Ink jet recording apparatus

Abstract: There is disclosed an ink jet recording apparatus capable of recovery operation of the ink jet recording head in secure manner. For this purpose the apparatus is provided with an endless belt (304) for transporting a recording sheet by electrostatic attraction; a charger for the endless belt; a cleaner for the endless belt; a recording head unit (305) with plural full-line ink jet heads; a recovery unit having a cleaning blade (88) and an ink absorbing member (3) movable between a recovery position and a stand-by position; and a mechanism for moving the head unit to a recording position, a recovery position or a recovery unit introducing position and moving the recovery unit in relation to the recording head unit; in which the head unit, recovery unit and moving mechanism are integrated as a detachable unit.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an ink jet recording apparatus Related Background Art Non-impact recording methods are recently attracting attention due to their advantage that the noise level at the recording operation is negligibly low. Among these methods, the ink jet recording is particularly promising because of the possibility of high speed recording and the capability of recording on ordinary paper without particular fixing treatment. The recording head employed in the ink jet recording apparatus is generally provided with a small liquid discharge port (orifice), a liquid path, an energy applying part formed in said liquid path, and energy generating means for generating energy for liquid droplet formation, to be applied to the liquid present in said energy applying part. For such energy generating means there are already known an electromechanical converting member, such as a piezoelectric element; an irradiation with an electromagnetic wave, such as a laser beam, which is absorbed in the liquid and generates heat therein for generating and discharging a liquid droplet; and an electrothermal converting element such as a heat-generating resistor for heating the liquid thereby discharging a liquid droplet. Among these, a recording head for causing liquid droplet discharge by thermal energy has various advantages as disclosed in the U.S. Patents Nos. 4,740,796 and 4,723,129. In contrast to the so-called serial scanning recording method in which the printing is conducted by reciprocating motion of the recording head on a stopped recording sheet, the U.S. Patent No. 4,692,778 discloses a fixed recording head consisting of an array of plural recording heads and enabling full-line printing. Said patent discloses various apparatus, may of which are already reduced to practice. A similar apparatus is shown in document US-A-4,748,459 However a full-line recording head obtained by combining plural recording heads is expensive, and a complex structure is required for the positioning of each head. Also the entire recording head becomes inevitably bulky if plural full-line recording heads are employed. The present inventors have made numerical designs of a full-line recording head consisting of a long single head for satisfying the requirements of compactization of the apparatus, stable image formation and high speed recording, but have been unable, in any design, to avoid the drawbacks related to the means for recovering the discharge function of the recording head. The present inventors have therefore reached a novel structure capable of preventing the drawbacks encountered mentioned above. SUMMARY OF THE INVENTION An object of the present invention is to provide an ink jet recording apparatus which can be compactized and which can provide improved reliability achieved by the reduction of structures affecting the precision, through said compactization. This object is achieved by an apparatus according to claim 1 or 3. An advantage of the present invention is to provide an ink jet recording apparatus in which a recording head unit and a recovery unit are integrated to achieve an improved precision of positioning with respect to the apparatus. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic cross-sectional view of an embodiment of the ink jet recording apparatus of the present invention; Figs. 2A and 2B are partial cross-sectional views of a head recovery system shown in Fig. 2; Figs. 3A and 3B are schematic views of a fixed part for recording head positioning; Figs. 4A and 4B are schematic views of a drive unit for the recording head; Figs. 5A, 5B and 5C are schematic views of a driving unit for the recovery system; Figs. 6A and 6B are schematic views of a driving unit for a cap for the recovery system; Figs. 7A and 7B are views of a squeezing unit for an ink absorbing member of the recovery system; Figs. 8A and 8B are views of a wiping unit for a discharge face of the recording head; Fig. 9 is a cross-sectional view of a capped state of the recording head shown in Fig. 2; Fig. 10 is a cross-sectional view of an idle discharge operation of the recording head shown in Fig. 2; Figs. 11A to 11D are views showing states of an ink pressure-circulating operation; Figs. 12A to 12F are views showing states of the recovery system shown in Fig. 9, from a stand-by state to a printing state; Fig. 13 is a detailed cross-sectional view of a belt conveyor unit shown in Fig. 1; Fig. 14 is a detailed cross-sectional view of a sheet fix/exhaust unit shown in Fig. 1; Fig. 15 is a flow chart showing a head control sequence; Fig. 16 is a schematic view showing the structure of a long recording head and ink supply means; Fig. 17 is a schematic view of an ink jet recording head applicable in the present invention; DESCRIPTION OF THE PREFERRED EMBODIMENTS Now the present invention will be clarified in detail by embodiments thereof shown in the attached drawings. Fig. 1 is a schematic cross-sectional view of an embodiment of the ink jet recording apparatus of the present invention. A scanner unit 301 reads an original document and converts it into an electrical signal, and a drive signal based on said signal is supplied to a recording head unit 305 of a printer unit 302. Recording sheets, constituting recording materials, or recording media, and stored in a sheet feed unit 303 are advanced, one by one when needed, to