Device for recovering the operation of nozzles of ink-jet printing devices

Abstract: The device comprises a manually-operated device (7) for generating vacuum cycles, connectible to the various outlets (3) of the ink-injection nozzles by means of flexible pipes (6, 26) kept permanently closed by means of manual gripping devices which are released individually in order to transmit a vacuum cycle to the nozzle in which a restoration cycle is to be carried out by suction. The vacuum-cycle generator is constituted by a resilient bellows (7) which can receive a manual compression opposed by a spring (8), and which is connected to a distributor (19) from which the flexible pipes extend towards each nozzle outlet (3). Application is for recovering the operation of blocked nozzles in ink-jet printing devices.

Description: The present invention relates to a new device for recovering the operation of the printheads of devices for ink-jet injection printing. Ink-jet injection devices have printheads through which droplets of ink are projected at high speed forming the so-called "ink jets" which are intended to fall on the printing substrate, normally paper, in order to effect the expected trace. One of the problems of the said ink-jet printing devices consists of loss of functionality of the printheads, particularly owing to blockage thereof which usually takes place as a result of partial drying of the residual ink in the printheads. In order to mitigate the said effect, many known ink-jet printing devices have systems for hermetically sealing the printheads once they have stopped working, which decreases the chance of evaporation of the ink and the formation of sediments which give rise to blockage. However, in spite of these measures, in many cases, blockages of some printheads appear, preventing correct operation thereof. This phenomenon may occur mainly in multi-coloured ink-jet printing devices and, in particular, for the colours which are used less frequently. In order to restore the operation of the obstructed printheads, devices of various types have been devised, which usually involve a rotary vacuum pump which produces a sub-pressure in a chamber which is put into communication at the desired moment with the printhead with defective operation, whereby the fall in pressure brought about at the outlet of the printhead forces the ink to come out, consequently eliminating the blockage, resulting in the recovery of the operation of the printhead. EP 0 622 200 assigned to the applicants of the present application refers to a thermal ink-jet printer which has a manually actuated vacuum source for conveying priming vacuum to the cap for sealing the nozzle array of the printhead, such that the printhead cartridge is primed without removal thereof from the cartridge. However, said document does not disclose means for keeping various communication pipes closed for normal operation and permitting optional opening thereof for recovery cycles. EP 0 622 201 assigned to the same applicant of the present patent application refers to a priming apparatus for thermal ink-jet printhead cartridges, having a plurality of vacuum conveying elements associated with the caps for the printheads. However, said document does not disclose that the communication pipes are closed for normal operation, opening the same at the moment when it is necessary for the recovery cycle by means of gripping devices which may be individually released. The main disadvantage of the currently-known devices for recovering printheads consists of their mechanical complexity, their weight and their high cost which constitutes a disadvantage in the development of cheap devices for multi-coloured ink-jet printing. The object of the present invention is to provide a device which has appreciable features of novelty and inventive step, enabling the operation of the printheads for the injection of ink to be recovered effectively and at the same time by simple and cheap means. To achieve its object, the present invention comprises a device for recovering the operation of printheads according to claim 1. The mechanical device for generating a vacuum comprises a resilient bellows element which tends to remain in a slackened position owing to the action of a return spring and which can be compressed by the operation of a manual control which, for greater convenience, is provided with a simple push-button and an intermediate rocker arm which acts on the bellows and compresses it. The automatic release of the compression of the bellows will cause rapid expansion of the spring and therefore a suction effect in the pipe connected to the printhead to be restored. The various pipes can preferably be closed by a key system with individual mechanisms for gripping and closing the various pipes and for interlocking the various controls in its normal position which corresponds to the closure of the flexible pipes. The device is so generally arranged