US 3698529 A
A serial printer is provided having a movable type-carrying member, a carriage bearing a pair of printing hammers having heads partially superimposed and a fixed interposer having a plurality of elements disposed between the type-carrying member and the hammers. Printing is effected by cooperation of the print hammers and the type-carrying member through the interposer.
Claims available in
Description (OCR text may contain errors)
United States Patent Cattaneo [451 Oct. 17,1972
1541 SERIAL PRINTER WITH FIXED INTERPOSER  Inventor: Sergio Cattaneo, Pavia, Italy  Assignee: Honeywell Information Systems Italia, Caluso, Italy  Filed: July 12, 1971  Appl. No.: 161,581
 Foreign Application Priority Data July 14, 1970 Italy ..27391 A/70  US. Cl. ..197/49, 197/18, 101/93 C  Int. Cl. ..B41j 1/26  Field of Search ..197/18, 53,49; 101/93C  References Cited UNITED STATES PATENTS 2,831,424 4/1958 MacDonald ..101/93 3,012,499 12/1961 Amada ,.10l/93 3,388,782 6/1968 Schwend ..197/49 3,542,182 11/1970 Langenberger ..197/8 3,565,230 2/1971 Webberley ..197/49 3,651,915 3/1972 Folkens ..197/53 Primary Examiner-Edgar S. Burr Attorney-Fred Jacob et a1.
 ABSTRACT A serial printer is provided having a movable type-carrying member, a carriage bearing a pair of printing hammers having heads partially superimposed and a fixed interposer having a plurality of elements disposed between the type-carrying member and the hammers. Printing is effected by cooperation of the print hammers and the type-carrying member through the interposer.
11 Claims, 6 Drawing Figures PATENTEDHBHH 3.698.529
SHEET 1 OF 3 Sergio CATTANEO /NVE/ /TOR ATTORNEY SERIAL PRINTER WITH FIXED INTERPOSER BACKGROUND OF THE INVENTION The present invention relates to high speed impact printers utilized in data processing systems, and particularly to on-the-fly serial printers.
Many different constructive arrangements have been adopted for these printers, so that they may be distinguished in synchronous or asynchronous, front printing or back printing serial printers.
In any case such printers comprise: a type-carrying member kept in continuous motion for bringing in succession all characters of a character set in registration with each predetermined print position; a printing member or printing hammer, actuated at the proper instants, that is when the character which has toprint is in the proper printing position; and a carriage member for moving the printing hammer and, in most cases, also the type-carrying member, along the line of print.
It is known that the required characteristics for such printers are a high printing speed, and a fine quality of printing, and that these characteristics are, in a sense, mutually incompatible.
It is also known that, in order to obtain better performances from the printer, it is suitable to arrange the characters on the type-carrying member as mutually close as possible, so that, for a given time needed for the type-carrying member to bring all characters in front of a given print position, the effective speed of each character while passing through said position may be as low as possible. However, the packing of the characters as mutually close as would be permitted by their dimensions is usually not possible due to other reasons, such as the width of the printing hammer, which in some printers should extend substantially over two adjacent print positions, but must not print two characters at a time; the danger of mechanical interference, the restoration time of the printing hammer, and others.
Some attempts to obviate these disadvantages have been made by introducing an intermediate member in the printing operation, but the mechanical devices employed for these purposes have poor reliability, are limited to peculiar constructive arrangements, and do not completely solve the problem. Some of these constructive arrangements comprise intermediate movable members mounted on the carriage, and associated means for transmitting the motion to these members. The inertia of the carriage is thereby increased and the elements are subject to wear.
In particular, in some printers the motion of the print carriage is not uniform, but is made by steps, and therefore is subject to sharp accelerations and decelerations. In this instance the use of an intermediate member and of the associated means for transmitting the motion, mounted on the carriage, is a negative factor which is prejudicial to the requirement of reduced inertia of the carriage.
An object of the present invention therefore is to increase the packing density of the characters borne by the typecarrying member without increasing the inertia of the carriage, thereby improving the quality of the printing and the performance of the printer.
SUMMARY OF THE INVENTION The aforesaid object is attained, according to the invention, by the use of a fixed intermediate member interposed between printing hammer and typecarrying member, such intermediate member being called henceforth an interposer, said interposer being rigidly mounted on the main frame of the printer extending along the whole print line, and cooperating with a pair of partially superimposed printing hammers.
BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described with reference to the accompanying drawings, wherein:
FIG. 1 is a schematic perspective view of a printer embodying the instant invention;
FIG. 2 is a schematical diagram showing both a top view of the mechanical arrangement and the logical circuit for controlling the operation, according to the invention;
FIG. 3 is a partial front elevation section of a constructive detail of the printer of FIG. '2; and
FIGS. 4a, 4b and 4c are respectively schematic top view, front elevation view and side elevation view of a constructive detail forming a variant of the invention.
DESCRIPTION OF PREFERRED EMBODIMENT FIG. 1 illustrates in its essential elements an asynchronous, on-the-fly, serial printer, of the backprinting type. The drawing is partially sectional, to permit a better overall illustration of the device.
The printer comprises a main frame, including a base plate 1 and two side frames 2 and 3. Cylindrical guidebars 4,5,6,7,8, and 9 along which suitable moving members may glide, are mounted between the side frames 2 and 3. A first print carriage 10, on which a bevel gear pair 11 is mounted, glides along bars 4 and 5. On a shaft 12 of one of the gear wheels, a type-carrying member 13 is mounted, which member takes the form of a wheel, bearing in relief and on its periphery, a set of characters or of other signs. The type-carrying member 13 is kept in continuous rotation at constant speed through a bevel gear pair II operated by a prismatical bar 30 which isdriven by motor means not shown. A second print carriage 14, on which two printing hammers l5 and 16 with a pair of associated electromagnets l7 and 18 are mounted, is disposed to glide along guidebars 6 and 7.
The two hammers l5 and 16 are suitably pivoted so that their printing head may be displaced, by energization of the electromagnets l7 and 18, towards the typecarrying member 13, which is aligned with the hammers.
Suitable brackets mounted on the side frame 2 support two driving pulleys 19 and 20 secured to the shaft 21 which is driven by a motor 22, which may be a stepping motor, or any motor of a type suitable for imparting an incremental motion to the carriage 14.
Two idler pulleys, concealed by the side frame 3, and therefore not shown in FIG I, are mounted on the side frame. Two pulling cables 23 and 24 are stretched between the driving pulleys and the associated idler pulleys, and are respectively hooked to the print carriages l0 and 14. Due to the action of the motor 22 both carriages move therefore in synchronism, and constant mutual alignment, along the print line.
According to the invention, an interposer is formed by a rigid cross piece 25 fixed to the printer frames and bearing a set of flexible blades 26 each having the free tip thereof levelled with the print line, and interposed between the two carriages l and 14.
Each blade 26 is in registration with a print position on which a character may be printed; the distance between their centerlines being therefore equal to a print pitch.
According to one aspect of the invention, each tip of the blades 26 is provided with a relief on its back side, that is, on the side towards the printing hammers l5 and 16. These reliefs are arranged on two orders at two different levels, each order cooperating selectively with a printing hammer or 16. In other words, the blades 26 having a first order relief correspond to the oddnumber print positions,'-and the blades with the second order relief correspond to the even-number print positions. The first of the printing hammers 15, 16 may operate the printing only on the odd-number print position and the second of the hammers l5, 16 only on the even-number print position.
The width of each hammer 15 or 16 in the direction I of the print line is suitably larger than a print pitch and not larger than two print pitches. The reason for this will be clearly explained as the description proceeds. The print receiving medium, not shown, together with the ink ribbon 27, is disposed in the printer between the type-carrying member 13 and the interposer 25, and substantially leans on the blades 26 and on a paper output plate 28 which is conveniently shaped.
On the upper part, the print receiving medium is engaged by two traction devices 29, each one comprising a sprocket chain and a pressing pad. Thetwo traction devices 29 may be moved along the guides 8 and 9 to adjust their mutual distances and the distances from the side frames to the width and the position of the medium, which usually is provided with lateral perforations engageable with the devices 29.
In FIG. 1 only one such device 29 is shown, that is the left one, as seen from the front of the printer.
Both traction devices 29 are driven by a suitable motor means, not shown.
The printer is completed by motor means for driving the ink-ribbon, not shown, and a timing device comprising a timing wheel integral with the typecarrying element and a pick-up device mounted in fixed position on the same carriage and cooperating with the timing wheel.
These devices per se are well known and therefore not illustrated in FIG. 1. For instance, the timing wheel may consist of a disk of ferromagnetic material provided at its periphery with teeth or notches each one associated with a character of the type-carrying element.
