US 3726213 A
A print hammer having a repetition rate of at least a few hundred cycles per second is disclosed. The high repetition rate is achieved by employing an actuating arm which is electromagnetically driven but most is non-magnetic. The actuating arm is designed to have a small moment of inertia and so that the center of percussion strikes the electromagnet. The electromagnet is a low inductance device. The longitudinal motion of the printing hammer is at least twice the distance travelled by the center of percussion of the actuating arm. The moment of inertia of the printing hammer is kept low by making it of lightweight material and providing a central cavity therein. Impression control is provided by having an energy absorbing means included in the cavity of the hammer. The actuating arm is inhibited from rebounding from its home position because the backstop includes an anti-rebound material. A single spring means is provided to restore the hammer and the actuating arm to their at rest position. Circuit means are provided to open circuit the electromagnet before the hammer has reached the printing position.
Claims available in
Description (OCR text may contain errors)
Unite States atet [191 Herbert 51 Apr. 10, 1973 75 Inventor: Donald G. Herbert, Pittsford, N.Y.
 Assignee: The Singer Company, San Leandro,
 Filed: Dec. 7, 1970  Appl. No.: 95,645
 US. Cl. ..101/93 C  Int. Cl. ..B41j 9/42  Field of Search ..101/93 C, 287, 297, l01/109, 93 MN  References Cited' UNITED STATES PATENTS 1,780,674 11/1930 Ewald ..101/109 2,787,210 4/1957 Shepard ..101/93 C 2,874,634 2/1959 Hense ..101/93 C 3,090,297 5/1963 Wilkins et al. ..101/93 C 3,139,820 7/1964 Kittler ..lOl/93 C 3,152,540 10/1964 Pensavechia et al.. ..101/93 C 3,266,418 8/1966 Russo ..101/93 C 3,266,419 8/1966 Erpel et al. ...101/93 C 3,315,597 4/1967 Elsner 101/109 3,386,376 6/1968 Mutz et al..... ...l0l/93 C 3,504,623 4/1970 Staller ..101/93 C Primary ExaminerWilliam B. Penn Attorney-George W. Killian, Patrick J. Schlesinger, Charles R. Lepchinsky and Jay M. Cantor [5 7] ABSTRACT A print hammer having a repetition rate of at least a few hundred cycles per second is disclosed. The high repetition rate is achieved by employing an actuating arm which is electromagnetically driven but most is non-magnetic. The actuating arm is designed to have a small moment of inertia and so that the center of percussion strikes the electromagnet. The electromagnet is a low inductance device. The longitudinal motion of the printing hammer is at least twice the distance travelled by the center of percussion of the actuating arm. The moment of inertia of the printing hammer is kept low by making it of lightweight material and providing a central cavity therein. Impression control is provided by having an energy absorbing means included in the cavity of the hammer. The actuating arm is inhibited from rebounding from its home position because the backstop includes an anti-rebound material. A single spring means is provided to restore the hammer and the actuating arm to their at rest position. Circuit means are provided to open circuit the electromagnet before the hammer has reached the printing position.
16 Claims, 3 Drawing Figures PATENTEUAPR 1 01975 Fig. 3
INVENTOR. DONALD s. HEBERT AGENT PRINT HAMMER WITH HIGH PETITION BACKGROUND OF THE INVENTION In the impact printing art, a wide variety of printing techniques have been used, including those employed in the ubiquitous typewriter, the drum printer, the wheel printer and the chain or belt printer. With drum and/or chain printers, it is conventional to provide a print hammer for each character position and therefore, in such applications, each print hammer operates only once per printed line and therefore, other considerations and components usually limit the speed of operation. That is, the recycling rate of the printing hammer is not usually a limiting factor in those applications which employ an individual print hammer for each printing position. In other types of printers, notably the wheel or disc printer, it is not unusual to employ a single print hammer. In such applications, the single print hammer, together with the printing wheel or disc, must move character-by-character relative to the document and the hammer must go through an operating cycle for the printing of each character. In such applications, the maximum frequency within which the hammer may be recycled often limits the printing speed. More specifically, the repetition rate of the hammer determines the minimum time which must elapse between the printing of two successive characters.
