JP4577579B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

In general, the image forming apparatus forms a developer image on a photosensitive member, and the developer image is formed on the sheet material when the sheet material conveyed by the conveyance mechanism enters a transfer position between the photosensitive member and the transfer member. Transcript. Here, Patent Document 1 discloses a technique for automatically determining the type of sheet material conveyed by a conveyance mechanism. Specifically, the output voltage applied to the transfer member is detected while the current flowing through the photosensitive member is controlled to be constant. Since this output voltage changes according to the type of sheet material and the like, the type of sheet material is determined based on whether or not the output voltage exceeds a predetermined value.
JP 7-43960 A

However, the technique disclosed in Patent Document 1 compares the absolute value of the output voltage with a predetermined value. Since the absolute value of the output voltage changes depending on the impedance of not only the sheet material but also the transfer member or the photosensitive member, the type of the sheet material may not be accurately determined.
The present invention has been completed based on the above situation, and an object of the present invention is to provide an image forming apparatus capable of accurately determining the type of sheet material.

As means for achieving the above object, an image forming apparatus according to a first aspect of the present invention includes an image carrier that carries a developer image, a transfer member, and constant current control or power supply while supplying power to the transfer member. Power supply means for performing constant voltage control, a fixing device, a transport mechanism for transporting the sheet material toward the fixing device through a transfer position between the image carrier and the transfer member, and the transfer Detection means for detecting both the voltage value and the current value of the power supplied to the body, and the voltage value detected by the detection means before and after the sheet material conveyed by the conveyance mechanism enters the transfer position . When the amount of change is greater than or equal to the first threshold, or when the condition that the amount of change in the current value detected by the detection means before and after the sheet material enters the transfer position is greater than or equal to the second threshold. One kind of sh It determines that the bets material, and a discrimination unit for discriminating as being another type of sheet material does not satisfy the condition.

According to a second invention, in the first invention, the determination unit determines that the sheet material has a resin portion when the condition is satisfied, and the sheet material is determined when the condition is not satisfied. If it is determined that the sheet material does not have a resin portion, and the determination unit determines that the sheet material has the resin portion, before the sheet material reaches the fixing device. And a controller for stopping the transport mechanism.

  According to a third aspect of the present invention, in the first or second aspect, the power supply means performs constant current control, and the determination unit is configured to determine whether the sheet material has entered the transfer position before and after. The type of the sheet material is determined based on the maximum difference in current value and the amount of change in the voltage value before the sheet material enters the transfer position and at the time of transfer.

<First invention>
The type of the sheet material is determined based on the relative change amount of the detection value (voltage value or current value of the power supplied to the transfer body) before and after the sheet material enters the transfer position. Therefore, variation elements other than the entry of the sheet material (for example, the impedance of the image carrier) can be eliminated, so that the impedance change according to the type of the sheet material is compared with the conventional technique that compares the absolute value of the output voltage with a predetermined value. Can be grasped more clearly, and the type of sheet material can be accurately determined.

<Second invention>
When it is determined that the sheet material conveyed by the conveyance mechanism has a resin portion, the conveyance mechanism is stopped before the sheet material reaches the fixing device. Accordingly, it is possible to avoid the problem that the resin portion is melted by heat of the fixing device and the sheet material is wound around the fixing device.

<Third invention>
The type of the sheet material is determined based on the maximum difference between the current value before and after the sheet material enters the transfer position, and the amount of change in the voltage value before and after the sheet material enters the transfer position. .

An embodiment of the present invention will be described with reference to FIGS.
1. 1 is a side sectional view showing a schematic configuration of a laser printer (hereinafter referred to as “printer 1”) of the present embodiment. In the following description, the right side in FIG.

  The printer 1 (an example of an “image forming apparatus”) is a direct transfer tandem color laser printer, and includes a substantially box-shaped casing 2 as shown in FIG. A sheet feed tray 7 on which the sheet material 4 is stacked is attached to the lower part of the casing 2 so as to be able to be drawn forward. In the sheet feed tray 7, a sheet pressing plate 9 is provided that can be tilted so as to lift the front end side of the sheet material 4 by the bias of the spring 8.