a belt conveyor unit 304. In passing said belt conveyor unit 304, the recording sheet is subjected to image recording by said recording head unit 305, and is then advanced to a tray 420 through a fix/exhaust unit 307. A recovery capping unit 306 serves to maintain said recording head unit 305 always in a recordable state. The detailed structure of these units will be explained in the following. At first reference is made to Fig. 16, for explaining the ink supply to a long full-line recording head employed in the present embodiment. Fig. 16 schematically shows the structure of said long recording head and ink supply means, wherein shown are a recording head 1601, a common liquid chamber 1652, and liquid discharge ports 1653 formed on a liquid discharge face 1654. The discharge ports 1653 of the present embodiment are arranged almost in accordance with the maximum recordable width of the recording material, and the recording liquid is discharged by selective drive of heat-generating elements provided in unrepresented liquid paths communicating with said discharge ports 1653, thereby achieving recording without scanning motion of the recording head itself. There are also shown a liquid supply tank 1655 for supplying the recording head 1601 with the recording liquid, and a main tank 1656 for replenishing the recording liquid in said supply tank 1655. The recording liquid is supplied from the supply tank 1655 through a supply tube 1657 to the common liquid chamber 1652 of the recording head 1601. In the replenishing of the recording liquid, it can be replenished into the supply tank 1655 from the main tank 1656, through a one-directional check valve 1658 and a recovery pump 1659. There are also provided a one-directional check valve 1960 used in the recovery operation of the discharge function of the recording head 1601, a circulating pipe 1661 containing said check valve 1660, a solenoid valve 1662 provided in said first supply pipe 1657, and an air discharge valve 1663 for the supply tank. In such recording head 1601 and associated supply and recovery systems, the solenoid valve 1602 is maintained open at the recording, whereby the recording liquid is supplied by gravity from the supply tank 1655 to the common liquid chamber 1652 and then to the discharge ports through unrepresented liquid paths. In the recovery operation for eliminating the bubbles remaining in the common liquid chamber or in the supply system and cooling the recording head 1601, the recovery pump 1659 is activated to feed the recording liquid through the circulating pipe 1661 to the common liquid chamber 1652 and to return the recording liquid therefrom to the supply tank 1655 through the first supply pipe 1657. Also at the initial filling of the liquid paths, the solenoid valve 1662 is closed and the pump 1659 is activated to pressurize the recording liquid to the common liquid chamber 1652 through the circulating pipe 1661, thereby discharging the recording liquid from the discharge ports 1653 together with the discharge of bubbles. Such recording head, in normal non-recording state, is left with the ink inside the discharge ports. Thus there is provided capping means with a cap member capable of fitting to or on a face of the recording head having the discharge ports and said cap is fitted on the recording head in the non-recording state, whereby the recording head is covered and tightly sealed from the surrounding atmosphere. In addition the space formed by the cap and the recording head is filled with the vapor of the ink to the saturated vapor pressure thereof, thereby preventing the ink evaporation in the liquid paths, and the increase in viscosity or drying of the ink in the liquid paths resulting therefrom. However, in a low humidity situation or in a prolonged pause between recording operations, the increase in ink viscosity may still occur even when the ink evaporation is prevented by the capping as explained above, so that failure or unstability in ink discharge may be encountered in the recording after a pause. In the present text, the term "first discharge problem" means failure of first ink discharge after a pause. For copying with said first discharge problem, there is also used the ink circulating/pressurizing means for circulating the ink under pressure by the recovery pump 1659 as explained above, thereby discharging the ink from all the discharge ports of the recording head. On the other hand, if said failure in discharge is slight, all the energy generating means of the recording head are activated to effect the ink discharge in the same manner as in the recording operation. Such ink discharge will be called "idle discharge" in the present text, in order to distinguish it from the ink discharge for image recording. As explained above, the recording head recovers the recordable state either by the pressurized circulation of ink in case the ink becomes viscous or is dried in the discharge port and/or liquid path after a prolonged non-recording state, or by an idle discharge operation if such ink drying is slight after a relatively short non-recording state. In the following there will be explained the recording material advantageously employed in the present embodiment. In the ink jet recording method, a liquid droplet of recording liquid, called ink, is emitted and deposited on a recording sheet such as paper. Therefore the ink should not ooze excessively on the sheet in order not to blurr the print. Also the recording material should preferably be capable of rapidly absorbing the ink deposited thereon, does not show oozing or leaking of ink even when inks of different colors are deposited in a same place within a short time, and suppressing the spreading of the print dot to the extent not deteriorating the sharpness of image. These requirements are often not sufficiently satisfied by the copying paper ordinarily employed in the electrophotographic copying machines or by other usual recording papers. These sheets can often provide satisfactory image quality in the printing of a single color or two superposed colors, but cannot frequently provide satisfactory image quality when the amount of ink deposited on the sheet increases, as in the printing of a full-color