Title:
WIRE MATRIX PRINT HEAD
United States Patent 3672482
Abstract:
A Z-shaped support having upper and lower shelves carries a plurality of electromagnetically controlled print wire actuators on its lower shelf for actuating a plurality of print wires which are attached to the actuator armatures and are converged into a vertical array by a wire guide attached to the upper shelf.
US Patent References:
WIRE PRINTING HEAD
Chou et al. - July 1971 - 3592311
Permanent magnet hammer module in high speed printers
Barnes - November 1964 - 3156180
Print hammer having braking means
Belson - November 1967 - 3351006
High speed electro-mechanical interference-type transducer
Fomenko et al. - October 1956 - 2766686
High speed printer
Preisinger - October 1963 - 3108534
WIRE PRINTING HEAD
Chou et al. - July 1971 - 3592311
Permanent magnet hammer module in high speed printers
Barnes - November 1964 - 3156180
Print hammer having braking means
Belson - November 1967 - 3351006
High speed electro-mechanical interference-type transducer
Fomenko et al. - October 1956 - 2766686
High speed printer
Preisinger - October 1963 - 3108534
Inventors:
Brumbaugh, Philip A. (Endicott, NJ)
Harrington, Richard H. (Vestal, NJ)
Nemier, Stanley E. (Endicott, NJ)
Nielsen, Thomas C. (Endwell, NJ)
Harrington, Richard H. (Vestal, NJ)
Nemier, Stanley E. (Endicott, NJ)
Nielsen, Thomas C. (Endwell, NJ)
Application Number:
05/068278
Publication Date:
06/27/1972
Filing Date:
08/31/1970
View Patent Images:
Export Citation:
Assignee:
International Business Machines Corporation (Armonk, NY)
Primary Class:
Other Classes:
101/93.050
International Classes:
B41J2/265; B41J2/235; B41J3/12
Field of Search:
101/93C 197/1
US Patent References:
Primary Examiner:
Pulfrey, Robert E.
Assistant Examiner:
Crowder, Clifford D.
Claims:
What is claimed is
1. In a wire printing device for printing on a record member, a print head comprising,
2. The invention as defined in claim 1 characterized by an additional cantilever leaf spring secured in spaced relation with said first leaf spring by means of a spacer at one end and having a free end at the other end so positioned relative to said first leaf spring that said first leaf spring engages the free end of said additional cantilever spring after predetermined movement of said armature.
3. The invention as defined in claim 2 characterized by said opening in one pole being a slot through said pole piece and also open at the end of said pole piece.
4. The invention as defined in claim 3 characterized by said actuator magnetic core structure having said one pole piece comprising a lower leg with a pair of feet extending therefrom for supporting said actuator on said support member and an upright extension at one end comprising said slotted pole piece, and an overhanging projection at the other end supporting said permanent magnet means between it and an upper leg which comprises said other pole piece.
5. The invention as defined in claim 1 characterized by the support member being substantially a sector of a circle with a plurality of actuators arranged about the arc thereof and said guide means having a plurality of wire passages extending therethrough in merging relation horizontally from one end to the other and a centrally disposed one traversing from the top of said guide means at said one end to the bottom at said other end in the center, and ones on opposite sides of the center being directed alternately to successively higher positions at the other end in a vertical line.
6. The invention as defined in claim 1 characterized by said opening being within the pole piece so that the armature is surrounded thereby and said armature moves in a straight line in said opening.
7. The invention as defined in claim 1 characterized by said biasing means for the armature being positioned within said upper leg of said core structure.
1. In a wire printing device for printing on a record member, a print head comprising,
2. The invention as defined in claim 1 characterized by an additional cantilever leaf spring secured in spaced relation with said first leaf spring by means of a spacer at one end and having a free end at the other end so positioned relative to said first leaf spring that said first leaf spring engages the free end of said additional cantilever spring after predetermined movement of said armature.
3. The invention as defined in claim 2 characterized by said opening in one pole being a slot through said pole piece and also open at the end of said pole piece.
4. The invention as defined in claim 3 characterized by said actuator magnetic core structure having said one pole piece comprising a lower leg with a pair of feet extending therefrom for supporting said actuator on said support member and an upright extension at one end comprising said slotted pole piece, and an overhanging projection at the other end supporting said permanent magnet means between it and an upper leg which comprises said other pole piece.
