EP0082329A2

EP0082329A2 - Compact shuttle printer mechanism

Info

Publication number: EP0082329A2
Application number: EP82110808A
Authority: EP
Inventors: Dennis Harry Kekas; Charles Martin Mccray; William Andrew Grubbs
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1981-12-23
Filing date: 1982-11-23
Publication date: 1983-06-29
Also published as: EP0082329A3; ES8401378A1; EP0082329B1; ES518465A0; DE3273055D1

Abstract

The present dot printer comprises a suspension spring and frame element (1) constituted by two identical E-shaped plate spring elements (2, 3), having each a stile (10), and an upper (11), a central (12) and a lower (13) legs. A member (7) supporting the dot printing elements (22) is connected to the upper pair of legs (10) and positioned in front of and parallely to a platen (26). The central pair of legs (11) are connected to a frame piece (9) which is rigdly affixed to the printer frame. The upper and lower pairs of legs (10, 12) are connected together through a bar (6). Both stiles (10) of both E-shaped elements (2, 3) are also connected together. Driving means (14,15,16) connected to the free ends of both the upper and lower pairs of legs (10, 12), imparts a reciprocating motion, thereto, with a substantial linear velocity, in a direction parallel to a print line. The linear velocity is obtained either through electronic or mechanical means.

Description

Field of the Invention `• ·

This invention relates to dot matrix printers in general and to print head suspension or carrier systems for such printers in particular, and to drive mechanisms for oscillating the print head carrier or suspension systems therein.

Prior Art

A wide variety of dot matrix print mechanisms are known, of course. Those employing a shuttle principle in which print heads are affixed to a movable carrier are commonplace, but those in which the print heads and the carrier move together as a single piece are relatively few. Only U. S. Patent 4,127,334 is presently known to the applicant for this latter type of design.
This patent utilizes a generally E-shaped pair of flexible spring elements to support a rigid frame on which are mounted one or more print heads for reciprocation along a print line. The E-shaped spring elements are known to provide a linear translation when the top and bottom legs of the E-shaped springs are anchored to framework and the center leg is flexed back and forth. Two sets of such E-shaped springs are employed in this known patent, with one set of springs at each end of a general printing region and with the print head framework being affixed to the center legs of the E-shaped springs. This obscures the printing since the line of print produced is in a lower vertical position than the top of the springs. This patent also includes an off-center crank reciprocating driving means operating as an ordinary connecting rod and crank mechanism. This mechanism introduces forces which are not in the desired line of travel and hence introduces unwanted vibrations in a direction perpendicular to the desired printing line. Also, such a mecanism cannot impart a linear velocity to the print head framework and, therefore, makes the control of the printing operation much more complex. In addition, this patent employs compound springs built up from several pieces requiring mechanical affixation in an interconnection with the other elements such as the print head mounting framework and requires additional frame elements for mounting the springs themselves. The complex assembly of multiple pieces is subject to requiring periodic adjustment, lay involve additional manufacturing and maintenance expense, and may also produce a higher degree of unreliability due to the.numerous parts and concommitant potential areas for mechanical failure.

Objects of the Invention

In view .of the foregoing difficulties with the known prior art, it is an object of this invention to provide an improved reciprocating shuttling printer of reduced cost and complexity.
An additional object of the present invention is to provide improved reciprocable driving means to provide a pure linear velocity in direct axial alignment with the motion of the shuttle framework along the printing line.
Still a further object of this invention is to provide a compact, low cost printer of modular form that can be added in replication to a given terminal or printing application where one or more printing stations may be required for the same machine.

Summary

The dot printer according to the invention comprises =

an elongated printing element support member,
. one or more dot printing elements mounted on said support member orthogonally thereto,
. a platen arranged adjacent to and parallel with said support member,
a suspension spring and frame element essentially composed of two identical parallel E-shaped plate spring elements having each a style and three legs, said support member being rigidly mounted between the free ends of the first (upper) pair of legs, the free ends of the second (central) pair of legs being connected to a frame piece which is rigidly affixed to the frame of said printer, said support member and the free ends of the third (lower) pair of legs being connected together through a connector bar, and said styles of both E- shaped element being connected together through braces, and
. drive means causing a linear speed reciprocation movement of said printin element support member in a direction parallel to said platen, without orthogonal or off-axis forces,

