JP3784225B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus having a sensor for detecting the presence or absence of magnetic powder toner used as a developer in a developing device.
[0002]
[Prior art]
Conventionally, a frequency type using the inductance of a coil has been used as a sensor for detecting magnetic powder toner used as a developer in a developing device, but a method using a piezoelectric element has been common.
[0003]
[Problems to be solved by the invention]
However, in the case of a conventional piezoelectric element, the toner and the piezoelectric element must be brought into direct contact. When the developing device is detachable from the main body of the image forming apparatus, the developing device receives an electrical signal via the main body and the connector. There is a problem that the developer adheres to the connector to cause contact failure or the number of parts increases and the cost increases.
[0004]
[Means for Solving the Problems]
The present invention has been made in view of the above problems, and in an image forming apparatus comprising a toner presence / absence detection sensor for detecting the presence / absence of magnetic powder toner in a developing device, the toner presence / absence detection sensor comprises a primary coil. And a secondary coil are wound on the same bobbin to form a differential transformer, a driving circuit for driving the primary coil with a triangular wave or a sine wave, and a DC voltage divided from a power supply voltage to the secondary coil An application circuit for superimposing, a first comparator having a hysteresis width for comparing the divided DC voltage and an AC voltage generated in the secondary coil, and the first comparator The image forming apparatus includes a second comparator for comparing a voltage that has passed through a low-pass filter from the output side with a reference voltage .
[0005]
The developing device of the present invention is either a developing device main body that stirs the developer and conveys it to the photoreceptor side, or a toner container that supplies the developing device to the developing device.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a circuit diagram showing a toner presence / absence detection sensor, where T1 is a differential transformer, U1 is a comparator, and OSC is an oscillation circuit for driving a differential transformer.
[0007]
First, the differential transformer T1 is composed of primary coils L1 and L2 driven by OSC and a secondary coil L3 which is a detection coil, which are connected so as to be in opposite phases with each other, and there is no toner in the developing device. In this state, since the inductances of L1 and L2 are balanced, the voltage induced in the detection coil is zero (0).
[0008]
On the other hand, when the toner is present, that is, when the magnetic powder approaches either L1 or L2, the balance of the inductance is lost, and an AC voltage having the same frequency as when the primary coil is driven is generated in the detection coil L3.
[0009]
It should be noted that the differential coil, that is, the side having two coils operates on either the primary side or the secondary side. However, in order to perform voltage discrimination, the side having one coil as in this embodiment is set to two. The secondary side is preferable for increasing Q.
[0010]
As a sensor that uses a magnetic bridge of a differential transformer, it is widely used as an actuator that converts a mechanical displacement amount into an electrical signal. However, in the field of electrophotography, it is also used as a density sensor for two-component toner. The major difference between the present invention and the conventional density sensor is in the method of processing the magnetic bridge output signal. The density sensor is a phase discrimination method composed of circuits such as an oscillation circuit, a bridge output amplifier circuit, a waveform shaping, a phase comparison, a low-pass filter, and the like. It is characterized by superimposing a DC voltage that is a voltage. In other words, since the DC voltage fluctuation can be canceled, signal processing becomes simple, and it is not necessary to amplify the bridge output with a configuration such as an oscillation circuit, a voltage comparison, or a low-pass circuit, and it is possible to reduce the size and cost. became.
[0011]
FIG. 2 is an explanatory diagram of the operation of the differential transformer, and shows the relationship between the phase of the differential transformer and the secondary side output. If the core is adjusted to a point where the inductances of L1 and L2 connected in directions opposite to each other are equal, the output voltage of the secondary coil L3 becomes zero (0) (point A in FIG. 2). If magnetic powder (toner) approaches L2, L2 fluctuates and the balance is lost, and the operating point moves to point B. A difference voltage P is generated at L3, and whether or not this voltage exceeds the threshold value. Judgment can be made.
[0012]
The OSC is a Colpitts oscillation circuit formed of a transistor, a differential transformer, a capacitor, and the like. Since the phase difference between windings of the differential transformer is picked up as a differential voltage at L3, the influence of fluctuations in the oscillation frequency. Will not receive unless it is significant. Since the oscillation amplitude is operated completely in the clamped state, the amplitude fluctuation is small and there is a slight waveform distortion, but there is almost no influence on the secondary output waveform.
