JPH10123632A - Lighting control device for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an abnormality by a software control when a zero cross circuit makes a wrong detection, and improve the reliability of an equipment by controlling a switching means synchronously with a zero cross signal only when the switching means is in ON state. SOLUTION: A microcomputer 20 as control means controls a switching means 13 synchronously with a zero cross signal outputted from a zero cross detecting circuit 19, in the lighting of an exposure lamp 2, only when the switching means 13 is in ON state. In such a lighting control, a trigger-on flag is used, and this flag is raised only once when the lamp trigger is ON, so that zero cross interruption is performed only once to one ON of the lamp trigger. Thus, during the time from the start to stop of a phase angle timer, the zero cross interruption processing is laid in prohibited state. Thus, even if the waveform of a commercial ac power source is disturbed by the instantaneous interruption of the power source, the reset of the phase angle timer can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illumination control device for an image forming apparatus such as a copying machine and a facsimile.

[0002]

2. Description of the Related Art In an illumination control device of an image forming apparatus such as a copying machine or a facsimile, phase control is generally performed in order to precisely control the amount of light from an exposure lamp. The phase control basically controls the power applied to the exposure lamp by adjusting the duty between the energizing period and the non-energizing period of each cycle of the AC waveform. Hereinafter, an example of a lighting control device in a conventional image forming apparatus will be described.

FIG. 4 is a view for explaining an image forming process of a copying machine as an image forming apparatus. In FIG. 4, as is well known, an original is set on a contact glass 1, and illumination light emitted from an exposure lamp 2 as an illumination light source below the contact glass 1 is reflected on the original surface.
This reflected light passes through the first mirror 3a, the second mirror 3b, the third mirror 3c, the imaging lens 4, the fourth mirror 3d, the fifth mirror 3e, the sixth mirror 3f, and reaches the photosensitive drum 5,
It converges on the surface of the photosensitive drum 5. As a result, the image of the document is formed on the photosensitive drum 5. At this time, the first scanner 6 equipped with the exposure lamp 2 and the first mirror 3a scans along the document surface, and the second scanner 7 equipped with the second mirror 3b and the third mirror 3c operates the first scanner
The scanner scans in the same direction along the document surface at half the speed of the scanner 6 and rotates the photosensitive drum 5 in synchronism with the scanning. It is formed as an electrostatic latent image. Then, the electrostatic latent image formed on the photoreceptor 5 is developed with toner, the toner image is transferred to a sheet, and the image is formed on the sheet by fixing it by heating and pressing.

In the above-described image forming process, an exposure lamp 2 used in a step of optically scanning a document image is used.
Is controlled by a circuit as shown in FIG. Exposure lamp 2
Is connected to an AC power supply 11 via a relay 12 capable of interrupting a circuit, a bidirectional switching element 13 such as a triac, and a fuse 21. A primary side of a transformer 15 is connected to both ends of the exposure lamp 2. The voltage of the AC power supply 11 is stepped down by the transformer 15, and the voltage is detected by the full-wave rectifier 16 on the secondary side of the transformer 15. 17, a voltage signal detected by the voltage detection circuit 17 is supplied to a microcontroller (hereinafter referred to as a “microcomputer”) 2
Input to 0. On the other hand, a zero-cross circuit 19 is also connected to the AC line via a transformer 18, and the microcomputer 2 uses the zero-cross signal obtained by the zero-cross circuit 19 as a basic control timing based on the detected voltage.
0 turns on the triac 13 through the trigger circuit 14.
Control off. With such a circuit, control for keeping the light amount from the exposure lamp 2 constant is performed.