image recording with three or more colors. In the ink jet recording apparatus of the present embodiment, there is preferably employed, as the sheet satisfying the above-mentioned requirements, a recording material composed of a base paper having a coating satisfying said requirements, for example fine powder of silica, as disclosed in the Japanese Laid-Open Patent Sho 56-148583. The ink is deposited on the coated face of the recording material. Consequently, in the present embodiment, there is selectively used such coated paper in case of image recording with inks of three or more colors for achieving higher image quality, or a non-coated paper in case of image recording with one or two colors. However it is naturally possible to record an image of one or two colors on such coated paper. In the scanner unit 301, there are shown an original document 401, and an original scanning unit 402, which incorporates a rod lens array 403, a same-size color separating line sensor (color image sensor) 404, and exposure means 405. At least while the original scanning unit 402 is moved in a direction A for reading the image of the original 401 placed on an original support plate, an exposure lamp in the exposure means 405 of the scanning unit 402 is turned on, and the reflected light from the original 401 is guided through the rod lens array 403 and is focused on the line sensor 404 (hereinafter called image sensor) for reading the color image information of the original in respective colors and converting said information into digital signals. Said digital signals are transmitted to the printer unit 302, and the recording head of each color effects liquid discharge by receiving drive signals based on said digital signals. Figs. 2A and 2B are partial cross-sectional views of the printer unit of an ink jet recording apparatus of the present invention. In the following there will be explained the state of the recording head in the recovery operation, with reference to Fig. 2A. Ink jet recording heads 1C, 1M, 1Y, 1Bk respectively receiving inks of cyan, magenta, yellow and black are precisely fixed in a head block 6, with a level of parallelism and a mutual distance with a desired precision. In the vicinity of discharge ports of said heads 1C, 1M, 1Y, 1Bk there are provided ink absorbing members 3C, 3M, 3Y, 3Bk, corresponding to the discharge ports of said recording heads. Said ink absorbing members 3C, 3M, 3Y, 3Bk are supported by a guide 7 so as to be engageable with and detachable from the discharge face of said recording heads. In Fig. 2A, the ink absorbing members 3C, 3Y are shown in a separate state from the discharge face of the recording heads 1C, 1Y, while the absorbing members 3M, 3Bk are shown in-contact with the discharge face of the recording heads 1M, 1Bk. Between the neighboring ink absorbing members there is provided an ink partition 8. Between each partition 8 and the head block 6 there is provided an ink seal 4 for separating inks of different colors. In the vicinity of each ink absorbing member, there is provided an ink squeezing member 5 for squeezing each of the ink absorbing member 5 for squeezing each of the ink absorbing members 3C, 3M, 3Y, 3Bk to remove the ink absorbed therein, by means of an unrepresented lever. Fig. 2A shows a state that the ink absorbing member 3Y of the yellow recording head 1Y is squeezed. The head block 6 on which the recording heads 1C, 1M, 1Y, 1Bk are fixed is detachably inserted into a block stay 9 by means of a rail 15. Said block stay is rotatable, together with the head block 6 and the recording heads of different colors, about a shaft N. A recovery reservoir 2 is rendered movable, by means of an unrepresented moving mechanism, from a state of recovery operation shown in Fig. 2A, to a retracted position shown by double-dotted chain line position. The recovery reservoir 2 is provided at the bottom thereof with an ink exhaust opening, whereby the inks discharged from the recording heads 1C, 1M, 1Y, 1Bk, then absorbed by the ink absorbing members, 3C, 3M, 3Y, 3Bk and recovered therefrom is guided to an unrepresented used ink tank, through an unrepresented ink hose. Fig. 2B is a partial cross-sectional view showing the recording heads in the image recording state. After the recovery reservoir 2 is moved from the state in Fig. 2A to the retracted position shown by chain lines, the recording heads rotate to a horizontal position as shown in Fig. 2B. In this state the ink is discharged, in response to the image recording signal, from the recording heads, thereby forming an image on a recording sheet transported at a desired distance from the discharge face P of the recording heads. The recording head most suitable for the present invention employs an electrothermal converting element as the energy generating means, prepared by semiconductor manufacturing process. Corresponding to each discharge port (orifice) there is provided a liquid path, and said electrothermal converting element is provided in each liquid path for applying thermal energy to the liquid in said liquid path thereby discharging said liquid from the corresponding discharge port and forming a flying droplet. The liquid is supplied to the liquid paths from a common liquid chamber. Fig. 17 schematically shows the structure of said ink jet recording head adapted for use in the present invention, prepared through semiconductor manufacturing steps such as etching, evaporation and sputtering and comprising a substrate 1102, electrothermal converting elements 1103 formed thereon, electrodes 1104, liquid path walls 1105, and a cover plate 1106. The recording liquid 1112 is supplied, from an unrepresented liquid reservoir to a common liquid chamber 1108 of the recording head 1101 through a liquid supply pipe 1107. A connector 1109 is provided for the liquid supply pipe. The liquid 1112 supplied into the common liquid chamber 1108 is supplied by capilary phenomenon into the liquid paths 1110 and is stably maintained therein by forming a meniscus at the plane of discharge port at the end of the liquid path. By energization of the electrothermal converting element 1103, the liquid present thereon is rapidly heated to generate a bubble, and the liquid is discharge, forming