According to a specific aspect of the invention, the various part of the suspension spring and frame element and the printing element support member are molded as one piece plastic element,
According to another aspect of the invention the drive means comprise a fixed field magnet and a coil suspended in the field of the magnet and moving thereto upon application of electrical current to the coil, and electronic control means connected to said coil to modify the current in said coil in terms of its displacement, and to move this coil with a linear speed between both ends of its displacement,
According to another aspect of the invention the drive means comprise a uniformly rotating motor, a meshed pair of non circular gears, one of which being coupled to the motor, the other one being coupled to the driving shaft of a crank and rod type mechanism, the geometrical configuration of said non circular gears being such that said driving shaft is rotated at an irregular angular velocity which, when transmitted to said crank and rod type mechanism cause, the free and of said rod to move at a substantially linear velocity.
The invention will now be described with regard to preferred embodiments showing the best modes contemplated for utilizing the invention as shown in the accompanying drawings as follows.

Brief Description of the Drawings

Figure 1 illustrates a pictorial view of the one-piece molded plastic print head suspension, compound cantilever spring and head mounting frame element.
Figure 2 illustrates an exploded schematic view of the major components for the printer utilizing the one-piece molded suspension and spring assembly of the present invention as well as the voice coil driver assembly of the present invention and other elements of the preferred embodiment.
Figure 3 illustrates a schematic cross-sectional view taken toward the edge of the paper in a printer constructed according to the general scheme shown in Figure 2.
Figure 4 illustrates the emitter output, velocity of the print head and direction of travel for several half cycles of operation.
Figure 5 illustrates the air moving function of the vanes of the rear of the E-spring assemblies which are integrally molded with the device shown in Fig. 1.
Figure 6 illustrates an electrical flow chart and schematic diagram for the control and feedback of the voice coil linear driver mechanism shown in Fig. 2.
Figure 7 illustrates the detail of the voice coil winding employed in the preferred embodiment.
Figure 8 is a force and displacement chart for operation of the mechanism shown in Fig. 2 over a complete cycle of oscillation from left to right and back.
Figure 9 is a force and displacement chart for the forces to be generated by the drive means to drive the carrier assembly as shown in Fig. 2.
Figure 10 illustrates an alternative reciprocating drive mechanism utilizing noncircular gears to provide an irregular angular velocity and provide abrupt transitions in direction with a smooth and linear velocity profile intermediate the transitions.
Figure 11 is a comparison of the velocity output profile developed by a mechanism depicted in Fig. 7 as contrasted with normal circular gearing output results.
Figures 12 and 13 schematically illustrate the nomemclature and measurement conventions adopted for describing the non- circular gear set values in connection with Appendix Table I.