5. The invention as defined in claim 1 characterized by the support member being substantially a sector of a circle with a plurality of actuators arranged about the arc thereof and said guide means having a plurality of wire passages extending therethrough in merging relation horizontally from one end to the other and a centrally disposed one traversing from the top of said guide means at said one end to the bottom at said other end in the center, and ones on opposite sides of the center being directed alternately to successively higher positions at the other end in a vertical line.
6. The invention as defined in claim 1 characterized by said opening being within the pole piece so that the armature is surrounded thereby and said armature moves in a straight line in said opening.
7. The invention as defined in claim 1 characterized by said biasing means for the armature being positioned within said upper leg of said core structure.
Description:
CROSS-REFERENCE TO RELATED APPLICATION
This invention is an improvement over the invention of co-pending application, Ser. No. 764,474, filed Oct. 28, 1968, now U.S. Pat. No. 3,592,311, of E. A. Brown and A. S. Chou and assigned to the assignee of this invention.
DESCRIPTION OF PRIOR ART
Heretofore, the wires in matrix printers have been actuated by rotating cam mechanisms or by magnetostrictive actuators such as in the Preisinger U.S. Pat. No. 3,108,534, which issued Oct. 29, 1963, and is assigned to the assignee of the present invention.
SUMMARY OF THE INVENTION
Generally stated it is an object of this invention to provide a new and improved wire matrix print head.
More specifically, it is an object of this invention to provide an improved wire matrix print head in which the print wires are normally held retracted by permanent magnet means.
Another object of the invention is to provide an electromagnetic actuator for each of a plurality of print wires wherein a movable armature moves in a slot in one pole piece of a magnetic structure toward and away from another pole piece disposed in spaced relation therewith.
Yet another object of the invention is to provide for securing an individual permanent magnet between two pole pieces for producing magnetic flux therebetween for attracting a movable armature positioned in a slot in one of said pole pieces against the bias of a spring, and altering said magnetic flux to permit said spring to actuate said armature and move a print wire attached thereto.
It is also an object of the invention to provide for mounting a plurality of individual electromagnetic print wire actuators complete with individual permanent magnet holding means on a common support so that they may be adjusted relative to a wire guide without affecting performance of the permanent magnet holding means.
Still another object of this invention is to provide for mounting a plurality of print wire actuators on a common support in an arcuate configuration in conjunction with a guide for the print wires which directs the individual print wires from entry points in a common horizontal plane about an arc to a vertical configuration, with the wires entering the guide toward the middle of the arc having a path which depresses them in a curved path in a vertical plane to compensate for the increased length of the print wires toward the outer ends of the arc caused by the curvature of said print wires in a horizontal plane toward the common vertical plane and make the wire friction in center equal the friction on ends due to offset in guide.
Another important object of this invention is to provide for having an armature movable in a slot in one pole piece of a no-work electromagnetic actuator controlled by a pair of cantilever spring members which are positioned in spaced apart relation so as to be effective in different degrees over different portions of the armature travel.
Yet another important object of the invention is to provide for using a first support spring member which is secured to a movable electromagnet armature and deflected when the armature is attracted to a spaced apart pole piece, and a second spring member, which is positioned in spaced relation with said support spring member, to be engaged thereby after predetermined movement of said armature toward said spaced apart pole piece.
Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 illustrates a partial plan view of a portion of a printer embodying a plurality of print wire actuators in a print head utilizing the present invention.
FIG. 1a is an enlarged partial view in end elevation of the upper end of the Vertical Core portion of one of the actuators of FIG. 1.
FIG. 2 is a side elevational view partly in section of the print head shown in FIG. 1.
FIG. 2a is an enlarged partial side elevational view of a portion of the actuators of FIG. 2 showing how the flat springs are secured.
FIG. 3 is an enlarged plan view of the wire guide shown in FIG. 1.
FIG. 4 is a further enlarged side elevational view of the wire guide of FIG. 3.
FIG. 5a is an end elevational view of the wire guide of FIG. 4.
FIG. 5b is a cross-sectional view taken along the line 5b -- 5b of FIG. 4.
FIG. 5c is a sectional view taken along the line 5c -- 5c of FIG. 4.
FIG. 6a is an enlarged partial view in side elevation of a portion of an electromagnetic actuator showing a different arrangement of the main and auxiliary leaf springs.
FIG. 6b is a similar view to that shown in FIG. 6a with the armature in the attracted position.
