PRINT WHEEL ALIGNING APPARATUS AND ROTARY PRINT WHEEL

Abstract: In an impact printer of the type wherein a print wheel is rotated to a print position by a drive motor, and printing is caused by impacting a particular character on the print wheel by a print hammer, the print wheel has coarse alignment and fine alignment means formed on the print wheel. The coarse alignment means such as large pitch radial teeth, is used to drive the wheel, and the fine alignment means, such as fine pitch teeth, is utilized to locate the print wheel angularly immediately prior to the respective spoke of the print wheel being struck by the print hammer (31).

Description: PRINT WHEEL ALIGNMENT APPARATUS The invention relates to serial printing devices and, more particularly, to high-speed serial printers having print fonts arranged upon a disc member, which disc member rotates the lonts past an impacting printing hammer. In a high-speed, high-quality printing system, it is necessary to accurately and quickly position the disc member so that the printed characters will be aligned and spaced correctly. Heretofore, expensive and complicated systems have been utilized to provide the positional accuracy required. Attempts to utilize, for example, inexpensive stepper motors in such systems have not been totally successful. The invention as claimed is intended to provide a remedy. It solves the problem of how to utilize inexpensive stepper motors in highspeed printers without sacrificing alignment or spacing accuracy. The print wheel positioning means of this invention utilizes two sets of positioning means; one, a coarse alignment means connected to the drive motor; and the second, a fine alignment means, which is stationary and comes into play only after the coarse alignment means has been deactivated. The print wheel disc contains mating coarse and fine aligning means. One way of carrying out the invention is described in detaiL below with reference to the drawings, which illustrate two specific embodiments, in which: Figure 1 is a side-view schematic representation of the print wheel aligning means of this invention in the drive mode; Figure 2 is a side-view schematic representation of the print wheel alignment means of this invention in the fine aligning mode; Figure 3 is a partial side-view schematic showing another embodiment for the fine alignment or positioning means, and Figure 4 is an end view of the print wheel drive showing the coarse aligning drive teeth and the fine alignment teeth or serrations. For clarity of understanding, the same parts are given the same designations in the various Figures. Preferring now to Figures I and 2, there is seen stepper motor 1 having drive shaft 3 mounted thereon for rotation. Attached to drive shaft 3 is flexible member 5 which may be, for example, a spring or a rubber disc, which spring or rubber disc is flexible in the axial direction relative to the drive shaft 3. In turn, fixed flexible member5 is a ferromagnetic axially movable coupling drive member 7, which has drive teeth 9 formed thereon. Flexible member S is designed to bias drive member 7 towards the print wheel, generally designated as 11. Attached to fixed stepper motor body J is stationary couplingsupport housing -13, which has- stationary fine alignment teeth 15 mounted or formed thereon. Housing 13 also supports efrctromagnet 17, which is located and of strength such that when activated, it will pull drive member 7 axially with respect to drive shaft 3 away from print wheel 11 as shown in Figure 2. The movement of drive member 7 is sufficient to disconnect drive teeth 9 from mating print wheel teeth 19 and to allow-teeth 21 on print wheel 11 to contact fixed fine alignment teeth 15. Although in Figure 2 teeth 19 are shown completely separated from -drive teeth 9, it is not necessary to back off drive member 7 more than a very small amount to loosen its grip on print wheel 11 and allow contact with teeth 15. Drive-teeth 19 are shown separated from print wheel teeth 19 for purposes of explanation only. Print wheel 11 is urged into contact with fine alignment teeth 15 by plate spring 23 acting through ball pivot25. Plate spring 23 is mounted in print wheel cartridge case 27. In operation, stepper motor 1 is activated and by means of a controller (not shown) directed to turn shaft 3 to one -of 100 radial positions corresponding to the character desired tobe printed. In this example, it is assumed that there are 25 coarse- alignment drive teeth 9 and 19 and 100 fine alignment teeth 15 and 21. Since electromagnet 17 is rrot activated during the drive cycle, coarse alignment drive teeth 9 and print wheel drive teeth 19 are in contact, as shown in Figure 1, with plate spring 23 urging print wheel drive teeth 19 into contact with drive shaft drive teeth 9 Ball 25 acts as a pivot for radial rotation of print wheel 11. When a desired character 29 is aligned with print hammer 31, dri-ve shaft 3 stops, which coarse aligns character 29 with platen 33. Electromagnet 17 is then activated, which pulls drive member 7 away from print wheel I1 sufficiently to uncouple coarse alignment drive teeth 9 and 19 as shown in Figure 2. - As drive member 7 is pulled away from print wheel 11 by electromagnet-17, plate spring 23 acting through ball pivot point 25 pushes print-wheel 11 to the Jeft, as seen in Figure 2, so that fixed fine alignment positioning teeth 15 and print wheel fine alignment teeth 21 are in contact. This provides fine alignment of character 29 so that when print hammer 31 is activated, character 29 will be in the correct position relative to platen 33. Normally, a print ribbon (not shown) and print-receiving paper (not shown) are provided between character 29 and platen 33. Figure 3 shows a partial side-view schematic of another useful emodiment of the present invention. Here the fixed fine alignment teeth 15 are located on the print wheel cartridge case 27 itself instead of on a housing 13 connected to the stepper motor 1 as in Figures 1 and 2. In the embodiment shown in Figure 3, when the drive wheel is pulled away from print wheel 11, plate spring 23 mounted on cartridge 27 urges print wheel 11 to the left as shown in Figure 3 until fine alignment print wheel teeth 21 are brought into contact with fixed fine alignment teeth 15, which thereby accomplishes the fine positioning of print wheel 11. Figure 4 shows a stepper motor I arrangement with fixed fine alignment teeth 15 and movable coarse alignment drive teeth 9. As explained in detail in connection with Figures 1- and 2, drive teeth 9 are mounted for rotation to coarse position the print wheel 11 and also is mounted for axial movement so that the coarse alignment means can be disengaged from print wheel 11 allowing print wheel 11 to contact fine alignment means 15. Other advantages of the present invention are that the radially extending teeth 9, 19, 15 and 21 center the print wheel with great accuracy and rigidity. Further, wear does not affect the accuracy this positioning device. The fewer number of teeth on the drive member 7 allows for a greater misalignment between print wheel 11 and drive member 7 when they are being engaged.

