GB2131747A - Variable speed dot line printer - Google Patents

Abstract

The dot line printer has a shuttle 36 which is reciprocated in directions perpendicularly intersecting a direction of feed of printing paper, whereby printing needles regularly arranged on the shuttle are projected onto the paper thereby to conduct desired printing operations. The printer has the feature that the reciprocatory speed of the shuttle 36 is selectively adjustable, whereby the printing is selectively switched depending upon whether normal printing or high density printing in the lateral direction is required. The switching is conducted by switching of the speed of a motor 38 for driving the shuttle. The printer can also be used to form overlapping characters (e.g. see Fig. 5). <IMAGE>

Description

SPECIFICATION Dot line printer This invention relates to a dot line printer, and in particular to a shutter-type dot line printer having'a shuttle including a plurality of printing needles or styluses which is oscillated in directions perpendicularly intersecting a direction of feeding of printing paper.

There have heretofore been known dot printers in which printing needles are projected on to printing paper in accordance with predetermined printing data and desired characters, signs etc. which are thus formed from a plurality of dots. These printers are used, for example, as output printing devices for information processing machines. Furthermore, there have been known dot line printers which the above-described dot printer is further improved in that a plurality of printing needles is arranged at equal intervals in a line on the printing paper.

While the printing needles are reciprocated across a needle pitch, the paper feed is effected in a direction perpendicular to the directions of the reciprocation, thereby to perform desired printing operations successively. The dot line printer is advantageous in that it can carry out printing operations at very high speed and in large quantities as compared with a serial type dot printer. Since an oscillating element reciprocating across a needle pitch, in which a plurality of printing needles are arranged is referred to as a shuttle, the above-described printer is known as a shuttle-type dot line printer.

It is well known that, unlike the printing-type method, desired characters and the like are formed in a dot line printer by a gathering of dots formed by needle points being projected and driven to the printing paper, whereby, even when, for example, a single line is to be drawn, it is difficult to remove very small irregularities of dots in a single scan. As a result, satisfactory printing quality is not always obtainable, thus presenting a disadvantage that the resultant characters and the like are hard to read. This disadvantage is more serious with more complicated characters.

Recently, there have been proposed measures leading to improvements of various types in the printing quality of dot printers, whereby high density printing, in which the dot density is increased, has been performed to secure printing quality at a level equal to other printing methods.

The fundamental principle of high density printing, which has heretobefore been practised, resides in that the paper feed is temporarily stopped and a plurality of dot printing scannings are carried out on one and the same line. For example, in the device described in Japanese published patent application No. 55-85985, printing on one line is effected by one cycle of reciprocation of the shuttle, i.e., two scans, or by two cycles of reciprocation i.e., four scans, whereby high density printing is achieved.

As described above, high density printing has been achieved by repeated printings on one and the same line on the assumption that the speed of movement of the shuttle is fixed at a predetermined value. In this way, the printing quality is highly improved. On the other hand, the printing speed is decreased with the increase in number of the scans, thus presenting the disadvantage that the speed of printing, one important advantage of the dot line printer, is impaired.

The present invention has been developed to alleviate or solve the above-described problem of the prior art and has as its object the provision of a printer and printing method in which high density printing can be achieved while the printing speed is maintained high.

To this end, it is a feature of the present invention that the speed of reciprocal mption of the shuttle, which has heretofore been regarded as having a predetermined value, is made selectively adjustable and the speed of reciprocal motion of the shuttle, at which the desired high speed printing is achievable, is selected, so that high density printing on a desired dot line can be achieved by one scan at the speed selected. Further, the present invention provides that at least two of the selected speeds as described above are present in the device, and that these speeds can advantageously be switched in response to a normal printing command and a high speed printing command respectively, so that the desirable high density printing can be achieved, while the highest speed permissible in the device is maintained for use in response to a printing command.

In dot line printers, the printing speed is mainly determined by a period of time required for the projection and retraction of the printing needles and a period of time required for the control circuit. In the conventional device, both the former and the latter are controlled independently of each other, without being adjusted to each other.

Furthermore, to vary the dot density, only control of the paper feed and control of the driving timing of the printing needles are effected, with the scanning cycle set at a constant value, thus presenting the disadvantage that, for example, four scans of the shuttle are required for achieving the above-described high density printing. With such an arrangement, dot pitch irregularities tend to occur.

Reference is now made to Fig. 1 of the drawings which is an explanatory view showing the printing operation of a dot line printer.

