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(11) | EP 0 107 502 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Matrix dot printer with printed dot density control |
| (57) In a dot matrix printer the dot density printed is controlled by adjustably setting
the printing angle of the print head at vertical or at some predetermined angle from
the vertical. Setting it at an angle increases the number of passes required to complete
a line of print but allows the portion of the line of print in the path of head travel
to be completed in one pass at the desired dot density or with the desired degree
of dot overlap. A principal advantage of this printer is a cost reduction in the electronic
circuitry since all vertically adjacent dots of characters or graphics are printed
at one time. |
[0001] This invention is an improved dot matrix printer having a frame, platten carriage and print head of known construction but modified to permit mechanical rotation of the print head to a predetermined angle of registration for any one printing operation which while increasing the number of passes to complete a line of printing, permits all dots in a given area to be printed in one pass with such dot overlap as may be desired thereby simplifying the electronics required for the printer and offering other advantages.
[0002] This printing method also allows a new design of a print wire-print head not permitted by previous printer designs, viz: the print wire solenoids can be located in a tight linear series rather than circumferentially. This new print head is inherently simpler and of lower cost and because of the lower mass of the pins and armatures can be several times faster allowing increased print speed.
[0003] Dot matrix printers presently in use include a print head mounted on a carriage to allow lateral movement of the print head over the recording medium. The print head may be of the print wire or ink jet type and may move across the recording medium or paper in either discrete steps, at a constant or variable speed.
[0004] In the print wire dot matrix head the head includes a plurality of thin wires which are usually arranged in double staggered rows such as a 5-4 or a 8-8 arrangement. One end of each wire is connected to an actuator which can be energized to cause the wire to impact. The impact end of the wires are aligned in a vertical straight line close to the platen. A ribbon is inserted between the wires and the paper such that when the actuator is energized the wire moves forward and impacts the ribbon against the paper leaving a dot on the paper. Each print wire is actuated by its own actuator which for compactness are arranged circumferentially around the print wires. The wires of necessity are angled or curved within the printing head to be arranged at their impact ends in a linear series.
[0005] One of the problems in dot matrix printers of both the wire and ink jet type is the necessity of trading off the quality of the characters printed against the print speed and printer wear. The quality of the character printed is partially determined by the number of dots or dot density produced in a given area of the character. In the prior art, high dot density and thus better character definition has been achieved by having the print head making multiple passes over a given line with interlacing or overlapping of the dots. Generally, there are no open spaces between the dots and at a reasonable viewing distance the characters can appear to have almost letter press quality. Making multiple passes over a given print area does of course decrease the print speed of the printer, for example, by one-half if two passes are used.
[0006] Much of the output of a printer does not have to be of high quality. Often the operator will be satisfied with draft quality printing, even of relatively poor quality. Printers have been provided that allow quality/speed flexibility at 2 - 4 levels. For example, high quality can be obtained from printers having a 7 - 9 pin head configuration at 4 passes per line at line print speeds of 32 - 55 characters per second (cps). Depending on the machine, medium quality can be produced at 60 - 100 cps, quality draft characters at 120 - 200 cps, and a rough draft quality at 220 - 400 cps. These printers obtain high quality at four passes, medium quality with two passes at the same print speed, quality draft characters with two interlaced passes at twice the print head speed, and draft quality with a single pass at the higher speed. Some of the printers accomplish the interlacing by moving the papers slightly and others tilt the print head or move the end of the pins to get the same motion with respect to the paper and placement of the dots thereon as if the paper had been moved so as to cause the dots to be printed slightly above or below the dots printed on the previous pass.
[0007] The present invention proposes a novel way of effecting controllable variations in the print density or dot overlap of a dot matrix printer to provide the quality/print speed choice users desire. This is accomplished by providing for the mechanical rotation of the print head with respect to the line being printed such that - depending upon the degree of rotation - a line that may be printed in one pass without rotation of the head can be printed in 2, 3, 4 or more passes with a corresponding increase in the dot density printed but with a decrease in the printing speed of the machine.
