Sheet Conveying Means and an Ink Jet Recording Apparatus Having the Same

1. Field of the Invention

This invention relates to sheet conveying means and an ink jet recording apparatus having the same.

2. Related Background Art

Sheet conveying means for conveying a sheet conveys the sheet with a spur brought into contact with the sheet with a pressure force. In order to make the sheet conveying means compact, there is one in which the shaft of the spur is provided by a resilient member to thereby obtain the pressure force against the sheet. In such construction, however, it has been difficult to obtain a stable pressure force irrespective of the thickness of a sheet being conveyed.

It is an object of the present invention to provide sheet conveying means in which a stable pressure force is obtained irrespective of the thickness of a sheet being conveyed.

Now, the following problems have been encountered when the above-described conventional sheet conveying means provided with a spur is applied to the field of an ink jet recording apparatus.

Where an ink droplet is large, or where it is difficult for a sheet itself such as an OHP sheet to absorb ink, or where the ink fixativeness of plain paper or the like is not good, if the pressure force of the spur against the sheet is too great, ink will adhere to the spur and the ink will again adhere to the sheet to stain the sheet.

Further, if the pressure force of the spur against the uneven portion of a sheet which is created by being wet with ink is too great, stable conveyance of the sheet will not be realized.

So, it is another object of the present invention to provide an ink jet recording apparatus provided with sheet conveying means which can realize stable conveyance of a sheet by an appropriate pressure force against the presence of the unfixed or unfixated portion of an ink droplet and the presence of the uneven portion of the sheet wet with ink.

It is another object of the present invention to provide sheet conveying means for conveying a sheet characterized by a rotatable member, a spur provided in opposed relationship with said rotatable member, and a resilient member supporting said spur and provided in a curved state so as to press said spur against said rotatable member.

It is another object of the present invention to provide a recording apparatus for effecting recording on a sheet characterized by sheet conveying means having a rotatable member, a spur provided in opposed relationship with said rotatable member, and a resilient member supporting said spur and provided in a curved state so as to press said spur against said rotatable member, and recording means for effecting recording on the sheet.

It is another object of the present invention to provide an ink jet recording apparatus characterized by a recording head having a discharge port for discharging ink therethrough to thereby effect recording on a recording medium, conveying means for conveying said recording medium having a conveying roller, a spur provided in opposed relationship with said conveying roller, and a resilient member supporting said spur and provided in a curved state so as to press said spur against said conveying roller, and a carriage capable of moving said recording head in a predetermined direction.

FIG. 1A is a perspective view showing a first embodiment of the present invention.

FIG. 1B is a front view showing the first embodiment of the present invention.

FIG. 2 is a schematic perspective view showing an ink jet recording apparatus to which an embodiment of the present invention is applied.

FIG. 3 is a graph showing the relation between the displacement and load of a spring in an embodiment of the present invention.

FIG. 4 illustrates a method of applying the load of FIG. 3.

FIGS. 5A and 5B show another embodiment of the present invention.

An ink jet recording apparatus to which sheet conveying means according to the present invention can be suitably applied will hereinafter be described with respect to an embodiment thereof shown. FIG. 2 schematically shows the construction of an ink jet printer to which the present invention is applied. In FIG. 2, a recording head 1 discharges ink by a recording signal, and is supplied with ink by an ink tank 2. A carriage 4 carrying thereon the recording head 1 and the ink head 2 is guided by guide shafts 3, and is reciprocally moved along the guide shafts 3 by a belt transmission mechanism and a driving motor, not shown. A recording sheet 5 is held from the back thereof by a platen 6 lying at a location opposed to the recording head 1. The recording sheet 5 is brought into intimate contact with the platen 6 by a paper keep plate 7. The recording sheet 5 thus brought into intimate contact with the platen is fed by a paper feeding roller 8. The recording paper 5 on which recording has been effected is discharged by a discharge roller 9. Spurs 10 are provided in opposed relationship with the discharge roller 9 and urge the recording sheet 5 against the discharge roller. The spurs 10 are biased toward the recording sheet 5 by an urging force by the flexure of a shaft which will be described later. The roller 8 and the roller 9 are driven by a paper feeding motor 12. A recovery system device 13 performs the recovery operation for preventing the clogging or the like of the discharge port of the recording head 1, and further performs the capping operation for preventing the desiccation of the discharge port when recording is not effected. This recovery system device 13 is driven by a recovery system driving motor 14.

