Abstract:
A device for controlling the head pressure in a miniature printer is disclosed. A pair of hinge parts with an elongate shaft retaining slot in each of them are installed on the bottom of the head frame so as for a printer head to be closely contacted to the surface of a platen roller. Elastic members are fixed to the head frame, and a supporting bracket is installed in rear of the head frame across the elastic members so as to be pivoted together with the head frame, so that a stable running of the printer paper is ensured, and that the printing state is made clear. A shaft passes through the shaft retaining elongate slots, and thus, the head frame and a supporting bracket are secured on a base plate. A locking piece is installed in contact with the supporting bracket.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a miniature printer used in a cash register or the like. Particularly the present invention relates to a device for controlling the head pressure in a miniature printer, in which a pair of hinge parts with an elongate shaft retaining slot in each of them are formed on the bottom of a head frame so as for a printer head to be closely contacted to the surface of a platen roller. Elastic members are fixed to the head frame, and a supporting bracket is installed in rear of the head frame across the elastic members so as to be pivoted together with the head frame, so that a stable running of the printer paper is ensured, and the printing state is made clear. 
     2. Description of the Prior Art 
     In the generally known miniature printers used in a cash register or the like, as shown in FIG. 1, a printer head  10  is integrally formed with a head frame  12 , and at the rear of the head frame  12 , there is installed a supporting bracket  16  to be elastically supported by springs, so that the head frame  12  and the supporting bracket  16  would be elastically supported. A pair of hinge parts  18  are formed on the bottom of the head frame  12  and the supporting bracket  16 . 
     Further, a shaft  22  is formed upon a base plate  20 , and a locking piece  28  is pivotally installed on the rear face of the supporting bracket  16 . When the lower end of the locking piece  28  contacts a projected step  24 , the printer head  10  contacts a platen roller  26 . 
     In the above described printer, the head frame  12  together with the printer head  10  is pivoted forward by a certain angle to be contacted to the platen roller  26  (the printing paper passes by the roller  26 ), thereby carrying out the printing. In this case, springs  14  are installed to the rear face of the head frame  12 , and thus the supporting bracket  16  pivots together with the head frame  12 . Thus if the locking piece  28  is turned downward, the supporting bracket  16  pivots around the shaft  22 . Under this condition, the head frame  12  together with the printer head  10  pivots forward to make the printer head  10  contact the platen roller  26 , and therefore, a printing operation is carried out on the paper which passes through the platen roller  26 . 
     However, in the above described printer, the head frame  12  is pivoted in accordance with the pivoting of the locking piece  28 . Therefore, when a contacting force acts on the platen roller  26 , a part of the printer head  10  closely contacts with the platen roller  26  owing to the incoming paper, while gaps remain at either of the end portions of the printer head  10 . Due to these gaps between the printer head  10  and the platen roller  26 , a clear printing cannot be realized. 
     A printer related to this technique is disclosed in Japanese Patent Application Laid-open No. Hei-7-25084. 
     This printer is illustrated in FIG.  2 . As shown in this drawing, springs  52  are secured to the rear face of a head frame  50 , and a printer head  54  is supported by the springs  52 . A platen rubber member  64  is supported by a shaft  58  which is secured on a base frame  56 . Inside the platen rubber member  64 , there are installed a main platen supporting member  62  and an auxiliary platen supporting member  60 , so that the platen rubber member  64  can be closely contacted to the shaft  58 . Further, the platen supporting members  60  and  62  respectively have contacting parts  66 ′ and  66 . A printing paper roll  68  is disposed on a side of the base frame  56 . 
     In the above described printer, when the printer head  54 , which is elastically supported by the springs  52  of the head frame  50 , is contacted to the platen rubber member  64 , the platen rubber member  64  contacts both of the contacting parts  66 ′ and  66 , and therefore, a stable position is maintained all the time. The contacting parts  66  and  66 ′ which are formed respectively within the platen supporting members  60  and  62  contact with the shaft  58  so as to be rotated together with the shaft  58 . Accordingly the printer head  54  stably contacts with the platen rubber member  64 , thereby carrying out a printing on the paper of the paper roll  68 . 
