EP0033226B1

EP0033226B1 - Character selecting mechanism for a serial printer

Info

Publication number: EP0033226B1
Application number: EP19810300288
Authority: EP
Inventors: Shigemitsu Matsumori
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 1980-01-23
Filing date: 1981-01-22
Publication date: 1985-06-19
Also published as: JPS5928473B2; DE3170969D1; EP0033226A2; JPS56104079A; EP0033226A3

Description

This invention relates to a character selecting mechanism for a print head for a serial printer and it has application to a print head comprising a petal-type print thimble. The invention is particularly concerned with a character selecting mechanism which can be used for selecting one from two characters each arranged at a different distance along the length of a print head.
In a previously proposed serial printer, a petal-type print thimble comprises cylindrically disposed fingers on each of which two characters are arranged vertically one above the other. For character selection, the print thimble is rotated bidirectionally and/or it is moved vertically to select the character.
To accomplish character selection with this previously proposed arrangement, a mechanical movement must be carried out in both the rotational and the vertical directions. For this purpose, a prior art printer, as disclosed in the U.S-A-3,696,410, comprises a character selection motor for rotating the print thimble and a longitudinal selection motor for moving the print thimble in the vertical direction. The character selection motor has a hollow rotating shaft, and an inner shaft is extended in the hollow-portion of the rotating shaft. The inner shaft is vertically moved by the longitudinal selection motor. The print thimble is mechanically connected with both the rotating shaft and the inner shaft by a torque-transmission mechanism including a ball and socket assembly and a cylindrical housing. Since the ball and socket assembly is required to rotate together with the housing and moves vertically in the housing projections are provided around the ball and socket assembly and grooves are provided inside of the housing so as to engage the projections. However, in this arrangement, the rotation of the housing cannot be transmitted accurately to the ball and socket assembly because a certain amount of gap is unavoidable between the projections and the grooves so that the ball and socket can smoothly slide in the housing in the vertical direction. Owing to this, the rotation of the character selection motor cannot be transmitted to the print thimble secured to the ball and socket assembly with great precision, with the result that a selected character on the print thimble cannot be precisely positioned opposite to a platen. Therefore the character cannot be clearly printed. Further in the previously proposed arrangement, the torque-transmission mechanism is complicated and it includes many parts. Therefore, its manufacture is difficult and it is liable to break down more easily.
For vertical character selection, the magnet selects predetermined print positions (up and down) of the thimble. To print at a position other than those determined by the predetermined print positions of the thimble, for example where H ₂0 or H² is to be printed, it is common practice to shift the printing paper by a half of the character size. However, such minute shifting of the paper is very difficult. In the case of printing in the German language, where the vertical positions of umlauts (· ·) for a capital and a small letter are different from each other there is a further problem. It is difficult with the previously proposed printer to use a single umlaut type or character element for both a capital and a small letter, unless a minute shifting of the printing paper is carried out.
It is, therefore, an object of this invention to provide a character selecting mechanism for a serial printer with a simplified construction and a high positioning accuracy.
The character selecting mechanism preferably can be shifted longitudinally (or vertically) by a minute value.
According to this invention, there is provided character selecting mechanism for a serial printer comprising a print thimble having a plurality of circumferential lines and a plurality of characters in each said line, a driving motor for rotating said print thimble around an axis thereof and a longitudinal movement selecting means for moving said print thimble axially, said driving motor having a rotating shaft, a rotor fixed to said shaft and a stator characterised in that one end of said shaft is fixed to said print thimble, said rotor being movable together with said shaft in the longitudinal direction, said stator having a sufficient length to extend over the entire length of the longitudinal movement of said rotor and said longitudinal movement selecting means contacting the other end of said shaft for moving said shaft in the longitudinal direction.
The above and other objects and advantages of this invention will be apparent from the following description of a preferred embodiment of the invention given, by way of example with reference to the accompanying drawings, wherein:

Figure 1 is a perspective view of an embodiment of the invention;
Figure 2 (a) is a vertical sectional view of the embodiment shown in Figure 1;
Figures 2 (b) and 2 (c) are side views of a cam 11 used in the said embodiment;
Figure 3 illustrates a relationship between the print thimble position and the stepping number positions of the stepping motor; and
Figure 4 shows diagrammatically the characters to be printed and the order of operating the fingers of the thimble.