The pick-up device may consist of a magnetic flux path having an air gap which is bridged by the timing wheel. The teeth or the notches on the wheel change the width of the air gap, and a winding linked with the flux produces a signal each time a notch or a tooth is in front of the pickup device.
The operation of the described printer is now illustrated for better understanding with reference to the logical-mechanical diagram of FIG. 2, and to the detailed drawing of FIG. 3.
FIG. 2 shows schematically the essential mechanical parts of the printer and the associated electronic circuit for the logical control of the same. There is shown a top view of the typecarrying member 13, having a timing wheel 40, integral thereto, and a pick-up device 41; all mounted on the first print carriage 10. The carriage 10 glides along the print line in proximity to the ink ribbon 27 and a print receiving medium 33. On the opposite side there is located the second print carriage 14 on which two print hammers 15, 16 are mounted. Only the printing heads of the hammers 15, 16 schematically indicated by the rectangles 42 and 43 (FIGS. 2 and 3).
The interposer is located between the printing heads of the hammers and the print receiving medium. It consists of a plurality of flexible blades 26 arranged along the print line and supported by a rigid cross piece as already shown and described with reference to FIG. 1. The flexible blades 26, in correspondence of the print line, have a width equal or slightly larger than the maximum width of the characters to be printed, and are arranged along the print line at a mutual distance equal to the print pitch. The blades 26 bear on the back (with respect to the print medium), reliefs alternatively arranged on two levels.
In FIG. 2, the reliefs of the blades and the heads of the hammers are viewed in a section along the plane BB of FIG. 3. It may be noted that, in FIG. 2, the hammer head 43 is viewed in section from the top, and the hammer head 42, which is at the lower level, is concealed by the former. Similarly the reliefs 44,46, 48, 50 of the blades 26 are viewed in section, and the reliefs 45, 47, 49 are viewed from the top.
FIG. 3 is a front elevation section of the blades and hammers, along the plane AA of FIG. 2 and clearly exhibits the arrangement of the reliefs in two orders. In addition the FIGS. 2 and 3 show that the width of the hammer heads is substantially equal to two print positions. According to the position assumed by the carriage 14 along the print line, the hammer head 43 acts at any one time on a single one of the reliefs 44, 46, 48, 50 and hammer head 42 acts on a single one of the reliefs 45, 47, 49
In addition, FIG. 2 shows in schematic form a block diagram of the circuit controlling the operation of the printer, the diagram being limited to what is needed for an understanding of the invention.
The operation of the printer is controlled by a unit indicated by reference numeral and generically called a logical control unit. This unit 60 produces command signals for executing in due order, and at the required times, the different operations, such as the printing, the advancing of the print carriage from a print position to the following one, carriage return, line feed or jump, backspace, etc.
In particular, through a set of leads 61 the binary code combinations of the different characters to be printed are applied in succession to a comparator circuit 62. The comparator circuit 62 receives in succession, through a lead set 63, the binary code combinations of the different characters of the type-carrying member 13 which are in the proper print position. These code combinations are set up by a counter circuit 64 which receives a succession of timing character pulses emitted by the pick-up device 41.
When the comparison between pulses is positive, that is the two code combinations coincide, the comparator circuit 62 emits a print command signal which is applied through a lead 65 to a variable delay circuit 66. The measure of the delay depends on the time interval occurring between the reception of a clock signal emitted by the logical control unit 60 through leads 68 and 69 and the reception of the print command signal generated by the comparator circuit 62 and received through lead 65.
The signal sent by the logical control unit 60, through lead 70 initiates the carriage advancing operation carried on by circuit 71, and through lead 72, selects one of the two printing hammers through a hammer selecting circuit 73.
The print command signal, suitably delayed by circuit 66 is applied through leads 74 and 75 to a first input lead of two AND gates 76 and 77. An enabling signal, generated by the hammer selecting circuit 73 alternatively for the even-number and odd-number print positions, is alternatively applied to each one of the second inputs of the AND gates 76 and 77 through the leads 78 and 79. The print command signal is therefore applied, at the proper time, through one of the leads 80 and 81, to a predetermined hammer or 16.
Consider now the operation of the summarily described printer, and assume that both print carriages l0 and 14 are in the position shown in FIG. 2 and are standing still. This may be for instance the initial condition for printing a character line.