The print hammer of the present invention is intended for use in a printer which could present successive characters, in their respective printing positions, with only a few milliseconds time separation. The prior art print hammers having the fastest known repetition rate required at least twice as long as was desired for the application for which the hammer of the present invention was designed. Accordingly, the physical characteristics and operating limits of prior art devices were studied and new and novel methods used to obtain a new and improved hammer having improved operating characteristics which permit a hitherto, unattained high repetition rate.
SUMMARY OF THE INVENTION The present invention is characterized by design considerations which provide optimum operating characteristics. These characteristics are provided through use of carefully selected component materials and the incorporation of desired characteristics by giving due consideration to every feature of the design. For example, the location of center of gravity and the center of percussion of the hammer actuating arm have been carefully and judiciously placed at positions which allow optimum operating characteristics. In addition, the moment of inertia of moving parts has been reduced to a minimal value to facilitate rapid motions and high repetition rates. The features which characterize the invention will be found in the following specification and the new and novel aspects of the invention are distinctly set forth in the claims annexed to and forming a part of this specification. Some of the objects of the invention are:
To provide a print hammer for use in a character-bycharacter printer which has a higher repetition rate than prior art hammers;
To provide a print hammer which compensates for document thickness by having an energy absorbing structure which are returned to their at rest position by a single spring;
To provide an actuating armature which has the center of gravity and the center of percussion critically located to prolong the life of the armature and its associated pivot;
To provide a structure having a minimum moment of inertia consistent with the required range of motion of the hammer;
To provide an actuating armature backstop which substantially eliminates any tendency for the armature to rebound from the backstop and wherein the hammer and operating structure have a prolonged life and require a minimum of field adjustments;
These objects, together with other objects, advantages and features of the invention, together with a manner of implementing them will become more apparent as the following description is considered together with the drawing.
BRIEF DESCRIPTION OF THE DRAWING The inventive characteristics of the high repetition rate print hammer will be more clearly understood when reference is bad to the following description considered together with the accompanying drawing, which comprises three figures and wherein:
FIG. 1 is a view of an assembly incorporating the invention;
FIG. 2 is a cross-section view of the hammer assembly of FIG. I, and
FIG. 3 is a cross-section along line 3--3 of FIG. 2.
In accordance with standard drawing practice, a given element of the embodiment incorporating the invention is always identified by the same reference numeral in all figures.
DESCRIPTION OF THE PREFERRED EMBODIMENT ture 10 are mounted on, and supported by, a mounting plate 15, with mounting holes 16 and 17 (see FIG. 2), upstanding portions 18 and 19 for supporting and guiding a longitudinal hammer 31, and upstanding portion 20 for supporting backstop screw 21 and impression control screw 22. Frame members 24 and 25 provide support for pivot pin 26 on which longitudinal actuating means 27 is pivoted. An electromagnetic coil 28 is wound on one leg 23 of a U-shaped magnetic core 29 which is adjustably fastened to the mounting plate 15 by screws 30. Connections, not shown, for selectively completing an electrical circuit to the coil 28 are provided.
The longitudinal hammer 31 is of a rectangular configuration with a rectangular cross section. More specifically, the longitudinal hammer 31 comprises two sides 32 and 33 and ends 34 and 35. Coupled to end 35 is the hammer anvil 36 which is made of a material having the necessary hardness and other desirable characteristics for providing good print quality as it drives the document 37 towards the print wheel 38 to effect a character impression. The longitudinal hammer 31 has a hollow interior. Or, in other words, the longitudinal hammer sides 32 and 33, together with ends 34 and 35 effectively comprise a box without top or bottom. A portion of the end 34 is suitably formed to coact with the longitudinal actuating arm 27, so that when the actuating arm 27 pivots on its pivot 26 and moves in a counterclockwise direction, as seen in FIG. 2, the longitudinal hammer 31 will be driven from right to left and guided by the upstanding portions 18 and 19 of the mounting plate 15. The hammer end 34 and the actuating arm 27 are in contact at point 71 but are separable. Accordingly, when the actuating arm 27 is stopped in its motion by the contact between the magnet insert 67 and the pole face 70, the hammer 31 will continue. in free flight towards the printing impact position. The end 34 of hammer 31 also has a portion 62 formed thereon towards the interior of the longitudinal hammer 31 which serves a dual function to be described more fully hereinafter.