Referring to Figure 1, a type carriage assembly 100 for a serial printer includes a print head incorporating a petal-type print thimble 3. The print thimble 3 has sixty four fingers 15 arranged cylindrically. Two characters 14 are arranged vertically on, i.e at different distances along, each finger, allowing for a total of one hundred and twenty eight characters on the print thimble 3. The print thimble 3 is mounted on a mounting member 4, which is secured to a shaft 5 of a servomotor 1, in the form, for example, of a stepping motor. The servomotor 1 drives the mounting member 4 which in turn rotates the print thimble 3 to the desired finger position. For character selection from two vertically arranged characters 14 on a finger 15 and for vertical shifting by a minute value, a longitudinal movement or vertical selecting means 2 is provided below the servomotor 1.
A print hammer (not shown) is incorporated in such a way that its action strikes the inside wall of a finger 15 of the print thimble 3. The print hammer carries a magnet. When it is energized by the action of a solenoid driver (not shown), the hammer is driven in free flight and strikes the finger 15 of the selected print thimble character 14. The hammer is reseated in its original position by virtue of the reaction produced by a recoil force, together with the force exerted by the magnet.
Referring to Figure 2(a), the stepping motor 1 comprises a stator 6, a rotor 7 secured to the shaft 5, and bearings 8 and 9 for supporting the shaft 5. The shaft 5 carrying the rotor 7 is not only able to rotate but it is also able to move vertically. The longitudinal or vertical selecting means 2, incorporates, for example, a stepping motor having a rotor and a stator and a shaft 10 which is connected to a cam 11. A roller 12 provided on the shaft 5 contacts the cam 11 in order to minimise the effects of friction. Rotation of the cam 11 moves the shaft 5 vertically by a distance defined by the angle of rotation of the cam 11. A difference in distance between the uppermost and the lowermost positions of the shaft 5 corresponds to the pitch of the vertically disposed characters 14 on the finger 15. A spring 13 provided in the stepping motor 1 urges the shaft 5 towards the cam 11.
When the cam 11 is positioned in the way shown in Figure 2(b), the print thimble 3 is at the uppermost position D, as shown by a solid outline in Figure 2(a), and when the cam 11 is positioned in the way shown in Figure 2(c), the print thimble 3 is at the lowermost position E, as shown by a dotted outline in Figure 2(a).
Referring now also to Figure 3, assume that the print thimble 3 moves vertically from the position D to the position E, the stepping motor 2 moving by a stepping number of 6, it is possible to assign the print thimble 3 to one of the positions h, i, j, k, and I, as shown in Figure 3, by setting the stepping number. The positions h, i, j, k and I are adjustable, as required, by properly desgining the shape of the cam 11.
From Figure 3, it can be seen that the position h of the thimble 3 is shifted downwards from the position D by a minute value m, and the position k of the thimble 3 is shifted upwards from the position E by a value n. Thus, the print thimble 3 may be positioned, with a high degree of accuracy, at a position determined by the stepping number of the stepping motor 2.
Such a facility has considerable value, for example when in the German language A and a are to be printed. In such a situation only one printing element ".." (umlaut) is used for the umlauts required for printing both A and ä. As shown in Figure 4, the printing element ".." on a finger 15 is moved downwards by a minute amount p for use with "a", from the position which it occupied for use with "A".
It will be appreciated that, although the invention has been described, by way of example, with reference to a particular embodiment, variations and modifications can be made. For example, although in the preferred embodiment, it is explained that the shaft 5 is able to move vertically, it will be understood that the movement to which reference is made is that along the longitudinal axis of the shaft, which, in other embodiments, could be arranged to extend in a direction other than the vertical. Furthermore, other forms of motor 1 and 2 and other forms of lever mechanism than the rotatable cam 11 may be employed. It will also be understood that although the invention is particularly applicable to a printer having a petal-type print thimble, it can be employed with other types of print head having characters arranged radially about an axis.

Claims

1. A character selecting mechanism for a serial printer comprising a print thimble (3) having a plurality of circumferential lines and a plurality of characters in each said line, a driving motor (1) for rotating said print thimble around an axis thereof and a longitudinal movement selecting means (2) for moving said print thimble axially, said driving motor (1) having a rotating shaft (5), a rotor (7) fixed to said shaft (5) and a stator (6), characterised in that one end of said shaft (5) is fixed to said print thimble (3), said rotor (7) being movable together with said shaft (5) in the longitudinal direction, said stator (6) having a sufficient length to extend over the entire length of the longitudinal movement of said rotor (7), and said longitudinal movement selecting means (2) contacting the other end of said shaft (5) for moving said shaft in the longitudinal direction.

2. The character selecting mechanism as claimed in Claim 1 characterized in that said longitudinal movement selecting means (2) includes a cam means (11) rotatable to move said shaft (5) axially and a stepping motor arranged to rotate said cam means.

3. The character selecting mechanism as claimed in Claim 2 characterized in that said cam means (11) includes a rotational axle attached to an output shaft (10) of said stepping motor and a contact face contacted with said other end of said shaft (5), said contact face having such a cam profile that the longitudinal position of said shaft (5) as a function of the angle of rotation of said cam means varies slowly for a part of each rotation of said cam means and varies steeply for the remaining part of each rotation.

4. A character selecting mechanism as claimed in any one of the preceding claims characterized in that there is provided a spring (13) arranged to urge the shaft (5) against axial movement by the longitudinal movement selecting means (2).

5. A character selecting mechanism as claimed in any one of the preceding claims characterized in that a roller (12) is provided between the shaft (5) and the longitudinal movement selecting means (2).