Scanning optical device and image forming apparatus

Abstract

To cause a safety circuit of a laser scanner to securely operate even when there is an abnormality in firmware operations when an abnormality occurs during laser emission.SOLUTION: A scanning optical device comprises a safety circuit 207 that receives input of a synchronization signal 232 from a DB 6, wherein after the lapse of predetermined time according to the time constant of the circuit, its output voltage 233 changes, and the output voltage 233 is connected to a load SW 212. The output voltage 233 of the safety circuit 207 changes when the synchronization signal 232 is not input from the BD 6 for a predetermined time from when the load SW 212 is switched to an on-state by output voltage 234 of a CPU 208. The safety circuit 207 switches the load SW 212 to an off-state regardless of the state of the output voltage 234 of the CPU 208.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a scanning optical device and an image forming device, and more particularly to a laser scanning device mounted in, for example, a laser beam printer. [Background technology]

[0002] IEC (International Electrotechnical Commission) 60825-1 specifies safety standards for laser-equipped products to prevent injury to users. JIS (Japanese Industrial Standards) C 6802, based on IEC 60825-1, classifies laser products according to their level of risk (laser class) and specifies the safety measures required for each class. Laser classes are classified according to risk, from Class 1 to Class 4, with Class 4 being the most dangerous. The risk level of a laser class is determined by the laser's emitted power, wavelength, and duration of emission. Lasers commonly used in laser beam printers fall into Class 3. Class 3 is further classified into Class 3B and Class 3R in descending order of risk. Class 3B requires an interlock mechanism consisting of a laser shutter, while Class 3R does not. Designing lasers to be Class 3R or lower is important to achieve compact and affordable laser-equipped products.

[0003] A laser scanner installed in a laser beam printer scans a laser using a rotating polygon mirror that is driven to rotate, and emits light outside the laser scanner. Even if the laser power emitted from the laser is the same, the amount of light exposure per unit time and unit area is lower when the laser is in a scanning state compared to when it is in a non-scanning (stationary) state. In other words, from the perspective of laser light exposure, a stationary light state is deemed more dangerous. Therefore, it is relatively easy to meet the Class 3R requirements if the laser does not emit light when it is not in a scanning state. Therefore, a method has been proposed in which a rotation status output signal unit that notifies the rotation status of the driver that drives the rotating polygon mirror is provided, and power is supplied to the laser emitter only when the rotation status output status from the rotation drive signal indicates normal rotation (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-088441 Summary of the Invention [Problem to be solved by the invention]

[0005] However, a laser scanning device configured as in the conventional example, in which light cannot be emitted until the rotating polygon mirror reaches a normal rotation speed, presents the following problems. A circuit is required to count the FG signal and determine the motor's rotation state in order to determine the rotation state of the rotating polygon mirror before supplying power to the laser emitter. Laser scanning devices installed in laser beam printers and other devices are equipped with a synchronization signal detection means for synchronizing the laser emission timing. When the laser is emitting light, it is possible to determine whether the laser is in a scanning or non-scanning (stationary) state based on the presence or absence of the synchronization signal. Because the laser cannot be emitted upon activation of the rotating polygon mirror's rotation device, a startup time is required for the laser scanning device. It also takes time for the laser light intensity to stabilize at a predetermined level after the laser emission starts. To shorten the startup time of a laser scanning device, laser emission must be initiated upon activation of the rotating polygon mirror's rotation device.

[0006] Furthermore, the upper limit of Class 3R laser power specified in IEC 60825-1 varies depending on the duration of emission. For example, for 790 nm laser light used in laser beam printers, upper limits for laser power emission are specified for durations of 100 sec (10 sec to 30,000 sec category) and 100 msec (18 us to 10 sec category). Even if the laser power emitted during an abnormality exceeds the upper limit for the 100-sec category, it is sufficient as long as the safety circuit operates within the 100-second duration and the laser power falls below the lower limit. Therefore, it is important to set an appropriate delay time for the safety circuit to operate. On the other hand, if the safety circuit's operation delay time is managed by firmware built into the CPU, there is a risk that the safety circuit will not operate properly if there is an abnormality in the firmware operation. Laser safety circuits must be configured solely with hardware, without firmware intervention.

