JPH0548201Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Technical Field of the Invention] The present invention relates to an image forming apparatus using a two-component developer such as an electrophotographic copying machine, and more specifically, to an image forming apparatus that uses a two-component developer to stop image forming operation at a preferable time in response to changes in toner concentration of the two-component developer. The present invention relates to an image forming apparatus. [Prior art and its problems] In an image forming apparatus that performs development using a two-component developer consisting of a carrier and toner, if the toner concentration in the developer decreases to a predetermined concentration or less, the image forming operation is hindered. To achieve this, a sensor for detecting the toner concentration is provided in the developing device, and when it is detected from the sensor output that the toner concentration has fallen below a predetermined concentration, the image forming operation is stopped. Conventionally, this method of stopping is as follows:
After completing only the image forming operation that is being executed when a low density detection output from the sensor occurs,
There are controls that immediately prohibit image forming operations, and controls that allow image forming operations only a predetermined number of times from the moment the sensor detects low density.
There is a method that controls the image forming operation to be prohibited when the number of times the image forming operation is executed. However, in the case of the former control method, since the device is prohibited from operating at a certain density setting, image forming may suddenly start at a certain point even though a considerable amount of toner still remains in the developing device. This resulted in the inconvenience of not being able to respond to emergency image forming requests. In addition, in the case of the latter control method, even after detecting a low density, it is possible to permit image forming operations a predetermined number of times. In this case, the toner is completely consumed before the permitted predetermined number of image forming operations are completed, resulting in a disadvantage that the image quality is significantly impaired. [Purpose of the invention] In view of the above-mentioned problems, the present invention makes it possible to detect changes in toner density step by step, accurately detects toner deficiency, and automatically starts image forming operations before image defects occur. An object of the present invention is to provide an image forming apparatus that can be stopped automatically. [Key points of the invention] According to the invention, the above purpose is to improve the toner concentration by acting on a part of the two-component developer consisting of toner and carrier stored in the developing device and outputting an output signal corresponding to the toner concentration. a sensor, a toner replenishment mechanism that replenishes the toner stored in the hopper into the developer, and a vibration waveform signal that periodically vibrates with a predetermined amplitude is superimposed on the output signal of the toner concentration sensor,
a comparison means for comparing the superimposed signal with a reference voltage; a frequency counting means for counting the frequency at which a predetermined comparison relationship occurs in the comparison means within a predetermined period; replenishment mode selection means for selecting one of a plurality of modes of toner replenishment operation in which the operation time of the toner replenishment mechanism is different; and a drive control circuit that operates the toner replenishment mechanism for a time corresponding to an output of the replenishment mode selection means. and a counter that counts the number of consecutive toner replenishment operations in the toner replenishment mode with the longest operating time, and when the counter counts a predetermined number of times, the image forming operation is prohibited. This is achieved by providing an image forming apparatus that does the following. [Embodiments of the invention] Hereinafter, embodiments of the invention will be described in detail with reference to the drawings. FIG. 1 is a circuit block diagram showing one embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a toner concentration sensor which is provided inside a developing device 2 for carrying out a developing step in the image forming process with its detection surface facing downward, and is composed of an electrostrictive vibrator. Toner density sensor 1
detects the toner density based on the contact pressure with the developer a, and outputs an analog signal corresponding to the toner density. That is, the developer a flows as the developing sleeve 3 rotates, but since it is regulated by the regulating plate 4 for regulating the spike height of the developer a, the developer a flows in the upper part of the developing sleeve 3. A bulge is formed. This bulge of developer a comes into contact with the detection surface of the toner concentration sensor 1, and since the developer a has a property that fluidity changes depending on the toner concentration, the contact pressure changes depending on the toner concentration. . Therefore, the output of the toner concentration sensor 1 changes depending on the toner concentration; as the toner concentration decreases, the output level decreases, and as the toner concentration increases, the output level increases. The output of the toner concentration sensor 1 is sent to a synthesis circuit 5, and the synthesis circuit 5 synthesizes the output of the toner concentration sensor 1 and the output of the triangular wave generation circuit 6. That is,
The toner concentration sensor 1 outputs an analog signal corresponding to the toner concentration, and a triangular wave output from the triangular wave generation circuit 6 is superimposed on this analog signal.
