changes correspondingly to the light reception intensity of the light beam. The scan timing detection device generates the synchronous signal by comparing the comparison voltage offset with respect to the voltage level of the detection AC signal in a case where there is no change in the light detection signal with the voltage level of the detection AC signal immediately after the light beam is detected and the light detection signal changes.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a scanning timing detection device, and more particularly to a scanning timing detection device for determining the start timing of scanning a light beam that is irradiated onto a photosensitive drum when forming an electrostatic latent image on the surface of the photosensitive drum, and an image forming apparatus equipped with this scanning timing detection device. [Background technology]

[0002] Conventionally, image forming devices have been equipped with an exposure device that irradiates a photosensitive drum with a light beam, and the light beam is scanned across the surface of the photosensitive drum, which is charged to a predetermined potential, to form an electrostatic latent image on the surface of the photosensitive drum. Furthermore, a light beam detection device is provided to determine the timing to start scanning with the light beam, and a BD sensor (beam detect sensor) made up of a photodiode, which is a light receiving element, is provided near the photosensitive drum.

[0003] When the BD sensor is irradiated with the light beam by scanning, the photodiode outputs a detection signal having a magnitude corresponding to the amount of light of the light beam. The timing (write start timing) for starting to form an electrostatic latent image on the surface of the photosensitive drum is set based on the position of the peak of the magnitude of this detection signal. In conventional image forming apparatuses, there are those that use one photodiode to set the write timing, and those that use two photodiodes to set the write timing.

[0004] For example, in Patent Document 1, one BD sensor is used, the voltage value of the detection signal output from the BD sensor is compared with a predetermined threshold voltage, a predetermined synchronization signal is output when the detection signal exceeds the threshold, and the write timing is set based on the change in the signal level of the synchronization signal.

[0005] In addition, in Patent Document 2, two photodiodes are used, and the two photodiodes are arranged at a predetermined interval so that the scanned light beam is irradiated sequentially onto the light receiving surfaces of the two photodiodes, and the voltage values ​​of the detection signals output from the two photodiodes are compared. Since the voltage value of each detection signal changes depending on the amount of light received from the light beam, a synchronization signal is output that changes at the point where the voltage values ​​of the two detection signals cross, and the timing at which the voltage values ​​of the two detection signals cross is set as the write timing based on the change in the signal level of the synchronization signal. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-134381 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-123872 Summary of the Invention [Problem to be solved by the invention]

[0007] However, it is known that the light intensity and beam diameter of the light beam change due to temperature changes around the image forming apparatus, aging, and the like, and it is difficult to always keep the light intensity and beam diameter constant. When the light intensity of the light beam changes, the magnitude of the detection signal changes, and the slope of the signal waveform leading to the peak of the detection signal also changes, causing a shift in the write start timing. Furthermore, when the beam diameter of the light beam changes, the slope of the signal waveform leading to the peak of the detection signal changes, causing a shift in the write start timing.

[0008] Conventional light beam detection devices using one photodiode can reduce device costs compared to devices using two photodiodes, but when the light intensity or beam diameter of the light beam changes, as described above, the slope of the signal waveform of the detection signal changes, making it difficult to accurately adjust the write timing. Furthermore, conventional light beam detection devices using two photodiodes can improve the accuracy of write timing compared to devices using a single photodiode, but require a device in which the two photodiodes are precisely positioned, and the use of two photodiodes results in increased costs, which has been an issue.

[0009] Therefore, this invention has been made in consideration of the above circumstances, and has an object to provide a low-cost scan timing detection device that uses a single photodiode to set the write timing, and that prevents the timing (write timing) at which an electrostatic latent image starts to be formed on the surface of a photosensitive drum from changing even when the light intensity or beam diameter of the light beam changes, and an image forming apparatus that is equipped with the scan timing detection device. [Means for solving the problem]

[0010] The present invention provides a scan timing detection device comprising: an optical scanning unit comprising a light source that emits a light beam and an optical scanning unit that changes the irradiation direction of the light beam; an optical detection unit comprising one light-receiving element that receives the light beam emitted from the light source and a detection signal generation unit that generates a light detection signal corresponding to the received light intensity of the light beam; and a synchronization signal generation unit that compares the generated light detection signal with a predetermined comparison voltage to generate a synchronization signal for determining the timing to irradiate the light beam at a scanning start position of the light beam to be scanned on an object to be scanned, wherein the light detection signal comprises a detection AC signal that is an AC component of the detection signal that changes corresponding to the received light intensity of the light beam, and the synchronization signal generation unit generates the synchronization signal by comparing a comparison voltage that is offset with respect to the voltage level of the detection AC signal when there is no change in the light detection signal that is generated when no light beam is detected, with the voltage level of the detection AC signal immediately after a change in the light detection signal that is generated when the light beam is detected.

[0011] In addition, a reference voltage having a predetermined constant voltage value is superimposed on the detection AC signal, the comparison voltage is a voltage obtained by adding a predetermined non-zero offset voltage to the reference voltage, and the synchronization signal is a signal generated by comparing the detection AC signal superimposed with the reference voltage and the comparison voltage.

[0012] The synchronization signal generating unit is further characterized in that it includes a comparator, the detection AC signal on which the reference voltage is superimposed and the comparison voltage are input to the comparator, and the comparator compares the detection AC signal on which the reference voltage is superimposed with the comparison voltage and outputs the comparison result as the synchronization signal.

[0013] The comparison voltage is changed in accordance with the amount of light of the light beam received by the light receiving element. The present invention is also characterized in that light-intensity-corresponding reference voltage information, which associates a reference light intensity setting value corresponding to the light intensity of the light beam received by the light-receiving element with a reference voltage setting value corresponding to the voltage level of the comparison voltage, is stored in advance, and the comparison voltage is set to a voltage level equivalent to the reference voltage setting value associated with the reference light intensity setting value corresponding to the light intensity of the light beam emitted from the light source, using the light-intensity-corresponding reference voltage information.

[0014] The comparison voltage is changed in response to a change in temperature in the vicinity of the optical scanning unit. The present invention is also characterized in that a temperature sensor is provided near the optical scanning unit, and temperature-corresponding reference voltage information is stored in advance, which associates a temperature setting value corresponding to the temperature near the optical scanning unit with a reference voltage setting value corresponding to the voltage level of the comparison voltage, and the comparison voltage is set to a voltage level equivalent to the reference voltage setting value associated with the temperature setting value corresponding to the temperature measured by the temperature sensor using the temperature-corresponding reference voltage information.

[0015] The optical scanning device further includes a scanning control unit that controls the emission timing of the light beam using the synchronization signal generated by the synchronization signal generation unit, and the scanning control unit includes a noise mask unit that prevents spike-like noise contained in the synchronization signal from being detected, and the noise mask unit disables detection of the synchronization signal during a noise mask period between the output timings of two adjacent synchronization signals generated by the synchronization signal generation unit.

[0016] The scanning control unit further includes a noise detection unit that detects spike-like noise contained in the synchronization signal, and the noise detection unit generates a noise detection signal that detects the position of spike-like noise that occurs in the synchronization signal during a noise mask period between the output timings of two adjacent synchronization signals generated by the synchronization signal generation unit.

