GB2161758A - Printer - Google Patents

Abstract

A printer comprising a guide shaft (10) on which is slidably mounted a carriage (12) having a print head (11) thereon; a base plate (13) provided with carriage drive means (7) for effecting sliding movement of the carriage (12) on the guide shaft (10); a platen (2) disposed adjacent the print head (11) and arranged for the passage of a recording medium (25) therebetween; a frame (3a) provided with drive means (4) for driving the platen (2) so as to feed the recording medium (25); a recording medium guide (22) a portion (22b) of which has a shape corresponding to that of the platen (2); means (45, 47) carrying an electrical circuit; means (48) carrying a power source; and an outer casing (1) having integral portions which support the guide shaft (10), base plate (13), platen (2), frame (3a), recording medium guide (22), and the means (45, 47, 48) carrying the electrical circuit and the power source. <IMAGE>

Description

SPECIFICATION Printer This invention relates to a printer.

Hitherto, in the field of printers to be connected to personal computers and the like, each printer was manufactured by assembling together the mechanical parts required for the print section, paper feed section, etc. into individual units and fixing these units, together with an electric circuit and a power source etc., to an outer casing by screwing or like means. In many cases, the outer casing was moulded from synthetic resin for aesthetic or price reasons, whereas the mechanical section was made up of metal parts to provide mechanical strength. Because the so-manufactured outer casing was structurally weak but was required to support weighty mechanical sections, the conventional printer had several drawbacks, such as misalignment of the print due to vibration, misalignment of parts of the printer itself, and loosening of screws due to shock.Further, because the outer casing and the mechanical sections were prepared independently, the price of the conventional printer was relatively high owing to the manufacturing costs required for the number of parts and their assembly.

Although the invention is primarily directed to any novel integer or step, or combination of integers or steps, as herein disclosed and/or as shown in the accompanying drawings, nevertheless according to one aspect of the present invention, to which, however, the invention is in no way restricted, there is provided a printer comprising a guide shaft on which is slidably mounted a carriage having a print head thereon; a base plate provided with carriage drive means for effecting sliding movement of the carriage on the guide shaft: a platen disposed adjacent the print head and arranged for the passage of a recording medium therebetween; a frame provided with drive means for driving the platen so as to feed the recording medium a recording medium guide a portion of which has a shape corresponding to that of the platen; means carrying an electrical circuit; means carrying a power source: and an outer casing having integral portions which support the guide shaft, base plate, platen, frame, recording medium guide, and the means carrying the electrical circuit and the power source.

The outer casing is preferably formed of synthetic resin material.

The said recording medium guide preferably has a recessed portion, and a recording medium feed roller unit is provided in said recessed portion.

Said recording medium feed roller unit may comprise at least one recording medium feed roller mounted on a feed roller shaft; at least one spring member for supporting the feed roller shaft; and a spring holder for the or each spring member and within which the or the respective spring member is mounted.

The or each spring holder may have on its outer periphery a curved surface which conforms to the curved surface of the recording medium guide.

The recessed portion may be provided with a plurality of ribs each of which has a curved surface conforming to the curved surface of the recording medium guide.

The said base plate may be made of metal and may be attached to the outer bottom face of the outer casing.

There may also be an auxiliary plate positioned on the print head side of the recording medium guide, said auxiliary plate being arranged to push the recording medium onto said platen.

The auxiliary plate may have a length substantially equal to the whole length of said platen, the auxiliary plate being provided with first projecting portions which fit into holes formed in the recording medium guide, and with second projecting portions which abut against said guide shaft.

The said auxiliary plate may be earthed through said guide shaft.

Preferably, said frame is constituted by a first side frame and there is a second side frame opposite to said first side frame, recording medium push levers being mounted respectively on said side frames and being coupled to the ends of a recording medium push roller shaft.

