JPH02235075A - Electrostatic recording device - Google Patents

Abstract

PURPOSE:To easily form an excellent image at low cost irrelevantly to the thickness of a recording material by controlling a recording signal voltage by a device which performs recording, development, and image transfer at the same time according to the thickness of the recording material. CONSTITUTION:A piezoelectric sensor 19 outputs a paper thickness detected value to a recording voltage control circuit 24 according to variation in the pressure of a coil spring 20 with the paper thickness of the recording paper P. The circuit 24 applies the recording voltage 4f corresponding to the detected value of the sensor 19 to an auxiliary electrode 21 and also applies it to the segment electrode 4d of a printing head 4 through a driving circuit 26 and a switch 4e according to image information. A linear electrode 4g which is laid on a screw ball 4b is grounded. Consequently, the recording voltage is controlled to the best voltage to obtain a sharp image with sufficient density at low cost by the simple constitution irrelevantly to the paper thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an electrostatic recording device that simultaneously performs recording, development, and image transfer.

[Prior art and its problems]

PPC is a type of electrostatic recording device that can record on plain paper.
There is an electrostatic recording device that uses this method. In this PPC method, an electrostatic latent image is usually formed on an image carrier according to a recording signal, developed with toner, and then transferred onto plain paper.

After the toner image has been transferred, the surface of the image carrier is cleaned and the formation of a new electrostatic latent image is started again. As described above, since the PPC type electrostatic recording device consists of many processes such as recording, development, transfer, and cleaning, the structure tends to be complicated and large.

Therefore, a plain paper electrostatic recording method has been proposed in which the three steps of recording, development, and transfer are combined into one step to simplify the structure. FIG. 9 shows an example of a recording head section in the simultaneous development and transfer recording method. The recording paper P and the toner conveying body 93 run in the same direction A while maintaining a predetermined gap through an electrode facing part F where a signal electrode 91 and a common electrode 92 face each other, to which a voltage is applied according to a recording signal. There is. Signal electrode 91
When a voltage is applied to , an electric field is formed in the electrode facing part F,
Along this line, the toner on the toner transport gap 93 is transferred to the recording paper surface PI, and one dot d of the recorded image is formed. Here, when the common electrode 92 is a linear electrode extending in the moving direction A of the recording paper P, the lines of electric force of the electric field formed in the electrode facing portion F are directed to the common electrode 92 as shown by broken lines. It has the characteristic of spreading radially toward the surface. For this reason, the dots d, which form the basis of the recorded image, cannot be formed sharply.

As a method of preventing the spread of electric lines of force, as shown in FIG.
A possible method is to interpose it between the two.

A slit is provided in the portion of the auxiliary electrode 94 facing the signal electrode 91.
-94a is drilled. By providing such an auxiliary electrode 94, the electric field is formed into a spindle shape as shown by the broken line.
Sharp dots can be formed.

However, even if the electric field is formed into a spindle shape, the paper thickness a of the recording paper P
When this changes, the intensity of the electric field formed in the electrode facing portion F changes, and the quality of the recorded image deteriorates. When using thick paper with a large paper thickness a, the electric field strength at the electrode facing portion F decreases, resulting in poor toner transferability. Therefore, if the recording voltage applied between the electrodes 91 and 92 is set to a high level so that a sufficient electric field can be obtained even for thick paper, the recording voltage will become too strong and the lines of electric force will spread in the case of thin paper. , dots cannot be formed sharply.

[Purpose of the invention]

An object of the present invention is to provide an electrostatic recording device that can stably form a good recorded image without being affected by changes in the thickness of the recording material, and that has a simple structure and is inexpensive. do.

[Key points of the invention]

The gist of the present invention is to achieve the above object by providing an electrostatic recording device according to the present invention, which includes a toner conveying body that carries toner on its surface and moves along a predetermined path, and a toner carrying surface of the toner conveying body. a first electrode provided on the side, a second electrode provided opposite to the first electrode on the opposite side of the toner carrying surface, and a second electrode running between the toner conveying body and the first electrode. a material thickness detecting means for detecting the thickness of the recording material to be recorded; and a control means for controlling a recording signal voltage applied between the first and second electrodes in accordance with a detected value of the material thickness detecting means. The point is that it is configured so that it has the following characteristics.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to FIGS. 1 to 8.