Detailed Specification

The print head suspension framework and mounting system which is depicted in Figure 1 is an integrally molded single piece of plastic. The design was originated to obtain the lowest possible parts cost. It requires, due to the flexing of the E-shaped cantilever spring members, a relatively low tensile modulus in order to keep the spring rate as low as possible since the spring loads will be reflected as loads on the moving voice coil driver system. However, creep modulus of the selected material must be sufficiently high so as to minimize cold flow problems. A number of materials were surveyed and parts were modeled. The most effective material is a polysulfone having a creep modulus of 22,750 kg/cm² at 5°C and 280 kg/cm² load, a tensile modulus of 24780 kg/cm² and a specific gravity of 1.37. Other suitable materials are a polyester and copolymers of engineering structural polymer. In general, the desired materials must have 1.1 to 1.4 specific gravity, 23800 kg/cm2 minimum tensile modulus and a creep modulus of 22400 kg/cm² minimum at 50⁰c and 105 kg/cm ² load.
Turning to Figure 1, the one-piece molded print element shuttle suspension and frame member 1 is seen to comprise two relatively E-shaped cantilever spring elements at the ends 2 and 3 respectively.
The molded E-shaped spring members are made such that each member.2 and 3 has first, second and third legs numbered 11, 12 and 13, respectively. Legs 12 are made twice the width of legs 11 and 13 so that the spring rate of the outer leaves 11 and 13 exactly equals that of the center leaf 12. The outer ends forming the bar or stile of the E-shape on each of the spring suspension members 2 and 3 connected together through braces 10a and lOb, the styles and the braces being formed together in a common piece 10. As will be seen later, when the suspension elements of the molded spring assembly are operated in flexure, the end pieces 10 can be utilized to provide a fanning and cooling action for electronic components necessary for the operation of the printer.
Print head carrier frame 7 and aligning member 8 are integrally molded with the spring suspension system. A connector bar 6 connecting the upper framework elements 7 and 8 to the lower framework elements 4 and 5 assures that elements 4, 5, 7 and 8 will move together in reciprocation. Framework element 5 is not visible on the figure because it connects both legs of element 4 and is hidden behind connector bar 6. The oscillatory drive means applies reciprocating forces along the lines EE in Figure 1. This means will be described in greater detail below.
Elements 7 and 8 are shown with alignment holes for accepting wire matrix print heads. It is equally advantageous to employ ink jet dot printers, thermo electric printers, and the like. The holes shown in members 7 and 8 are therefore only indicative of the relative position of a plurality of dot forming heads which may be carried by members 7 and 8.
The frame piece 9 is integrally molded with the E-spring elements and is affixed to the center legs 12 of each Eshaped sprihg end piece 2 and 3,- respectively. Frame piece 9 is affixed to rigid framework in the printing machine mechanism not shown. Thus the center legs 12 are rigidly anchored by the attachment frame members 9 to a mechanical ground.
The element 5 may have attached to it an optical apertured grid strip to serve as a timing emitter of the well known sort normally employed in wire matrix or dot matrix printers to give appropriate timing pulses for use in electronic control system for synchronizing the firing of the dot matrix solenoids or the like to construct the desired characters.
Turning to Figure 2, the overall major component of a preferred embodiment of a dot matrix printer mechanism utilizing the integrally molded spring framework suspension and carrier assembly 1 are shown. A linear voice coil actuator 14 having a movable armature or coil 15 and a driving bulkhead 16 as utilized in the preferred embodiment are also shown together with other elements in the preferred design. A roller member not shown in Figure 2 is affixed to the bottom of the frame member 5 or 4 to interact with the cam member 17 at each end of oscillatory stroke. This action rocks the cam member 17 in a clockwise or counter clockwise direction depending upon the direction of motion of member 4. A oneway clutch 18 torqued by cam 17 provides a unidirectional rotary motion output on shaft 19 for the purpose of incrementing a paper feed roller 20 and driving a ribbon drive spindle 21.
An individual print element 22 is shown positioned coaxially in line with a set of the apertures in the frame member 7 and 8, it being understood that one or more such print-heads 22 may be employed and that they may be of any of a variety of types. An emitter aperture grid 23 containing numerous apertures or slots 24 may be affixed to member 4 or 5 for oscillation back and forth with the carrier and suspension. The emitter grid 23 may pass between the typical photo source and sensor mounting block 25. This block contains a light emitting diode and a photo s.ensor on opposite sides of a slot through which the emitter grid 23 reciprocates in a well known fashion.
A fixed platen 26 is shown positioned adjacent the printing area where the print head 22 will be reciprocated. Paper feed roll 20 can, through a normal friction feeding engagement with a paper supply 2, cause the paper to increment by one dot height. It is necessary to feed the paper supply at the end of each reciprocating stroke of the carrier to begin printing a new dot. This is done by means of cam member 17, one way clutch 18, etc.