that the level of underpressure transmitted to the pen is independent of the manual handling of the device by the user, given the fact that the rapid expansion of the spring and the stroke of the member which creates the underpressure do not directly receive the action from the user who activates the pusher. The present invention also extends to the method of recovering the operation of the printheads of an ink-jet printing device according to claim 10. For a better understanding of the present invention, some drawings illustrating a preferred embodiment of the subject thereof are appended. Figure 1 is a cross-section showing schematically the subject of the present invention, as a whole. Figures 2, 3, 4, 5 and 6 are respective cross-sections taken in the section planes indicated in Figure 1, showing details of the mechanisms which form parts of the present invention. Figure 7 is a longitudinal cross-section of the push-button device for operating the manually operated means for generating vacuum cycles. Figure 8 is an elevational view corresponding to the push-button of Figure 7. Figures 9, 10, 11, 12, 13 and 14 are respective cross-section details in the section planes indicated, which show the support for the closure of the printheads in the rest position as well as the manner in which it is set and released. Figures 1, 2 and 3 show the main mechanisms of the device of the present invention. The said figures show the movable unit 1 which is intended to close the various printheads of the ink-jet printing device which comprises ink cartridges, indicated 2 and shown in broken outline, for each of the colours required. The movable closure device 1 blocks the outlet 3 of the cartridge and therefore the corresponding printhead, by means of its base plate 76, in the rest position of the head of the ink-jet printing device, generally indicated 4, the guide for the longitudinal displacement of which is indicated 5. The detailed construction of the movable closure unit 1 will be described below. Each of the outlets 3 is connected, by means of a bout or nipple formed in the plate 76, to a flexible pipe 6 which communicates with the manually-operated means 7 for generating vacuum cycles in a manner such that each cycle for the recovery of a printhead will involve the operation of the means 7 and its communication with the obstructed printhead through the corresponding duct 6. Naturally, the device will have as many pipes 6 as the ink-jet printing device has injection printheads, which is normally four for colour printing. In the preferred embodiment of the present invention, the vacuum generating means 7 will comprise a bellows device with a return spring 8 and an operating push-button 9 which can preferably be disposed vertically to facilitate the exertion of the compression effort in the most ergonomic position for the arm. The said push-button is acted on by a return spring 10 (Figure 7) and has a projecting stub 11 which is intended to bear on the intermediate rocker arm 12 which has an arm 13 and bears on a thrust element 14 incorporated in the end of the manually operated means for generating vacuum cycles 7. The said rocker arm 12 is pivotable about a transverse axis 77 in the body 15 supporting the vacuum unit and also has a resilient abuttment 16 which, in combination with a fixed abuttment 17 of the support 18, actuates the devices for gripping the various pipes. The arc described by the end of the tilting rocker arm 12 intersects the vertical path of the actuating stub 11 of the manual push-button 9 thus permitting automatic disconnection thereof once the whole downstroke of the push-button 9 has been performed, allowing the bellows to expand again under the action of the spring 8. By virtue of this arrangement, vertical displacement of the push-button 9 brings about pivoting of the rocker arm 12 and compression of the bellows 7 by means of the thrust element 14, expelling the air inside the bellows through a tubular distributor 19 into which the individual pipes for the recovery of each of the printheads are connected and which has, at its end, a non-return valve 20 which allows the air inside the vacuum generating unit to be discharged to the atmosphere but does not allow air to enter the interior of the said chamber when its volume increases again during its expansion movement brought about by the spring 8. The recovery effect is brought about automatically when, during its downstroke, the push-button 9 reaches a point at which the rocker arm 12 is released from the actuating stub 11, causing the rocker arm to rise again and the bellows 7 to return to an extended position in which a vacuum effect will be exerted in the internal chamber thereof and in the pipe for the recovery of a printhead, through the distributor 19. It will be appreciated that the underpressure obtained by means of the device does not depend on the action exerted by the user on the push button -9- given