FIG. 6 is a schematic cross-sectional view showing the overall configuration of an electrostatic recording device as an embodiment of the present invention. In the figure, 1 is a paper feed cassette, and the recording paper P is plain paper without surface treatment.
It is stored on the upper side of the fuselage and is removably installed. A paper feed roll 1a is disposed above the leading end of the paper feed cassette 1 in the insertion direction so as to be rotatable in the direction of the arrow.

A pair of standby rolls 2 is disposed in front of the paper feed roll 1a in the paper feed direction A, and after the recording paper P fed out by the paper feed roll 1a is temporarily stopped from advancing and its transport posture is adjusted, Feed again in synchronization with the leading edge of the image. The standby roll pair 2 of this example has a built-in heater 2C in the upper roll 2a, and heats and dries the recording paper when it is supported and conveyed between the two rolls 2a + 2b that roll into contact with each other. This removes moisture from the recording paper and increases its resistance, thereby improving toner transfer efficiency in the printing process described later. still,
The heater 20 may be built in the lower roll 2b,
Furthermore, it may be incorporated in both rolls. Also, standby roll pair 2
A drying roll or a drying heater may be provided separately.

On the downstream side of the standby roll pair 2 in the recording paper conveyance direction,
A static eliminating brush 3 is provided. The static elimination brush 3 extends over substantially the entire width of the recording paper conveyance path, and removes the electrical charges by bringing its tip close to or in sliding contact with the entire area of the recording paper. Thereby, it is possible to prevent an adverse effect during printing due to the charged charges. In this example, the back side of the recording paper (
Although the static elimination brush 3 is brought into sliding contact with the surface (on which no image is printed), the present invention is not limited to this, and it may be brought into sliding contact with the surface or both sides of the recording paper.

A printing section consisting of a print head 4 and a toner supply device 5 is installed downstream of the static elimination brush 3. The print head 4 includes a segment ball 4a and a screw pole 4.
A dielectric drum 6 having toner uniformly adhered to its surface is passed through an electrode facing portion F in which both balls 4a + 4b are opposed, and at the same time, the toner is applied onto the recording paper being conveyed. Selectively transferring toner to form an image. The configuration of the print head 4 will be explained in detail later.

In the toner supply device 5, a dielectric drum 6 as a toner conveying body is rotatably supported in a housing 5a that stores toner t. This dielectric drum 6 is driven and rotated in the direction of arrow B by a driving means (not shown). In this example, a single-component toner t containing no carrier is used. Inside the dielectric/electric drum 6, the screw ball 4
A corona discharger 7 as a toner adhesion means is disposed on the upstream side of b. In the vicinity of the outer peripheral surface of the dielectric drum 6 and on the downstream side of the electrode facing portion F, a scraper 8 serving as a cleaner is disposed such that its tip is in sliding contact with the outer peripheral surface of the dielectric drum θ. This scraper 8 causes toner t to remain on the circumferential surface of the dielectric drum 6 without being used for printing. ' is scraped off. In this example, two stirring rolls 9, 9 are disposed at the bottom of the toner supply device 5, and these are as follows.
While stirring the stored toner t, it is frictionally charged to a predetermined, for example, unipolar property.

In the toner supply device 5 configured as described above, corona ions having a polarity of 10 polarities, which is opposite to the frictionally charged polarity of the toner t, are first discharged by the corona discharger 7 toward the back surface of the dielectric drum 6, and are electrostatically attracted. The force causes the toner t to adhere uniformly to the circumferential surface of the dielectric drum 6. Then, as the dielectric drum 6 rotates, the toner t0 adhered and carried around the dielectric drum 6 is transported to the electrode facing part F, where it is applied to the print head 4.
The image is selectively transferred onto the recording paper according to the image information, and the image is printed.

The toner to' remaining on the circumferential surface of the dielectric drum 6 after the printing process is removed by a scraper 8 that is in sliding contact with the downstream side of the dielectric drum 6.
The toner t is scraped off and returned to the stored toner t. The scraped toner to' is sufficiently stirred and mixed with the stored toner t by stirring rolls 9, 9, and used for printing again. Further, the circumferential surface of the dielectric drum 6 from which the toner to' has been removed is immersed in the toner t, and then reaches the position where the corona discharger 7 is disposed, where toner is applied again. In this case, since the circumferential surface of the dielectric drum 6 has been restored to its substantially initial state by once removing all the adhered toner to' by the scraper 8, the toner is always adhered uniformly and there is no risk of generating an afterimage. . Note that a brush-like cleaner may be provided in place of the scraper 8.

On the downstream side of the print head 4, an air conveyance belt 10 is stretched horizontally.