[0008] If the print head is vertical or at 0° rotation and can print a full line of characters in a single pass, then if it rotated 60° so as to be 300 with respect to the horizontal two passes will be required to complete a line of printing. If it is tilted to be 14.47° from the horizontal, then the equivalent of 4 pass printing is done in a single pass but for a smaller vertical part of the character.
[0009] According to this invention, other sets of angles may be used besides the 90°, 30° and 14.47° mentioned above, such as 45°, 20.7°, and 10.18° or any sets of three angles whose sines are related by 4, 2, 1. It is also possible to vary the angles selected to obtain the equivalent of 3 pass, 5 pass or 2 1/2 pass printing with a standard print head. This can be quite advantageous for certain topographical and graphic applications.
[0010] While print heads of known construction can be used in the practice of this invention, particular advantage offered by the present invention is that the printing elements while desirably arranged in a single linear series preferably of just 4 elements, do not have to be arranged as compactly or tightly as in the prior art devices. In a wire dot matrix print head the print wires can according to this invention be arranged in a linear series the spacing between which is equal to the pin solenoid diameter which is typically about one-half inch. In this case while the linear length of the series of wires can be quite large, e.g. 1 1/2 inches for four print wires. If the print head is angled sufficiently from the vertical one nevertheless can achieve printing fully equivalent to the double staggered row print wire heads now used. For example, such a head could be provided to be placed at angles of 1.6 °, 0.8 , and 0.4 from the horizontal for the printing quality options the user may desire.
[0011] The ability to place the print wire solenoid in a straight line permits the construction of a very simple low cost print head with the print wires being directly in line with the armatures of the solenoid and of much less length than those presently used. Alternatively, four solenoids can be placed in two tight compact staggered rows with the print wires curved to print in a single line between the two rows, the print ends of the wires being spread apart half the diameter of the solenoids. In either case this print head, because of the lower mass of the pins and armatures is, several times faster and allows increased print speed. In addition, its simpler low friction pin-armature-spring assembly allows electronic damping which also improves print quality besides ameliorating wear.
[0012] The pins of a print head rotated as in this invention are not in vertical alignment and provision must be made for compensating for the horizontal distance between the pins in the inclined row of pins. This is readily accomplished by introducing a sequential pin firing delay equal to the horizontal distance between the pins divided by the head traverse rate.
[0013] In brief compass, the present invention is a dot matrix printer having a print head with a linear series of printing elements producing a linear series of substantially uniform dots if printed at one time on a recording medium. For the usual printer, the series in vertical register span a distance equal to the vertical height of the line to be printed. This need not always be true as a printer could print, for example, a maximum of one-half a line width per pass. The improvement of this invention allows controlling the dot density or degree of dot overlap printed per pass and comprises a first means for setting the printing angle of the print head such that its axis is inclined from the vertical a predetermined set degree for any one printing operation. There are other means associated with the control unit for establishing the firing order of printing elements of the printhead with respect to the angle of inclination and for establishing the vertical height of the portion of a line to be printed per pass and thus the number of passes of the print head required to complete a line of printing at the dot density desired.
[0014] Usually, the print head will be set in one of three predetermined angular positions, the ratio of sines of the angles thereof from the horizontal being in the ratio of 4, 2 and 1 with the number of passes required to complete a line of printing therewith being in the ratio 1, 2 and 4 respectively.
[0015] Other than provision for the rotation of the print head and modification of the electronic circuitry to accommodate this rotation, the printer of the present invention uses the same circuitry and components heretofore used in dot matrix printers. Generally these include a frame which may be inclusive of the electronic control unit, a platen mounted on the frame, a carriage supported by a carriage way on the frame for travel parallel to the platen, and a print head carried by the carriage for printing on a receptor sheet interposed between the platen and print head. Any of several known means for traversing the carriage at a preselected speed laterally over the receptor sheet can be used and this preferably is done in conjunction with a generated timing signal with the print head travelling one horizontal matrix position between timing pulses. Print data or commands are introduced into the print head in synchronism with the timing signal to fire the dot printing elements only in the areas to be printed during the traverse of the carriage. In accordance with this invention means are included for controlling the order of firing of the print elements in the print head with respect to the selected angle of registration that the print head has been placed in. All of the dots in any one pass level are printed at one time with the amount of dot overlap desired without the need of a second pass thereover. Means are provided for advancing the receptor sheet a predetermined distance to produce the required number of passes to complete the printing in the quality desired without interlacing.