[0007] The present invention was made under these circumstances, and its purpose is to ensure that the safety circuit of a laser scanning device operates reliably when an abnormality occurs during laser emission, even if there is an abnormality in firmware operation. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0009] (1) A scanning optical device comprising: a laser element; a deflector that deflects light emitted from the laser element; output means that receives the light deflected and scanned by the deflector and outputs a synchronization signal; switch means that is provided on a supply path that supplies current to the laser element and switches between an on state in which current is supplied to the laser element and an off state in which the supply of current to the laser element is cut off; and control means that controls the on state or the off state of the switch means by a control signal, wherein the synchronization signal is input from the output means and an output changes when a predetermined time corresponding to a time constant of the circuit has elapsed, the output of the protection circuit being connected to the switch means, and the protection circuit changes its output when the synchronization signal is not input from the output means for the predetermined time after the switch means is switched to the on state by the control signal from the control means, and the protection circuit switches the switch means to the off state regardless of the state of the control signal from the control means.

[0010] (2) An image forming apparatus comprising: a scanning optical device according to (1); an image carrier on which an electrostatic latent image is formed by the scanning optical device; a developing means for developing the electrostatic latent image with toner to form a toner image; a transfer means for transferring the toner image to a transfer material; and a fixing means for fixing the toner image transferred by the transfer means. [Effects of the Invention]

[0011] According to the present invention, when an abnormality occurs during laser emission, the safety circuit of the laser scanning device can be reliably operated even if there is an abnormality in firmware operation. [Brief explanation of the drawings]

[0012] [Figure 1] Image diagram of the image forming apparatus of Examples 1 and 2 [Figure 2] Image diagram of the scanning optical device of Examples 1 and 2 [Figure 3] Control block diagram of the scanning optical device of the first and second embodiments [Figure 4]Configuration diagram of the safety circuit of Example 1 [Figure 5] FIG. 10 is a diagram showing the relationship between the BD signal and the charge voltage in the first embodiment. [Figure 6] Safety circuit configuration diagram of Example 2 DETAILED DESCRIPTION OF THE INVENTION [Example]

[0013] [Image forming device] A first embodiment will be described with reference to FIG. 1. In the first embodiment, a laser beam printer using an electrophotographic system will be described as an example. FIG. 1 is a diagram showing an image forming apparatus 150. The image forming apparatus 150 includes a scanning optical device 100 as a laser scanning device. The image forming apparatus 150 includes a paper feed unit 110 on which a transfer material P is placed, a paper feed roller 111, a transfer roller 102 as a transfer means, and a fixing roller 113 and a pressure roller 112 as a fixing means. The image forming apparatus 150 also includes a process cartridge C as an image forming means, located opposite the transfer roller 102 on a transport surface 106 that transports the transfer material P. The process cartridge C includes a photosensitive drum 101 as an image carrier. The process cartridge C includes a charging roller 103, a developing device 105, and a cleaner 109. The charging roller 103 uniformly charges the surface of the photosensitive drum 101. A developing device 105 as a developing means develops the electrostatic latent image on the photosensitive drum 101 with toner to form a toner image T.

[0014] When printing starts, a transfer material P is fed from a paper feed unit 110 by a paper feed roller 111, and the toner image T formed on the photosensitive drum 101 is transferred onto the transfer roller 102 to which a transfer voltage is applied by an application unit 107. Thereafter, the unfixed toner image T on the transfer material P is fixed to the transfer material P by heat and pressure in a fixing roller 113 and a pressure roller 112. The transfer material P with the fixed toner is output to the outside of the image forming apparatus 150 by a discharge roller (not shown), and printing is completed. Note that the image forming apparatus in which the scanning optical device 100 of the present invention is mounted is not limited to the configuration described in FIG. 1.