the fact that the driving action on the bellows -7- takes place by the action of the spring -8- and the compression stroke is determined by the rocker arm -12- independently of the manual action exerted by the user. The actual embodiment of the flexible pipes, one of which is indicated 6 in Figure 1, can be seen in the said drawing which shows an intermediate distributor body 21 provided with a number of individual chambers 22, 23, 24 and 25 corresponding to the number of printheads to be controlled by the device, each chamber receiving a pipe, as indicted by the reference numeral 6, for connecting it to the corresponding outlet opening in the plate 76, which will be described below, and a further flexible pipe for communication with the outlet distributor 19 of the vacuum generating means. One of these pipes is indicated 26 in Figure 1, a characteristic of the said pipes being that they are normally closed by being gripped, for which reason the vacuum suction produced by the expansion of the manually operated means for generating vacuum cycles 7 brought about by the spring 8 is effective only in the pipe which is in the open condition owing to the cancelling of the gripping action. It will therefore be appreciated that the connection pipes between the suction-cycle generating unit and the printhead outlets 3 are constituted by two pipe portions 6 and 26, of which one portion 26 is connected between the end distributor 19 of the vacuum-cycle generator and a fixed intermediate distributor body 21 which has as many individual chambers 22, 23, 24 and 25 as there are flexible pipes, the second pipe portion 6 being connected at one end to a corresponding outlet of one of the said individual chambers and at the other end being connected to the movable plate 76 carrying the seals for closing the outlets of the injection printheads. The intermediate distributor body 21 has, as indicated, a series of individual chambers 22 to 25 in which the ink which will be discharged from the corresponding printhead under the action of the vacuum at the outlet 3 of each of the cartridges 2 can be deposited. For the closure by gripping and the optional release of the various pipes 26 corresponding to each chamber of the body 21 and, finally, to each individual injection printhead, the present invention provides for a key system having individual keys for gripping the various pipes. The said key system is shown, in particular, in Figures 3, 5 and 6 in which can be noted the various keys 27, 28, 29 and 30, the bodies of which have large lower windows, for example, the window indicated 31 for the key 28, the lower edge 32 of which will grip the corresponding pipe which extends through the said window 31 and which is not shown for greater clarity, trapping it against the upper edge 33 of the fixed body 18 carrying the said key. Lower return springs such as the spring 34 for the key 28, act on each key and restore the position of the key once it is released, as will be explained below. In order to lock the keys in the depressed position, as shown for the key 28 of Figure 6, which corresponds to the position in which the corresponding pipe is not gripped, the present device comprises a transversely movable slider 35 which receives the returning action of its own spring 36 and which, for each of the keys, has a projection 37 the upper edge 38 of which is inclined downwardly and which defines, by means of a chamfer 39, a lower flat region 40. A projection 41 of the key 28 is disposed in a position perpendicular to the said projection 37 in a manner such that, when the key is displaced vertically, the said projection pushes the transverse slider 35, acting on the inclined plane 38 until, upon passing over the projection 37, the slider 35 will return to the original position, retaining the projection 41 beneath the flat region 40, this position being shown in Figure 6. In this position, the corresponding pipe which extends through the window 31 is not gripped, that is, it is subject to the effect of the vacuum which will be produced by the expansion of the bellows element after the compression thereof. It will therefore be understood that the device of the present invention will operate in the following manner: In the normal position, all of the pipes for communication with the printheads disposed in the outlets 3 of the cartridges 2 will be closed by the combined action of the edges 32 of the windows 31 with the projections 33 of the fixed portion of the body 18 of the key. At the moment when it is desired to carry out a cycle for the recovery of a printhead, the corresponding key of the group of keys 27-30 is pressed, releasing the grip and thus opening the corresponding flexible pipe 26 which will communicate, through the corresponding chamber of the body 21, with the corresponding pipe 6 which will communicate with the corresponding outlet opening of the movable body 1 for closing the printheads. Immediately