The type-carrying member 13 rotates at constant speed in the direction indicated by the arrow around the axis 0, and so does the timing disk 40. As the different characters as the one indicated by reference numeral 82 come in registration with the print position, the pick-up 41 emits pulses which let the counter 64 to count on. These pulses are emitted with a leading interval to take into account the finite operation time of the hammers 15, 16.
The counter 64 shows therefore, on its output leads 63, a binary code combination representative of the character which at each instant is in registration with the print position identified by the relief 46.
If at a given instant the logical control unit 60 applies to the comparator circuit 62 a code combination representing a given character to be printed, a waiting time, or latency time, is initiated, which may vary from a null value to a maximum value equal to the rotation period of the typecarrying member 13.
At the end of this latency time, the character to be printed is in the print position and the counter 64 shows at its output leads a code combination coincident with one of the characters to be printed. The comparator circuit 62 emits therefore a print command signal. As no carriage advancing operation has been initiated beforehand, the print carriages l0 and 14 remain standing, and the print command signal is transferred without delay to the selected printing hammers, so that the printing head 43 of the hammer is pushed towards the type-carrying member 13, driving in its motion the blade 26 by means of the associated relief. The print receiving medium 33 and the ink-ribbon 27 are thus pressed for a short time between the blade 26 and the type-carrying member 13, and the medium receives the imprint of the character.
It may be remarked that, even if the width of the hammer head is equal to two print positions, only one character may be printed at a time because the hammer head 43 acts only on the relief 46 and not on relief 47. Therefore, there is no danger of double printing, independently from the spacing of the characters on the typecarrying member 13, as the hammer acts on a single blade at a time, and the width of each blade is equal to the maximum width of the characters to be printed. Thus, the characters may be closely packed on the type-carrying member so, that each one is contained in a case whose width is equal to the maximum width of the character to be printed, the cases being mutually contiguous.
From FIG. 2, it may also be remarked that the rotation center of the type-carrying member 13 at the considered instant is not aligned on the centerline of the print position corresponding to relief 46, but on the middle line between the print positions corresponding to reliefs 46 and 47. The character in print position is therefore slightly oblique with respect to the print plane. This obliqueness is negligible and does not prejudice the print quality. For a type-carrying member having 64 characters equally distributed along its periphery, there results an angle of about 3. However, by a suitable concave shaping of the printing heads, a corresponding convex shaping of the reliefs, and taking advantage of the torsional elasticity of the blades, it is possible to obtain a small twisting of the blades so that the print pressure is uniformly distributed.
The print command signal is transferred also to the logical control unit which in response thereto sends a carriage advancing command to move the carriages to the following print position according to a predetermined law of motion.
According to the invention, by taking advantage of the double hammers and interposed arrangement, when executing the printing of a character in the following position, corresponding to relief 47, the printing may take place during the motion of the carriages 10, 14, without waiting for the carriages to complete the travel of a print pitch.
Assume now that the printing of a character in position 46 (henceforth the print position will be identified by the reference numeral assigned to the reliefs of the corresponding interposer blades 26), has just happened, and that the carriages 10, 14 have started to move toward the right. The logical control unit 60 applies to the comparator circuit 62 the code combination of the new character to be printed. Assume that the counter 64 sends out the same code nearly at the same instant. This means that, as soon as the carriage initiates its displacement, the character to be printed in position 47 is sensed by the pick-up device 41 as present in the print position.
As the printing must be made on position 47, the print command signal coming out of the comparator circuit 62 is suitably delayed in such a way, as to give to the type-carrying member 13 the time necessary for bringing the character into registration with the position 47 The structure of the delay circuit is not relevant for the embodiment of the invention, and there are many technical solutions which may be adopted. Some of these are for instance described in detail in the Italian Pat. No. 885,844, filed Jan. 29, 1970. The print command signal suitably delayed activates the printing by means of the hammer head 42.
The proper hammer is fired because the signal for starting the advancing of the carriages has also been sent to the hammer selecting circuit which in its simpler form may be a flip-flop circuit.
The fact that the hammer 42 has a width equal to two print positions permits printing in position 47 even if the displacement of the carriage has not yet taken place. On the other hand, the interposer permits only a character at a time to be printed, even if the characters are closely set and if the printing head has a width equal to two print positions. The alternative use of two printing hammers, in addition, permits the printing of two characters in close succession, without waiting for the first hammer to be restored to the starting position.