[0017] The light receiving element is a photodiode, and the detected AC signal is output from a capacitor connected to the anode of the photodiode and is supplied to the comparator. The light receiving element is a photodiode, and the detected AC signal is output from a capacitor connected to the cathode of the photodiode and is provided to the comparator.

[0018] The present invention also provides an image forming apparatus comprising any one of the above-described scanning timing detection devices and a photosensitive drum that is a scanned body that is scanned with a light beam, wherein the light detection unit is disposed in the vicinity of the photosensitive drum, and scans the light beam toward the photosensitive drum in response to the synchronization signal generated by the synchronization signal generation unit, thereby forming an electrostatic latent image on the surface of the photosensitive drum.

[0019] The present invention also provides a scan timing detection method for a scan timing detection device having a light source and one light receiving element, comprising: a light receiving step of receiving a light beam emitted from the light source by the light receiving element; a light detection step of generating a light detection signal consisting of a detection AC signal which is an AC component of the detection signal which changes according to the received light intensity of the received light beam; a comparison voltage generation step of generating a comparison voltage which is offset with respect to the voltage level of the detection AC signal when there is no change in the light detection signal which is generated when the light beam is not detected; and a synchronization signal output step of comparing the comparison voltage with the voltage level of the detection AC signal immediately after a change in the light detection signal which is generated when the light beam is detected, and outputting a synchronization signal for determining the timing to irradiate the light beam to a scan start position of the light beam to scan an object to be scanned. [Effects of the Invention]

[0020] According to this invention, the device is provided with one light receiving element that receives the light beam emitted from the light source, and generates a light detection signal consisting of a detection AC signal that is an AC component of the detection signal that changes in response to the received light intensity of the light beam, and compares a comparison voltage that is offset with respect to the voltage level of the detection AC signal when there is no change in the light detection signal generated when no light beam is detected with the voltage level of the detection AC signal immediately after the light detection signal generated when the light beam is detected changes, thereby generating a synchronization signal for determining the timing to irradiate the light beam at the scanning start position of the light beam to be scanned on the scanned object.Therefore, even if the light intensity or beam diameter of the light beam changes, the timing to irradiate the light beam at the scanning start position of the light beam can be accurately detected, and the cost of the scan timing detection device can be reduced. For example, in an image forming apparatus equipped with a scanning timing detection device, it is possible to provide a low-cost image forming apparatus in which the write timing, which is the timing at which formation of an electrostatic latent image on the surface of the photosensitive drum begins, does not change even if the light intensity or beam diameter of the light beam irradiated onto the photosensitive drum changes. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is an explanatory diagram of an embodiment of a schematic configuration of a scanning timing detection device for an image forming apparatus according to the present invention; [Figure 2] 1 is a schematic block diagram of an embodiment of a scanning timing detection device according to the present invention; [Figure 3] 1 is an explanatory diagram of a first embodiment of a light beam detection circuit of a scanning timing detection device of the present invention; [Figure 4] 4 is a timing chart of detection signals etc. in the first embodiment of the light beam detection circuit of the present invention. [Figure 5] FIG. 4 is an explanatory diagram of a second embodiment of the light beam detection circuit of the scanning timing detection device of the present invention. [Figure 6] 10 is a timing chart of detection signals etc. in a second embodiment of the light beam detection circuit of the present invention. [Figure 7]FIG. 4 is an explanatory diagram of a third embodiment of the light beam detection circuit of the scanning timing detection device of the present invention. [Figure 8] 10 is a timing chart of detection signals etc. in a third embodiment of the light beam detection circuit of the present invention. [Figure 9] 10 is a timing chart of detection signals etc. in a third embodiment of the light beam detection circuit of the present invention. [Figure 10] 10 is an explanatory diagram of an example of light-intensity-corresponding reference voltage information in which a reference voltage setting value corresponding to a reference light intensity is preset; FIG. [Figure 11] 10 is an explanatory diagram of an embodiment of temperature-corresponding reference voltage information in which reference voltage setting values ​​associated with temperatures are preset; [Figure 12] 10 is a timing chart relating to a process of making noise in a synchronization signal undetectable by utilizing a start point detection signal of the synchronization signal according to the present invention; [Figure 13] 4 is a timing chart relating to a process for detecting noise in a synchronization signal according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments.

[0023] <Configuration of Scanning Timing Detection Device> In the following embodiment, a scanning timing detection device provided in an image forming apparatus will be described. The image forming device has a photosensitive drum, which is a scanned body that is scanned with a light beam, and scans the light beam toward the photosensitive drum in response to a synchronization signal generated by a scanning timing detection device, as described below, to form an electrostatic latent image on the surface of the photosensitive drum.

[0024] However, the scanning timing detection device of this invention can be used not only in image forming devices, but also in any case where it is necessary to set the scanning start position of the irradiated light beam and the timing to irradiate the light beam at the scanning start position when scanning and irradiating a specified object (scanned body) with a light beam. For example, the scanning timing detection device of the present invention can be used in laser processing devices, projectors, and the like.

[0025] FIG. 1 is an explanatory diagram showing a schematic configuration of an embodiment of a scanning timing detection device for an image forming apparatus according to the present invention. The scanning timing detection device of the present invention is a device that detects the scanning timing of the light beam L that is irradiated onto the surface of the photosensitive drum 50 in order to form an electrostatic latent image thereon. The scanning timing detection device is mainly composed of an optical detection section 10, an optical scanning unit 60, and a scanning control section 40. The scanning control section 40 is a section that provides the optical scanning unit 60 with an irradiation request signal for controlling the emission timing of the light beam L, the output intensity of the light beam L, the scanning timing, and the irradiation direction.

[0026] The optical scanning unit 60 is a device that irradiates a light beam L in the direction in which the photosensitive drum 50 is located based on an irradiation request signal sent from the scanning control unit 40, and is mainly composed of a light source 62 that emits the light beam L and an optical scanning unit 61 that changes the direction in which the light beam L is irradiated. For example, the light beam L is emitted from the optical scanning unit 60 in the direction of the photosensitive drum 50 and the light detection unit 10 within the scanning range R in Figure 1, and is scanned from the left side of the light detection unit 10 toward the right side of the photosensitive drum 50.

[0027] The light detection section 10 is a section that receives the light beam L and outputs an electrical signal corresponding to the light intensity of the received light beam (also referred to as received light intensity). As shown in Figure 2, which will be described later, the light detection unit 10 is composed of a light receiving element (also called a light detection element) that receives the light beam L emitted from the light source 62 and a detection signal generation unit 12, and corresponds to a BD sensor (beam detect sensor). As the light receiving element, for example, a photodiode (PD) 11 is used, and in the present invention, the light detecting section 10 includes one photodiode (PD) 11.

[0028] The photodiode PD is disposed near the photosensitive drum 50 and is fixedly disposed mainly in the direction of extension of the rotation axis of the photosensitive drum 50. Furthermore, as shown in FIG. 1, when the scanning direction of the light beam L is from the left side to the right side of the photosensitive drum 50, the photodiode PD is positioned on the left side of the photosensitive drum 50 with its light receiving surface facing the light source, at a predetermined distance (for example, about 10 mm) from the left end of the photosensitive drum 50.