Turning to Figure 3, a schematic cross section of the major elements depicted for the assembly in Figure 2 is illustrated. As may be seen, the feed roll 20 is depicted as roll pair 20A and 20B which frictionally grip and drive the paper 27. The cantilever suspension assembly 1 is rigidly affixed by the frame pieces 9 attached to the center leg 12 of each of the E-shaped spring members. The molded framework 7 and 8 are shown together in a mere schematic representation. The print heads 22 would be coplanarly arranged with respect to the printing line on platen 26 as indicated. An overall cover which may incorporate a plastic tearing knife or guide bar 28 is also shown.
Turning to Figure 4, a timing diagram for a preferred embodiment of the printer as schematically illustrated in Figures 2 and 3 is shown.
In Figure 4 line A illustrates a velocity chart versus time. An initial "set up" time between point A and point _C during which the one-piece molded carrier and print head assembly is accelerated from 0 to 396 millimeters per second velocity is shown. This time period may be arbitrary, but typically requires approximately 20 milliseconds. From point C to point D on line A, one full cycle of printing consisting of a left to right and a right to left printing stroke is indicated. The elapsed time of 111 milliseconds (H) is arbitrary and of course longer print lines or greater or lower speeds might be employed. The desired printing stroke covers approximately 16.6 millimeters which is sufficient to encompass 10 dot matrix characters of 5 dots of primary width each. As shown by section E in Figure 4, a brief period at the end of each printing stroke left to right or right to left is allowed for paper feeding time, approximately 13.6 milliseconds as shown. The left to right and right to left print strokes are indicated in sections F and G, respectively, and are truncated to show only a few of the 50 emitter pulses on line B which would be desired. Between the times labeled T_l and T₅₀, these emitter pulses would be produced by the aperture emitter 23 shown in Figure 2. Each emitter pulse has a total duration I which corresponds to a distance of approximately .339 millimeters of lateral travel. Wire firing for wire matrix print heads can be easily timed to the rising or falling edge of such pulses produced by an emitter.
Turning to Figure 5, a plan view of a portion of the integrally molded spring and suspension means 1 is shown. Only the leaves of the E-shaped spring members 11, 12 and 13 and the connecting end pieces 10 are indicated. The rest position is identified as position A in which only the top most leaf 11 of the E-shaped member is visible. On a printing stroke to the right (to position B for element 10) the center leaf 12 becomes exposed as leaves 11 and 13 flex to the left (equivalent to the print head carrier 7, 8 moving toward the right in Figure 1 and 2). In the opposite direction of travel from the rest position A, printing is also accomplished. The left is indicated by the position of element 10 indicated by a letter C. This back and forth motion of the leaves 11, 13 and the common connector members 10 produces a significant air flow shown generally by the arrows in Figure 5 which may be directed or channeled to impinge upon a circuitboard 29 carring electronic component 30 schematically shown as resistances. As is well known in the printer field, electronic circuit boards 29 typically require small cooling fans or other source of air flow to provide adequate cooling and stable operation of sensitive electronic components. By adding a fan shaped flap 10 as the common connector illustrated in Figures 1 and 2, etc., the integrally molded spring and suspension carrier assembly also serves as a fan to provide this cooling flow of air.
The linear voice coil driving assembly 14, 15 and 16 indicated in Figure 2 can be driven electronically using power drive amplifiers -similar to those employed in the audio or high fidelity industry. -The specific drive coils are mounted in the armature 15 and are supplied with current by the circuit shown schematically in Figure 6. An additional winding is supplied in the armature 16 to provide a back electromotive force (EMF) pick up signal providing feedback for the control of the precise velocity and position of the armature 16. The circuitry of Figure 6 schematically shows the overall drive and feedback control technique.
Separate windings 31 and 32 are schematically illustrated and will be described further with respect to specific figures depicting them later. A waveform generator 33 generates a rising voltage waveform of the proper shape and duration (to be described below) at its output 34. This is summed with the feedback coming on line 35 which provides a small correction to the output signals which are then applied to a power driving amplifier 36 for eventually driving coil 31. As current is applied to coil 31 by the amplifier 36, the fixed pole piece 14 (not shown in Figure 6) interacts with the electromagnetically generated field of the coil 31 to cause the coil to move inward or outward along the pole piece in element 14 in a manner similar to which a voice coil drives an ordinary audio speaker element. Feedback signals are generated by an EMF generated in coil 32 through a load resistor 37. These signals are sensed at an input buffer amplifier and inverted in inverter 39 where they may be at the output compared or summed with the output from the waveform generator in the summer 40. These provide, if any difference or excess exists, a feedback control on line 35 to the summer 41 for modifying. the input of power drive amplifier 36 to more accurately control the velocity and position of the moving coil 31. Overall limits on the voltage excursions can be compared in threshold gate 42 and employed to drive an indicator which will be described in further detail below.
