PRINT DEVICE FOR TYPEWRITERS AND LIKE PRINTING MACHINES

Abstract: The print apparatus comprises a character-carrying element (41) of the 'daisywheel' type with flexible spokes which can be selectively positioned in front of a platen roller (11), a print hammer (91) for moving a selected character towards the platen roller, an actuating solenoid (51) for the print hammer and a damping mechanism (70) which acts on the hammer after the printing of each character. The hammer is directly connected to a movable armature (84) of the solenoid and is returned by a return spring (97). During the return phase, the armature displaces, against a travel limiting stop (69), a counteracting weight (73) which is urged towards an intermediate stop (76) by the force of a counteracting spring (78). A first damping element (86) is disposed between the movable armature and the counteracting weight and a second damping element (79) is disposed between the weight and the travel limiting stop. The two damping elements, operating sequentially, minimise the time required for the hammer to settle down.

Description: The present invention relates to a print device for a typewriter or like printing machine. The device is of the kind comprising a character-carrying element having flexible spokes which can be selectively positioned in front of a platen roller, a print hammer for moving the selected character towards the platen roller, and an activating solenoid for the print hammer. In a first aspect, the invention concerns in particular a device having a damping mechanism for reducing the time for the hammer to settle down after the printing of each character. In such devices, the print hammer covers a relatively long distance in going from a rest position in which it is spaced from the character-carrying spokes to the print position in which the selected spoke is first flexed and then caused to strike against the platen roller. In view of the substantial amounts of energy involved, damping of the vibrations of the hammer is essential in order to achieve a high print rate. In a known device, damping of the hammer is effected by a rubber block carried by a counteracting lever which in turn is pivoted on a fixed pin and is held in contact against a stop by a suitable counteracting spring. A coil spring which is wound around the pin acts as a friction element between the layer and the pin. That damping mechanism is fairly expensive while in addition the time required for the hammer to settle down is fairly high and is not suitable for high-performance printers. One object of the present invention is therefore to provide a print device which is simple, compact and economical and which also permits a substantial reduction in the time for settlement of the hammer after printing of the selected character. To this end, the print device according to the present invention is characterised in that the damping mechanism comprises a series of mutually independent and movable damping elements which perform sequential damping functions, minimising the time for the print hammer to settle down. Other aspects of the invention are defined in the appended claims. The invention will be described in more detail, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal view of part of a typewriter on which a print device embodying the invention is mounted, Figure 2 is a partly sectional front view on an enlarged scale of the device shown in Figure 1, Figure 3 is a view on an enlarged scale of some details from Figure 2, Figure 4 is a front view of an alternative embodiment of the device shown in Figure 2, and Figure 5 shows a block circuit diagram of the circuit for actuating the device shown in Figure 1. Referring to Figure 1, the print device 10 embodying the invention is fitted to a typewriter comprising a platen roller 11 having a point of typing 12 and a carriage 13 which is movable on a cylindrical guide 14 parallel to the roller 11. The carriage 13 comprises two side members 16 and 17 which are orthogonal to the axis of the guide 14. The carriage 13 is displaced by a motor (not shown in the drawings) by way of a belt 18 which is connected to the side members 16 and 17. A frame structure 19 which is disposed between the side members 16 and 17 of the carriage 13 is of such a configuration as to provide two side members 21 and a plate 22 which is parallel to the platen roller 11 and on which the print device 10 is mounted. The side members 21 of the frame structure 19 are fixed to two bushes 24 on the carriage 13, which are coaxial with respect to the cylindrical guide 14. In that way the frame structure 19 is pivotable with respect to the cylindrical guide 14 and can follow the movement of the carraige 13. A bridge lever or bail 29 which can be actuated manually is provided for tilting the frame structure 19 with respect to the side members 16 and 17 and comprises two arms 31 (only one thereof is visible in the drawing) which are parallel to the side members 16 and 17, and a transverse member 32. The two arms 31 are each pivoted on a pin 34 which is fixed to the side members 16 or 17 of the carriage 13 and each arm 31 is provided with a slot 36 with which a peg 37 on the frame structure 19 co-operates in such away that a clockwise rotary movement of the lever 29 produces a clockwise rotary movement of the frame structure 19. The print device comprises a character-carrying disc or 'daisywheel' 41 of known type, for example of the type described in our published European patent application EP 0 118 277, having a central hub 42 and a plurality of radial flexible spokes 43. The central hub 42 