Zero-cross detection circuit and image formation device

Abstract

To provide a zero-cross detection circuit which can prevent wrong detection and can precisely determine frequencies.SOLUTION: A zero-cross detection circuit 100 includes: a conversion circuit 62 for converting an alternate current input from a primary side to a direct current and outputting the direct current from a secondary side; a signal generation unit for generating a zero-cross detection signal used to detect a zero-cross point on the basis of a branch signal output from the secondary side of the conversion circuit 62; and a zero-cross detection unit for detecting a zero-cross point on the basis of the zero-cross detection signal.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a zero-cross detection circuit for detecting a zero-cross point and an image forming apparatus including the same.

Background Art

[0002] Conventionally, in a fixing device used in an electrophotographic image forming apparatus such as a copying machine or a printer, a toner image that has not been fixed is formed on a sheet by applying pressure and heat, thereby fixing the toner image. Such an image forming apparatus generally operates using electric power supplied from an AC power source, and when taking out electric power from the AC power source, it often uses the zero-cross point as a reference.

[0003] By the way, in an AC power source, noise such as momentary power outages may occur, and as a result, the zero-cross point may be erroneously detected. Therefore, a method for determining an accurate zero-cross point even when noise or the like occurs has been proposed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] A conventional zero-cross detection circuit includes a zero-cross detection unit that detects a zero-cross point of an AC power source, a power supply voltage detection unit that detects the voltage of the AC power source at predetermined intervals, and zero-cross determination means that determines a zero-cross point based on the detection results of the zero-cross detection unit and the power supply voltage detection unit. Then, the power supply voltage detection unit determines whether the detected voltage is within a predetermined voltage range and decides whether to permit or prohibit the detection of the zero-cross point.

[0006] However, in a conventional zero-cross detection circuit, only the voltage range for detecting the zero-cross point is narrowed. When noise or the like exists within a predetermined voltage range, there is a risk of detecting an incorrect zero-cross point.

[0007] The present disclosure has been made to solve the above problems, and an object thereof is to provide a zero-cross detection circuit and an image forming apparatus that can prevent false detection and perform frequency determination with high accuracy.

Means for Solving the Problems

[0008] The zero-cross detection circuit according to the present disclosure includes a conversion circuit that converts alternating current input from the primary side into direct current and outputs it from the secondary side, and a signal generation unit that generates a zero-cross detection signal used for detecting a zero-cross point based on a branch signal output from the secondary side of the conversion circuit, and a zero-cross detection unit that detects a zero-cross point based on the zero-cross detection signal.

[0009] The zero-cross detection circuit according to the present disclosure may be configured to include a filter circuit that extracts and outputs a frequency component from the branch signal.

[0010] In the zero-cross detection circuit according to the present disclosure, the signal generation unit may be configured to output the binarized zero-cross detection signal based on a threshold value set for the branch signal.

[0011] In the zero-cross detection circuit according to the present disclosure, the signal generation unit may be configured to be mounted on a circuit board different from the conversion circuit.

[0012] The image forming apparatus according to the present disclosure is characterized by including the zero-cross detection circuit according to the present disclosure.

Effects of the Invention

[0013] According to the present disclosure, since a zero-cross detection signal is generated from the secondary side output, even if noise or voltage drop occurs in the alternating current input to the primary side, the zero-cross point can be detected without being affected by it, false detection can be prevented, and frequency determination can be performed with high accuracy.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0015] Hereinafter, an image forming apparatus according to an embodiment of the present disclosure will be described with reference to the drawings.

[0016] FIG. 1 is a schematic side view of an image forming apparatus according to an embodiment of the present disclosure.

[0017] An image forming apparatus 1 according to an embodiment of the present disclosure includes a main body that performs image formation, a document reading unit 44 and a document conveyance unit 45 provided at the upper part, and a paper feeding device 50 provided at the lower part. The paper feeding device 50 includes a device main body 52 and a paper feeding cassette 51 inserted into the device main body 52.

