GB1563779A - Printing apparatus - Google Patents

Description

(54) PRINTING APPARATUS (71) We, NCR CORPORATION Dayton in the State of Ohio, and Baltimore in the State of Maryland, United States of America, a corporation organized under the laws of the State of Maryland, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to printing apparatus of the kind including support means adapted to support a plurality of elongated printing elements for axial movement therethrough, and driving means adapted to drive said elements to effect printing.

Such printing apparatus finds applicacation in wire matrix printers wherein characters are printed in the form of a plurality of dots produced by the impact of elongated printing wire elements with a record medium, in conjunction with an ink ribbon.

One problem which has arisen in the use of wire matrix printers is that of fatigue breakage of the printing wires which results from bending and vibration of wires caused by the high force employed to drive the wires over a short distance to impact upon the record medium.

It is an object of the present invention to provde a printing apparatus of the kind specified wherein the above disadvantage is alleviated.

Thus, according to the invention, there is provided a printing apparatus including a frame; at least one support member loosely mounted in said frame and supporting at least one elongated printing element for axial movement therethrough; and driving means operatively connected to said printing element for axially driving said printing element to effect printing; said support member being free to move with respect to said frame in response to non-axial movement of said printing element to dampen any lateral movement thereof.

The printing apparatus according to the preceding paragraph has the further advantages that dampening of the bending and vibration of the printing wires is achieved without substantial drag on the print wires, that the printing apparatus is inexpensive both in terms of cost of the parts and cost of assembly, and that the apparatus is durable and reliable in operation.

Preferably, the apparatus includes a plurality of support members, each in a plane substantially perpendicular to the axis of the printing elements, and movable in at least two directions in said plane.

In order that the invention be better understood, an embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a sectional view of a printing apparatus in accordance with the present invention: Fig. 2 is an elevational view, partly broken away, showing the frame, the elongated printing elements and the dampening means, of the printing apparatus: Fig. 3 is an enlarged cross-sectional view, taken along line 3-3 of Fig. 2: Fig. 4 is an enlarged cross-sectional view, taken along line 4-4 of Fig. 2; Fig. 5 is an enlarged cross-sectional view, taken along line 5-5 of Fig. 2; and Fig. 6 is an enlarged bottom view of the frame of Fig. 2, taken along line 6-6, showing the printing end of the printing apparatus.

Referring now particularly to Fig. 1 of the drawings, a print head 10 of the wire matrix type is shown. A frame 12 is provided to support a plurality of elongated printing elements or print wires 14, only two of which are shown, for purposes of simplification and ready understanding of the drawings. Each wire 14 has a cap 16, which may be made of plastic or other suitable material, attached to its impactreceiving end to enlarge the area of the impact-receiving surface. Each wire also has a spring 18 disposed at its upper end, which exerts an upward force upon the cap 16 to resiliently bias the wire upwardly relative to the frame 12. The spring 18 has been omitted from one of the wires of Fig. 1, in order that the cap 16 may be more clearly depicted.

The frame 12 includes three side walls 20, 22 and 24, a print end support member 26 and an upper end support member 28. Both of the members 26 and 28 are formed integral with the side walls 20, 22 and 24 of the frame 12, in the illustrated embodiment, although it is clear that they could equally well be formed separately and secured to the frame 12.

In addition to the support members 26 and 28, a plurality of intermediate support members, two in the illustrated embodiment, are provided. A first intermediate support member 30 is provided with a plurality of aperture 32 in a predetermined pattern, through which apertures the print wires 14 are passed. The apertures are of larger diameter on one surface of the support member than on the opposite surface, in order to accommodate the slightly curved path of the print wires 14 and to facilitate insertion of the wires into the apertures. The member 30 in cludes a portion 34 of reduced size which is shaped generally in accordance with the circumferential pattern of the apertures 32 in the member 30, and also includes an enlarged portion 36 of generally rectangular configuration.The edge portions 38 and 40 (Fig. 5) of the enlarged portion 36 of the member 30 cooperate with grooves 42 and 44 formed in side walls 20 and 22 of the frame 12 for loosely positioning the member 30 in the frame 12. The width of the grooves 42, 44 is only slightly greater than the width of the enlarged portion 36 of the member 30, to enable said member to slide freely in said grooves. However, the length and depth of the enlarged portion 36 of the member 30 are sufficiently less than the corresponding dimensions defined by the grooves 42, 44 to enable the member 30 to move with considerable latitude and freedom in all directions at substantially right angles to the longitudinal axis of the frame 12.