[0015] [Scanning optical device] FIG. 2 is an explanatory diagram of a scanning optical device 100 according to a first embodiment. In FIG. 2, the scanning optical device 100 includes a laser unit 1, an anamorphic collimator lens 2, an aperture stop 3, a rotating polygon mirror 4, a deflection device 5, a beam detector (hereinafter referred to as a BD) 6, an fθ lens 7, and an optical box 9. The laser unit 1 emits a laser beam L (light). The anamorphic collimator lens 2 is a lens formed by integrally molding a collimator lens, a cylindrical lens, and a BD lens 14. The BD lens 14 is a lens for guiding the laser beam L reflected by the rotating polygon mirror 4 to the BD 6. The rotating polygon mirror 4 has multiple (for example, four in FIG. 2) reflecting surfaces 12. The deflection device 5, which functions as a deflector, rotates the rotating polygon mirror 4. The BD 6 detects the laser beam L and outputs a synchronization signal (a writing start position signal). As shown in FIG. 2, the BD 6 receives the laser beam L outside the area (the area surrounded by the dashed line) on the photosensitive drum 101 where the laser beam L is scanned. The fθ lens 7 is a scanning lens. The optical box 9 houses the optical members described above. The direction in which the laser beam L scans the photosensitive drum 101 (the direction of the rotation axis of the photosensitive drum 101) is called the main scanning direction (Dm), and the direction perpendicular to the main scanning direction (the direction of rotation of the photosensitive drum 101) is called the sub-scanning direction.

[0016] In this configuration, the laser beam L emitted from the laser unit 1 is converted by the anamorphic collimator lens 2 into a substantially parallel beam or a convergent beam in the main scanning direction and into a convergent beam in the sub-scanning direction. The laser beam L then passes through an aperture stop 3, where its beam width is limited, and is focused on a reflecting surface 12 of the rotating polygon mirror 4 as a focal line extending long in the main scanning direction. The laser beam L is then deflected and scanned by rotating the rotating polygon mirror 4. The reflected laser beam L is incident on the BD lens 14 of the anamorphic collimator lens 2. The laser beam L that has passed through the BD lens 14 is incident on the BD 6. At this time, the BD 6, which serves as an output means, outputs a synchronization signal in response to receiving the laser beam L, and the timing for starting writing of an image is determined based on this timing.

[0017] Next, the laser beam L enters the fθ lens 7, which is formed of an aspherical lens. The fθ lens 7 is designed to focus the laser beam L to form a spot on the photosensitive drum 101 and to maintain a constant scanning speed of the spot. The laser beam L that passes through the fθ lens 7 is imaged and scanned on the photosensitive drum 101. The laser beam L is deflected and scanned by the rotation of the rotary polygon mirror 4, and main scanning is performed on the photosensitive drum 101 by the laser beam L, and sub-scanning is performed by rotating the photosensitive drum 101 about the axis of its cylinder. In this way, an electrostatic latent image is formed on the surface of the photosensitive drum 101.

[0018] If the scanning optical device 100 is to be classified as Class 3R under the IEC 60825-1 standard, the amount of light of the laser beam L that passes through the fθ lens 7 and exits the scanning optical device 100 must be equal to or less than a specified value. As described in the conventional example, the amount of light per unit area of ​​the laser beam L is lower when it is deflected and scanned by the rotating polygon mirror 4 than when it is not deflected and scanned.

[0019] [Control configuration] 3 shows a block diagram of the parts related to the control of the scanning optical device 100 of Example 1. The scanning optical device 100 includes an emission control unit 203 that controls the emission of a semiconductor laser 202 (laser element), a deflection device control unit 206 that rotates and drives the deflection device 5 of the rotating polygon mirror 4, and a BD 6 that outputs a synchronization signal.

[0020] The main control unit 201 includes a voltage conversion circuit 220, a CPU 208, a safety circuit 207, and a load switch (hereinafter referred to as load SW) 212. The voltage conversion circuit 220, which serves as a power supply, converts AC voltage supplied from an AC power supply into DC voltage. In the first embodiment, the voltage conversion circuit 220 outputs two output voltages, +3.3V and +24V. These voltages are also referred to as a 3.3V power supply and a 24V power supply hereinafter. The 24V power supply is supplied to the deflection device control unit 206. The CPU 208, which serves as control means, operates by firmware. The CPU 208 also controls the ON / OFF state of the load SW 212 using an output voltage 234, which serves as a control signal (described later). The safety circuit 207 is a protection circuit for the scanning optical device 100, which will be described later. The load SW 212, which serves as switching means, is a switch formed of a P-channel MOSFET.

