United States Patent 3770092
Abstract:
A wire printing head comprising a plurality of solenoids mounted within a frame and a plurality of spring lever arms cantilevered to the frame and having attached to the free end of the arms print wires. The print wire is moved in the direction of the medium to be printed by the movement of the solenoid armature by magnetic force in the direction of the free end of the print wire. The print wire is returned to a ready position by the spring action of the lever arm.
Application Number:
05/225714
Publication Date:
11/06/1973
Assignee:
Autotronics, Incorporated (Joplin, MO)
International Classes:
B41J2/275; B41J2/27; (IPC1-7): B41J3/10
Field of Search:
197/1 101
Primary Examiner:
Burr, Edgar S.
Claims:
I claim
1. In a wire print device of the type having a circular frame, and a plurality of wire print assembly members mounted within said frame, with each of said wire print assembly members comprising a solenoid having a central core member which has a pole face at one end thereof and movable armature means, the improvement wherein said movable armature means comprises
2. said lightweight magnetizable member having a cross sectional area substantially equal to the cross-sectional area of the pole face on said central core member,
3. A wire print device as defined in claim 1 wherein a closed magnetic circuit is provided for said solenoid by means of an open-topped magnetizable body which surrounds said central core member, said magnetizable body having an openings in the bottom thereof to receive said lightweight magnetizable member mounted on said flexible leaf spring member, and said central core member being substantially T-shaped in cross-section to provide a closed magnetic path across the top of said open-topped magnetizable body.
Description:
This invention relates to wire printing devices, and more specifically to a wire print head.
In general, wire printing devices are composed of individual wires that are moved to impinge upon the medium to be printed. These devices usually contain seven print wires and when these wires are moved to impact a record medium printed characters are produced. It is common practice that electromagnetic devices such as solenoids are used to move the wires so that the wires impinge on the medium to be printed. Usually, the wire is directly attached to the solenoid armature and the distance that wire must be moved is equal to the distance that the solenoid armature must be moved. The distance that the armature moves is a major factor in determining the size of the solenoid required for a particular wire printing device. It is an object of this invention to reduce the size of the solenoid required to perform the printing function.
Another factor in determining the size of the solenoid is the mass that the solenoid must accelerate or move to impart sufficient force to the print wire to accomplish the printing action. In past designs the size of the solenoid and geometric arrangement of solenoids has required that longer print wires (i.e. larger mass) be employed and when longer print wires are required larger solenoids are required, thus creating a vicious cycle. The disadvantage of long print wires is further compounded by the fact that the wires bend and therefore, require that the armature must move a greater distance than would normally be necessary. To offset the wire flexing problem wire guides or tubes are used, but these in turn create resistance to the movement of the wire and therefore require larger solenoids. It is an object of this invention to reduce the length of the print wire required to perform the printing function.
A further disadvantage of long print wires and longer distance that solenoid armatures must travel is that these factors increase the cycle rate of the solenoid;as the cycle rate of the solenoid is increased the size of the solenoid must be increased to withstand temperature buildup resulting from the increased current flows required. It is an object of this invention to reduce the current required to perform the printing function.
The primary object of this invention is to provide a novel and improved printing head as will become apparent from the detailed description that follows.
To summarize the invention, it is a wire print device comprising a frame to which is cantilevered a flexible spring member. At the free end of the spring member is attached a print wire that travels within a wire guide that is also attached to the frame. Attached to the spring member is a magnetizable member or armature that is located parallel to the print wire and is moved by magnetic force in the direction of the free end of the print wire so that the print wire strikes the surface to be printed. After the magnetic force is released on the armature the spring action of the flexible member returns the print wire to a ready position.
FIG. 1 is a perspective view of the subject invention having a portion cut away to show certain inventive features.
FIG. 2 is a schematic drawing of a control curcuit suitable for use with the subject invention.