     However, the printer head  54  which closely contacts with the platen rubber member  64  always contacts with a side of the base frame  56 . Therefore, if the platen supporting members  60  and  62  are damaged, then a part of the printer head  54  contacts with the platen rubber member  64 , while a gap is formed between the other ends of the printer head  54  and the platen rubber member  64 . At this situation, the adjustment of the gap is very difficult, and therefore, the printing quality is aggravated, or the paper is ejected in a skew posture, or the paper may be jammed. 
     SUMMARY OF THE INVENTION 
     The present invention is intended to overcome the above described disadvantages of the conventional techniques. 
     Therefore it is an object of the present invention to provide a device for controlling the head pressure in a miniature printer, in which a gap between a printer head and a platen roller is compensated by elongate slots of hinge parts, so that the contact between the platen roller and the printer head is improved, that a clear printing can be maintained, that a paper jam can be prevented to avoid the damage of the head, and that a running stability can be ensured to extend the life expectancy of the printer. 
     In achieving the above object, the device for controlling a head pressure in a miniature printer according to the present invention includes: a printer head installed on front of a head frame; a platen roller for carrying a printing paper in contact with the printer head; a supporting bracket connected through elastic members to the rear face of the head frame; a frame pivoting part with the head frame and the supporting bracket pivotally connected thereto; a frame supporting part installed on the head frame, for preventing a biasing of the frame pivoting part; a frame degapping part formed on the frame pivoting part, for making both ends of the head frame degapped; and a locking piece for preventing the pivoting of the supporting bracket back and forth. 
     In another aspect of the present invention, the device for controlling a head pressure in a miniature printer according to the present invention includes: a printer head installed on front of a head frame; a platen roller for carrying a printing paper in contact with the printer head; a supporting bracket connected through elastic members to the rear face of the head frame; a frame pivoting part with the head frame and the supporting bracket pivotally connected thereto; a frame supporting part installed on the head frame, for preventing a biasing of the frame pivoting part; a frame degapping part formed on the frame pivoting part, for making both ends of the head frame degapped; a locking piece for preventing the pivoting of the supporting bracket back and forth; a frame connecting part for connecting the supporting bracket to the head frame; and a bracket pivoting part for allowing the supporting bracket to move back and forth. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above object and other advantages of the present invention will become more apparent by describing in detail the preferred embodiment of the present invention with reference to the attached drawings in which: 
     FIG. 1 (consisting of FIGS. 1A and 1B) schematically illustrates the critical portion of the general miniature printer; 
     FIG. 2 is a sectional view showing a conventional miniature printer; 
     FIG. 3 (consisting of FIGS. 3A,  3 B and  3 C) illustrates the miniature printer according to the present invention, in which a printer head, a head frame, a supporting bracket and a hinge part are included; 
     FIG. 4 illustrates the coupling of the supporting bracket to the head frame according to the present invention; 
     FIG. 5 (consisting of FIGS. 5A and 5B) is a sectional view showing the securing state of the shaft of the supporting bracket; 
     FIG. 6 (consisting of FIGS. 6A and 6B) is an exploded view showing the securing state of the locking piece for locking the supporting bracket in a second embodiment of the present invention; and 
     FIGS. 7A and 7B are sectional views showing the coupling between the head frame and the supporting bracket in the second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 3 illustrates the miniature printer according to the present invention, in which a printer head, a head frame, a supporting bracket and a hinge part are included. FIG. 4 illustrates the coupling of the supporting bracket to the head frame according to the present invention. FIG. 5 is a sectional view showing the securing state of the shaft of the supporting bracket. As shown in these drawings, elastic members  130  are installed on the rear side of a head frame  120  with a printer head  110  fixed thereto, so that the printer head  110  can be contacted to a platen roller  190 . The other ends of the elastic members  130  contact with the front face of a supporting bracket  200 , so that the supporting bracket  200  can be pivoted together with the head frame  120 . 
