Printing needle drive
United States Patent 3892175
In a wire printer, in which a plurality of selected printing needles are simultaneously advanced to print a character, each printing needle is operated by a lever to which the plunger armature of an electromagnet is secured at a smaller distance from the lever fulcrum than the printing needle so that the needle stroke is greater and faster than the armature stroke. The lever is preferably resilient, and the mass of the needle is selected so that upon actuation of the armature, the lever is at first slowed down by the mass of the printing needle and then recoils to move at a higher speed than the armature, and to continue in a free stroke when the armature is stopped at the end of the armature stroke. Preferably, the attaching end portion of the wire which forms the printing needle, is wound in a coil around the lever to permit resilient yielding of the printing needle when abutting a printing surface at the end of the needle stroke.
US Patent References:
Printing device
Foley et al. - July 1963 - 3099711
Electromagnetic actuating means for wire printers
Bradshaw - November 1965 - 3217640
Print hammer assembly for high speed printers
Russo - August 1966 - 3266418
Flexible wire guide cable
Nordin - August 1967 - 3333667
PRINTING MEMBER SELECTOR AND DRIVE MEANS
Rapparlie et al. - February 1971 - 3561355
Printing device
Foley et al. - July 1963 - 3099711
Electromagnetic actuating means for wire printers
Bradshaw - November 1965 - 3217640
Print hammer assembly for high speed printers
Russo - August 1966 - 3266418
Flexible wire guide cable
Nordin - August 1967 - 3333667
PRINTING MEMBER SELECTOR AND DRIVE MEANS
Rapparlie et al. - February 1971 - 3561355
Inventors:
Heindke, Armin (Pfaffenweiler, DT)
Mutz, Gerhard (Villingen, DT)
Hirt, Albert (Villingen, DT)
Winkler, Werner (Furtwangen, DT)
Mutz, Gerhard (Villingen, DT)
Hirt, Albert (Villingen, DT)
Winkler, Werner (Furtwangen, DT)
Application Number:
05/370059
Publication Date:
07/01/1975
Filing Date:
06/14/1973
View Patent Images:
Export Citation:
Assignee:
Kienzle Apparte GmbH (Villingen, DT)
Primary Class:
Other Classes:
400/124.310, 335/230
International Classes:
B41J2/26; B41J2/285; B41J2/25; B41J2/27; B41J3/10; H01F7/08
Field of Search:
197/1R 101/93R,1R,93MN,93.05 335/230,324
US Patent References:
Primary Examiner:
Eickholt E. H.
Attorney, Agent or Firm:
Striker, Michael S.
Claims:
We claim
1. Printing needle drive comprising supporting means; elongated lever means having a fulcrum mounted on said supporting means and being formed over the whole length thereof from resilient material; printing needle means secured to a first portion of said lever means and projecting therefrom transversely to said lever means; and electromagnetic means including a movable armature connected with a second portion of said lever means spaced from said fulcrum a smaller distance than said first portion so that when said armature is moved in an armature stroke of predetermined length, said needle means is moved in a needle stroke of proportionally greater length, and at a higher speed than said armature, the mass of said needle means having a predetermined magnitude to prevent movement of said first portion of said lever means during the first part of said armature stroke whereby said resilient lever means is resiliently deformed and tensioned so that said resilient lever means recoils during the second part of said armature stroke and accelerates said needle means faster than said armature is accelerated when said electromagnet means is energized.
2. Printing needle drive as claimed in claim 1 wherein said supporting means include pivot means at one end of said lever means for mounting said fulcrum of said lever means; wherein said first portion is an end portion, located at the other end of said lever means; and wherein said armature is connected with said second portion intermediate said ends.
3. Printing needle drive as claimed in claim 1 wherein said electromagnetic means includes an annular winding; wherein said armature is axially movable in said annular winding and has an armature end portion projecting from said winding and directly secured to said second portion of said lever means.
4. Printing needle drive as claimed in claim 1 wherein said lever means is a resilient steel rod having said second portion located in a bore in said armature.
5. Printing needle drive as claimed in claim 1 wherein said printing needle means includes a wire having a projecting printing end portion, and a resilient attaching end portion attached to said first portion of said lever means so that said wire is resiliently secured to said lever means.
6. Printing needle drive as claimed in claim 5 wherein said resilient attaching portion of said wire is wound to form a coil tightly surrounding said first portion of said lever means so that said printing end portion of said wire is resiliently secured to said lever means.
7. Printing needle drive as claimed in claim 2 wherein the thickness and rigidity of said wire is selected so that at least the first turn of said coil resiliently spreads and increases the diameter thereof when said projecting printing end portion abuts a printing surface at the end of said needle stroke.
