INK JET PRINTER

Abstract: An ink flow control means for regulating the supply of ink from an ink reservoir (24) to a bi-directionally movable print head (12) of an ink jet printer. The control means deals with the problem of rapid starting and stopping of the ink to minimize fluctuations thereof during print head (12) reversal in direction of movement. An ink flow control valve (30) interposed in the ink supply line (28, 32) is arranged to close by reason of inertial forces on the valve (30) when the print head (12) is decelerated and accelerated near the two ends of its travel.

Description: INK JET PRINTER Technical Field This invention relates to an ink jet printer and, in particular, to an ink flow control means for regulating the supply of ink from an ink reservoir to the print heads of the printer. Background Art In the field of non-impact printing, the most common types of printers have been the thermal printer an <3 the ink jet printer. When the performance of a non¬ impact printer is compared with that of an impact printer, one of the problems in the non-impact machine has been obtaining and maintaining the required control of the printing operation. As is well-known, the impact printing operation depends upon the movement of impact members typically by reason of an electromechanical system which is believed to enable a more precise control of such impact members. The advent of non-impact printing as in the case of thermal printing brought out the fact that the heating cycle must be controlled in a manner to obtain maximum repeated operations. Likewise, the control of ink jet printing must deal with the problem of rapid starting and stopping movement of the ink fluid from a supply of such fluid in order to minimize fluctuations thereof during print head reversal in direction of move¬ ment. An arrangement for minimizing pressure fluctu¬ ations in an ink jet printer is disclosed in U.S. Patent No. 4,125,845. This patent describes a printer including a pulse trap chamber which is in constant fluid communi¬ cation with one or more ink ejecting chambers. The pressure within the pulse trap chamber is maintained within fixed limits by an ink supply valve controlling the flow of ink from an ink container into the pulse trap chamber. A strain gage is provided for generating a signal proportional to the pressure of ink within the pulse trap chamber which signal causes the ink supply valve to open or close at appropriate times. A disadvantage of this flow control arrange- ment is that it requires expensive sensing equipment and elaborate electrical circuitry. Disclosure of the Invention It is an object of the invention to provide in an ink jet printer a simple, efficient and low-cost flow control arrangement which alleviates the problem of un¬ desirable oscillations of ink through the print heads and onto the record medium. Thus, according to the invention there is provided an ink jet printer including at least one print head movable in side-to-side directions in the printer, a stationary ink reservoir, an ink supply line for supplying ink from said ink reservoir to said at least one print head, and ink flow conttol means interposed in said ink supply line, characterized in * that, by reason of inertial forces acting on said ink flow con¬ trol means, said ink supply line is closed on one side of said ink flow control means when said at least one print head is decelerated and accelerated near one end of its travel, and is closed on the other side of said ink flow control means when said at least one print head is decelerated and accelerated near the other end of its travel, and in that said ink supply line is open when said at least one print head is moving at substantially constant speed. A further advantage of the invention is that the formation of air bubbles in the system is substan¬ tially eliminated. Brief Description of the Drawings Embodiments of the invention will now be des- cribed, by way of example, with reference to the accom¬ panying drawings, in which: Fig. 1 is a top plan view in partial section of a portion of an ink jet printer of the present invention; Fig. 2 is an enlarged side view of the valve means as shown in Fig. 1; and Fig. 3 is an enlarged side view of a modifica¬ tion of valve means for use in the present invention. Best Mode for Carrying Out the Invention Referring to Fig. 1, there is shown a simpli- fied diagrammatic representation of a portion of an ink jet printer of the present invention. A record medium or paper 10 is caused to be driven by drive means (not. shown) past a printing station adjacent and formed by the position of a plurality of ink jet print elements or heads 12, which print heads 12 are supported from and carried by a carriage 14 which is caused to be driven in reciprocating side-to-side movement by means of a drum cam 16 having a rail 18"operably engaged with the carriage 14 in well-known manner. A pair of spaced rails or shafts 20 and 22 carried by the printer support the car¬ riage 14 in its side-to-side movement. An ink supply is contained in a stationary reservoir 24 having a vent 26 and ink is caused to be transported from the reservoir 24 through a flexible conduit or like passageway 28 to valve means 30. The ink flows from the valve means 30 into a manifold 32 and then through individual lines 34 to the respective print heads 12. The print heads 12 are held in secure manner on the carriage 14 by a support member 35 maintaining same along a straight line for printing a line of dots. Each print head 12 includes a piezoelectric crystal or like