Preferably, on each of said side frames there is a shaft at the centre of rotation of the respective push lever and a pawl for preventing removal of said push lever.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which: Figure 1 is an exploded perspective view of a printer which is an embodiment of the present invention, Figure 2 is a broken-away side sectional view of a part of the printer of Figure 1, Figures 3(a) and (b) are a plan view and a sectional view respectively showing how a base plate of the printer of Figure 1 is joined to an outer casing thereof, Figure 4 is an exploded perspective view illustrating the way in which a paper feed roller unit which forms part of the printer of Figure 1 is assembled;; Figure 5 is a sectional view showing a release lever of the printer of Figure 1 in its assembled state, Figure 6 is a sectional view showing a paper push roller mounted on a paper push roller shaft forming part of the printer of Figure 1, Figure 7 is a sectional view showing a support structure for an electric circuit section of the printer of Figure 1, and Figure 8 is a perspective view showing a support structure for a power source section of the printer of Figure 1.

A printer constituting an embodiment of the present invention comprises an outer casing 1 onto which there is integrally moulded a synthetic resin or plastics paper guide 22 which is arranged to force a recording paper 25 (Figure 2) to be entrained around a platen 2. The paper guide 22, which is shaped to correspond to the shape of the platen 2, has a substantially U-shaped recessed portion 23 midway thereof into which there have been introduced from above a paper feed roller shaft 28, which carries a plurality of paper feed rollers 27, and a corresponding plurality of paper feed springs 29. The recessed portion 33 has oppositely disposed, spaced apart, upstanding side walls 23a, 23h and a base wall 23c. The platen 2 is disposed adjacent a print head 11 and is arranged for the passage of the recording paper 25 therebetween. The print head 11 is carried by a carriage 12.

As shown in Figure 4, inside the recessed portion 23 there are formed a plurality of projections 30 on each of which a respective paper feed spring 29 has been fitted from above. Then, the unit consisting of the paper feed roller shaft 28 and the plurality of paper feed rollers 27 mounted on the paper feed roller shaft 28 is set in the recessed portion 23 so that the roller shaft 28 is supported on the paper feed springs 29. Inside the recessed portion 23 there are provided ribs 33 which project from each of the side walls 23a 23b, leaving in the centre of the recessed portion 23 a space for the paper feed roller shaft 28.

Figure 4 illustrates only the ribs 33 which project from the side wall 23b, the ribs 33 projecting from the side wall 23a being omitted. A plurality of pairs of ribs 33 are provided each pair of which has a respective projection 30 therebetween and each rib 33 having a curved face 33a forming a continuation of a curved face 22b of the paper guide 22.

A plurality of paper feed spring holders 26 are mounted in the recessed portion 23, each of the paper feed spring holders 26 being of inverted Ushape and having a hollow interior to hold the respective paper feed spring 29 therein. The upper portion of the interior of each inverted U-shaped paper feed spring holder 26 accommodates the paper feed roller shaft 28. The upper peripheral surface 26a of each paper feed spring holder 26 is curved as to be continuous with the curved face 22b of the paper guide 22.

As illustrated in Figure 4, after the paper feed roller shaft 28 has been positioned from above so as to abut on the paper feed springs 29, the paper feed spring holders 26 are set in position by introducing projecting portions 26b thereof into mounting holes 31 formed on opposite sides of each projection 30. The paper feed spring holders 26 thus function to prevent the paper feed springs 29 from toppling over and guide the vertical movement of the paper feed roller shaft 28 so that it may move smoothly. The paper feed spring holders 26 also eliminate a depression in the recording paper 25 which would otherwise exist as the latter moves over the recessed portion 23 of the paper guide 22. Additionally, the paper feed spring holders 26 prevent the recording paper 25 from striking against a wall 32, and permit easy setting of the recording paper 25 in the printer.