The conveyance belt 10 suctions the back side of the recording paper after printing and conveys it toward the fixing device 11 provided in front of it. The fixing device 11 includes a heating roll 11a and a pressure roll 1l.
The recording paper is supported between both rolls and thermally fixed when being conveyed. After the fixing, the recording paper is discharged from the discharge port 12 onto the paper discharge tray 3 in a face-down state with the image side facing down, and is stacked thereon.

As described above, in the electrostatic recording apparatus of this example, the entire recording paper transport process from paper feeding to paper ejection. Since the path is formed in a substantially straight shape, the paper passing operation is generally smooth, and paper passing defects such as printing defects and jams are unlikely to occur. or,
Another advantage is that page alignment is not required and a face-down paper discharge state, which is preferable for the recording apparatus, can be achieved using the above-mentioned straight paper passage path.

Here, the configuration of the print head 4 will be explained using FIG. 5. Note that FIG. 5 shows only the central portion of the print head 4 that is involved in direct printing, and both ends are omitted for convenience of explanation (the configurations of both ends are shown in FIGS. 1 and 2).

The print head 4 is made up of a segment ball 4a and a screw ball 4b arranged to face each other, and a dielectric drum θ runs between them in the direction of arrow B. The segment pole 4a is formed by fixing a large number of segment electrodes 4d to both sides of an insulating plate 4C at equal intervals with a predetermined distance therebetween.

The segment electrodes 4d are arranged in two rows in a staggered pattern along a direction (main scanning direction) perpendicular to the recording paper conveyance direction indicated by an arrow. A variable high voltage power source 4f is connected to each segment electrode 4d via a switch 4e. The variable high-voltage power supply 4f applies a voltage having a polarity opposite to that of the toner t, ie, a voltage of 10 polarities in the wooden example, to each segment electrode 4d in accordance with the opening/closing operation of each switch 4e. This variable high voltage power supply 4f is connected to a recording voltage control circuit 24 (see FIG. 7) which will be described later.

On the other hand, the screw pole 4b is made up of a plurality of linear electrodes 4g laid spirally on the circumferential surface of a cylindrical base 4h, and is directed in the direction of arrow C (clockwise direction) opposite to the direction of the dielectric drum 6.
is rotated at a predetermined speed.

Here, each linear electrode 4g does not contact each other,
Moreover, all the linear electrodes 4g are grounded.

Next, the structure of both ends of the print head 4 and its electrode facing portion F will be described in detail with reference to FIGS. 1 to 3. 2 is a side view of one end of the print head 4 viewed from the direction in which the recording paper P is carried in, and FIG. 3 is an enlarged explanatory diagram showing the electrode facing portion F.

A gap material 14 is laid over the entire circumference of the circumferential surface of both ends of the dielectric drum 6 corresponding to the non-printing area. In this example, the thickness (gap) g of the gap material 14 is 30μ
It is set to m. A gap roller 15 provided on the end surface of the print head 4 is brought into contact with the upper surface of the gap material 14 via the recording paper P. As a result, the distance between the image surface PI of the recording paper P and the surface of the dielectric drum 6 can be maintained at a constant minute gap g at all times, and even recorded images with high dot density can be clearly printed. . The print head 4 is
A stopper 18 is inserted through a sliding rod 16 installed on its upper surface.
It is suspended on the. The sliding rod 16 is slidably pushed through a through hole bored in the support member 17 and a through hole of a stopper 18, and the stopper 18 is fixed to the main body of the device.

A piezoelectric sensor 19 is fixed to the lower surface of the support member 17. A through hole that is the same as or slightly larger than the hole provided in the above-mentioned support member 17 is also bored in the center of the piezoelectric sensor 19, and the sliding rod 16 is inserted into the through hole so as to be able to move up and down. Conductive wires b+c are drawn out from a pair of electrodes 19a and 19b of the piezoelectric sensor 19, respectively. These lead lines b and C are connected to a recording voltage control circuit 24 (seventh
(see figure). A coil spring 20 is extrapolated to the base side of the sliding rod 16. coil spring 20
is interposed between the print head 4 and the piezoelectric sensor 19, and its both ends are always in contact with the upper surface of the print head 4 and one electrode 19a of the piezoelectric sensor 19, respectively.

Therefore, depending on the thickness of the recording paper P carried into the electrode facing section F, the rollers 15, the print head 4, and the sliding rod 16 move up and down together, and the coil spring 20 moves up and down against the electrode 19a of the piezoelectric sensor.
pressure changes. This pressure change is converted into a voltage value by the piezoelectric sensor 19, and outputted to the recording voltage control circuit 24 as a paper thickness detection value.