Fig. 1(A) shows one example of high density printing at the fixed shuttle speed of the prior art.

Only four printing needles 1 Oa, lOb, 1 Oc and 1 Od out of the plurality of printing needles provided in the shuttle are shown. Each of these needles reciprocally moves in directions B and C perpendicularly intersecting a direction A of paper feed of the printing paper. The regions over which the needles move are indicated by reference numerals 1 2a, 1 2b, 1 2c and 1 2d and the printing needles 1 Oa to 1 Od simultaneously move across these regions 1 2a to 1 2d.

Suppose now that high density printing is required of a type formed by dots indicated by black (shaded) circles arranged along a dot line 100.

More specifically, to simplify the explanation, a normal pitch P is set for the respective printing needles 1 Oa, 1 Ob, 1 Oc and 1 Od. However, with respect to the printing needle 1 Oa as a reference, the printing position of the succeeding printing needle 1 Ob is shifted by P/4, the printing position of the printing needle 1 Oc by P/2, and the printing position of the printing needle 1 Od by 3P/4. Since the respective regions 1 2a to 1 2d are simultaneously controlled by a single control circuit, the control circuit is required to effect the high density printing between the respective regions.More specifically, in order to control simultaneously a plurality of printing needles regularly arranged, as in the dot line printer, by a common control circuit, it is necessary to give consideration to a difference in control timing between the respective printing needles as shown in Fig. 1(A), and it is readily understood that one quarter of the normal pitch P can form this difference in control timing between the respective printing needles.

In consequence, when the shuttle speed is regarded as being constant as in the prior art, in order to achieve the high density printing, it has been necessary to conduct a plurality of scans on one and the same line. For example, in the case of printing as shown in Fig. 1(A), four scans (two reciprocations) are required as indicated by lines 201 to 204, thus presenting such a disadvantage that the printing speed is reduced to one quarter of the normal printing speed.

Fig. 1(B) of the drawings explains the difference between the printing method of the prior art and that according to the present invention, reference being made to only one printing needle. It will be readily understood that, according to the present invention, high density printing is achieved, while the character font rule is skilfully utilized to control the lowering of the printing speed.

Now, it is assumed that high density printing data are arranged along a dot line 110. Here, it is important to know that, if the character font rule is followed, then the printing dots indicated by black (shaded) circles are not arranged continuously.

The printing method of the prior art, indicated by lines 211 to 214, is of a constant velocity type, wherein the speed of movement of the shuttle cannot be varied, whereby the printing pitch is P, thereby presenting the disadvantages that only one of a circle and a triangle disposed adjacent to each other can be printed and four scans (two reciprocations) are required due to the restriction caused by the control operation required for the control circuit between the respective printing needles as explained in Fig. 1(A).

The present invention is intended to obviate the aboveaescribed disadvantages of the prior art. For example, in the case of Fig. 1 , the shuttle speed, which has heretofore been regarded as being fixed, is reduced to one half, whereby a period of time T, which has heretofore been required for one pitch P, is reduced to T/2, so that one scan can achieve the half dot printing. Since the reduction of the shuttle speed is associated not only with the period of time required for the projection and retraction of the printing needles 1 0 but also with the period of time required for the control circuit, the shuttle speed reduced to one half makes it possible to conduct 1/4 P printing (quarter dot printing) by one scan, so that the high density printing on the dot line 10 shown in Fig. 1 can be achieved by one scan.Namely, only the normal shuttle speed is reduced to one half, whereby the high density printing is increased to four times, so that a very remarkable result can be achieved.

More specifically, 220 in Fig. 1(B) indicates the printing operation according to the present invention, in which the printing pitch P is reduced to one half as compared with that of the prior art by switching to the reduced shuttle speed. In consequence, if simply this reduction is made then the printing density should be doubled. When the density is simply doubled, only the circular dots in the dot line 220 can be printed. However, according to the present invention, as shown in the dot line 220, also the triangular dots corresponding to P/2 can be printed, so that the present invention has the feature that the high density printing as many as four times has been substantially achieved.This is because, according to the present invention, based on the character font rule, in which adjacent dots are not continuously arranged in one character, this fact is skilfully utilized so that, even when the speed is reduced to one half, the circular dot and the triangular dot (which are not continuously arranged) can be printed on the dot line 220 having four times the density.