The previous description is made under the assumption that the second printing operation takes place immediately after the first one, but it should be clear that, depending on the instant at which the character to be printed is identified by the comparator 65, the printing may take place at any time during the travel of the carriage, applying a correction delay which takes into account the fraction of the print pitch already travelled, as well as when the travel is accomplished, that is without delay.
It is also clear that a third printing operation on position 48 may be effected only when the travel of the carriage from position 46 to position 47 is accomplished.
The described example has been made with reference to a serial asynchronous printer with backprinting. It is however self-evident that the invention may be applied also to synchronous printers, as well as to front-printing printers, that is, to any arrangement in which a movable type-carrying member brings the different characters in registration with at least two conti guous print positions by a local motion substantially in the direction of the print line, and whereby the printing members are mounted on a print carriage movable along the print line.
In the instance of a front-printing device it is also clear that the different members that is, printing hammer, interposer, type-carrying member, ink-ribbon, print receiving medium, and platen will be arranged in a different order from that described. The use of an interposer as described, rigidly mounted on the frame of the printer, does away with any problem of transmission of motion, and permits one to design movable members with substantially reduced inertia.
Many changes and modifications may be adopted without departing from the spirit and scope of the invention. ln particular, it is now convenient to describe an arrangement whereby each blade of the interposer may co-operate with both hammers, which are selectively controlled, not in accordance with an evenor odd-number print position, but in accordance with the position of the hammer within a print pitch, that is, according to whether the carriage is moving through the first half or the second half of a print pitch. FIGS. 4a, 4b, and 4c illustrate such an arrangement applied, by way of example, to a front-printing printer. Only the parts necessary for an understanding of the invention are shown in the drawing.
FIG. 4a is a top view showing a portion of a platen 90, a portion of a print receiving medium 91, a portion of an ink-ribbon 92, a portion of a type-carrying member comprising three radial tongues 93, 94, 95, a
portion of an interposer comprising reliefs 96, 97, 98 at the tips of as many blades, and two printing hammers 99 and 100.
FIGS. 4b and 4c are respectively a front elevation view and a side elevation sectional view of the same elements and illustrate with greater particularity their relative locations, one to the other.
The type-carrying member is formed by a daisy of flexible tongues 93, 94, each bearing at its extremity a character in relief. The daisy is secured to a shaft 105 which is kept in rotation by suitable motor means (not shown).
The reliefs of the interposer, one for each printing position, and aligned in a single order, are formed from the blades 93, 94, 95, which may be fabricated from hardened steel, by twisting their tip at 90. The interposer is mounted on the printer frame and extends through the entire length of the print line; the type-carrying member and the hammers 96 and 97 are mounted on the print carriage and are moved together according to a prefixed law along the print line.
It may be seen from the drawing that the hammers 96 and 97 are vertically arranged at two different levels so that they overlap partially.
The hammers have a width slightly larger than half print pitch and are arranged horizontally and so staggered that together they cover a whole print pitch or a width slightly larger.
The operation of the printer is, in this instance, as follows. Assume that FlG. 4a shows a rest position of the carriage, and that a predetermined character is to be printed on the print position identified by blade 93. When the character to be printed is brought in registration with said print position, by effect of the motion of the type-carrying member the printing is operated by firing the hammer 99. Directly afterward, the advancement of the carriage to the following position may be initiated.
However, it is not necessary to wait for the carriage travel to be completed to effect the printing in the following print position. It may be remarked that the hammer 100, staggered with respect to the hammer 99, is in suitable position for printing during the whole halfperiod of displacement of the carriage, whereas during the second half period it is the hammer 99 which is in suitable position for printing. Therefore, according to the instant in time during the travel of the carriage at which, the printing must be effected, the hammer 99 or the hammer 100 is selectively fired.
The design of the circuits for operating such selection would not offer difficulty to one skilled in the art and may be adapted to the different specific characteristics of the printer, as in the instance, of an asynchronous or a synchronous type printer. In FIG. 4a a further constructive detail of the interposer is shown. A crosspiece 101 supporting the interposer is provided with an extension 102 having a groove 103 on which a resilient pad 104 is located. This pad 104 is provided to damp the oscillations of the flexible blades of the interposer when the blades return to a rest position.
It is apparent that other constructive arrangements may be considered, for example one whereby the reliefs of the interposers are mounted on rigid pivoted members provided with return springs, or are glidable along suitable guides and so on, without departing from the spirit and scope of the present invention.