  When the uppermost sheet material 4 of the paper feed tray 7 is pressed toward the pickup roller 10 by the paper pressing plate 9 and is sandwiched between the pickup roller 10 and the separation pad 11 by the rotation of the pickup roller 10. Separated one by one. Then, the separated sheet material 4 is sent to the registration roller 13 by the paper feed roller 12. The registration roller 13 feeds the sheet material 4 onto the rear belt unit 15 at a predetermined timing.

  The belt unit 15 (an example of a “conveyance mechanism”) includes a conveyance belt 18 provided between a pair of support rollers 16 and 17. The belt 18 circulates and moves counterclockwise in FIG. 1, for example, when the rear support roller 17 is rotationally driven by the motor 17a, and conveys the sheet material 4 placed on the belt 18 backward. .

  The scanner unit 27 irradiates the surface of the corresponding photosensitive drum 31 (an example of “image carrier”) with high-speed scanning with the laser light L for each color based on the image data.

  The process unit 25 includes, for example, four image forming units 26 (26K, 26C, 26M, and 26Y) corresponding to each color of black (BK), cyan (C), magenta (M), and yellow (Y). . The four image forming units 26K, 26C, 26M, and 26Y corresponding to the respective colors have the same structure. Each image forming unit 26 includes a photosensitive drum 31, a scorotron charger 32, a developing cartridge 34, and the like.

  The developing cartridge 34 is provided with a toner storage chamber 38 in the upper part, and a supply roller 39, a developing roller 40 and a blade 41 are provided on the lower side thereof. Each toner storage chamber 38 stores toner of each color of black, cyan, magenta, and yellow as a developer.

  The toner is stirred by the agitator 42 and discharged from the toner storage chamber 38, and is supplied to the developing roller 40 by the rotation of the supply roller 39, and is positively frictionally charged between the supply roller 39 and the developing roller 40. Further, the toner supplied onto the developing roller 40 enters between the blade 41 and the developing roller 40 and is carried on the developing roller 40 as a thin layer having a constant thickness.

  The surface of the photosensitive drum 31 is uniformly positively charged by the charger 32. Thereafter, exposure is performed with the laser light L from the scanner unit 27, and an electrostatic latent image corresponding to an image to be formed on the sheet material 4 is formed. The rotating shaft 31a of the photosensitive drum 31 is grounded.

  Next, the toner carried on the developing roller 40 is supplied to the electrostatic latent image on the surface of the photosensitive drum 31. As a result, the electrostatic latent image on the photosensitive drum 31 is a visualized developer image.

  Thereafter, the developer image carried on the surface of each photosensitive drum 31 is transferred by the sheet material 4 conveyed by the belt 18 between the photosensitive drum 31 and the transfer roller 19 (an example of a “transfer body”). While passing through the position X, the images are sequentially transferred to the sheet material 4 by the negative transfer voltage V applied to the transfer roller 19. The sheet material 4 to which the developer image has been transferred in this way is then conveyed to the fixing device 43.

  The fixing device 43 fixes the developer image on the sheet material 4 by heating the sheet material 4 carrying the developer image while being sandwiched between the heating roller 44 and the pressure roller 45 and transported. Then, the heat-fixed sheet material 4 is conveyed to a discharge roller 47 provided on the upper portion of the casing 2 by a conveyance roller 46 disposed obliquely above and rearward of the fixing device 43, and discharged by the discharge roller 47. It is discharged onto the tray 5.

2. Bias Application Circuit FIG. 2 shows a block diagram of the main configuration of the power supply device 60. The power supply device 60 (an example of “power supply means”) is for applying the transfer voltage V to the transfer roller 19.

  The power supply device 60 includes a CPU 61 and a bias application circuit 62. The bias application circuit 62 is connected to a connection line 90 connected to the roller shaft 19 </ b> A of the transfer roller 19. In addition, the power supply device 60 includes a current detection circuit 83 (an example of “detection means”) that outputs a detection signal S4 corresponding to the value of the current flowing through the connection line 90. The bias application circuit 62 is subjected to constant current control by PWM (Pulse Width Modulation) control of the CPU 61. The memory 61 is connected to the CPU 61. The memory 100 stores a target value Iref, a first threshold value M, a second threshold value N, and a relationship table between temperature / humidity and the first and second threshold values, which will be described later.