drive element 36 for driving ink from an ink chamber 37 through a passageway 38 in the print head 12 and out through a nozzle 40 to deposit droplets of ink onto the paper 10. The operation of the print head drive element 36 is well-known in the art, however, suffice it to say that the chamber 37 is filled with ink and energization of the piezoelectric element 36 causes a pulsating motion in pumping the ink through the passageway 38 and out the nozzle 40. As illustrated in Fig. 1, such valve means 30 is installed between the supply line 28 and the manifold 32 and includes a body 42 having a cavity 44 containing a ball 46 of proper mass and freely movable within the cavity. As further illustrated in Fig. 2, the valve 30 includes an ink inlet port 48 connected with the supply line 28 and an ink outlet port 50 connected with the manifold 32. The cavity 44 also has a low portion which subjects the ball member 46 to the force of gravity and provides a center position for the ball. Construction of the valve means 30 may prefer¬ abl comprise two pieces in a molding process including molding a lower portion 52 and an upper left portion 54 in one piece and molding an upper right portion 56 in a second piece. After ball member 46 is placed in the cavity 44, the portion 56 may then be welded by ultra¬ sonic or like means to portions 52, 54. Suffice it to say that other ways and means may be used to make up the valve assembly 30. In the operation of the preferred valve means 30, the ball 46 member will be in the center position, as seen in Fig. 2, when the carriage 14 along with the print heads 12 are being moved in side-to-side manner. Assuming that the print heads 12 are moving from left to right, the ball 46, upon deceleration of the carriage 14 at the right side of the printer, is caused to move to the right by reason of its inertia and seat over the inlet port 48, as shown by the phantom line position of the ball member 46, thus sealing the port 48 and shut- ting off the flow of ink from the reservoir 24 into the cavity 44. After the carriage 14 has reached the right side and reverses direction to move toward the left, i.e. IHJRH OMPI . - W1 in a carriage 14 and print head 12 turnaround motion, the acceleration in the leftward direction causes the ball 46 to be held in the seated position until the printing speed is reached, whereupon the ball 46 will roll toward the center or low position of the cavity 44 by reason of gravity. Then, as the carriage 14 ap¬ proaches the left side, the deceleration thereof causes the ball 46 to move to the left due to its inertia and seat over the outlet port 50, as again shown by the phantom line position of the ball member 46, thus seal¬ ing the port 50 and shutting off the flow of ink from the cavity 44 into the manifold 32. After the carriage 14 has reached the left side and reverses direction to move toward the right, again in the print head 12 turn- around motion, the acceleration in the rightward direc¬ tion holds the ball 46 in the seated position until the printing speed is reached, whereupon the ball 46 again rolls toward the center position of the cavity 44 by reason of gravity. A modified valve means or assembly 60 shown in Fig. 3 may be utilized in a printer environment less sen¬ sitive to being level and wherein the carriage 14 sup¬ ports a body 62 having a cavity 63 containing a movable plunger member 64. The plunger member 64 may include a square-formed washer or plate having a flat side for moving along a lower surface 65 of the body 62. As il¬ lustrated, the member 64 includes identical right and left side portions 66 and 68 which are circular in shape and which terminate in right and left cone portions 70 and 72, respectively. Cone portion 70 fits with a right side conical opening 74 formed in the body 62 and cone portion 72 fits with a left side conical opening 76 formed in the body 62. The right side opening 74 con¬ nects with an inlet port 78 of the body 62, in turn con- nected with the ink supply tube 28, and the left side opening 76 connects with an outlet port 80 of the body 62, in turn connected with the manifold 32. . _OMPI Light springs 82 and 84 encircle the respec¬ tive right and left side portions 66 and 68 to provide a force necessary to restore and maintain the movable plunger member 64 at the central position permitting ink flow between the supply tube 28 and the manifold 32 during.the time of printing when the carriage 14 is moving at a constant velocity and when neither accelera¬ tion or deceleration is taking place. In a manner sim¬ ilar to that described above for the preferred valve means 30, movement of the plunger member 64 to the right and left for closing off the respective inlet and outlet ports 78 and 80 takes place automatically as inertial forces resulting from acceleration and deceleration of the carriage 14 causes the plunger member 64 to overcome the associated springs 82 and 84 accordingly. In this modification of the invention, the plunger and spring ratios can easily be changed for accommodating various peak acceleration loads. It is thus seen that herein shown and dis- closed is an ink jet printer having valve means position¬ ed in the path of the flow of ink which is subjected to the acceleration and deceleration of the print heads and which valve means is effective to control the flow of ink during bidirectional printing movement. The valve means includes a member which is freely movable in a cavity by reason of the inertial forces thereon to open and close the inlet and outlet ports of the body of the valve means.