[0016] The rotation of the print head, particularly if a low cost printer is desired, can be done manually by the operator as the operator rarely wants to change the quality of printing on any one page. It can, however, be rotated by a servo motor (e.g. under software command using operator input from the keyboard) or by interaction between the carriage and printer frame, at the end of pass, by extending the carriage travel.
[0017] The improved wire dot matrix print head permitted by this invention includes a housing, solenoids arranged as a compact linear series supported and retained by the housing, each of which solenoids is spring biased to be in a normally retracted position. There is a like series of pin wires activated by the solenoids each of which in one embodiment is straight and is aligned with the center line of its respective solenoids. The print wires are guided by the frame to impact the record medium with a linear series of dots if all are printed at one time. While anywhere from 2 to 10 or more print wires can be contained in the linear series, as a practical matter 4 will usually be sufficient with the spacing of the centers of the linear series of dots produced being about equal to the spacing of the centers of the solenoids. In another embodiment by placing each alternate solenoid on opposite sides of the line of pin wires, the pin spacing can be reduced by a factor of 2, although this requires the print wires to be angled or curved.
[0018]
Fig. 1 is a diagrammatic perspective front view with cover removed of the mechanical components of a printer constructed in accordance with the present invention. It is much similar to the one described in U.S. patent 4,159,882 except for the modification to permit rotation of the print head as here proposed;
Fig. 2 is an enlarged view of one form of print head useful in this invention with provision for mechanical rotation thereof to a predetermined angle;
Fig. 3 is a schematic illustration in vertical section of one embodiment of the improved wire dot matrix print head of this invention;
Fig. 4 is an enlarged schematic cross sectional view of the solenoid-armature-spring-pin assembly used in the print head of Fig. 3;
Fig. 5 is a diagrammatic plan view of a four element print head of this invention wherein the solenoids are arranged in two compact staggered rows with the wires imprinting on a common line;
Fig. 6 is an alternative diagrammatic view of a four element print head of this invention wherein the solenoids are disposed around a linear row of their associated wires.
Fig. 7 is a diagrammatic block diagram of the printer control and operation; and
Figs. 8 - 11 are a diagrammatic presentation of the printing of the letter "E" in four passes according to this invention, using a four print wire print head.
[0019] Referring to Fig. 1, the printer of this invention essentially comprises a base 10 which may contain the control unit and carrying a frame 11. Mounted on frame 11 is a platen 12 and a carriage 13 carried by a carriage rail 14. Platen 12 is driven by motor 15 and carriage 13 is driven on rail 14 via motor 17. Carriage 13 mounts printing head shown generally at 16, in a position to print on a paper sheet (not shown) interposed between the- print head and platen 12.
[0020] Referring to Fig. 2, illustrated the wire dot matrix print head 16. It has a back plate 20 mounted on carriage 13 and carrying the print head proper 21 with its solenoid unit (not shown) which activate the print wires, the ends of which are shown at 22. Head 21 can be manually rotated by pulling a spring loaded detent 23, rotating the head to the desired angle, and allowing detent 23 to engage the holes or depression 24 therefor which are located to set the head at the predetermined desired angle of registration. As illustrated, the head is set at an angle of 30° from the horizontal.