FIG. 6c is a partial end elevational view of the Auxiliary Spring and Armature of FIG. 6a, and
FIG. 7 is a partial side elevational view of an electromagnetic actuator embodying the invention in a different form.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to FIGS. 1 and 2 of the drawing, it will be seen that the Print Head 10 of the subject invention comprises a substantially Z-shaped Support 12 having a Lower Shelf Portion 14 and an Upper Shelf Portion 15 connected by a central Vertical Leg Portion 16. The Lower Shelf Portion 14 is provided with Tabs 14a for securing the Print Head to a carriage (not shown) for moving it relative to a Platen 18, which is positioned behind a Ribbon 19 and a Document or Paper 20 on which a printing operation is to be performed. The printing is performed by a plurality of Print Wires 22, which are selectively operated by electromagnetic Actuators 24, mounted on the Lower Shelf Portion 14 for moving the Print Wires to project through a Print Wire Guide 26 attached to the Upper Shelf Portion 15 for impacting the ends of the Wires 22 against the Ribbon 19 and Paper 20.
The Wire Guide 26 comprises a generally sector-shaped body having an Arcuate End Surface 26a with Conical Openings 27a- -g positioned in a horizontal line through which the Wires 22 enter the guide. The Wires 22 pass through Passages 28a- g which traverse from the Openings 27a- g at the Arcuate End 26a of the Wire Guide to the other end where they exit in a vertical row of openings. The Wire Guide 26 may be molded from a bronze powder-filled epoxy with the Passages 28a- g being formed therein during the molding by means of wires (not shown) positioned in a mold which are slightly larger than the Print Wires 22, which wires (not shown) are then withdrawn after the molding process to provide the Passages 28a- g for the Print Wires 22. As shown in FIGS. 3, 4, 5a, 5b, and 5c, the Passages 28a- g are so arranged that the Central Passage 28d dips considerably as it traverses the Wire Guide to provide the lowermost Print Wire at the right-hand end. The Passages 28c and 28e on either side dip somewhat less to provide the next two higher openings at the right-hand end, while the Passages 28a and 28g provide the upper two openings at the right-hand end. By reason of this configuration, the dip of the Passages in the vertical plane compensates for the differences in curvature of the Passages in the horizontal plane, so as to provide a more nearly uniform frictional effect or drag on the Print Wires, so that flight time and print force will be more uniform, regardless of the position of the particular Print Wire. This greatly improves the uniformity of wear and the quality of the printing. Print forces on the several Print Wires may thus be held to between 2.4 to 3 pounds instead of varying from less than 2 to more than 5 pounds.
Referring again to FIGS. 1 and 2, it will be seen that the Actuators 24 each comprise an electromagnetic structure having a Lower Core Member 30 provided with Support Feet 32 and 34 with Slots 32a and 34a therein for receiving Screws 36 whereby the Core Member 30 is adjustably secured to the Lower Shelf Portion 14 of the Support 12. A plurality of Ribs 12a- h provide guide surfaces for aligning the electromagnetic Actuators 24. The Core Member 30 is provided with a substantially Vertical Upstanding Core Portion 38 at one end, which is provided with a Slot 38a at the upper end with upstanding portions of the Core Portion 38 disposed on each side for slidably receiving an Armature 40. A Permanent Magnet 42 is positioned at the other end of the Core Member 30 for supporting an Upper Leg 44 of the core structure on the Lower Core Member 30, and holding the Armature 40 attracted to the Pole Face 46 against the bias of a Spring 50. Means such as a Screw 45 secures the Upper Leg 44 and the Permanent Magnet 42 to the Core Member 30. The Upper Leg 44 is provided with a curved Pole Face 46 positioned in close proximity to the upper end of the Vertical Leg Portion 38 so as to provide a predetermined Air Gap 48 therebetween. A substantially tangential relation exists between the Armature 40 in its attracted position and the Pole Face 46. An Operating Winding 51 is positioned on the Leg 44 and is disposed to be selectively pulsed in order to oppose the magnetic effect of the Permanent Magnet 42 to release the Armature 40 for printing. The Armature 40 is restored by the combined effects of rebound and the magnetic flux to seal against the Pole Face 46.