a droplet, from the discharge port 1111 by the expan and contraction of said bubble. By forming the above-explained structure with a high density such as 16 nozzles/mm, there can be obtained a multi-nozzle ink jet recording head with 128 or 256 nozzles, or with a width corresponding to the entire recording width. Figs. 3A and 3B illustrate the recording heads and a positioning mechanism therefor, respectively in a schematic plan view and a schematic lateral view. Referring to Fig. 3A, engaging portions 1a at both ends of the head 1 are inserted into recesses of head fixing members 20, 21 whereby the head is fixed in directions A and B in Fig. 3A. Also the position in the vertical direction C in Fig. 3B is determined by positioning shafts 18, 19. Pressing pins 22 press the heads, inserted into the fixing members 20, 21 toward engaging portions 20a, 21a by means of springs 23, thereby defining the positions of said heads. An adjust screw 24 is used for adjusting the position of each head in a direction A, namely in a direction perpendicular to the direction of sheet advancement (hereinafter called "left margin"). Eccentric pins 25 are provided for adjusting the inclination of the heads. Rotation of each eccentric pin 25 shown in Fig. 3A displaces the engaging portion 1a of each head 1, thereby moving said head in the direction B. The above-explained adjusting mechanism allows easy adjustment of the mounting position of each head. It is therefore possible to obtain an image of high quality, by correcting the aberration among images of different colors. Now reference is made to Figs. 4A and 4B for explaining the head moving mechanism. The rotation of a head unit drive motor 26 is transmitted through a gear 27 to a head frame 28, which is rotatable, as indicated by an arrow, about a rotation shaft ℓ . As will be understood from Fig. 1, the recording sheet is transported on a conveyor belt from upper left in Fig. 5. Since the gap between the recording heads and the conveyor belt is as small as 0.3 to 2.0 mm, sheet jamming tends to occur relatively frequently in said pag. For this reason, the rotating center of the above-explained head moving mechanism is positioned at the downstream side of the transporting direction of the recording sheet. Thus, when the heads are moved by rotation, the discharge ports are present at the left side of the drawing, or at the upstream side. Consequently, even if a sheet jamming occurs in this part, there can be prevented the damage on the discharge face of the head or ink dragging thereon by the jammed sheet. Also in the ink jet recording apparatus, a fixing unit is usually provided at the downstream side of the heads. Therefore, the discharge ports positioned at the upstream side of the present embodiment minimizes the influence of hot air or high temperature generated by said fixing unit, thereby enabling to protect the discharge face of the recording heads and prevent drying or failed discharge of the ink. The head frame 28 is provided with a rail 29 whereby the head block 6 on which the heads 1 are mounted can be integrally removed and replaced. The removal or insertion of the head block 6 is conducted in a state where the head frame 28 matches a cut-off portion (not shown) formed in a front plate. The head from 28 can be stopped at (i) a recovery position, (ii) print position, (iii) a retracted position, or (iv) a head unit replacement position. Figs. 4A and 4B show the (i) recovery position. The retracted position (ii) corresponds to the retracted position of the recording head 305 shown in Figs. 12A and 12B for moving the recovery reservoir 2. The print position (ii) corresponds to a head down position shown in Fig. 12D. In the present embodiment, said retracted position (iii) is same as the head unit replacement position (iv). These positions can be detected exactly by a light shield plate 52 provided on the head frame 28, serving to cover detecting areas of sensors 51 provided corresponding to said stop positions. Fig. 4B shows a structure employing a worm reducer for moving the head moving mechanism. There are provided a worm gear 59 and a worm wheel 60. Because of the characteristics of such worm reducer, the head frame 28 can only be moved by the motor, whereby it can be prevented from spontaneous falling due to the weight of plural heads mounted on the head frame and can be maintained fixed when the motor is deactivated. Figs. 5A and 5B are partial lateral views of a drive mechanism for the head recovery unit, seen from the same side as in Figs. 4A and 4B. Fig. 5C is a partial magnified view, seen from the rear side, of a left-hand portion of the drive mechanism shown in Fig. 5A. The rotation of a recovery unit drive motor 30 is transmitted, through gears 31 - 36, to a driving screw 37, which converts the power of the motor 30 into a linear movement of a screw nut 38, thereby moving the recovery reservoir 2 from the recovery (capping) position to the retracted position. A nut holder 39 engaging with the screw nut 38 is linked by a link pin with the recovery reservoir 2 thereby enabling the reciprocating movement thereof by the rotation of the motor 30. On the front and rear faces of the recovery reservoir 2, there are respectively provided two arms 41, 42 (those on the rear side not shown) in rotatable manner. On the arm 42 there is rotatably supported a roller 45, and a roller 45a is provided on a lateral plate 47 of the unit opposite to the arm 42 of the recovery reservoir 2. Rollers similar to 45, 45a are provided also on the arm 41. Rails 48, 49 with grooves for engaging with the recovery reservoir 2 at the reciprocating motion thereof are provided on both sides thereof. Torsion coil springs 44 are provided on the arms 41, 42 so as to bias the rollers toward the grooves of said rails. The rotation of the motor 30 is transmitted, through the gears 31 - 36, screw 37, nut 38, nut holder 39 and link pin 40, to the arms 41, 42 and is converted into the reciprocating motion of the recovery reservoir 2. Said motion is achieved along said grooves without play, because the rollers 45, 45a rotatably supported on the arms 41, 42 are biased by the torsion coil springs 44 toward said grooves of the rails 48, 49. Consequently