[0021] The image signal output unit 209 generates an image signal based on image information input from outside the image forming apparatus 150. The light emission control unit 203 controls the light emission of the semiconductor laser 202 based on the image signal supplied from the image signal output unit 209 and a laser control signal supplied from the CPU 208.

[0022] The deflection device control unit 206 drives and rotates the rotary polygon mirror 4 based on a deflection control signal supplied from the CPU 208. The BD 6 sends a synchronization signal 232 to the CPU 208 and the safety circuit 207. The synchronization signal 232 outputs a high level when the laser beam L is not incident on the BD 6, and outputs a low level when the laser beam L is incident on the BD 6.

[0023] The CPU 208 operates by firmware, detects various states of the image forming apparatus 150, and sends control signals at predetermined timing to the image signal output unit 209, the light emission control unit 203, the deflection device control unit 206, and the load switch 212. The CPU 208 also controls the components not shown in FIG. 3, such as the aforementioned paper feed roller 111, transfer roller 102, and fixing roller 113.

[0024] The load SW212 has a source terminal connected to the 3.3V power supply of the voltage conversion circuit 220, and a drain terminal connected to the light-emission control unit 203, the BD6, and the safety circuit 207. When the load SW212 is turned on, a 3.3V current is supplied to the scanning optical device 100 via a power supply line 231 serving as a supply path. That is, the load SW212 is provided on the power supply line 231 (on the supply path) that supplies current to the semiconductor laser 202. More specifically, when the load SW212 is turned on, a 3.3V current is supplied to the light-emission control unit 203 and the BD6 of the scanning optical device 100 via the power supply line 231. That is, the load SW212 switches between an ON state in which a current is supplied to the semiconductor laser 202 and an OFF state in which the supply of current to the semiconductor laser 202 is cut off. Note that, although the load SW212 is configured using a P-channel MOSFET in the first embodiment, the present invention is not limited to this. For example, a semiconductor switch such as a transistor may be used as the load SW 212, or an electromagnetic switch may be used as the switch means, as long as the switch means can be controlled between an on state and an off state by the safety circuit 207 described later.

[0025] A gate terminal of the load SW 212 is connected to a voltage obtained by dividing the 3.3V power supply and the output voltage 234 output from the CPU 208 by voltage dividing resistors 210 and 211, and to an output voltage 233 of the safety circuit 207 via a diode 213. The anode terminal of the diode 213 is connected to the safety circuit 207, and the cathode terminal is connected to the gate terminal of the load SW 212. The load SW 212 is turned on only when the output voltage 234 of the CPU 208 is at a low level and the output voltage 233 of the safety circuit 207 is at a low level; that is, the load SW 212 supplies the 3.3V power supply downstream. When the output voltage 233 of the safety circuit 207 is at a high level, the load SW 212 is turned off regardless of the level of the output voltage 234 of the CPU 208.

[0026] [Safety circuit] 4, the circuit configuration of the safety circuit 207 will be described. The safety circuit 207 as a protection circuit is a circuit in which a synchronization signal 232 is input from the BD 6, and an output voltage 233 (output) changes after a predetermined time according to the time constant of the circuit has elapsed, and the output voltage 233 is connected to a load SW212.

[0027] The safety circuit 207 includes a capacitor 301, resistors 302, 303, and 304, voltage dividing resistors 306 and 307, a transistor 305, and a comparator 308. The transistor 305 has a base terminal connected to the BD6 synchronization signal 232 via a resistor 304, an emitter terminal connected to the power supply line 231 via resistors 302 and 303, and a collector terminal grounded. That is, the safety circuit 207 receives power from the voltage conversion circuit 220 via a load SW 212.

[0028] One end of capacitor 301 is connected to the connection point between resistors 302 and 303, and the other end is grounded. Comparator 308 uses the voltage of power supply line 231 as its power source, and has an inverting input terminal (- terminal) connected to the connection point between resistors 306 and 307, and a non-inverting input terminal (+ terminal) connected to one end of capacitor 301. One end of resistor 306 is connected to power supply line 231, and the other end is connected to one end of resistor 307. The other end of resistor 307 is grounded.