[0029] The detection signal generating section 12 is a section that generates a light detection signal K corresponding to the intensity of the received light beam from the electrical signal obtained from the photodiode PD. The light detection signal K is a signal having a voltage value corresponding to the intensity of received light, and is made up of a detection AC signal (V_AC), as will be described later. The detected AC signal is an AC component of the detected signal that changes in response to the received light intensity of the light beam. Furthermore, a reference voltage having a predetermined constant voltage value is superimposed on the detected AC signal (V_AC). This superimposed reference voltage is, for example, Vcc / 2 in FIG. 3, which will be described later.

[0030] The light detection unit 10 is connected to a synchronization signal generation unit 30 shown in FIG. 2, which will be described later, and a detection AC signal (V_AC), which is an AC component of the detection signal corresponding to the received light intensity of the light beam, is output to the synchronization signal generation unit 30. In the image forming apparatus, the synchronization signal generation unit 30 generates a synchronization signal D for determining the timing (write start timing) at which the light beam is irradiated to the start position for forming an electrostatic latent image on the surface of the photosensitive drum. This synchronization signal D is a signal generated by comparing the detection AC signal (V_AC) on which the reference voltage is superimposed with a comparison voltage, which will be described later.

[0031] FIG. 2 shows a schematic block diagram of an embodiment of the scanning timing detection device of the present invention. 2, the scan timing detection device is made up of the optical detection section 10, optical scanning unit 60, and scan control section 40 shown in FIG.

[0032] The comparison voltage output section 20 is a section that outputs a comparison voltage H to be compared with the light detection signal K. The comparison voltage H is given to the synchronization signal generation section 30. As will be described later, the comparison voltage H is a voltage having a constant voltage value, and is a voltage obtained by adding a predetermined non-zero offset voltage to the reference voltage superimposed on the above-mentioned detected AC signal (V_AC). The comparison voltage H will also be referred to as V_REF hereinafter. For example, as shown in FIG. 3, which will be described later, the comparison voltage H is a constant voltage (V_REF) obtained by dividing the power supply voltage Vcc by resistors R3 and R4 having different resistance values.

[0033] The synchronization signal generating unit 30 is a part that generates a synchronization signal D(V_OUT) for determining the timing of irradiating the light beam to the scanning start position of the light beam scanning the scanned object by comparing the generated light detection signal K with a predetermined comparison voltage H. In particular, in this invention, the synchronization signal generating unit 30 generates the synchronization signal D by comparing a comparison voltage that is offset with respect to the voltage level of the detection AC signal when there is no change in the photodetection signal generated when no light beam is detected with the voltage level of the detection AC signal immediately after the photodetection signal generated when a light beam is detected changes.

[0034] As will be described later, the synchronization signal generating unit 30 is equipped with a comparator, to which the detected AC signal (V_AC) superimposed with the reference voltage and a comparison voltage are input, and the comparator outputs a comparison result between the detected AC signal (V_AC) superimposed with the reference voltage and the comparison voltage as a synchronization signal D.

[0035] When a light beam is scanned and irradiated onto the photodiode PD, the received light intensity of the light beam gradually increases, reaches a certain peak value, and then gradually decreases. In response to this change in the received light intensity, the voltage value of the electrical signal (detection signal) corresponding to the received light intensity also changes with a similarly constant peak. For example, a synchronization signal D that changes like a pulse is generated in accordance with the timing at which a change occurs in the voltage value of the electrical signal (detection signal) corresponding to the intensity of the received light.

[0036] That is, the timing at which the synchronization signal D is generated is the position at which a change occurs in the voltage value of the detection signal, and the timing at which this synchronization signal D is generated is used to determine the write timing. The scanning control unit 40 uses the synchronization signal D generated by the synchronization signal generating unit 30 to control the emission timing of the light beam and the scanning.

[0037] This invention is characterized in that when the received light intensity of the light beam or the beam diameter of the light beam changes, even if the magnitude of the voltage value of the electrical signal corresponding to the received light intensity changes and the voltage value of the detection signal changes, a synchronization signal D is generated to minimize deviation from the timing that should be detected.

[0038] The configuration of the electrical circuit (light beam detection circuit) of the scanning timing detection device that generates the synchronization signal D that determines the write timing without being affected by changes in the received light intensity of the light beam or changes in the beam diameter of the light beam will be described below using several examples.

[0039] <Example of a light beam detection circuit of a scanning timing detection device> (Light beam detection circuit: First embodiment) FIG. 3 shows an explanatory diagram of a first embodiment of the light beam detection circuit of the scanning timing detection device. FIG. 4 shows a timing chart of detection signals etc. in the first embodiment of the light beam detection circuit. In the light beam detection circuit of the scan timing detection device of Figure 3, when a light beam L is incident on a photodiode PD, a predetermined synchronization signal (V_OUT) is output by a combination of resistors (R1 to R5), a capacitor C, and a comparator (CP1). The DC power supply voltage applied to the light beam detection circuit is designated as Vcc. A reference voltage that is superimposed on the detected AC signal is generated from this DC power supply voltage Vcc.

[0040] In this first embodiment, as shown below, the synchronization signal generating unit 30 outputs a signal voltage that is the differential voltage between the detected AC signal (V_AC) and the comparison voltage (V_REF), and this output signal voltage is the synchronization signal V_OUT.

[0041] 3, the photodetector 10 is mainly composed of a photodiode PD, a resistor R1, and a capacitor C. The comparison voltage output unit 20 is configured by a combination of resistors R3 and R4, and supplies a comparison voltage (V_REF) to a comparator (CP1). Resistors R3 and R4 are connected in series, and a comparison voltage V_REF is applied from a connection point P1 between the resistors R3 and R4 to one input terminal (positive terminal) of a comparator (CP1). The synchronization signal generating unit 30 is configured by a combination of a resistor R5 and a comparator (CP1), and outputs a synchronization signal V_OUT.

[0042] In the photodetector 10 of FIG. 3, a photodiode PD and a resistor R1 are connected in series, a power supply voltage Vcc is applied, and a detection signal V_PD is output from a connection point Pa between the photodiode PD and the resistor R1. In FIG. 3, a power supply voltage Vcc is applied to the cathode of the photodiode PD, and the anode of the photodiode PD is connected to a connection point Pa. The detection signal V_PD is, for example, a signal having a voltage change as shown in Figure 4, and in response to the change in the received light intensity of the light beam, which gradually increases, reaches a certain peak value, and then gradually decreases, the detection signal V_PD is also a signal that changes with a certain peak in a similar manner.

[0043] A connection point Pa between the photodiode PD and the resistor R1 is connected to one end of a capacitor C. The other end of the capacitor C is connected to one input terminal (negative terminal) of the comparator CP1. That is, the detected AC signal V_AC is output from a capacitor C connected to the anode of the photodiode PD and is given to a comparator CP1.