[0018] The document reading unit 44 has a document placement table 43 on which a document is placed provided on the upper surface, reads an image of the document on the document placement table 43, creates image data, and transmits it to the image forming apparatus 1. The document conveyance unit 45 automatically conveys the document onto the document placement table 43. Further, the document conveyance unit 45 is rotatably attached to the image forming apparatus 1, and by rotating it to open the upper part of the document placement table 43, the document can be placed manually.

[0019] In the main body of the image forming apparatus 1, an optical scanning unit 11, a developing device 12, a photosensitive drum 13, a cleaning device 14, a charger 15, an intermediate transfer belt 21, a fixing device 17, a paper discharge tray 39, and a paper conveyance path R1 are provided. According to the image data transmitted from the outside or the document reading unit 44, color and monochrome images are formed on a predetermined sheet of paper.

[0020] The image data processed in the image forming apparatus 1 corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y). Therefore, the developing device 12, the photosensitive drum 13, the charger 15, and the cleaning device 14 are each provided in four units so as to form four types of latent images corresponding to each color, and are respectively set to black, cyan, magenta, and yellow. Four image stations Pa, Pb, Pc, and Pd are configured by these.

[0021] The photosensitive drum 13 is disposed substantially at the center of the image forming apparatus 1. The charger 15 uniformly charges the surface (circumferential surface) of the photosensitive drum 13 to a predetermined potential. The optical scanning unit 11 exposes the surface of the photosensitive drum 13 to form an electrostatic latent image. The developing device 12 develops the electrostatic latent image on the surface of the photosensitive drum 13 to form a toner image on the surface of the photosensitive drum 13. By the above-described series of operations, toner images of each color are formed on the surface of each photosensitive drum 13. The cleaning device 14 removes and recovers the residual toner on the surface of the photosensitive drum 13 after development and image transfer.

[0022] The intermediate transfer belt 21 rotates and moves in the direction of arrow C, the residual toner is removed and recovered by the intermediate transfer belt cleaning device 25, and the toner images of each color formed on the surface of each photosensitive drum 13 are sequentially transferred and superimposed to form a color toner image on the surface of the intermediate transfer belt 21.

[0023] The image forming apparatus 1 further includes a secondary transfer device 26 including a transfer roller 26a. A nip area is formed between the transfer roller 26a and the intermediate transfer belt 21, and the paper conveyed through the paper conveyance path S is sandwiched and conveyed in the nip area. When the paper passes through the nip area, the toner image on the surface of the intermediate transfer belt 21 is transferred.

[0024] The image forming apparatus 1 forms an image using the paper stored in the paper feed cassette 51. The paper feeding device 50 is provided below the optical scanning unit 11. Also, the paper discharge tray 39 is provided below the document reading unit 44 and is a tray for placing the paper on which the image has been formed.

[0025] The paper is pulled out from the paper feed cassette 51 by the pickup roller 33 and supplied to the S-shaped paper conveyance path R1. Along the paper conveyance path R1, further, a conveyance roller 35, a registration roller 34, a secondary transfer device 26, a fixing device 17, and a paper discharge roller 36 are arranged.

[0026] The registration roller 34 temporarily holds the paper conveyed from the paper feed cassette 51 and conveys the paper to the transfer roller 26a at the timing when the leading edge of the toner image on the photosensitive drum 13 and the leading edge of the paper are aligned. The conveyance roller 35 is a small roller for assisting the conveyance of the paper.

[0027] The fixing device 17 receives the paper on which the unfixed toner image is formed, sandwiches the paper between the heating roller 31 and the pressure roller 32, heats and pressurizes the paper, and fixes the toner image on the paper. The fixing device 17 is provided with a heating unit (not shown) for heating the heating roller 31. The fixed paper is discharged onto the paper discharge tray 39 by the paper discharge roller 36.