[0029] The input section of the safety circuit 207 is connected to a synchronization signal 232 and a power supply line 231 from BD6, and an output voltage 233 is output from the output section. As described above, the output voltage 233 is connected to the gate terminal of the load SW212 via the diode 213. The synchronization signal 232 is connected to the base terminal of the transistor 305 via the resistor 304. When the synchronization signal 232 is at a low level, the collector and emitter terminals of the transistor 305 are in a conductive state. When the voltage of the power supply line 231 is 0 V, the output voltage 233 of the safety circuit 207 is at a low level.

[0030] When 3.3V is supplied to power supply line 231, output voltage 233 is determined to be high or low depending on the input voltages to the inverting input terminal and non-inverting input terminal of comparator 308. A voltage (hereinafter referred to as the reference voltage) obtained by dividing power supply line 231 using voltage dividing resistors 306 and 307 is input to the inverting input terminal of comparator 308, and the charge voltage of capacitor 301 is input to the non-inverting input terminal. Output voltage 233 is high when the charge voltage of capacitor 301 is higher than the reference voltage, and conversely, is low when the charge voltage of capacitor 301 is lower than the reference voltage.

[0031] (Determining the time constant) When the synchronization signal 232 is in a high level state, i.e., when the laser light beam L is not incident on the BD6, the charge voltage of the capacitor 301 rises to the same voltage as the power supply line 231 with a time constant τ1 as the first time constant determined by equation (1). τ1=(resistance value of resistor 302)×(capacitance of capacitor 301) Equation (1) When the load SW 212 is switched to the ON state, if the synchronization signal 232 is not input from the BD 6, the charge voltage of the capacitor 301 increases with a time constant τ1. Note that the safety circuit 207 switches the load SW 212 to the OFF state when the charge voltage of the capacitor 301 exceeds a predetermined voltage (reference voltage).

[0032] On the other hand, when the synchronization signal 232 is in a low level state, that is, when the laser beam L is incident on the BD6, the charge voltage of the capacitor 301 drops to 0 V with a time constant τ2, which is the second time constant of the following equation (2): τ2=(resistance value of resistor 303)×(capacitance of capacitor 301) Equation (2) When the load SW 212 is switched to the on state, if the synchronization signal 232 is input from the BD 6, the charge voltage of the capacitor 301 drops with a time constant τ2.

[0033] In the first embodiment, the resistance value of resistor 303 is set to 1 / 100 or less of the resistance value of resistor 302 (resistance value of R303 ≦ (1 / 100) × resistance value of resistor 302), and the constants are selected so that the relationship τ1 >> τ2 holds. That is, in the first embodiment, the resistance value of resistor 302 is set to be greater than the resistance value of resistor 303, so that the time constant τ1 is greater than the time constant τ2. The synchronization signal 232 outputs a low level only when the laser beam L is incident on the BD 6. When the rotating polygon mirror 4 is rotating at a constant speed, the frequency of the synchronization signal 232 outputting a low level is approximately 1 / 50 of the frequency of the time when the synchronization signal 232 outputs a high level (see FIG. 2). Therefore, it is important to satisfy the relationship τ1 >> τ2. The time constant τ1 is set based on the laser emission duration specified in the safety standard IEC 60825-1.

[0034] In this way, the capacitor 301, resistor 302, and resistor 303 function as a state-holding unit that transitions with a time constant. When the load SW 212 is switched to the ON state, if the synchronization signal 232 is not input from the BD 6, the state-holding unit transitions toward the first state with a time constant τ1. On the other hand, when the synchronization signal 232 is input from the BD 6, the state-holding unit transitions toward a second state different from the first state with a time constant τ2 that is smaller than the time constant τ1. When the state-holding unit transitions to the first state with the time constant τ1, it switches the load SW 212 to the OFF state. The first state is a state in which the capacitor 301 is charged and the charge voltage rises and exceeds a predetermined voltage. The second state is a state in which the capacitor 301 is discharged and the charge voltage drops.