An auxiliary electrode 21 is interposed between the screw pole 4b and the dielectric drum 6. The auxiliary electrode 21 is supported by a support 22 made of an insulating material as shown in FIG.
It is installed only in the vicinity of the area. A slit 21a is provided in the portion of the auxiliary electrode 21 facing the tip of the segment electrode 4d.
has been drilled.

This auxiliary electrode 21 is connected to the variable high voltage power supply 4f described above.

Here, the strength of the electric field formed at the electrode facing portion F will be explained.

In Fig. 3, the electrode facing direction in the electrode facing part F is the Y axis,
The running direction opening (sub-scanning direction) of the recording paper P is assumed to be the X axis. Further, e: Distance between the tip surface of the segment electrode 4d and the surface of the auxiliary electrode 21 f: Distance between the recording paper image plane PI and the surface of the auxiliary electrode 21 ) Distance in the X-axis direction from the edge C: Approximate value of inter-electrode capacitance ε: Dielectric constant V: Recording voltage, then the Y-axis direction component Ery of the electric field E formed between both electrodes is as follows. Become. Now, for example, Case■ Paper thickness...100μm gap g
・・・・・・50μm dielectric drum thickness・・・・・・
20μm, so e=170tLm f=70μm Case■ Paper thickness...200μm gap g
・・・・・・50μm dielectric drum thickness・・・・・・
20 μm, assuming two cases where e=270 μm and f=70 μm, Ery in each case is determined by the above equation and compared, as shown in FIG. 4.

In FIG. 4, Ell+ is the electric field strength in the Y-axis direction component necessary to transfer the toner from the surface of the dielectric drum 6 to the recording paper image PI. In a case where ordinary recording paper is used, a toner image can be formed because E and E exceed the required electric field Em in a region where X is small. However, in case ■ where cardboard is used, E
Since ry is less than the required electric field Effl, a toner image cannot be formed. Therefore, in case (2), only the recording voltage V is increased by 1.3 times. As a result, the characteristic curve of Ery is approximately equal to the characteristic curve of Case E. 1) Characteristic curve ■' (
(shown with a broken line). Therefore, it can be seen that even when the paper thickness is large, a toner image can be formed by increasing the recording voltage V.

In the present invention, based on the above-mentioned knowledge, the above-mentioned piezoelectric sensor 1
The recording voltage V applied to the print head 4 is controlled according to the paper thickness detection value of the recording paper P obtained by the paper thickness detection mechanism equipped with 9, and a recorded image is always stably formed regardless of the paper thickness. plan something. FIG. 7 shows a circuit configuration for realizing the printing operation.

In FIG. 7, the lead wire C from one electrode of the piezoelectric sensor 19 described above is grounded, and the lead wire B from the other electrode is connected to the ground.
It is connected to a recording voltage control circuit 24 via an amplifier 23. The recording voltage control circuit 24 applies a recording voltage to the segment electrode 4d described above. A variable high-voltage power supply 4f is connected. This variable high voltage power supply 4f, as shown in FIG.
Each segment electrode 4d is connected via a switch 4e. The switch 4e is selectively opened and closed according to image information by a drive circuit 26 connected to a line memory 25 into which image information is input.

The line memory 25 stores image information for one main scanning line. This image information is output to the drive circuit 26 in synchronization with each part of the electrostatic recording device. The drive circuit 26 selectively opens and closes the switch 4e according to the image information, and a recording voltage is selectively applied to each segment electrode 4d by the variable high voltage power supply 4f. This recording voltage is optimally controlled by the recording voltage control circuit 24 according to the paper thickness of the recording paper P. That is, the larger the paper thickness of the recording paper P (piezoelectric sensor 1
The output voltage of the variable high voltage power source 4f is controlled such that the higher the output voltage of the variable high voltage power source 4f, the higher the voltage applied to the segment electrode 4d. As a result, when the paper is thick, sufficient electric field strength E can be obtained for toner image formation, and when the paper is thin, a spindle-shaped electric field with no spread is formed, resulting in a sharp and sufficient density regardless of the paper thickness. It is possible to stably obtain recorded images.