  The bias application circuit 62 includes a smoothing circuit 70, a transformer drive circuit 71, a booster circuit 72, and a voltage detection circuit 73 (an example of “detection means”).

  Among these, the smoothing circuit 70 plays a role of receiving and smoothing the PWM signal S 1 from the PWM port 61 a of the CPU 61 and supplying it to the transformer drive circuit 71. The transformer drive circuit 71 is configured to flow an oscillating current through the primary winding 75b of the booster circuit 72 based on the received PWM signal S1.

  The booster circuit 72 includes a transformer 75, a diode 76, a smoothing capacitor 77, and the like. The transformer 75 includes a secondary winding 75a, a primary winding 75b, and an auxiliary winding 75c. One end of the secondary winding 75 a is connected to a connection line 90 connected to the roller shaft 19 </ b> A of the transfer roller 19 via a diode 76. On the other hand, the other end of the secondary winding 75a is grounded via a resistor 88, a resistor 89, and a resistor 91. In the present embodiment, the resistor 89 is a detection resistor, and the detection signal S4 corresponding to the value of the current flowing through the detection resistor 89 is fed back to the A / D port 61d of the CPU 61. A smoothing capacitor 77 and a discharge resistor 78 are connected in parallel to the secondary winding 75a.

  With such a configuration, the oscillation current of the primary winding 75b is boosted and rectified by the booster circuit 72, and the transfer voltage V is applied to the roller shaft 19A of the transfer roller 19 connected to the output end A of the power supply device 60. As applied.

  The voltage detection circuit 73 is connected to the auxiliary winding 75 c of the transformer 75 of the booster circuit 72 and the CPU 61. The voltage detection circuit 73 is configured to detect the output voltage Vb generated between the auxiliary windings 75c and to input the detection signal S2 to the A / D port 61b of the CPU 61.

  As described above, during the transfer operation, the CPU 61 applies the PWM signal S1 to the bias applying circuit 62 and drives it so that the current value becomes the target value Iref based on the detection signal S4 corresponding to the current value flowing through the connection line 90. In addition, constant current control for outputting the PWM signal S1 with the duty ratio appropriately changed to the smoothing circuit 70 is executed.

3. Configuration for Determining Sheet Type (1) Glossy Paper for Inkjet Printers Here, glossy paper for inkjet printers (paper with a resin coating on the surface) used for, for example, photographic printing is commercially available. However, if the glossy paper is used for printing in the printer 1 which is a laser printer, the heat of the heating roller 44 of the fixing device 43 may melt the resin on the surface of the glossy paper and the glossy paper may be wound around the heating roller 44. There is. Then, for example, the glossy paper is interposed between the heating roller 44 and a temperature control thermistor (not shown) for measuring the surface temperature, and the surface temperature of the heating roller 44 is accurately determined by the thermistor. Therefore, the temperature control of the heating roller cannot be performed normally. Therefore, in general, glossy paper cannot be used in a laser printer. However, if the glossy paper is erroneously set in the paper feed tray 7, it should be prevented that the glossy paper is conveyed to the fixing device 43.

  Therefore, the printer 1 of the present embodiment has a function of determining the type of the sheet material being conveyed on the belt 18. More specifically, it has a function of discriminating between glossy paper for the ink jet printer (an example of “having a resin portion”) and other types of sheet materials (for example, plain paper or cardboard). .

(2) Variation in Current and Voltage Supplyed to Transfer Roller FIG. 3 shows a graph relating to variation in current and voltage supplied to the transfer roller 19.