According to the present invention, of course, the aforesaid shuttle speed need not necessarily be limited to one half of the normal speed, and it is possible to set at a reduced speed slightly lower than one half of the normal speed. These speeds are set in consideration of both the period of time required for the projection and retraction of the printing needles and the period of time required for control of the circuit, and determined by the highest optimal speed obtainable in each of the devices. According to the present invention, predetermined setting of these speeds makes it possible to achieve the desirable selection of the predetermined plurality of speeds of switchingly controlling these speeds in accordance with any one of desirable high density printings, so that the high density printings of various types can be selectively conducted by use of a single printer.

In consequence, according to the present invention, varied printing qualities can be selected and, as a portion of the printing, some special characters, e.g., doubly imprinted characters, can be printed and incorporated within a sentence as a part thereof. With double imprinted characters, the same characters are slightly shifted from each other for double imprintings, whereby remarkable printing effects differing from other characters can be achieved. A whoie line having the above described double imprinting command is subjected to the printing operation by use of the high density printing differing from other lines, so that the function of the device can be greatly improved.

The invention will be better understood from the further illustrative description following and from the remaining drawings, in which: Fig. 2 is a schematic perspective view of a preferred dot line printer for high density printing according to the present invention; Fig. 3 is a block circuit diagram of a control circuit for the printer of Fig. 2; Fig. 4 is an explanatory view showing an example of the printing data; Fig. 5 is an explanatory view showing double imprinting; and Fig. 6 is an explanatory view showing the printing data used in Fig. 5.

Fig. 2 shows a preferred embodiment of the dot line printer to which the present invention is applied, in which a platen 26 is rotatably supported by side walls 22 and 24 affixed to a base frame 20, and printing paper 28 is placed along the surface of the platen 26. The printing paper 28 is supported for click feeding at its opposite edges by paper feed receivers 30 and 32 and is driven by rotation of a feed shaft 34 in the direction indicated by the arrow A.

The base frame 20 is provided with a shuttle 36 supported to reciprocate in the directions B and C which perpendicularly intersect the aforesaid direction A of paper feeding. On the shuttle 36, there are regularly arranged a plurality of printing needles for projecting onto the printing paper 28.

These printing needles correspond to predetermined positions and are adapted to project to the printing paper in operational association with the reciprocatory motion of the shuttle 36, whereby simultaneous printing in the direction of a line is conducted on the printing paper 28 through a ribbon or the like. Although the construction of the respective printing needle 10 and a solenoid driving device are not shown in detail in Fig. 2, an arrangement similar to that of a normal dot printer is provided for each of the printing needles.

To reciprocate the shuttle 36 in the directions B and C, a driving motor 38 consisting of a DC motor or the like is affixed to the base frame 20 and a flywheel 40 is solidly secured to a shaft of the motor. A crankshaft including two eccentric shafts, not shown, is mounted on the front face the flywheel 40. One end of a connecting rod 42 is engaged with the crankshaft and the other end the connecting rod 42 is engaged with the shuttle 36 through a shaft 44. It will be readily understood that the shuttle 36 can be reciprocated in the directions B and C through the connecting rod 42 as a result of rotation of the driving motor 38.

The shuttle 36 includes therein a plurality of printing needles and printing needle actuators for driving the printing needles. These driving portions are integrated into a hammer bank. The hammer bank is comparatively large in weight and its inertial force is high during operation of the driving motor. The hammer bank therefore tends to impart unnecessary vibrations and the like to the device itself. To absorb the inertial force, the device is provided with a counterweight 46 reciprocating in a direction opposite to that of the shuttle 36. The counterweight 46 is connected to the aforesaid crankshaft through a second connecting rod 48, whereby the shuttle 36 and the counterweight 46 move in directions opposite to each other.The inertial force and the reaction force caused by an acceleration offset each other through the utilization of the reaction forces of the both members, so that vibrations are prevented from being caused to the device. The shuttle 36 and the counterweight 46 are supported for their respective movements in the directions B and C by receiving bases 50 and 52 affixed to the base frame 20.

A slit disc 54, affixed to the tail end of the motor 38, electrically and accurately detects the stage of the reciprocatory motion of the shuttle 36 by co-operation with a photo-interruptor 56.

The characteristic feature of the present invention resides in that the speed of movement of the shuttle 36 in the directions B and C, i.e., the rotational speed of the driving motor 38 is variable. Fig. 3 shows one example of a control circuit. When the printing data, not shown, are applied to an interface 58, the interface 58 controls the rotation of the motor 38 and controls the shuttle 36 in response to the printing data. In the normal case, ordinary printing is conducted and the motor 38 is rotated at high speed, so that simultaneously high speed printing is conducted.