[0028] Also, when forming an image not only on the front surface but also on the back surface of the paper, the paper is conveyed in the reverse direction from the paper discharge roller 36 to the reverse path Rr, the front and back of the paper are reversed, the paper is guided to the registration roller 34 again, and an image is formed on the back surface in the same manner as on the front surface, and the paper is carried out to the paper discharge tray 39.

[0029] The image forming apparatus 1 includes a zero-cross detection circuit 100 having a conversion circuit 62 (see FIG. 2 described later) that converts the alternating current input from the primary side into direct current and outputs it from the secondary side. Next, the zero-cross detection circuit 100 having the conversion circuit 62 will be described with reference to FIG. 2.

[0030] FIG. 2 is a circuit configuration diagram showing the outline of the zero-cross detection circuit.

[0031] In the zero-cross detection circuit 100, a conversion circuit 62 is provided between the AC power supply 61 and the load 63. Hereinafter, for the sake of explanation, the side connected to the AC power supply 61 of the conversion circuit 62 may be referred to as the primary side, and the side connected to the load 63 may be referred to as the secondary side.

[0032] The AC power supply 61 is provided outside the image forming apparatus 1 and is connected to the image forming apparatus 1 via a terminal such as an outlet. The load 63 is provided in each part of the image forming apparatus 1 and is a part that operates with direct current.

[0033] The conversion circuit 62 includes a rectifying section that rectifies current and a transformer section 62a that transforms voltage. The rectifying section may be configured by, for example, diodes connected in a bridge, and is a general rectifying circuit. The transformer section 62a is configured by, for example, a coil. In the conversion circuit 62, the alternating current input to the primary side is converted into direct current by the functions of the rectifying section and the transformer section 62a, adjusted to a desired voltage, and output from the secondary side. Note that the conversion circuit 62 is not limited to the above-described configuration, and may appropriately include electronic components such as switching elements and capacitors.

[0034] A path branched separately from the load 63 is provided on the secondary side of the conversion circuit 62, and a filter circuit 71 and a signal generation circuit 72 are connected to the path. Hereinafter, for the sake of explanation, the output to this path may be referred to as a branch signal.

[0035] The filter circuit 71 extracts and outputs frequency components from the branch signal. The signal generation circuit 72 has the functions of a signal generation unit that generates a zero-cross detection signal used for detecting zero-cross points and a zero-cross detection unit that detects zero-cross points. The filter circuit 71 and the signal generation circuit 72 only need to have the functions described above, and may be configured by appropriately combining various electronic components. Next, with reference to FIGS. 3 and 4, the process of detecting zero-cross points from the branch signal will be described.

[0036] FIG. 3 is a characteristic diagram showing the input waveform and the output waveform in the conversion circuit.

[0037] In the upper part of FIG. 3, the input waveform AC in the conversion circuit 62, which is the voltage of the AC power supply 61, is shown, and in the lower part of FIG. 3, the output waveform DC in the conversion circuit 62, which is the voltage output toward the load 63, is shown.

[0038] The voltage (input waveform AC) supplied from the AC power supply 61 has a waveform in which the positive and negative are periodically switched like a sine wave. The voltage becomes zero at the timing when the positive and negative of the voltage are switched, and this moment is called the zero-cross point. By the way, although not shown in FIG. 3, in the AC power supply 61, due to noises such as momentary power outages and various factors, the voltage may suddenly change instantaneously, and the zero-cross point may be erroneously detected.

[0039] The conversion circuit 62 converts and outputs to DC, and the output waveform DC is designed to maintain a substantially constant value. However, in reality, the value fluctuates slightly due to various factors such as ripple caused by the operation of the switching element and ripple caused by the frequency of the AC power supply 61. FIG. 4 below shows the output ripple waveform with the portion pointed by the arrow A enlarged.

[0040] FIG. 4 is a characteristic diagram showing the relationship between the branch signal and the zero-cross detection signal.