The Armature 40 is slidably positioned in the Slot 38a in the upstanding Portion 38 of the Core Member 30 where it in effect floats because of the balanced magnetic attraction between it and the portions of the Core Portion 38 defining the Slot 38a. It is preferably supported by means of a Flat Leaf Spring 50 secured to the Armature 40 and mounted on the Vertical Core Portion 38 by means of Screws 52. An Auxiliary Spring 60 is mounted between the Spring 50 and the Leg Portion 38, the Spring 50 being separated therefrom by means of a Spacer 56. A Set Screw 58 threadably disposed in the Leg Portion 38 engages the Auxiliary Spring 60 to provide an adjustable stop for the Main Spring 50 so as to provide a line contact between the two springs. The Spring 50 may be secured to the Armature 40 by having an opening which receives a reduced Tail Portion 40a of the armature. The Tail Portion 40a has an opening which receives one end of the Print Wire 22. A swaging operation deforms the metal of the Tail Portion sufficiently to grip the Wire and the Spring.
The Permanent Magnet 42 has a cross-section of 0.35 inches by 0.35 inches and has a total flux on the order of 2,000 to 3,000 lines, which provides sufficient force to hold the Armature 40 attracted to the Pole Face 46 against the bias force of the Spring 50. When the Operating Winding 51 is pulsed to oppose the flux of the Permanent Magnet 42, the Armature 40 is released under the bias of the Spring 50 and moves rapidly away from the pole face, causing the free end of Print Wire 22 to impact the Ribbon 19 and Paper 20 to print a dot thereon and return to seal against the Pole Face 46.
In one embodiment of the invention which was successfully operated, the Print Wires 22 were formed from tungsten wire having a diameter on the order of 0.011 inches. The Armature 40 was made of 2 1/2 percent silicon iron, approximately 0.20 inches high by 0.050 inches thick so as to operate close to magnetic saturation, and the Slot 38a in which it is positioned had a width of 0.053 inches. The Air Gap 48 was on the order of 0.040 inches with the Armature 40 projecting beyond the Vertical Leg Portion 38 on the order of 0.013 inches in the unattracted position. The Pole Face 46 is curved so as to provide on the order of 0.0015 inches clearance at the upper and lower edges of the Armature when the Armature contacts the Pole Face, producing a more uniform relation between the pole face and the face of the Armature 40 in the attracted position. The longitudinal axis of the Armature 40 is inclined downward on the order of 2° to the horizontal when in the attracted position. The Armature 40 is plated to reduce wear and corrosion and provide a residual air gap. Chrome plating has proved very satisfactory and nickel plating can be used, being heated treated after plating to a hardness of RC60 to 65. The Pole Face 46 is preferably hardened to a depth of 0.003 - 0.005 inches, also to a hardness of RC60 to 65.
Referring to 6a it will be seen that a modified spring arrangement is shown. The Armature 40 is supported by the Main Spring 50 as heretofore and which is secured to the Vertical Leg Portion 38 by means of the Screws 52. However, an Auxiliary Spring 60 in the present instance extends up about a portion of the Armature 40 having a Slot 62 at the upper end which loosely fits about the body portion of the Armature 40 projecting from the Slot 38a. The tips of the Spring 60 may be coated with a Plastic Coating 60a such as polyurethane to provide a further damping action. The Main Spring 50 is separated from the Auxiliary Spring 60 by a Spacer 56 so that the Main Spring 50 moves part way when the Armature returns to the attracted position, before engaging the upper end of the Auxiliary Spring 60, whereupon both Springs move together until the Armature 40 seals against the Pole Face 46. The Auxiliary Spring 60 thus acts as a buffer and there is a transfer of energy to the Auxiliary Spring, which reduces the velocity and impact force of the Armature 40. This reduces wear of the Armature 40 and Pole Face 46 to a minimum. By utilizing Main and Auxiliary Springs in this manner better Armature action is secured and a spring force curve more nearly approaching the magnetic operating curve of the Armature 40 is attained.
In an operating model utilizing this spring arrangement, the Spacer 56 has a thickness on the order of 0.021 inches, the Spring 50 had a thickness of 0.018 inches and a spring rate of 15 pounds per inch, while the Auxiliary Spring 60 had a thickness on the order of 0.035 inches and a spring rate on the order of 110 pounds per inch. The Auxiliary Spring 60 has a clearance on the order of 0.015 inches between it and the Vertical Core Leg 38, and in operation the two springs travel together for approximately 0.006 inches during the return stroke. Utilizing the arrangement shown in FIGS. 6a and 6b, the Auxiliary Spring 60 acts as a buffer, and the return velocity of the Armature 40 could readily be maintained between 25 to 40 inches per second while having a print force on the order of 2.5 to 2.8 pounds. A higher repetition rate of operation of the Armature 40 and Print Wire 22 is therefore possible. Whereas with a 2 ampere pulse, at 24 volts, of 600 microseconds duration, the Actuator of FIGS. 2 and 6a, 6b can operate with a repetition rate on the order of 2 milliseconds, or at 500 cycles per second; with the Main and Auxiliary Spring design of FIGS. 6a, 6b we have found that it is possible to obtain at least 750 cycles per second operation with a repetition rate of 1.4 milliseconds to print at 100-125 characters per second, as contrasted with the previous 85 characters per second.