[0013]
The AC voltage generated at L3 is superimposed on the DC voltage obtained by dividing the supply voltage VC by R1 and R2, and is compared with the DC voltage obtained by dividing the supply voltage VC by R1 and R2 by a comparator U1 having a hysteresis width. When an AC voltage exceeding a certain level is generated, the AC voltage is amplified and output to the output terminal of the comparator U1.
[0014]
The hysteresis width of the comparator U1 may be set to, for example, a reference voltage ± 25 mV, and the presence of toner may be detected by adjusting the core of the differential transformer so that the L3 output becomes 50 mVp-p or more. However, in actuality, the output of the comparator U1 has a phase shift due to the slew rate and needs to be overdriven, and the peak value of the input waveform needs to be about twice the hysteresis width. An error in the hysteresis width occurs in the input offset voltage, and the influence on the offset current and the bias current hardly occurs because the input resistance is low. Of course, these errors are included in the adjustment of the differential transformer core. The input signal to be compared has an AC component superimposed on the reference voltage (DC), and in order to compare the AC voltage amplitude, it becomes a relative fluctuation with respect to the fluctuation of the reference voltage, that is, both inputs have the same ratio. The detection level will not change.
[0015]
The amplified output voltage is removed from the AC by a low-pass filter composed of R5 and C1, converted into a DC voltage, input to the comparator U2, and compared with the reference voltage Vref, the noise component is removed and the comparator U2 The output value is a sensor output value for detecting the presence or absence of toner. For example, the reference voltage may be set to 1.37V, the presence of toner may be converted to L = 0V, and the absence of toner may be converted to H = 5V and supplied to the input port of the image forming apparatus engine.
The waveforms in the circuit diagram of FIG. 1 are diagrams showing output waveforms at the respective positions (A to E).
[0016]
FIG. 3 is a diagram showing a toner presence / absence detection sensor in which the circuit of FIG. 1 is incorporated. Become.
[0017]
In the present invention, with such a configuration, it is not necessary to perform amplification by an arithmetic circuit or the like, and it is not necessary to perform phase comparison, etc., so that a highly stable operation can be ensured with a simple configuration and high sensitivity. More reliable detection of magnetic powder toner from a remote location becomes possible.
[0018]
This eliminates the need to bring the toner presence / absence detection sensor 7 shown in FIG. 3 into contact with the developing device 8 as shown in FIG. 4, thereby increasing the degree of freedom in design.
[0019]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, the toner presence / absence detection sensor is formed by winding a primary coil and a secondary coil on the same bobbin to form a differential transformer, and the primary coil is formed with a triangular wave or a sine wave. By connecting a drive circuit for driving and an application circuit for superimposing a DC voltage on the secondary coil, it is possible to guarantee extremely stable operation while maintaining high sensitivity, and the degree of freedom of installation of the toner presence / absence detection sensor. The image forming apparatus can be increased.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a toner presence / absence detection sensor of the present invention.
FIG. 2 is a diagram showing the operation of the differential transformer of the present invention.
3 is a diagram showing a toner presence / absence detection sensor of the present invention incorporating the circuit of FIG. 1. FIG.
FIG. 4 is a diagram showing a partial configuration diagram of an image forming apparatus according to the present invention.
[Explanation of symbols]
1: differential transformer 2: comparator 3: oscillation transistor 4: resistor / capacitor 5: wire 6: connector 7: toner presence / absence detection sensor 8: developing device

Claims (1)

In an image forming apparatus comprising a toner presence / absence detection sensor for detecting the presence / absence of magnetic powder toner in the developing device, the toner presence / absence detection sensor forms a differential transformer by winding a primary coil and a secondary coil on the same bobbin. And a driving circuit for driving the primary coil with a triangular wave or a sine wave, an application circuit for superimposing a DC voltage divided from a power supply voltage on the secondary coil, and the divided DC voltage And a first comparator having a hysteresis width for comparing the AC voltage generated in the secondary coil with a reference voltage for comparing a voltage passing through a low-pass filter from the output side of the first comparator. An image forming apparatus comprising a second comparator .

Images