Since the print wires 14 follow varying curved paths through the frame 12, it will be seen that the member 30 is free to move in directions which are substantially, but not precisely, perpendicular to the longitudinal axes of the print wires 14. As will subsequently be described in greater detail, vibration and lateral movement of the print wires 14 cause the member 30, which is "floating" in the grooves 42, 44, to move transversely within such grooves, in response to forces applied thereto by the wires 14.

As shown in Fig. 5, a notch 46 is formed on corner of the enlarged portion 36 of the member 30 and cooperates with a key 48 in the groove 44 to insure that the member 30 is placed correctly in the groove.

In the illustrated embodiment, a second intermediate support member 50 having print wire apertures 52, a reduced portion 54, an enlarged portion 56, edge portions 58 and 60, and a notch 66 cooperating with a key 68 (Fig. 4), is positioned in grooves 62, 64 in the side walls 20, 22 of the frame 12. This second intermediate support member 50 functions in the same manner as the member 30, described above.

The members 26, 28, 30 and 50 guide the various print wires 14 to follow desired paths, and to accomplish the translation of the wires from a circular formation at the upper end, as seen in Fig. 3, to a linear formation at the printing end, as seen in Fig. 6. This translation is accomplished by passing each wire 14 through a separate aperture 70 in the upper member 28, through apertures 32 and 52 in the members 30 and 50, and into a defined position within a bearing 72 in the print end support member 26, as shown in Fig.

6. The bearing 72 is of a material which resists wear, and has a low coefficient of friction.

A pair of mounting flanges 78 and 80 extend laterally from the upper ends of side walls 20 and 22. The frame 12 is circular in cross-sectional shape above the flanges 78, 80 as seen in Fig. 1, and terminates in the upper end support member 28, which is of circular configuration. An apertured post 82 extends from the member 28 and provides means for assembling the driving means for the wires 14 to the frame 12, as will subsequently be described in greater detail.

As shown in Fig. 1, a plate 84 is provided with a central aperture 86 and is secured to the flanges 78, 80 on the frame 12 by suitable fastening means 88. The circular portion of the frame 12 extends through the aperture 86. A plurality of holes 90 are provided in the plate 84 for mounting a corresponding plurality, nine in the illustrated embodiment, of actuat ing means for the wire printing elements 14.

A coil 92, a center pole 94, an shaped outer pole 96 and an armature 98 form the electro-magnetic actuating means used in the print head. An armature shim I00 spaces the armatures 98 away from the poles 94 for the purpose of effecting faster armature release.

A unitary connector 102 is mounted by means of a screw 104 and a washer 106 to the post 82 of the frame 12. The connector 102 has a circular central portion 108 with an annular groove 110 provided in its bottom surface. An O-ring 112 is inserted in the groove 110 to act as a shock absorber and to provide a reference surface for the cap 16 of the print wire 14 striking the end of the armature 98. Nine arms 114 are formed integral with the central portion 108 of the connector 102 and extend therefrom. Each arm 114 has associated with it a first armature receiving structure 116 and a second armature receiving structure 118. One end of each armature 98 is received and held in place by the structure 116 and the other end of each armature is received and guided by the structure 118.With the connector 102 installed in the position shown, the arms 114 apply forces to the cantilevered distal ends of the armatures, causing their print wire impacting ends to rotate about the fulcrum formed by the top edge of the pole 96 and upwardly into engagement with the O-rings 112. The caps 16 associated with the print wires 14 are maintained in contact with the ends of the armature 98 by means of the forces applied by the spring 18.