[0044] In addition, two resistors R2 are connected in series, one end of one of the resistors R2 is connected to a DC power supply, the power supply voltage Vcc of the DC power supply is applied, and the connection point P2 between the two resistors R2 is connected to the other end of the capacitor C and to the input terminal (- terminal) of the comparator CP1. At this connection point P2, the detected AC signal V_AC and a reference voltage (Vcc / 2) having a predetermined constant voltage value are superimposed, and this superimposed input signal is input to the input terminal (- terminal) of the comparator CP1.

[0045] That is, the DC component of the detection signal V_PD is blocked by the capacitor C, and a voltage obtained by superimposing a reference voltage (Vcc / 2) on the detection AC signal V_AC, which is the AC component of the detection signal V_PD, is input to the input terminal (negative terminal) of the comparator CP1. The detected AC signal V_AC is, for example, a signal having a voltage change as shown in FIG. 4, and is a signal that changes sinusoidally in response to changes in the detected signal V_PD.

[0046] When the light beam L is not detected by the photodiode PD, the detection signal V_PD does not change and remains at a constant value, and the detection AC signal V_AC similarly does not change and remains at a constant voltage value (Vcc / 2). When the light beam L is detected by the photodiode PD, the detection signal V_PD changes (rises) sharply, and almost simultaneously with the timing at which the detection signal V_PD rises, the detection AC signal V_AC also changes (rises) sharply.

[0047] When the amount of light of the detected light beam L increases, the detection signal V_PD rises, and when the amount of light changes from increasing to decreasing, the detection signal V_PD reaches a peak. At the position where the detected signal V_PD reaches its peak, the detected AC signal V_AC also reaches its peak. When the detected signal V_PD subsequently decreases, the detected AC signal V_AC also decreases, and the sign of the detected AC signal V_AC relative to the reference voltage (Vcc / 2) changes.

[0048] On the other hand, in the comparison voltage output section 20, two resistors R3 and R4 are connected in series, the power supply voltage Vcc is applied to one end of the resistor R3, and the connection point P1 between the two resistors R3 and R4 is connected to the other input terminal (+ terminal) of the comparator CP1. The two resistors R3 and R4 have different resistance values.

[0049] Since the resistance values ​​of resistors R3 and R4 are different, a comparison voltage V_REF, whose voltage value is offset from a reference voltage (Vcc / 2) having a predetermined constant voltage value, is input to the input terminal (+ terminal) of comparator CP1. If the offset value is ΔV, the comparison voltage V_REF is Vcc / 2+ΔV. In this case, the comparison voltage V_REF is greater than Vcc / 2 and greater than the voltage level of the detected AC signal V_AC when there is no change in the detected signal V_PD. That is, the comparison voltage V_REF is a voltage offset with respect to the voltage level (Vcc / 2) of the detection AC signal V_AC when there is no change in the photodetection signal (V_PD) generated when no light beam is detected. It is preferable that the set value of the offset value ΔV is as small as possible, as will be shown in the setting criteria described later.

[0050] The comparator CP1 compares the signals (V_AC, V_REF) input to its two input terminals, and outputs the output signal (V_OUT) resulting from the comparison from its output terminal. This output signal (V_OUT) serves as a synchronization signal. When the detection AC signal (V_AC) and the comparison voltage (V_REF) shown in FIG. 4 are input to the comparator CP1, an output signal (V_OUT) that changes as shown in FIG. 4 is output from the output terminal of the comparator CP1. That is, the level of the output signal (V_OUT) changes as shown in FIG. 4 by comparing the detected AC signal (V_AC) with the comparison voltage (V_REF).

[0051] In FIG. 4, when the detected AC signal (V_AC) is lower than the comparison voltage (V_REF), an output signal (V_OUT) at the "H" level is output. However, when the detection AC signal (V_AC) changes and the voltage level of the detection AC signal matches the voltage level of the comparison voltage (V_REF), and then becomes higher than the voltage level of the comparison voltage (V_REF), an output signal (V_OUT) at an "L" level is output. That is, when the detected AC signal (V_AC) is on a rising trend, the output signal (V_OUT) changes from the "H" level to the "L" level at the point when the detected AC signal (V_AC) rises and matches the comparison voltage (V_REF) (point T1 in Figure 4).

[0052] Thereafter, the voltage level of the detected AC signal (V_AC) further increases, and even at the peak of the detected AC signal, the output signal (V_OUT) remains at the "L" level. Also, when the voltage level of the detected AC signal (V_AC) passes its peak and starts to fall, if the voltage level of the detected AC signal (V_AC) is still higher than the comparison voltage (V_REF), the output signal (V_OUT) remains at the "L" level.

[0053] However, when the voltage level of the detection AC signal (V_AC) matches the voltage level of the comparison voltage (V_REF) and then becomes lower than the voltage level of the comparison voltage (V_REF), an output signal (V_OUT) of "H" level is output. That is, when the detected AC signal (V_AC) is on a falling trend, the output signal (V_OUT) changes from the "L" level to the "H" level when the detected AC signal (V_AC) falls and matches the comparison voltage (V_REF) (time T2 in Figure 4).

[0054] As shown in FIG. 4, the output signal (V_OUT), which is a synchronization signal, is at the “L” level during the period between time T1 and time T2 in FIG. 4, and this period always includes the peak position of the detection signal V_PD.

[0055] (Setting criteria for offset value ΔV) The magnitude of the offset value ΔV is determined by the resistance values ​​of resistors R3 and R4. Furthermore, the timing at which the level of the output signal (V_OUT), which is a synchronization signal, changes varies depending on the magnitude of the offset value ΔV. Therefore, the offset value ΔV also affects the determination of the write timing, and therefore must be set appropriately.

[0056] For example, comparing the detected AC signal (V_AC) with the comparison voltage (V_REF) at a portion where the rising slope of the detected AC signal (V_AC) is steep will reduce the influence of noise contained in the signal, resulting in better jitter performance. From this perspective, a smaller offset value ΔV is preferable. When the detection AC signal (V_AC) rises from a constant voltage value (Vcc / 2), the slope of the rise is steep at first, and then becomes gentler as it approaches the peak. The part of the detection AC signal (V_AC) where the slope of the rise is steep occurs immediately after a change in the optical detection signal generated when a light beam is detected.

[0057] On the other hand, if the offset value ΔV is made too small, the effects of noise and the like cannot be ignored, so the resistance values ​​of resistors R3 and R4 must be selected so that the offset value ΔV is within an appropriate range. If the offset value ΔV is reduced, the effects of variations in the resistance values ​​of resistors R2, R3, and R4 included in the circuit configuration in Figure 3, the input offset voltage of the comparator (CP1), and noise included in the detected AC signal and comparison voltage may become significant.

[0058] Therefore, for example, the resistance values ​​of resistors R3 and R4 may be selected so that the offset value ΔV falls within the following voltage value range: 50mv < ΔV < (V_AC_MAX - Vcc / 2) / 2 Here, V_AC_MAX is the maximum value of the detected AC signal that is determined from the sensitivity of the light receiving element, the light intensity and beam diameter of the light beam.

[0059] As described above, the position where the synchronization signal V_OUT changes from the "H" level to the "L" level indicates the start position for detecting the write timing, and the write timing can be determined based on the timing of this synchronization signal V_OUT.