Referring to FIG. 7 it will be seen that in another embodiment of the invention the electromagnetic Actuator 64 may comprise a substantially L-shaped Core Member having a Lower Leg 64a secured to a Support 12A with a Vertical Leg 64b at one end. A Permanent Magnet 65 supports an elbow-shaped Core Member 66 which includes the Upper Core Leg 68 carrying the Operating Winding 69. The Lower Leg 64a, Permanent Magnet 65, and Core Member 66 may be connected together by means of a Screw 63. Instead of having the armature operate in a slot as in the previous arrangements, the Vertical Leg 64b is provided with a Cylindrical Opening 70 in which is slidably disposed a Cylindrical Armature 72 having an enlarged Head Portion 74 adjacent the Core Member 68. The Core Member 68 has a Cylindrical Bore 75 in which is located a Spring 76 and a threaded adjusting Screw 78 to provide the biasing force for operating the Armature 72 when the Operating Winding 69 is pulsed to overcome the magnetic attraction of the Permanent Magnet 65. The Print Wires 22 are directed by a Wire Guide 26, as previously described, and the Print Wires may be secured to the Armature 72 by swaging or in any other suitable manner. With 0.014 wire diameter this design provides dynamic adjustment capability and reduced wear as important advantages. The simplified armature design makes it easier to manufacture and maintain uniform operating results.
From the above description and the accompanying drawing it will be realized that we have provided a simple and effective wire matrix print head wherein the electromagnetic actuators may be readily adjusted to obtain uniform operation of the Print Wires 22 without affecting the magnetic circuit or the operating characteristics thereof. By utilizing permanent magnets to provide the retracting force for the print wires, they will always be retained in the retracted position even though there be an electrical power failure, thus preventing damage to the Document or forms by virtue of the Print Wires being accidentally released.
A Print Head embodying the principles of our invention is inexpensive and easy to manufacture while retaining close operating tolerances. Uniform and stable operation of the Print Head is easily obtained.
While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be evident to those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention.
This invention is an improvement over the invention of co-pending application, Ser. No. 764,474, filed Oct. 28, 1968, now U.S. Pat. No. 3,592,311, of E. A. Brown and A. S. Chou and assigned to the assignee of this invention.
DESCRIPTION OF PRIOR ART
Heretofore, the wires in matrix printers have been actuated by rotating cam mechanisms or by magnetostrictive actuators such as in the Preisinger U.S. Pat. No. 3,108,534, which issued Oct. 29, 1963, and is assigned to the assignee of the present invention.
SUMMARY OF THE INVENTION
Generally stated it is an object of this invention to provide a new and improved wire matrix print head.
More specifically, it is an object of this invention to provide an improved wire matrix print head in which the print wires are normally held retracted by permanent magnet means.
Another object of the invention is to provide an electromagnetic actuator for each of a plurality of print wires wherein a movable armature moves in a slot in one pole piece of a magnetic structure toward and away from another pole piece disposed in spaced relation therewith.
Yet another object of the invention is to provide for securing an individual permanent magnet between two pole pieces for producing magnetic flux therebetween for attracting a movable armature positioned in a slot in one of said pole pieces against the bias of a spring, and altering said magnetic flux to permit said spring to actuate said armature and move a print wire attached thereto.
It is also an object of the invention to provide for mounting a plurality of individual electromagnetic print wire actuators complete with individual permanent magnet holding means on a common support so that they may be adjusted relative to a wire guide without affecting performance of the permanent magnet holding means.
Still another object of this invention is to provide for mounting a plurality of print wire actuators on a common support in an arcuate configuration in conjunction with a guide for the print wires which directs the individual print wires from entry points in a common horizontal plane about an arc to a vertical configuration, with the wires entering the guide toward the middle of the arc having a path which depresses them in a curved path in a vertical plane to compensate for the increased length of the print wires toward the outer ends of the arc caused by the curvature of said print wires in a horizontal plane toward the common vertical plane and make the wire friction in center equal the friction on ends due to offset in guide.