The circuit of Figure 6 may be further described as follows. The feedback coil 32 is physically attached to the mounting core of the power drive coil 31 so that the two coils move together in the presence of the same magnetic field. As the power coil 31 moves, an electro motive force will be generated in the feedback coil 32. Under normal operation, this feedback should be identical in amplitude waveform and frequency to that of the drive coil signal coming from the power drive amplifier 36. Should any aberration of motion occur during the operation of the printer such as by means of a paper jam or intrusion of a foreign object, the signal produced by the feedback coil will be different from that provided to the power amplifier 36. The circuit in Figure 6 processes the feedback signal to detect or correct for these conditions.
The feedback signal is sent to an inverting amplifier 39 through a buffer amplifier 38 to avoid any distortion interaction from the feedback coil 32 modifying the operation of the drive coil 31. From the inverting amplifier 39 the signal is summed with the original driving signal in the summer 40 to yield a correction signal. In normal operation the correction signal will be very small and will be centered about 0. The small signals are fed back into the drive amplifier 36 through summer 41. The resulting motion of tne drive coil 31 will be one that better tracks the input waveform. If there is a malfunction such that the motion of the drive coil 31 is impeded and differs significantly from the original driving signal, this will be detected by a threshold gate 42 detecting a level of feedback beyond set limits which may be chosen as desired. This event can be used to shut off power and illuminate a light or LED to notify the user that a regular operating condition has occured. A reset button or switch can be installed if'desired to reset and resume operation.
Details for the drive coil 31 and the feedback coil 32 in the preferred embodiment are as follows.
The drive coil consists of 240 turns in two layers of 120 turns each of close wound enamel insulated #31 gauge magnet wire and exhibits a total resistance of approximately 6.6 ohms. The feedback winding for coil 32 is one layer of 40 turns of #36 gauge enamel insulated magnet wire wound on a -76 mm pitch on the outer layer of the inner drive coil but insulated therefrom by a single layer of insulating tape between windings. This latter winding exhibits 3.6 ohm resis- tince. The return leg of the winding is brought back inside of the turns of the winding coil to hold it securely in place in the same manner that voice coils are wound on bobbins. The coil is shown schematically in Figure 7.
In Figure 7 the moving armature 15 and the driving cross head 16 are attached to a bobbin core 43 which may be of nonmagnetic metal, cardboard, plastic or the like. In the preferred embodiment, this bobbin is made of aluminum for strength and is machined to a smooth finish for a close but non-frictional fit into the aperture of the driving pole piece 14.
Figure 8 illustrates the spiing loading forces moving right and left including the forces occasioned by the cam paper incrementer mechanism 17 and 18, etc. These forces must be supplied by the driving coil and result in the total force shown in Figure 9 for one complete cycle from right to left and back to the right again. As may be understood, when the spring carrier suspension mechanism is deflected to the right or left of center, energy stored in the spring is released so that for at least a portion of the return stroke, the coil need not supply as much force. However, after crossing the center or 0 force position, additional energy must be supplied to deflect the spring in the opposite direction. When these forces are operated at or near the natural period of vibration for the spring suspension system, some efficiency in operation results.
If the frequency of oscillation of current reversal applied to the driving coil is adjusted to be at or approximately the same as the natural period of vibration of the spring and carrier mass suspension system, very small additional forces are required in order to keep the system in motion. These are chiefly those forces which are extracted by the paper incrementing mechanism near each end of the travel from left to right or right to left. Frictional losses are minimum since there are no bearings, pivots, slides, etc. Frictional losses due to air motion are the primary source of loss other than the direct mechanical loss due to extraction of force by the paper incrementing mechanism previously described.
Figure 10 illustrates an alternative mechanical gear and reciprocating crank mechanism to replace the voice coil driver. A motor 44 supplies a continuous uniform velocity output through the matched circular gear set 45 to shaft 46 carrying the first of a noncircular gear set 47A and 47B. The constant angular velocity output at shaft A is converted into an irregular angular velocity output by the non-circular gear set 47A and 47B to provide an irregular angular velocity output on shaft B labeled 48. The one to one circular gear set 49 applies this irregulai velocity to a matched circular gear set 50 through the shaft. In the circular gear set 50, each gear is supplied with a driving pin 51 connected to or journalled in individual arms of a flexible plastic connecting rod 52 like a conventional crank and rod mechanism. This rod 52 provides a direct linear output with no component of force orthogonal to the direction of travel at its output point 53.
