JP2005091941A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device which allows a prescribed output voltage to be obtained with a higher precision regardless of variance in characteristics of a P sensor by switching a ratio of a current value to a PWM value (voltage-current conversion ratio) and switching the voltage-current conversion ratio in accordance with characteristics of the P sensor. <P>SOLUTION: The image forming device having the P sensor provided with a light emitting means and a light receiving means for detecting a toner sticking density on a photoreceptor, is provided with a voltage generation circuit for generating an arbitrary voltage by PWM, and a voltage-current conversion circuit for converting the voltage generated by the voltage generation circuit to a current to be supplied to the light emitting means of the P sensor. The voltage-current conversion circuit is provided with: a first resistance value for determining a first voltage-current conversion ratio; a second resistance value for determining a second voltage-current conversion ratio; and a switching circuit for switching the first resistance value and the second resistance value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus having a P sensor for detecting the toner adhesion density of a photoconductor, and in particular, switches a ratio of a current value to a PWM value (voltage-current conversion ratio) and changes a voltage according to the characteristics of the P sensor. The present invention relates to an image forming apparatus capable of obtaining a predetermined output voltage with better accuracy even when the characteristics of the P sensor vary because the current conversion ratio is switched.

In general, an image forming apparatus that develops and transfers an electrostatic latent image formed on a photoconductor with toner has a P sensor for detecting the toner adhesion amount on the photoconductor.
As a prior art, Japanese Patent Laid-Open No. 2002-278383 (in order to keep the toner adhesion density on the photosensitive drum constant, the output voltage value of the light receiving means for the non-image portion of the photosensitive drum becomes a predetermined output voltage value. In addition, the current value of the light emitting means is adjusted in advance, and the toner density is detected by checking the output voltage value of the light receiving means with respect to the toner adhesion pattern portion in this state. In order to achieve this, a voltage-current conversion circuit using PWM is used).
JP 2002-278383 A

However, the above prior art has the following problems.
In JP-A-2002-278383, the output voltage of the light receiving means is adjusted to a predetermined value by adjusting the PWM value. At this time, the relationship between the PWM value and the output voltage may vary from machine to machine due to variations in P sensor characteristics, variations in P sensor assembly, and the like.
For example, it is assumed that a predetermined output voltage can be obtained with PWM 80% and a predetermined output voltage can be obtained with PWM 20%. At this time, in the case of PWM 80%, the output voltage can be finely adjusted, but in the case of PWM 20%, there is a drawback that the adjustment of the output voltage becomes rough.
The present invention has been made to solve the above-described conventional drawbacks, and its purpose is to switch the ratio of the current value to the PWM value (voltage-current conversion ratio) and to change the voltage-current conversion ratio according to the characteristics of the P sensor. Therefore, the present invention provides an image forming apparatus that can obtain a predetermined output voltage with better accuracy even when the characteristics of the P sensor vary.

In order to achieve the above object, an invention according to claim 1 is directed to an image forming apparatus having a P sensor provided with a light emitting means and a light receiving means for detecting the toner adhesion density of a photoreceptor, and an arbitrary voltage by PWM. And a voltage-current conversion circuit for converting the voltage generated by the voltage generation circuit into a current supplied to the light emitting means of the P sensor, the voltage-current conversion circuit, A first resistance value that determines a first voltage-current conversion ratio; a second resistance value that determines a second voltage-current conversion ratio; and a switching circuit that switches between the first resistance value and the second resistance value. It is characterized by providing.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, when the switching circuit adjusts the output voltage of the light receiving means to a predetermined voltage value, the output voltage value is set to a predetermined voltage value. Accordingly, the first resistance value and the second resistance value are switched and used.
According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the switching circuit has a PWM value of α% and an output voltage of the light receiving means equal to or higher than a predetermined voltage value in the first resistance value. The first resistance value is used as it is, and when the PWM value is α% and the output voltage of the light receiving means is equal to or lower than the predetermined voltage value, the first resistance value is switched to the second resistance value. .