However, in response to a high density printing command, the speed of the motor 38 is switched to a predetermined low speed.

Fig. 4 shows one example of the printing data, in which L, to L5 indicate the data of the respective dot lines, and character data CD of the respective lines are included as the printing data.

The interface 58 selects a desired character signal from a character selecting circuit in response to the character data CD and feeds a desired excitation signal to the printing needle actuators in the shuttle 36 through a hammer driver 62 to thereby project predetermined printing needles, whereby dot characters corresponding to the character data are successively formed. At this time, the rotational speed and rotational position of the motor 38 are detected from the photo interruptor 56, whereby the synchronizing operation of the hammer driver 62 is performed.

Also, the interface 58 feeds a specified shuttle speed to a motor controller 64 and takes in a speed signal from the rotational data of the motor 38 obtained from the photo-interruptor 56 through a motor speed detecting circuit 66, thereby to control the speed of the motor 38 by feedback.

According to the present invention, a speed switching command 300 indicated in Fig. 4 is applied to the printing data, whereby the motor controller 64 switches the speed to a predetermined low speed, in this embodiment, substantially one-half of the normal speed. At this time, a high density printing command is fed from the interface 58 to the character selecting circuit 60, so that a desired high density printing can be achieved in co-operation with the low speed driving of the shuttle 36.

As described above, in this embodiment, because two shuttle speeds are preset in the device, either one of the predetermined speeds is switchingly selected depending upon whether the normal printing or the high density printing is desired. This selection can be made at a desired position of the printing data, thus enabling a considerable improvement in the function of the device to be achieved.

Fig. 5 shows an actual example of printing, in which the double imprinting is effected in a line of printing in the region indicated by 400.

Specifically, in contrast to the normal "ABC" double imprinting is effected in the region 400, in which "ABC" is slightly shifted in the direction of the line, whereby the characters differing remarkably in characteristics from other characters are printed. The special printing described above can therefore be obtained according to the present invention.

Fig. 6 shows the case where a double imprinting command is present on the way of the above-described line. The double imprinting command DCD is incorporated in a portion of a line data. The speed switching command 300 is disposed immediately before the double imprinting command DCD. In consequence, when the printing data as shown in Fig. 6 is input, the device reads the data for one line printing (L,), when the speed switching command 300 is incorporated therein, a high density speed switching is applied to this line, so that the double printing in the region 400 as shown in Fig. 5 is reliably achieved. Needless to say, at this time, other printings in the lines in which no double imprintings are instructed are conducted at the ordinary density even when the shuttle 36 is driven at low speed, and the synchronizing operation therefor is constantly carried out.

As has been described hereinabove, according to the present invention, the speed of reciprocation of the shuttle is switchingly, controlled so that high density printing can be readily conducted, thereby improving the function of the dot line printer to a considerable extent.

Claims (8)

1. A dot line printer wherein a shuttle is reciprocable in directions perpendicularly intersecting a direction of feed of printing paper and printing needles arranged on the shuttle are operable to be projected onto the printing paper to conduct desired printing operations, the reciprocatory speed of the shuttle being selectively adjustable whereby the printer can selectively produce normal printing or high density printing.

2. A dot line printer as claimed in claim 1, wherein character data and a speed switching command are incorporated in printing data, said character data is fed to a character selecting circuit and said speed switching command to a motor controller, and selection of the shuttle speed and selection of the characters cooperate with each other.

3. A dot line printer as claimed in claim 1 or 2, wherein double imprinting is effected by utilization of the high density printing.

4. A dot line printer as claimed in claim 1,2 or 3, wherein the high density printing is conducted at a speed substantially one-half of the normal printing speed.

5. A dot line printer substantially as herein described with reference to figs 2 and 3 of the accompanying drawings.

6. A method of operating a dot line printer, wherein a plurality of printings of at least one character of a printed line are made in laterallydisplaced but overlapping relationship in a single traversed of the printed line.

7. A method as claimed in claim 6, wherein the portion or portions of the line containing the said character or characters is/are traversed at substantially one-half of the speed at which the remaining portion of portions of the line is traversed.

8. A method of operating a dot line printer, the method being substantially as hereinbefore described with reference to any of figures 2 to 6 of the drawings.