JPS6318026Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing bias circuit for a copying machine using a one-component developer.

As a developing method for electronic copying machines, there is a so-called non-contact developing method in which a one-component developer containing no carrier is caused to fly onto an electrostatic latent image portion of a photoreceptor. This developing method uses a complicated AC bias circuit, unlike the case where a two-component developer containing a carrier and toner is used.

FIG. 1 is a simple block diagram of a conventional development bias circuit used in a non-contact development method using a one-component developer. In FIG. 1, the voltage from a commercial power source 2 is transformed to an appropriate value by a transformer 4, and then
applied to the rectifier 6. The DC stabilized power supply 8 stabilizes the output of the rectifier 6 and is used as a power supply for the oscillator 10 and the DC bias circuit 12. The output of the oscillator 10 is applied to a driver circuit 14 at the next stage. The frequency of the output of the oscillator 10 is, for example, approximately
It is 300~2000Hz. The output of the driver circuit 14 is stepped up to a predetermined voltage by a transformer 16 and applied to the magnet roll of the developing device via an output terminal 18. Note that the output terminal 20 is grounded, and the output obtained from the output terminal 18 is connected to the DC bias circuit 12.
A desired DC bias is applied by.

Next, non-contact development using an alternating current bias voltage, which is the output of the circuit shown in FIG. 1, will be briefly explained with reference to the bias voltage waveform shown in FIG. In Figure 2, A is the dark level indicating the potential of the part with the highest electrostatic potential on the photoreceptor, and B is the electrostatic voltage or ground potential of the part of the photoreceptor with no charge (corresponding to the white background of the transfer paper). This is the light level that indicates. The alternating current bias voltage is applied to a magnet roll provided near the photoreceptor. The AC bias voltage waveform shown in FIG. 2 is DC-biased by potential C in the positive direction. Near the valley of the bias voltage (a), the bias voltage is lower than the light level B, so toner flies from the magnet roll to the dark level part of the photoconductor with an electrostatic force corresponding to the potential _a1 , and the photoconductor An electrostatic force corresponding to potential a ₂ acts on the toner in the direction of the light level part of the body. On the other hand, near the peak of the bias voltage (b), the bias potential is higher than the dark level A, so the toner in the dark level portion of the photoconductor is attracted to the magnet roll by an electrostatic force corresponding to the potential _b1 , and Toner in the light level part of the body is attracted to the magnet roll by an electrostatic force corresponding to potential _b2 .
By the way, b ₁ < a ₁ and a ₂ < b ₂ , and the frequency of the bias voltage is approximately 300 to 2000 Hz as described above.
Therefore, in reality, as a whole, the dark level part of the photoreceptor is developed by toner flying off the magnet roll due to the electrostatic force due to the potential difference a ₁ - b ₁ , and the toner is developed in the light level part of the photoreceptor in the direction of the magnet roll. Toner does not adhere because of the electrostatic force caused by the potential difference b ₂ −a ₂ .

The above is a brief explanation of the principle of the conventional circuit shown in Fig. 1 and the non-contact developing method.The circuit shown in Fig. 1 has a stabilized power supply circuit, a bias circuit, etc. in addition to two transformers, There are problems in that the circuit configuration is complex and the manufacturing cost is high.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a developing bias circuit for a copying machine which has a simple circuit configuration and is therefore inexpensive to manufacture.

Hereinafter, one embodiment of the present invention will be described with reference to the attached FIGS. 3 to 6. 3 is a developing bias circuit according to the present invention, and FIGS. 4 to 6 are modified diagrams for explaining the circuit of FIG. 3.

The primary side of the transformer 24 is connected to the commercial power supply 22,
The secondary side is connected to a rectifier 26. Rectifier 26
In this embodiment, it is composed of diodes 28 and 30 and resistors 32, 34, 36, and 38. Connection point F between resistors 32 and 34 is diode 4
0 to the collector of transistor 42, and the connection point G between resistors 36 and 38 is connected to diode 4
4 to the collector of a transistor 46. The emitters of transistors 42 and 46 are each grounded, the base of transistor 42 is connected to the connection point of resistors 50 and 52, while the base of transistor 46 is connected to the connection point of resistors 54 and 56. The pulses applied from switching pulse generator 62 through diodes 58 and 60 are divided by resistors 50-52 and 54-56, respectively, and applied to the bases of transistors 42 and 46. Transistor 42 is on only during the positive half period of the switching pulse, and transistor 4
6 is turned on only during the negative half period of the switching pulse. Connection points H and K are connected to resistors 64 and 6, respectively.
6 to a potentiometer 68 for DC bias control. The slider of potentiometer 68 is connected to output terminal 70, and the output of the circuit of FIG. 3 is taken from output terminals 70,72.