[0060] When the light intensity or beam diameter of the light beam changes, the slope of the signal waveform leading to the peak of the detection signal V_PD and the magnitude of the peak change, and the position of the peak of the detection signal V_PD may shift from the position of the expected ideal write timing. However, in the light beam detection circuit of the scanning timing detection device shown in Figure 3, even if the light intensity or beam diameter of the light beam changes, the timing at which the synchronization signal V_OUT output from the comparator (CP1) changes from the "H" level to the "L" level is almost constant, so it is possible to set the write timing with a certain degree of accuracy.

[0061] Therefore, even if the light intensity or beam diameter of the light beam changes, the write timing does not change significantly, and it is possible to obtain the same write timing as a light beam detection circuit that uses two photodiodes, and it is also possible to obtain the same performance in terms of jitter. Furthermore, as shown in Figure 3, the circuit configuration of the light beam detection circuit is simple and has a small number of components, making it less susceptible to the effects of stray capacitance present in the board pattern of the light beam detection circuit and the impedance inside the comparator, enabling the realization of a low-cost scanning timing detection device.

[0062] (Light beam detection circuit: second embodiment) FIG. 5 shows an explanatory diagram of a second embodiment of the light beam detection circuit of the scanning timing detection device of the present invention. FIG. 6 shows a timing chart of detection signals etc. in the second embodiment of the light beam detection circuit of the present invention. In the light beam detection circuit of Figure 5, the arrangement of the photodiode PD and resistor R1 belonging to the light detection unit 10 and the input position of the detection AC signal (V_AC) and comparison voltage (V_REF) given to the comparator (CP2) are different from those of the light beam detection circuit of Figure 3 described above. 6 is different from the timing chart of FIG. 4 in that the signal waveforms of the detection signal V_PD and the detection AC signal (V_AC) change in the opposite direction to those in the timing chart of FIG.

[0063] In FIG. 5, the anode of the photodiode PD is grounded, a power supply voltage Vcc is applied to one end of a resistor R1, and the other end of the resistor R1 and the cathode of the photodiode PD are connected to a connection point Pa. A detection signal V_PD corresponding to the received light intensity of the light beam is output from the connection point Pa.

[0064] A connection point Pa between the photodiode PD and the resistor R1 is connected to one end of a capacitor C. Unlike FIG. 3, the other end of the capacitor C is connected to one input terminal (positive terminal) of the comparator CP2. That is, the detected AC signal V_AC is output from a capacitor C connected to the cathode of the photodiode PD and is given to a comparator CP2.

[0065] In addition, two resistors R2 are connected in series, one end of one of the resistors R2 is connected to a DC power supply, the power supply voltage Vcc of the DC power supply is applied, and the connection point P2 between the two resistors R2 is connected to the other end of the capacitor C and to the input terminal (+ terminal) of the comparator CP2. At this connection point P2, the detected AC signal V_AC and a reference voltage (Vcc / 2) having a predetermined constant voltage value are superimposed, and this superimposed input signal is input to the input terminal (+ terminal) of the comparator CP2.

[0066] In FIG. 5, the arrangement of the photodiode PD and resistor R1 at the connection point Pa is different from that in FIG. 3, and therefore the waveforms of the detection signal V_PD and detection AC signal V_AC output from the connection point Pa change differently from those in FIG.

[0067] When the light beam L is not detected by the photodiode PD, the detection signal V_PD does not change and is a constant value, as in Figure 4, and the detection AC signal V_AC also does not change and is a constant voltage value (Vcc / 2). However, when the light beam L is detected by the photodiode PD, the detection signal V_PD changes abruptly (falls), and almost simultaneously with the timing at which the detection signal V_PD falls, the detection AC signal V_AC also changes abruptly (falls).

[0068] When the amount of light of the detected light beam L increases, the detection signal V_PD decreases, and when the amount of light changes from increasing to decreasing, the detection signal V_PD exhibits a downward peak. At the position where the detected signal V_PD shows a downward peak, the detected AC signal V_AC also shows a downward peak, and when the detected signal V_PD increases thereafter, the detected AC signal V_AC also increases and changes its sign relative to the reference voltage (Vcc / 2).

[0069] On the other hand, in the comparison voltage output section 20, two resistors R3 and R4 are connected in series and the power supply voltage Vcc is applied to one end of the resistor R3, just like in FIG. 3, but it differs from FIG. 3 in that the connection point P1 between the two resistors R3 and R4 is connected to the other input terminal (negative terminal) of the comparator CP2.

[0070] Since the resistance values ​​of resistors R3 and R4 are different, a comparison voltage V_REF, whose voltage value is offset from a reference voltage (Vcc / 2) having a predetermined constant voltage value, is input to the input terminal (negative terminal) of comparator CP2. In the case of FIG. 5, if the offset value is ΔV, the comparison voltage V_REF is Vcc / 2−ΔV. In this case, the comparison voltage V_REF is smaller than Vcc / 2 and is smaller than the voltage level of the detected AC signal V_AC when there is no change in the detected signal V_PD.

[0071] 3 in that the comparator CP2 compares signals (V_AC, V_REF) input to two input terminals and outputs an output signal (V_OUT) resulting from the comparison from the output terminal of the comparator CP2. When the detection AC signal (V_AC) and the comparison voltage (V_REF) shown in FIG. 6 are input to the comparator CP2, an output signal (V_OUT) that changes as shown in FIG. 6 is output from the output terminal of the comparator CP2, and the timing at which the level of the output signal (V_OUT) changes is the same as in FIG. 4.

[0072] In FIG. 6, when the detected AC signal (V_AC) is on a falling trend, the output signal (V_OUT) changes from the “H” level to the “L” level when the detected AC signal (V_AC) falls and matches the comparison voltage (V_REF) (time T1 in FIG. 6). On the other hand, when the detected AC signal (V_AC) is on a rising trend, the output signal (V_OUT) changes from the "L" level to the "H" level when the detected AC signal (V_AC) rises and matches the comparison voltage (V_REF) (time T2 in Figure 6).

[0073] In the timing shown in Figure 6, as in Figure 4, the output signal (V_OUT), which is a synchronization signal, becomes "L" level during the period between time T1 and time T2 in Figure 6, and this period always includes the peak position of the detection signal V_PD.

[0074] As described above, the position where the synchronization signal V_OUT changes from the "H" level to the "L" level indicates the start position for detecting the write timing, and the write timing can be determined based on the timing of this synchronization signal V_OUT.

[0075] Furthermore, even with the optical beam detection circuit of Figure 5, the write timing does not change significantly even if the light intensity or beam diameter of the optical beam changes, and it is possible to obtain write timing equivalent to that of an optical beam detection circuit using two photodiodes, and it is also possible to obtain equivalent performance in terms of jitter.

[0076] (Light beam detection circuit: third embodiment) Here, an embodiment in which the comparison voltage H is changed in response to the amount of light of the light beam received by the light receiving element 11, and an embodiment in which the comparison voltage H is changed in response to changes in temperature near the optical scanning unit 60 will be described.