Each paper feed roller 27 is urged in the upward direction by its respective paper feed spring 29 so that it pushes the recording paper 25 against the platen 2. One end of the paper feed roller shaft 28 is coupled (by means not shown) to a release member 36 (Figures 1 and 5) so that, as this release member is pivoted, the paper feed roller shaft 28 moves downward in opposition to the spring force of the paper feed springs 29 and the pressure of the paper feed rollers 27 against the platen 2 is released.

The ribs 33 provided on opposite sides of the recessed portion 23 are so positioned as to allow space for the paper feed spring holders 26 therebetween. The ribs 33 function to prevent toppling over of the paper feed spring holders 26 and define, together with the paper feed spring holders 26, the path of vertical movement of the paper feed roller shaft 28 so that the latter may move smoothly.

In the present embodiment, the printer includes two paper feed rollers 27 and four paper feed spring holders 26, but it will be appreciated that these particular numbers are merely exemplary.

As shown in Figure 1, the outer casing 1 has respective supporting portions for the platen 2, guide shaft 10 and side frames 3a, 3b. The platen 2 and guide shaft 10 are designed so that they can be mounted on and fixed to the outer casing 1 from above. Moreover, the side frames 3a, 3b may be mounted on and fixed to the outer casing 1 by screws from above. The side frame 3a is, prior to being so mounted, provided with a paper feed motor 4 and with an intermediate gear 5 which is in gear with the paper feed motor 4. Thus when the side frame 3a is fixed in position, the intermediate gear 5 comes into gear with a platen gear 6 so that, in operation, the driving force of the paper feed motor 4 can be transmitted to the platen 2.

On the side of the paper guide 22 adjacent the print head 11 there is provided a metal paper guide auxiliary plate 34. The paper guide auxiliary plate 34 has a length corresponding substantially to the whole length of the platen 2. The paper guide auxiliary plate 34 is formed with projecting portions 34a which are arranged to fit into respective holes 22a of the paper guide 22. The paper guide auxiliary plate 34 also has projecting portions 35 engageable with the guide shaft 10. The projecting portions 35 abut against the guide shaft 10 so that the paper guide auxiliary plate 34 pushes the recording paper 25 onto the platen 2 under a certain pressure, the projecting portions 35 being earthed through the guide shaft 10 so that there is no build up of static electricity. The paper guide auxiliary plate 34 prevents the recording paper 25 from catching on the print head 11 when the recording paper 25 is set in position, and also prevents the recording paper 25 from parting from the platen, thereby reducing printing noise.

As shown in Figure 5, the release member 36, which is annular in shape, is rotatably mounted on the side frame 3b and has one end coupled to the paper feed roller shaft 28. On the side frame 3b there is integrally moulded a projection or shaft 37 which is positioned at the centre of rotation of the release member. The side frame 3b is also provided with a resilient pawl 38 disposed adjacent the release member 36 and the projection 37.

Since the relationship between the gap a between the projection 37 and the pawl 38, and the radial thickness b of the release member 36 is designed so that a < b, when the release member 36 is inserted along the projection 37, the relationship becomes a 3 b due to the resilience of the pawl 38, whereas when the insertion of the release member 36 is completed it comes a < b again. By this means the structure described above serves to position the release member 36 relative to the side frame 3b and prevent accidental removal of the release member 36.

Paper posh levers 39, 40 are respectively attached to the side frames 3a, 3b in a manner similar to the mounting of the release member 36. To one end of each of the paper push levers 39, 40 there is coupled a paper push roller shaft 42 having paper push rollers 41.