Claims: CLAIMS: 1. Print wheel aligning apparatus including a print wheel (11) mounted for selective rotation by a drive means (7), characterised in that the print wheel has coarse alignment means (19) and fine alignment means (21) thereon, in that the drive means (7) are movable into and out of engagement with the coarse alignment means, and in that means (23) are provided to urge the fine alignment means on the print wheel into engagement with adjacent fixed fine alignment means (15) when the drive means is disengaged from the coarse alignment means. 2. The apparatus of claim 1 characterised in that said coarse alignment means is a series of teeth (19) formed on said print wheel (11), and in that said drive means (7) includes matching teeth (9) for mating with the teeth (19). 3. The apparatus of claim 1 or 2 characterised in that said fine alignment means is a series of teeth (21) formed on said print wheel, and in that said fixed fine alignment means is teeth (15) for mating with the teeth (21). 4. The apparatus of any preceding claim, characterised in that said print wheel (11) is mounted for rotation within a cartridge (27), and in that the fixed fine alignment means (15) are formed thereon. 5. The apparatus of any preceding claim, characterised in that the fine and coarse alignment teeth extend radially. 6. A rotary print wheel (11) characterised by coarse alignment means (19) for receiving a print wheel drive means, and fine alignment means (21) for contacting adjacent fixed fine alignment means (15) upon disengagement of the drive means from the print wheel. 7. The print wheel of claim 6, characterised in that said coarse alignment rrieans are teeth (19) formed on the print wheel. 8. The print wheel of claim 6 or 7, characterised in that said fine alignment means are teeth (21) formed on the print wheel. 9. The print wheel of claim 7 or 8, characterised in that the teeth (19 or 21) extend radially of the axis of rotation of the print wheel.

Inventors: BABLER, EGON S.
Applicants: XEROX CORPORATION
Application year: 1981
Main classification: B41J1
IPC codes: B41J1