the reservoir 2 can be moved along a desired trajectory formed by the rails 48, 49. Presence of plural rollers in an arm disperses the load of the reservoir 2, thereby enabling smooth movement thereof. Also presence of arms and rollers on both sides of the reservoir 2 achieves smooth transmission of the driving force by a single screw for moving the reservoir 2. The recovery reservoir 2 is stopped either at the recovery position 2a or at the retracted position 2b, which are precisely defined by the engagement of a light shield plate 50, mounted on the nut holder 39, with the detecting portion of a sensor (photointerruptor) provided at each stopping position. In the following there will be explained the recovery mechanism for capping, idle discharge and ink pressurized circulation, with reference to Figs. 6A and 6B showing the cap driving unit of the recovery unit of the present invention, respectively in a state where the absorbing member is separated from or attached to the discharge face of the recording head. The rotation of a cap driving motor 60 is transmitted through gears 61 - 64 to a rack 65, and, further through members 66, 67, to a cap driving slide arm 68 slidable along slide pins 72. The reciprocating motion of said slide arm 68 is converted, by arms 69, into a vertical movement of the absorbing member guide 7. Each ink absorbing member guided by said guide 7 is pinched by a stopper and is rendered vertically movable by the engagement of slide pins 71 with guide grooves 73a formed in a lateral plate 73. Thus the rotation of the motor 60 is transmitted for contacting or separating motion of the ink absorbing members 3 to or from the discharge face of the heads 1. Said contacted or separated positions are detected by microswitches 80, 81 mounted on the reservoir 2, engaging with a detection member 65a mounted on the rack 65. In the following there will be explained a preferred embodiment of the squeezing mechanism for the ink absorbing members of the recovery unit of the present invention, with reference to Figs. 7A and 7B, respectively showing a stand-by state and a squeezing state. In the present embodiment, the aforementioned cap driving motor 60 is used as a squeezing motor. The capping mechanism and the squeezing mechanism are selectively driven by a solenoid clutch (not shown). The rotation transmitted by said clutch is transmitted, through gears 75 - 78, to a squeezing cam 79, generating a reciprocating motion of a slide arm 82. The movement of said slide arm 82, rendered linearly movable by means of slide pins 83 provided on the lateral plate, is transmitted through levers 84 to squeezing members 5 for the ink absorbing members, thereby pressing said absorbing members toward the guides 7 and removing the ink absorbed therein (Fig. 7B). The squeezing members for different colors are mutually linked by a link bar 86 to enable simultaneous squeezing motion for all the colors. In the present embodiment, the squeezing mechanism is activated when the ink absorbing members 3 are separated from the discharge faces of the recording heads, and the position of the squeezing mechanism is detected by a microswitch 87 engaging with and detecting the rotation of the cam 79. Ordinarily, a unit operation of squeezing consists of a revolution of the cam. The ink absorbing members 3 of which absorbing power is refreshed by said squeezing operation are again brought into discharge face of the heads, thereby achieving complete cleaning. In the following there will be explained a wiping mechanism for the discharge faces of the recording heads, with reference to Figs. 8A and 8B respectively showing a stand-by state and a driven state of said mechanism. In the present embodiment, there are employed cleaning blades 88 for wiping the discharge faces of the recording heads. The aforementioned squeezing-motor 60 is used for driving said blades, and the wiping mechanism is not switched alone since the wiping operation is linked in sequence with the squeezing operation. The rotation of the motor 60 transmitted to the cam 79 through the gears 75 - 78 as explained above is transmitted to a blade driving slide arm 90. The movement of said arm 90, which is linearly movable by a slide pin 91 fixed on the lateral plate, is further transmitted to blade rotating arms 92, thereby rotating blades 88 mounted on blade support members 93, about shafts 94. Said shafts are naturally so positioned as to efficiently wipe off the dusts and ink deposited or adhered on the discharge faces of the recording heads. In the present embodiment, as explained above, the wiping mechanism is driven by the source for the squeezing mechanism, and is so constructed as to drive the blades in a state where the ink absorbing members are separated from the discharge faces of the recording heads. The blade driving is also detected, as in the squeezing operation, by the microswitch 87 engaging with the cam 79. Thus the squeezing of the ink absorbing members and the driving with blades are simultaneously conducted by the motor 60 while the ink absorbing members 3 are separated from the discharge faces of the recording heads. In the following there will be given a more detailed explanation on the recovery operation by the recovery system. For the purpose of clarity, the recovery operation will be divided into (A) capping, (B) idle discharge and (C) ink disposal, in the following description. At first there will be explained the capping operation (A) with reference to Fig. 9 showing the capped state of the recording head. The recording heads 1C, 1M, 1Y, 1Bk arranged in parallel manner in the head block 6 engage with the recovery capping unit 306. The recovery reservoir 2 is provided with the ink seals 4, partitions 8, and ink absorbing members 3C, 3M, 3Y, 3Bk which are normally spaced by a predetermined gap from the discharge faces of the heads, whereby the vicinity of the discharge ports of said recording heads is surrounded by the ink seals 4, partitions 8 and ink absorbing members 3C, 3M, 3Y, 3Bk to maintain suitable moisture and to prevent the discharge ports from drying. As explained above, the capping prevents the generation of failed ink discharge during the pause between the recording