The longitudinal hammer 31 may be thought of as having a longitudinal axis through the center line of the hammer 31. In response to the pivotal reciprocal motion of the longitudinal actuating arm 27, the longitudinal hammer 31 will move reciprocally along the iongitudinal axis of the hammer 31. As already indicated, the hammer 31 is confined within a guiding channel comprising the upstanding portions 18 and 19 of the mounting plate and a portion of the mounting plate 15, itself. In addition, hammer retainer 41 provides an additional guide and retaining means for the longitudinal hammer 31. The hammer retainer 41 bridges upstanding portions 18 and 19 of the mounting plate 15, and it is retained in position by screw 42. The hole 43 (see FIG. 3) in hammer retainer 41 and through which screw 42 passes is an elongated hole which thereby permits some longitudinal motion of the hammer retainer 41 relative to the screw 42. The threaded portion 48 of screw 42 is threaded into tapped hole 49 in the mounting plate 15. The screw 42 has a shoulder 50 which prevents turning the screw 42 far enough that the head of the screw 42 will come in contact with the hammer retainer 41. However, the flat pressure spring 44 does provide sufi'icient pressure to hold the hammer retainer 41 against the upstanding portions 18 and 19 of mounting plate 15. The pressure applied by spring 44 is not so great that the hammer retainer 41 may not be moved longitudinally within the limits of the dimensions of the hole 43.
The impression control screw 22 passes through a hole in upstanding portion of mounting plate 15 and has a threaded end which engages mating threads in hammer retainer 41. Spring 45 surrounding screw 22 is compressed between the inner surface of the upstanding portion 20 of mounting plate 15 and the end 46 of hammer retainer 41 to thereby maintain the head of screw 22 against the upstanding portion 20 and to maintain the hammer retainer 41 at a maximum distance from the upstanding portion 20 of the mounting plate 15. By clockwise rotation of the screw 22, the hammer retainer 41 may be drawn closer to the upstanding portion 20; and by counterclockwise rotation of screw 22, the hammer retainer 41 will be caused to move away from the upstanding portion 20 of mounting plate 15 by the force of spring 45. As will be seen from another portion of this specification, the position of the hammer retainer 41 will provide an impression control means.
As may be seen in FIGS. 2 and 3, the hammer retainer 41 includes a depending portion 51 which supports and retains an impression control energy absorber 61 which is made of an elastomeric material. That is, the energy absorber 61 is designed and positioned to absorb predetermined and selected quantities of energy from the hammer 31. More specifically, when the hammer 31 is actuated by the actuating means 27, the hammer 31 moves from its position of rest which is at the right as viewed in FIGS. 2 and 3 towards the actuated position which is at the left. In response to this motion, the projection 62 on end 34 of the longitudinal hammer 31 will come in contact with the energy absorber 61 and thereby momentarily deform the energy absorber 61. The amount of energy that is absorbed by the energy absorber 61 is a function of several factors including at least: the velocity and mass of the hammer 31, the initial distance between the energy absorber 61 and the projection 62, the total space between the print element 38 and the print anvil 36, and the thickness of the document 37 as well as the force of the spring 63 and the physical properties of the absorber 61. It should be apparent that the spacing between the energy absorber 61 and the projection 62 may be adjusted by moving the hammer retainer 41 in response to rotation of the impression control screw 22. Obviously, the lastmentioned adjustment will influence the maximum deformation of the energy absorber 61 when the hammer 31 is at its maximum leftward position as viewed in FIGS. 2 and 3. it should also be obvious that the thickness of the document 37 will be a factor which limits the maximum leftward position of the hammer 31. As one contemplates the energy that is required to insure satisfactory quality printing, it will be apparent that a lesser quantum of energy is required to print on a relatively thin document 37 than on a relatively thick document 37 of a document pack comprising a plurality of documents and associated carbon paper. Accordingly, it will be seen that the structure shown, including energy absorber 61 and projection 62, comprises an automatic means for adjusting the energy level of the hammer 31 at the time of printing impact so that the energy level is a function of the thickness of the document. To obtain satisfactory results by this means, the elastomeric material used for the energy absorber 61 must have a deflection curve which is suitable to absorb the required quantities of energy to provide optimum print quality. A variety of shapes of the energy absorber 61 combined with the selection of the elastomeric material and the spring 63 may be selected to produce the desired result.
