MULTIPLE NOZZLE INK JET DOT PRINTER

Abstract: The printer comprises a serial ink jet print head (38) having five print elements (40) in side-by-side relationship, each provided with an ink ejector nozzle (46). Each print element is connected to the head by means of a resilient blade (66) which is centrally pivoted on the head, and the print element is movable in two directions, respectively parallel and perpendicular to the direction of movement of the head, to vary the relative position of the nozzles, by means of an eccentric pin (74) in a slot (72) in one end of the blade and a screw (82) bearing on the other end of the blade (66), to which the element (40) is attached. The nozzles (46) are disposed along a straight line which is inclined with respect to the direction of movement of the head. The head can be rotated about a hinge (86) to vary the inclination of the nozzles, thereby to provide different print definitions, by means of a stepped face cam (92) bearing on a post (100) fixed to the head carriage (10). The printer further comprises a parking station for the head in which, during prolonged stoppages of the printing operation, the nozzles are cleaned and kept in contact with an atmosphere saturated with a solvent for the ink, to prevent the ink from drying out in the nozzles.

Description: The present invention relates to an ink jet dot printer of the kind defined in the pre-characterizing part of claim 1. Ink jet dot printers are known in which the head comprises a plurality of print elements. One known head is mounted on a movable carriage and is formed by a single block of resin in which a large number of ink jet print elements are incorporated. Each element is formed by a tube provided with a nozzle and associated with a piezoelectric transducer for on-demand expulsion of drops of ink. In the heads of such printers, the print elements must be positioned with a high degree of accuracy, involving the use of complicated and expensive equipment. In addition such heads require accurate manufacture of the parts which are coupled to the carriage whereby the printer is altogether expensive and complicated in construction. A printer in accordance with the pre-characterizing part of claim 1 is known from EP-A-0 031 449 which provides for adjustment of a nozzle in the directions parallel to and perpendicular to the line of print. The object of the present invention is to provide an ink jet printer which is simple in construction and of low cost and in which each of a plurality of print elements can easily be adjusted individually. The invention accordingly provides a printer as defined in claim 1. Those and other features of the invention will be more clearly apparent from the following description of a preferred embodiment which is given by way of non-limiting example with reference to the accompanying drawings in which: Figure 1 is a plan view of part of the printer according to the invention, Figure 2 is a side view of the printer taken along line II-II in Figure 1, Figure 3 is a partly sectional plan view of the print head on an enlarged scale, Figure 4 is a view of the head in section taken along line IV-IV in Figure 3, Figure 5 is a view of the head in section taken along line V-V in Figure 2, Figure 6 is a diagrammatic representation of the print definitions which can be obtained with the head, Figure 7 is a simplified electrical block circuit diagram of a control circuit of the printer. Referring to Figures 1 and 2, a carriage 10 is slidable on guides 12 and 14 parallel to and fixed with respect to a frame structure 15 of the printer. The carriage 10 is entrained by a cord 16 which is fixed at its ends to the carriage and which is passed around direction-changing pulleys 20 and a drive roller 22. The roller 22 is rotated by a d.c. motor 24 which is rotatable in both directions. A platen roller 30 is rotatable on the frame structure 15 and is rotated by a stepping motor 32 by way of an endless worm 33 and a helicoidal wheel 34 for producing intermittent line-spacing movements of a print carrier 35, normally a sheet of paper, which is wound around the roller 30. Mounted on the carriage 10 is a print head 38 (see Figures 3 and 4) comprising a support 39 which, in accordance with a preferred but non-limiting embodiment, carries five ink jet dot print elements 40 which are arranged in side-by-side relationship and which are each provided with a nozzle 46 for expulsion of the drops of ink. The nozzles 46 are aligned along a straight line 'r' (see Figure 6) which is inclined with respect to the direction 'x' of movement of the carriage in such a way that each nozzle 46-1...46-5 prints on lines m which are spaced from each other by a predetermined constant distance dl. The print elements 40 (see Figure 4) may be of any known type, for example of the type described in EP-A-0 215 595. More particularly each element 40 is formed by a glass capillary ejector tube 42 on which is fixed a sleeve-type piezoelectric transducer 43 which is activated by electrical pulses to expel drops of ink from a nozzle 46 disposed at one end 44 of the tube 42. The tube 42 may also be of metal or ceramic material and communicates at the other end 48 with an elastic ink feed conduit 50. The conduit 50 is provided with a porous capillary filter 52 such as to prevent emptying of the conduit 50 and the tube 42. The hydraulic characteristics of the conduit 50 with respect to the pressure waves generated by the transducer 43 in the tube 42 are such that it is equivalent to a reservoir of infinite capacity whereby the pressure waves reflected by the ends 44 and 48 of the tube 42 are automatically damped, as described in detail in EP-A-0 200 457. The conduit 50 communicates with an auxiliary reservoir 54 which is common to all five print elements 40 and which is fixed to the support 39 of the head. The auxiliary reservoir 54 is connected by means of a flexible conduit 56 and 56′ to a main reservoir 57 (see Figures 1 and 2) for the ink which is interchangeable and fixed to the frame structure 15. The conduit 56 is reinforced by two ribs 156 and 256 connected laterally to the central tube 55 to permit flexing of the conduit 56 during movement of the head. The central part of the tube 42 with the associated transducer is embedded in a block 60 of resin, from which the tube 42 projects by means of the ends 44 and 48 thereof. The end 44 passes through an opening 62 in the support 39 and is protected by a portion 64 of the block 60. By virtue of small variations in the speed of expulsion of the drops from the various nozzles 46 or by virtue of slight structural differences in the print elements 40, some drops may reach the paper 35 in non-aligned positions in the preselected dot matrix, with a corresponding deterioration in the quality of the print. According to the invention, to permit speedy adjustment of the position of the nozzles in the horizontal direction 'x' of movement of the carriage 10 and in the vertical direction 'y' (Figure 6), each print element 40 is connected to the support 39 (see Figures 3 and 4) of the head by a resilient plate or blade 66. The blade 66 is fixed at one of its ends 68 (see Figure 4) to the block 60 and at approximately halfway along its length is pivoted on a pin 69 which is fixed to the support 39. The blade 66 is fixed to the block 60 by means of welding or ultrasound but alternatively it may be fixed in position by being glued or encased within the block 60. Another end 70 of the blade 66 is provided with a slot 72 engaged with an eccentric boss or lug 74 on an adjusting pin 76 which is rotatable in the support 39. Rotary movement of the pin 76 causes rotary movement of the blade 66 about the pin 69 and thus displacement of the nozzle 46, as indicated by the double-headed arrow 80 in Figure 3, parallel to the line of printing. A screw 82 mounted on the support 39 bears against the end 68 of the blade 60. Rotating the screw 82 in one direction or the other produces corresponding displacement of the nozzle 46 in the direction 'y' (see Figure 6). Careful adjustment of the screw 82 and the pin 76 provides that the drops of ink from each nozzle 46 fall precisely on the corresponding rows m and perfectly disposed in columns in direction 'y'. In the printer according to the invention, the angle of inclination of the line 'r' in which the nozzles 46 are aligned (see Figure 6) may be varied to vary the print definition, that is to say the distance d between the printing lines m. To provide for different angles of inclination of the line r, the support 39 (see Figure 5) is pivotally mounted on a pin 86 which is fixed to the carriage 10 and perpendicular to the direction 'x' of movement of the carriage 10. Mounted on a projection 90 on the support 39 is a face cam 92 which is fixed with respect to a journal 94 which is rotatable on the projection 90. The cam 92 is provided with a stepped profile, having for example three steps 96, 97 and 98, engaged with a cam follower in the form of a post 100 which is fixed with respect to the carriage 10. The cam 92 can be rotated manually by means of a handle 102, to assume three angular positions corresponding to each of the three steps 96 to 98 and consequently the head 38 is rotated about the pin 86 against the action of a return spring 93, assuming three selectible angles of inclination as diagrammatically indicated in Figure 6 by 'r', 's' and 't'. Thus, a different print definition, for example: 300; 240; 200 dots/inch corresponds to each position of the cam 92. The cam 92 (see Figure 5) comprises a switch 104 formed by electrical contacts 105 disposed on an upper face 106 of the cam 92 and bearing against corresponding tracks 107 of a printed circuit 108 fixed to the support 39. By means of a flexible cable 109, for each angular position of the cam 92 the switch 104 transmits signals corresponding to each preselected print definition by means of an analog-digital converter 150 (see Figure 7) of a control circuit. The converter 150 conditions a character generator 152 controlled by a microprocessor-type control unit 154 for selecting the pitch between the successive dots printed in accordance with the preselected print definition. A control circuit 156 connected to the generator 152 then activates the print elements 40. At the same time the unit 154 activates a circuit 158 for controlling the motor 32 to set the line spacing corresponding to the preselected print definition.

Claims: An ink jet printer for serially printing dots on an information support along a printing line according to a predetermined print matrix, comprising a carriage (10) movable parallel to the printing line, a print head (38) mounted on the carriage (10) and having a print element (40), provided with an ejector tube (42) secured to a support block (60), the tube (42) terminating at one end with a nozzle (46), and adjusting means (66, 76, 82) interposed between the print element (40) and the head (38) to adjust the nozzle position in both of the directions respectively parallel and perpendicular to the print line, characterized in that there are a plurality of the print elements (40) individually adjustable on the print head (38), and in that the adjusting means (66, 76, 82) comprises in respect of each ejector tube (42) a resilient blade (66) elongated parallel to the ejector tube (42), the blade (66) having a first end fixed to the corresponding support block (60) and engaged by a blade bending element (82) to adjust the corresponding nozzle (46) in the said perpendicular direction, and a second end provided with a slot (72) engaged by manually operable eccentric element (76), each blade (66) being pivoted on the head (38) at a point (69) between its ends to allow an individual adjusting movement of each nozzle (46) in the said parallel direction. An ink jet printer according to claim 1, characterized in that the print head (38) is pivotally mounted on the carriage (10) for adjusting the angle of a line through the nozzles (46) relative to the printing line, and in that the adjusting means further comprise a cam (92) rotatable about a vertical axis on the print head (38), the cam (92) having a lower profile provided with a plurality of steps (96, 97, 98) associated with a plurality of degrees of print definition and engaging a cam follower (100) provided on the carriage (10) and spring means (93) urging the said profile against the cam follower (100), the cam being integral with a manipulative member (102) for selectively rotating the cam to engage a selected step (96, 97 or 98) with the cam follower (100) and thereby select the said angle. A printer according to claim 2, characterized in that the cam (92) comprises an electric switch (104) connected to a circuit (150, 152) for controlling the printing operation for selecting the pitch between the print positions in accordance with each of the print definitions. A printer according to claim 3, characterized in that the switch (104) comprises two contacts (105) which slide against conducting tracks (107) on a base of a printed circuit (108) fixed to the head (38), the tracks being connected to the control circuit (150, 152).

Inventors: ACCATTINO, ANDRE, CHIARO, ALDO
Applicants: ING. C. OLIVETTI & C., S.P.A.
Application year: 1986
Main classification: B41J2
IPC codes: B41J2