8. Printing needle drive comprising support means; lever means having a fulcrum mounted on said supporting means and an end portion opposite said fulcrum; printing needle means including a wire having a printing end portion projecting transversely from said end portion of said lever means and a resilient attaching end portion forming a coil tightly surrounding said end portion of said lever means so that printing end portion is resiliently secured to said lever means; an oscillation supressing jacket consisting of synthetic material and enveloping said coil, said end portion in said coil, and a portion of said wire adjacent said coil; and electromagnetic means including a movable armature connected with a second portion of said lever means spaced from said fulcrum a smaller distance than said end portion so that when said armature is moved in an armature stroke of predetermined length, said needle means is moved in a needle stroke of proportionally greater length, and at a higher speed than said armature.
9. Printing needle drive as claimed in claim 8, wherein said lever means is resilient, and including stop means on said supporting means for stopping said armature at the end of said armature stroke; and a damping member mounted on said support means adjacent said end portion of said lever means and on the side thereof opposite the side from which said printing end portion of said needle means projects, said damping member being engaged with said jacket when said lever means reverses and resiliently returns to the initial postion thereof after said needle means has performed said needle stroke.
10. Printing needle drive as claimed in claim 8 wherein said coil has an axis; wherein said wire includes an intermediate portion between said printing end portion and said coil, said printing end portion being straight and being located in an imaginary line passing through said axis of said coil, and said intermediate portion being cranked out of said line and extending tangentially to the first turn of said coil.
11. Printing needle drive comprising supporting means;
12. Printing needle drive as claimed in claim 11, and including adjustable stop means mounted on said supporting means and engaging said armature when the latter is returned by said return spring to said rest position.
13. Printing needle drive comprising supporting means; resilient lever means having a fulcrum mounted on said supporting means; printing needle means secured to a first portion of said lever means and projecting therefrom transversely to said lever means; and electromagnetic means including a movable armature connected with a second portion of said lever means spaced from said fulcrum a smaller distance than said first portion so that when said armature is moved in an armature stroke of predetermined length, said needle means is moved in a needle stroke of proportionally greater length, and at a higher speed than said armature, the mass of said needle means having a predetermined magnitude to prevent movement of said first portion of said lever means during the first part of said armature stroke whereby said resilient means is resiliently deformed and tensioned so that said resilient lever means recoils during the second part of said armature stroke and accelerates said needle means faster than said armature is accelerated when said electromagnet means is energized, said supporting means including stop means for stopping said armature at the end of said armature stroke so that said recoiling resilient lever means continues to move said needle means in a free needle stroke after said stop means has stopped said armature, and said supporting means including further a damping member located adjacent said first portion on the side of said lever means remote from said needle means, and being engaged by said first portion when said lever means reverses and resiliently returns to the initial position thereof after performing said free needle stroke.
1. Printing needle drive comprising supporting means; elongated lever means having a fulcrum mounted on said supporting means and being formed over the whole length thereof from resilient material; printing needle means secured to a first portion of said lever means and projecting therefrom transversely to said lever means; and electromagnetic means including a movable armature connected with a second portion of said lever means spaced from said fulcrum a smaller distance than said first portion so that when said armature is moved in an armature stroke of predetermined length, said needle means is moved in a needle stroke of proportionally greater length, and at a higher speed than said armature, the mass of said needle means having a predetermined magnitude to prevent movement of said first portion of said lever means during the first part of said armature stroke whereby said resilient lever means is resiliently deformed and tensioned so that said resilient lever means recoils during the second part of said armature stroke and accelerates said needle means faster than said armature is accelerated when said electromagnet means is energized.
2. Printing needle drive as claimed in claim 1 wherein said supporting means include pivot means at one end of said lever means for mounting said fulcrum of said lever means; wherein said first portion is an end portion, located at the other end of said lever means; and wherein said armature is connected with said second portion intermediate said ends.
3. Printing needle drive as claimed in claim 1 wherein said electromagnetic means includes an annular winding; wherein said armature is axially movable in said annular winding and has an armature end portion projecting from said winding and directly secured to said second portion of said lever means.
4. Printing needle drive as claimed in claim 1 wherein said lever means is a resilient steel rod having said second portion located in a bore in said armature.
5. Printing needle drive as claimed in claim 1 wherein said printing needle means includes a wire having a projecting printing end portion, and a resilient attaching end portion attached to said first portion of said lever means so that said wire is resiliently secured to said lever means.
6. Printing needle drive as claimed in claim 5 wherein said resilient attaching portion of said wire is wound to form a coil tightly surrounding said first portion of said lever means so that said printing end portion of said wire is resiliently secured to said lever means.