[0021] While a 4 pin head is shown and is preferred, the head may have any desired pin configuration such as 2 to 10 or more in a linear arrangement. Also, while this invention advantageously permits the use of a single row of pins, a double row of pins such as a 7 - 9 or 5 - 4 arrangement can be used or indeed even a triple staggered row could be used for some applications. However, in such arrangements, provision must be made to adjust the pins upon rotation of the print head,,or to provide individual axes of rotation for each row, in order to provide a desired relative location of the pins to produce a desired dot spacing. While the invention is described with particular reference to a print wire dot matrix print heads, it is equally applicable to ink jet printers and offers the same advantages thereto.
[0022] As the rotation of the line of printing elements on the print head as here proposed permits print head configuration to be used regardless of the linear spacing between the print elements, the solenoids in a print wire-type of head can be arranged in a compact linear series as shown in Fig. 3 rather than in the circular arrangement heretofore necessarily used in to achieve compactness, as is illustrated in U.S. Patent No. 4,284,363. In Fig. 3, the 4 print wire solenoids 30 are contained in the housing 31 mounted to the print head plate 21. With reference to Figs. 3 and 4, each solenoid 30 has the requisite winding 43 contained in a metallic housing 42 which activitates an armature 41. Armature 41 is held by and biased in a normally retracted position by a spring 32 at one end. The other end of armature 41 carries print wire 22, the center lines of the two being aligned. It is to be noted that as compared to prior art design, print wire 22 is quite short and is straight, i.e. there is no need to bend the print wire to affect linear alignment of the print wires.
[0023] While Fig. 3 illustrates a linear series of 4 print elements, in some instances it may be desirable to arrange the 4 elements in a more compact staggered 2 - 2 configuration as is shown in Fig. 5 or in an arrangement as shown in Fig. 6. In such configurations a solenoid, spring, pin assembly as disclosed in copending by Royden C. Sanders and John Forsyth filed on even date herewith may advantageously be utilized to provide aligned pins. In Fig. 5 four such solenoids are shown at 51 arranged in two compact rows. The pins 52 thereof are offset from the solenoids in order to impact on a straight line 53 as indicated by the dots 54..
[0024] In Fig. 6 solenoids 51 and their associated pin-assemblies are disposed as one opposed pair on the straight line 53 with a second pair disposed transversely of line 53 in opposed offset relationship to provide a linear row of equi-spaced pins 52.
[0025] In Fig. 7, control unit 60 contains the electronics and software for the printer system. It will preferably contain a timing signal generator 61 and will have means 62 for introducing the text or data to be printed, as is known. For the purposes of this invention, the angle at which the print head is to print is introduced from 63 into tl.3 controller. If the position of the print head is set manually as above described, then this may be from a keyboard input. Alternatively and without much difficulty a print head position detector can obtain this information or alternatively the print head can be rotated by a servo motor 19, which may, if desired, be under command of the software after the operator has selected the desired print head position by keyboard input. Also alternatively the print head may be rotated by mechanical means, i.e. a rachet arrangement, which is engaged by the head or carriage when the carriage is moved beyond its normal printing traverse on command of an operator and/or software.
[0026] In a known manner control 60 operates the platen drive 15, the print head firing sequence 16, a carriage drive 17, and a ribbon drive 18 if the print wire print head is used. As previously indicated, because of the rotation of the print head controller 60 provides for a delay in the print element firing sequence proportionate to the horizontal distance between the pins. This horizontal distance varies with the angle of registration that is selected. In bi-directional printing what was the lead pin in one direction of motion becomes the back or last pin in the other direction of printing and the delay must be reset or reversed to compensate. The method of introducing the delay can be through hardware such as a set of shift registers or through a hardware-software arrangement in which the character generator is unloaded to a pin fire digital buffer and then unloaded with the delay being introduced either in the loading or unloading of the pin fire buffer by software.