What is claimed is:
1. An on-the-fly printer for serially printing along a print line, comprising a main frame, a type-carrying member in steady motion for bringing, in succession, to a print position, every character of a character set, with the direction of movement being substantially parallel to the direction of the print line, a print carriage movable along the print line for occupying in succession all possible positions printing along the print line, a printing member mounted on said print carriage comprising at least two printing hammers having printing heads at least partially superimposed, an interposer member mounted on said frame comprising a rigid crosspiece supporting a plurality of interposer elements, one interposer element being provided for each print position, interposed said interposer elements being between said type-carrier member and said printing hammers, the printing operations being effected by cooperation of said type-carrying member with one of the printing hammers through one of said interposer elements.
2. An on-the-fly printer for serially printing along a print line, comprising a main frame, a print carriage movable along the print line for occupying in succession all possible printing positions along the print line, a type-carrying member mounted on said carriage in steady motion for bringing in succession, to a print position, every character of a character set, with the direction of movement being substantially coincident with the direction of the print line, a printing member mounted on said print carriage comprising at least two printing hammers having printing heads at least partially superimposed, an interposer member mounted on said frame comprising a rigid crosspiece supporting a plurality of interposer elements, one interposer elements being for each print position, said interposer elements being interposed between said type-carrier member and said printing hammers, the printing operations being effected by cooperation of said type-carrying member with one of the printing hammers through one of said interposer elements.
3. A serial on-the-fly printer, comprising a main frame, a first carriage movable along the print line, a type-carrying member in steady motion for bringing in succession to a print position every character of a character set, with the direction of movement being substantially coincident with the direction of the print line, said type-carrying member being mounted on said first carriage, a second carriage movable along the print line for occupying in succession all possible printing positions along the print line, in coincidence with the position occupied at any time by said first carriage, a printing member mounted on said second carriage comprising at least two printing hammers having printing heads at least partially superimposed, an interposer member mounted on said frame comprising a rigid crosspiece supporting a plurality of interposer elements, one interposer element being provided for each print position, said interposer elements being interposed between said type-carrier member and said printing hammers, the printing operations being effected by cooperation of said type-carrying member with one of the printing hammers through one of said interposer elements.
4. The on-the-fly printer of claim 1 whereby the printing heads of said printing hammers are entirely sugerimposed at, at least a first and a second level and ave a width substantially equal to two print positions,
said interposer elements being alternatively provided with reliefs in correspondence of said first and said second level, for cooperating with a single one of said two hammers.
5. The on-the-fly printer of claim 2, whereby the printing heads of the said printing hammers are entirely superimposed at, at least, a first and a second level and have a width substantially equal to two print positions, said interposer elements being alternatively provided with reliefs in correspondence of said first and said second level, for cooperating with a single one of said two hammers.
6. The on-the-fly printer of claim 3, whereby the printing heads of the said printing hammers are entirely superimposed at, at least, a first and a second level and have a width substantially equal proximate to two print positions, said interposer elements being alternatively provided with reliefs in correspondence of said first and said second level, for cooperating with a single one of said two hammers.
7. The on-the-fly printer of claim 1, whereby the printing heads of said printing hammers are partially superimposed on two different levels, and have each a width substantially equal to half the length of a print position.
8. The on-the-fly printer of claim 2 whereby the printing heads of said printing hammers are partially superimposed on two different levels, and have each a width substantially equal to half the length of a print position.
9. The on-the-fly printer of claim 3, whereby the printing heads of said printing hammers are partially superimposed on two different levels, and have each a width substantially equal to half the length of a print position.
10. A serial printer comprising: type-carrying means linearly movable adjacent a plurality of print positions, carriage means linearly movable in a parallel direction with respect to said type-carrying means, printing means disposed on said carriage means and comprising at least two printing hammers partially superimposed, and interposer means comprising a plurality of interposer elements equal to the number of printing positions disposed between said type-carrying means and said printing heads and fixed with respect to linear movement parallel to said type-carrying means and said carriage means whereby printing is effected on a printing medium by movement of one of said printing hammer in a direction perpendicular to said direction of linear movement which printing head movement is translated to said type-carrying means through one of said interposer elements.
11. The serial printer of claim 10 wherein said printing heads are entirely superimposed at, at least a first and a second level and have a width substantially equal to two print positions, said interposer elements being alternatively provided with reliefs corresponding with said first and second levels whereby alternate interposer elements cooperate with a single one of said printing hammers to effect printing.