Next, the operation of the circuit shown in FIG. 3 will be explained.
The commercial voltage applied to the primary side of the transformer 24 (the fourth
(see Figure A) is rectified by the rectifier 26, and the upper half waveform shown in Figure 4B appears at the connection point F, and the lower half waveform shown in Figure 4C appears at the connection point G. On the other hand, when transistor 42 is turned on by a switching pulse from switching pulse generator 62 (in this case, transistor 46
is off), the connection point H is approximately at ground potential, and
When the transistor 46 is turned on (in this case, the transistor 42 is turned off), the connection point K becomes approximately at ground potential, so that the waveforms shown in FIG. 4D and E appear at the connection points H and K, respectively. Thus, by adjusting the potentiometers, the waveforms shown in FIG. 5A, B or C can be obtained from output terminals 70 and 72, for example. Incidentally, FIG. 5A shows the case where the DC bias is zero, and FIGS. 5B and C show the waveforms when the DC bias is applied in the negative and positive directions, respectively.

Next, referring to FIG. 6, with the AC bias voltage obtained from the circuit according to the present invention (FIG. 3),
The electrostatic force that is applied to the toner existing between the magnet roll and the photoconductor when they are closest to each other will be explained. FIG. 6 shows the waveform when the potentiometer 68 biases the DC voltage C in the positive direction. In FIG. 6, the downward solid line indicates the electrostatic force applied to the toner from the dark level portion of the photoconductor in the direction of the magnet roll, and the downward broken line indicates the electrostatic force applied to the toner from the light level portion of the photoconductor in the direction of the magnet. Indicates electrostatic force. On the other hand, the upward solid line indicates the electrostatic force (i.e., the development direction) applied to the toner from the magnet roll toward the dark level portion of the photoconductor, and the upward dashed line indicates the electrostatic force applied to the toner from the magnet roller toward the photoconductor. It shows the electrostatic force applied in the direction of the light level part. Note that A and B in FIG. 6 indicate dark level and light level potentials, respectively. Therefore, we decided to apply the AC voltage shown in Figure 6 (or Figure 5) to the magnet roll after appropriately applying a DC bias to the commercial frequency voltage (however, it has been appropriately boosted). Therefore, from a macroscopic perspective, toner flies from the magnet roll to the dark level portion of the photoconductor, and electrostatic force acts to prevent toner from adhering to the light level portion of the photoreceptor, so as explained in Figure 2, A similar effect can be obtained. Furthermore, according to the present invention, it is possible to obtain a developing bias circuit in which toner does not adhere to the light level portion (that is, there is no staining in the white background portion) with a simpler circuit configuration than the conventional developing bias circuit. be.
In particular, one of the great features of the circuit configuration of the present invention is that the DC bias can be changed simply by changing the position of the slider of the potentiometer.

In the circuit shown in FIG. 3, when obtaining a high output voltage, V _CEO of transistors 42 and 46 is
If the maximum rated voltage between the collector and emitter when the base is open is insufficient, two layers may be used.
According to experiments, no ripples (stripe patterns on the image that appear perpendicular to the direction of movement of the transfer paper) caused by direct use of commercial frequencies were observed.

As described above, according to the present invention, it is possible to simplify the development bias circuit of a copying machine using a one-component developer.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a developing bias circuit of a conventional copying machine, FIG. 2 is a waveform diagram for explaining the non-contact developing method, FIG. 3 is a circuit diagram of a developing bias circuit according to the present invention, and FIG. 4 6 to 6 are waveform diagrams for explaining the circuit diagram of FIG. 3. 22... Commercial power supply, 26... Rectifier, 42,4
6...transistor, 62...switching pulse generator, 68...potentiometer.

Claims (1)

[Scope of utility model registration request] A transformer that transforms commercial voltage from a commercial power source;
a rectifier for rectifying the output of the transformer; a switching pulse generator for generating switching pulses; switching means for controlling passing and blocking of the output of the rectifier in response to the switching pulses; 1. A developing bias circuit for a copying machine, comprising: control means for receiving an output from the means and controlling a DC bias of the output.