[0077] FIG. 7 shows an explanatory diagram of a third embodiment of the light beam detection circuit of the scanning timing detection device of the present invention. 8 and 9 show timing charts of detection signals etc. in the third embodiment of the light beam detection circuit of the present invention. The timing chart in Figure 8 shows the case where the light beam quantity detected by the photodiode is a predetermined reference light quantity, and the timing chart in Figure 9 shows the case where the light beam quantity detected by the photodiode is double the reference light quantity.

[0078] In the light beam detection circuit of FIG. 7, the arrangement of components such as resistors is the same as in the light beam detection circuit of FIG. However, it differs from FIG. 3 in that the power supply voltage applied to one end of the resistor R3 that generates the comparison voltage V_REF is not a fixed value (Vcc), but is set to a voltage value corresponding to the reference light amount on the sub-scanning side. By making this power supply voltage variable, the comparison voltage V_REF is changed.

[0079] In FIG. 7, the power supply voltage applied to one end of the resistor R3 is V_DAC instead of Vcc. This power supply voltage V_DAC means, for example, the output voltage of a DA converter that converts a digital value into an analog voltage value. By setting the digital value to a predetermined value, the power supply voltage V_DAC to be applied to one end of the resistor R3 is determined, and by changing the digital value, the power supply voltage V_DAC can be changed. This digital value is called the reference voltage setting value.

[0080] The reference light amount on the sub-scanning side means the reference light amount in the rotation direction of the photosensitive drum, and is set in advance by the scan control unit. In a configuration in which the reference light amount on the sub-scanning side affects the intensity of the received light beam, changing this reference light amount changes the amount of light beam irradiated onto the photodiode, and the write start timing also fluctuates. The voltage value of the comparison voltage V_REF to be compared with the detected AC signal (V_AC) can be changed by changing the power supply voltage applied to one end of the resistor R3.

[0081] Therefore, a reference voltage setting value that determines the power supply voltage to be applied to one end of resistor R3 is set in advance in accordance with the reference light amount on the sub-scanning side, and by applying a power supply voltage that corresponds to the reference light amount on the sub-scanning side to one end of resistor R3, the effect of changes in the light amount of the light beam is offset and the write timing is prevented from fluctuating.

[0082] In FIG. 7, if the power supply voltage applied to one end of the resistor R3 is V_DAC, the comparison voltage V_REF is R4 / (R3+R4)×V_DAC. By appropriately setting the resistance values ​​of resistors R3 and R4 and the reference voltage setting value of V_DAC, the comparison voltage V_REF can be set to a voltage value slightly greater than the reference voltage Vcc / 2, as shown in FIG. 8, and an appropriate synchronization signal V_OUT can be generated, as in Example 1 described above.

[0083] The potential difference between the comparison voltage V_REF, which corresponds to R4 / (R3+R4)×V_DAC in FIG. 8, and the reference voltage Vcc / 2 corresponds to the offset voltage ΔV. The timing relationship between the waveform of the detection signal and the synchronization signal V_OUT shown in the timing chart of FIG. 8 is the same as that shown in FIG. 4, and therefore will not be described again. The timing chart in Figure 9 differs from Figure 8 only in that the light intensity of the light beam is doubled, but the timing relationship between the waveform of the detection signal and the synchronization signal V_OUT is the same as that shown in Figures 4 and 8.

[0084] As shown in Figure 8, when the light beam intensity is the reference light intensity, the rising slope of the detection signal waveform is slightly gentler than in the case of double the light intensity in Figure 9, and the timing at which the synchronization signal D is generated is relatively delayed, so it is better to set the power supply voltage V_DAC to a lower value than in the case of double the light intensity. Conversely, in the case of double the light intensity in Figure 9, the rising slope of the detection signal waveform becomes somewhat steeper, and the timing at which the synchronization signal D is generated becomes relatively earlier, so it is better to set the power supply voltage V_DAC to a higher value than in the case of the standard light intensity.

[0085] As described above, a reference voltage setting value that determines the power supply voltage to be applied to one end of resistor R3 is set in advance in correspondence with the reference light intensity on the sub-scanning side, and the following light intensity-corresponding reference voltage information showing this correspondence is stored in advance in a storage medium such as a ROM or hard disk provided in the image forming apparatus.

[0086] (Light intensity-corresponding reference voltage information in which a reference voltage setting value corresponding to a reference light intensity is preset) Here, the light intensity-dependent reference voltage information is used to change the comparison voltage V_REF in accordance with the light intensity of the light beam received by the light receiving element. Light-intensity-corresponding reference voltage information that associates a reference light intensity setting value corresponding to the light intensity of the light beam received by the light receiving element with a reference voltage setting value corresponding to the voltage level of the comparison voltage is stored in advance, and the comparison voltage V_REF is set to a voltage level equivalent to the reference voltage setting value associated with the reference light intensity setting value corresponding to the light intensity of the light beam emitted from the light source using the light-intensity-corresponding reference voltage information.

[0087] FIG. 10 is an explanatory diagram of an example of light-amount-corresponding reference voltage information in which reference voltage setting values ​​corresponding to reference light amounts are preset. The light intensity-corresponding reference voltage information in FIG. 10 shows information in which the reference light intensity setting value is associated with the reference voltage setting value. The reference light amount setting value is numerical information for determining the reference light amount on the sub-scanning side, and the reference voltage setting value is numerical information for determining the power supply voltage V_DAC to be applied to one end of the resistor R3 as described above.

[0088] In Figure 10, for example, when the reference light intensity setting value is zero, the reference voltage setting value is 112, and when a light beam with a reference light intensity corresponding to a reference light intensity setting value of zero is irradiated, the power supply voltage V_DAC corresponding to this number "112" is applied to one end of resistor R3. Furthermore, when the reference light intensity setting value is 96, the reference voltage setting value is 124, which means that when a light beam with a reference light intensity corresponding to the reference light intensity setting value of 96 is irradiated, the power supply voltage V_DAC corresponding to this number "124" is applied to one end of resistor R3. Once the power supply voltage V_DAC is determined, a comparison voltage V_REF equivalent to R4 / (R3+R4)×V_DAC is input to the comparator.

[0089] Like this light intensity-corresponding reference voltage information, a reference voltage setting value that determines the power supply voltage to be applied to one end of resistor R3 is set in advance in correspondence with the reference light intensity on the sub-scanning side, and by using the light intensity-corresponding reference voltage information to apply a power supply voltage that corresponds to the reference light intensity on the sub-scanning side to one end of resistor R3, the effects of changes in the light intensity of the light beam can be offset and the write timing can be prevented from fluctuating.

[0090] (Temperature-based reference voltage information that pre-sets the reference voltage setting value associated with the temperature) FIG. 11 is an explanatory diagram of an example of temperature-associated reference voltage information in which reference voltage set values ​​associated with temperatures are preset. As described above, when the reference light amount on the sub-scanning side is changed, the amount of light beam irradiated to the photodiode changes, and the write timing also fluctuates slightly. Similarly, when the light detection section 10 or a component (for example, a lens) included in the optical scanning unit 60 that constitutes the scan timing detection device is deformed, the position at which the light beam is irradiated changes, and the write timing may also fluctuate.