In FIG. 5, when the screw ball 4b is now rotated in the direction of arrow C (counter-scanning direction), the linear electrode 4g moves in parallel in the arrangement direction of the segment electrodes 4d (main-scanning direction) in the electrode facing part F. . During this movement, when a ten-polar high voltage is applied to the segment electrode 4d, an electric field is formed at the intersection of the segment electrode 4d and the linear electrode 4g, as shown in FIG. The toner t is monopolarly charged along the curve shown in FIG. is transferred onto the recording paper image surface P1, and 1 dot d is printed. By forming one of the opposing electrodes in the shape of a screw ball in this manner, the structure of the print head 4 can be significantly simplified. On the other hand, as shown in FIG. 9, a problem arises in that the lines of electric force spread radially and dots cannot be formed sharply. In this example, since the auxiliary electrode 21 is provided on the linear electrode 4g, the electric lines of force are prevented from spreading and are formed into a spindle shape.

As a result, it is possible to form sharp dots and obtain a clearer image. In addition, since the voltage is applied via the dielectric drum 6, the strength of the electric field is less likely to change depending on the electrical resistance value of the recording paper P, and good print quality can always be stably obtained even in a high humidity environment. be able to. Furthermore, since unnecessary charges on the recording paper P are also removed by the static elimination brush 3, the print quality becomes more stable.

FIG. 8 shows another embodiment of the invention. Note that the same components as those in the above embodiment are given the same reference numerals, and the explanation thereof will be omitted.

In this example, the paper thickness detection mechanism is not provided in the print head 4, but is provided at an appropriate location on the path for carrying the recording paper P into the print head 4. A roller 27 is provided at the tip of the sliding rod 16, and this roller 2
7, a backup roller 28 is provided with the recording paper P in between. The other configurations are the same as those of the above embodiment. By providing the paper thickness detection mechanism separately from the print head 4 in this manner, the configuration of the print head 4 is simplified. This facilitates maintenance of the print head 4 and reduces running costs.

It should be noted that the present invention is not limited to the preferred embodiments described above, and it goes without saying that various modifications can be made within the technical scope of the present invention. For example, a signal electrode may be disposed on the opposite side of the toner carrying surface of the toner conveying body to selectively repel toner toward the common electrode. The present invention can also be applied to a case where a multi-stylus head in which ordinary needle-like electrodes are arranged side by side is used as the print head, without using the screw ball 4b. In this case, the auxiliary electrode is not required. Furthermore, instead of grounding the linear electrode 4g, it may be connected to a bias power source having the same polarity as the charging polarity of the toner.

〔Effect of the invention〕

As described in detail above, according to the present invention, by having a configuration in which the voltage applied to the recording electrode is changed depending on the thickness of the recording material used for printing, regardless of the thickness of the recording material,
An electric field suitable for image recording, which has sufficient strength to transfer toner and whose spread is suppressed, can be stably formed at all times. Therefore, regardless of the thickness of the recording material used, it is possible to consistently form sharp, high-density, and good recorded images even on plain paper. In addition, since recording, development, and image transfer are performed simultaneously, the structure is extremely simple.
It becomes possible to provide an electrostatic recording device that exhibits the above-mentioned effects at a low cost.

[Brief explanation of the drawing]

FIG. 1 is a side view showing the configuration of a recording section in an electrostatic recording device as an embodiment of the present invention, FIG. 2 is a front view showing one end of the recording section, and FIG. 3 is a front view of the recording section. FIG. 4 is a graph showing the electric field strength characteristics at the electrode facing portion, FIG. 5 is a perspective view showing the print head in the electrostatic recording device, and FIG. FIG. 7 is a block diagram showing the configuration of a printing control circuit in the electrostatic recording device, and FIG. 8 shows a paper thickness detection mechanism as another embodiment of the present invention. The side view, FIG. 9, and FIG. 10 are explanatory diagrams showing the structure of the electrode facing portion in a conventional electrostatic recording device, respectively. 4...Print head 4a...Segment ball 4b...Screw pole 4d...Segment electrode 4f...Variable high voltage power supply (for applying segment ball) 4
g... Linear electrode 14... Gap material 15.27... Gap socket 19... Piezoelectric sensor 20... Coil spring 21... Auxiliary electrode 24... Recording voltage control circuit

Claims (1)

[Claims] a toner transporting body that carries toner on its surface and moves along a predetermined path; a first electrode provided on the toner carrying surface side of the toner carrying body; and a first electrode provided on the opposite side of the toner carrying surface. a second electrode provided facing each other, a material thickness detecting means for detecting the thickness of the recording material running between the toner conveying body and the first electrode, and a detection value of the material thickness detecting means. an electrostatic recording device comprising: control means for controlling a recording signal voltage applied between the first and second electrodes in accordance with the first and second electrodes.