A helical thread mounted on a drum 54 operates with fixed interposer pins attached to an incrementing wheel.(not shown) to increment the wheel by one thread pitch length on the helix 54 with each rotation of the shaft. Each full rotation of the shaft 51 provides an increment at the beginning of a rotation (end of the.previous rotation) and another increment halfway through a revolution. Thus, the helical thread is configured to present a cam surface which is not sloped for approximately one-half of a revolution and then it is stepped upward by the distance equal to a given dot row height representing the end of one left to right or right to left stroke at the output 53. This will increment the paper by one dot height. Then, with continued rotation of shaft the shaft, further increment will occur at the end of the return stroke- These details of the helical thread path on drum 54 would be obvious to one of ordinary skill in the art and are not described further.
The flexing drive coupling member 52 can be molded of plastic to reduce cost as is done in the preferred embodiment. The non-circular gear set 47A and 47B is utilized to better control the output motion at point 53. The velocity profile obtained differs substantially from that that would be obtained with normal circular gearing. Figure 11 illustrates the difference.
In Figure 11, the upper curves illustrate the tracing obtained of velocity and time given a normal circular gear set with an input drive rotating at 540 RPM which yields approximately nine cycles per second or 111 milliseconds per cycle. The velocity labeled VI is slightly greater than that at V2 from the effect of the crank pin and angular thrust output being different at one end of the throw from the other as is well known in the mechanical arts.
The lower portion of Figure 11 illustrates the velocity profile versus time that may be obtained with the noncircular gearing shown in Figure 10. Initial high velocity acceleration rates followed by a flat sustained velocity and an abrupt but smooth transition to the opposite direction are shown. The velocity profiles can be designed so that the maximum VI and V2 velocities are equal and that the velocity is maintained at a very steady rate over the interval of a print line which is most desirable.
The non-circular gear set comprises two identical gear of non-circular form. They are so designed that the sum of radii measured from each gear center to their common mesh point is constant. In the case illustrated, the constant is 30 mm. This can be verifed in Appendix Table 1 by adding the radii Rl and R2 at each degree of rotation measured as R for gear 1 in the Table. A full set of radius values for each gear in one-degree increments for 0 through 360 is listed in the Table. For gear 1, r is zero when the longest diameter is horizontal in the small Figure 12. Since each gear will rotate by an amount that will produce an equal peripheral travel and Rl does not equal R2, it follows as shown in Figure 13, that r_l does not equal r₂ for most gear positions. The starting position is shown in Figure 12 with gear 1 set with its longest axis horizontal and defined as 0 degree rotation for purposes of this description. Also for purposes of description, gear 1 in Figure 12 is assumed to rotate counter clockwise. Gear 2 will be engaged with a slight amount of pre-rotation in the clockwise direction as shown in Figure 12 and in the first entry in Table I as 1.49198681 degrees of rotation (measured in this case relative to the gear's shortest axis positioned horizontally). The other table entries follow the same format under each degree of rotation for gear 1. The entries are : degree of rotation r₁, gear designation (gear 1), Rl (tangent radius for gear 1), r ₂ degree of rotation for gear 2, and R2 (tangent radius for gear 2). Further details of the non-circular gear set employed in the preferred embodiment are given below in the Appendix, Table 1 which shows the radius of the gears as a function of angular rotation for one full 360° arc. These gears can be of molded plastic for quiet operation and low cost manufacture. This arrangement has the result of achieving a flat velocity profile across the print line distance. This is of interest in providing high forces for the incrementing function without the limitation of requiring these forces to be extracted from-the maximum ends of travel of a voice coil as disclosed above where the force available requires higher currents at these points.
The flexing V-shaped coupling element 52 provides the unique result of counter balancing orthogonal forces. The two counter rotating gears provide orthogonal forces that directly cancel in the V flex coupling 52. Only the resultant straight linear thrust along the axis of symmetry midway between the two shafts of the output gears are produced along the line shown at the output coupling 53.
This mechanical design for the drive mechanism has the additional advantage in that the motor 44 can supply at its output pulley a continuous rotary drive for driving printing ribbon and the like without the necessity of the more complex stepwise camming and incrementing arrangement necessary with the above disclosed voice coil prime driver designs However, the voice coil design is easily constructed with a minimum of mechanical cost and complexity and provides a basically electronically controlled mechanism. Either drive may be satisfactorily employed provided that appropriate spacings in the emitter grid are used to adjust the aforementioned velocity profile differences.It will be understood that the non- constant velocity output of the voice coil is not a detriment in such operations since actual wire firing timings for printing the dots are derived from a physical displacement registered by the emitter grid.