[0035] As mentioned above, the Class 3R laser beam printer with a wavelength of around 790 nm defines an upper limit standard for laser power with an emission duration of 100 seconds. Therefore, for example, the safety circuit 207 is set to operate in 50 seconds. That is, the resistance value of resistor 302 and the capacitance of capacitor 301 are selected so that the time constant τ1 is 50 seconds. The voltage dividing resistors 306 and 307 may be set so that the reference voltage obtained by dividing the voltage of the power supply line 231 by the voltage dividing resistors 306 and 307 is approximately 63.2% of the voltage of the power supply line 231.

[0036] FIG. 5 shows the relationship between the charge voltage of capacitor 301 and the BD signal. The left vertical axis represents the charge voltage of capacitor 301, and the right vertical axis represents the synchronization signal 232 as a BD signal (high level (H), low level (L)). The horizontal axis represents time. The reference voltage mentioned above is also shown as Vref (dashed line). Ra represents the region in which the synchronization signal 232 (BD signal) is normally input to the safety circuit 207. On the other hand, Rb represents the region in which the synchronization signal 232 (BD signal) is not input to the safety circuit 207. In region Ra, the synchronization signal 232 periodically alternates between high and low levels, and the voltage of capacitor 301 is repeatedly charged and discharged, so it does not exceed the reference voltage Vref. At this time, the safety circuit 207 outputs a low-level output voltage 233. However, in region Rb, the synchronization signal 232 is fixed at a high level, and the charge voltage of capacitor 301 continues to rise and exceeds the reference voltage Vref. As a result, the safety circuit 207 outputs a high level output voltage 233, and regardless of the level of the output voltage 234 of the CPU 208, the load SW 212 is switched to the OFF state, and the power supply line 231 is cut off.

[0037] In this way, the safety circuit 207 changes the output when the synchronization signal 232 is not input from the BD 6 for a predetermined time after the load switch 212 is switched to the on state by the output voltage 234 of the CPU 208. The safety circuit 207 switches the load switch 212 to the off state regardless of the state of the output voltage 234 of the CPU 208.

[0038] As described above, after CPU 208 turns on load SW 212, the following operation occurs. If deflection device control unit 206 is not instructed to rotate polygon mirror 4 and light emission control unit 203 is not instructed to control light emission of semiconductor laser 202 within the operating time of safety circuit 207, which is determined by time constant τ1, safety circuit 207 operates to forcibly turn off load SW 212. This is because synchronization signal 232 is not input to safety circuit 207 in this state. For example, if deflection device control unit 206 fails to rotate polygon mirror 4 within a predetermined time after CPU 208 turns on load SW 212 due to a malfunction of deflection device control unit 206, safety circuit 207 also operates to forcibly turn off load SW 212. If light emission control unit 203 fails to rotate polygon mirror 4 within a predetermined time after CPU 208 turns on load SW 212 due to a malfunction of light emission control unit 203, safety circuit 207 also operates to forcibly turn off load SW 212. In either case, the synchronization signal 232 is not input to the safety circuit 207.

[0039] As described above, the safety circuit 207, which operates with the time constant τ1, forcibly turns off laser emission if the synchronization signal 232 is not output for a predetermined time after the semiconductor laser 202 is enabled to emit light, regardless of the operation of the CPU 208. As a result, in the first embodiment, it is possible to provide an inexpensive and safe scanning optical device.

[0040] As described above, according to the first embodiment, when an abnormality occurs during laser emission, the safety circuit of the laser scanner can be reliably operated even if there is an abnormality in firmware operation. [Example]

[0041] An optical scanning device according to a second embodiment will be described. Components similar to those in the first embodiment will be assigned the same reference numerals, and a description thereof will be omitted. In the case of the configuration of the safety circuit 207 described in the first embodiment, after the safety circuit 207 operates and the load SW 212 is turned off, the load SW 212 is turned on again when the voltage of the power supply line 231 drops. The second embodiment is characterized in that after the safety circuit 207A operates, the safety circuit 207 is latched until the 3.3V power supply of the voltage conversion circuit 220 is turned off, and the forced OFF state of the load SW 212 continues.

