Abstract:
A printing apparatus for printing dots on a printing web comprises: a printer body frame; a single rotational drive motor for producing drive rotational force; rotational force transmission for transmitting the rotational force; a spring-biased link rotatable around a rotary shaft supported by the printer body frame; printing web feeding device; a printing drum having helical printing projections thereon, disposed so as to face the printing web, and supplied with the rotational force through the transmission at all times, the drum being rotatably mounted on the link; and an interlock including a transmission gear engaging with the drum and a ratchet gear engageable with a ratchet pawl pivotable in response to a solenoid to thereby achieve the printing shot by use of the single rotational drive motor when the solenoid is energized.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a printing apparatus for printing marks such as letters and figures on printing webs such as papers. 
     There has been heretofore provided a so-called printer for printing letters, figures and the like on materials such as printing papers. In such a prior art printing machine, a printing drum is driven by a suitable motor to align in printing positions the letters and the like to be printed and then a hammer disposed on an opposite side to the printing drum is driven by solenoid means to hit the drum thereby completing the print on the printing papers positioned between the hammer and the drum. 
     However, the prior art printing apparatus requires the motor to rotate the printing drum and also the solenoid means having a large capacity enough to drive the hammer. Accordingly, the apparatus is disadvantageous in that the structure thereof is intricate with a large size and a large amount of an electrical power is required to drive the solenoid means. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a printing apparatus eliminating the above-noted drawbacks inherent to the prior art system, having a simple structure leading to a miniaturization, and having an extremely small amount of an electrical power to be expended. 
     Another object of the invention is to provide a novel printing apparatus having a simplified structure wherein a printing drum is supported to rotate and swing, utilizing a single drive motor. 
     A further object of the invention is to provide a printing apparatus enabling to feed a paper web synchronized with the single drive motor. 
     A still further object of the invention is to provide a printing apparatus wherein the line slant angle of the printed dotted marks is reduced to a negligible extent. 
     A still further object of the invention is to provide a printing apparatus ensuring the original position establishment by using a detecting switch. 
     These and other objects of the present invention will be achieved by the printing apparatus for printing marks on a printing web comprising: a printer body frame; a single rotational drive motor for producing drive rotational force; rotational force transmission means for transmitting the rotational force; spring-biased link means rotatable around a first rotary shaft supported by the printer body frame; printing web feeding means; a printing drum having helical printing projection thereon, disposed so as to face the printing web, and supplied with the rotational force through said transmission means at all times, said drum being rotatably mounted on said link means; and interlock means including a transmission gear engaging with said drum and a ratchet gear engageable with a ratchet pawl pivotable in response to solenoid means whereby by the transmitted rotational force derived from the drive motor said printing drum is rotated to abut against the printing web backed-up by said feeding means when the ratchet gear is operatively engaged with and slid on the ratchet pawl pivotally moved by the solenoid means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings; 
     FIG. 1 is a plan view of the printing apparatus of the present invention, in which the printer outer body frame is omitted for a ready understanding; 
     FIG. 2 is a side elevational view of the apparatus as viewed from the right of FIG. 1; 
     FIG. 3 is a side elevational view of the apparatus as viewed from the left of FIG. 1; 
     FIG. 4 is an illustration of the printed dots according to the apparatus shown in FIGS. 1 to 3; and 
     FIG. 5 is a modification showing the printing drum according to the present invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention will hereinafter be described with reference to the accompanying drawings. A printing drum designated generally by reference numeral 1 is rotatably supported through a shaft 2 by a pair of link members 3 and 4 which are coupled to each other through a plate 34. The drum 1 is provided with a strip-shaped projection 1a arranged in a helical manner. On the strip-shaped projections 1a are provided a number of dot projections 1a&#39; each defining a printing point to thereby form letters or figures on the paper in combination. A gear 1c is secured to one side end of the printing drum, and a cam member 1d is secured to the other. A shouldered portion 1d&#34; (FIG. 2) is formed in a cam surface 1d&#39; which is formed inside of a peripheral wall of the cam member 1d and is engageable with an extension 5a of a paper feeding lever 5, the extension 5a having a semicircular cross section as shown by a dotted line in FIG. 2. 
     The above described link members 3 and 4 are rotatably mounted around a shaft 6 on which right and left transmission gears 7 and 8 are fixedly secured, respectively. The shaft 6 is rotatable but not movable with respect to the printer base frame (not shown). The right side gear 7 meshes with a drive gear 9 coupled to a suitable shaft cooperating with a motor M which is a drive source, whereas the left side gear 8 meshes with the gear 1c of the drum 1. Accordingly, as the motor M rotates, the rotational torque is transmitted through the drive gears 9 and the transmission gear 7, the shaft 6, the transmission gears 8 and the gear 1c of the drum in that order, to thereby rotate the printing drum 1. 
     On the other hand, a gear assembly or unit 11 is, as best shown in FIG. 3, rotatably coupled to the left side link member 4 through a shaft 10. The unit 11 includes a ratchet gear 11a and a normal gear 11b both of which are coaxially secured to each other, the latter gear being always engaged with the gear 1c of the drum. A stopper or pawl 12 which is rotatably supported at a shaft 12a and is operative to solenoid means (not shown) is positioned so as to enable meshing with a ratchet tooth 11a of the ratchet wheel 11. Reference numeral 30 designates a limiter member for the ratchet pawl 12. Thus, the interlock means includes the gear assembly 11, the pawl 12 and the solenoid which is well known in the art, and so the description of the structure thereof may be omitted. Reference numerals 13 and 14 denote stationary abutment portions suitably formed in the printer body frame for the levers 3 and 4 as shown in FIGS. 2 and 3, respectively. Reference numeral 15 denotes an ink roller which at all times abuts against an outer surface of the printing drum so as to feed the helically arranged projections 1a&#39; on the strip 1a with ink. 