[0027] In the printing of variable quality characters or graphics in accordance with the present invention, the print head is preferable transversed across the width of the recording medium at a preselected speed. A timing signal is generated as at 61 in Fig. 7 such that the head travels a distance equal to one horizontal matrix position between pulses. Printing commands responsive to the introduced character information or data are fed the printing element synchonously with the timing signal. Alternatively, firing position pulses may be generated and a variable carriage traverse speed is controlled by these position pulses. These print commands with respect to each individual printing element in a series are delayed sequentially equal to the horizontal distance between each of the print elements. As the angle of the rotation of the print head determines the number of passes it is necessary to make to complete a line of printing, controller 60 so programs the movement of platen drive 15 as to accomplish this after it has received the print head angle information from 53.
[0028] A principal advantage of this invention is the cost reduction allowed in the electronic circuitry since all vertically adjacent dots in the characters or graphics being printed are printed at one time with such dot overlap as has been selected in the area of the pass of the printing head without need of a subsequent repass and interlacing of the dots. This simplifies character generation from compressed digital storage and minimizes complexity in printing graphics on CRT screen dumps. It allows a variable vertical matrix depending upon the user's needs.
[0029] As much of the output of the printer need not be of high quality, this invention permits maximum utiliation of a printer. Alphanumeric characters of acceptable quality can be printed at a far greater rate than if the printer were constrained to do essentially high quality printing.
[0030] Further, and of importance, the mechanical rotation of the head permits use of a print wire dot matrix printing head with only a few printing elements, preferably 4, and with the solenoids therefor arranged in a linear manner rather than the circular manner heretofore found necessary by the prior art. The linear arrangement of the solenoids allows a construction in one embodiment of a very simple low cost print head with straight strike through of the print wires. Because of the lower mass of pins and armatures, this head is several times faster and allows increased printing speeds. Its simpler construction reduces friction in the pin-armature-spring assembly and allows for the use of electronic damping which not only improves print quality but prolongs the life of the element.
[0031] Referring to Figs. 8 - 11, the method which a printer according to this invention prints a line of characters will be made clear. With a print head having 4 print wires arranged as in Fig. 5 and rotated and set at 14.47° from the horizontal, the alpha numeric character "E" is printed in four horizontal traverses (each printing all of a substantially discrete band of one quarter the height of the "E") of the print head with high dot density with substantially no overlap. (The only overlap is less than one dot diameter, e.g. sufficient to provide dot overlap to result in a desired even distribution of dots in the transition between images printed on different traverses.) In the first pass shown in Fig. 8, the top one-quarter horizontal portion of the letter is printed. The recording medium is then moved to alignment for the second pass. In the second pass during the return flight of the print head the top intermediate portion is printed as illustrated in Fig. 9. Thereafter, as shown in Fig. 10, the bottom intermediate portion isprinted during the third pass and finally during the fourth pass the bottom one-quarter horizontal portion is printed,
1. In a dot matrix printer having a print head with a linear series of dot printing
elements, the improvement controlling the dot density printed characterized by:
a first means setting the printing angle of said print head such that the axis of said print head can be set in besides the vertical a predetermined angle from the vertical for any one printing operation, and second means responsive to the angular setting of said print head and establishing the number of passes of said print head required to complete a print line at a predetermined dot density without any substantial overlapping between passes.
2. The printer of claim 1 characterized in that a series of three of said predetermined
angles are used, with the ratio of the sine of the angles thereof being 4, 2 and 1,
and the number of said passes corresponding thereto being in the ratio 1, 2 and 4
or wherein said series of three predetermined angles are selected from the group consisting
of, as stated from the horizontal:
(a) 90°; 30°; 14.47°
(b) 45°; 20.70°; 10.18°
(c) 1.6°; 0.8°; 0.4°
3. In a dot matrix printer having a print head with a series of printing elements
producing a series of substantially uniform dots which series in vertical register
span a distance equal to the vertical height of the line to be printed, characterized
by the improvement for controlling the dot density printed per traverse of the print
head comprising:
a first means for setting the printing angle of said print head such that the axis of said series can be set in besides the vertical a predetermined angle from the vertical for any one printing operation, and second means responsive to the angular setting of said head and establishing the number of passes required to complete a line of printing at a predetermined dot distribution density with all printing in a single band of traverse being completed in one pass without substantial overlap between passes.