FIG. 5 shows the control waveform. As shown in FIG. 5, first, a zero-cross signal is generated at each zero-cross point by the zero-cross circuit 19 with respect to an AC input waveform (AC input waveform), and the microcomputer 20 incorporates the microcomputer 20 in synchronization with the zero-cross signal. Start the current phase angle timer. In the phase angle timer, a time corresponding to the duty of the energization time and the non-energization time is set based on the voltage value detected by the voltage detection circuit 17 in advance, and the phase angle timer is set. When the time is counted, a timer interrupt occurs. The trigger circuit 14 is turned on by the timer interrupt, and a trigger waveform as shown in FIG. 5 and a ramp applied voltage waveform corresponding to the trigger waveform are obtained. Since the triac 13 is used as the switching element in the example of FIG. 3, once the trigger is applied, the energization continues until the AC input waveform reaches the zero cross point. On the other hand, when the AC input voltage decreases to near the zero cross point, the next zero cross signal is generated, and the microcomputer 20 sets and starts the phase angle timer again. In such a control cycle, a lamp detection voltage as shown in FIG. 5 is obtained, and the lamp light amount becomes substantially constant.

However, in the case of a copying machine or the like, a commercial AC power supply is generally used as the AC input voltage, and its waveform is not always a sine wave. Therefore, the zero-cross signal obtained from the commercial AC power supply waveform is also, for example, 50
In the case of [Hz], the cycle is originally 10 [msec], but phenomena such as an irregular cycle and an instantaneous interruption of the power supply can sufficiently occur. In this case, since the phase of the zero-cross signal and that of the AC input are different, the energized state or non-energized state for one cycle or more may be continued without switching on / off of energization. As a result, in an image forming apparatus such as a copying machine, a white band or a black band occurs in the formed image, and in the worst case, the image becomes a blank image or a black image.

As techniques for coping with such a phenomenon, Japanese Patent Application Laid-Open No. 63-95850 and Japanese Patent Application Laid-Open No. 8-693 are known.
There is a technique described in Japanese Patent Application Publication No. 27-273. JP-A-63-95850
The technology described in Japanese Patent Application Publication No. JP-A-2002-115686 deals with a case where a zero-cross signal is lost, and uses a timer to monitor the zero-cross signal loss. When the zero-cross signal loss is detected, a phase angle timer is started instead of the zero-cross signal. Things. Further, the technique described in Japanese Patent Application Laid-Open No. 8-69327 relates to a fixing heater of a copying machine instead of an exposure lamp. However, the purpose of the technique is to deal with an instantaneous interruption of the power supply. At this time, the power supply to the fixing heater is stopped, and thereafter, when the AC power supply is restored and the polarity inversion occurs, the power supply to the fixing heater is started. The techniques described in the above two publications are both examples of a method of controlling the AC power supply when the AC input waveform is disturbed.

[0008]

However, the techniques described in JP-A-63-95850 and JP-A-8-69327 are all methods for coping with the loss of the zero-cross signal. Here, for example, as in the case of an alternating current (AC) input waveform shown at the top of FIG. 6, it is assumed that noise or instantaneous interruption occurs at a position that is not near the zero cross point. At this time, in the conventional control methods described in the above publications, the phase angle timer is first started by inputting a normal zero-cross signal. However, in the example of FIG. 6, noise is present before the phase angle timer stops due to timeout, and this noise causes the zero-cross detection circuit 19 to perform erroneous detection and output a signal. This signal causes the microcomputer 20 to generate a timer interrupt, reset the phase angle timer, and restart the timer. Therefore, the control is different from the normal on / off duty. The example shown in FIG. 6 is an example in which the amount of lamp light is reduced without a lamp trigger being applied. However, depending on the control circuit, a phenomenon in which the lamp is fully lit with a duty of 100% may also occur. For such a phenomenon,
JP-A-63-95850 and JP-A-8-69 described above.
The method of coping with the loss of the zero-cross signal described in Japanese Unexamined Patent Publication No. 327 cannot cope with the problem.

Further, when a copying machine is taken as an example, since it generally has a structure including an exposure lamp and a fixing heater, the AC load of both of them causes an AC input fluctuation as shown in FIG. This is considered sufficiently, and control by hardware such as a circuit configuration or software control is required, and some countermeasures are required.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art. A first object of the present invention is to provide a switching means for controlling on / off of energization of an exposure lamp, and a predetermined means synchronized with a zero cross signal. In a lighting control device of an image forming apparatus having a control unit for controlling ON / OFF of the switching means at a timing, a fluctuation of an AC input voltage due to external noise or other internal AC load occurs, and a zero cross circuit is generated. It is an object of the present invention to provide a lighting control device for an image forming apparatus which prevents a control abnormality by software control when a false detection occurs, improves the reliability of the device, and is relatively inexpensive.

