Electrostatic recording apparatus with automatic movement of the recording electrodes between a recording and a nonrecording position

Abstract

In an electrostatic recording apparatus, the recording electrode and the back electrode are pressed against each other across a sheet of moving recording paper, to ensure effective recording, but move away from each other just before the sheet moves away from the electrodes, to avoid an electrical short. This has the advantages of efficient recording, which have been previously possible only with recording on a continuous web, and the advantages of efficient use of paper, which have been associated previously only with spaced-apart electrodes recording on individual sheets of paper.

Description

BACKGROUND OF THE INVENTION

The invention relates to electrostatic recording devices. More particularly, it is concerned with an apparatus in which an electrostatic latent image is formed by applying electrical signals on electrostatic recording paper in sheet form moving between opposing recording electrode means and back electrode means, and the electrostatic latent image which has been so formed is later developed into a visible image.

In one type of electrostatic recording devices used in facsimile receivers or print-out devices attached to electronic computers, a continuous web of recording paper is used for recording an electrostatic latent image, and the web is later cut into sheets of proper sizes. In this type of devices, the recording electrode means and the back electrode means are at all times pressed against each other across the web of paper. The disadvantage of this type of electrostatic recording devices is that much paper is wasted.

Other electrostatic recording devices work with recording paper in sheet form, and can economize on the use of paper. However, it is required in this type of devices to maintain a gap between the recording electrode means and the back electrode means in order to avoid short circuiting when no sheet of paper is held between them. Because of this gap between the electrode means, the recording process is less efficient.

SUMMARY OF THE INVENTION

An object of the invention is to obviate the disadvantages of the prior art electrostatic recording devices discussed above, and to provide a device which has the recording efficiency previously possible only with devices using continuous webs, but to avoid waste of paper, and to provide the savings in paper previously possible only when using electrodes that are spaced from each other by a suitable gap and record on individual sheets of paper.

The invention resides in arranging recording electrode means and back electrode means for movement toward and away from each other, and in providing first paper sensor means and second paper sensor means disposed anterior to and posterior to the two electrode means respectively as seen in the direction of movement of electrostatic recording paper, and means for causing the two electrode means to move toward each other when both sensor means have sensed paper and for causing them to move away from each other when at least one of the sensor means stops sensing paper.

Other features and advantages of the invention will become evident from the description set forth hereinafter when considered in conjunction with the accompanying drawings.

Brief Description of the Drawings

FIG. 1 is a schematic view of an electrostatic recording apparatus embodying the invention.

FIG. 2 is a perspective view of the electrostatic recording apparatus showing a frame supporting back electrode means and the upper rollers of two pairs of paper feed rollers, said frame being disposed in an upper position.

FIG. 3 is a perspective view of the means for moving and driving the pair of paper feed rollers and for moving the back electrode means.

FIG. 4 is a perspective view of a second paper sensor.

FIG. 5 shows an electric circuit used in the apparatus of FIG. 1.

DETAILED DESCRIPTION

In FIG. 1, the recording apparatus 1 of a facsimile receiver comprises recording electrode means 2 and back electrode means 3 facing each other. A pair of paper feed rollers 4 and 5 are disposed anterior to the two electrode means and another pair of paper feed rollers 6 and 7 are disposed posterior thereto as seen in the direction of movement of recording paper (not shown).

Upper rollers 5 and 7 of the two pairs of paper feed rollers, which are follower rollers, and the back electrode means 3 are mounted on a frame 8. The frame 8 is pivotally supported by a shaft 8A and adapted to move to an upper position as shown in broken lines, so that the rollers 5 and 7 and the back electrode means 3 can be moved to the upper position with the frame 8. By this arrangement, the electrodes 2 and 3 can be separted from each other.

In FIG. 2, a large number of pin electrodes are arranged on an electrode surface 2A of the recording electrode means 2. Voltages are impressed selectively on the pin electrodes as signals are applied from an outside source (not shown) while a sheet of electrostatic recording paper (not shown) moves along the path between the recording electrode means 2 and the back electrode means 3, so that an electrostatic latent image can be formed on the electrostatic recording paper. The electrostatic recording paper on which the electrostatic latent image is formed is delivered by the paper feed rollers 6 and 7 to a developing station (not shown) where the latent image is developed into a visible image.

In order to detect the presence of recording paper between the electrodes 2 and 3, paper sensor means 9 is disposed anterior to the electrode surface 2A of the recording electrode means 2 and another paper sensor means 10 is disposed posterior thereto as seen in the direction of movement of paper. As shown in FIG. 3, the first sensor means 9 comprises a light source 11 and a light receiving element 12 which are arranged such that, when paper is not disposed below the first sensor 9, the light emanating from the light source 11 is not incident on the light receiving element 12, and when paper moves below the first sensor 9, the light emanating from the light source 11 is reflected by the paper and is incident on the light receiving element 12, thereby permitting the passage of paper to be ascertained.