Another important object of this invention is to provide for having an armature movable in a slot in one pole piece of a no-work electromagnetic actuator controlled by a pair of cantilever spring members which are positioned in spaced apart relation so as to be effective in different degrees over different portions of the armature travel.
Yet another important object of the invention is to provide for using a first support spring member which is secured to a movable electromagnet armature and deflected when the armature is attracted to a spaced apart pole piece, and a second spring member, which is positioned in spaced relation with said support spring member, to be engaged thereby after predetermined movement of said armature toward said spaced apart pole piece.
Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 illustrates a partial plan view of a portion of a printer embodying a plurality of print wire actuators in a print head utilizing the present invention.
FIG. 1a is an enlarged partial view in end elevation of the upper end of the Vertical Core portion of one of the actuators of FIG. 1.
FIG. 2 is a side elevational view partly in section of the print head shown in FIG. 1.
FIG. 2a is an enlarged partial side elevational view of a portion of the actuators of FIG. 2 showing how the flat springs are secured.
FIG. 3 is an enlarged plan view of the wire guide shown in FIG. 1.
FIG. 4 is a further enlarged side elevational view of the wire guide of FIG. 3.
FIG. 5a is an end elevational view of the wire guide of FIG. 4.
FIG. 5b is a cross-sectional view taken along the line 5b -- 5b of FIG. 4.
FIG. 5c is a sectional view taken along the line 5c -- 5c of FIG. 4.
FIG. 6a is an enlarged partial view in side elevation of a portion of an electromagnetic actuator showing a different arrangement of the main and auxiliary leaf springs.
FIG. 6b is a similar view to that shown in FIG. 6a with the armature in the attracted position.
FIG. 6c is a partial end elevational view of the Auxiliary Spring and Armature of FIG. 6a, and
FIG. 7 is a partial side elevational view of an electromagnetic actuator embodying the invention in a different form.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to FIGS. 1 and 2 of the drawing, it will be seen that the Print Head 10 of the subject invention comprises a substantially Z-shaped Support 12 having a Lower Shelf Portion 14 and an Upper Shelf Portion 15 connected by a central Vertical Leg Portion 16. The Lower Shelf Portion 14 is provided with Tabs 14a for securing the Print Head to a carriage (not shown) for moving it relative to a Platen 18, which is positioned behind a Ribbon 19 and a Document or Paper 20 on which a printing operation is to be performed. The printing is performed by a plurality of Print Wires 22, which are selectively operated by electromagnetic Actuators 24, mounted on the Lower Shelf Portion 14 for moving the Print Wires to project through a Print Wire Guide 26 attached to the Upper Shelf Portion 15 for impacting the ends of the Wires 22 against the Ribbon 19 and Paper 20.
The Wire Guide 26 comprises a generally sector-shaped body having an Arcuate End Surface 26a with Conical Openings 27a- -g positioned in a horizontal line through which the Wires 22 enter the guide. The Wires 22 pass through Passages 28a- g which traverse from the Openings 27a- g at the Arcuate End 26a of the Wire Guide to the other end where they exit in a vertical row of openings. The Wire Guide 26 may be molded from a bronze powder-filled epoxy with the Passages 28a- g being formed therein during the molding by means of wires (not shown) positioned in a mold which are slightly larger than the Print Wires 22, which wires (not shown) are then withdrawn after the molding process to provide the Passages 28a- g for the Print Wires 22. As shown in FIGS. 3, 4, 5a, 5b, and 5c, the Passages 28a- g are so arranged that the Central Passage 28d dips considerably as it traverses the Wire Guide to provide the lowermost Print Wire at the right-hand end. The Passages 28c and 28e on either side dip somewhat less to provide the next two higher openings at the right-hand end, while the Passages 28a and 28g provide the upper two openings at the right-hand end. By reason of this configuration, the dip of the Passages in the vertical plane compensates for the differences in curvature of the Passages in the horizontal plane, so as to provide a more nearly uniform frictional effect or drag on the Print Wires, so that flight time and print force will be more uniform, regardless of the position of the particular Print Wire. This greatly improves the uniformity of wear and the quality of the printing. Print forces on the several Print Wires may thus be held to between 2.4 to 3 pounds instead of varying from less than 2 to more than 5 pounds.