7. Printing needle drive as claimed in claim 2 wherein the thickness and rigidity of said wire is selected so that at least the first turn of said coil resiliently spreads and increases the diameter thereof when said projecting printing end portion abuts a printing surface at the end of said needle stroke.
8. Printing needle drive comprising support means; lever means having a fulcrum mounted on said supporting means and an end portion opposite said fulcrum; printing needle means including a wire having a printing end portion projecting transversely from said end portion of said lever means and a resilient attaching end portion forming a coil tightly surrounding said end portion of said lever means so that printing end portion is resiliently secured to said lever means; an oscillation supressing jacket consisting of synthetic material and enveloping said coil, said end portion in said coil, and a portion of said wire adjacent said coil; and electromagnetic means including a movable armature connected with a second portion of said lever means spaced from said fulcrum a smaller distance than said end portion so that when said armature is moved in an armature stroke of predetermined length, said needle means is moved in a needle stroke of proportionally greater length, and at a higher speed than said armature.
9. Printing needle drive as claimed in claim 8, wherein said lever means is resilient, and including stop means on said supporting means for stopping said armature at the end of said armature stroke; and a damping member mounted on said support means adjacent said end portion of said lever means and on the side thereof opposite the side from which said printing end portion of said needle means projects, said damping member being engaged with said jacket when said lever means reverses and resiliently returns to the initial postion thereof after said needle means has performed said needle stroke.
10. Printing needle drive as claimed in claim 8 wherein said coil has an axis; wherein said wire includes an intermediate portion between said printing end portion and said coil, said printing end portion being straight and being located in an imaginary line passing through said axis of said coil, and said intermediate portion being cranked out of said line and extending tangentially to the first turn of said coil.
11. Printing needle drive comprising supporting means;
12. Printing needle drive as claimed in claim 11, and including adjustable stop means mounted on said supporting means and engaging said armature when the latter is returned by said return spring to said rest position.
13. Printing needle drive comprising supporting means; resilient lever means having a fulcrum mounted on said supporting means; printing needle means secured to a first portion of said lever means and projecting therefrom transversely to said lever means; and electromagnetic means including a movable armature connected with a second portion of said lever means spaced from said fulcrum a smaller distance than said first portion so that when said armature is moved in an armature stroke of predetermined length, said needle means is moved in a needle stroke of proportionally greater length, and at a higher speed than said armature, the mass of said needle means having a predetermined magnitude to prevent movement of said first portion of said lever means during the first part of said armature stroke whereby said resilient means is resiliently deformed and tensioned so that said resilient lever means recoils during the second part of said armature stroke and accelerates said needle means faster than said armature is accelerated when said electromagnet means is energized, said supporting means including stop means for stopping said armature at the end of said armature stroke so that said recoiling resilient lever means continues to move said needle means in a free needle stroke after said stop means has stopped said armature, and said supporting means including further a damping member located adjacent said first portion on the side of said lever means remote from said needle means, and being engaged by said first portion when said lever means reverses and resiliently returns to the initial position thereof after performing said free needle stroke.
Description:
BACKGROUND OF THE INVENTION
The present invention relates to a wire printer or needle printer in which the characters to be printed are formed by a plurality of points printed by printing wires or needles. Matrix printers are known in which, for example, 5 times 7 needles are arranged in lines and columns in the printing head, and selectively operated to form and print the desired character. After a tabulating step, the next character is printed in the same manner. Another wire printer is known in which only seven needles are mounted in the printing head, which are arranged in a column at right angles to the line direction. A character to be printed is formed in several steps of the printing head, the selected printing needles of the columns being operated after each step so that after for example, five steps, a character is completed. After corresponding spacing steps by which the normal spacing between characters is obtained, the printing of the next following character is carried out in the same manner.
Modern wire printers of this type use an electromagnet for actuating each printing needle or wire. When the electromagnet is energized, the respective needle is rapidly advanced out of an initial position of rest to a printing position abutting the ink ribbon, and producing imprints on a paper sheet, and if desired on carbon copies, as disclosed, for example, in the German OS 1,943,675.
The printing needles or wires are substantially straight, or slightly bent toward the respective electromagnets, and partly guided in guide tubes, so that a rigid connection is formed between the printing surface and the armature of the electromagnet when the printing operation is carried out. This requires an extremely precise adjustment of the printing needle stroke, since otherwise, if the stroke is too long, the ink ribbon and even the paper sheet is perforated, or if the needle stroke is too short, only a weak impression or no impression at all is made. If the needle stroke is far too great, excessive bending and buckling forces are produced, which may cause breakage of the needle. Particularly, at high printing frequencies, the danger of breakage of the needles due to oscillations is great.