Claims

1. A dot printer comprising: •

at least one dot printing element (22);

an elongated support member (7) for said printing element,

a platen (26) arranged adjacent to and parallel with said support member,

a suspension spring and frame element (1) comprising two identical and parallel E-shaped plate spring elements (2, 3) having each a stile (10), a first (upper), a second (central) and a third (lower) legs (11, 12, 13), forming a pair of stiles and three pairs of legs, the ends of said support member (7) being respectively connected to the free ends of one pair of said legs, the free ends of at least one of the remaining pairs of legs being rigidly affixed to the frame of said printer to support the whole suspension element, and

drive means (14-16) for reciprocating said support member in a direction parallel to said platen,

characterized in that : :

the ends of said support member (7) are respectively rigidly connected to the free ends of the first (upper) pair of legs (11),

the free ends of the second (central) pair of legs (12) are connected to a frame piece (9) which is rigidly affixed to the frame of said printer,

said support member (7) and the free ends (4) of the third (lower) pair of legs (13) are linked together through a connector bar (6),

said stiles (10) of said E-shaped elements are connected together through braces (10a, 10b),

said drive means are designed to cause a linear speed reciprocation movement of said printing element support member without orthogonal or off-axis forces.

Dot printer according to claim 1, characterized in that said E-shape plate spring elements (2, 3), said support member (7), said frame piece (9) and said connector bar (6) constitute a unitary molded flexible plastic element.

Dot printer, according to claim 1 or 2, characterized in that said drive means are arranged to reciprocate both the first (upper) and the third (lower) pairs of legs (11, 13), thus flexing said first and second pair of legs and moving said support member (7) and said dot printing element (22) back and forth along a print line parallel to said platen (26).

Dot printer according to claim 1, 2 or 3, characterized in that the combined spring rates of said first and third pairs of legs equals that of said second pair of legs.

Dot printer according to any one of the preceding claims characterized in that said drive means comprise :

a fixed field magnet (14),

a winding coil (15) suspended in the field of said magnet and moving with respect thereto upon application of electrical current to said coil, the external end of said coil being connected to said printing element support member for reciprocation thereof, said coil (15) comprising:

a first winding (31) receiving a driving current from a waveform generator (33) and

a second winding (32) including a circuit containing an inverting amplifier (38, 39) sommation means (40, 41) and control means for modifying the driving current applied to said first winding to produce exact tracking between input driving signals to said winding and the resulting physical motion thereof.

Dot printer according-to any one of the previous claims, characterized in that it further comprises :

paper print media drive means (20) for feeding said paper (27) incrementally past said platen (26),

incremental cam and clutch means (17, 18), and

an interposer means so affixed to said suspension spring and frame element as to be reciprocated therewith and to interact with said cam and one way clutch means for providing intermittent rotary output, said intermittent rotary output being connected to said paper media drive and incrementing means (20) to increment said paper at the end of each said reciprocation.

Dot printer according to any one of claims 1 to 4, characterized in that said drive means comprise :

a uniformly rotating motor (44),

a meshed pair of non-circular gears (47A, 47B), one of which (47A) being coupled to said motor (44), the other one (47B) being coupled to the driving shaft of a crank and rod type mechanism (50, 51, 52), the geometrical configuration of said non-circular gears being such that said driving shaft is rotated at an irregular angular velocity which, when transmitted to said crank and rod type mechanism causes the free end of said rod (52) to move at a substantially linear velocity, said free end being connected to said support member (7) to provide said linear reciprocation movement.

Dot printer according to claim 7, characterized in that said driving shaft of said crank and rod mechanism is coupled to the shaft of another identical crank and rod type mechanism arranged symmetrically with respect to the first one, the respective free ends of both rods (52) being connected together and both rods being so mounted that they always form a V, more or less flared according to the angular position of the shafts, but having always the same symmetry axis, which symmetry axis is parallel to the direction of said reciprocating movement.

Dot printer according to any one of the preceding claims, characterized in that said stiles(10) of said E-shaped elements are adapted to cause a fanning of air whenever said legs are flexed back and forth by said reciprocation.

Dot printer according to any one of claims 2 to 9, characterized in that said unitary molded flexible element is molded integrally of a plastic: having a specific gravity of at least 1.06, a tensile modulus of at least 23800 kg/cm ² and a creep modulus of at least 22400 kg/cm² at 5°C and 105 kg/cm 2 load.