As already indicated, the hammer 31 and the actuating arm 27 are not in contact at the time of printing impact. Thus, the energy available for printing is in the kinetic energy of the hammer 31. As is well known, the best printing quality is obtained, in an on-the-fly printer, when the printing energy is derived from a hammer of low mass and high velocity. Accordingly, the hammer 31 is designed to have a minimum mass, and the electromagnet control means 12, including actuating arm 27, are designed to impart a high velocity to the hammer 31.
If printing is to be down on only one type of document, the impression control means, including energy absorber 61 and projection 62, could be omitted and the desired kinetic energy adjusted by control of the air gap 69, the inductance of the coil 28 and/or the mass of hammer 31 and other well known techniques.
It should be understood that the hammer 31 is in free flight at the time projection 62 contacts absorber 61.
After printing impact, the hammer 31' rebounds and is urged towards its home position by spring 63. When contact between end 34 of hammer 31 and the actuating arm 27 is reestablished, the spring 63 helps to restore the actuating arm.
Some consideration will now be given to the electromagnetic control means 12, the electric energization of which initiates the rightward to leftward propulsion and free flight of the hammer 31. As already set forth, the screws 30 through magnetic core 29 retain the electromagnetic control means 12 on the mounting plate 15. Optimum positioning of this structure 12 may be obtained inasmuch as the holes 66 through which screws 30 pass are elongated to permit the desirable relative motion between the magnetic core 29 and the mounting plate 15. The longitudinal actuating means 27 is designed to have a minimum moment of inertia in order to permit very fast operation and recycling thereof. Accordingly, the actuating means 27 is, for the most part, constructed of a lightweight material which has the desirable and necessary qualities of strength and rigidity. However, -such material is not a magnetic material and therefore, would not be affected by the electrical energizing of coil 28. Accordingly, the longitudinal actuating means 27 has a magnetic insert 67. It should be observed that the magnetic insert 67 is made of a high quality material and has the minimum dimensions which provide acceptable magnetic operation. In addition, the magnetic insert 67 on the actuating arm 27 has its mass located relatively close to the pivot point 26 so that the effect of the mass of the magnetic insert 67 on the total moment of inertia of the actuating arm 27 is kept at a minimum. It should also be understood that the dimensions and mass distribution of the actuating arm 27 have been carefully selected and designed so that the center of percussion thereof is located at approximately point 68. In accordance with well-known principles, relative to moving and rotating bodies, this structure imparts a pure rotational movement to the arm 27 with respect to the pivot point 26. Accordingly, the wear at the pivot point 26 is minimal. In addition, a structure built in accordance with the principles set forth will be quieter in operation than structures having a center of percussion at some other location.
In order to increase the actuating speed of the print hammer 31, the coil 28 is designed with a minimum inductance. Also, to increase the magnetic efficiency of the circuit, the air gap 69 between the magnetic insert 67 and the pole faces 70 of the magnetic core 29 is held to a minimum. However, the hammer 31 must be moved through a greater longitudinal distance than that of the air gap 69, and it is desired to impart a maximum velocity to the hammer 31. Accordingly, the contact point 71 between the actuating arm 27 and the hammer 31 is removed from the pivot point 26 a distance which is at least twice the distance of the center of percussion 68 from the pivot point 26. Accordingly, the longitudinal motion of contact point 71 and hammer 31 will be at least twice the distance of the air gap 69. The hammer 31 will also move an additional amount in free flight. In the design of the actuating arm 27, careful consideration must be given to the effect of the moment of inertia of the arm 27 as the contact point 71 is moved further away from the pivot point 26. An optimum balance between high velocity at point 71 and the detrimental affect of an increased moment of inertia must be obtained.