The German AS 1,270,858 discloses a printer of this type in which the printing needle is connected with the armature by a hook and eye connection providing some lost motion. However, this arrangement has not been fully successful.
The German Pat. No. 1,270,859 discloses an arrangement in which the armature of the electromagnet is tiltable and provided with an elastic arm on which the rear end of the printing needle abuts. Since the arm is elastic, the connection between the armature and the printing needle is not rigid, but the frequency of the needle actuations is substantially reduced because a tiltable armature has a very low efficiency due to the inherently large stray field, as compared with a plunger armature. To compensate this disadvantage a slot and pin connection between the printing needle and the armature is used.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved printing needle drive which operates at high efficiency and is capable of operating the printing needles at a high speed.
Another object of the invention is to combine the high efficiency of an electromagnet with a plunger armature, with transmission of motion from the armature to the printing needle by resilient means.
Another object of the invention is to connect the armature with the respective printing needles by a lever in such a manner that the armature stroke is shorter than the printing needle stroke.
Another object of the invention is to mount the printing needle on resilient means, so that breakage due to a rigid connection between the armature and the printing needle is avoided.
Another object of the invention is to connect an armature by means of a resilient lever with the printing needle to obtain free movement of the printing needle due to elastic recoil when the armature is stopped at the end of its stroke.
Another object of the invention is to provide a form-locking connection between the printing wire and the respective armature.
With these objects in view, an embodiment of the invention comprises lever means having a fulcrum; a printing needle means secured to a first portion of the lever means; electromagnetic means including a movable armature connected with a second portion of the lever means spaced from the fulcrum a smaller distance than the first portion so that when the armature is moved in an armature stroke of predetermined length, the needle means is moved in a needle stroke of proportionally greater length, and at a higher speed than the armature. In the preferred embodiment of the invention, pivot means are provided at one end of the lever means, the first portion is an end portion located at the other end of the lever means and the armature is connected with the second portion intermediate the ends of the second lever means. Preferably, the armature is a plunger armature movable in an annular winding and having a portion projecting from the winding and secured to the second portion of the lever means.
In the preferred embodiment of the invention, the lever means is resilient, and the mass of the needle means has such a predetermined magnitude to momentarily prevent movement of the first portion during the first part of the armature stroke by the resilient lever means resiliently deforms and is tensioned so that the lever means recoils during the second part of the armature stroke and accelerates the needle means faster than the armature is accelerated.
A stop means is provided for stopping the armature at the end of the armature stroke so that the recoiling resilient lever means continues to move the needle means in a free needle stroke after the stop means has stopped the armature.
The printing needle means preferably includes a wire having a projecting printing end portion, and a resilient attaching end portion wound in a coil surrounding the end portion of the lever means.
It is particularly advantageous to provide a wire including an intermediate portion between the printing end portion and the coil. The printing end portion is located in an imaginary line passing through the axis of the coil, and the intermediate portion is cranked out of the imaginary line and extends tangentially to the first turn of the coil so that the same spreads when the printing end portion abuts a printing surface.
The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is an axial sectional view illustrating an embodiment of a printing needle drive according to the invention;
FIG. 2 is a side view illustrating one printing needle;
FIG. 3 is a plan view illustrating the printing needle of FIG. 2; and
FIGS. 4a, 4b and 4c are fragmentary sectional views illustrating successive positions of the armature and needle means during a printing operation.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to FIG. 1, an electromagnet 1 includes an annular or tubular winding 1a surrounding a plunger armature 2 and a fixed core 10 forming a stop 10a for the axially movable armature 2. A return spring 9 is mounted on a supporting frame 40 and passes through a bore in the end portion 3 of armature 2 so that armature 2 is biased to a position abutting an adjustable screw 4 threaded into the supporting frame 40 and secured by a nut 5. When winding 1a is energized, the plunger armature is pulled against the action of spring 9 until abutting the stop portion 10a of the fixed core 10.
In addition to the bore 3b, the end portion 3 of armature 2 has a bore 3a through which the portion 6b of the elastic lever 6 passes. A member 7a is secured to one end of lever 6 and carries a pivot pin 7b mounted on a bracket 41 of the supporting means so that lever 6 is turnable about the fulcrum formed by the pivot 7b. The other end of lever 6 has an end portion 6a to which a printing needle 8 is attached by a form-locking connection. The printing needle portion 8b is only partly shown in FIG. 1, and it will be understood that the printing end portions 8b of a plurality of printing needles are combined in a printing head for printing points which together form a character. The printing head has bores for guiding the printing end portions 8b, respectively, during the printing stroke.