The second sensor means 10 comprises, as shown in FIG. 4, a lever 13 including an upper arm 13A disposed in the path of movement of paper, a light source 14 and a light receiving element 15. The lever 13 includes a lower arm 13B which is adapted to be disposed between the light source 14 and the light receiving element 15 to intercept the light emanating from the former and prevent the same from being incident on the latter.

The lever 13 is pivotally supported by a shaft 16 and is normally urged by the biasing force of a helical spring 17 wound on the shaft 16 to move such that the lower arm 13B is disposed in front of the light receiving element 15 to prevent the light from the light source 14 from being incident on the light receiving element 15. When the leading end of a moving sheet of recording paper pushes the upper arm 13A, the lever 13 is pivoted about the shaft 16 to move the lower arm 13B into a position in which it is out of index with the light receiving element 15. This permits the light emanating from the light source 14 to be incident on the light receiving element 15, so that the sensor means 10 senses the arrival of the sheet of paper.

Referring to FIG. 2, the pair of rollers 6 and 7 are formed with annular grooves 6A and 7A respectively at their central portions. The upper arm 13A of the lever 13 is aligned at its upper end with the annular grooves 6A and 7A.

Referring to FIG. 3 again, the lower rollers 4 and 6 of the pair of rollers are driven for rotation by an electric motor 18 through a timing belt 19, a pulley 20 engaged by the timing belt 19, a pinion 21 fixed to the pulley 20 and two gears 22 and 23 which are in meshing engagement with the pinion 21. There is provided a solenoid 24 including a plunger 24A which supports the right arm of a lever 25 pivoted at 25A, with the left arm of the lever 25 being in contact with the front arm of a lever 26 which is pivoted at 26A and normally urged to move counterclockwise by the biasing force of a spring 27. The back arm of the lever 26 is urged by the biasing force of the spring 27 to move into contact with a pin 28 projecting laterially from the right end of the back electrode means 3 and extending through an opening 29 formed in a side plate. An arm 30, which is loosely supported at its back end by the shaft supporting the roller 5, is pivotally connected at its front end to the pin 28.

The operation of the aforementioned apparatus is described with reference to an electric circuit shown in FIG. 5. When the main switch (not shown) of the apparatus is turned on, the motor 18 (FIG. 3) rotates and the rollers 4 and 6 are rotated through the timing belt 19, pinion 21 and gears 22, 23. Rotation of the rollers 4 and 6 results in the follower rollers 5 and 7 being rotated thereby. When no paper is fed, the back electrode means 3 is away from the electrode surface 2A of the recording electrode means 2, at the non-recording position shown in FIG. 3, because the pin 28 is moved upwardly by the lever 26 under the influence of the spring 27.

When a sheet of electrostatic recording paper is inserted in the apparatus and moved through the paper feed rollers 4 and 5 to the first sensor means 9, the paper is sensed by the sensor means 9. At this time, an AND circuit 31 shown in FIG. 5 is not actuated, because only one of its inputs is active. Then, the paper moves along its path of travel between the two electrode means 2 and 3, which at this time are spaced apart from each other, and pushes the upper arm 13A of the lever 13 of the second sensor 10, so that the lever 13 is pivoted about the shaft 16 to cause the light from the light source 14 to be incident on the light receiving element 15. Thus, the paper is sensed by the second sensor means 10.

When the paper is sensed by the two sensor means 9 and 10, the AND circuit 31 shown in FIG. 5 is actuated, since both its inputs are now active, to impress a voltage on the base of a transistor 32 to fire the same. This actuates a relay 33 and contacts 33A and 33B thereof are closed. Closing of contact 33A energizes the solenoid 24 while closing of contact 33B impresses a reference voltage on the pin electrodes on the electrode surface 2A. Energization of the solenoid 24 moves the plunger 24A downwardly, so that lever 26 is pivoted clockwise against the biasing force of the spring 27 through lever 25. Pivotal movement of lever 26 causes the back electrode means 3 resting on the other arm of lever 26 by its own weight through the arm 28 to move downwardly, so that the back electrode means 3 moves to a recording position in which it is against the electrode surface 2A, with the electrostatic recording paper being interposed at this time between the electrodes 2 and 3.

At this time, voltage signals are supplied from an outside source (not shown) so as to selectively impress voltages on the pin electrodes on the electrode surface 2A, thereby forming an electrostatic latent image on the recording paper. When the trailing end of the sheet of paper is released from engagement with the first sensor means 9, the sensor 9 is rendered inoperative and the AND circuit 31 is de-actuated since one of its inputs is now not active. This cuts off the voltage signal applied to the base of the transistor 32, so that the solenoid 24 is de-energized and the reference voltage applied to the recording electrode means 2 is stopped, since the contacts 33A and 33B are now open. Additionally, the back electrode means 3 is moved away from the recording electrode means 2 and impression of voltages on the pin electrodes is stopped.