     A frame pivoting part  300  is formed under the head frame  120  and the supporting bracket  200 , so that the frame pivoting part  300  can be pivoted together with the head frame  120  and the supporting bracket  200 . The frame pivoting part  300  includes hinge parts  140  and  140 ′ to secure the bottoms of the head frame  120  and the supporting bracket  200 . A shaft  160  passes through the hinge parts  140  and  140 ′, and is secured on a base plate  210 . 
     A frame supporting part  310  is formed at an intermediate point of the head frame  120 , for preventing the same direction movement of the both ends of the head frame  120 . In this frame supporting part  310 , an integral securing piece  260  protrudes from the bottom of the head frame  120 , and the shaft  160  is inserted into a through hole  240  of the securing piece  260 . That is, the securing piece  260  has the through hole  240  and a sloped part  250 , so that the head frame  120  can be moved in both directions. 
     A frame degapping part (device)  320  is provided to enable both ends of the head frame  120  to move in opposite directions while being secured to the shaft  160  by the securing piece  260 . Such movement is permitted by reason of the hinge parts  140  and  140 ′ respectively having elongate slots through which the shaft  160  extends. 
     A locking piece  150  is installed to prevent the back-and-forth movements of the supporting bracket  200  when the supporting bracket  200  contacts with the base plate  210 . 
     FIG. 6 is an exploded view showing the securing state of the locking piece  150  for locking the supporting bracket  200  in a second embodiment of the present invention. FIGS. 7A and 7B are sectional views showing the coupling between the head frame  120  and the supporting bracket  200  in the second embodiment of the present invention. Referring to these drawings, a plurality of elastic members  130  consisting of compression coil springs are installed between the supporting bracket  200  and the head frame  120 . The head frame  120  is attached to a printer head  110 , in such a manner that the printer head  110  contacts with the platen roller  190 . 
     A frame pivoting part  300  which is formed beneath the head frame  120  and the supporting bracket  200  has hinge parts  140  and  140 ′ to elastically support the head frame  120  and the supporting bracket  200 . A shaft  160  passes through the hinge parts  140  and  140 ′ to be secured on the base plate  210 . 
     A frame supporting part  310  is formed at an intermediate point of the head frame  120 , for preventing the same direction movement of the both ends of the head frame  120 . In this frame supporting part  310 , an integral securing piece  260  protrudes from the bottom of the head frame  120 , and the shaft  160  is inserted into a through hole  240  of the securing piece  260 . That is, the securing piece  260  has the through hole  240  and a sloped part  250 , so that the head frame  120  can be moved in both directions. 
     A frame degapping part (device)  320  is provided to enable both ends of the head frame  120  to move in opposite directions while being secured to the shaft  160  by the securing piece  260 . Such movement is permitted by reason of the hinge parts  140  and  140 ′ respectively having elongate slots through which the shaft  160  extends. 
     A locking piece  150  is installed to prevent the back-and-forth movements of the supporting bracket  200  when the supporting bracket  200  contacts with the base plate  210 . 
     A frame connecting part  330  is installed at the rear of the head frame  120 , so that the supporting bracket  200  connected through the elastic members  130  to the head frame  120  can be unitizingly pivoted. The frame connecting part  330  includes a supporting bar  220  which is protrudently installed at the rear of the head frame  120 . 
     A bracket pivoting part (device) is provided to permit up and down movement of the supporting bar  220  which extends rearwardly from the head frame  120  and through the supporting bar  220 . The bracket pivoting part  340  includes an elongate vertical slot  230  in the supporting bar  220  and in which the supporting bar  220  can move up and down. 
     The device of the present invention constituted as above will now be described as to its actuation. 
     As shown in FIGS. 3 to  5 , the printer head  110 , which is unitizingly attached to the head frame  120  of the miniature printer (which is used in a cash register or the like), is made to contact with the platen roller  190 . Then a printing paper is fed into between the platen roller  190  and the printer head  110 , and at the same time, the platen roller  190  is rotated, thereby carrying out a printing. 
     A plurality of elastic members  130  consisting of compression springs are disposed between the head frame  120  and the supporting bracket  200 , in such a manner that there should be maintained a certain distance between the head frame  120  and the supporting bracket  200 . The locking piece  150  which is pivotally installed on the rear face of the supporting bracket  200  is made to pivot, so that the supporting bracket  200  would be pivoted, and that the printer head  110  would contact with the platen roller  190 . 
     The head frame  120  together with the supporting bracket  200  is connected through the integral hinge parts  140  and  140 ′ to the shaft  160  which is secured upon the base plate  210 . 
     Thus, the head frame  120  together with the supporting bracket  200  is pivoted around the shaft  160 . That is, the head frame  120  together with the supporting bracket  200  pivots forward so as for the printer head  110  to be contacted with the platen roller  190 , thereby making it possible to carry out a printing. 
     Under this condition, the securing piece  260  which is formed at an intermediate position between the hinge parts  140  and  140 ′ receives the shaft  160  to be supported by the securing piece  260 , while each of the hinge parts  140  and  140 ′ has an elongate slot  180  to loosely retain the shaft  160 . Thus, the central portion of the head frame  120  is secured by the securing piece  260 , while the both end portions of the head frame  120  can move in the opposite directions as much as the elongate slots  180  permit. Thus, when the both end portions of the head frame  120  move, the both end portions of the head frame  120  move in the opposite directions to each other. 
     Thus, the head frame  120  and the supporting bracket  200  can be pivoted forward by a certain angular degrees around the shaft  160  and the hinge parts  140  and  140 ′ upon pivoting the locking piece  150  downward (the locking piece  150  being positioned at the center of the supporting bracket  200 ). Consequently, the printer head  110  which is unitizingly coupled to the head frame  120  is contacted to the platen roller  190 . 
     Under this condition, each of the elongate slots  180  of the hinge parts  140  and  140 ′ either has an arcuate shape correspondingly with the track of the pivoting of the head frame  120  for making the printer head  110  contact with the platen roller  190 , or has a straight horizontal elongate form so as for the head frame move back or forth when the printer head  110  contacts the platen roller  190 . 
     Therefore, even if there occurs a gap between the printer head  110  and the platen roller  190 , the both end portions of the head frame  120  are slightly pulled or pushed in the opposite directions owing to the elongate slots  180  by being secured by the securing piece  260 . Therefore, the printer head  110  can be made to be perfectly contacted to the platen roller  190  without any partial gaps. 
     Further, the securing piece  260  which is formed between the hinge parts  140  and  140 ′ is positioned at the center of the head frame  120 , so that the load of the head frame  120  at the both sides of the securing piece  260  would be equal to each other. The securing piece  260  has a through hole  240  to receive the shaft  160 , and this securing piece  260  is for preventing the both end portions of the head frame  120  from moving in the same direction. 
     Further, the through hole  240  of the securing piece  260  together with the shaft  160  fixes the center of the head frame  120 , while only the both end portions of the head frame  120  can freely move in the opposite directions as much as the elongate slots  180  permit. As a result, the printer head  110  perfectly contacts to the platen roller  190  without leaving any gap. 
     Further, the elongate slots  180  which are respectively formed in the hinge parts  140  and  140 ′ and which are for receiving the shaft  160  may have a horizontally elongate shape, and thus, the both end portions of the head frame  120  can move straightly in the opposite directions when the supporting bracket  200  closely contact owing to the locking piece  150 . Alternatively, the elongate slots  180  may have an arcuate shape, so that the both end portions of the head frame  120  can move along an arcuate track in the opposite directions. 
     Meanwhile, as shown in FIGS. 6 and 7, the head frame  120  is installed through the shaft  160  fixed to the base plate  210 , and thus, the printer head  110  which is unitizingly coupled to the head frame  120  is made to contact with the platen roller  190 . 
     Further, the supporting bracket  200  is coupled through a plurality of elastic members  130  to the head frame  120 , and the hinge parts  140  and  140 ′ are secured through the shaft  160  to the base plate  210 , thereby unitizingly coupling the supporting bracket  200  to the head frame  120 . 
     Here, if the locking piece  150  which is secured to the rear face of the supporting bracket  200  is turned to be fixed to the stepped portion of the base plate  210 , the supporting bracket  200  exerts an elastic force to the head frame  120  through the elastic members  130 . 
     Further, one end portion of a supporting bar  220  is inserted into one of the elastic members  130 , and the other end portion of the supporting bar  220  is inserted into the vertical elongate guide slot  230  which is formed in the supporting bracket  200 . Thus when the supporting bar  220  is secured by the locking piece  150 , the elastic members  130  stably exert elastic forces to both the head frame  120  and the supporting bracket  200 . 
     Thus the supporting bar  220  is inserted into the guide slot  230  of the supporting bracket  200  to be mated with the locking piece  150 , so that the head frame  120  together with the supporting bracket  200  is elastically supported, and that the head frame together with the supporting bracket  200  can be pivoted. Therefore, any gap between the printer head  110  and the platen roller  190  is eliminated owing to the compression between the head frame  120  and the supporting bracket  200 , and owing to the pivotal or straight movements of the head frame  120  together with the supporting bracket  200 . That is the elimination of the gaps owes to the existence of the elongate vertical guide slot  230  and the elongate horizontal slots  180 , thereby improving the contact between the printer head  110  and the platen roller  190 . (Conventionally, the supporting bracket  200  is fixed, and only the head frame  120  moves.) 
     When the leading end of the supporting bar  220  of the head frame  120  is inserted into the guide slot  230 , the side areas of the supporting bar  220  contact with the inside of the guide slot  230 , so that the vertical movements of the both end portions of the head frame  120  can be prevented. 
     As shown in FIG. 7A, the supporting bar  220  which protrudes from the head frame  120  has a straight form, and when the supporting bar  220  is inserted into the guide slot  230 , the supporting bar  220  is secured by the locking piece  150 . 
     If a gap is formed between the platen roller  190  and the printer head  110 , the supporting bar  220  of the head frame  120  advances backward to be freely moved up or down within the guide slot  230 . In this manner, the contact between the platen roller  190  and the printer head  110  is improved. 
     Under this condition, when the locking piece  150  which secures the supporting bar  220  moves so as to move the supporting bar  220  up, the locking piece  150  is stopped by a protuberance  290 . 
     Alternatively, as shown in FIG. 7B, the supporting bar  220  may have an arcuate form, and thus, when the arcuate supporting bar  220  is inserted into the guide slot  230 , the locking piece  150  can maintain almost the same vertical position, and the sliding of the supporting bar  220  within the guide slot  230  can be minimized. 
     The supporting bracket  200  may be formed in an arcuate shape same as the track which it draws when moving. Under this condition, when the head frame  120  together with the supporting bracket  200  pivots around the shaft  160 , the head frame  120  and the supporting bracket  200  draw the same arcuate track. Therefore, the locking piece  150  which contacts with the rear face of the supporting bracket  200  generates minimal frictions, when the head frame  120  and the supporting bracket  200  move. 
     If a gap occurs between the platen roller  190  and the printer head  110 , the supporting bar  220  (with its leading end secured to the locking piece  150 ) freely moves, so that the gap between the platen roller  190  and the printer head  110  would be eliminated. If the head frame  120  moves back, the supporting bracket  200  also moves up or down in contact with the locking piece  150 , and therefore, the contact between the platen roller  190  and the printer head  110  is improved. 
     Further, When the supporting bar  220  is pushed backward, the head frame  120  also easily moves back. Further, the supporting bracket  200  also moves up or down, so that the contact between the printer head  110  and the platen roller  190  can be improved, thereby making it possible to carry out a clear printing. 
     According to the present invention as described above, when the locking piece is pivoted, the gap between the platen roller and the printer head is eliminated owing to the existence of the horizontal elongate slots which loosely retain the shaft, thereby improving the contact between the platen roller and the printer head. Thus a clear printing quality can be maintained, and jamming of the paper can be prevented, with the result that the damage of the printer head due to the jamming can be prevented. 
     In the above, the present invention was described based on the specific embodiments and the drawings, but it should be apparent to those ordinarily skilled in the art that various changes and modifications can be added without departing from the spirit and scope of the present invention.