When the winding 1a is energized, the armature 2 is drawn into the electromagnet 1, tensioning the return spring 9 and moving the lever 6. The downward armature stroke of armature 2 as viewed in the drawing, is limited by the stop portion 10a of the fixed iron core 10, and is preferably 0.4 mm. Since the center portion 6b of lever 6 moves the same distance as the armature 2, its end portion 6a moves a distance of 0.8 mm. taking along the printing needle 8, so that the needle stroke is twice as great than the armature stroke due to the fact that the distance between the armature 3 and the pivot 7b is only half the distance between the lever end portion 6a and the pivot means 7b. In this manner a small armature stroke results in a larger printing stroke of the printing needle 8, and in a high speed of the needle movement. As a result, the armature stroke can be very small, which permits a very high frequency of the armature strokes.
As shown in FIGS. 1 and 2, the printing needle 8 has a resilient attaching portion which is constituted by a coil 8a formed of the wire which ends in the printing needle 8. The wire of the printing needle 8 is preferably formed as shown in FIGS. 2 and 3, whereupon the coil 8a is pushed onto the free end portion 6a of lever 6, so that the needle 8 is connected with the lever 6 for performing the printing stroke, although removal of the printing needle wire 8 from the end portion 6a is possible in axial direction. The resilient pressure of the coil 8a on the lever end portion 6a secures the printing needle to lever 6.
As shown in FIG. 3, the printing needle 8 preferably has a straight printing needle portion 8b located on an imaginary line 8d passing through the axis of the coil 8a. The intermediate portion 8c is cranked out of the imaginary line 8d, and tangentially connected with the first turn of the coil 8a, as best seen in FIG. 3. Consequently, the first turn of the coil 8a resiliently yields when the leading end of the printing needle 8 impinges the printing surface or the ink ribbon. The resilient mounting of the printing needle 8 on the lever 6 permits the impingement of the printing needle portions 8b on a steel plate, without any damage to the printing needle 8.
However, it has been found that at a very high printing speed and frequency of the needle operations, breakage may occur in the first turns of the wire coil 8a, and to overcome this defect, coil 8a, and the intermediate portion 8c of the printing needle 8 are embedded in a jacket consisting of a synthetic plastic mass which has only little influence on the resiliency of the coil 8a, but prevents undesired oscillations.
In the preferred embodiment of the invention, the lever 6 is a rod consisting of spring steel so that the elasticity of the connection between the driving armature 2, 3 and the printing needle end portion 8 is increased.
FIGS. 4a, 4b and 4c show the positions of the above described parts during an operation. FIG. 4a shows an initial position of rest in which the end portion 3 of the armature 2 abuts the adjusting screw 4, resilient lever 6 is not deformed, and the jacket 11 abuts the damping member 12 which is secured to the supporting frame 3, as also shown in FIG. 1. The inner end of the armature 2 is spaced from the stop portion 10a of core 10.
When the winding 1a of the electromagnet 1 is energized, the armature 2 moves rapidly into the annular winding 1a. The mass of members 8 and 11, and the resiliency of lever 6 are selected, so that during the first part of the stroke of the armature 2,3, the lever 6 is resiliently bent, while the lever end portion 6a momentarily remains in the same position whereby the lever 6 is resiliently deformed and tensioned. Thereupon the lever 6 recoils and rapidly accelerates the printing needle 8 toward the printing surface during the second part of the armature stroke. When the armature 2 abuts stop portion 10a as shown in FIG. 4c, the printing needle 8 with the coil spring 8a and the end portion 6a of the resilient lever 6 move due to inertia in a free movement toward the end of the printing stroke independently of, and beyond the armature strokes. In this manner, a further increase of the needle stroke of the printing stroke of the needle 8 from 0.8 mm. to 1 mm. is obtained.
FIG. 4c schematically shows the positions of the parts in the moment of impact of the printing needle on the printing surface.
Due to the free flight of the printing needle 8 at the end of the printing stroke, lever 6 is tensioned when the printing end portion 8b has impinged on the printing surface, but this time in the opposite direction than before described with reference to FIG. 4b. Due to the elastic tension in lever 6 in the position shown in FIG. 4c, after the impinging of the printing needle 8 on the printing surface, the return force of resilient lever 6 is added to the force applied by the return spring 9 on the armature 2, 3 so that the printing needle 8 is further accelerated during the return stroke.