operations or during the stand-by state, and protects the discharge ports from the adhesion or deposition of dusts to the vicinity of the discharge ports. In the following there will be explained the idle discharge operation (B) with reference to Fig. 10. The ink absorbing members 3C, 3M, 3Y, 3Bk are maintained at the predetermined gap from the discharge faces of the recording heads as in the capping operation explained above, and the energy generating means of all the recording heads 1C, 1M, 1Y, 1Bk are given an arbitrary number of ink discharge pulses. In this manner it is rendered possible to prevent failed discharge from the drying of ink, or defective discharge resulting from viscosified ink in all the discharge ports and deterioration in the printed image. The idle discharge is usually conducted when a copying instruction is given. In the following there will be explained the ink exhaust operation with reference to Figs. 11A to 11D, showing the function of the capping unit 306 in the pressurized ink circulation in the ink supply system for ink exhausting. The function of the capping unit 306 consists of four cycles, namely a normal capping (Fig. 11A), a pressurized ink circulation (Fig. 11B), squeezing of ink absorbing members and wiping (Fig. 11C), and engagement of ink absorbing members (Fig. 11D). Said capping cycle is same as the aforementioned capping (A) in the normal stand-by or pause state. If the pressurized ink circulation mode is selected in this state by a command from the host computer or an instruction from the operator, there is assumed a state shown in Fig. 11B, in which the ink absorbing members 3C, 3M, 3Y, 3Bk maintained at a certain gap from the recording heads are brought into contact therewith. In this state, unrepresented ink supply pumps of the recording heads 1C, 1M, 1Y, 1Bk are activated to elevate the ink supply pressure forcedly. Thus the ink circulates in the ink supply system through the recording head to eliminate the bubbles therefrom, and to discharge the pressurized ink from the discharge ports. The dusts adhered to the discharge face are eliminated together with the discharged ink, whereby the vicinity of the discharge ports is cleaned. The ink discharged from the discharge ports is absorbed, without leaking, by the ink absorbing member 3 maintained in contact with the discharge face, and the ink exceeding the maximum capacity of said member drops by gravity into the recovery reservoir 2 through said absorbing member, and is guided to the used ink tank (not shown) through the ink exhaust outlet 13 and the used ink hose 12. The period of such pressurized circulation, or of the energizing time of the supply pump, is preferably in the order of 0.5 to several seconds in consideration of the efficiency of elimination of solidified ink or of bubbles. Now there will be explained the squeezing of the absorbing member and the wiping shown in Fig. 11C. After the pressurized circulation shown in Fig. 11B, the ink absorbing member 3 is again separated from the discharge face of the recording head, and, in this state, the ink absorbing member in almost saturated state is squeezed with the squeezing member 5. The squeezed ink drops by gravity into the recovery reservoir 2 through the guide 7 and the partitions 8, and is guided to the used ink tank through the ink exhaust outlet 13 and the used ink hose 12. Simultaneous with the separation of the ink absorbing member 3 from the discharge face of the recording head and the squeezing of said member, the wiping blade 88 is activated to wipe off the ink, dusts and other deposited substances remaining on said discharge face. The wiped ink etc. drops onto the ink absorbing member 3, and, due to the simultaneous squeezing operation, further drops into the recovery reservoir 2 and into the used ink tank together with the squeezed ink. Thus, simultaneous with the separation of the ink absorbing member 3 from the discharge face, the substances remaining on said face are removed by the blade 88 and are eliminated together with the excessive ink squeezed from the ink absorbing member. These squeezing and wiping operations are illustrated in Fig. 11C. By the squeezing with the squeezing member 5, the ink absorbing member 3 recovers the absorbing ability for the next absorbing operation. The absorbing member 3 is advantageously composed for example of sponge of PVF resin of a high absorbing ability, preferably capable of withstanding repeated use. In the present embodiment there is employed, for example, a material known under a trade name Bel-Ita supplied by Kanebo. After said squeezing of ink, the absorbing member is again brought into contact with the discharge face of the head, as shown in Fig. 11D. This cycle intends to completely clean the discharge face, by absorbing the ink, left in the cycle (B) due to the almost saturated state of the absorbing member, by the absorbing member of which absorbing ability is refreshed by squeezing. After the cycles shown in Figs. 11A to 11D, the capped stand-by state shown in Fig. 11A is again assumed to maintain the cleaned head in satisfactory condition. Such pressurized circulating operation is usually conducted at the start of power supply in the apparatus or after a prolonged pause. The above-explained capping, idle discharge and pressurized ink circulation serve to prevent the deterioration of the recorded image resulting from defective ink discharge at the image formation. In the following there will be explained the printing operation. Figs. 12A to 12F illustrate states in transition from the aforementioned stand-by state of the recovery system to the printing operation. Fig. 12A shows the above-explained capped state corresponding to the ordinary stand-by or pause state. If the print (copy) mode is selected in this state, there is at first effected the idle discharge explained above. Then assumed is a head-up state shown in Fig. 12B, in which the recording head unit 305 is retracted upwards. In this state the recovery reservoir 2, or the capping unit 306, is retracted to upper right to reach a unit open state shown in Fig. 12C. Then there is effected a head-down operation shown in Fig. 12D, whereby the recording head is brought to a position