The unitary connectori 102 serves a number of functions in the assembly and operation of the print head 10, including retaining the armatures 98 in proper relationship to the remainder of the structure, acting as a biasing means for the armatures, providing means for adjusting the air gap between the armatures 98 and corresponding centre poles 92, forming a reference surface for the armatures 98 and print wire caps 16 to assure that all actuated print wires 14 impact the record medium at substantially the same time during a printing cycle, and, by means of the O-ring 112, absorbing energy from the armatures 98 and the print wires 14 on return motion after actuation.

Characters such as numbers, letters or symbols are generated by the print head by a sequence of print cycles. Selective actuation of predetermined combinations of print wires 14 through energization of their corresponding coils 92 during each cycle results in the formation of the desired character on the record medium with the print head being shifted one position with respect to the record medium after each cycle to be properly located for the next printing cycle.

When a coil 92 is energized, a magnetic flux is created which causes armature 98 to be drawn into contact with centre pole 94. The movement of armature 98 transmits energy into print wire 14, causing it to move in an axial direction in the frame 12. The force imparted into the wire 14 causes it to move against the spring 18 and its inertia causes it to continue to move downwardly out of contact with the armature 98 after said armature bottoms out against centre pole 94. The impact delivering end of the print wire extends beyond bearing 82 and strikes the record medium, causing a dot to be imprinted. The energy stored in the moving print wire 14 is partially absorbed by the impacted record medium and partially returned to the print wire 14, aiding the spring 18 in returning hte print wire 14 to its rest position.

At approximately the same time that the print wire 14 is impacting the record medium, the coil 92 is de-energized. The movement exerted on the armature 98 by the arm 114 causes it to rotate away from the centre pole 94 and to return into contact with the during 112.

An inherent consideration in the design of print heads of the wire matrix type is the relatively high length-to-diameter ratios of the print wires. The print wires such as the wires 14 are small in diameter in order to produce proper character line width, a typical diameter being 0.3556 millimeters. Print wire length is relatively long (typically 76.2 millimeters), in order to enable the print wires to be fanned out from their tight linear pattern at the bearing 72 to the larger circular pattern required tp coact with the armatures 98. Due to the large ratio of wire length to wire diameter, and the fact that a relatively large impact force (approximately 2 kilograms) is required to print, the wire 14 has a tendency to buckle.A further factor increasing the tendency of the wire to buckle is the initial curvature of the wire through the frame of the print head which is required for access to the wire of the actuating means.

In order to obtain the required impact force for satisfactory printing, it is necessary to reduce the effective length-to-diameter ratio of the print wire by adding intermediate guide members for the print wire. This lower ratio increases the critical buckling force, so that buckling still occurs but only at a much higher force. Thus a relatively higher force may be applied to the wire, which enables the delivery of more printing force to the printing media.

The lower ratio also increases the natural lateral oscillation frequency of the print wire to the point at which this frequency is close to the operating frequency of the printing cycle. As these two frequencies approach the same point, reasonance develops and the amplitude of lateral oscillation increases to the point that it creates stresses in the print wire above the critical level for extended operation without fatigue failures. The higher natural frequency also adds many fatigue cycles to the wire beyond those required in the printing cycles consequently decreasing the fatigue life of the print wires.

By permitting the intermediate support members 30 and 50 shown in the drawings to translate laterally in all directions, these members add additional effective mass to the print wire at each guide or support member location and consequently reduce the natural frequency of the lateral oscillations of the print wires. In the illustrated embodiment, the total mass of the intermediate support members is substantially in excess of the total mass of the print wires, though this factor is not, in itself, believed to be critical. It should be noted that the "effective" mass of a support member at any given time, with respect to the print wires 14, may differ from its actual mass, since the support member may be partially supported by those wires which are not being fired at that instant, and therefore will not exert its full dampening effect upon the wires which are being fired at that time.

The support members 30 and 50 are located laterally by the combined array of print wires 14 extending through the inter- mediate support members and by the fixed support members 26 and 28 at either ends of the frame 12, which are located close to the ends of the print wires 14. This arrangement also achieves optimum lateral location of the intermediate support members 30 and 50 for best alignment of; and minimum frictional drag on, the print wires 14.

WHAT WE CLAIM IS: 1. A printing apparatus including a frame; at least one support member loosely mounted in said frame and supporting at least one elongated printing element for axial movement therethrough; and driving means operatively connected to said printing element for axially driving said printing element to effect printing; said support member being free to move with respect to said frame in response to non-axial movement of said printing element to dampen any lateral movement thereof.