Referring now to FIG. 1 wherein is shown printing head 10 a preferred embodiment of the subject invention. The frame 11 is of a high heat transfering material such as aluminum or aluminum alloy or similar type material. The frame acts in this embodiment as to a heat sink and therefore fins 12 are added to help dissipate the heat generated by coil assemblies 13. The coil assembly 13 comprises a body 14 that can be screwed into the frame 11, a core 15 that is constructed of magnetizable material such as ingot iron and a coil 16 that is connected to a control circuit such as is illustrated in FIG. 2, by terminals 17. When the coil is energized, a pole face is created at point 18 on the magnetic core 15. This pole face 18 attracts the magnetizable member 19 which is attached to the flexible member 20. The magnetizable member 19 can also be described as an armature of coil assembly 13. The armature can be constructed of any well known magnetizable materials. The coil assembly 13 is also referred to herein as a solenoid. The flexible member 20 is attached to the frame 11 by bolts 21, only one bolt is shown in the drawing. This bolting arrangement can also be described as cantilevering the flexible member 20. At the non-bolted end of the flexible member is attached to the print wire 22. The print wire is positioned in the wire guide 23 which is a jewel-lined cylinder. The wire guide bearing block 24 contains seven wire guides that print wires translate through. The paper or ribbon, not shown, would be translated across the face of bearing block 24, by means not shown, and when solenoid 13 is activated air gap 25 would be closed by the movement of pole face 26 contained in armature 19. The air gap is quite small in the present invention, that is between 0.005 inches and 0.020 inches and preferrable between 0.012 inches and 0.018 inches, because of the mechanical advantage realized from employing the lever arm 20. That is to say if the distance from bolt 21 to the armature 19 is one unit and the distance from armature 19 to print wire 22 is two units and the distance between pole face 26 and pole face 18 is denoted by dy the print wire 22 travels a distance of 3 × dy when the air gap 25 is closed. This arrangement of components has the two fold advantage of reducing the size of the solenoid required, by reducing the length of the air gap and reducing the force necessary to be imparted to the armature, and by reducing the length of the print wire employed. A typical wire length useable in the present invention is 0.75 inches with a diameter of 0.013 inches. Thus, a ratio of wire length to diameter of less than 60 is readily useable in a machine employing the subject invention, a ratio very difficult if not impossible to provide in previously known printing machines.
The portion of flexible member 20 from the bolt 21 to the armature 19 is made of a spring material and imparts the spring action to this member to return the print wire 22 to a ready position when the solenoid 13 is deactivated. The portion of the flexible member from the armature 19 to the print wire 22 is a light weight rigid member that acts as a lever arm. The relative light weight or low mass of this member further enhances the efficiency of this printing device.
The air gap or stroke of the armature can readily be adjusted by using various size shims 27. As can be seen from the drawing the use of the lever arm type arrangement allows the solenoids to be grouped around the wire guide in a circular fashion, reducing the overall size of the print head and thereby a very compact design is realized.
To control the energization of the coil 13 and thereby regulate the printing action of the print wires, each coil 13 is connected to a control circuit as shown in FIG. 2, by terminals 17. In this circuit, a trigger signal causes transistor Q1 to conduct momentarily lowering its collector potential. Capacitor C1 couples this potential drop to the base of transistor Q3 cutting it off. The rise in collector potential of Q3 turns transistor Q4 on through resistor R6 and thus exciting coil L1 which is the same as coil 16 in FIG. 1. Simultaneously, transistor Q2 conducts by means of resistor R2 and R3. This electrical state is maintained until the potential at the base of Q3 rises by means of charging C1 through R4 sufficiently to cause Q3 to conduct. When Q3 conducts, Q4 is cut off and the excitation to coil 16 ceases. This type of circuit is commonly known as a one shot multivibator and is used to provide excitation to coil 16 for a fixed period of time after the trigger signal.
By following the teachings of this invention a highly efficient wire printer is produced that is fast acting, can be recycled at very high rates, and requires a small amount of energy for actuation.
It is to be understood that the above disclosure is by way of specific example and that numerous modifications and variations are available to those of ordinary skill in the art with departing from the true spirit and scope of the present invention.