Platen-gap regulating apparatus

Abstract: A platen-gap regulating apparatus for regulating a carriage (1) with respect to a platen of a printer, comprises: a pair of guide members (3,4) rotatably mounted on the printer via an eccentric portion (3a,4a), for running the carriage; and regulating means for imparting the same rotational displacement quantity to both the guide members, wherein the carriage (1) is separated from and drawn near to a printing reference plane (P) in parallel thereto.

Description: BACKGROUND OF INVENTION The present invention relates to an platen-gap regulating apparatus for regulating the space between a platen and a recording head in proportion to the thickness of a recording medium. A typical conventional platen-gap regulating apparatus for regulating a gap between a platen and a recording head in proportion to the thickness of a recording medium is, as shown in Fig. 6, adapted to change the distance from a platen face or a printing reference position to a recording head h by rotating a guide member g1 situated closer to the recording head h out of a pair of guide members g1, g2 for guiding a carriage c by the displacement quantity of an eccentric shaft. Since the recording head h in a conventional printer is turned by an angle Δ equivalent to a gap regulating quantity δ centering on the other guide member g2 before and after the gap is adjusted, the parallelism between the recording medium s and the recording head h is spoiled by the angle Δ ; this results in inconvenience in that the printing position is displaced to that degree in the direction of a line or otherwise an image is deformed lengthwise in the direction of the line. In the case of a printer for forming color images in particular, the trouble is that the tone and the like are affected by the aforementioned displacement or deformation. SUMMARY OF INVENTION An object of the present invention made in view of the foregoing problems is to provide a novel platen-gap regulating apparatus which is free from causing an image to be badly affected before and after the gap is adjusted. Another object of the present invention is to provide a novel platen-gap regulating apparatus capable of automatically moving a recording head to an optimum position of a recording medium and in parallel to the recording medium. In order to accomplish the objects above, there is provided a platen-gap regulating apparatus according to the present invention, for regulating a carriage with respect to a platen of a printer, the platen-gap regulating apparatus comprising: a pair of guide members rotatably mounted on the printer via an eccentric portion, for running the carriage; and regulating means for imparting the same rotational displacement quantity to both the guide members, wherein the carriage is separated from and drawn near to a printing reference plane in parallel thereto. Furthemore, in the platen-gap regulating apparatus described above, the regulating means regulates both the guide members forwardly and reversely by the same quantity in the same direction in response to the forward and reverse rolling of paper-feed driving means, and the regulating means engages with or detaches from both the guide members in response to moving the carriage. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a side view of a platen-gap regulating apparatus according to an embodiment of the present invention in a normal state; Fig. 2 is a side view of the apparatus above when an adjustment is made to enlarge the gap; Figs. 3(a) and 3(b) are a plan and a sectional view of an intermediate gear for use in the apparatus above; Fig. 4 is a diagram of the principal part of the apparatus above by reference to the movement of a carriage; Fig. 5 is a diagram showing an example of a printer using the apparatus above; and Fig. 6 is a diagram depicting problems concerning a conventional apparatus. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS An embodiment of the present invention will subsequently be described. Referring to Fig. 5 first, there is given a description of a printer under an ink-jet recording system using a platen-gap regulating apparatus according to the embodiment of the present invention. In Fig. 5, reference numeral 1 denotes a carriage for running a recording head that is carried by the carriage. Further, a pair of front and rear guide rods 3, 4 for guiding the carriage 1 are rotatably mounted on a guide frame (not shown) via eccentric pins 3a, 4a which are biased in the same direction and installed at both the respective ends of the carriage 1. When the guide rods 3, 4 are operated by a carriage regulating unit 10, which will be described later, so that the guide rods are turned in the same direction, the carriage 1 which the guide rods 3, 4 support is separated from or drawn near to a platen or a printing reference plane p in the absence of such a platen. In this case, reference numeral 6 denotes a paper feed roller; and 7, a paper discharge roller. Figs. 1 - 4 show a gap regulating unit 10 according to an embodiment of the present invention, which gap regulating unit 10 is mounted on a side frame on one side of a printer body (not shown) via a unit frame 11. When the gap regulating unit 10 is operated by the carriage thus moved, it is driven by a paper feeding motor (not shown) to turn the two guide rods 3, 4 by the same quantity. A detailed description will subsequently be given of the gap regulating unit 10. A switch lever 13 which is displaced toward a position where it engages with an intermediate gear 20, which will also be described later, when it is pressed by the carriage 1 is supported pivotally, rotatably, and slidably in the axial direction at the end of a paper discharge roller shaft 8 driven by the paper feeding roller (not shown), the rotation of the paper discharge roller shaft 8 being integral with that of the paper discharge roller 7. The switch lever 13 is thus supported in such a state that it is urged by a spring 19 installed with respect to the unit frame 11 and always held in a non-engaging position. A sun gear 16 is slidably fitted to the square shaft portion 8a of the paper discharge roller shaft 8 in the center of the switch lever 13. Further, two different-in-level planet gears 17, 18 which are kept in engagement with the sun gear 16 are supported on both sides of the switch lever 13, respectively. When the switch lever 13 is pressed by the carriage 1 and displaced, one of the planet gears 17, 18 is used to transmit gap regulating torque to the intermediate gear 20 according to the direction in which the paper feeding motor is rotated. On the other hand, the intermediate gear 20 is, as shown in Fig. 3, formed with two different-in-level gear portions without teeth 21, 22 having a phase difference so that these gear portions selectively engage with the planet gears 17, 18, and a deformed Geneva gear portion 23 which engages with and disengages from a sector gear 25, which will be described later. The intermediate gear 20 is rotated by a predetermined quantity, irrespective of the rotational quantity of the planet gears 17, 18, so as to rotate the sector gear 25 by a predetermined angle. On the contrary, the sector gear 25 is fixed to the end portion 3b of one guide rod 3 so that it is rotated integrally with the guide rod 3. Further, a small fan-shaped gear 26 which is integral with the sector gear 25 engages with an airfoil sector gear 27 installed between both the guide rods 3, 4 in order that unidirectional torque is transmitted via the gear 27 to a small fan-shaped gear 28 fixed to the end of the shaft 4b of the other guide rod 4. In this case, reference numeral 14 denotes a pawl formed on the back surface of the switch lever 13 and used to hold the switch lever 13 always in the non-engaging position by mating with an arcuate mating hole 12 bored in the unit frame 11. With the arrangement above according to this embodiment of the present invention, the recording head 2 is made to hold a gap matching the thickness of ordinary paper by turning and positioning the two guide rods 3, 4 so as to keep the eccentric pins 3a, 4a substantially horizontally via the small fan-shaped gears 26, 28 engaging with the airfoil sector gear 27 as shown in Figs. 1, 5 in such a normal state that information is recorded/written onto the ordinary paper. In that state, the pawl 14 projecting from the back surface of the switch lever 13 engages with the arcuate mating hole 12 of the unit frame 11 and holds the switch lever 13 in the position shown by a solid line of Fig. 4, that is, the non-engaging position. In that state, further, an operating button on a panel (not shown) is depressed or an instruction as to permitting the platen gap to be altered is given from a personal computer in order to record/write information onto thick recording paper such as special paper for color printing, postcards and so on to move the carriage 1 to a platen-gap switching position at the beginning of the recording-writing operation, whereby the carriage 1 presses down part of the switch lever 13 with its projected end portion 1a with the effect of displacing the switch lever 13 toward the engaging position shown by a chain double-dashed line of Fig. 4. On the other hand, the paper feeding motor (not shown) simultaneously rotates the paper discharge roller shaft 8 counterclockwise to turn the switch lever 13 counterclockwise via the planet gears 17, 18 engaging with the sun gear 16 at the end of the paper discharge roller shaft 8. Further, the one planet gear 17 is caused to engage with and rotate the intermediate gear 20 in the direction of an arrow in the drawing and then rotates the sector gear 25 by the predetermined quantity up to a position where the sector gear 25 engaging with the deformed Geneva gear portion 23 of the intermediate gear 20 is brought into contact with a stopper 23a. Further, the guide rod 3 integral with the sector gear 25 is turned clockwise in the drawing and the airfoil sector gear 27 is rotated in the direction of an arrow in the drawing via the small fan-shaped gear 26 integral with the sector gear 25. Further, the other guide rod 4 is turned in the same direction via the other small fan-shaped gear 28 engaging with the airfoil sector gear 27, and the carriage 1 is raised in parallel to the printing reference plane p by means of both the guide rods 3, 4. When the platen-gap regulating apparatus is adapted for thin recording paper, it is needless to say only needed to regulate the platen gap by reversely rotating the paper feeding motor. Although a description has been given of a case where the carriage 1 is automatically displaced by the paper feeding motor in parallel to the printing reference plane p via the guide rods 3, 4 in the above-described embodiment of the present invention, two of the front and rear guide rods 3, 4 may be displaced manually in the same direction in order to displace the carriage 1 or the recording head 2 itself in parallel. As set forth above, according to the present invention, since the pair of guide members for running the carriage mounted on the printer body are subjected to the same quantity of rotational adjustment of the sort described above via the eccentric portion, the carriage supported and guided by these guide members can always be regulated in parallel to the printing reference plane in proportion to the thickness of a recording medium, whereby print quality is held to be constant at all times, irrespective of the gap regulating operation. Since the regulating means for regulating the carriage in the direction in which the carriage is separated from and drawn near to the printing reference plane according to the forward and reverse rotation of the paper-feed driving means is capable of engaging detachably with the guide members in such a way that the engagement of the regulating means therewith is interlocked with the movement of the carriage, the gap regulating operation is automatically performable only when the gap adjustment is made in accordance with a recording medium for printing.