[0091] Since deformation of components is mainly caused by temperature changes, it is preferable to set in advance a reference voltage setting value that corresponds to temperature changes. That is, the comparison voltage V_REF is changed in response to changes in the temperature in the vicinity of the optical scanning unit and the like. For example, a temperature sensor is provided near the optical scanning unit, and temperature-corresponding reference voltage information is stored in advance, which associates a temperature setting value corresponding to the temperature near the optical scanning unit with a reference voltage setting value corresponding to the voltage level of the comparison voltage, and the comparison voltage V_REF is set to a voltage level equivalent to the reference voltage setting value associated with the temperature setting value corresponding to the temperature measured by the temperature sensor, using the temperature-corresponding reference voltage information.

[0092] The temperature changes that affect the deformation of parts are changes in temperature near the polygon motor, dehumidifying heater, etc., so for example, a temperature sensor can be attached near the optical scanning unit, near the polygon motor, or in the housing that houses the optical scanning unit. Alternatively, if the temperature is easily affected by the dehumidifying heater, the temperature sensor may be attached near the dehumidifying heater. A reference voltage setting value that determines the power supply voltage to be applied to one end of resistor R3 is set in advance in accordance with the temperature measured by the temperature sensor, and by applying a power supply voltage corresponding to the temperature to one end of resistor R3, the effects of changes in the light intensity of the light beam are offset, preventing fluctuations in the write timing.

[0093] The temperature-corresponding reference voltage information in FIG. 11 shows information in which temperature setting values ​​are associated with reference voltage setting values. The temperature setting value is numerical information of the measured temperature, and the reference voltage setting value is numerical information for determining the power supply voltage V_DAC to be applied to one end of the resistor R3 as described above.

[0094] In FIG. 11, for example, when the measured temperature (temperature setting value) is 10°C, the reference voltage setting value is 124, which means that the power supply voltage V_DAC corresponding to this number "124" is applied to one end of resistor R3. Also, when the measured temperature (temperature setting value) is 40° C., the reference voltage setting value is 132, which means that the power supply voltage V_DAC corresponding to this value "132" is applied to one end of resistor R3.

[0095] Like this temperature-responsive reference voltage information, a reference voltage setting value that determines the power supply voltage to be applied to one end of resistor R3 is set in advance in accordance with the temperature near the optical scanning unit, and by using the temperature-responsive reference voltage information, a power supply voltage that corresponds to the actually measured temperature near the optical scanning unit is applied to one end of resistor R3, thereby offsetting the effects of temperature changes and preventing fluctuations in the write timing.

[0096] <Example of noise countermeasures for synchronization signals> (Example of nullifying noise occurring in synchronization signals) Here, a process for making noise occurring in a synchronization signal non-detectable by utilizing a start point detection signal of the synchronization signal will be described. FIG. 12 shows a timing chart relating to the process of making noise in a synchronization signal undetectable by utilizing a start point detection signal of the synchronization signal.

[0097] As described above, the synchronization signal V_OUT is a signal that changes between two values ​​(H, L) based on the comparison between the detected AC signal (V_AC) and the comparison voltage (V_REF). For example, in FIG. 4, the synchronization signal V_OUT is a signal that exhibits an L level from the time when the rising edge of the detected AC signal (V_AC) matches the comparison voltage (V_REF) to the time when the falling edge of the detected AC signal (V_AC) matches the comparison voltage (V_REF).

[0098] Ideally, only this synchronization signal V_OUT is periodically output to generate accurate write timing, but spike-like noise due to high-voltage leakage noise may occur in the synchronization signal V_OUT. Spike noise is easily propagated to lines with high impedance. In particular, the circuit that generates the detection AC signal (V_AC), which consists of resistor R1 and capacitor C, is a differential circuit, so spike noise is easily generated.

[0099] For example, spike-like noise (n1, n2, n3) occurs between periodically output L-level signals, like the synchronization signal V_OUT shown in FIG. Such spike-like noise is generally sufficiently small compared to the duration of the L level of the synchronization signal V_OUT, but when spike-like noise occurs, the same edge as when the L level changes is detected, and therefore the write timing may be significantly delayed due to the influence of the spike-like noise.

[0100] Therefore, in order to avoid the influence of spike-like noise, a period (noise mask period) is set in which the synchronization signal V_OUT is invalidated during the period from when an edge is detected at the time of the L level change of the synchronization signal V_OUT until when an adjacent edge is detected at the time of the normal L level change. For example, the scan control unit 40 (ASIC) to which the synchronization signal V_OUT is input is provided with a noise mask unit that prevents spike-like noise contained in the synchronization signal V_OUT from being detected. This noise mask section disables detection of the synchronization signal during a noise mask period between the output timings of two adjacent synchronization signals generated by the synchronization signal generating section 30.

[0101] To disable the detection of the synchronization signal, for example, the timing at which the synchronization signal V_OUT changes from H level to L level is detected. That is, as shown in FIG. 12, a signal (called a start point detection signal) indicating the timing at which the synchronization signal V_OUT changes from H level to L level is generated. As shown in FIG. 12, the start point detection signals are signals (K1, K2) that are generated at predetermined time intervals (for example, 300 μsec) when the synchronization signal V_OUT changes from H level to L level. The time interval between these two adjacent start point detection signals (K1, K2) corresponds to the period (noise mask period) during which the synchronization signal V_OUT is invalidated. The scanning control unit 40 does not detect the synchronization signal V_OUT during this noise mask period, and ignores any level changes that may occur during the noise mask period.

[0102] The noise mask period is set in advance according to, for example, the scanning speed. In this way, by setting the noise mask period using a signal (starting point detection signal) that indicates the timing at which the synchronization signal V_OUT changes from H level to L level, spike-like noise that occurs in the synchronization signal can be made non-detectable, and the write timing can be prevented from being affected by noise in the synchronization signal.

[0103] (Detection of noise occurring in synchronization signals) Here, a process for detecting spike-like noise occurring in the synchronization signal V_OUT during the noise mask period will be described. FIG. 13 shows a timing chart relating to the process of detecting noise occurring in the synchronization signal.

[0104] As mentioned above, if high-voltage leak noise occurring in the synchronization signal V_OUT is left unchecked, the level of the leak noise will gradually increase, which may cause streaks to appear in the formed image and may even cause communication errors between boards. Therefore, it is preferable to take measures to suppress the occurrence of high-voltage leak noise before the level of the leak noise becomes too large.

[0105] For example, if a signal with a relatively short duration is detected in the synchronization signal V_OUT during the noise mask period, spike-like noise is occurring, and there is a high possibility that high-voltage leak noise is occurring. In such a case, the occurrence of high-voltage leak noise can be suppressed by replacing a high-voltage part such as a charging device (for example, a spring contact member at the charging position of the photosensitive member).

[0106] Therefore, the scan control unit 40 includes, in addition to the noise mask unit described above, a noise detection unit that detects spike-like noise contained in the synchronization signal. This noise detection section generates a noise detection signal that detects the position of spike-like noise that occurs in the synchronization signal during the noise mask period between the output timings of two adjacent synchronization signals generated by the synchronization signal generation section 30.