[0042] [Safety circuit] A specific configuration will be described with reference to Fig. 6. The safety circuit 207A is configured to maintain the load SW 212 in the off state until the supply of current is stopped when the charge voltage of the capacitor 301 exceeds the reference voltage Vref and the load SW 212 is switched to the off state. One end of the resistor 306 of the safety circuit 207A is connected to the 3.3V power supply instead of the power supply line 231. That is, the safety circuit 207 is supplied with power from the voltage conversion circuit 220 without passing through the load SW 212. Compared to the safety circuit 207 described in the first embodiment, the power supply of the comparator 308 is changed to the 3.3V power supply of the voltage conversion circuit 220, and the output of the comparator 308 is connected to the non-inverting input terminal and the capacitor 301 via a diode 309 and a resistor 310.

[0043] When safety circuit 207A is not operating, output voltage 233 of comparator 308 is at a low level, and therefore no current flows from the output terminal of comparator 308 to the non-inverting input terminal. On the other hand, when safety circuit 207A operates and output voltage 233 becomes a high level, current flows from the output terminal to the non-inverting input terminal via diode 309 and resistor 310. As a result of current flowing from the output terminal to capacitor 301, the voltage of the non-inverting input terminal is maintained at a voltage higher than the voltage of the inverting input terminal, and therefore safety circuit 207A can continue to operate even when the voltage of power supply line 231 has dropped.

[0044] 6, when safety circuit 207A operates, it is possible to continue the prohibited state of laser emission until image forming apparatus 150 itself is powered off, regardless of the operation of CPU 208. This makes it possible to provide an inexpensive and safe scanning optical device.

[0045] As described above, according to the second embodiment, when an abnormality occurs during laser emission, the safety circuit of the laser scanner can be reliably operated even if there is an abnormality in firmware operation.

[0046] The disclosure of this embodiment includes the following configuration. (Configuration 1) a laser element; a deflector that deflects the light emitted from the laser element; an output means for receiving the light deflected and scanned by the deflector and outputting a synchronization signal; a switch means provided on a supply path for supplying a current to the laser element, the switch means being switched between an ON state for supplying a current to the laser element and an OFF state for cutting off the supply of the current to the laser element; a control means for controlling the on state or the off state of the switch means by a control signal; A scanning optical device comprising: a protection circuit that receives the synchronization signal from the output means and changes its output when a predetermined time corresponding to a time constant of the circuit has elapsed, the protection circuit having the output connected to the switch means; The protection circuit changes the output when the synchronization signal is not input from the output means for the predetermined time after the switch means is switched to the on state by the control signal from the control means, and switches the switch means to the off state regardless of the state of the control signal from the control means. (Configuration 2) the protection circuit has a state holding unit that transitions with the time constant, When the switch means is switched to the on state, When the synchronization signal is not input from the output means, the state holding unit transitions toward the first state with a first time constant; when the synchronization signal is input from the output means, the state holding unit transitions to a second state different from the first state with a second time constant smaller than the first time constant; 2. The optical scanning device according to configuration 1, wherein the state holding unit switches the switch means to the off state when the state transitions to the first state with the first time constant. (Configuration 3) the state-holding unit has a capacitor, the first state is a state in which the capacitor is charged and the charge voltage rises and exceeds a predetermined voltage, 3. The optical scanning device according to configuration 2, wherein the second state is a state in which the capacitor is discharged and the charge voltage drops. (Configuration 4) the protection circuit includes a capacitor; When the switch means is switched to the on state, When the synchronization signal is not input from the output means, the charge voltage of the capacitor increases with a first time constant, When the synchronization signal is input from the output means, the charge voltage of the capacitor decreases with a second time constant that is smaller than the first time constant, 2. The scanning optical device according to claim 1, wherein the protection circuit switches the switch means to the off state when the charge voltage of the capacitor exceeds a predetermined voltage. (Configuration 5) 5. The scanning optical device according to any one of configurations 2 to 4, wherein the first time constant is set based on a laser emission duration specified in IEC 60825-1, a safety standard. (Configuration 6) a power supply unit that supplies power to the protection circuit; 6. The scanning optical device according to any one of configurations 1 to 5, wherein the protection circuit is supplied with power from the power supply unit via the switch means. (Configuration 7) 5. The scanning optical device according to claim 3, wherein when the charge voltage of the capacitor exceeds the predetermined voltage and the switch means is switched to the off state, the protection circuit maintains the off state of the switch means until the supply of current is stopped. (Configuration 8) a power supply unit that supplies power to the protection circuit; 8. The optical scanning device according to configuration 7, wherein the protection circuit is supplied with power from the power supply unit without passing through the switch means. (Configuration 9) a scanning optical device according to any one of configurations 1 to 8; an image carrier on which an electrostatic latent image is formed by the scanning optical device; a developing means for developing the electrostatic latent image with toner to form a toner image; a transfer means for transferring the toner image onto a transfer material; a fixing unit for fixing the toner image transferred by the transfer unit; An image forming apparatus comprising: [Explanation of symbols]