Figure 6 illustrates in a sectional view the mounting of one of the paper push rollers 41 on the paper push roller shaft 42. The paper push roller 41 shown in Figure 6 has at one end a plurality of notches 43 extending to its outer periphery and a plurality of projections 44 on its inner periphery. The relationship between the diameter d of a circle joining the projections 44, the diameter e of the paper push roller shaft 42, and the diameter f of a groove 45 formed on the paper push roller shaft 42 is designed to be e > d > f. Thus, when the papeSpush roller shaft 42 is inserted into the paper push rollers 41 the relationship becomes e = d because of the notches 43, whereas when the projections 44 coincide in position with the groove 45 the relationship e > d > f is obtained again.By this means the paper push rollers 41 can be positioned accurately on the paper push roller shaft 42 and can readily rotate about the paper push roller shaft 42. The fixing of the paper push levers 39, 40 with the paper push roller shaft 42 is also achieved in a similar manner to that described above. Further, the coupling portions between the paper push levers 39, 40 and the paper push roller shaft 42 are made long, so that, in response to the movement of either the paper push lever 39 or 49, the other lever can move correspondingly.

Though not illustrated in Figure 1, on the rear of the paper guide 22 there are provided supporting structures for an electrical circuit and a power source, these supporting structures being made of synthetic resin and being integrally moulded to the casing 1. Figure 7 illustrates the supporting structure for the electrical circuit and Figure 8 illustrates the supporting structure for the power sources.

As shown in Figure 7, on the outer casing 1 a plurality of struts 43 are provided to mount an electric circuit board B, 47, and a corresponding plurality of resilient pawls 44 are also moulded integrally to the outer casing in the vicinity of the struts 43 to fix an electric circuit board A, 54. The latter has holes 46 through which the struts 43 extend. The relationship between the gap g between a strut 43 and a respective pawl 44, and the distance h between the edge of a hole 46 and the adjacent edge 54a of the electric circuit board A, 54, is designed to be g < h. Thus, when a hole 46 in the electric circuit board A, 54 is aligned with and fitted over the strut 43, the relationship becomes g h due to the resilient property of the pawl 44 and upon completion of insertion it becomes g < h.Accordingly, by these means the position of the electric circuit board A, 54 can be settled by the struts 43 in the horizontal direction as viewed in the drawing and by the pawls 44 in the vertical direction.

As shown in Figure 8, guide rails 49, 50 are provided which are moulded integrally to the outer casing 1 (not shown in Figure 8), the guide rails 49, 50 serving to guide a power source circuit board 48 into a position between the guide rails 49, 50 where it may be retained by a resilient pawl 51. In the power source circuit board 48 there is provided a hole 52 into which fits a projection 53 of the pawl 51. Because these elements are designed so that when the power source circuit board 48 is inserted along the guide rails 49, 50 the projection 53 of the pawl 51 overlaps the power source circuit board 58. When the position of the hole 52 of the power source circuit board 48 coincides with the projection 53 of the pawl 51, the projection 53 of the pawl 51 fits into the hole 52.Thus the position of the power source circuit board 48 is settled in the horizontal direction by the guide rails 49, 50 and in the vertical direction by the pawl 51.

Since the outer casing 1 is a single unit moulded from synthetic resin, a metal base plate 13 is attached thereto from the under side to reinforce the outer casing 1. In order to cater for the difference in thermal expansion between resin and metal, the coupling portion between the outer casing 1 and the base plate 13 is designed to have the shape shown in Figure 3 so that the height H of an attachment boss 1a on the outer casing 1 is equal to the thickness T of the base plate 13. Thus the difference in thermal expansion can be absorbed without causing play when the base plate 13 is fixed in position.

A drive pulley 8 and a driven pulley 9 are rotatably supported on the base plate 13. A timing belt 24, which has substantially the same coefficient of thermal expansion as that of the base plate 13, is entrained around the pulleys 8, 9, and a CR motor 7 for effecting reciprocation of a carriage 12 is also mounted on the base plate 13, the motor 7 having a gear drive with the drive pulley 8. The print head 11 is mounted on the carriage 12. In the outer casing 1 there are bored holes at positions corresponding to a driven pulley shaft 14, a drive pulley shaft 15, and motor struts 16, 17. By virtue of these holes the tension of the timing belt 24 can be maintained constant even if the outer casing 1 expands or contracts in response to thermal variation. Thus smooth operation of the carriage 12, which is mounted on the guide shaft 10, is assured within the range of service temperatures. Further, the base plate 13 functions as an electromagnetic shield when the printer is placed on a CRT, so as to protect the picture.