Claims: CLAIMS : 1. An ink jet printer including at least one print head (12) movable in side-to-side directions in the printer, a stationary ink reservoir (24), an ink supply line (28, 32) for supplying ink from said ink reservoir (24) to said at least one print head (12), and ink flow control means (30, 60) interposed in said ink supply line (28, 32), characterized in that, by reason of inertial forces acting on said ink flow control means (30, 60), said ink supply line (28, 32) is closed on one ' ' side of said ink flow control means (30, 60) when said at least one print head (12) is decelerated and acceler¬ ated near one end of its travel, and is closed on the other side of said ink flow control means (30, 60) when said at least one print head (12) is decelerated and accelerated near the other end of its travel, and in that " said ink supply line (28, 32) is open when said at least one print head (12) is moving at substantially constant speed. 2. Ink jet printer according to claim 1, characterized in that said ink flow control means is a valve (30, 60) having a body (42, 62) with a cavity (44, 63) therein, and an element (46, 64) movable within said cavity (44, 63) to open and close said ink supply line (28, 32). 3. Ink jet printer according to claim 2, characterized in that said cavity (44, 63) has an inlet port (48, 74) connecting said cavity (44, 63) with said ink reservoir (24), and an outlet port (50, 76) connec- - ting said cavity (44, 63) with said at least one print head (12), the arrangement being such that said inlet port (48, 74) is blocked by said element (46, 64) when said at least one print head (12) is decelerated and accelerated near said one end of its travel, said outlet OMPl 3 . ( concluded ) port (50, 76) is blocked by said element (46, 64) when said at least one print head (12) is decelerated and accelerated near said other end of its travel, and neither of said ports is blocked when said at least one print head (12) is moving at substantially .constant speed. 4. Ink jet printer according to claim 3, characterized in that said element is a ball (64) which is movable within said cavity (63) by inertial forces to block one or other of said ports (48, 50) to close said ink supply line (28, 32) and is movable by reason of gravity to open said ink supply line (28, 32). 5. Ink jet printer according to claim 3, 'characterized in that said element (64) is movable within sai cavity (63) . by inertial forces to block one or other of said poςts (74, 76) to close said ink supply line (28, 32) and is urged by resilient means (82, 84) to open said ink supply line (28, 32). 6. Ink jet printer according to claim 5, characterized in that said inlet port (74) and outlet port (76) are conically shaped, and in- that said element (64) includes conical end portions (70, 72) for mating with said inlet and outlet ports (74, 76). 7. Ink jet printer according to claim 1, characterized in that said at least one print head (12) is mounted on a movable carriage (14) also supporting said ink flow control means (30, 60) for movement there¬ with. 8. Ink jet printer according to any one of the preceding claims, characterized by a plurality of print heads (12), said ink supply line (32) being ar¬ ranged to be connected with each of said print heads (12) for movement therewith. OMP 9.. Ink jet printer according to claim 8, characterized in that each print head (12) is connected with said ink supply line (32) by an individual supply duct (34).

Inventors: ITALIANO V
Applicants: NCR CO, NCR CORP
Application year: 1980
Main classification: G01D15
IPC codes: B41J2, B41J27, G01D15