However, such acceleration during the return stroke of the printing needle 8 is desirable only at the beginning of the return stroke of printing needle 8, and the energy stored in the resilient lever 6 must be dissipated when the initial position of rest, shown in FIG. 4a, is obtained, so that undesirable oscillations of the drive are prevented. For dampening such oscillations, a damping member 12 is secured to the supporting means 40 adjacent the end portion 6a of lever 6 and cooperating with the jacket 11 which envelops the coil 8a. At the end of the return movement, the printing needle 8 with the coil 8a and the jacket 11 impinges the stationary damping member 12 which preferably consists of a foam plastic material, or similar damping material. The damping member must be designed and selected to prevent recoil of the armature 2 when its end portion 3 impinges the adjusting screw 4.
Due to the elasticity of lever 6, together with the high efficiency of the plunger armature 2 surrounded by winding 1a, an accelerated advance of the printing needle 8 is obtained, which, due to the resiliency of the lever 6, results in a free flight of the printing needle toward the printing surface at the end of the needle stroke. The cooperation of elements 2, 6, 8a, and 8 in the illustrated embodiment of the invention, results in a substantial increase of the frequency of the printing strokes of the needles, and in a relatively great needle stroke, while the danger of breakage of the printing needles 8 is substantially reduced as compared with known needle or wire printers. The printing needle drive of the invention can be advantageously applied to all kinds of modifications of matrix printers, point printers, and other wire printers in which a printing head, guiding a plurality of printing needles, is used for forming characters of printed dots.
It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of printing needle drives differing from the types described above.
While the invention has been illustrated and described as embodied in a printing needle drive in which the effective lever arm of the needle is greater than the effective lever arm of an armature, so that the printing needle moves at a higher speed than the armature, and in which resilient means produce free needle movements due to inertia and independent of the movement of the armature, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.
Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.
What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.
The present invention relates to a wire printer or needle printer in which the characters to be printed are formed by a plurality of points printed by printing wires or needles. Matrix printers are known in which, for example, 5 times 7 needles are arranged in lines and columns in the printing head, and selectively operated to form and print the desired character. After a tabulating step, the next character is printed in the same manner. Another wire printer is known in which only seven needles are mounted in the printing head, which are arranged in a column at right angles to the line direction. A character to be printed is formed in several steps of the printing head, the selected printing needles of the columns being operated after each step so that after for example, five steps, a character is completed. After corresponding spacing steps by which the normal spacing between characters is obtained, the printing of the next following character is carried out in the same manner.
Modern wire printers of this type use an electromagnet for actuating each printing needle or wire. When the electromagnet is energized, the respective needle is rapidly advanced out of an initial position of rest to a printing position abutting the ink ribbon, and producing imprints on a paper sheet, and if desired on carbon copies, as disclosed, for example, in the German OS 1,943,675.
The printing needles or wires are substantially straight, or slightly bent toward the respective electromagnets, and partly guided in guide tubes, so that a rigid connection is formed between the printing surface and the armature of the electromagnet when the printing operation is carried out. This requires an extremely precise adjustment of the printing needle stroke, since otherwise, if the stroke is too long, the ink ribbon and even the paper sheet is perforated, or if the needle stroke is too short, only a weak impression or no impression at all is made. If the needle stroke is far too great, excessive bending and buckling forces are produced, which may cause breakage of the needle. Particularly, at high printing frequencies, the danger of breakage of the needles due to oscillations is great.
The German AS 1,270,858 discloses a printer of this type in which the printing needle is connected with the armature by a hook and eye connection providing some lost motion. However, this arrangement has not been fully successful.
The German Pat. No. 1,270,859 discloses an arrangement in which the armature of the electromagnet is tiltable and provided with an elastic arm on which the rear end of the printing needle abuts. Since the arm is elastic, the connection between the armature and the printing needle is not rigid, but the frequency of the needle actuations is substantially reduced because a tiltable armature has a very low efficiency due to the inherently large stray field, as compared with a plunger armature. To compensate this disadvantage a slot and pin connection between the printing needle and the armature is used.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved printing needle drive which operates at high efficiency and is capable of operating the printing needles at a high speed.
Another object of the invention is to combine the high efficiency of an electromagnet with a plunger armature, with transmission of motion from the armature to the printing needle by resilient means.
Another object of the invention is to connect the armature with the respective printing needles by a lever in such a manner that the armature stroke is shorter than the printing needle stroke.
Another object of the invention is to mount the printing needle on resilient means, so that breakage due to a rigid connection between the armature and the printing needle is avoided.
Another object of the invention is to connect an armature by means of a resilient lever with the printing needle to obtain free movement of the printing needle due to elastic recoil when the armature is stopped at the end of its stroke.
Another object of the invention is to provide a form-locking connection between the printing wire and the respective armature.