A second object of the present invention, in addition to the first object, is to define a control method at the start of exposure lamp lighting so as to unify the control when the exposure lamp is turned on and off. Another object of the present invention is to provide an illumination control device for an image forming apparatus that can reduce the source of control software.

A third object of the present invention is to provide a switching means for controlling on / off of energization of an exposure lamp and a control unit for controlling on / off of the switching means at a predetermined timing in synchronization with a zero cross signal. It is an object of the present invention to provide an illumination control device for an image forming apparatus, which further enhances the stability of the amount of lamp light and realizes highly reliable control.

[0013]

According to the first aspect of the present invention,
An exposure lamp driven by an AC input from an AC power supply, a zero-cross detection circuit for detecting a zero-cross point of the AC input, switching means for turning on and off the exposure lamp, and a zero-cross signal output from the zero-cross detection circuit In the illumination control device of the image forming apparatus having a control unit that controls on / off of the switching unit at a predetermined timing, the control unit is configured to control the switching unit only when the exposure lamp is on and the switching unit is on. ,
The switching means is controlled in synchronization with a zero-cross signal output from the zero-cross detection circuit.

According to a second aspect of the present invention, the control means includes:
Only when the exposure lamp is turned on, the switching means is controlled in synchronization with the zero-cross signal output from the zero-cross detection circuit, even if the switching means is not in the ON state.

According to a third aspect of the present invention, there is provided an exposure lamp driven by an AC input from an AC power supply, a zero-cross detection circuit for detecting a zero-cross point of the AC input, and switching means for turning on / off the energization of the exposure lamp. And, in synchronization with the zero cross signal output from the zero cross detection circuit,
In the illumination control device for an image forming apparatus having a control unit for controlling on / off of a switching unit at a predetermined timing, even if a zero-cross signal is input within a predetermined time determined by a frequency of an AC input of the AC power supply, the control is performed. A monitoring timer is provided so that the means does not perform on / off control of the switching means.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an illumination control device for an image forming apparatus according to the present invention will be described with reference to the drawings. According to the present invention, in the copying machine having the image forming process shown in FIG. 4 already described, the exposure lamp 2 as the illumination light source for optically scanning the original image is replaced with the exposure lamp 2 shown in FIG.
Since the hardware configuration such as the image forming process and the circuit configuration is the same as the conventional configuration, the description of the image forming process and the circuit configuration will be omitted. To

FIG. 1 shows a control flow of an embodiment of an illumination control device for an image forming apparatus according to the present invention. This control flow is executed in the microcomputer 20 of the circuit shown in FIG. When the exposure lamp 2 is turned on and the exposure lamp 2 in FIG. 3 is turned on, and a zero-cross interrupt by a zero-cross signal is input, first, in step S1, a flag indicating whether the trigger is on is checked. Here, "trigger on" refers to a case where the switching means 13 in FIG. 3 is in an on state. If the trigger is off, it returns and returns without performing any control. If the trigger is ON, the trigger ON flag is set to 0 in step S2, and the phase angle timer is started in step S3. When the phase angle timer times out and stops in step S4, the lamp trigger is turned on in step S5. Now that the exposure lamp has been energized,
At this time, the trigger on flag is set to 1 in step S6.

When the phase angle timer times out, the lamp feedback voltage is read in step S7 as a separate flow, the next phase angle timer value is calculated (step S8), and the calculated phase angle timer value is set. In advance (step S9), the above-described flow waits for the next zero-cross interruption. Note that, in the trigger off, in the example of the circuit diagram shown in FIG. 3, a triac is used as the switching element 13, so that the triac itself gates off when the AC input becomes close to zero.