The output of the synthesis circuit 5 is sent to the comparison circuit 7, and the comparison circuit 7 compares the output of the synthesis circuit 5 with the reference voltage. When the output of the synthesis circuit 5 is higher than the reference voltage, it is at a high level, and when it is lower, it is at a high level. Convert to low level pulse signal. And, as will be explained in detail later,
By the control circuit 8 counting the pulses output from the comparison circuit 7 during an arbitrary sampling period,
The output of the toner concentration sensor 1 is detected. Based on this detection result, the control circuit 8 controls the operating time of the motor 9. The motor 9 is a toner supply roll 10
As the operating time of the motor 9 becomes longer, the rotation time of the replenishment roll 10 becomes longer. Therefore, when the concentration of toner b in the hopper 11 is lower than that in the control circuit 8, the amount of toner b in the hopper 11 is
0 is rotated for a long time to increase the replenishment amount of toner b, and when the concentration is high, the toner b is rotated for a short time to decrease the replenishment amount of toner b. Further, as will be described in detail later, when a toner replenishment operation in which the replenishment roll 10 is rotated for a long period of time is performed three times in succession, the control circuit 8 causes the display 12 to indicate that the toner concentration has decreased. let Furthermore, when the toner replenishment operation in which the replenishment roll 10 is rotated for a long time is performed 15 times in succession, it is determined that the toner concentration in the developer a has reached the developable limit, and the image forming operation is controlled. Formation control section 13
Control is performed to send a signal to prohibit the image forming operation. FIG. 2 shows the triangular wave generation circuit 6, the synthesis circuit 5,
A specific example of the comparison circuit 7 is shown. The triangular wave generation circuit 6 creates a triangular wave using IC12 for triangular wave generation, and in this embodiment,
NE555 manufactured by Signetix was used as IC12. The frequency of the triangular wave is determined by the charging characteristics of resistors R ₁ and R ₂ and capacitor C ₁ , and the discharge characteristics of resistor R ₂ and capacitor C ₂ , and the frequency is determined by the voltage follower circuit in composite circuit 5 from the output terminal (pin 6). Sent on 13th. In this embodiment, the frequency of the triangular wave was 200 Hz, and the peak-to-peak voltage V of the triangular wave was 1/3 of the power supply voltage _Vc . Voltage follower circuit 1
3 is a buffer that receives the triangular wave at high impedance and outputs it at low impedance, and the output of the triangular wave generating circuit 6 is sent to the voltage follower circuit 1.
3. The signal is sent to the non-inverting terminal of the comparator ₁₄ forming the comparison circuit 7 via the resistor R4. On the other hand, the output of the toner concentration sensor 1 is also sent to the voltage follower circuit 15 in the synthesis circuit 5 in the same manner as described above. Comparator 14 via resistor R ₃
is input to the non-inverting terminal of The output of the synthesis circuit 5,
That is, the voltage at the connection point of resistors R ₃ and R ₄ is the DC component of the toner concentration sensor 1, which is obtained by combining the output of the toner concentration sensor 1 with the output of the triangular wave generation circuit 6, as shown as A in FIG. The signal is obtained by superimposing the alternating current component of the triangular wave generation circuit 6 on the signal. The output of the synthesis circuit 5 is compared with the reference voltage V _ref in the comparator circuit 7, as described above, and converted into a pulse signal. The output of the comparison circuit 7 is sent to the control circuit 8, and the control circuit 8 counts the number of times the output of the synthesis circuit 2 becomes lower than the reference voltage _Vref during a predetermined sampling period. That is, when the output of the combining circuit 5 and the reference voltage V _ref are compared, if the output of the combining circuit 5 becomes lower than the reference voltage, there is a toner shortage state. Since the comparison result of the comparison circuit 7 is output as a pulse signal, by counting the pulses, the ratio of the toner shortage state can be determined. In other words, since the output of the combining circuit 5 varies depending on the output of the toner concentration sensor 1, when the toner concentration decreases, the combining circuit 5 changes as shown in FIG.
The output of the combining circuit 5 becomes low, and as the toner density increases, the output of the combining circuit 5 becomes high. Therefore, as the concentration decreases, the number of times the output of the combining circuit 5 becomes lower than the reference voltage V _ref increases. As a result, if the number of times is counted during an arbitrary sampling period, the ratio of the number of times the output of the synthesis circuit 5 becomes lower than the reference voltage V _ref will be high, as shown by B in FIG. 3, and the toner shortage rate will be high. I understand that. Conversely, as the toner concentration increases, the output of the combining circuit 5 also increases, so the ratio at which the output of the combining circuit 5 becomes lower than the reference voltage decreases. The control circuit 8 detects the toner concentration by counting the pulse signals output from the comparison circuit 7, and controls the operating time of the motor 9 as described above based on the detection result. In this embodiment, as shown in the table below, the ratio x at which the synthesis circuit 5 becomes lower than the reference voltage _Vref is divided into five stages, and the operation time of the motor 9 (operation time of the supply roll 10) is set for each stage. . That is, when x is 0%, the mode is set to 0, and in this case, since the output of the combining circuit 5 never becomes lower than the reference voltage, toner is not replenished. Also, mode 1 is for 0<x≦25%, in which case the motor 9 is rotated for 0.3 seconds, and mode 2 is for 25%<x
≦50%, in this case motor 9
Rotate for 0.5 seconds. Furthermore, mode 3 is 50% < x
≦75%, mode 4 is when 75%<x≦100%, and in mode 3, motor 9 is operated for 0.7 seconds, mode 4
Now rotate for 0.9 seconds. In addition, in this example,
The sampling period was 3 seconds, and the number of samplings during this period was 1000 times. In this case, the sampling frequency is 333Hz.