afterwards, the vertical push-button 9 is pressed, its downstroke signifying the compression of the bellows 7 and the discharge of air through the non-return valve 20 by the action of the intermediate rocker arm 12 and of the thrust element 14. Upon the release of the rocker arm 12 from the stub 11 during the downstroke of the push-button 9, the latter will return to its original position as the bellows 7 returns under the action of the spring 8. Given the existence of the non-return valve 10, this will mean the creation, inside the bellows 7, of a certain momentary vacuum which will be transmitted through the pipe 26, the corresponding chamber of the body 21, and the pipe 6, to the printhead to effect its recovery. The ink which comes out of the said printhead will be deposited in a tank 42 in the bottom of the corresponding chamber of the body 21. The said tanks will have different dimensions, according to the maximum or peak underpressure which is desired for the different pens being variable, specially taking into colour pens and black pens. For example, one of the printheads may have a tank 43 with much larger dimensions than the others. Each chamber of the body 21 which includes the tank 42 and the corresponding projection of those indicated 22 to 25 will also have a small opening, indicated 44, by means of which, after the recovery cycle of the vacuum generating means, it can return to atmospheric pressure after a certain time as atmospheric air is drawn through the said opening 44. The dimensions of said venting openings will be used for the adjustment of the descending part of the underpressure curve created in the corresponding chamber, which will vary according to the entrance of ambient air. The vertical push-button 9 has a laterally expanded portion 45 with an inverted U-shaped slot 46 and projecting teeth in its central region 47 in which is inserted an end tooth 48 of a resilient arm 49 fixed to the base 50 of the fixed body carrying the vacuum generating unit. The formation and arrangement of the movable unit 1 which carries the means for closing the printhead outlets and which houses the assembly 4 carrying the ink cartridges will now be described. As will be appreciated from Figure 9, the assembly 4 which forms part of the movable carriage, carries various housings such as those indicated 51, 52, 53 and 54, for the various ink cartridges, which will supply the corresponding injection printheads, the said body being coupled to the unit 1 which carries the means for closing the outlets of the printheads on one side by means of a lateral fin 55 carrying straight lateral flanges 56 and 57 which are coupled with respective straight housings 58 and 59 of a lateral projecting rib 60 which is present on the body 4 and can guide the latter during entry and exit relative to the unit 1 and to the lateral fin 55. On the opposite side to the lateral fin 55, the assembly 4 fits onto lateral projections 61, Figure 1, which form part of the unit 1 carrying the means for closing the printhead outlets. The said projections 61 can also be seen in Figure 10 in which it is also possible to see the lower springs 62 and 63 which lift the unit 1 which, laterally, has respective pairs of inclined profiles 64 and 65 which, in combination with downwardly-projecting abuttments which form respective pairs of projections, one of which 66 and 67 is shown in Figure 12, forming part of the fixed body on which the unit 1 is guided, and cooperating with the springs 62 and 63 to convert the longitudinal displacement of the carriage which entrains the body 4 carrying the cartridges 2 into an upward movement of the unit 1 when the carriage reaches the home or rest position, in order to bring about the closure of the printheads, and into a downward movement of the said unit 1 when the carriage departs again towards the working positions. In order close the printheads, the plate 1 carries a series of suitable seals, indicated 68, 69, 70 and 71 in Figure 13, the number of seals being equal to the number of printheads to be controlled, the seals having complementary profiles for fitting the outlets of the cartridges 2 carrying the printheads as indicated in broken outline in Figure 1, with respective surrounding sealing lips as indicated 72 in Figure 14. Intermediate walls, indicated 73 and 74, between each of the successive closures, are made, like the seals and the lips 72, from synthetic rubber to permit easy deformation thereof when the lateral displacements of the carriage take place. The unit 1 has lower fixed bouts or nipples 75 in which the lower flexible pipes indicated 6 in Figure 1 are coupled. The foregoing description arises from a preferred, although not limiting, embodiment of the present invention and it should be understood that experts in the art may introduce variations of the detailed characteristics of the embodiment described without departing from the scope of the appended claims.

