EP0038691B1

EP0038691B1 - Impact printer including a replaceable print wheel

Info

Publication number: EP0038691B1
Application number: EP19810301703
Authority: EP
Inventors: Egon S. Babler
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1980-04-18
Filing date: 1981-04-16
Publication date: 1984-07-11
Also published as: BR8102315A; DE3164682D1; EP0038691A1

Description

On current impact printers utilizing a rotatable print wheel, such as the Xerox 800, a motor, hammer mechanism and ribbon cartridge are all supported on a frame, which frame is pivotally mounted on a moving carriage. The frame must be pivoted from a print position in order to replace the print wheel. Further, because of interfering structure, the ribbon cartridge must be removed to allow pivoting of the frame. It is desirable to replace the print wheel in the printer using as simple a mechanism as possible.
DEA2 822 313 discloses a printer using a replaceable print wheel mounted in a cassette. During insertion of the cassette into its operating position a locking member movable with a rotary drive shaft engates first loosely and then tightly in a notch in the print wheel so as to determine its final angular position, and to transmit rotary motion thereto.
US-A-4 198 169 relates to a similar type of daisy wheel printer, but one without a cassette, in which the printer wheel is located angularly by a retractable tooth engageable with respective recesses in the same face of the print wheel as is engaged by its rotary drive means.
The invention as claimed is intended to provide a simplified mechanism of a special construction by which a print wheel can be easily inserted into a printer, and further to allow the use of a stiffer, more-durable, print wheel.
The advantages offered by the invention are that not only is the print wheel easy to load, but the mechanism for receiving the print wheel cartridge also automatically aligns the print wheel in the print wheel drive position. These benefits arise mainly from the drive motor for the print wheels being located on the face of the print wheel, opposite the face of the print wheel on which the print hammer mechanism operates. Furthermore, because of the axial displacement of the print wheel towards the platen when engaging the fine-alignment teeth as claimed, the print wheel can be positioned closer to the platen thus allowing shorter, stiffer, hence more durable print wheels as mentioned above.
One way of carrying out the invention is described in detail below with reference to the accompanying drawings, which illustrate only one specific embodiment, in which:-

Figure 1 is a plan view of a print wheel, print wheel cartridge and cartridge gate in accordance with this invention showing the print wheel drive face of the print wheel.
Figure 2 is a partial side view of a motor, drive shaft, print wheel drive element and connection thereof to a cartridge gate, the cartridge gate print wheel and print wheel cartridge being shown in partial section as indicated by lines 2-2 in Figure 1.
Figure 3 is similar to Figure 2 but showing the print wheel, print wheel cartridge and gate in the print wheel removal and insertion positions.
Figure 4 is a plan view of the cartridge gate in accordance with this invention, which shows the spring plate bias member for the gate.
Figure 5 shows a gate that can be used to accommodate a print wheel not contained in a cartridge with the location of the print wheel indicated by the broken line circle.
Figure 6 shows a side view of the gate of Figure 5 with the print wheel located in the gate in the print wheel drive position.