With these objects in view, an embodiment of the invention comprises lever means having a fulcrum; a printing needle means secured to a first portion of the lever means; electromagnetic means including a movable armature connected with a second portion of the lever means spaced from the fulcrum a smaller distance than the first portion so that when the armature is moved in an armature stroke of predetermined length, the needle means is moved in a needle stroke of proportionally greater length, and at a higher speed than the armature. In the preferred embodiment of the invention, pivot means are provided at one end of the lever means, the first portion is an end portion located at the other end of the lever means and the armature is connected with the second portion intermediate the ends of the second lever means. Preferably, the armature is a plunger armature movable in an annular winding and having a portion projecting from the winding and secured to the second portion of the lever means.
In the preferred embodiment of the invention, the lever means is resilient, and the mass of the needle means has such a predetermined magnitude to momentarily prevent movement of the first portion during the first part of the armature stroke by the resilient lever means resiliently deforms and is tensioned so that the lever means recoils during the second part of the armature stroke and accelerates the needle means faster than the armature is accelerated.
A stop means is provided for stopping the armature at the end of the armature stroke so that the recoiling resilient lever means continues to move the needle means in a free needle stroke after the stop means has stopped the armature.
The printing needle means preferably includes a wire having a projecting printing end portion, and a resilient attaching end portion wound in a coil surrounding the end portion of the lever means.
It is particularly advantageous to provide a wire including an intermediate portion between the printing end portion and the coil. The printing end portion is located in an imaginary line passing through the axis of the coil, and the intermediate portion is cranked out of the imaginary line and extends tangentially to the first turn of the coil so that the same spreads when the printing end portion abuts a printing surface.
The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is an axial sectional view illustrating an embodiment of a printing needle drive according to the invention;
FIG. 2 is a side view illustrating one printing needle;
FIG. 3 is a plan view illustrating the printing needle of FIG. 2; and
FIGS. 4a, 4b and 4c are fragmentary sectional views illustrating successive positions of the armature and needle means during a printing operation.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to FIG. 1, an electromagnet 1 includes an annular or tubular winding 1a surrounding a plunger armature 2 and a fixed core 10 forming a stop 10a for the axially movable armature 2. A return spring 9 is mounted on a supporting frame 40 and passes through a bore in the end portion 3 of armature 2 so that armature 2 is biased to a position abutting an adjustable screw 4 threaded into the supporting frame 40 and secured by a nut 5. When winding 1a is energized, the plunger armature is pulled against the action of spring 9 until abutting the stop portion 10a of the fixed core 10.
In addition to the bore 3b, the end portion 3 of armature 2 has a bore 3a through which the portion 6b of the elastic lever 6 passes. A member 7a is secured to one end of lever 6 and carries a pivot pin 7b mounted on a bracket 41 of the supporting means so that lever 6 is turnable about the fulcrum formed by the pivot 7b. The other end of lever 6 has an end portion 6a to which a printing needle 8 is attached by a form-locking connection. The printing needle portion 8b is only partly shown in FIG. 1, and it will be understood that the printing end portions 8b of a plurality of printing needles are combined in a printing head for printing points which together form a character. The printing head has bores for guiding the printing end portions 8b, respectively, during the printing stroke.
When the winding 1a is energized, the armature 2 is drawn into the electromagnet 1, tensioning the return spring 9 and moving the lever 6. The downward armature stroke of armature 2 as viewed in the drawing, is limited by the stop portion 10a of the fixed iron core 10, and is preferably 0.4 mm. Since the center portion 6b of lever 6 moves the same distance as the armature 2, its end portion 6a moves a distance of 0.8 mm. taking along the printing needle 8, so that the needle stroke is twice as great than the armature stroke due to the fact that the distance between the armature 3 and the pivot 7b is only half the distance between the lever end portion 6a and the pivot means 7b. In this manner a small armature stroke results in a larger printing stroke of the printing needle 8, and in a high speed of the needle movement. As a result, the armature stroke can be very small, which permits a very high frequency of the armature strokes.
As shown in FIGS. 1 and 2, the printing needle 8 has a resilient attaching portion which is constituted by a coil 8a formed of the wire which ends in the printing needle 8. The wire of the printing needle 8 is preferably formed as shown in FIGS. 2 and 3, whereupon the coil 8a is pushed onto the free end portion 6a of lever 6, so that the needle 8 is connected with the lever 6 for performing the printing stroke, although removal of the printing needle wire 8 from the end portion 6a is possible in axial direction. The resilient pressure of the coil 8a on the lever end portion 6a secures the printing needle to lever 6.