The recording sheet 5 is inserted along a paper pan 15.

The operation of the above-described ink jet printer will now be described. The recording sheet 5 inserted along the paper pan 15 is fed to the platen 6 with the inserted leading end thereof turned into a U-shape by the roller 8 and is brought into intimate contract with the platen 6 by the keep plate 7. Ink is jetted from the recording head 1 by a recording signal and adheres to the recording sheet 5. By this adherence, characters or images are formed. As this recording operation progresses, the portions of the recording sheet 5 on which recording has been effected are successively fed upwardly by the roller 8. When the leading end portion of the recording sheet 5 arrives at the spurs 10, the recording sheet 5 is pushed from its recording surface by the spurs 10 and the back of the recording sheet is urged against the roller 9, and the recording sheet is further conveyed upwardly by the rotation of the roller 9 and is discharged outwardly.

Now, each spur 10 having pointed tip ends is constructed as shown in FIGS. 1A and lB.

In FIGS. 1A and 1B, the reference numeral 10 designates the spur, the reference numeral 22 denotes the shaft of the spur which comprises a closely wound tension coil spring, the reference numeral 9 designates the discharge roller formed of rubber or the like, and the reference numeral 24 denotes spur holders for supporting the spur 10 and the shaft 22 of the spur. In order that an appropriate pressure force necessary to convey the recording sheet 5 may be applied to the recording sheet 5 on which recording has been effected and which passes between the spur 10 and the discharge roller 9, the positions of the discharge roller 9, the spur 10 and the spur holders 24 are set so that the shaft 22 of the spur may somewhat flex as shown in FIG. 1B. An example of the graph of the displacement and load of the closely wound tension coil spring used in the present embodiment is shown in FIG. 3.

The graph of FIG. 3 shows the relation between the flexure .delta. of the center of the closely wound tension coil spring when, as shown in FIG. 4, a load is made to act vertically downwardly on the center of the spring supported at its opposite ends by a span l and said load.

When the experiment as shown in FIG. 4 is carried out by the use of a tension spring as a heretofore used resilient member instead of the closely wound tension coil spring, the following fact is found.

When the vertical elastic modulus of said tension spring is E and the cross-sectional secondary moment thereof is I and the span thereof is l and the flexure of the center of the span is .delta. and the load acting on the center of the span is F, the following equation is established: ##EQU1##

This equation (1) is the linear function of .delta. and F within the limit of elasticity of the spring. When this tension spring is used as the shaft of the spur of the sheet conveying means, this shaft flexes correspondingly to the thickness of the sheet being conveyed, and there is created the pressure force from the spur to the sheet which is found from equation (1). Thus, the pressure force varies greatly correspondingly to the thickness of the sheet being conveyed (as shown by (c) in FIG. 3). However, when the closely wound tension coil spring according to the present invention is used as the shaft of the spur, it will be seen that a pressure force corresponding to the initial tension F.sub.0 can be created even if flexure, i.e., the displacement .delta. of the shaft, is almost 0, while on the other hand, a pressure force slightly greater than the initial tension F.sub.0 is created even when the shaft is flexed by the sheet being conveyed.

The relationship of the closely wound tension coil spring shown in (a) of FIG. 3 which is used in the sheet conveying means according to the present invention is such that the pressure force created within the range of 0.5 mm to 2.0 mm of the displacement amount is about 17 g to about 21 g. Further, by varying the torsion applied to the coil when the coil is wound into a closely wound form, the initial tension F.sub.0 can be changed to F.sub.0 '. The relationship of the closely wound tension coil spring shown in (b) of FIG. 3 is such that the pressure force created within the range of 0.5 mm to 2.0 mm of the displacement amount can be changed from about 7 g to about 10 g.