Compared with the conventional lighting control, the lighting control according to the above embodiment uses a trigger on flag, which is set only once when the lamp trigger is turned on, and is set once when the lamp trigger is turned on. On the other hand, the zero-cross interrupt corresponds only once.
Therefore, the feature of the illumination control according to the above embodiment is that the zero-cross interrupt processing is in a prohibited state from the start to the end of the phase angle timer. Thereby, even if the commercial AC power supply has an irregular period or a momentary interruption of the power supply and the commercial AC power supply waveform is disturbed, the reset of the phase angle timer described above can be prevented,
It is possible to eliminate such a problem that the energization of the exposure lamp 2 is not switched on / off and a white band or a black band is generated in the formed image.

As can be seen from the above control flow, the microcomputer 20 as the control means is provided only when the exposure lamp 2 is turned on and the switching means 13 is on.
The switching means 13 is controlled in synchronization with a zero-cross signal output from the zero-cross detection circuit 19.

The control flow described above is the control when the exposure lamp is turned on. In this control flow, the trigger-on flag also controls the energization of the exposure lamp 2. That is, the operation of the flag can control the turning on and off of the exposure lamp, and has an advantage that the flag processing can be simplified as compared with the conventional illumination control. Specifically, when the exposure lamp is turned on, the trigger on flag is forcibly set.
As a result, it is possible to proceed to the step of setting the trigger-on flag of S2 to 0, and enter a lamp energization cycle synchronized with the zero-cross signal output from the zero-cross detection circuit 19. When the lamp is turned off, the lamp is turned off in a state immediately after the trigger is turned on, that is, by forcibly turning off the trigger-on flag after step S6. As described above, the microcomputer 20 as the control unit controls the switching unit 13 in synchronization with the zero-cross signal output from the zero-cross detection circuit 19 only when the exposure lamp 2 is turned on, even if the switching unit 13 is not on. Control.
This makes it possible to unify the control when the exposure lamp is turned on and when it is turned off, and to reduce software sources.

As a concern in the control flow described so far, the zero-cross interrupt processing is prohibited during the operation of the phase angle timer, but from the stop of the phase angle timer and the trigger on until the next zero cross signal. During that time, a zero-cross signal due to noise may be input. If a zero-cross signal due to noise is input after the trigger is turned on and before the next normal zero-cross signal is input, interrupt processing using this zero-cross signal is performed, and the next normal zero-cross signal is prohibited. Is expected. If the next regular zero-cross signal is prohibited, the duty ratio will be larger in the next energization cycle and the light quantity will fluctuate. However,
In the exposure lamp control, since the light amount is controlled by feeding back the lamp voltage, the correction is applied as the energizing cycle is repeated, and the fluctuation of the light amount is at a level that does not cause much problem.

However, even if the fluctuation of the light quantity is not so problematic, it is desirable to control the light quantity more stably in order to obtain a higher quality image. Thus, FIG. 2 shows an example of control that can further stabilize the amount of light. In the lighting control shown in FIG. 2, the determination of permission / inhibition of the zero-crossing interrupt process by the trigger-on flag in the lighting control shown in FIG. 1 is changed to a supplementary timer value. The supplementary timer referred to here is reset when the processing by the zero-cross signal is stared in step S11, performs a series of processing during the series of steps S3 to S9, and continues counting until the next zero-cross signal input. is there. In FIG. 2, 8 [mse
c], which means that the frequency of the AC input is 50 [Hz].
Is an example of a number arbitrarily set as a value close to 10 [msec] based on one cycle being 10 [msec]. Thereby, even if an extra zero-cross signal is output regardless of before or after the trigger is turned on during a period close to the predetermined period of the AC power supply, the extra zero-cross signal is ignored, and the extra zero-cross signal is not reset by the zero-cross signal. Zero-cross interrupt processing can be performed at appropriate timing. Therefore, the timing of reading the lamp feedback voltage in step S7 becomes appropriate,
The lamp light quantity characteristics are more stable.