Thus, when there is recording paper in the locality between the sensors 9 and 10, such that each of the sensors senses the presence of recording paper, the electrodes 2 and 3 are against each other, in the recording position shown in solid lines in FIG. 1, but when the recording paper does not cover the entire locality between the sensors 9 and 10, i.e., when either sensor is not sensing recording paper, the electrodes 2 and 3 are moved away from each other, to the nonrecording position shown in FIG. 2.

From the foregoing description, it will be appreciated that the apparatus embodying the invention causes the two electrode means 2 and 3 to move toward each other when a sheet of electrostatic recording paper is sensed by both the first and second sensor 9 and 10, and to move away from each other when no recording paper is sensed by one of both sensors, thereby ensuring that no short-circuiting of the two electrode means 9 and 10 can occur. The apparatus according to the invention permits sheets of paper of any desired length to be used, because the two electrode means are moved toward and away from each other by sensing the leading and the trailing end of the paper.

In the invention, the first and second sensor means each may include two or more individual sensors, so that a sheet of electrostatic paper fed in an inclined position can be positively sensed.

Claims

I claim:

1. An electrostatic recording apparatus comprising means for moving a recording sheet along a defined path, recording electrode means disposed at the other side of the path, means for supporting the electrode means, means for detecting the presence of a recording sheet at a defined portion of said path to provide control signals in response to detecting the presence of a sheet at said defined portion of the path, means responsive to the said control signals from the detecting means for causing the support means to maintain the two electrode means at a recording position adjacent and facing each other across said path when a sheet is present at said defined portion of the path and to maintain the two electrode means at a nonrecording position away from each other when no sheet is present at said defined portion of the path and to move the electrode means between said two positions, said defined portion of the path including the path portion which is between the two electrode means when the electrode means are at their recording position, wherein the detecting means comprises first sensor means disposed in the path of the recording sheet preceding at least one of the electrode means and second sensor means disposed in the path of the recording sheet after at least one of the electrode means, as seen in the direction of movement of the recording sheet along said path, each of said sensor means being actuated by the presence of a recording sheet at its location, said sensor means providing said control signals when actuated.

2. An electrostatic recording apparatus as in claim 1 wherein the supporting means comprises a frame carrying one of said electrode means and means for pivotally supporting the frame for movement between a recording position in which the two electrode means are at their recording position and a nonrecording position which the two electrode means are at their nonrecording position.

3. An electrostatic recording apparatus as in claim 2 wherein said frame carries the back electrode means.

4. An electrostatic recording apparatus as in claim 3 wherein the means for moving the recording sheet comprises a first and a second pair of feed rollers, with the first pair disposed before the electrode means and the second pair disposed after the electrode means as seen in the direction of movement of the recording sheet, each of said pair comprising a lower and an upper roller, with the upper roller of each pair secured to said frame and movable therewith between the recording and nonrecording position of the frame.

5. An electrostatic recording apparatus as in claim 1 wherein the support means and the means for causing the support means to maintain the electrode means in said recording and nonrecording position comprise a lever, means for pivotally supporting the lever for movement between a recording position at which the two electrode means are at their recording position and a nonrecording position at which the two electrode means are at their non-recording position, said lever engaging the support means for at least one of the electrode means, and electric circuit means responsive to the actuation of both switches to cause the lever to move to its recording position and responsive to the lack of actuation of either switch to cause the lever to move to its nonrecording position.

6. An electrostatic recording apparatus as in claim 5 wherein the lever engages the back electrode means only.

7. An electrostatic recording apparatus as in claim 6 wherein the electrical circuit means comprises a relay actuated when both the first and the second switch are actuated, a solenoid energized when the relay is actuated, and means responsive to the energized state of the solenoid to move the lever to its recording position and responsive to the nonenergized state of the solenoid to move the lever to its nonrecording position.

8. An electrostatic recording apparatus as in claim 7 including means for normally biasing the lever to its nonrecording position.

9. An electrostatic recording apparatus comprising: means for moving a recording sheet along a defined path; recording electrode means disposed at one side of the path, and back electrode means disposed at the other side of the path; means for supporting the electrode means for motion toward and away from each other, between a recording position at which the electrode means are close to each other and a nonrecording position at which the electrode means are further away from each other; means for detecting the presence of a continuous length of a recording sheet within a continuous span of said path, which span has a portion before and a portion after the electrode means, as seen in the direction of movement of the sheet along the path, to provide first type control signals in response thereto, and for detecting the absence of a sheet at any portion of said span to provide second type control signals; means for moving the electrode means to said recording position in response to said first type control signals and for maintaining the electrode means at said recording position until the detecting means provide said second type control signals, and for moving the electrode means to said nonrecording position in response to said second type control signals and for maintaining the electrode means at said nonrecording position until the detecting means provide said first type control signals.