EP0037217B1

EP0037217B1 - Printer

Info

Publication number: EP0037217B1
Application number: EP81301179A
Authority: EP
Inventors: Noriaki Okano; Keisuke Murakami; Susumu Matsuda
Original assignee: Tokyo Electric Co Ltd
Current assignee: Toshiba TEC Corp
Priority date: 1980-03-25
Filing date: 1981-03-19
Publication date: 1985-06-19
Also published as: CA1159711A; JPS56140452U; DE3170991D1; EP0037217A1

Description

The present invention relates to a printer. More particularly, the present invention relates to a printer of the type in which the quality of printed letters is significantly influenced by a slight change of the space between the top end of a printing head and the surface of a recording paper, such as a dot printer.
In the conventional printer of the type in which a printing head is reciprocatively shifted along a platen, the paper thickness is changed when the number of recording papers is increased or decreased or when a chit or the like is selectively inserted in ordinary recording papers and printing is carried out in this state. In this case, it is desired that the quality of printed letters should be uni- formalized by changing and adjusting the relative position of the printing head to the platen. This can be achieved by detecting the paper thickness and determining the position of the printing head according to the detected thickness. Various means have been proposed and adopted for attaining this purpose. For example, US-A-3,988,984 discloses a printer provided with such means. The printer disclosed in this U.S. Patent is not different from the conventional printer in that a printing head is disposed reciprocatively movably on the front face of a cylindrical. platen horizontally located, but in this printer, a detecting roller engaging with recording papers wound around the platen is attached to a lever in the lower portion of the platen. This lever is connected to a lever on the side of the printing head through a rotary shaft or other connecting lever, so that the position of the printing head is determined by the movement of this lever. In short, in this printer, since the paper thickness-detecting portion is much spaced from the position of the printing head and the operation directions of these two members are opposite to each other, a complicated lever mechanism should inevitably be interposed. Therefore, the number of connecting and coupling members is large and the structure is commensurately complicated. Hence, it is very difficult to precisely adjust the relationship between the value of the change of the paper thickness and the quantity of the movement of the printing head. Accordingly, in order to attain the intended object effectively, it is necessary to manufacture respective parts with high precision. Further, adjustment at the assembling step is difficult, and it is difficult to maintain certain capacities in the printer.
In DE-A-2550963 a printer is described as comprising an assembly of a paper press roller, a printing head and a printing head carriage therefor, said assembly comprising a pair of parallel shafts spaced from each other, the first shaft bearing the press rollers, and the second shaft carrying the carriage, said shafts being carried by two pairs of levers of which each constitutes a joint linkage so that the position of the rollers dictates the position of the carriage. However the printing position also moves relatively upward and downward as the paper thickness changes.
It is a primary object of the present invention to provide a printer in which the position of a printing head can be more precisely determined according to the thickness of recording papers and which is simpler in construction.
Accordingly, the present invention is characterized in that the press rollers contact the paper in use immediately downstream of the printing head whereby the position of the printing head can be precisely determined according to the thickness of the papers utilized.
The present invention will now be described by way of illustration only with reference to the accompanying drawings, in which:

Figure 1 is a perspective view showing one embodiment of the printer of the present invention in the state where a printing head is taken out;
Figure 2 is an enlarged view of the printer in the state where a frame is dismounted;
Figure 3 is a top plan view showing a part of the printer shown in Fig. 2; and Fig. 4 is a fragmentary perspective view illustrating a part of a mechanism for driving a carrier.