  As shown in FIG. 1, sensors 20 and 21 for detecting the sheet material 4 are respectively provided before and after the registration roller 13 in the conveyance path of the sheet material 4. Then, at the first timing t1 when the front end of the sheet material 4 is detected by the sensor 20 or when the front end of the sheet material 4 is detected by the sensor 21, the CPU 61 activates the bias application circuit 62 to transfer the transfer roller 19. Is applied with the transfer voltage V, and the above-described constant current control is started so that the transfer current I flowing through the transfer roller 19 becomes the target value Iref. Of course, at the first timing t1, the sheet material 4 does not reach the transfer position X ′ (transfer position positioned on the most upstream side of the sheet material conveyance path) corresponding to the black (BK) image forming unit 26K.

  Thereafter, as shown in FIG. 3, the transfer current I reaches the target value Iref and is substantially stabilized before the second timing t2 when the leading edge of the sheet material 4 reaches the transfer position X ′. Accordingly, the transfer voltage V is also almost stabilized at the voltage value Vref. However, when the leading edge of the sheet material 4 reaches the transfer position X ′ (second timing t2), the sheet material 4 is interposed between the photosensitive drum 31 and the transfer roller 19, and the photosensitive drum 31. And the transfer roller 19 suddenly and greatly change. Therefore, immediately after the sheet material 4 enters the transfer position X ′ due to the follow-up delay of the power supply device 60, the transfer current I temporarily decreases to the current value I1. Thereafter, with a slight delay, the transfer voltage V is raised to the voltage value V1 by the power supply device 60, whereby the transfer current I, which has been temporarily reduced, is restored to the target value Iref. As a result, the transfer current I is again almost stabilized at the target value Iref.

  Thereafter, the black developer image carried on the photosensitive drum 31 at the third timing t3 when a later-described second reference time T2 (= t3-t1) elapses from the first timing t1 is transferred to the transfer roller 19. The sheet is transferred to the sheet material 4 by the applied transfer voltage V. Then, at the subsequent fourth timing t4, the sheet material 4 reaches the fixing device 43, and the developer image is thermally fixed.

  Now, the impedance of the sheet material 4 is greatly different between when it is glossy paper and when it is other than glossy paper such as plain paper. That is, the degree ΔI (= Iref−I1 “maximum difference in current value”) of the transfer current I immediately after the second timing is a case where the sheet material 4 is glossy paper and plain paper. Is particularly large compared to Therefore, the type of the sheet material 4 can be determined based on the degree of decrease ΔI.

  Further, the amount of change ΔV (= an example of “V1−Vref“ amount of change in voltage value ”) of the transfer voltage V before and after the second timing is an amount corresponding to the degree of decrease ΔI of the transfer current I. Therefore, the type of the sheet material 4 can be determined based on the change amount ΔV of the transfer voltage V. In the present embodiment, as shown below, the type of the sheet material 4 is determined based on both the degree of decrease ΔI of the transfer current I and the change amount ΔV of the transfer voltage V.

(3) Control contents of the CPU The CPU 61 causes the bias application circuit 62 to start the constant current control based on the detection signal output from the sensor 20 or the sensor 21 at the first timing t1, and the control shown in FIG. Execute. First, a timer is started in S1 and time measurement of the elapsed time T from the first timing t1 is started. Then, in S2, it is determined whether or not the transfer current I has reached the target value Iref. When the transfer current I has reached the target value Iref (S2: Y), the detection signal S2 from the voltage detecting means is read in S3. The transfer voltage Vref is recorded in the memory 100.

  Thereafter, when the elapsed time T reaches the first reference time T1 (S4: Y), the detection signal S4 from the current detection circuit 83 is read, and the transfer current I1 at this time is recorded in the memory 100. (S5). Here, the first reference time T1 is a time from the first timing t1 to the timing (t2 ′) when the transfer current I temporarily decreases immediately after the sheet material 4 enters the transfer position X ′. is there. The difference between the second timing t2 and the timing t2 ′ corresponds to the delay time (several ms to several tens of ms) of the boosting circuit 72 with respect to the bias application circuit 62, particularly the PWM command from the CPU 61. The first reference time T1 can be calculated by, for example, the conveyance speed of the belt 18 and the distance from the sensors 20 and 21 to the transfer position X ′. Moreover, it can obtain | require by the experiment conducted previously.