Claims: Device for recovering the operation of printheads of ink-jet printing devices, of the type comprising manually operated means for applying a vacuum cycle to the various printheads of an ink-jet printing device for the purpose of recovering its operation, characterized in that the manually-operated means (7) for generating vacuum cycles, is connected to each of the ink-injection printheads (3) by means of individual sets of flexible pipes (6, 26) which are kept usually closed by means of gripping devices which are individually releasable in order to transmit a vacuum cycle to the printhead in which a recovery cycle is to be carried out by suction. Device according to claim 1, characterized in that each set of pipes connecting the means for generating vacuum cycles and the corresponding printhead (3) is constituted by two pipe portions (6 and 26), of which one portion (26) is connected between the end distributor (19) of said means for generating vacuum cycles and a fixed intermediate body (21) which has as many individual chambers (22, 23, 24 and 25) as there are flexible pipes, the second pipe portion (6) being connected at one end to a corresponding outlet of one of the said individual chambers and at the other end being connected to the movable plate (76) carrying the seals for the closure of the printheads. Device according to Claims 1 and 2, characterized in that the means for generating vacuum cycles receive the manual compression impulse by means of a vertical push-button (9) acting on a tilting rocker arm (12) which transmits its movement to the means for generating vacuum-cycle, which rocker arm (12) is constituted by a structure which is capable of oscillating on a fixed portion of the body of the device and which has two arms inclined at an angle to one another, one of the arms (13) receiving the action of a stub (11) of the vertical push-button and the other (13') acting on a thrust element (14) coupled to the end of a bellows (7). Device according to Claim 3, characterized in that the arc described by the end of the tilting rocker arm (12) intersects the vertical path of the actuating stub (11) of the manual push-button (9), thus permitting automatic disconnection thereof once the whole downstroke of the push-button (9) has been performed, allowing the bellows to expand again under the action of the spring (8). Device according to Claim 1, characterized in that the means for gripping the flexible pipes (26) transversely are constituted by the movable stems of a key system with a number of throttling keys (27, 28, 29 and 30) equal to the number of pipes and printheads to be controlled. Device according to Claim 5, characterized in that the flexible pipes (26) extend through respective windows (31) in the movable stems of the gripping keys which can hold the pipes firmly by the action of return springs (34) which act in each of the keys and which press the respective pipes against abuttment portions of the fixed body (18) carrying the key system. Device according to Claims 3 and 5, characterized in that the body (18) carrying the key system carries, coupled therewith, a transverse slider (35) for retaining the keys, having a return spring (36) as well as respective inclined planes (38) with which respective projections (41) of the movable stems of the keys establish contact, the said inclined planes (38) terminating at their lower ends in housings (40) for retaining the said projecting ends (41) of the movable stems in positions corresponding to the release of the corresponding flexible pipes. Device according to claim 2, characterised in that the volume of the individual chambers (22), (23), (24) and (25) is specifically dimensioned in order to obtain a pre-determined peak underpressure, depending on the nature of the ink of the corresponding printhead. Device according to Claims 2 and 8, characterized in that each of the individual chambers (22, 23, 24 and 25) which receive the flexible pipes has a small hole (44) for communication with the atmosphere to allow the bellows device to recover after a vacuum cycle as a result of the entry of ambient air, which diameter is adjusted to vary the shape of the descending curve for the underpressure created within the corresponding chamber. A method of recovering the operation of the printheads of ink-jet printing devices with the use of the device which is the subject of Claims 1 to 9, characterized in that it comprises: a) the closing of all the pipes connecting the means for generating vacuum cycles to each of the printheads; b) the selection of communication between the means for generating vacuum cycles and the printhead to be restored, before the generation of the vacuum cycle, c) the generation of an individual vacuum cycle in said means for generating vacuum cycles d) the application of the individually-generated vacuum cycle to the selected printhead to be recovered.

Inventors: CLARAMUNT DAVID, CLARAMUNT, DAVID
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1995
Main classification: B41J2
IPC codes: B41J2