As is apparent from the foregoing description, in the printer described above, parts, such as platen 2 or guide shaft 10, are attached directly to the outer casing 1. That is to say, the outer casing 1 has integral portions which support the guide shaft 10 over which the carriage 12 is reciprocated by the motor 7, the base plate 13, the platen 2, the side frames 3a, 3b, the paper guide 22 and the structure 45, 47, 48 carrying the electrical circuit and the power source. Therefore, the number of parts can be reduced by 40% by comparison with a printer having a conventional structure. As a result, the costs of the parts and of the assembly work can be cut down, thereby rendering it possible to offer a low-priced printer to the user. Further, because the structure permits direct mounting of the parts, the weight of the parts can be spread over the whole outer casing, whereby a printer which can withstand vibration and mechanical shock can be manufactured. Moreover, because the parts can be fitted from above to the outer casing of the printer, the latter is well suited to an automated assembly line employing robots or the like, and the assembly time can thus be shortened.

Claims (13)

1. A printer comprising a guide shaft on which is slidably mounted a carriage having a print head thereon; a base plate provided with carriage drive means for effecting sliding movement of the carriage on the guide shaft; a platen disposed adjacent the print head and arranged for the passage of a recording medium therebetween; a frame provided with drive means for driving the platen so as to feed the recording medium; a recording medium guide a portion of which has a shape corresponding to that of the platen; means carrying an electrical circuit; means carrying a power source; and an outer casing having integral portions which support the guide shaft, base plate, platen, frame, recording medium guide, and the means carrying the electrical circuit and the power source.

2. A printer as claimed in claim 1 in which the outer casing is formed of synthetic resin material.

3. A printer as claimed in claim 1 or 2 wherein said recording medium guide has a recessed portion, and a recording medium feed roller unit is provided in said recessed portion.

4. A printer as claimed in claim 3 wherein said recording medium feed roller unit comprises at least one recording medium feed roller mounted on a feed roller shaft; at least one spring member for supporting the roller shaft; and a spring holder for the or each spring member and within which the or each respective spring member is mounted.

5. A printer as claimed in claim 4 wherein the or each spring holder has on its outer periphery a curved surface which conforms to the curved surface of the recording medium guide.

6. A printer as claimed in any of ciaims 3 to 5 wherein said recessed portion is provided with a plurality of ribs each of which has a curved surface conforming to the curved surface of the recording medium guide.

7. A printer as claimed in any preceding claim wherein said base plate is made of metal and is attached to the outer bottom face of the outer casing.

8. A printer as claimed in any preceding claim wherein there is also an auxiliary plate positioned on the print head side of the recording medium guide, said auxiliary plate being arranged to push the recording medium onto said platen.

9. A printer as claimed in claim 8 wherein said auxiliary plate has a length substantially equal to the whole length of said platen, the auxiliary plate being provided with first projecting portions which fit into holes formed in the recording medium guide, and with second projecting portions which abut against sai & widW1F snaft.

10. A printer as claimed in claim 9 wherein said auxiliary plate is earthed through said guide shaft.

11. A printer as claimed in any preceding claim wherein said frame is constituted by a first side frame and there is a second side frame opposite to said first side frame, recording medium push levers being mounted respectively on said side frames and being coupled to the ends of a recording medium push roller shaft.

12. A printer as claimed in claim 11 wherein on each of said side frames, there is a shaft at the centre of rotation of the respective push lever and a pawl for preventing removal of said push lever.

13. Any novel integer or step, or combination of integers or steps, hereinbefore described and/or shown in the accompanying drawings, irrespective of whether the present claim is within the scope of, or relates to the same or a different invention from that of, the preceding claims.