JPS6250843A - Copying machine - Google Patents

Abstract

PURPOSE:To make image density constant axially by varying the gap between a corona discharger for electrostatic charging and the surface of a photosensitive drum axially according to axial variation in the surface potential of the photosensitive drum. CONSTITUTION:Two potential sensors 2f and 2r which detect the surface potential of the photosensitive drum 1 are placed almost at both ends of the photosensitive drum 1 and detected potentials Vf and Vr of the potential sensors 2f and 2r when a dummy original is exposed are compared with each other. When the difference is larger than a specific value, a stepping motor 11 is rotated forward or backward by as many times as specified according to the polarity to move a main charger 3 upward or downward, bit by bit, around a hinge 10 as a fulcrum through a worm gear 12a or 12b. Consequently, the gap between the surface of the photosensitive drum and corona discharger for electrostatic charging is adjusted properly and the axial surface potential of the photosensitive drum is made constant to uniform the image density.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a copying machine having a function of controlling image density to a constant level.

(B) Conventional technology Conventionally, this type of copying machine detects the surface potential of the photoreceptor drum with a sensor, and if the surface potential differs from a predetermined value, changes the output of the charging corona discharger to charge the photoreceptor drum. The surface potential on the drum is controlled (for example, see Japanese Patent Laid-Open No. 55-29856). (c) Problems to be Solved by the Invention However, in such conventional copying machines, Only the surface potential of the part where the sensor is installed is detected, and the output of the charging corona discharger is controlled based on the detected value. It was difficult to adjust the directional surface potential bias.

This invention was made in consideration of these circumstances, and by adjusting the distance between the photoreceptor drum surface and the charging corona discharger, the surface potential on the photoreceptor drum is made uniform over its axial direction. The purpose of this invention is to provide a copying machine that can be controlled to an appropriate value.

(d) Means for Solving the Problems The copying machine of the present invention includes a movable means for varying the distance between the surface of the photoreceptor drum and the charging corona discharge T1 device, and detecting the surface potential in the axial direction of the photoreceptor drum. A special feature (e) characterized by comprising a plurality of detection means for detecting and a control means for controlling the movable means in accordance with the detected surface potential. The surface potential of the photoreceptor drum increases as the distance between the
As the distance increases, the surface potential decreases.

Therefore, by detecting the surface potential distribution in the axial direction of the photoconductor drum, controlling the movable means in accordance with the surface potential distribution, and adjusting the distance between the photoconductor drum surface and the charging corona discharge electrode, the photoconductor drum can be The surface potential of the drum becomes uniform from one end of the drum to the other, thereby preventing deviations in image density of copies.

(f) Examples Hereinafter, the present invention will be described in detail based on examples shown in the drawings. Note that this invention is not limited to this.

In Fig. 1 (ω mountain), (1) is the photoreceptor drum, (2
f) (2r) is a potential sensor that detects the surface potential at almost both ends of the photoreceptor drum (1), and (3) is the main charger (
Charging corona discharger), (41 is a corona discharge electrode wire, (5) is a developing device, (6) is a cleaning device,
(7') is a static elimination lamp that removes the charge from the charged photoreceptor drum, (8) is an AC charger, and (9) is a transfer charge t! , (G)) is a hinge that supports one end of the main charger (3), (11) is a stepping motor, and (12) is a hinge that supports one end of the main charger (3).
A) is a worm gear driven by a stepping motor, and (12b) is a gear fixed to the other end of the main charger (3) and arranged to mesh with the worm gear (12a).

Figure 2 shows (131GtRAM, ROM, CPU
The microcomputer (hereinafter referred to as microcomputer) with a built-in
51 and potential sensor (2f) (2r) output is I
Color of the high voltage unit that is input to the microcomputer 03) through the 10 port (14) and applies high voltage to the main charger (3), stepping motor 0υ, indicator light side, exposure lamp for copying (18), various types of copying The operating copying motor e and the like are controlled by signals from the microcomputer 03) outputted via the I10 baud 1- (14).

The operation of such a configuration will be explained using the flowchart shown in FIG.

The photoreceptor drum (1) rotates in the direction of the arrow (A) by inputting the input key (15) (Fig.
) is cleaned of surface charges (step 101).
. Next, when the surface of the cleaned photoreceptor drum (1) is charged by the discharge of the main charger (3), a simulated original (not shown) is exposed to light by an exposure lamp 08), and the image light is emitted as shown in FIG. is irradiated from the direction of arrow (B), and a simulated original image is formed on the surface of the photosensitive drum (1) (step 102).

The surface potential in the simulated original image is detected by the potential sensor (2f)
(2r>), each is read as f1Vr (step 103).

By the way, as shown in FIG. 4(a), the surface potential (Vs
) depends on the distance between the main charger and the drum surface (S>), and as the distance (S) increases, the surface potential (Vs
) decreases. In this example, the main charge? S = 10m with the applied voltage in (3) constant at 6KV
m, Vs = 700V, and S =
In the vicinity of 10 mm, the surface potential (VS) changes almost linearly with respect to the change in distance (S).