capable of recording, and the recovery reservoir 2 is placed in the retracted position. In this state the recording sheet is introduced from right with a predetermined gap from the discharge faces of the recording heads while the image signals are introduced to the recording heads 1C, 1M, 1Y, 1Bk to discharge inks therefrom, thus forming a print on the recording sheet. After the printing by ink discharge, there is again conducted the head-up operation as shown in Fig. 12F, from which the recovery reservoir 2 moves toward the head to restore the capped stand-by state shown in Fig. 12A, for the next printing operation. The normal copying operation is conducted by the steps shown in Figs. 12A to 12F. The above-explained ink circulating operation can be conducted at a predetermined timing in the capped stand-by state shown in Fig. 12A, for example at the start of power supply of after the lapse of a predetermined time, and it is possible in this manner to obtain a satisfactory image without sacrificing the through-put. Fig. 13 schematically illustrates conveyor means (belt conveyor) for the recording material (paper). The recording paper P advanced by registration rollers (415, 416 in Fig. 1) reaches a conveyor belt 101 along guide plates 417, 418. Said conveyor belt is composed of two layers; an insulating layer (with preferable volume resistivity at least equal to 10¹² Ω·cm) at a side in contact with the recording sheet, and a conductive layer (with preferable volume resistivity not exceeding 10⁸ Ω·cm) at the opposite side. Said conveyor belt 101 is mounted around a driving roller 102, an idler roller 102 and tension rollers 104, 105 with a tension of 2 - 5 kg, for example, and is driven in a direction AA, by a motor (not shown) connected to the driving roller 102. The recording sheet P is placed on the conveyor belt 101, at a position immediately in front of a conductive roller 107. The surface of the conveyor belt 101 is given a potential of several hundred volts to several thousand volts by a charger 106. Upon reaching the grounded conductive roller 107, the recording sheet P is maintained in close contact with the conveyor belt 101 by electrostatic attractive force, whereby the sheet P is moved together with the conveyor belt 101. In this state the recording sheet P reaches a recording area opposed to the recording head unit 305, containing the head block 6 and the recording heads 1C, 1M, 1Y, 1Bk, opposed to which there is provided a platen 115 across the conveyor belt 115. The platen 115 is provided with a pin 116, and is pressed against the recording head unit 305 by means of springs 117 and guide pins 118. For obtaining a recorded image of high quality, the distance between the recording heads 1C, 1M, 1Y, 1Bk and the recording face of the sheet P in the recording area is maintained at the predetermined value, preferably with a precision of about 100 µm. For this purpose, in order that the conveyor belt 101 is substantially flat in the recording area, the platen 115 has a flatness in the order of several ten microns in a face thereof in contact with said conveyor belt 101. Also the recording heads 1C, 1M, 1Y, 1Bk are so positioned in the head block 6 that the plane formed by the discharge planes of said heads have a flatness not exceeding several ten microns. The platen 115 is provided with a positioning pin 116 so that a gap ℓ for passing the recording sheet is formed by the engagement of the upper end of said pin 116 with the head block 6, when the platen 115 is lifted by the springs 117 toward the head block 6 along the guide pins 118. When the recording sheet is transported in such structure, while it is maintained in close contact with the conveyor belt 101 by electrostatic attractive force, the distance between the recording face of said sheet and the discharge planes of the recording heads can be maintained within a desired precision with respect to the predetermined value. In passing said recording area, the recording sheet is subjected to image recordings in succession by the recording heads 1C, 1M, 1Y, 1Bk. If the velocity of the conveyor belt 101 involves significant fluctuation, the recording positions of the recording heads are mutually aberrated thus resulting in aberrations or unevenness in the colors of the image. In order to prevent such defects, the thickness of the conveyor belt 101, diameter of the driving roller 102 and revolving speed of the driving motor are controlled within predetermined precision to maintain the fluctuation of the velocity of the conveyor belt at a practically negligible level. After image recording in the recording area, the recording sheet reaches the position of the driving roller 102 in contact with the conveyor belt 101, then separated therefrom by the curvature of said belt formed by the driving roller 102, and is advanced to the fixing unit. Subsequently the surface of the conveyor belt 101 is cleaned with a cleaner 120 provided with an ink absorbing member 119, which is composed for example of a continuous pore foam of polyvinyl formal resin, and the absorbed ink flows out from an aperture 120 and is recovered. In the present embodiment, the conveyor belt 101 has a two-layered structure composed of an insulating layer and a conductive layer, but it is also possible to constitute the conveyor belt 101 with a single insulating layer of a desired volume resistivity, or to adopt a multi-layered structure in the insulating layer and/or conductive layer. In the following the structure of the fixing unit will be explained in detail. In the ink jet recording, the ink is deposited on the recording material, and is fixed by penetration therein, or by evaporation of the solvent of said ink. However the fixing speed, or the time from the deposition of ink to the fixing thereof, varies significantly not only by the structure and physical properties of the recording material but also by the condition of surrounding atmosphere. Also the spontaneous fixing speed cannot be shortened beyond a certain limit determined by the physical properties. In the conventional serial scanning recording apparatus, the image fixing could be achieved with a relatively simple structure in consideration of the recording speed. However in