PRINT WHEEL FOR IMPACT PRINTER

Abstract: A print wheel (5) for an impact printer using two or more hammers (17) includes at least two characters (11) carried by each print wheel beam (9). The characters on each row are shaped such that when they are moved into contact with the print wheel platen, they will contact the platen uniformly, compensating for the bending and torsional forces applied to the beam by impact of the respective hammer on the back of the character to be printed.

Description: PRINT WHEEL FOR IMPACT PRINTER The invention relates to a print wheel for serial printing devices and particularly to high-speed serial printers having multiple print characters arranged on beams of a disc member. There are two types of systems known wherein characters are arranged In two or more concentric circles on the disc. In the first, the disc is caused to move up or down relative to a horizontal line of printing depending on whether a character on the inner row or a character on the outer row of characters is to be printed. In the second, two or more print hammers are provided, one for each row of characters, and the axes of the characters In each row differ so that they are aligned correctly for printing at diffferent rotationai positions. This invention relates to an improvement In print wheels for the system using more than one hammer. The invention as claimed is intended to provide a multi character row print wheel which is relatively easy to mold as a one-piece plastics wheel, and wherein each row of characters and corresponding pads is formed to align accurately with the face of the printer platen when Impacted by its associated hammer. One way of carrying out the invention is described in detail below with reference to the drawings, which illustrate only one specific embodiment, in which: Figure 1 shows prior art character-beam relationships. Figure 2 shows a partial plan view of a print wheel in accordance with this Invention. Figure 3 is a cross-sectional side view of the print wheel of Figure 2 taken along line 3-3 of Fig. 2; Figure 4 is a top view of the print wheel of Figure 2 taken along line 4-4 of Fig. 2; Figure 5A is a top view showing greatly enlarged the relationship between the inboard and outboard print wheel hammers, characters and platen at rest, in dashed lines, and at the moment of printing. Figure 5B Is a top view showing greatly enlarged the relationship between the outboard print wheel hammer, outboard character and platen at rest, in dashed lines, and at the moment of impact. Figure 6 is a side view showing an inboard character greatly enlarged at the moment of printing. Figure 7 is a side view showing an outboard character greatly enlarged at the moment of printing. Figure 8 snows a further choracterOeam relationship in accordance with this invention. The Figures are not drawn to scale, and certain features are exaggerated in size for purposes of explanation. Referring now to Figure 1, there are shown three prior art character-bearing beams. Beam I is the standard print wheel beam that carries one character li per beam. Beam 2 has two concentric circular rows of characters on it, the axis of each of the characters being aligned with the long axis of the beam. To print using a beam 2 type print wheel, a single print hammer is used, and the print wheel is lowered or mised depending on whether a character from the imer (I la) or outer (l lb) row of characters is desired to be printed A print wheel with charcrterbecring spokes such as beam 3 utilize two print hammers. The print wheel is rotated into the position shown in Figure I where the lower or inner character is to be printed. The print wheel is rotated in the plane of the disc until the outer character is aligned with the line of printing to print the outer character. The centers of characters I la and I Ib are aligned on the long axis of the beam on which they are mounted. An explanation of how this print wheel can be used in a auelEammer print wheel system is disclosed in U.S. Patent 4,069,907. Referring now to Figures 2-4, there is seen a print wheel disc designated generally as 5, which is made up of a hub 7 and, extending therefrom, a plurality of radiallytxtending beams 9. Formed on beams 9 are inboard character pods I Ia and outboard character pads I Ih It can be seen that beams 9 are straight and that outboard character pads I lb are formed at an angle to the beams 9. Structurally, it is preferred to have character pads I Ia and tfb formed such that their centers are on the center of a straight beam 9, but they may also have the arrangement shown in the abovementioned patent or generally can be placed on a beam of any non-linear shape. Drive means 13 is provided for rotating print wheel 5. Drive means 13 may be driven, for example, by a servo or stepper motor for rotating print wheel 5 to align the desired character pad Ila or I lb as desired on line of printing 15. Print hammers 17a and 17b shown as dashed circles in Figure 2 are provided to impact inboard character pads lla and outboard character pads I Ib in line with line of printing 15, respectively. A platen 19 is provided against which printing occurs. In operation, as print wheel 5 is moved along the line of printing 15 by carriage means (not shown), a controller (not shown) activates drive means 13, which rotates print wheel 5 until preselected character pad I la or I Ib is aligned with line of printing 15. The appropriate print hammer 17a, 17b is then activated moving in the direction shown by arrow 21 toward the platen, impacting the preselected character pad I Ia or I Ib and driving it toward platen 19. A wedgeback is provided on the pads carrying characters I la and I Ib, and the hammers 17a and 17b are Notched correspondingly to ensure a proper capture even in the case of misalignment (hammer to pad) due to manufacturing tolerances accumulation or print-on-the-fly technique. Conventionally, a print ink ribbon (not shown) and a print-receiving member such as poper (not shown) are placed between the print wheel and platen 19 to effect printing. Depending on how much distance there is between hammers 17a and 17b, it may be necessary to move the print wheel 5 relative to the platen 19 to space the printed characters evenly. Also, the controller can be programmed to type outboard characters out of sequence since outboard characters are printed a number of spoces away from inboard characters so that print wheel 5 movement relative to platen 19 would proceed conventionally without the necessity for rapid back and forth movement. While printing the irboard character Ila, pure bending stress is induced in the beam 9. It has been found in this system that the beams 9 are subject to either pure bending or bending and twisting during operotion when the outboard character pods I lb are printed, depending on the shape of the beam. The straight beam shown in Figure 2 is subject to bending only; and the beam 3, shaped as shown in Figure I, is subject to both bending and torsion. When outboard character pod I lb is impocted against platen 19, because of its offset position from the vertical centerline of the print wheel and also because of the bend or twist of bearing beam, the character 23b does not meet platen 19 exactly flush but meets instead at an angle, which can cause shoded printed characters. In order to overcome the problem recited above, the outboard character pads I Ib and characters 23b formed thereon are designed to meet the platen 19 flush and yet allow the print wheel beams to be formed in a single plane, confining complex cutting angles to the character pads 11 b and characters 23b only. Referring now to Figures and6, there is shown an inboard character pad I la having character 230 formed thereon. The foce of character pad Ila, which contacts print hammer 17a, is formed as a male dihedral 25a, which is shaped to mate with female dihedml 27a in inboard print hammer 17a. The purpose of the dihedral mating surfaces is to align and stabilize the character 23a with reference to the platen 19 at the time of printing. The character pod I la and print hammer 17a shown in dashed lines represent the position of the character pad I la and print hammer 17a in the zat rest" position; the solid lines represent the character pod I Ia and print hammer 17a at the moment of printing It can be seen in connection with Figure SA that, as print hammer 17a moves forward in direction 21, character 19 will be flush or strike at a right angle in rebtion to a mdius of platen 19 at the time of impacts shown in Figures SA and 6. The impact surface 29a is formed with a surface curvature to match the curve of the platen. It can be seen, however, that, where, for example, the outboard character pad I lb (as seen in Figure 2) is driven toward the platen, the right hand and lower portions of character pad lib will impact the platen 19 first, causing a shaded printed character and begum 9 either bending (in the case of straight beam in Figure 2) or bending and twisting (when the beam has the shape of beam 3 depicted in Figure 1). Referring now to Figures SB and 7, there is shown, in accordance with this invention, a character pad 1 Ib and character 23b designed to allow character 23b to be presented flush to platen 19 at the moment of printing as shown in Figure 7. Figure 58 shows in dashed lines the relationship between outboard character pod I Ib and outboard print hammer 17b in the at rest position. Outboard character pod I lb is provided with male dihedral 25b, and outboard print hammer 17b is provided with female dihedml f < xm 27b for alignment and stabitization of character 23b at the time of impact with platen 19. In order for the surface 29b of character 23b to be aligned with the paten 19 horizontally at the time of impact, character printing surface 29b is formed such that at rest it is aligned at a predetermined angle Y relative to platen surface 19. For convenience in molding, outboard character pad II b surface 31b is formed in the same plane as inboard character pad Ila surface 31a. This plane is perpendicular to the axis of rotation of print wheels. The character pad I Ib is, however, formed at angle Y to the surface 31b. Then as print wheel S is moved toward platen 19 and constrained in an arc by beam9, printing surface 29b will meet platen 19 flush as shown in solid line in Figure SB. The bisecting line 33 of male dihedral 25b of outboard pad I Ib is formed also at angb Y to the axis of rotation of print wheel 5. This will enable the V-surface 27b of outboard hammer II b to properly engoge the pad ilb at rest and drive it towards the platen 19 when printing, so that the bisecting line 33 takes the final position 34 perpendicular to platen 19 at the moment of contact as shown in Figure SB. Also, in order to have outboard character surface 29b meet platen 19 flush vertically, it is necessary to provide a slant of printing surface 29b of angle X versus the surface 31b as shown in Figure 7. The superposition of cutting angles X, Y defines the spatial position of a plane tangent to the curved print surface of the character at rest such that when impacting the platen, this surface will uniformly comply with the curvature of platen 19. In a particularly preferred embodiment, the beams are spaced at 3S from one another providing room for 100 beams 9 on the circumference of hub 7. In Figure 2, the angular span 30 between two spokes 9 bearing pads I la and lib and aligned with line of printing 15 is 32.40. From the center of the hub 7 to the center of the character pads I Ia on the inner character row is 1.4789 inches. The outer character llb centers are 1.7516 inches from the center of the disc. The outer characters 1 lb are placed further out thon geometrically required since the beams 9 become, in effect, shorter when bent by hammer 17 impact. Also, as shown in Figure 5B, the axis 33 of character pad I lb is offset from the axis 35 of print hammer 17b an angle Y of about 0 4±)5 . This also is the angle Y that print surface 29b is formed in relationship to surface 31b of character pad I Ib as shown in Figure SB. The angle 4 shown in Figures 6 and 7 is designed to be 11.20; the angle X, 3.050; and the angle p to be 8.150. The outboard hammer 17b is spaced nine intervals (or ten spokes) 0 away from inboard print hammer 17a, equivalent to 32.4 on the print wheel 5. Referring now to Figure 8, the concept is subject to genemlization to a print wheel with more than two rows of characters and two printing hammers. In Figure 8 is depicted a print wheel with three rows. The three characters carried by the same beam are formed at different angles with the long axis of the beam. These angles, along with the diameter of each row, ensure the proper spacing between characters when all three rows are used to print on the same line. Also, each row will have its own Y and X angles built on fonts and pad wed-ock and, consequently, its own hammer angle IL Depending on design constraints (e g., distance between print wheel and platen 19), either both angles X, Y or only one of them can be equal to zero or a given row. While the principles of the invention have been made clear in the illustrative embodiments, there will be many modifications in structure, arrangement, proportions, etc., which will occur to those skilled in the art. For example, although this invention was described in connecfion with two character rows and two print hammers, obviously more than two character rows and print hammers could be used employing the same principtes. Further, although the preferred print wheel beam in accordance with this invention is straight, this invention would apply to print wheels having beams such as shown in US. Patent 4,069,907 or of any other shape

Claims: Claims: 1. A print wheel (5) for an impact printer having two or more hammers (17) and a platen (19), which comprises: (a) a disc hub (7); (b) beams (9) extending outwardly in a common plane from said hub, and (c) at least two concentric circular rows of characters (11) formed on said beams, at least one of said rows of characters having printing surfaces which are not formed in the same plane as the printing surfaces of characters of the or each other row of characters. 2. The print wheel of Claim 1, wherein at least one of said rows of characters has characters shaped to compensate for the otherwise-uneven impact of the character on the platen. 3. A print wheel as claimed in claim 1 or 2, in which there is a nonplanar anvil surface (25) at the back of each character adapted to cooperate with a complementary impact face (27) on the respective hammer. 4. A print wheel as claimed in claim 3, in which the anvil surface is protruberant, and the hammer surface recessed. 5. A print wheel as claimed in claim 4, in which the anvil and hammer surfaces are wedge-shaped in at least one cross-section. 6. A print wheel as claimed in any preceding claim, in which the longitudinal axes of the characters on the same beam are at different angles to a radius passing through the respective character.

Inventors: LEE, YU-CHUAN, MORRIS, LYLE E., NITESCU, PETRU N.
Applicants: XEROX CORPORATION
Application year: 1984
Main classification: B41J1
IPC codes: B41J1