In accordance with standard procedures and good design practice which are well known to those skilled in the art of high speed electromechanical mechanisms, any of a variety of electronic techniques (not shown) may be employed for energizing coil 28 to initiate actuation of arm 27 and to de-energize the coil 28 at an optimum time which will assure that the hammer 31 will be propelled to its maximum leftward position at maximum velocity and yet be ready to return towards the rest position when the hammer 31 rebounds from the printing impact and is driven towards the rest position by spring 63. That is, the hammer structure 10 is designed for an on-the-fly printer wherein the print wheel 38 is constantly rotating. Accordingly, the anvil 36 must strike the document 37 and press it against a character on the type wheel 38 and start on its return motion in a minimum period of time in order to avoid smearing the print on the document. Therefore, by the time the character from the print wheel 38 has been printed on the document 37, the coil 28 has been deenergized and the hammer 31 is free to move to its rightward position and the actuating arm 27 is free to pivot in the clockwise direction about pivot pin 26. As previously mentioned, the energy absorbing element 61 coacting with the projection 62 controls the residual energy of the hammer 31 at the time of printing impact. It should be observed that the energy absorber 61 is mounted on the hammer retainer 41 and that the energy absorber 61 does not move with the hammer 31 except to the extent that the energy absorber 61 is momentarily deformed by the projection 62 on the hammer 31. Coupled between the energy absorber 61 and the projection 62 is a compression spring 63. The energy stored in the compression spring 63 when the hammer 31 is propelled to its leftward position is used to drive the hammer 31 and the actuating arm 27 to their rightward and clockwise positions, respectfully.
The clockwsie rotational limit of the actuating arm 27 is controlled by backstop screw 21 which has an elastomeric insert 76 with which the actuating arm 27 comes in contact. The elastomeric insert 76 serves to completely damp the motion of the actuating arm 27 so that it does not rebound from the elastomeric insert 76. Accordingly, the actuating arm 27 is immediately available for a reactuation. The air gap 69, and therefore, the total maximum travel of the hammer 31 may be controlled by the rotation of backstop screw 21. That is, to reduce the air gap 69, the backstop screw 21 may be turned in a clockwise direction; and to increase the air gap 69, the backstop screw 21 may be rotated counterclockwise. In addition, of course, a course control over the air gap space 69 may be obtained by loosening screws 30 and positioning the magnetic core 29 relative to the frame 15.
The backstop screw 21 is not located in line with the center of percussion 68 as it is desired to have spring 63 apply a slight force to position actuating arm 27 in a fixed location. That is, if the backstop screw 21 were in line with the center of percussion 68, the actuating arm 27 would be floating and the air gap 69 would not be constant and therefore, the operating characteristics would not be consistent. Also with the backstop screw 21 closer to the point 71, it is easier to provide the desired adjustment of the air gap 69.
In order to hold and retain the document 37 in the desired position between the print wheel 38 and the hammer anvil 36 during printing, appropriate and conventional paper guides are provided. For example, paper guide 80 is attached to upstanding portion 18 of mounting plate 15 by screws 81. By means not shown and which do not form a part of the present invention, the paper guide 80 is spring biased towards the print wheel 38 to lightly clamp the document 36 between the paper guide 80 and another document supporting paper guide (not shown) between the print wheel 38 and the document 37. Obviously, the paper guide 80 has a window, or cutaway portion, so that printing may be facilitated. The drawing of the present invention does not illustrate the use of any type of inking ribbon between the print wheel 38 and the document 37. This is because in the embodiment illustrated, the print wheel 38 is inked as it passes over an inked roller. However, if desired, a conventional inked ribbon could be employed.
While there has been shown and described what is considered at present to be the preferred embodiment of the invention, modifications thereto will readily occur to those skilled in the related arts. It is not desired, therefore, that the invention be limited to the specific embodiment shown and described, and it is intended to cover in the appended claims, all such modifications as may fall within the true spirit and scope of the invention.