[Table] In addition, the control circuit 8 performs the toner replenishment operation as described above, and at the same time constantly monitors the state of the toner replenishment operation, and controls to display a warning of a decrease in toner density or stop the image forming operation depending on the state. I do. That is, when the replenishment operation in mode 4 in which the motor 9 operates for a long time is executed continuously, the replenishment toner b in the hopper 11 decreases, and the replenishment operation due to the repeated long rotation of the motor 9 decreases. It is considered that the toner concentration has reached a state where it does not recover even if Therefore, when the replenishment operation in mode 4 is continuously performed a predetermined number of times, the control circuit 8 causes the display 12 to
When the replenishment operation in mode 4 is performed a predetermined number of times, a signal is sent to the image forming control unit 13 to instruct the image forming operation to stop. Upon receiving this signal, the image forming control section 13 completes the image forming operation currently in progress and then stops the image forming operation. In this embodiment, the number of consecutive executions of mode 4 for displaying a warning is set to three times, and the number of consecutive executions of mode 4 for stopping the image forming operation is set to 15 times. This operation will be explained in detail below with reference to FIG. As shown in FIG. 4, the control circuit 8 includes the comparison circuit 7.
Sample the output of (ST1) and determine the ratio x (ST2). If x is 0%, mode 0 is set as described above, and toner is not replenished. Further, in mode 1, the motor 9 is rotated for 0.3 seconds (ST3), and in mode 2, the motor 9 is rotated for 0.5 seconds (ST4) to replenish toner. Furthermore, in mode 3, the motor 9 is rotated for 0.7 seconds (ST5), and in mode 4, it is rotated for 0.9 seconds (ST6) to replenish toner. Then, only when mode 4 is executed, the value of a counter (not shown) included in the control circuit 8 is incremented by +1 (ST6). When modes 0 to 3 are executed, the value of the counter is reset (ST7). Through this operation, the toner shortage is displayed and the image forming operation is stopped only when the mode 4 toner replenishment operation is performed completely continuously. Next, check whether the counter value exceeds 3 (ST8). If the counter value is 3 or more, mode 4 toner replenishment has been performed three or more times in a row, so a toner shortage warning is displayed ( ST9). Further, it is checked whether the counter value has reached 15 (ST10), and if it has reached 15, a signal for prohibiting the image forming operation is generated (ST11) and the image forming operation is forcibly stopped. If step (ST10) is NO, steps ST1 to ST12 are repeated until it is determined in step (ST12) that the print operation is finished. [Effects of the invention] As explained above, according to the invention, changes in the toner concentration in the developer are identified in stages, the continuous occurrence of toner replenishment operations in the maximum toner replenishment mode is monitored, and the number of occurrences of toner replenishment operations is monitored. Since the display of toner shortage and prohibition of image forming operation are controlled according to the integrated value of toner, it is possible to accurately detect and warn of a decrease in toner density due to a shortage of replenishing toner, and to detect a decrease in toner density immediately before the image is affected. image forming operations can be prohibited. In addition, the number of image forming operations that are permitted during the period from when a toner shortage condition is detected to when image forming operations are prohibited is also controlled in accordance with changes in toner concentration, so there is no risk of forming defective images. do not have.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram and circuit block diagram of the main parts of an embodiment of the present invention, FIG. 2 is a circuit diagram showing the structure of the main parts of an embodiment of the invention, and FIG. 3 shows the output of the synthesis circuit, FIG. 4 is a characteristic diagram showing the relationship between the output of the combining circuit and the ratio at which it becomes lower than the reference voltage, and FIG. 4 is a flowchart showing the operation of the above embodiment. 1... Toner concentration sensor, 5... Synthesis circuit,
6... Triangular wave generation circuit, 7... Comparison circuit, 8...
Control circuit, 9...Motor, 10...Toner supply roll, a...Developer, b...Toner.

Claims (1)

[Claim for Utility Model Registration] A toner concentration sensor that acts on a part of a two-component developer consisting of toner and carrier stored in a developing device and outputs an output signal according to the toner concentration; a toner replenishment mechanism that replenishes toner into the developer; and a comparison device that superimposes a vibration waveform signal that periodically vibrates with a predetermined amplitude on the output signal of the toner concentration sensor and compares the superimposed signal with a reference voltage. means, a frequency counting means for counting the frequency at which a predetermined comparison relationship occurs in the comparison means within a predetermined period, and a plurality of modes in which the operating time of the toner replenishing mechanism differs depending on the counting result of the frequency counting means. replenishment mode selection means for selecting one of the toner replenishment operations; a drive control circuit that operates the toner replenishment mechanism for a time corresponding to the output of the replenishment mode selection means; and toner replenishment in the toner replenishment mode having the longest operating time. An image forming apparatus comprising: a counter that counts the number of times an operation has been performed consecutively; and when the counter counts a predetermined number of times, the image forming operation is prohibited.