FIGS. 5A and 5B show another embodiment of the present invention. The closely wound tension coil spring used in this embodiment is that shown in (b) of FIG. 3, and the spring constant thereof is 44 g/mm, the diameter of the wire thereof is 0.2 mm.+-.0.01 mm, the outer diameter of the coil thereof is .phi.9.+-.0.05 mm, the length thereof is 18.4.+-.0.2 mm, the effective number of turns thereof is 92, the span thereof is 16 mm, and the load F when the spring is displaced by .delta.=1 mm at the center of the span is 9.+-.1 g. The material of the spring is a so-called spring material such as SUS or piano wire.

Also, the spur used is of a pillar-like shape having a diameter of 6 mm and a thickness of 2.2 mm and having pointed projections provided on the center of the direction of thickness over the side of the pillar. The material of the spur may be, for example, a metal if it is a water repellent material, but may suitably be fluorine resin, polyacetal or the like.

The spur 30 is threaded through a shaft made of a closely wound tension coil spring, and is resilently mounted on the apparatus by means of members 25 and 25. At this time, the spur is provided so as to protrude toward the sheet conveying surface by 1 mm. That is, the spring is provided in a curved state on the apparatus while supporting the spur. The spur is restricted in its horizontal movement by the members 25 and 25.

When paper (having a thickness of 0.1 mm-0.2 mm) or an envelope (having a thickness of about 0.5 mm) is to be conveyed as a sheet, the displacement amount of the spring is 1.1 mm to 1.5 mm and the pressure force can keep a substantially constant value of about 9.5 g-10.5 g. Therefore, where this spur is used in an ink jet recording apparatus, the pressure force obtained is substantially constant even if the thickness of the paper material varies, and stable conveyance of the paper material is possible.

Further, if the wire material of the closely wound tension coil spring is thickened and the initial tension is increased to 50 g-100 g, there can be provided sheet conveying means which will require a great pressure force for the conveyance of a paper material such as continuous paper.

The spring constant of the closely wound tension coil spring which can be suitably used in the present embodiment is greater than 10 g/mm and less than 100 g/mm, and preferably greater than 30 g/mm and less than 50 g/mm, and most preferably greater than 40 g/mm and less than 45 g/mm.

The outer diameter of the coil is greater than 0.5 mm and less than 2 mm, and preferably greater than 0.8 mm and less than 1.0 mm.

The thickness of the wire material used, with about 1/5 of the outer diameter of the coil as the standard, is greater than 0.1 mm and less than 0.4 mm, and preferably greater than 0.15 mm and less than 0.2 mm.

The span is determined by the wire diameter of the spring material used, the displacement amount and the pressure force obtained, and is preferably greater than 5 mm and less than 30 mm, and more preferably greater than 10 mm and less than 20 mm.

Also, the flexure amount (the displacement amount) .delta. is greater than 1 mm and less than 2 mm, and preferably greater than 1 mm and less than 1.5 mm if the sheet material is plain paper, and preferably greater than 1 mm and less than 1.2 mm if the sheet material is continuous paper.

The present invention brings about an excellent effect particularly in a recording head and a recording apparatus of the ink jet type which utilize heat energy to form flying droplets and accomplish recording, among the ink jet recording systems.

The typical construction and principle of such system may preferably be based on the basic principle disclosed, for example, in U.S. Pat. No. 4,723,129 or U.S. Pat. No. 4,740,796. This system is applicable to both of the so-called on-demand type and the so-called continuous type, and particularly in the case of the on-demand type, it is effective because at least one driving signal corresponding to recording information and providing a rapid temperature rise exceeding nucleate boiling is applied to an electro-thermal conversion member disposed correspondingly to a sheet or a liquid path in which liquid (ink) is retained, whereby heat energy is generated in the electro-thermal conversion member to thereby cause film boiling on the heat-acting surface of a recording head with a result that a bubble in the liquid (ink) corresponding at one to one to said driving signal can be formed. By the growth and contraction of this bubble, the liquid (ink) is discharged through a discharge opening to thereby form at least one droplet. If this driving signal is made into a pulse-like shape, the growth and contraction of the bubble will take place appropriately on the spot and therefore, the discharge of the liquid (ink) particularly excellent in responsiveness can be achieved, and this is more preferable.