Claims: A platen-gap regulating apparatus for regulating a carriage with respect to a platen of a printer, the platen-gap regulating apparatus comprising: a pair of guide members rotatably mounted on the printer via an eccentric portion, for running the carriage; and regulating means for imparting the same rotational displacement quantity to both the guide members, wherein the carriage is separated from and drawn near to a printing reference plane in parallel thereto. The platen-gap regulating apparatus as claimed in claim 1, wherein the regulating means regulates both the guide members forwardly and reversely by the same quantity in the same direction in response to the forward and reverse rolling of paper-feed driving means, and the regulating means engages with or detaches from both the guide members in response to moving the carriage. A platen-gap regulating apparatus in a printer in which a carriage is moved along a pair of guide rods, the platen-gap regulating apparatus comprising: eccentric pins, each eccentricaly supporting the respective guide rod on the printer; and a linking portion linking to the eccentric pins, for moving the eccentric pins such that the guide rods are moved in parallel by the eccentric pins. The platen-gap regulating apparatus according to claim 3, wherein the linking portion comprises: small fan-shaped gears, each fixed to the respective eccentric pin; and an airfoil sector gear having sector gear portions engaging with the small fan-shaped gears of the eccentric pins. The platen-gap regulating apparatus according to claim 4, further comprising: a sector gear pivotable together with one of the eccentric pins; an intermediate gear engaging with the sector gear; and a switch lever selectively driving the intermediate gear.

Inventors: KISHIDA TAKEO, KOMURO KIYOTO, KISHIDA, TAKEO, KOMURO, KIYOTO
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1998
Main classification: B41J25
IPC codes: B41J23, B41J25