Therefore, the difference vf - Vr is calculated from the surface potential read in step (103), and if it exceeds IOV, the difference vf - Vr is calculated. The distance ΔS (=Sr −3f) to be adjusted to make Vf=vr is calculated using the following formula α(
vr −vr > (step 105)
. And the main charger (3) in Figure 1+b+
The movable end of is (1/2) from the surface of the photoreceptor drum (1)
The stepping motor (111) is rotated (clockwise in this case) so as to be separated by ΔS (step 107).The above routine is repeated up to three times, and the front surface potential (Vf) gradually changes to the rear surface. Approach potential (■“).

If the number of adjustments (nl) is 4 or more times, it is considered an abnormality and the indicator lamp lights up (steps 106 and 108).
). In addition, the difference in surface potential Vr-Vr read in step (103) is calculated, and if it is less than -10V (step 109), the difference in surface potential is The distance △S (=Sr −3r) that should be adjusted to make Vf = Vr is expressed by the following formula α(
Vf - Vr ) (step 110)
. And the main charger (3) in Figure 1(b)
The movable end of is (1/2)ΔS on the surface of the photoreceptor drum (1)
The stepping motor D is rotated (in this case, rotated to the left) so that the stepping motor D approaches the distance (step 112). The above routine is repeated up to three times, gradually increasing the front surface potential (V
f) approaches the rear surface potential (Vr). If the number of adjustments (n2) is four or more times, it is regarded as an abnormality and the indicator light is turned on (steps 111, 113).

Furthermore, as shown in FIG. 4 (b+), the surface potential (Vs
) depends on the main charger applied voltage (Vh), and as the applied voltage (Vh) increases, the surface potential (Vs
) will rise. In this example, the main charger (3)
Distance between and photosensitive drum (1), S = 10m111 constant, Vh = 6KV, then VS = 700V
Therefore, in the vicinity of Vh = 6KV, the surface potential (V
S'') changes almost linearly with the applied voltage (Vh). Therefore, the surface potential (Vr
) (Vr), the average value of the surface potential (Vf + Vr)/2 is calculated and compared with the set value (Vo), and it is determined that -
If it is below 10V (step 114),
), the set value (Vo) and the average value (Vf +
From the difference of Vr )/2, the increment △V of the applied voltage that should be adjusted to eliminate the difference is expressed by the linear formula β(Vo (Vf
+Vr)/2) (Step 11)
5). Then, the applied voltage of the main charger (3) is (
1/2) The high voltage unit A) in FIG. 2 is controlled to increase by 8V (Step 111). The above routine is repeated up to three times, and the average plane potential (Vf + Vr)/2 gradually approaches the set value (vo).

If the number of adjustments (n3) is 4 or more, it is considered an abnormality and the indicator light a turns on (steps 116 and 118).
).

In addition, the average value of the surface potential (Vf + Vr)/2
is calculated, and if it exceeds the set value (Vo) by 1°■ (step 119), the difference between the set value (Vo) and the average value (Vf+Vr)/2 is calculated according to the relationship shown in Figure 4 +b>. , the increment ΔV of the applied voltage that should be adjusted to eliminate the difference is expressed by the linear formula β(VO-(Vf +Vr)/2
) (step 120). Then, the high voltage unit (2) in FIG. 2 is controlled so that the voltage applied to the main charger (3) is reduced by 1/2 ΔV (step 122).

The above routine is repeated up to three times, and the average plane potential (Vf +Vr)/2 gradually approaches the set fil(Vo). If the number of adjustments (n4) is 4 or more, it is considered abnormal and the indicator light On turns on (step 121).
, 123).

In this way, the deviation of the surface potential in the axial direction of the photoreceptor drum (1) is corrected, and the surface potential is set to a predetermined value, and then the copying operation is started (step 1).
23).

(G) Effects of the Invention According to this invention, by adjusting the distance between the photoreceptor drum surface and the charging corona discharger, the surface potential in the axial direction of the photoreceptor drum is automatically adjusted to be constant at all times. As a result, a copying machine with uniform and stabilized image density can be obtained.

[Brief explanation of drawings]

Fig. 1 (ω(b) is an explanatory diagram showing the configuration of an embodiment of the present invention, Fig. 2 is a block diagram showing the electric circuit of the embodiment of Fig. 1, and Fig. 3 shows the operation of Fig. 2. The flowchart shown in FIG. 4 (■+b) is a graph showing the characteristics of the surface potential of the embodiment shown in FIG. 1. (1)...Photosensitive drum, (2f) (2r)... ...Potential sensor, (3)
...Main charger, [K)) ...Hinge, (11J...Stepping motor, (1
2a)... Worm gear, (12b)...
...Gear, 03)...Microcomputer. Figure 1 (a) 7 Moe Beg〉pu 8 AC+w-z (b) 3 Main 4--Jise 2f4 Yuo S/su 2r4 Shito Zenzo Figure 2

Claims (1)

[Claims] 1. A movable means for varying the distance between the surface of the photoreceptor drum and the charging corona discharger, a plurality of detection means for detecting the surface potential in the axial direction of the photoreceptor drum, and movable means corresponding to the detected surface potential. A copying machine characterized by comprising: a control means for controlling the means.