2. An apparatus according to Claim 1, including a plurality of support members, each in a plane substantially perpendicular to the axis of said printing element, and movable in at least two directions in said plane.

3. An apparatus according to Claim 2, wherein the inner surface of said frame is provided with a plurality of grooves each for receiving a respective support member, said support members having a thickness allowing them to slidably fit within the respective grooves.

4. An apparatus according to either Claim 2 or 3, wherein said frame is elongated and has a substantially rectangular cross-section, and wherein said support members are plates of corresponding shape loosely fitting in said frame.

5. An apparatus according to any one of the preceding Claims, including a plurality of printing elements supported by said at least one or said plurality of support members.

6. An apparatus according to Claim 5, wherein the total mass of said printing elements is less than the total mass of said support members.

7. An apparatus according to any one of Claims 3 to 6, including key means on said support members co-operating with corresponding key means in each groove to insure proper orientation of said support members in said frame.

8. An apparatus according to any one of the preceding Claims, forming part of a printing head of a wire matrix printer.

9. An apparatus substantially as hereinbefore described with reference to Figs.

1 to 6 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. The lower ratio also increases the natural lateral oscillation frequency of the print wire to the point at which this frequency is close to the operating frequency of the printing cycle. As these two frequencies approach the same point, reasonance develops and the amplitude of lateral oscillation increases to the point that it creates stresses in the print wire above the critical level for extended operation without fatigue failures. The higher natural frequency also adds many fatigue cycles to the wire beyond those required in the printing cycles consequently decreasing the fatigue life of the print wires. By permitting the intermediate support members 30 and 50 shown in the drawings to translate laterally in all directions, these members add additional effective mass to the print wire at each guide or support member location and consequently reduce the natural frequency of the lateral oscillations of the print wires. In the illustrated embodiment, the total mass of the intermediate support members is substantially in excess of the total mass of the print wires, though this factor is not, in itself, believed to be critical. It should be noted that the "effective" mass of a support member at any given time, with respect to the print wires 14, may differ from its actual mass, since the support member may be partially supported by those wires which are not being fired at that instant, and therefore will not exert its full dampening effect upon the wires which are being fired at that time. The support members 30 and 50 are located laterally by the combined array of print wires 14 extending through the inter- mediate support members and by the fixed support members 26 and 28 at either ends of the frame 12, which are located close to the ends of the print wires 14. This arrangement also achieves optimum lateral location of the intermediate support members 30 and 50 for best alignment of; and minimum frictional drag on, the print wires 14. WHAT WE CLAIM IS:

1. A printing apparatus including a frame; at least one support member loosely mounted in said frame and supporting at least one elongated printing element for axial movement therethrough; and driving means operatively connected to said printing element for axially driving said printing element to effect printing; said support member being free to move with respect to said frame in response to non-axial movement of said printing element to dampen any lateral movement thereof.

2. An apparatus according to Claim 1, including a plurality of support members, each in a plane substantially perpendicular to the axis of said printing element, and movable in at least two directions in said plane.

3. An apparatus according to Claim 2, wherein the inner surface of said frame is provided with a plurality of grooves each for receiving a respective support member, said support members having a thickness allowing them to slidably fit within the respective grooves.

4. An apparatus according to either Claim 2 or 3, wherein said frame is elongated and has a substantially rectangular cross-section, and wherein said support members are plates of corresponding shape loosely fitting in said frame.

5. An apparatus according to any one of the preceding Claims, including a plurality of printing elements supported by said at least one or said plurality of support members.

6. An apparatus according to Claim 5, wherein the total mass of said printing elements is less than the total mass of said support members.

7. An apparatus according to any one of Claims 3 to 6, including key means on said support members co-operating with corresponding key means in each groove to insure proper orientation of said support members in said frame.

8. An apparatus according to any one of the preceding Claims, forming part of a printing head of a wire matrix printer.

9. An apparatus substantially as hereinbefore described with reference to Figs.

1 to 6 of the accompanying drawings.