is fixed removably to a shaft 47 of a selector motor (not shown in the drawings). The end of each spoke 43 bears in raised form a print character 44 which is disposed on the side which is towards the platen roller 11 and, on the opposite side, a positioning wedge-shaped portion 46. The print device as described hereinbefore is substantially the same as that described in our published European patent application 0 122 039. In accordance with the invention, the print device 10 (see Figure 2) comprises a solenoid 51 and a striker hammer 52 which is capable of being actuated by the solenoid 51 to engage and guide a selected print character 44 towards the platen roller 11. The solenoid 51 comprises a cylindrical casing 53 with a front core 54 and a rear core 56, all of ferromagnetic material, "front" and "rear" meaning towards the typist and towards the platen respectively. The solenoid further comprises an excitation coil 64, a movable armature 84, of ferromagnetic material and connected to the hammer 52 by way of a cylindrical stem 83, and a damping mechanism 70. The casing 53 is hollow in its interior and is fixed by means of screws 57 to a flange 58 which in turn is fixed by means of screws 59 to the plate 22. The front core 54 and the rear core 56 having internal pole pieces 61 and 62 respectively, of a frustoconical configuration, and on the outside surface are in contact with a frame 63 of plastics material, on which the excitation coil 64 is wound in layers. The front core 54 further comprises a projection portion 66 having a seat 67 for removably accommodating a bush 68 of non-magnetic material, for example sintered bronze, which by means of an opening 89 guides a part of the stem 83 of the striker hammer 52, which projects forwardly from the armature 84. The portion 66 is closed at its front by a travel limiting stop or cover member 69 of ferromagnetic material having a hole in which one end 72 of the stem 83 is housed. The bush 68, which weight around 3 grams, constitutes a counteracting weight of the damping mechanism 70 and is provided with a rearward sleeve portion 73 of reduced diameter forming a flange 74 co-operable with a shoulder 76 on the front core 54 which forms an intermediate stop element for the bush 68. The bush 68 has an internal seat or opening 77 for housing a counteracting coil spring 78 which is coaxial with the stem 83. The spring 78 has a front end thereof bearing against the disc 69 and urges the bush 68 towards the rearward part, holding it in a position of abutment with the flange 74 against the shoulder 76. A damping disc 79 of plastics or rubber material is fixed on the front surface of the bush 68 and is co-operable with the cover 69, as will be described hereinafter. The striker hammer 52 of non-magnetic material and weighing around 5 grams comprises a rear end 91 of rectangular section integral with a cylindrical portion 81 which in turn is fixed to the cylindrical stem 83. Fitted on the portion 81 is a spring guide bush 82 of plastics material while disposed on the stem 83 is the magnetic armature 84. Mounted between the armature 84 and the bush 68 are a disc 86 of plastics or rubber material, adjacent the armature 84 and providing a damping function, and a thin disc 87 of plastics material, which is provided for avoiding the danger of the elastic disc 86 and the bush 68 sticking together. In order further to prevent sticking, the bush 68 has a rear surface 88 (see Figure 3) which is a corrugated configuration so that the disc 87 bears against the projecting convex wall portions which alternate with recessed concave wall portions which are connected together as shown in Figure 3. The striker hammer 52 (see Figure 2) is guided movably by means of the stem 83, by the opening 89 in the bush 68, and, at the rear, by means of the end 91, by an opening 92 of rectangular section, in a bush 93 of non-mgnetic material which is fixed on the flange 58. The end 91 is shaped so as to provide a recess 94 of V-shaped section, capable of engaging with the corresponding positioning wedge-shaped portion 46 on each spoke 43 while the selected character 44 is caused to strike against the platen roller 11. A spring guide bush 96 of plastics material is mounted within the rear core 56. The bushes 96 and 82 guide a coil return spring 97 of non-magnetic material. The spring 97 holds the striker hammer 52 spaced from the character-carrying disc 41, bearing against shoulders 98 and 99 of the bushes 82 and 96 and being guided axially by the bushes 82 and 96 which prevent radial vibration of the spring. The coil 64 of the solenoid 51 is excited with a current of substantially constant amplitude. By means of the described configuration, the kinetic energy of the hammer 52 is proportional to the time t for excitation of the coil 64. A control circuit 101 (see Figure 5) varies the time t in dependence on the character to be printed, the printing strength and the characteristics of the striker device 10 generally, substantially as described in our U.S. patent 4 308 794. The characters, according to the size thereof, are subdivided into four groups which are stored in a ROM 102 and can be recalled by means of a bus 103 by an input device 104 which may be for example an electronic keyboard. Depending on the group to which the character to be printed belongs, the time t is automatically increased or reduced. In addition the overall strength of striking may be varied by means of selectors 106 and 107 of known type which are connected to the ROM 102. The circuit 101 comprises a binary counter 108 which counts the pulses OS generated by an oscillator 109 and generates a pulse CD at the end of each counting operation. The signal CD resets a flip-­ flop 111 which has its set input connected to a signal AB for enabling printing. The signal AB is also applied to the oscillator 109 while the output signal DF of the flip-flop 111 is applied to the base of a transistor 112 of pnp type which has its emitter connected to one end of the coil 64 of the solenoid 51. The other end of the coil 64 is connected to earth. The collector of the transistor 112 is connected to a reference voltage + Vcc. The print device 10 shown in Figure 2 and the alternative embodiment shown in Figure 4 differ only in regard to the loading of the springs 78 and 97. In the device shown in Figure 2, the load of the spring 78 is around 35 grams while the load of the return spring 97 is around 65 grams. In the rest condition, the hammer 52 is held spaced from the character-carrying disc 41 by the force of the return spring 97 which, producing a greater force than the spring 78, holds the hammer 52 with the armature 84, the disc 86 and the disc 87, in a condition of abutment against the corrugated surface 88 and the bush 68 with the disc 79 in a condition of abutment against the limit stop element 69. To provide for striking of a print character 44, after the selected character 44 has been moved in any known manner in front of the strike hammer 52, the coil is excited, thus producing a magnetic flux which causes the armature 84 to move towards the pole piece 62 against the force of the spring 97. The hammer 52 moves towards the platen roller 11 and, after having engaged the positioning wedge-like portion 46 of the selected character 44 by means of the V-shaped recess 94 in the hammer 52, causes the corresponding character to be struck against the platen roller 11, compensating for any misalignment of the character with respect to the point of printing 12. As soon as the striker 52 begins its movement towards the platen roller 11, the spring 78 moves the bush 68 axially until it comes to bear with the flange 74 against the shoulder 76. As has been set forth hereinbefore, the time t for excitation of the coil 64 is variable in dependence on the character selected by the keyboard and the strength of striking as selected by the selector 106. The group to which the selected character belongs causes the ROM 102 to generate a code which presets the counter 108. When the character-carrying disc 41 moves the selected character into the print position, the signal AB is generated which permits the oscillator 109 to generate the pulses OS and enables the flip-­ flop 111 for generation of the signal DF which causes excitation of the coil 64 to begin. After a certain time which is dependent on the preset time, the counter 108 generates the signal CD for the end of the counting operation, the flip-flop 111 is reset and excitation of the coil 64 is terminated. After printing of the character, the return spring 97 (see Figure 2) returns the hammer 52 and the armature 84 towards the rest position. During that travel, the armature 84 encounters the counteracting weight 68 which is temporarily in a stopped condition with the flange 74 bearing against the shoulder 76. The damping mechanism 70 comprising the weight 68, the spring 78 and the elements 86 and 79 damps the shock due to the rapid return movement of the hammer 52 and the armature 84 without appreciable oscillations and in successive phases. Firstly the elastic disc 86 strikes against the front surface 88 of the bush 68 and a first damping phase occurs, then the bush 68 also moves together with the hammer 52 and the armature 84 against the force of the spring 78 and a second damping phase occurs, and finally the elastic disc 79 strikes against the disc 69 and a third damping phase takes place, with total dissipation of the residual kinetic energy of the hammer 52 and the armature 84. Under operating conditions, the hammer 52 completes its strike movement which is about 7.6 mm in about 5 msec and the return travel which is due to the force of the spring 97 in about 6 msec. The damping mechanism 70 damps the blow and the vibration due to the rapid return movement of the hammer 52 in about 2 msec and permits excitation of the coil 64 for fresh strike cycles about every 13 msec. In the alternative embodiment shown in Figure 4, the force of the counteracting spring 78 is around 105 grams while that of the return spring 97 is around 65 grams. In the rest condition, the striker hammer 52 is held spaced from the character-carrying disc 41 but the spring 97 is not capable of moving the bush 68 from its intermediate stop position. In particular, the hammer 52 with the armature 84, the disc 86 and the disc 87 remain in an abutting condition against the corrugated surface 88 of the bush 68. The bush 68 is in turn held in a stopped position by the force of the spring 78 with the flange 74 bearing against the shoulder 76. The mode of operation of the embodiment shown in Figure 4 is substantially identical with regard to the strike operation to that described above with the single exception of the absence of movement of the counteracting bush 68. The return movement of the hammer 52 to the rest position differs only in regard to the part thereof subsequent to the impact of the armature 84 against the weight 68. After striking of the selected character, the spring 97 returns the hammer 52 and the armature 84 to the rest position while the spring 78 holds the bush 68 in a stopped condition with the flange 74 bearing against the shoulder 76. In this case also, the elastic disc 86 strikes against the front surface 88 of the bush 68; the bush 68 then moves with the hammer 52 against the force of the spring 78 and finally the elastic disc 79 strikes against the stop element 69 in accordance with the three damping phases of the arrangement shown in Figure 2. The difference in the arrangement shown in Figure 4 is that the force of the spring 78 which is greater than that of the spring 97 provides that the spring 78, after impact with the bush 68, moves the bush 68 with the disc 68, the armature 84 and the hammer 52 towards the rearward part of the solenoid 51 until the bush 68 is again moved into a position of bearing with the flange 74 against the shoulder 76. In the embodiment shown in Figure 4, the hammer 52 completes the strike travel in about 5 msec while the time for the return movement thereof, whichis due to the force of the spring 97, is about 6 msec, and the damping mechanism 70 damps the vibration of the hammer 52 in about 6 msec. In this case therefore the coil 64 can be excited for fresh strike cycles every 17 msec approximately. It will be apparent that the print device 10 as described hereinbefore has very short excitation times and reduced moving masses, by virtue of its structure; in addition the damping mechanism 70 shown in Figure 2 or the mechanism shown in Figure 4 associated therewith minimise the times required for the hammer 52 to settle down after the print operation. The discs 79 anbd 86 do not have to be fixed in the manner described above. For example, the disc 86 could be fixed to the weight 73 and/or the disc 79 could be fixed to the stop disc 69.

Claims: 1. A print device for typewriters and like printing machines comprising a character-carrying element (41) having flexible spokes (43) which can be selectively positioned in front of a platen roller (11), a print hammer (91) which can be selectively actuated to move the selected character against the platen roller, an actuating solenoid (51) for the print hammer and a damping mechanism (70) for the hammer, characterised in that the damping mechanism (70) comprises a series of movable damping elements (86, 73, 79) which produce sequential damping functions, minimising the time for the print hammer (91) to settle down. 2. A print device according to claim 1, characterised in that the hammer (91) is directly connected to an actuating element (84) and in that the series of damping elements (86, 73, 79) is disposed on the side of the actuating element opposite to the hammer and comprises at least two elastic elements (86, 79) spaced along the direction of actuation of the hammer. 3. A print device according to claim 1 or 2, wherein the hammer (91) is movable with an armature (84) of solenoid (51), characterised in that a damping element (86) of the said series is mounted on a surface of the armature (84) remote from the platen (11). 4. A print device according to claim 3, characterised in that the hammer (91) is guided by a movable bush (73) and is held spaced from the platen roller (11) by means of a return spring (97), a first damping element (86) is interposed between the armature (84) and the movable bush, a second damping element (79) is interposed between the movable bush and a travel limit element (69), and a counteracting spring (78) tends to move the movable bush in the direction of the actuating movement of the hammer up to an intermediate stop element (76). 5. A print device according to claim 4, characterised in that said first damping element (86, 87) cooperates with a corrugated surface (88) of the movable bush (73), such as to initiate against sticking. 6. A print device according to claim 4 or 5, characterised in that the first and second damping elements (86, 79) comprise two elastic discs. 7. A print device according to any of claims 1 to 3, characterised in that the damping mechanism (70) comprises a movable counteracting weight (73) which is entrained by the hammer (91) during its return travel movement, after striking of the character. 8. A print device according to claim 7 and any of claims 4 to 6, characterised in that the counteracting weight (73) is formed by the movable bush and the counteracting spring (78) is of coil type and urges the movable bush in an arrested condition against the intermediate stop element (76). 9. A print device according to claim 8, characterised in that the return spring (97) provides a greater force than that of the counteracting spring (78) and in that the hammer (91) with the armature (84) engages through the first damping element (86) with the movable bush (73) for a first damping phase, subsequently continues its travel with the movable bush and compresses the counteracting spring (78) for a second damping phase, and stops with the second damping element (86) against the travel limit element (69) for a third damping phase. 10. A print device according to claim 8, characterised in that the return spring (97) provides a force which is less than that of the counteracting spring (78) and in that the hammer (91) with the armature (84) engages through the first damping element (86) with the movable bush (73) for a first damping phase, subsequently continues its travel with the movable bush and compresses the counteracting spring (78) for a second damping phase, and stops with the second damping element (79) against the travel limit element (69) for a third damping phase, and wherein the counteracting spring (78) then moves the movable bush back against the intermediate stop element (76) at the end of the third damping phase. 