As described above, even if the above-mentioned zero-cross signal is input within a predetermined time determined by the frequency of the AC input of the AC power supply, the above-mentioned supplementary timer allows the control means (corresponding to the microcomputer 20 in FIG. 3) to perform the above-mentioned switching. It has a function as a monitoring timer for monitoring so as not to perform on / off control of the means. Therefore, according to the example of the control flow shown in FIG. 2, even when the AC input voltage fluctuates due to external noise or other internal AC load, etc., and the zero-crossing detection circuit erroneously detects the zero-crossing, a zero-crossing period other than the predetermined cycle occurs Since all of the signals can be ignored, the phase angle timer determined by the lamp feedback voltage can be accurately set with good timing, and more reliable lighting control with stable lamp light quantity characteristics can be realized.

[0025]

According to the first aspect of the present invention, in the illumination control device of an image forming apparatus such as a copying machine, the control means includes:
Since control is performed so that synchronization with the zero-cross signal is only accepted when the trigger is on, even if the AC input voltage fluctuates due to external noise or other internal AC load, etc., even if the zero-cross circuit causes false detection, the phase Since the angle timer is not reset, control abnormality can be prevented, and highly reliable lighting control in which a white band image or a black band image does not occur can be realized.

According to the second aspect of the present invention, the control means according to the first aspect of the present invention provides the control means only when the exposure lamp is turned on.
2. A lighting method according to claim 1, wherein a control method at the start of exposure lamp lighting is defined as controlling the switching means in synchronization with a zero cross signal output from a zero cross detection circuit even when the switching means is not in an on state. In addition to the effect of the control, it is possible to obtain the effect of unifying the control when the exposure lamp is turned on and turning off the exposure lamp, thereby reducing the source of software.

According to the third aspect of the present invention, in the illumination control device for an image forming apparatus such as a copying machine, even if a zero-cross signal is input within a predetermined time determined by the frequency of the AC input of the AC power supply, the control means is provided. A monitoring timer is provided so as not to perform on / off control of the switching means, so that even if the zero-cross circuit erroneously detects due to fluctuations in the AC input voltage due to external noise or other internal AC loads, etc. Zero-crossing signals other than the period can be ignored, and the timing of the phase angle timer determined by the lamp feedback voltage can be accurately set. Can be realized.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating an embodiment of an illumination control device of an image forming apparatus according to the present invention.

FIG. 2 is a flowchart showing another embodiment of the illumination control device of the image forming apparatus according to the present invention.

FIG. 3 is a block diagram showing an example of an electric circuit applicable to the present invention.

FIG. 4 is a front view schematically illustrating an example of a general image forming apparatus.

FIG. 5 is a timing chart illustrating an example of illumination control of a conventional image forming apparatus.

FIG. 6 is a timing chart showing another example of the illumination control of the conventional image forming apparatus.

[Explanation of symbols]

 2 Exposure lamp 11 AC power supply 13 Switching means 19 Zero cross detection circuit 20 Microcomputer as control means

Claims (3)

[Claims] 1. An AC power supply, an exposure lamp driven by an AC input from the AC power supply, a zero-cross detection circuit for detecting a zero-cross point of the AC input, and switching for turning on / off the energization of the exposure lamp. Means for controlling the on / off of the switching means at a predetermined timing in synchronization with a zero-cross signal output from the zero-cross detection circuit. An illumination control device for an image forming apparatus, wherein the switching unit is controlled in synchronization with a zero-cross signal output from the zero-cross detection circuit only when the switching unit is on when the lamp is turned on. 2. The control means controls the switching means only when the exposure lamp is turned on in synchronization with a zero-cross signal output from the zero-cross detection circuit, even if the switching means is not on. The illumination control device for an image forming apparatus according to claim 1. 3. An AC power supply, an exposure lamp driven by an AC input from the AC power supply, a zero-cross detection circuit for detecting a zero-cross point of the AC input, and switching for turning on / off the energization of the exposure lamp. Means for controlling the on / off of the switching means at a predetermined timing in synchronization with a zero cross signal output from the zero cross detection circuit. Lighting control of the image forming apparatus, characterized in that the control means does not perform on / off control of the switching means even if the zero-cross signal is input within a predetermined time determined by the frequency of apparatus.