As shown in FIG. 3, the printing needle 8 preferably has a straight printing needle portion 8b located on an imaginary line 8d passing through the axis of the coil 8a. The intermediate portion 8c is cranked out of the imaginary line 8d, and tangentially connected with the first turn of the coil 8a, as best seen in FIG. 3. Consequently, the first turn of the coil 8a resiliently yields when the leading end of the printing needle 8 impinges the printing surface or the ink ribbon. The resilient mounting of the printing needle 8 on the lever 6 permits the impingement of the printing needle portions 8b on a steel plate, without any damage to the printing needle 8.
However, it has been found that at a very high printing speed and frequency of the needle operations, breakage may occur in the first turns of the wire coil 8a, and to overcome this defect, coil 8a, and the intermediate portion 8c of the printing needle 8 are embedded in a jacket consisting of a synthetic plastic mass which has only little influence on the resiliency of the coil 8a, but prevents undesired oscillations.
In the preferred embodiment of the invention, the lever 6 is a rod consisting of spring steel so that the elasticity of the connection between the driving armature 2, 3 and the printing needle end portion 8 is increased.
FIGS. 4a, 4b and 4c show the positions of the above described parts during an operation. FIG. 4a shows an initial position of rest in which the end portion 3 of the armature 2 abuts the adjusting screw 4, resilient lever 6 is not deformed, and the jacket 11 abuts the damping member 12 which is secured to the supporting frame 3, as also shown in FIG. 1. The inner end of the armature 2 is spaced from the stop portion 10a of core 10.
When the winding 1a of the electromagnet 1 is energized, the armature 2 moves rapidly into the annular winding 1a. The mass of members 8 and 11, and the resiliency of lever 6 are selected, so that during the first part of the stroke of the armature 2,3, the lever 6 is resiliently bent, while the lever end portion 6a momentarily remains in the same position whereby the lever 6 is resiliently deformed and tensioned. Thereupon the lever 6 recoils and rapidly accelerates the printing needle 8 toward the printing surface during the second part of the armature stroke. When the armature 2 abuts stop portion 10a as shown in FIG. 4c, the printing needle 8 with the coil spring 8a and the end portion 6a of the resilient lever 6 move due to inertia in a free movement toward the end of the printing stroke independently of, and beyond the armature strokes. In this manner, a further increase of the needle stroke of the printing stroke of the needle 8 from 0.8 mm. to 1 mm. is obtained.
FIG. 4c schematically shows the positions of the parts in the moment of impact of the printing needle on the printing surface.
Due to the free flight of the printing needle 8 at the end of the printing stroke, lever 6 is tensioned when the printing end portion 8b has impinged on the printing surface, but this time in the opposite direction than before described with reference to FIG. 4b. Due to the elastic tension in lever 6 in the position shown in FIG. 4c, after the impinging of the printing needle 8 on the printing surface, the return force of resilient lever 6 is added to the force applied by the return spring 9 on the armature 2, 3 so that the printing needle 8 is further accelerated during the return stroke.
However, such acceleration during the return stroke of the printing needle 8 is desirable only at the beginning of the return stroke of printing needle 8, and the energy stored in the resilient lever 6 must be dissipated when the initial position of rest, shown in FIG. 4a, is obtained, so that undesirable oscillations of the drive are prevented. For dampening such oscillations, a damping member 12 is secured to the supporting means 40 adjacent the end portion 6a of lever 6 and cooperating with the jacket 11 which envelops the coil 8a. At the end of the return movement, the printing needle 8 with the coil 8a and the jacket 11 impinges the stationary damping member 12 which preferably consists of a foam plastic material, or similar damping material. The damping member must be designed and selected to prevent recoil of the armature 2 when its end portion 3 impinges the adjusting screw 4.
Due to the elasticity of lever 6, together with the high efficiency of the plunger armature 2 surrounded by winding 1a, an accelerated advance of the printing needle 8 is obtained, which, due to the resiliency of the lever 6, results in a free flight of the printing needle toward the printing surface at the end of the needle stroke. The cooperation of elements 2, 6, 8a, and 8 in the illustrated embodiment of the invention, results in a substantial increase of the frequency of the printing strokes of the needles, and in a relatively great needle stroke, while the danger of breakage of the printing needles 8 is substantially reduced as compared with known needle or wire printers. The printing needle drive of the invention can be advantageously applied to all kinds of modifications of matrix printers, point printers, and other wire printers in which a printing head, guiding a plurality of printing needles, is used for forming characters of printed dots.
It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of printing needle drives differing from the types described above.
While the invention has been illustrated and described as embodied in a printing needle drive in which the effective lever arm of the needle is greater than the effective lever arm of an armature, so that the printing needle moves at a higher speed than the armature, and in which resilient means produce free needle movements due to inertia and independent of the movement of the armature, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.
Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.
What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.