11. A print device for typewriters and like printing machines of the type having a platen roller (11) defining a point of printing, a character-carrying element (41) having flexible spokes (43) provided at the periphery with a series of characters (44) which can be selectively positioned in front of the point of printing, a print hammer (91) which can be actuated selectively to move a selected character against the platen roller, an actuating solenoid (51) for the print hammer and a return spring (97) for returning the hammer to the rest position after printing of each character, characterised by a housing (54, 56) internal to the solenoid (51) and housing a portion of the hammer (91) with the return spring (97), a magnetic armature (84) of the solenoid which is fixed with respect to the hammer movable longitudinally in the housing and urged in the rest condition against a travel limit stop (69) of the housing and a counteracting spring (78) acting between the hammer (91) and the travel limit stop (69) and operable to counteract the return spring (97) to reduce the time for damping of the hammer after printing of each character. 12. A print device according to claim 11, characterised by a counteracting weight (73) movable in the same direction as the hammer (91) between an intermediate stop (76) and the travel limit stop (69) of the solenoid and in that the counteracting spring (78) acts between the counteracting weight and the travel limit stop. 13. A print device according to claim 12, characterised in that the counteracting weight (73) comprises a seat (98) for guiding the hammer (91) in its print travel movement and its movement for return to the rest condition. 14. A print device according to claim 12 or 13, characterised by a pair of damping elements (86, 79) acting sequentially on the armature (84) and on the counteracting weight (73) respectively. 15. A print device for typewriters and like printing machines having a platen roller (11) defining a point of printing, a character-carrying element (41) having flexible spokes (43) provided at the periphery with a series of characters (44) which are capable of being selectively positioned in front of the point of printing, a print hammer (91) which can be actuated selectively to move a selected character against the platen roller, a solenoid (51) having an actuating armature (84) for the print hammer and return means (97) for rapidly returning the hammer to the rest condition after printing of each character, characterised by an internal housing (54, 56) in the solenoid housing the armature (84), a counteracting weight (73) movable in the same direction as the armature between an intermediate stop (76) and a travel limit stop (69) of the housing, and capable of co-operating with the armature during the return movement of the hammer to the rest condition, and damping elements (86, 79) for reducing the time for damping of the hammer after printing of each character. 16. A device according to claim 15, characterised in that the return means comprise a return spring (97) and in that a counteracting spring (78) acts between the counteracting weight (73) and the travel limit stop (69) for counteracting the action of the return spring. 17. A print device according to claim 16, characterised in that the internal housing (54, 56) of the solenoid (51) houses the return spring (97) coaxially with the hammer (91) and comprises a seat (92) for guiding the hammer during the travel thereof and in that the counteracting spring (78) is coaxial with the hammer. 18. A device according to claim 16 or 17, characterised in that the counteracting spring (78) provides a greater force than the force of the return spring (97) and normally holds the counteracting weight (73) in a stopped condition against the intermediate stop (76), to counteract the action of the return spring. 19. A print device according to claim 16 or 17, characterised in that the counteracting spring (78) provides a force which is less than the force of the return spring (97) and is capable of counteracting the action of the return spring in the rest position of the hammer. 20. A print device according to any of claims 15 to 20, characterised by damping elements (86, 79) which are operative sequentially on the hammer (91) and on the counteracting weight (73) respectively. 21. A print device for typewriters and like printing machines comprising a character-carrying element (41) having flexible spokes (43) which can be selectively positioned in front of a platen roller (11), a print hammer (91) which can be selectively actuated to move the selected character against the platen roller, an actuating solenoid (51) for the print hammer and a damping mechanism (70) for the hammer, characterised in that the damping mechanism comprises an inertial damping weight (73) which is biased by a spring (78) towards the platen (11) and a resilient damping pad (86) between tfhe hammer (91) and the damping weight (73) so that a first damping occurs when the pad is struck by the hammer against the weight and a second damping occurs as the weight is accelerated by the hammer. 22. A print device according to claim 21, characterised in that the damping mechanism comprises an inertial damping weight (73) which is biased by a spring (78) towards the platen (11) and a resilient damping pad (86) between the hammer (91) and the damping weight (73) so that a first damping occurs when the pad is struck by the hammer against the weight and a second damping occurs as the weight is accelerated by the hammer.

Inventors: FALCONIERI, REMO, GIANOTTI, ESTER GIOVANNI
Applicants: ING. C. OLIVETTI & C., S.P.A.
Application year: 1986
Main classification: B41J9
IPC codes: B41J9