The signal as described in U.S. Pat. No. 4,463,359 or U.S. Pat. No. 4,345,262 is suitable as said pulse-shaped driving signal. The adoption of the conditions described in U.S. Pat. No. 4,313,124 which discloses an invention relating to the temperature rise rate of said heat-acting surface would lead to the possibility of accomplishing more excellent recording.

As regards the construction of the recording head, besides the combination (straight liquid flow paths or right-angled liquid flow paths) of discharge ports, liquid paths and electro-thermal conversion members as disclosed in the above-mentioned patents, a construction using U.S. Pat. No. 4,558,333 or U.S. Pat. No. 4,459,600 which discloses a construction in which the heat-acting portion is disposed in a crooked area is also covered by the present invention.

In addition, a construction based on Japanese Laid-Open Patent Application No. 59-123670 which discloses a construction in which a slit common to a plurality of electro-thermal conversion members provides the discharge portion of the electro-thermal conversion members or Japanese Laid-Open Patent Application No. 59-138461 which discloses a construction in which an opening for absorbing the pressure wave of heat energy corresponds to a discharge portion is also effective for the present invention.

Further, the full line type recording head having a length corresponding to the width of the largest recording medium on which recording can be effected by a recording apparatus may be either of the construction as disclosed in the above-mentioned publications wherein the length of the head is satisfied by a combination of a plurality of recording heads and a construction as a unitarily formed single recording head, and the present invention can display the above-described effect more effectively.

In addition, the present invention is effective when use is made of an interchangeable chip type recording head which can be electrically connected to the apparatus body or can be supplied with ink from the apparatus body by being mounted on the apparatus body, or a cartridge type recording head having an ink tank integrally provided in itself.

Also, the addition of recovery means, preliminary auxiliary means, etc. to the recording head in the construction of the recording apparatus of the present invention is preferable in that it can more stabilize the effect of the present invention. More specifically, these include capping means for the recording head, cleaning means, pressing or suction means, an electro-thermal conversion member or a heating element or preheating means comprising a combination of these, and carrying out the preliminary discharge mode in which discharge discrete from that during recording is effected is also effective to accomplish stable recording.

Further, the recording mode of the recording apparatus is not limited to the recording mode for the main color such as black, but the recording head may be unitarily constructed or provided by a combination of a plurality of heads, and the present invention is also very effective for an apparatus provided with different colors or at least one of full colors by mixed colors.

In the above-described embodiment of the present invention, the ink has been described as liquid, but the ink may be ink which solidifies at room temperature or below and softens or is liquid at room temperature, or ink which assumes its liquid phase when the recording signal used is imparted, because it is usual with the above-described ink jet system that ink itself is temperature-controlled within the range of 30.degree. C. to 70.degree. C. so that the viscosity of the ink may be within a stable discharge range.

Furthermore, the recording apparatus according to the present invention may adopt the form of an apparatus provided integrally with or discretely from an information processing instrument such as a word processor or a computer as the image output end thereof, or a copying apparatus combined with a reader, or a facsimile apparatus having the signal transmitting and receiving functions.

As described above, according to the present invention, there is provided sheet conveying means which creates a stable pressure force irrespective of the thickness of a sheet material being conveyed.

Further, according to the present invention, there is provided an ink jet recording apparatus provided with sheet conveying means which can realize stable sheet conveyance by an appropriate pressure force against the presence of a portion to which an ink droplet does not yet adhere and the presence of the uneveness of the sheet material wet with ink.