  Subsequently, when the third timing t3, that is, when the elapsed time T reaches the second reference time T2 (S6: Y), the detection signal S2 from the voltage detection means is read, and the transfer voltage V1 at this time is read. Is recorded in the memory 100 (S7). Then, in S8, it is determined whether or not the setting for performing control according to at least one of temperature and humidity is made. The presence / absence of this setting is performed by the user at an operation unit (not shown) of the printer 1, for example. If the above setting has not been made (S8: N), whether or not the decrease degree ΔI of the transfer current I is smaller than the fixed first threshold value M in S9 and the change amount ΔV of the transfer voltage V is fixed. 2. It is determined whether or not it is smaller than the threshold value N. At this time, the CPU 61 functions as an example of a “discriminating unit”.

  When the degree of decrease ΔI is smaller than the fixed first threshold value M and the change amount ΔV of the transfer voltage V is smaller than the fixed second threshold value N (S9: Y), the sheet currently being conveyed The material 4 is determined to be plain paper, not glossy paper, and the conveyance of the sheet material 4 by the belt 18 is continued as it is. As a result, the sheet material 4 to which the developer image has been transferred is conveyed to the fixing device 43.

  On the other hand, when the decrease degree ΔI is equal to or greater than the fixed first threshold value M or the change amount ΔV of the transfer voltage V is equal to or greater than the fixed second threshold value N (S9: N), currently being conveyed. It is determined that the sheet material 4 is glossy paper having an impedance larger than that of plain paper, and at this time, the driving of the motor 17a is stopped to stop the movement of the belt 18 (S10). This prevents the sheet material 4, which is glossy paper, from reaching the fixing device 43. At this time, the CPU 61 functions as an example of a “control unit”.

  If the setting for performing control according to at least one of temperature and humidity is made (S8: Y), the first threshold M ′ corrected according to the temperature or humidity at that time in S11. And the same process as S9 is performed using 2nd threshold value N '. For correction to the first threshold value M ′ and the second threshold value N ′, for example, a relationship table between the temperature or humidity and the first threshold value and the second threshold value is recorded in the memory 100 in advance, and the temperature sensor and humidity The first threshold value M ′ and the second threshold value N ′ corresponding to the current temperature and humidity may be read based on the detection signal from the sensor. Since the impedance of the transfer roller 19 and the sheet material 4 varies depending on the temperature and humidity, it is desirable to correct the first threshold and the second threshold according to the temperature and humidity.

4). Effects of this Embodiment The type of the sheet material 4 is determined based on the relative change amount of the transfer current I and the transfer voltage V before and after the sheet material 4 enters the transfer position X ′. Therefore, since the variation elements other than the sheet material 4 (for example, the impedance of the photosensitive drum 31) can be eliminated, the impedance corresponding to only the type of the sheet material 4 as compared with the prior art that compares the absolute value of the output voltage with a predetermined value. The change can be grasped more clearly, and the type of the sheet material 4 can be accurately determined.

  In addition, the type of the sheet material 4 is discriminated based on the transfer current I and the transfer voltage V at the transfer position X ′ between the photosensitive drum 31 and the transfer roller 19 positioned on the uppermost stream in the conveyance path of the sheet material 4. It is. Therefore, after the determination of the sheet material 4, the time until the sheet material 4 reaches the fixing device 43 can be earned as long as possible, and the sheet material 4 determined to be glossy paper can be surely received before reaching the fixing device 43. Can be stopped.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.
(1) The “image forming apparatus” is not limited to the four-color laser printer of the above embodiment, and may be a monochrome type or a multi-color type laser printer other than four colors as long as it is a laser printer.
(2) In the above embodiment, the “power supply unit” is configured to perform constant current control. However, the present invention is not limited thereto, and constant voltage control may be performed. At this time, the CPU 61 determines the sheet material based on the maximum difference between the voltage value before and after the sheet material enters the transfer position, and the amount of change in the current value before and after the sheet material enters the transfer position. It becomes the structure which distinguishes a kind.