What is claimed is:
l. A print hammer for an on-the-fly printer comprising:
a. a longitudinal hammer having a central longitudinal cavity and supported for linear reciprocal motion along the longitudinal axis thereof from a normal first position toward a second print position;
b. a hardened hammer face secured to one end of said longitudinal hammer for providing printing impact;
c. electromagnetic drive means for contacting said hammer at the end opposite the hammer face for imparting a fixed quantum of energy thereto as said drive means drives said hammer from said first position toward said second print position;
d. adjustable energy absorbing means positioned within said cavity and cooperating with said longitudinal hammer for absorbing a predetermined portion of said fixed quantum of energy wherein said predetermined portion is a function of the magnitude of the linear motion of said longitudinal hammer from said first position toward said second position,
e. frame means for supporting and guiding said longitudinal hammer; and wherein said f. energy absorbing means comprises:
1. a first element adjustably secured to the frame and extending into said hammer cavity; and
2. a second element formed on the interior of said hammer and extending into said cavity along the longitudinal axis of the hammer to contact said first element when the hammer is driven toward its print position.
2. The combination as set forth in claim 1 and including spring means positioned within said cavity and cooperating with said first and second elements for biasing said longitudinal hammer toward said first positron.
3. The combination as set forth in claim 1 wherein said adjusting means includes screw means securing the second element to the frame means for adjusting the position of said second element relative to said frame and along the longitudinal axis of the hammer so that said predetermined portion of said fixed quantum of energy which is absorbed may be selectively adjusted.
4. The combination as set forth in claim 1 wherein said drive means comprises:
a. a longitudinal actuating arm pivotally supported at one end for limited reciprocal motion and having the other end thereof positioned to contact said longitudinal hammer to drive the hammer toward its second position and wherein the longitudinal axes of said hammer, said actuating arm, and the pivot of said arms are substantially mutually perpendicular.
. The combination as set forth in claim 4 and includelectromagnetic control means to selectively apply a driving force to said actuating arm to impart said fixed quantum of energy to said longitudinal hammer when the arm contacts the hammer to drive it toward its second position.
6. The combination as set forth in claim 5 wherein said electromagnet control means includes pivot limiting means for limiting the pivotal motion of said longitudinal actuating arm when said longitudinal actuating arm is moving in the direction to drive said longitudinal hammer toward said second position, and wherein said driving force is terminated before said longitudinal hammer is completely driven to said second position.
7. The combination as set forth in claim 6 and wherein the center of percussion of said longitudinal actuating arm is situated in the area of the arm which engages said limiting means.
8. The combination as set forth in claim 7 and wherein the distance along said pivot to said center of percussion is less than the distance from said center of percussion to the point of contact between said other end of said actuating arm and said longitudinal hammer.
9. The combination as set forth in claim 8 and including a single spring means for urging said longitudinal hammer and said longitudinal actuating arm toward said first position.
10. The combination as set forth in claim 9 and including a backstop for limiting the pivotal motion of said longitudinal actuating arm as said longitudinal hammer is urged toward said first position thereof by said single spring means.
11. The combination as set forth in claim 10 wherein said backstop includes a vibration damping material.
12. The combination as set forth in claim 5 wherein said longitudinal actuating arm comprises a nonmagnetic material which is lightweight in comparison with magnetic material and a magnetic material insert is provided in the arm adjacent to said electromagnetic control means for control of the reciprocal motion of said arm thereby.
13. The combination as set forth in claim 12 wherein said longitudinal hammer comprises a nonmagnetic material which is lightweight in comparison with said magnetic material.
14. The combination as set forth in claim 13 wherein the moment of inertia of said longitudinal actuating arm is less than the moment of inertia of said longitudinal hammer.
15. The combination as set forth in claim 14 wherein the distance from the center of gravity of said longitudinal actuating arm to the axis of said longitudinal hammer is at least twice the distance from the center of gravity of said longitudinal actuating arm to the pivot point thereof.
16. The combination as set forth in claim 15 and including a. single spring means for urging said longitudinal hammer toward said first position thereof and the arm to one limit of its range of reciprocal movement.
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