[0047] 4 Rotating polygonal mirror 6BD 100 Scanning optical device 202 Semiconductor laser 207 Safety circuit 208 CPU 212 Road SW

Claims

1. a laser element; a deflector that deflects the light emitted from the laser element; an output means for receiving the light deflected and scanned by the deflector and outputting a synchronization signal; a switch means provided on a supply path for supplying a current to the laser element, the switch means being switched between an ON state for supplying a current to the laser element and an OFF state for cutting off the supply of the current to the laser element; a control means for controlling the on state or the off state of the switch means by a control signal; A scanning optical device comprising: a protection circuit that receives the synchronization signal from the output means and changes its output when a predetermined time corresponding to a time constant of the circuit has elapsed, the protection circuit having the output connected to the switch means; The protection circuit changes the output when the synchronization signal is not input from the output means for the predetermined time after the switch means is switched to the on state by the control signal from the control means, and switches the switch means to the off state regardless of the state of the control signal from the control means.

2. the protection circuit has a state holding unit that transitions with the time constant, When the switch means is switched to the on state, When the synchronization signal is not input from the output means, the state holding unit transitions toward the first state with a first time constant; when the synchronization signal is input from the output means, the state holding unit transitions to a second state different from the first state with a second time constant smaller than the first time constant, 2. The optical scanning device according to claim 1, wherein the state holding unit switches the switch means to the off state when the state transitions to the first state with the first time constant.

3. the state-holding unit has a capacitor, the first state is a state in which the capacitor is charged and the charge voltage rises and exceeds a predetermined voltage, 3. The optical scanning device according to claim 2, wherein the second state is a state in which the capacitor is discharged and the charge voltage drops.

4. the protection circuit includes a capacitor; When the switch means is switched to the on state, When the synchronization signal is not input from the output means, the charge voltage of the capacitor increases with a first time constant, When the synchronization signal is input from the output means, the charge voltage of the capacitor decreases with a second time constant that is smaller than the first time constant, 2. The optical scanning device according to claim 1, wherein said protection circuit switches said switch means to said off state when said charge voltage of said capacitor exceeds a predetermined voltage.

5. 5. The scanning optical device according to claim 2, wherein the first time constant is set based on a laser emission duration specified in IEC 60825-1, which is a safety standard.

6. a power supply unit that supplies power to the protection circuit; 5. The scanning optical device according to claim 1, wherein the protection circuit is supplied with power from the power supply unit via the switch means.

7. 5. The scanning optical device according to claim 4, wherein, when the charge voltage of the capacitor exceeds the predetermined voltage and the switch means is switched to the off state, the protection circuit maintains the off state of the switch means until the supply of current is stopped.

8. a power supply unit that supplies power to the protection circuit; 8. The optical scanning device according to claim 7, wherein the protection circuit is supplied with power from the power supply unit without passing through the switch means.

9. a scanning optical device according to any one of claims 1 to 4, 7, and 8; an image carrier on which an electrostatic latent image is formed by the scanning optical device; a developing means for developing the electrostatic latent image with toner to form a toner image; a transfer means for transferring the toner image onto a transfer material; a fixing unit for fixing the toner image transferred by the transfer unit; An image forming apparatus comprising:

Images