  (3) In the above embodiment, the timer is used to measure the transfer current I when the elapsed time T from the first timing t1 reaches the first reference time T1, but without using the timer, Using a falling peak hold circuit (for example, a combination of an inverting circuit and a peak hold circuit), the falling peak value of the transfer current I after the leading edge of the sheet material 4 enters the transfer position X ′, in other words, the sheet material 4. The falling peak value of the transfer current I based on the stable transfer voltage Vref before the leading edge of the toner enters the transfer position X ′ may be acquired.

  (4) In the above embodiment, the recording of the transfer voltage V1 after the leading edge of the sheet material 4 enters the transfer position X ′ (S7 in FIG. 4) is performed at the third timing t3 at the start of transfer. Not limited to this, the timing when the transfer voltage V is sufficiently stabilized after the leading edge of the sheet material 4 enters the transfer position X ′ and before the trailing edge of the sheet material 4 exits the transfer position X ′. I just need it.

  (5) In the above embodiment, the configuration is such that the glossy paper and other types of sheet material are discriminated. However, by adjusting the first threshold value and the second threshold value, for example, discrimination between plain paper and thick paper, etc. It is also possible to discriminate the type. Further, for example, it may be configured to discriminate between plain paper and an OHP sheet (an example of “sheet material having a resin portion”), specifically, although plain paper printing is designated. When an OHP sheet is set in the sheet feed tray and the OHP sheet is fed, the above determination is performed. When it is determined that the sheet is an OHP sheet, the conveying belt is stopped.

  (6) In the above embodiment, the type of the sheet material 4 is determined based on the current value and voltage value of the black (BK) transfer position X ′ located on the most upstream side of the conveyance path of the sheet material 4. However, the present invention is not limited to this, and the configuration may be such that the type of the sheet material 4 is determined based on the transfer position X of other colors and the current values and voltage values of the transfer positions of all colors (four colors). However, if the type of the sheet material 4 is discriminated at the black (BK) transfer position X ′ located on the most upstream side as in the above embodiment, the distance to the fixing device 43 is the distance of the other color toner. It is possible to more reliably prevent the sheet material 4 from being conveyed into the fixing device 43 by an amount longer than the transfer position X.

1 is a side sectional view showing a schematic configuration of a printer according to an embodiment of the present invention. Electrical configuration diagram of power supply means Graph of fluctuations in current and voltage supplied to the transfer roller Flow chart showing control contents of CPU

1. Printer (image forming device)
4. Sheet material 15. Belt unit (conveyance mechanism)
19. Transfer roller (transfer body)
31 ... Photosensitive drum (image carrier)
43 ... Fixer 60 ... Power supply device 61 ... CPU (discriminating unit, control unit)
73 ... Voltage detection circuit (detection means)
83 ... Current detection circuit (detection means)
X ... Transcription position

Claims (3)

An image carrier for carrying a developer image;
A transcript,
Power supply means for performing constant current control or constant voltage control while supplying power to the transfer member;
A fixing device,
A transport mechanism that transports a sheet material toward the fixing device through a transfer position between the image carrier and the transfer body;
Detection means for detecting both the voltage value and the current value of the power supplied to the transfer body;
The change amount of the voltage value detected by the detection means before and after the sheet material conveyed by the conveyance mechanism enters the transfer position is greater than or equal to a first threshold value, or the sheet material is at the transfer position. When the condition that the amount of change in the current value detected by the detecting means before and after entering is equal to or greater than the second threshold is satisfied, it is determined that the sheet material is of one type, and when the condition is not satisfied, An image forming apparatus comprising: a determination unit that determines that the sheet material is of a type . The image forming apparatus according to claim 1.
The determination unit determines that the sheet material has a resin portion when the condition is satisfied, and determines that the sheet material does not have the resin portion when the condition is not satisfied. And
When the determination unit determines that the sheet material has the resin portion, the control unit is configured to stop the conveyance mechanism before the sheet material reaches the fixing device. The image forming apparatus according to claim 1, wherein:
The power supply means is configured to perform constant current control,
The discriminating unit is based on the maximum difference between the current value before and after the sheet material enters the transfer position, and the amount of change in the voltage value before and after the sheet material enters the transfer position. The type of the sheet material is determined.

Images