the high speed recording in a line printer or the like or in the color image recording in recent years, the recording material may be brought out from the apparatus while the ink is not completely fixed. Therefore required is fixing means, as shown in Fig. 14, for effecting the image fixation more efficiently and reducing the time required therefor. In Fig. 14, a heating member 200 and another heating member 201 respectively heat the unrecorded face and the ink bearing face of the recording material 210. Said heating member can be composed of various devices such as a halogen lamp, a sheath heater or a thermistor. In the present embodiment, the heating member 200 is composed of several thermistors capable of temperature control, which are attached to the rear face of a heat-conductive support member 202 for heating the unrecorded face of the recording material by direct contact. The heating member 201 is composed of a halogen heater, and a hot air is sent by a fan 203 positioned above said heater 201 to heat the ink bearing face of the recording material 210 in non-contact state. Even when the recording material 210 is lifted from the support member 202 due to curling specific to the ink jet recording generated by the ink deposition, the recording material can be advanced securely along said support member 202 by the downward blow of the hot air from the fan 203. Consequently the both faces of the recording material 210 are sufficiently dried to accelerate the ink penetration, and the fixing time is significantly reduced by the multiplying effect. The fixing temperature is selected by a thermostat 204 controlling the temperature of said thermistor and heater, and can be suitably controlled according to the quality of the recording material. Also in order to prevent the undesirable effect of heat on the ink in the recording heads or in the supply system, there is provided a partition plate 205 having surfacial heat insulation composed for example of glass fibers and the heater holder 206 is composed of heat-resistant resin such as polyphenylene oxide (PPO), thereby avoiding unnecessary transmission of heat. Also provided is an exhaust fan 207 for discharging unnecessary heat. A heater cover 208, composed for example of a metal grating, is provided for the safety in case of jamming of the recording material. In the above-explained structure, the recording material 210 is doubly fixed by direct heating on the non-recorded face and by hot air heating on the ink bearing face, thereby preventing the failure in image fixation in the ink jet recording, particularly resulting from ondulation of the recording material, encountered in case repeated ink deposition for example for color image jet recording.

Claims: An ink jet recording apparatus comprising an endless belt for transporting a recording material (210) by electrostatic attraction; a charger for charging said endless belt; cleaning means for cleaning said endless belt; a recording head unit (305) containing a plurality of full-line recording heads (305) for discharging ink by forming bubbles therein by thermal energy; a recovery unit (1659; 3C, 3M, 3Y, 3BK) containing a cleaning blade member, an ink absorbing member and a linking mechanism therefor for each of said recording heads (1601; 1C, 1M, 1Y, 1BK; 1101), and being movable between a recovery position and a stand-by position with respect to said recording head unit (305); a moving mechanism (26-28) for moving said recording head unit (305) in a recording position opposed to said endless belt, a recovery position separate from said recording position, or a recovery unit (1659; 3C, 3M, 3Y, 3BK) introducing position separate from said recovery position, and for moving said recovery unit (1659; 3C, 3M, 3Y, 3BK) in relation to the movement of said recording head unit (305), wherein said recording head unit (305), recovery unit (1659; 3C, 3M, 3Y, 3BK) and moving mechanism (26-28) are integrally held and arranged as a unit removably attached to the apparatus body. An apparatus according to claim 1, wherein said recording head unit (305) is rendered rotatable about a center of rotation and the aperture of said rotatable part is directed toward the upstream side in the transporting direction of the recording medium. An ink jet recording apparatus for forming a record by discharging ink from a discharge port toward a face of a recording material (210), comprising a case integrally supporting an ink jet head, ink jet head support means, ink jet head moving means, an ink jet head recovery unit (1659; 3C, 3M, 3Y, 3BK) and drive means for said recovery unit, wherein these elements are integrally held and arranged in said integral casing which is detachable from the present apparatus. An apparatus according to claim 3, wherein said ink jet head and said head recovery unit (1659; 3C, 3M, 3Y, 3BK) are capable of mutual displacement and respectively have a recovery position, a retracted position and a printing position. An apparatus according to claim 3, wherein said ink jet head moving means is rotatable about a center of rotation, and is stoppable at a recovery position, a retracted position or a printing position. An apparatus according to claim 1 or 3, wherein the recording head (1601; 1C, 1M, 1Y, 1BK; 1101) is an elongate head having discharge ports arranged along and having the same width as the recording medium. An apparatus according to claim 1, further comprising cleaning means in contact with the endless belt to clean a surface of the conveying means, wherein the recording head (1601; 1C, 1M, 1Y, 1BK; 1101) discharges ink onto the surface of the endless belt. An apparatus according to claim 3, further comprising conveying means for conveying a recording medium on which an image is recorded and cleaning means for cleaning a surface of the conveying means, wherein the recording head (1601; 1C, 1M, 1Y, 1BK; 1101) discharges ink onto the surface of the conveying means.

Inventors: AOKI TOMOHIRO, MITOMI TATSUO, MURAYAMA YASUSHI, NEMURA MASAHARU, UCHIDA TAKASHI, AOKI, TOMOHIRO, MITOMI, TATSUO, MURAYAMA, YASUSHI, NEMURA, MASAHARU, UCHIDA, TAKASHI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1989
Main classification: B41J2
IPC codes: B41J2, B41J29, B41J11