     A paper feeding mechanism for feeding papers on which letters or figures are printed will now be described. The above described paper feeding lever 5 having a circular portion 5d is rotatably mounted on a rotary shaft 17 supported by the printer body frame and arranged parallel to the drum shaft 2, and a ratchet tooth 5b is formed on one side of the circular portion 5d of the lever 5. The ratchet tooth 5b, as shown in FIG. 1, meshes with a ratchet tooth 18a of a ratchet wheel 18 secured to the rotary shaft 17 which is rotatable but not movable with respect to the printer frame, so that one-directional clutch means may be formed by the engagement between the ratchet wheel 18 and the lever 5. A paper feeding roller 19 made of soft elastic material is fixed to the rotary shaft 17, and a printing paper 16 is frictionally engaged with the outer surface of the roller 19. Accordingly, as the roller 19 rotates, the printing paper is fed at a predetermined speed, and it is natural that the roller 19 be positioned on the confronting side to the printing drum. 
     On the other hand, a projection 5c is formed on peripheral surface of the paper feeding lever 5, and a leaf spring 20 is in abutment with the projection 5c of the paper feeding lever 5. With the spring force of the leaf spring 20, the lever 5 is biased to rotate around the shaft 17 counterclockwise (in FIG. 2), and also the levers 3 and 4 are biased to move obliquely upward (in FIG. 2) around the shaft 6 through the extension 5a, cam surface 1d&#39; and the shaft 2, while the link members 3 and 4 are stopping in abutment with the abutment portions 13 (in FIG. 2) and 14 (in FIG. 3), respectively. 
     The switch piece 21 is arranged to face the leaf spring 20, and a signal which is generated when the switch strip 21 is separated from the leaf spring 20 may be used as a starting position determining signal by which the printer is operated. 
     The operation of the apparatus thus constructed will now be described. When the motor M is driven, with the rotational force thereof the printing drum 1 is rotated in the A-direction as shown in FIGS. 2 and 3, and simultaneously therewith the cam member 1d is also rotated in the A-direction. With the rotation of the cam member 1d, the extension 5a is rotated along the cam surface 1d&#39; so that the lever 5 is rotated in the B&#39;-direction (in FIG. 2) overcoming the spring force of the leaf spring 20, and the paper feeding roller 19 is rotated in the B-direction through the engagement of the ratchet teeth 5b and 18a. When the roller 19 is rotated in the B-direction, the printing paper 16 is continuously fed in the C-direction at a constant speed. After the cam member 1d has been rotated by one revolution, the paper is fed a length as shown in FIG. 4. 
     When the printing drum is rotated to a position where the printing is to be performed, the pawl 12 is rotated in the D&#39;-direction (in FIG. 3) by the solenoid (not shown), to engage the pawl 12 with the ratchet tooth 11a and to prevent the gear unit 11 from rotating in the D-direction. At this time, since the gear wheel 1c of the drum 1 is engaged with the gear wheel 11b of the gear unit 11, the rotation of the gear wheel 1c is prevented but the ratchet teeth 11a of the gear unit 11 ride over the tip end of the pawl. That is, the link members 3 and 4 are rotated in the printing paper 16 direction, i.e., in the E-direction around the shaft 6, and with this rotational force, one of the projections 1a&#39; of the printing drum 1 abuts against the printing paper 16 interposed between the printing drum 1 and the roller 19 to thereby achieve the suitable printing job. This operation is repeated. When the printing is finished, the biasing energy of the solenoid is released, the pawl 12 escapes out of the ratchet tooth 11a, and the printing drum 1 returns to the original position. 
     Thus, during one rotation of the printing drum 1, a first line 16a is printed as shown in FIG. 4. In this case, the printing paper is continuously provided so that the first line 16a is slanted by a difference a from the beginning to the end. This slant is negligible in actual use. 
     When the printing drum 1 is rotated once, the extension 5a is pushed into the shouldered portion 1d&#34; of the cam surface 1d&#39; and the engagement between the ratchet teeth 5b and 18a is displaced by one step, and then the second line 16b printing will start. When the extension 5a is retracted in the shouldered portion 1d&#34;, the leaf spring 20 is separated from the switching piece 21 to thereby produce a signal which may be used for starting position determining signal. 
     Thus, in the specific embodiment, the printing drum 1 is rotated seven times whereby the printing from the lines 16a to 16g is achieved. This continuous operation thereby produces a complete one line in actual use. 
     FIG. 5 shows another embodiment according to the present invention, in which the skeletonized printing drum 1&#39; per se is formed in a helical manner. The minimal supporting structure is only required. By use of this form of the printing drum, the weight of the printing drum is effectively decreased to thereby lower the inertia force, leading to an improvement of the responsiveness. 
     It will be understood that instead of the projection 1a&#39;, a letter or a figure may be directly formed as a projection. Also, the above described interlock means may be applied to the right side transmission gear 7. 
     In a general manner while the present invention is described on the basis of practical and efficient embodiments, it is not limited thereto as there might be changes or modifications made in the arrangement, disposition and form of the parts without departing from the principle of the invention as comprehended within the scope of the appended claims.