Referring again to FIGS. 1 and 2, it will be seen that the Actuators 24 each comprise an electromagnetic structure having a Lower Core Member 30 provided with Support Feet 32 and 34 with Slots 32a and 34a therein for receiving Screws 36 whereby the Core Member 30 is adjustably secured to the Lower Shelf Portion 14 of the Support 12. A plurality of Ribs 12a- h provide guide surfaces for aligning the electromagnetic Actuators 24. The Core Member 30 is provided with a substantially Vertical Upstanding Core Portion 38 at one end, which is provided with a Slot 38a at the upper end with upstanding portions of the Core Portion 38 disposed on each side for slidably receiving an Armature 40. A Permanent Magnet 42 is positioned at the other end of the Core Member 30 for supporting an Upper Leg 44 of the core structure on the Lower Core Member 30, and holding the Armature 40 attracted to the Pole Face 46 against the bias of a Spring 50. Means such as a Screw 45 secures the Upper Leg 44 and the Permanent Magnet 42 to the Core Member 30. The Upper Leg 44 is provided with a curved Pole Face 46 positioned in close proximity to the upper end of the Vertical Leg Portion 38 so as to provide a predetermined Air Gap 48 therebetween. A substantially tangential relation exists between the Armature 40 in its attracted position and the Pole Face 46. An Operating Winding 51 is positioned on the Leg 44 and is disposed to be selectively pulsed in order to oppose the magnetic effect of the Permanent Magnet 42 to release the Armature 40 for printing. The Armature 40 is restored by the combined effects of rebound and the magnetic flux to seal against the Pole Face 46.
The Armature 40 is slidably positioned in the Slot 38a in the upstanding Portion 38 of the Core Member 30 where it in effect floats because of the balanced magnetic attraction between it and the portions of the Core Portion 38 defining the Slot 38a. It is preferably supported by means of a Flat Leaf Spring 50 secured to the Armature 40 and mounted on the Vertical Core Portion 38 by means of Screws 52. An Auxiliary Spring 60 is mounted between the Spring 50 and the Leg Portion 38, the Spring 50 being separated therefrom by means of a Spacer 56. A Set Screw 58 threadably disposed in the Leg Portion 38 engages the Auxiliary Spring 60 to provide an adjustable stop for the Main Spring 50 so as to provide a line contact between the two springs. The Spring 50 may be secured to the Armature 40 by having an opening which receives a reduced Tail Portion 40a of the armature. The Tail Portion 40a has an opening which receives one end of the Print Wire 22. A swaging operation deforms the metal of the Tail Portion sufficiently to grip the Wire and the Spring.
The Permanent Magnet 42 has a cross-section of 0.35 inches by 0.35 inches and has a total flux on the order of 2,000 to 3,000 lines, which provides sufficient force to hold the Armature 40 attracted to the Pole Face 46 against the bias force of the Spring 50. When the Operating Winding 51 is pulsed to oppose the flux of the Permanent Magnet 42, the Armature 40 is released under the bias of the Spring 50 and moves rapidly away from the pole face, causing the free end of Print Wire 22 to impact the Ribbon 19 and Paper 20 to print a dot thereon and return to seal against the Pole Face 46.
In one embodiment of the invention which was successfully operated, the Print Wires 22 were formed from tungsten wire having a diameter on the order of 0.011 inches. The Armature 40 was made of 2 1/2 percent silicon iron, approximately 0.20 inches high by 0.050 inches thick so as to operate close to magnetic saturation, and the Slot 38a in which it is positioned had a width of 0.053 inches. The Air Gap 48 was on the order of 0.040 inches with the Armature 40 projecting beyond the Vertical Leg Portion 38 on the order of 0.013 inches in the unattracted position. The Pole Face 46 is curved so as to provide on the order of 0.0015 inches clearance at the upper and lower edges of the Armature when the Armature contacts the Pole Face, producing a more uniform relation between the pole face and the face of the Armature 40 in the attracted position. The longitudinal axis of the Armature 40 is inclined downward on the order of 2° to the horizontal when in the attracted position. The Armature 40 is plated to reduce wear and corrosion and provide a residual air gap. Chrome plating has proved very satisfactory and nickel plating can be used, being heated treated after plating to a hardness of RC60 to 65. The Pole Face 46 is preferably hardened to a depth of 0.003 - 0.005 inches, also to a hardness of RC60 to 65.