[0107] In Figure 13, as in Figure 12, spike-shaped noise (n1, n2, n3) occurs in the synchronization signal V_OUT, and signals (starting point detection signals: K1, K2) are generated that indicate the timing when the synchronization signal V_OUT changes from H level to L level, and the interval between two adjacent starting point detection signals (K1, K2) is the noise mask period. As shown in FIG. 13, if a spike-like noise n1 occurs between two starting point detection signals (K1, K2), a signal that detects the occurrence point Kn1 of this noise n1 is the noise detection signal.

[0108] The noise detection signal in Figure 13 is a signal that detects spike-like noise that occurs during the noise masking period, and is a signal whose signal level changes from L to H when, for example, noise n1 occurs during the noise masking period and the synchronization signal V_OUT changes instantaneously from H level to L level. This noise detection signal can be generated by the scanning control unit 40 by constantly monitoring the synchronization signal V_OUT.

[0109] The noise detection signal generated by the scan control unit 40 is given to, for example, a control unit that controls the overall operation of the image forming apparatus. When the control unit detects that the signal level of the noise detection signal has changed from L to H during the noise mask period, the control unit may store the fact that noise has been detected at a timing different from the original synchronization timing of the start of writing. In addition, to notify the image forming device manager or repair person that an inappropriate spike-like noise has been detected, a warning message may be displayed on the image forming device's display device, indicating that noise has been detected and requesting the replacement of parts that may be causing the noise, such as spring contact members. Furthermore, the contents of this warning display may be notified by voice or may be sent to a mobile terminal or the like carried by the administrator or the like.

[0110] By displaying such a warning, it becomes possible to replace the part that is causing the noise, thereby preventing a deterioration in the quality of the images formed by the image forming apparatus. [Explanation of symbols]

[0111] 10 light detection unit, 11 photodiode, 12 detection signal generation unit, 20 comparison voltage output section, 30 Synchronization signal generation unit, 40 Scanning control section, 50 photosensitive drum, 60 optical scanning unit, 61 Optical scanning unit, 62 Light source

Claims

1. an optical scanning unit including a light source that emits a light beam and an optical scanning unit that changes the irradiation direction of the light beam; a light detection unit including a light receiving element that receives the light beam emitted from the light source and a detection signal generation unit that generates a light detection signal corresponding to the intensity of the received light beam; a synchronization signal generating unit that compares the generated light detection signal with a predetermined comparison voltage to generate a synchronization signal for determining the timing of irradiating the light beam at a scanning start position of the light beam that scans the scanned object, the light detection signal is composed of a detection AC signal which is an AC component of the detection signal that changes in response to the received light intensity of the light beam; the synchronization signal generation unit generates the synchronization signal by comparing a comparison voltage offset with respect to a voltage level of the detection AC signal when there is no change in the photodetection signal generated when no light beam is detected with a voltage level of the detection AC signal immediately after a change in the photodetection signal generated when a light beam is detected; A scanning timing detection device, characterized in that the comparison voltage is changed in response to a change in temperature in the vicinity of the optical scanning unit.

2. a reference voltage having a predetermined constant voltage value is superimposed on the detection AC signal; the comparison voltage is a voltage obtained by adding a predetermined non-zero offset voltage to the reference voltage, 2. The scanning timing detection device according to claim 1, wherein the synchronization signal is a signal generated by comparing the detection AC signal on which the reference voltage is superimposed with the comparison voltage.

3. the synchronization signal generation unit includes a comparator; the detection AC signal on which the reference voltage is superimposed and the comparison voltage are input to the comparator; 3. The scanning timing detection device according to claim 2, wherein the comparator outputs a comparison result between the detection AC signal on which the reference voltage is superimposed and the comparison voltage as the synchronization signal.

4. 4. The scanning timing detection device according to claim 1, wherein the comparison voltage is changed in accordance with the amount of light of the light beam received by the light receiving element.

5. storing in advance light-quantity-corresponding reference voltage information that associates a reference light quantity setting value corresponding to the light quantity of the light beam received by the light-receiving element with a reference voltage setting value corresponding to the voltage level of the comparison voltage; 5. The scanning timing detection device according to claim 4, wherein the comparison voltage is set to a voltage level equivalent to a reference voltage setting value associated with a reference light intensity setting value corresponding to the light intensity of the light beam emitted from the light source, using the light intensity-corresponding reference voltage information.

6. a temperature sensor provided in the vicinity of the optical scanning unit; temperature-corresponding reference voltage information that associates a temperature setting value corresponding to a temperature in the vicinity of the optical scanning unit with a reference voltage setting value corresponding to a voltage level of the comparison voltage is stored in advance; The scanning timing detection device described in claim 1, characterized in that the comparison voltage is set to a voltage level equivalent to a reference voltage setting value associated with a temperature setting value corresponding to the temperature measured by the temperature sensor, using the temperature-corresponding reference voltage information.

7. a scanning control unit that controls the emission timing of the light beam by using the synchronization signal generated by the synchronization signal generation unit; the scanning control unit includes a noise mask unit that prevents spike noise included in the synchronization signal from being detected; 4. The scanning timing detection device according to claim 1, wherein the noise masking unit disables detection of the synchronization signal during a noise masking period between output timings of two adjacent synchronization signals generated by the synchronization signal generating unit.

8. the scanning control unit further includes a noise detection unit that detects spike noise included in the synchronization signal; 8. The scanning timing detection device according to claim 7, wherein the noise detection unit generates a noise detection signal that detects the position of spike-like noise that occurs in the synchronization signal during a noise mask period between the output timings of two adjacent synchronization signals generated by the synchronization signal generation unit.

9. the light receiving element is a photodiode, 4. The scanning timing detection device according to claim 3, wherein the detection AC signal is output from a capacitor connected to the anode of the photodiode and is applied to the comparator.

10. the light receiving element is a photodiode, 4. The scanning timing detection device according to claim 3, wherein the detection AC signal is output from a capacitor connected to the cathode of the photodiode and is applied to the comparator.

11. a scanning timing detection device according to any one of claims 1 to 10; a photosensitive drum that is a scanned body that is scanned with a light beam; the light detection unit is disposed in the vicinity of the photosensitive drum, an image forming apparatus, characterized in that a light beam is scanned toward the photosensitive drum in response to the synchronization signal generated by the synchronization signal generating unit, and an electrostatic latent image is formed on the surface of the photosensitive drum.

12. A scanning timing detection method for a scanning timing detection device having a light source and one light receiving element, comprising: a light receiving step of receiving, by the light receiving element, a light beam emitted from an optical scanning unit including the light source; a light detection step of generating a light detection signal consisting of a detection AC signal which is an AC component of the detection signal that changes in response to the received light intensity of the received light beam; a comparison voltage generating step of generating a comparison voltage that is offset with respect to the voltage level of the detected AC signal when there is no change in the photodetection signal that is generated when the light beam is not detected; a synchronization signal output step of comparing the comparison voltage with a voltage level of the detected AC signal immediately after a change in the light detection signal generated when the light beam is detected, and outputting a synchronization signal for determining the timing of irradiating the light beam at a scanning start position of the light beam to scan the scanned object, A scanning timing detection method, characterized in that the comparison voltage is changed in response to a change in temperature in the vicinity of the optical scanning unit.

Images