One embodiment illustrated in the accompanying drawings will now be described. A pair of confronting frames 1 are disposed on the left and right sides, respectively, and levers 2 and 3 are held on the outer surfaces of the frames 1 so that the levers can turn along the frames 1 with shafts 8 being as the centers. Both the ends of a guide shaft 6 slidably supporting a carrier 5 having a printing head 4 for a dot printer stationarily assembled thereon are supported on the levers 2 and 3. Both the ends of another guide shaft 7 are supported on the frames 1 in the state where the shaft 7 is gripped in the rear portion of the carrier 5.
Fig. 2 is a side view in which the frames 1 are omitted to show the arrangement of parts. A motor 9 is secured to one frame 1 and gears 11, 12, 13, 14, 15 and 16 from a gear train to reduce the rotational speed of the motor 9 and transmit the reduced rotational speed to a cam 10. A paper feed cam 17 is disposed so that the cam 17 rotates coaxially with the gear 12. The cam 10 has a drum-like shape, and on the periphery of the cam 10, there is formed an endless spiral groove 18 starting from one end, extending to the other end and returning to said one end. A cam follower 19 to be engaged with this groove 18 is supported on the carrier 4 rotatably around the vertical axis.
A guide plate 21 is disposed between said frames 1 to guide a long recording paper 20 to a platen 25, and shafts 24 having paper feed rollers 22 and 23 fixed thereon are rotatably supported between the frames 1. A paper pressing roller 26 confronting the upper paper feed roller 22 is fitted in and held on a shaft 27 having both the ends supported on the levers 2 and 3. A pinch roller 28 as a pressing member confronting the lower paper feed roller 23 is supported by another lever 29. Ratchets 30 are fixed to one end of the shafts 24 of the paper feed rollers 22 and 23, respectively.
A seesaw lever 31 having one end confronting the paper feed cam 17 is attached to one frame 1 while the seesaw lever 31 is rotatably urged clockwise by a return spring 32. A stop lever 33 and a magnet 34 are held on one frame 1 so that the other end of the seesaw lever 31 is locked. A feed lever 35 to be engaged with the above-mentioned ratchet 30 is connected to the seesaw lever 31.
A stopper 36 for regulating the range of the turning movement of the lever 2, a switch 37 as detecting means, which is switched off by movement of the lever 2 in the counterclockwise direction to open a printing driving circuit, and a toggle spring 38 for urging the lever 2 in the clockwise or counterclockwise direction every time the lever 2 turns from one side to the other side with the neutral position being the center, are attached to the frame 1.
A printing ribbon 40 having both the ends held by spools 39 is located on the front face of the platen 25.
In the printer having the above-mentioned structure, the rotation of the motor 9 is transmitted to the cam 10 through the gears 11 through 16, and the carrier 5 having the cam follower 19 engaged with the groove 18 of the rotating cam 10 makes a reciprocative movement along the guide shafts 6 and 7 while the carrier 5 holds the printing head 4 thereon. During this process, the printing operation is performed. While the other cam 17 is being rotated, the seesaw lever 31 is pressed by a high part of the cam 17 and turned in the counterclockwise direction, and at this point, the magnet 34 is energized to attract the stop lever 23 in the counterclockwise direction. Accordingly, at the point when the high part of the cam 17 passes away, the seesaw lever 31 is turned in the clockwise direction by the force of the spring 32 to bring down the feed lever 35 and intermittently turn the ratchet 30, and the paper feed rollers 22 and 23 feed the recording paper 20 by one pitch.
When the printing operation is performed on a chit 41, the levers 2 and 3 are brought down in the counterclockwise direction. In this state, the levers 2 and 3 are urged in the bring-down direction by the toggle spring 38 but their positions are determined by the stopper 36. Accordingly, the guide shaft 6 is allowed to shift along a locus with the shaft 8 being as the center, and the printing head 4, together with the carrier 5, is separated from the platen 5. At this point, the rear portion of the carrier 5 slides in a direction rectangular to the other guide shaft 7, and therefore, the retreating movement of the carrier 5 from the platen 25 is not inhibited by the guide shaft 7. Furthermore, by virtue of an arrangement in which on both the ends of the cam 10, the groove 18 is extended in a direction rectangular to the axis of the cam 10, only the movement of the carrier 5 and printing head 4 in a direction separating from (or approaching to) the platen 25 is allowed while the movement of the carrier 5 and printing head 4 along the platen 25 is inhibited. Accordingly, the chit 41 can easily be inserted on the front face of the platen 25. Then, the levers 2 and 3 are returned in the clockwise direction and the paper press roller 26 is brought into engaging contact with the paper feed roller 22 by the force of the toggle spring 38. By this stopping action of the paper press roller 26, a clearance between the top end of the printing head 4 and the platen 25 can be adjusted to a predetermined size by a one- touch operation. While the chit 41 is set in the above-mentioned manner, the switch 37 detects the position of the lever 2 to put off the printing driving circuit, and therefore, an erroneous operation can effectively be prevented. The printed chit 41 is fed upwardly by the upper paper feed roller 22.
Incidentally, if the feed quantity of the upper paper feed roller 22 is made slightly larger than the feed quantity of the paper feed roller 23 in printing the printing paper 20, even when the recording paper 20 is slackened between the paper feed rollers 22 and 23, an upward tension is given to the recording paper 20 and the slack can be eliminated. Accordingly, by this arrangement, the recording paper 20 can be set on the platen 25 horizontally and catching of a dot needle can be prevented.
In the foregoing embodiment, the levers 2 and 3 are moved by a manual operation. In the present invention, however, there may be adopted a modification in which the levers 2 and 3 are moved by an electrical driving system using solenoids or the like. In this modification, the top ends of the levers 2 and 3 are not protruded from a cabinet and an operation switch button or the like is attached. It is preferred that a display device be disposed to indicate whether the levers 2 and 3 are located at positions capable of receiving a chit 41 or the like or they are in the paper-pressing state.

Claims

1. A printer comprising an assembly of a paper press roller (26) and a printing head (4), and a printing head carriage (5) therefor, reciprocally movable along a platen (25) said assembly comprising a pair of parallel shafts spaced from each other, the first shaft bearing the press roller(s) (26) and the second shaft carrying the carriage (5) so that the position of the press rollers (26) dictates the position of the carriage and a distance thereof from the recording paper, characterized in that the press roller (26) contacts the paper in use immediately downstream of the printing head, whereby the position of the printing head (4) can be precisely determined according to the thickness of the paper (20) utilized and in that said shafts are both mounted upon one pair of levers (2, 3).

2. A printer according to claim 1 characterized in that a paper feed roller (22) is disposed in engaging contact with the paper press roller (26).

3. A printer according to claims 1 or 2 characterized in that paper feed rollers (22, 23) are disposed respectively above and below a platen (25) to feed the recording paper, and the paper feed speed of the downstream paper feed roller (22) slightly higher than the paper feed speed of the upstream paper feed roller (23).

4. A printer according to any of Claims 1 to 3 wherein

the levers (2, 3) are urged by an over-the-centre toggle spring (38) in such a manner that the levers can be biased by the toggle spring either in a paper pressing direction or in a paper inserting direction.

5. A printer according to Claim 4, wherein a detecting member (37) for detecting the position of the lever (2) is disposed so that when the lever is in the paper inserting state, a printing driving circuit is switched off.