  According to the feature of the present invention, since the ratio of the current value to the PWM value (voltage-current conversion ratio) is switched and the voltage-current conversion ratio is switched according to the characteristics of the P sensor, even when the characteristics of the P sensor vary. A predetermined output voltage can be obtained with better accuracy.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram of a digital copying machine according to an embodiment of the present invention. This configuration is a copying machine 100 as an image processing apparatus, and a contact glass 6 is provided on the upper surface of the copying machine 100. Further, an automatic document feeder (hereinafter simply referred to as ADF) 1 is provided at the upper part of the copying machine 100, and this ADF 1 is connected to the copying machine 100 via a hinge or the like (not shown) so as to open and close the contact glass 6. Has been. The ADF 1 separates documents one by one from a document tray 2 as a document placement table on which a document bundle composed of a plurality of documents can be placed, and the document bundle placed on the document tray 2 toward the contact glass 6. The separation / conveying means that conveys the original and the original conveyed toward the contact glass 6 by the separation / conveying means are conveyed / stopped to the reading position on the contact glass 6 and the copy disposed below the contact glass 6. The document that has been read by the reading means 50 (known exposure lamp 51, mirrors 52, 55, 56, lens 53, CCD 54, etc.) of the machine 100 is carried out from the contact glass 6. The paper feed motor is driven by an output signal from the controller, and when the paper feed start signal is input from the copying machine 100, the controller drives the paper feed motor forward / reversely. When the paper feed motor is driven to rotate forward, the feed roller 3 rotates in the clockwise direction so that the uppermost original is fed from the original bundle and conveyed toward the contact glass 6. When the leading edge of the document is detected by the document set detection sensor 7, the controller rotates the paper feed motor in reverse based on the output signal from the document set detection sensor 7. This prevents subsequent documents from entering and prevents separation.

Further, when the document set detection sensor 7 detects the trailing edge of the document, the controller counts the rotation pulse of the conveyor belt motor from this detection point, and when the rotation pulse reaches a predetermined value, the controller By stopping the driving and the feeding belt 4, the document is stopped at the reading position of the contact glass 6. Further, when the trailing edge of the original is detected by the original set detection sensor 7, the controller drives the paper feed motor again, separates the subsequent original as described above, and conveys the original toward the contact glass 6. When the pulse of the paper feed motor from the time when the original is detected by the original set detection sensor 7 reaches a predetermined pulse, the paper feed motor is stopped and the next original is put on standby. When the original stops at the reading position on the contact glass 6, the copying machine 100 reads and exposes the original. When the reading and exposure are completed, a signal is input to the controller from the copying machine 100. When this signal is input to the controller, the controller drives the conveyor belt motor to rotate forward so that the document is transferred from the contact glass 6 by the conveyor belt 16. It is carried out to the discharge roller 5.
As described above, a document bundle placed on the document tray 2 in the ADF 1 with the image surface of the document facing up is pressed from the top document to the contact glass 6 when the print key on the operation unit is pressed. It is fed to a predetermined position. The fed original is read by the reading unit 50 on the image data of the original on the contact glass 6 and then discharged to the discharge port A (discharge port at the time of reverse document discharge) by the feeding belt 4 and the reverse driving roller. Further, when it is detected that there is a next document on the document tray 2, it is fed onto the contact glass 6 in the same manner as the previous document.
The transfer sheets stacked on the first tray 8, the second tray 9, and the third tray 10 are fed by the first sheet feeding unit 11, the second sheet feeding unit 12, and the third sheet feeding unit 13, respectively, and are vertically conveyed. The unit 14 is transported to a position where it abuts on the photoreceptor 15. The image data read by the reading unit 50 is written on the photoconductor 15 by the laser from the writing unit 57 and passes through the developing unit 27 to form a toner image. Then, the toner image on the photoconductor 15 is transferred while the transfer paper is conveyed by the conveyance belt 16 at the same speed as the rotation of the photoconductor 15. Thereafter, the image is fixed by the fixing unit 17 and conveyed to the paper discharge unit 18. The transfer paper conveyed to the paper discharge unit 18 is discharged to the paper discharge tray 19 when the staple mode is not performed.

FIG. 2 is a schematic view of an embodiment relating to the main part of the image forming apparatus according to the present invention.
As shown in FIG. 2, the image forming apparatus includes a photoreceptor 41 for forming an image by attaching toner, a light emitting unit 43 such as an LED and a phototransistor for detecting the toner adhesion density of the photoreceptor 41. A P sensor 42 formed by the light receiving unit 44, a PWM generation unit 45 that generates PWM, a filter circuit 46 that smoothes and integrates PWM, and a voltage-current conversion circuit that converts the voltage integrated by the filter circuit 46 into current 47, an A / D conversion unit 48 for detecting the output voltage from the light receiving unit 44.
The present invention relates to the voltage-current conversion circuit 47 described above. Hereinafter, the voltage-current conversion circuit 47 embodying the present invention will be described with reference to a conventional example.
FIG. 3 is a detailed diagram of a conventional voltage-current conversion circuit.
In FIG. 3, the voltage V <b> 1 integrated by the filter circuit 46 is input to the non-inverting input of the operational amplifier 49. At this time, due to the characteristics of the operational amplifier 49, the input voltage V2 of the inverting input is adjusted to be the same potential as the input voltage V1 of the non-inverting input. At this time, the current I flowing through the resistance value R is obtained by I = V2 / R from the voltage V2 of the inverting input. Here, as described above, V1 = V2. Therefore, the current flowing through the light emitting unit is approximately determined by I = V1 / R.
At this time, the voltage-current conversion ratio is determined by the resistance value R. Here, the voltage V1 is obtained in proportion to the PWM value. Thus, the current flowing through the light emitting unit 43 and the PWM value are in a proportional relationship, and the voltage-current conversion ratio depends on R.
FIG. 4 is a distribution graph showing variations in the current passed through the light emitting unit 43 when a predetermined output voltage is output to the light receiving unit 44. Here, n indicates a PWM value.
If the P sensor A obtains a predetermined output voltage V with the PWM value n, the setting resolution of the output voltage V is V / n. If another P sensor B obtains a predetermined output voltage V at a PWM value n / 4, the setting resolution of the output voltage V is 4 × V / n. In this way, the setting resolution of the output voltage of the P sensor B can be set only with four times the roughness of the setting resolution of the output voltage of the P sensor A.