[0041] In the upper part of FIG. 4, a branch signal from the conversion circuit 62 is shown, which is an output ripple waveform RH obtained by expanding the output waveform DC. By expanding as shown in FIG. 4, in the output ripple waveform RH, the fluctuations in the values in the output waveform DC are emphasized. As described above, the output ripple waveform RH is periodically increasing and decreasing in value under the influence of the frequency of the AC power supply 61, and the period in which the value fluctuates corresponds to the frequency of the AC power supply 61. Therefore, in the present embodiment, the branch signal is input to the filter circuit 71, and the filter extracts the frequency components in the branch signal.

[0042] In the middle part of FIG. 4, a frequency extraction signal FS extracted by the filter circuit 71 is shown. The frequency extraction signal FS shown in FIG. 4 is a wave with uniform width and height fluctuations continuously, like a full-wave rectified voltage waveform. In the present embodiment, a threshold value for the frequency extraction signal FS is set, and the signal generation circuit 72 outputs a zero-cross detection signal ZS by binarizing depending on whether it exceeds the threshold value.

[0043] In the lower part of FIG. 4, a zero-cross detection signal ZS generated by the signal generation circuit 72 is shown. In the zero-cross detection signal ZS, the value becomes "High" at the part corresponding to the joint of the waves in the frequency extraction signal FS, and the value becomes "Low" at the other parts. In the zero-cross detection signal ZS, since the timing at which the value becomes "High" corresponds to the frequency of the AC power supply 61, the zero-cross point can be detected based on the zero-cross detection signal ZS.

[0044] In the present embodiment, since the zero-cross detection signal ZS is generated from the secondary-side output, even if there are noises or voltage drops in the AC input to the primary side, the zero-cross point can be detected without being affected by them, false detection can be prevented, and the frequency determination can be performed accurately.

[0045] Also, by extracting the frequency components superimposed on the branch signal by the filter circuit 71, the frequency of the AC supplied from the AC power supply 61 can be accurately grasped.

[0046] Furthermore, by using the binarized zero-cross detection signal ZS, zero-cross points can be easily detected.

[0047] In the image forming apparatus 1, the signal generation unit (signal generation circuit 72) may be mounted on a circuit board different from the conversion circuit 62. With this configuration, since the primary-side alternating current is not directly supplied to the signal generation unit, there is no need to insulate it from the primary side, and the circuit scale can be reduced, achieving space saving and cost reduction.

[0048] It should be noted that the embodiments disclosed this time are illustrative in all respects and do not serve as a basis for restrictive interpretation. Therefore, the technical scope of the present disclosure is not interpreted only by the above-described embodiments, but is defined based on the description in the claims. Also, all changes within the meaning and scope equivalent to the claims are included.

Explanation of Reference Numerals

[0049] 1 Image forming apparatus 61 AC power supply 62 Conversion circuit 63 Load 71 Filter circuit 72 Signal generation circuit (an example of a signal generation unit and a zero-cross detection unit) 100 Zero-cross detection circuit

Claims

1. A conversion circuit that converts the alternating current input from the primary side into direct current and outputs it from the secondary side, A signal generation unit that generates a zero-cross detection signal used for detecting a zero-cross point based on a branch signal output from the secondary side of the conversion circuit, A zero-cross detection circuit including a zero-cross detection unit that detects a zero-cross point based on the zero-cross detection signal.

2. The zero-cross detection circuit according to Claim 1, characterized by comprising a filter circuit that extracts and outputs a frequency component from the branch signal. The zero-cross detection circuit.

3. The zero-cross detection circuit according to Claim 1, wherein the signal generation unit outputs the binary zero-cross detection signal based on a threshold value set for the branch signal. The zero-cross detection circuit.

4. The zero-cross detection circuit according to Claim 1, wherein the signal generation unit is mounted on a circuit board different from the conversion circuit. The zero-cross detection circuit.

5. An image forming apparatus including the zero-cross detection circuit according to Claim 1.

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