In each of the various Figures, the same parts are given the same reference numerals for ease in understanding.
Referring now to Figures 1-4, there is seen a print wheel generally designated as 1 having print or type characters 47 thereon. Print wheel 1 is contained in print wheel cartridge generally designated 3. The print wheel 1 and print wheel cartridge 3 are a self-contained unit, which unit can be readily removed from and inserted into a print wheel gate generally designated 5. Print wheel gate 5 is pivotally mounted on print wheel drive motor flange generally designated as 7. Flange 7 is a part of drive shaft housing 9, which, in turn, is a part of print wheel drive motor 11. Print wheel drive motor 11 is mounted to a frame (not shown) which frame is mounted for axial movement relative to printer platen 13. A typical frame mounting is shown in U.S. Patent 4,124,312, issued November 7, 1978, to the assignee of this invention. The frame is mounted on rails for movement axial to platen 108 as shown in that patent.
Print wheel gate 5 can be mounted for pivoting on flange 7 by means, for example, of flexible rubber-type bushings. Here, however, a spring steel plate 15 is attached to the inside of print wheel gate 5. Flange 7 has a beveled edge 17, which allows spring plate 15 to flex as shown in Figure 3. Eyes 19 of spring plate 15 are held firmly against fixed alignment means by screws 21. Gate 5 is allowed to pivot by the flexing of spring plate 15. As gate 5 moves from the print wheel removal position of Figure 3 to the print wheel drive position of Figure 2, print wheel drive teeth 23 mesh with print wheel drive shaft teeth 25 mounted on the drive shaft (not shown) of motor 11. A grooved handle 27 is mounted on the hammer guide 29, which, in turn, is mounted on print wheel gate 5 for ease in pulling gate 5 away from the print wheel drive shaft teeth 25. Spring 31 clamps the print wheel cartridge 3 between the flange 7 and the gate 5. Spring mounting means 45 are provided on the print wheel gate 5 and on flange 7. Print wheel spring plate 33 pressing against ball 35 provides the pivot point around which print wheel 1 freely rotates. When it is desired to print a character, print wheel drive shaft teeth 25 are pulled out of contact with print wheel teeth 23. Spring 33 acting against ball 35 urges print wheel registration teeth 37 into contact with fixed fine-alignment teeth 39. Hammer 41 is then driven by a hammer mechanism, shown generally as 43, into contact with a type ribbon and paper (not shown) placed between print wheel 1 and platen 13.
It can be seen that, when print wheel gate 5 is in the print wheel removal position shown in Figure 3, the print wheel cartridge 3 can be pulled straight out without concern for contacting any interfering structure. As a result of positioning print wheel drive motor 11 and drive shaft and drive shaft housing 9 on the side of print wheel 1, opposite the hammer mechanism 43, it is accordingly not necessary to pivot or move the print wheel drive apparatus with the print wheel to effect removal and insertion of a print wheel.
Referring now to Figures 5 and 6, it can be seen that, because of the axial displacement of the print wheel 1 towards platen 13 when engaging the fine-alignment teeth 39, the print wheel 1 can be positioned closer to platen 13, allowing shorter, stiffer, hence more durable print wheels to be used. It is also possible to provide print wheels that need not be protected by print wheel cartridges. The gate 5 shown in Figures 5 and 6 provides the functions of the gate 5 shown in Figures 3 and 4 and of the print wheel cartridge 3. Gate 5 in Figures 5 and 6 has two guides 36 that support the print wheel 1, shown as the broken circle 1 in Figure 5, when the print wheel 1 is dropped into the gate 5, while gate 5 is open in the position shown in Figure 5. As the gate is closed, spring 33 on gate 5 urges, through pivot ball 35, print wheel teeth 23 into contact with drive shaft teeth 25. Print wheel 1 is thereby centered so that it can rotate freely within the gate 5 as shown in Figure 6. Slot 34 allows movement of spring 33 when drive shaft teeth 25 are pushed against print wheel drive teeth 23 to drive print wheel 1 to a typing position. Also ribbon guide members 50 are provided on the gate 5. Gate 5 is mounted for pivoting on spring steel plate 15 as described in connection with Figures 1-4.

Claims

1. An impact printer including a replaceable daisy print wheel (1, 3) insertable transversely of the shaft of a rotary drive means (11, 25) between a platen (13) and a hammer (41), the print wheel when in position being biased axially (33) into driving contact with the shaft whereby the motor (11) of the drive means can rotate the print wheel, characterised in that

the drive means (11, 25) is on the side of the print wheel opposite to the hammer, and below the platen;

fixed fine alignment teeth (39) are circumferentially arranged to engage correspondingly arranged registration teeth (37) on the same face of the print wheel as is engaged by the drive means, and

the said drive means (11, 25) is axially retractable from the print wheel to permit the print wheel to move into registration contact with the fine alignment teeth (39) immediately prior to each hammer stroke.

2. A printer as claimed in claim 1, characterised in that one face of the print wheel has two annular sets of teeth, one set (23) being for engagement with drive shaft teeth (25), and the other set (37) for engagement with the fine alignment teeth (39).

3. A printer as claimed in claim 2, characterised in that the print wheel, when in position, is housed in a gate (5) pivotally mounted so that the print wheel can be pivoted between a load/unload position and a drive position in which it is engageable by the rotary drive shaft teeth (25).

4. A printer as claimed in claim 3, characterised in that the gate carries the print hammer at a location remote from the gate's pivotal axis.

5. A printer as claimed in claim 3 or 4, characterised in that the print wheel is biased towards the platen by a spring (33) extending between the gate and a projection (35) from the print wheel lying on the axis of rotation thereof.