FIG. 5 is a detailed view of an embodiment of the voltage-current converter circuit according to the present invention.
As shown in FIG. 5, the voltage-current conversion circuit 47 is configured to switch the resistance value R ′ of the resistor 62 by an open drain switch 61 (switching circuit) connected to the resistor 62.
Here, as shown in FIG. 5, assuming that the resistance value R ′ of the resistor 62 can be changed in two stages of R (first resistance value) and 4 × R (second resistance value), R ′ = 4. When it is changed to × R, I = V2 / R ′ = (V2 / R) / 4 = (V1 / R) / 4, and the current has a fineness of a quarter of the resistance value R ′ = R. I can be set.
Therefore, in the case of the P sensor B in FIG. 4, the output voltage can be set with the same resolution as the P sensor A by changing the resistance value R ′ to 4 × R.
FIG. 6 is an operation flowchart of one embodiment of the voltage-current conversion circuit shown in FIG.
As an actual use example, as shown in FIG. 6, R ′ = 4 × R is first set (step S100), and the output voltage value when the PWM value is n / 4 is measured (step S101).
If the output voltage value is equal to or higher than the predetermined voltage value (YES in step S102), the PWM is adjusted so that the predetermined output voltage value can be obtained while R ′ = 4 × R (steps S103 and S104). . If the output voltage value is less than or equal to the predetermined voltage value (NO in step S102), the resistance value is switched to R ′ = R, and then the PWM is adjusted so that the predetermined output voltage value is obtained (steps S105 and S106). ).
The open drain switch 62 (switching circuit) uses the first resistance value as it is when the PWM value reaches a predetermined voltage value at α% in the first resistance value. When the predetermined voltage value is not reached at α%, the second resistance value may be switched.

1 is a schematic configuration diagram of a digital copying machine according to an embodiment of the present invention. 1 is a schematic view of an embodiment relating to a main part of an image forming apparatus according to the present invention. It is a detailed view of a conventional voltage-current conversion circuit. FIG. 6 is a diagram showing a distribution graph showing variations in current flowing through the light emitting unit 43 when a predetermined output voltage is output to the light receiving unit 44. 1 is a detailed view of an embodiment of a voltage-current converter circuit according to the present invention. 6 is an operation flowchart of one embodiment of the voltage-current conversion circuit shown in FIG. 5.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 41 ... Photosensitive body, 42 ... P sensor, 43 ... Light emission part, 44 ... Light receiving part, 45 ... PWM production | generation part, 46 ... Filter circuit, 47 ... Voltage-current conversion circuit, 48 ... Conversion part, 49 ... Operational amplifier, 61 ... Open Drain switch, 62 ... resistor

Claims (3)

An image forming apparatus having a P sensor provided with a light emitting means and a light receiving means for detecting a toner adhesion density of a photoreceptor,
A voltage generation circuit for generating an arbitrary voltage by PWM;
A voltage-current conversion circuit for converting the voltage generated by the voltage generation circuit into a current supplied to the light emitting means of the P sensor,
The voltage-current conversion circuit includes a first resistance value that determines a first voltage-current conversion ratio, a second resistance value that determines a second voltage-current conversion ratio, the first resistance value, and a second resistance An image forming apparatus comprising: a switching circuit for switching values.   2. The image forming apparatus according to claim 1, wherein when the switching circuit adjusts the output voltage of the light receiving unit to a predetermined voltage value, the first resistance value is set according to the value of the output voltage with respect to the predetermined voltage value. An image forming apparatus, wherein the second resistance value is switched and used.   3. The image forming apparatus according to claim 2, wherein, when the PWM value is α% and the output voltage of the light receiving unit is equal to or higher than a predetermined voltage value, the switching circuit includes the first resistor as it is. The image forming apparatus is characterized in that a value is used, and when the PWM value is α% and the output voltage of the light receiving means is equal to or lower than a predetermined voltage value, the value is switched to the second resistance value.

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