4. The printer of claim 3 characterized in that said second means includes electronic
control means establishing the firing times of the said printing elements along said
series with respect to said angular setting.
5. A dot matrix printer producing printing of a predetermined quality, characterized
by:
(a) a frame
(b) a platen mounted on said frame
(c) a carriage and carriage way supported on said frame for travel of said carriage across said platen
(d) a dot matrix print head having spaced dot printing elements and carried by said carriage for printing on a receptor sheet interposed between said platen and print head,
said carriage having a first means to rotate said print head with respect to said platen to a predetermined angle of registration for any one printing operation.
6. The dot matrix printer of claim 5 characterized by second means traversing said
carriage and print head over said platen at a preselected speed with reference to
a generated timing signal with said print head traveling one horizontal matrix position
between timing pulses or by second means traversing said carriage and print head over
said platen at a variable speed with reference to a generated timing signal controlling
dot printing element operation.
7. The dot matrix printer of claim 6 characterized by third means introducing print
commands to said print head in synchronism with said timing signal to fire said dot
printing elements only in the areas to be printed during a traverse of said carriage,
said printing elements being arranged linearly, said third means controlling the order
of firing of said elements in said series with respect to said predetermined angle
of registration, all of the dots desired in any one pass level being printed.at one
time with a predetermined amount of dot overlap without need of a second pass thereover,
and
fourth means for advancing said sheet a predetermined distance with respect to said predetermined angle of registration to produce the required number of passes to complete the printing in the quality desired without substantially overprinting a previous pass.
8. The printer of claim 5 characterized by any one or more of the following features
in combination:
(a) said first means includes adjusting means permitting the operator to set said predetermined angle manually;
(b) said print head is set at said predetermined angle of registration by means of a servo motor mounted on said carriage;
(c) said print head has a linear series of said printing elements each comprising a print wire activated by a solenoid, said print wires being spaced apart a distance greater than the diameter of the solenoid therefor.
9. The printer of claim 8(c) characterized in that said print head contains at least
two of said series compactly interleaved to provide at least four pins linearly aligned
at the print ends thereof.
10. A method of dot matrix printing characterized by:
a) traversing a dot matrix print head over a recording medium receptive thereto,
said print head having printing elements disposed to print a linear series of dots,
b) setting the inclination of said print head with respect to the path of traverse at an angle predetermined for any one printing operation,
c) traversing said print head over a line to be printed, printing dots therewith within the areas to be printed, and relating the number of passes of said print head to complete a line of printing without substantial overlap to said angle in which said print head is placed, and
d) controlling the firing of said printing elements to give a desired dot density and dot overlap within said areas to be printed, all of a horizontal section of a line being printed in one pass.
11. The method of claim 18 characterized in that said dot density is determined by
the infinite t matrix technique and said angle is any one of a series of three the
sines of which are in the ratio of 4, 2 and 1, said number of passes corresponding
thereto being in the ratio 1, 2 and 4.
12. A method of dot matrix printing indicia of different print qualities on a dot
matrix printer with a print head having a linear array of at least two equi-spaced
print wires which prints indicia by the selective firing of the print wires as the
print head and a surface, to be printed on, traverse relative to one another characterized
by:
adjusting the angle of the array, relative to the direction of traverse to a desired one of a plurality of predetermined angular settings in dependence on the quality of print desired; and
operating the print head to print all of no more than a substantially discrete band, which extends in said direction, of said indicia on each said traverse; wherein in at least one of said angular settings at least two said traverses are required to complete the printing of each indicia.
13. A method according to claim 12 characterized in that in one said angular setting
said discrete band has a band width encompassing the maximum indicia dimension normal
to said direction; said angular settings are predetermined such that the maximum width
of said indicia normal to said direction is a whole number of said band widths; and
said print head and said surface are indexed relative to one another, normal to said
direction, an amount substantially equal to the width of said band, as determined
by said angular setting, between each said traverse.