Referring to 6a it will be seen that a modified spring arrangement is shown. The Armature 40 is supported by the Main Spring 50 as heretofore and which is secured to the Vertical Leg Portion 38 by means of the Screws 52. However, an Auxiliary Spring 60 in the present instance extends up about a portion of the Armature 40 having a Slot 62 at the upper end which loosely fits about the body portion of the Armature 40 projecting from the Slot 38a. The tips of the Spring 60 may be coated with a Plastic Coating 60a such as polyurethane to provide a further damping action. The Main Spring 50 is separated from the Auxiliary Spring 60 by a Spacer 56 so that the Main Spring 50 moves part way when the Armature returns to the attracted position, before engaging the upper end of the Auxiliary Spring 60, whereupon both Springs move together until the Armature 40 seals against the Pole Face 46. The Auxiliary Spring 60 thus acts as a buffer and there is a transfer of energy to the Auxiliary Spring, which reduces the velocity and impact force of the Armature 40. This reduces wear of the Armature 40 and Pole Face 46 to a minimum. By utilizing Main and Auxiliary Springs in this manner better Armature action is secured and a spring force curve more nearly approaching the magnetic operating curve of the Armature 40 is attained.
In an operating model utilizing this spring arrangement, the Spacer 56 has a thickness on the order of 0.021 inches, the Spring 50 had a thickness of 0.018 inches and a spring rate of 15 pounds per inch, while the Auxiliary Spring 60 had a thickness on the order of 0.035 inches and a spring rate on the order of 110 pounds per inch. The Auxiliary Spring 60 has a clearance on the order of 0.015 inches between it and the Vertical Core Leg 38, and in operation the two springs travel together for approximately 0.006 inches during the return stroke. Utilizing the arrangement shown in FIGS. 6a and 6b, the Auxiliary Spring 60 acts as a buffer, and the return velocity of the Armature 40 could readily be maintained between 25 to 40 inches per second while having a print force on the order of 2.5 to 2.8 pounds. A higher repetition rate of operation of the Armature 40 and Print Wire 22 is therefore possible. Whereas with a 2 ampere pulse, at 24 volts, of 600 microseconds duration, the Actuator of FIGS. 2 and 6a, 6b can operate with a repetition rate on the order of 2 milliseconds, or at 500 cycles per second; with the Main and Auxiliary Spring design of FIGS. 6a, 6b we have found that it is possible to obtain at least 750 cycles per second operation with a repetition rate of 1.4 milliseconds to print at 100-125 characters per second, as contrasted with the previous 85 characters per second.
Referring to FIG. 7 it will be seen that in another embodiment of the invention the electromagnetic Actuator 64 may comprise a substantially L-shaped Core Member having a Lower Leg 64a secured to a Support 12A with a Vertical Leg 64b at one end. A Permanent Magnet 65 supports an elbow-shaped Core Member 66 which includes the Upper Core Leg 68 carrying the Operating Winding 69. The Lower Leg 64a, Permanent Magnet 65, and Core Member 66 may be connected together by means of a Screw 63. Instead of having the armature operate in a slot as in the previous arrangements, the Vertical Leg 64b is provided with a Cylindrical Opening 70 in which is slidably disposed a Cylindrical Armature 72 having an enlarged Head Portion 74 adjacent the Core Member 68. The Core Member 68 has a Cylindrical Bore 75 in which is located a Spring 76 and a threaded adjusting Screw 78 to provide the biasing force for operating the Armature 72 when the Operating Winding 69 is pulsed to overcome the magnetic attraction of the Permanent Magnet 65. The Print Wires 22 are directed by a Wire Guide 26, as previously described, and the Print Wires may be secured to the Armature 72 by swaging or in any other suitable manner. With 0.014 wire diameter this design provides dynamic adjustment capability and reduced wear as important advantages. The simplified armature design makes it easier to manufacture and maintain uniform operating results.
From the above description and the accompanying drawing it will be realized that we have provided a simple and effective wire matrix print head wherein the electromagnetic actuators may be readily adjusted to obtain uniform operation of the Print Wires 22 without affecting the magnetic circuit or the operating characteristics thereof. By utilizing permanent magnets to provide the retracting force for the print wires, they will always be retained in the retracted position even though there be an electrical power failure, thus preventing damage to the Document or forms by virtue of the Print Wires being accidentally released.
A Print Head embodying the principles of our invention is inexpensive and easy to manufacture while retaining close operating tolerances. Uniform and stable operation of the Print Head is easily obtained.
While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be evident to those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention.