Abstract:
In a serial printer, a thermal printing head is mounted on a printing head holder which in turn is mounted for movement across the width of the paper and wherein a spring force is utilized to press the printing head onto the paper; a lever mounted on a lever pin is connnected to the printing head and the lever cooperates with two cam elements and a cam surface located at selected points of travel of the printing head whereby the printing head will be removed from or engaged with the paper when it reaches a limit of travel and will remain out of contact with the paper while the paper is advanced to the next printing position.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a small size serial printer for use, for example, small calculator, measuring equipment or electronic translator of pocket size. 
     2. Description of the Prior Art 
     Recently, electronic apparatuses provided with printer, for example printer-equipped pocket size calculators, become smaller and smaller. For such small sized electronics apparatuses with printers, there are strong demands to decrease the size of the printer and to decrease the size and power of the power sources. Furthermore, in order to decrease price of the printers, simplicity of the structure and decrease of number of components are also required. 
     For the abovementioned printers, serial printers of thermal printing type or discharge printing type have been widely used. In such serial printers, printing head is pressed on a recording paper by means of a spring pressure and the head is driven to sweep widthwide of the oblong recording paper for printing, and then at a completion of one line printing the paper is driven or transferred lengthwise. In order to reduce the friction force against the transferring of the paper, it has been general to carry out to remove the printing head away from the paper face. However, for the small sized electronic apparatus, the problem is that the load of transferring the paper and the load of moving away of the head are simultaneously impressed on a small motor, and therefore an extremely small motor can not be used. Furthermore, the conventional apparatus has comprised a considerable number of mechanical components thereby hampering decreasing of the size and thickness of the printer. 
     SUMMARY OF THE INVENTION 
     The present invention proposes to provide a small size serial printer for pocket type apparatuses which can be operated with a smaller power and constructed by less number of components. 
    
    
     BRIEF EXPLANATION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a serial printer embodying the present invention. 
     FIG. 2 is a sectional view of the front part taken at the center part of the head holder 7. 
     FIG. 3 is a unfolded view of a flat cable 11 to be connected to a printing head and other components. 
     FIG. 4 is a view of the flat cable 11 in a folded shape for connection in the apparatus. 
     FIG. 5 is an exploded perspective view of a pulse generator 14. 
     FIG. 6 is a perspective view of a coil 19 and a coil bobbin 18 of the pulse generator 14 of FIG. 5. 
     FIG. 7 and FIG. 8 are fragmental sectional views of the pulse generator 14 for explaining operation thereof. 
     FIG. 9 is a sectional side view of a worm wheel 21 and a snail cam 22 and a cam gear 23. 
     FIG. 10 is a timing phase chart showing relation between rotation of a worm wheel 21, motion of a paper driving roller 25, operation of a printing head 9, motion of a lever pin 33a, spring 32 and other related components. 
     FIG. 11 and FIG. 12 are perspective views of paper guiding plates 28 and related parts of frames 29 of other examples than FIG. 1. 
     FIG. 13(a) is a schematical plan view of a head holder 7, a printing head 9, the lever pin 33, cams 29d and 29e and related parts for explaining motion of the lever pin 33 and the head holder 7. 
     FIG. 13(b) is a schematical elevation view of the parts shown in FIG. 13(a). 
     FIG. 13(c) is a perspective view of the head holder 7 and related part. 
     FIG. 14 is a plan view showing a paper pad 36 and a paper pad base 37. 
     FIG. 15 is an exploded perspective view showing the paper pad 36, the paper pad base 37, related part of the frame 29 and related components thereto. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is elucidated hereinafter in detail referring to the accompanying drawings which show preferred example embodying the present invention. 
     (1) General configuration 
     FIG. 1 which shows overall configuration of the example, a box-like frame 29 comprises therein an electric motor 1, a synchronizing pulse generator 14, a head holder 7 having a head 9 thereon, a head holder driving shaft 5 and a paper driving roller 25. Revolving power of the motor 1 is transmitted through a motor shaft 1a, a pinion 2 fixed on the motor shaft 1a and an idler gear 3, to the driving shaft gear 4 which is fixed on the driving shaft 5. The driving shaft 5 has a loopcoiled groove 6 which comprises two oppositely coiled grooves end parts of which are connected with a smoothly curved groove thereby forming a groove of a twisted closed loop. A slider 8 (in FIG. 2) having a sliding edge 81 of a predetermined length is provided in a manner that the sliding edge 81 slides along in the groove 6 thereby tracing the closed loop groove 6 and hence driving the slider 8 reciprocatingly in the directions of arrows H 1  and H 2  along the driving shaft 5, as the driving shaft 5 is continuously turned by meamns of the gear 4. The slider 8 is mounted on the head holder 7, and the head holder 7 is slidably held by a sliding guide rod 34, and hence it is reciprocatingly driven along the sliding guide rod 34 by the rotation of the driving shaft 5. The printing head 9 prints numerals or characters on a recording paper 12 backed by a pad 36, so that the user can observe the printed characters from the direction Z. 
     As shown in FIG. 2, the printing head 9 has a number of heating elements 10 disposed in vertical line on its front face and the heating elements are selectively heated by currents supplied through a flat cable 11. The flat cable 11 are constructed in split type flat cable as shown in FIG. 3 and is put with their faces parallel to each other as shown in FIG. 4 and FIG. 1 in order to decrease width thereof. One end of the double flat cable is connected to the terminal leads 13 of the head 9 and a suitable part thereof is fixed on the rear end face of the motor 1 keeping a sufficient length of the cable therebetween in order to allow easy movement of the head 9 along the driving shaft 5. By adoption of the abovementioned parallel-disposed double flat cable, the width of the cable can be halved to about 4 mm from the conventional case using a single link flat cable. 
     (2) The pulse generator 14 
     The pulse generator 14 disposed at the back of the motor 1 is constituted as illustrated in FIG. 5, wherein a permanent magnet 15 is mounted on the rear end of the motor shaft 1a. The permanent magnet 15 has several poles disposed around its cylindrical face. Central part of a U-shaped yoke 16 and an end plate 17 to be connected to the end part of the yoke 16 have several pole pieces 16a and 17a provided by bending strip shaped torn parts of the yoke 16 and the plate 17, respectively. A bobbin 18 having a coil 19 is disposed in the space formed by the U-shaped yoke 16 and the end plate 17, and the pole pieces 16a and 17a are inserted in a through hole 18 of the bobbin 18. The pole pieces 16a and 17a are provided in a manner that when one kind poles of the permanent magnet 15 faces the pole piece 16a then the opposite kind poles of the permanent magnet 15 faces the other pole pieces 17a. The bobbin 18 has engaging projections 18a (in FIG. 6) which engage around the bearing 1b of the motor 1, and fixing tabs 1c are received in the holes of the bobbin 18 and calked thereon thereby to fix the yoke 16, the bobbin 18 and the end plate 17 to the motor 1 in an accurate coaxial relation to each other. 
     (3) Operation of the pulse generator 14 
     When the pole pieces 16a face N-poles of the permanent magnet 15, then the pole pieces 17a face S poles. Therefore, the magnetic flux flows from N-poles, through the pole pieces 16a, the yoke 16, the end plate 17 and the pole pieces 17a to the S-poles as shown by FIG. 7. As the motor 1 rotates the relation between the pole pieces 16a and 17a and magnetic poles are reversed as shown by FIG. 8, and in this period the magnetic flux decreases and become inversed. As a result of repetition of such rotation, an alternate current is induced at the terminal 19a of the coil 19, and the frequency of the alternate current is in synchronous with the revolution of the motor 1. Since the head holder 7 is driven reciprocally by the rotation of the motor 1 and the rotation of the same motor 1 make the pulse generator 14 issue pulse, the output pulse of the pulse generator 14 is in synchronous with the reciprocating motion of the head 9. 
     (4) Paper driving part 21-30: 
     The paper driving part comprises the components 21-30. A flat worm gear 20 is mounted on a part of the driving shaft 5, and a worm wheel 21 engages with the worm gear 20. The worm wheel 21 has on its lower face a snail-cam projection, namely a snail cam 22. A cam gear 23 mounted on a paper driving shaft 24 is disposed to engage the snail cam 22. The driving shaft 24 has a rubber roller 25. A guide plate 28 is hinge-held by a pin 28a which is fixed on the lower part of the frame 29, and held upwards by means of open-ends of a wire spring 26 which open ends disposed under the guide plate 28 push the bottom part thereof upwards. The guide plate 28 has receiving tabs 30 at the lower center part thereof, and the receiving tabs 30 receive a pinch roller 27 which contacts the lower part of the rubber roller 25, so that a recording paper is inserted inbetween and driven by the rubber roller 25 as its shaft 24 is driven by means of rotation of the cam gear 23. 
     (5) Operation of the paper driving part 
     When the motor rotates, the head 9 reciprocatingly moves in the directions shown by the arrows H 1  and H 2  by means of rotation of the driving shaft 5, and at the same time, the worm wheel 21 is driven by the rotation of the worm gear 20. Thereby, the snail cam 22 under the worm wheel 21 intermittently drives the gear cam 23. The gear ratio of the worm gear 20 and the worm wheel 21 is selected in such a manner that the worm wheel 21 turns for 360° during the period while the head holder 7 makes one period of reciprocating motion along the sliding guide rod 34. The motion of the cam gear 23 is limited only to the period of during 180° turning of the worm wheel 21, by means of the pattern of the snail cam 22, since the snail cam changes its radial displacement for the 180° turning only. In order to smoothly turn the cam gear 23 without backlash, the snail cam 22 is designed so as to have taller height h at the outer part than the inside part as shown in FIG. 9. The paper driving, the motion of the printing head and other related motions of the serial printer in relation to the angular position of the engaging of the snail cam 22 and the cam gear 23 is schematically shown in FIG. 10, wherein in the one cycle period of the reciprocating motion of the head 9, i.e. on cycle period of the worm wheel 21, a period p 1  to p 2  of about 120° of one turn is used for gradual driving of paper by driving the rubber roller 25 for shifting line of printing on the paper, and for the balance of the period, namely p 2  to p 1 , the paper is not driven wherein printing is made in a period of p 6  to p 7 . 
     FIG. 11 and FIG. 12 show other examples of the spring 26 to push the guide plate 28 upwards. In FIG. 11, the spring 26 is held by the pin 28a and a pin 28b, and in FIG. 12, the spring 26 is held by a hole 28c and pins 31. 
     (6) Head spring controlling device 29e, 29d, 32, 33 7a: 
     One of the important feature of the present invention lies in the novel structure of the head spring controlling device shown in FIG. 2 and in FIGS. 13(a), 13(b) and 13(c), which comprises head spring 32, a lever pin 33 comprising wings 33a and 33b and a pin 33c with the head spring 32 around it, and a lever catching recess 7a in the head holder 7 and further comprises projections 29d and 29e (FIG. 13(b)) disposed at both end parts of the moving range of the head holder 7. The head spring 32 is to give a force to press the pin lever 33 against a wall 29b in the frame 29, so as to give abutting force to the head holder 7 held on the sliding guide rod 34 towards a paper 12 (shown in FIG. 2). The paper 12 is led from the lower opening 29g, pinched between the rubber roller 25 and the metal pinch roller 27, led upwards, and is supported at its rear face by a pad 36 of rubber or the like elastic material. By means of the spring force, the head 9 is pressed to the paper 12, so that known small heaters vertically disposed on the head 9 are pressed on the paper face with an appropriate pressure. The lever 33b of the lever pin 33 has a knife-edge-like sloped or tapered face 33s, (FIGS. 13(b) and 13(c)) in order that the lever 33b can easily enter the slot 7a in the head holder 7 when slightly pushed towards the tip of the pin 33c and at the same time the lever 33a is pushed. On the wall 29b, at both end parts of the moving stroke of the head holder 9, a first projection 29d and a second projection 29e are provided, and near the first projection a tapered wall part 29c is also provided. 
     (7) Operation of the head spring controlling device: 
     When the head holder 7 travels in the direction shown by an arrow H 1 , the center projection 33d of the lever pin 33 slides on the sloped part 29c passing the position A, and hence the lever pin 33 is slightly pushed into the head holder 7, so that the lever pin 33b is pushed to the position easily to enter the slot 7a. And then, when the center of the lever pin 33 comes to the position B the lever 33a touches the first projection 29d, and therefore is turned clockwise as shown in FIG. 13(b), accordingly, the lever pin 33b enters in the slot 7a and retained there. Then the head-holder 7 travels back to the direction shown by the arrow H 2 . In almost all of this travelling in the H 2  direction, the lever 33b is retained engaging in the slot 7a, and therefore the spring 32 is clamped, and the spring force is deenergized or intercepted from pressing the head 9 on the recording paper. Accordingly, during the travelling in the H 2  direction, the head 9 is released from pressing to the paper 12. When the center of the lever pin 33 comes to the position C, then the lever 33a touches the projection 29e and hence the lever pin 33 turns counterclockwise as shown in FIG. 13(b), thereby releasing the lever 33s from the slot 7a and restores the lever pin 33 to press the wall 29b by its center projection 33d. Therefore, the spring 32 becomes in the state of pressing the paper by the head 9. Then, the head holder 7 reverses its direction of travelling to H 1  and travels to the position A and further to the position B. In this travelling in H 1  direction the spring 32 performs to press the head 9 to the recording paper 12. 
     (8) Relative operation of the worm wheel 21, paper driving roller 25 and the head spring controlling apparatus 
     The relative operation of the engagement position between the snail cam 22 of the worm wheel 21, paper driving roller 25 and the apparatus to control the head spring 32 is elucidated referring to the phase chart schematically illustrating the phase or timing of the operations thereof as shown in FIG. 10. 
     The apparatus is resting in the phase p 3  where the lever 33b is clamped in the slot 7a thereby preventing pressing of paper 12 by the head 9. When a signal ordering the printer is input, the motor 1 starts rotation from the resting phase p 3  which corresponds slightly before the position C. And after the head holder 7 slightly travels in H 2  direction, the clamping of the lever 33b in the slot is released at the phase of p 4  and the head 7 restores to press the paper 12 and the limit switch 35 is actuated. Immediately thereafter, and the head holder 7 comes to the position C, where the travel direction is reversed at the phase p 5  to the H 1  direction. By the actuation of the limit switch 35, a pulse signal from the pulse generator 14 is led to a control circuit, and at the phase p 6  when a predetermined number of pulses are sent to the circuit, and where the head 9 is slightly apart from the position C, the printing head 9 starts printing and the printing process continues to the phase of p 7 . At the phase p 7 , where the lever pin 33 comes to the position A, the printing stops and the clamping of the spring 32 starts. Then at the phase p 1 , which corresponds to the position B where the spring is clamped, the head travelling direction is reversed, and at the same time the paper driving starts under releasing of the head pressure on the paper 12. The paper driving continues from the phase p 1  to the phase p 2 , which is slightly before the resting position. At the phase p 2 , when necessary printing is over, a braking signal is impressed on the motor 1, and therefore after a very short time the motor stops at the phase p 3 . When printing is ordered successively for two lines or more on the paper 12, then the stop signal is not given at the phase p 2 , and therefore the process continuously advances passing p.sub. 3 to p 4  and thereafter. 
     As is elucidated in detail, the head spring control apparatus in accordance with the present invention enables releasing of the pressing force of the head spring 32, by a simple motion of lever pin 33 to clamp the spring force conveying protrusion 33d during the time period of driving the recording paper 12 for line shifting. And an important feature of the operation is that the clamping is made by utilizing stroking or travelling of the head and that during clamped state there is no power consumption for clamping as such since no holding-electromagnet or the like power-consuming component is used. Therefore, by selecting the phase of the clamping operation and release of clamping operation outside the paper driving period, the maximum motor power and maximum power consumption are limited low, thereby enabling use of a fairly small motor and a small power source. Besides, components used for the clamping of the head spring are very simple and cheap, the apparatus can be economically provided. 
     (9) Pad angle adjustment device 36 37 
     In order to obtain good printing, the pad 36 to back the recording paper 12 against the printing head 9 should have been mounted with suitable angle. Accordingly, the example shown by FIG. 14 and FIG. 15 afford a simple-structured pad angle adjustment device which can be easily adjusted. The pad 36 of rubber or the like elastic material is bonded on a pad holder 37, which comprises vertical pad-bonding face 37a having several holes 37h, horizontally bent part 37e and engaging tabs 37d formed at the side tips of the pad-bonding face 37a with narrow channel parts 37c  inbetween. The pad holder 37 is mounted on the frame 29 by inserting the engaging tabs 37d into slits 29h. The pad holder 37 has small recesses 37f on the horizontally bent part 37e. The pad 36 is bonded on the pad bonding face 37a with a suitable bond. It is preferable to form press formed protrusions 37g of a hemispherical shape, or a suitable shape, on the engaging tabs 37d, so that the protrusions 37g afford good fixing in the slits 29h. The holes 37h on the pad-bonding part 37a serves to ensure stronger bonding force by instrusion of bond layers in the holes. 
     The adjustment of the pad angle is carried out by inserting some tool such as a small screw driver or small fork shape tool in the recess 37f and plying it. 
     By embodying the present invention, the abovementioned miniature size thermal serial type serial printers are successfully manufactured and very stable operations are obtained. Their typical technical data are as follows: 
     
         ______________________________________width          62           mmdepth          49           mmheight         12           mmweight         45           gr.width of paper 38           mmmaximum input power          2,000        mWprinting speed 1.5 lines (× 15 letters)/sec,          (= 22.5 letters/sec)______________________________________