Carriage shifting apparatus and serial recording system

Abstract: The present invention provides a carriage shifting apparatus comprising a drive source (15), a suspension member suspended to transmit a driving force of the drive source, a carriage (6) connected to the suspension member (13) and reciprocally shiftable by the driving force of the drive source, a tension applying means for applying a tension force to the suspension member (13), and a weight body attached to the tension applying means via a viscoelastic member (17).

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a carriage shifting apparatus wherein a carriage is shifted by transmitting a driving force to the carriage via pulleys and a belt or rope, and a serial recording system utilizing such carriage shifting apparatus. Related Background Art In the past, as systems which are operated by reciprocally shifting a carriage, serial recording systems and original (document) readers of serial type are well known. For example, in such serial recording systems, as shown in Fig. 7, a recording head 51 is mounted on a carriage 50 and an image such as character is recorded on a recording medium 52 by serially scanning the carriage 50. Further, in the conventional serial original readers, an image sensor (in place of the recording head 51) is mounted on the carriage 50 and an image is read by serially scanning the carriage 50. Conventionally, in order to serially scan the carriage 50, generally, the carriage 50 is connected to an endless timing belt 56 extending between and mounted around a driving pulley 54 connected to a motor 53 and a driven pulley 55, and the carriage 50 is reciprocally shifted along a guide rail 57 by driving the motor 53 in normal and reverse direction alternately. Incidentally, in order to apply a tension force to the timing belt 56, a support plate 58 for supporting the driven pulley 55 is pivotally mounted on a shaft 59 and the support plate 58 is biased by a tension spring 60 to apply a tension force to the belt 56. One such mechanism is disclosed in US 4746237. With the above-mentioned arrangement for serially scanning the carriage, (1) when the total weight of the carriage 50 is increased (for example, when the number of the recording heads 51 mounted on the carriage is increased or when the capacity of the recording head is increased) and/or (2) when a shift stroke of the carriage 50 is increased (for example, when a size of the recording medium to be recorded or a size of an original to be read is great) and/or (3) when a scanning speed is increased, an output torque of the motor 53 is increased and the tension to the belt is also increased. However, generally, if the output torque of the motor 53 is increased, the greater vibration of the belt 56 will occur, thus generating the greater noise. Particularly, when a stepping motor is used as the drive motor, this phenomenon will more noticeable. Further, as the weight of the carriage 50 is increased, when the carriage is rapidly accelerated from a stopped condition to a steady state or when the carriage is rapidly stopped from the steady state to the stopped condition, the shock vibration will occur, thus easily generating the noise. For these reasons, the increase in the mounting ability of the carriage 50 and the increase in the scanning speed were limited. EP-A-0349814 discloses a belt stretcher for a serial printer. A spring imparts a predetermined force on a slide on which a belt turn idle pulley is mounted, thereby reducing resonance problems of the drive belt. A stop pad prevents or minimises displacement in the direction opposite to the direction the spring means imposes its force, to maintain positional accuracy. The present invention provides a carriage mechanism for moving a head member along a sheet member, said mechanism comprising: a carriage for holding the head member; a belt member for moving said carriage in a moving direction; a first pulley member for driving said belt member and being provided at one end of the mechanism relative to the moving direction of said carriage; a second pulley member for supporting said belt member at the other end of the mechanism relative to the moving direction of said carriage; and a support member for supporting said second pulley member, said support member being arranged to move with vibration of said second pulley member; characterised by: a vibration absorbing member for absorbing a vibration said vibration absorbing member having a viscoelastic member and a weight member, with said weight member being attached to said support member via said viscoelastic member. The present invention also provides noise reducing method and serial recording apparatus employing such carriage shifting apparatus. With this arrangement, during the shifting movement of the carriage, the vibration and noise due to the shifting movement of the carriage can be effectively reduced by the viscoelastic member and the weight member. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an elevational sectional view of a serial recording system according to a preferred embodiment of the present invention; Fig. 2 is a perspective view of a carriage shifting apparatus; Fig. 3 is an end view of the carriage; Fig. 4 is a view showing a condition that a viscoelastic member and a weight body are attached to tension applying means; Fig. 5 is a graph showing acceleration and deceleration conditions of the normal scan and reverse scan of the carriage; Fig. 6 is a graph showing a test result indicating the noise reduction effect; and Fig. 7 is a perspective view of a conventional carriage shifting apparatus. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be explained in connection with embodiments thereof with reference to the accompanying drawings. First of all, an embodiment wherein the present invention is applied to an ink jet serial recording system will be described. Fig. 1 is an elevational sectional view of the serial recording system, and Fig. 2 is a perspective view of a carriage shifting apparatus of the serial recording system. As shown in Fig. 1, the recording system is designed so that recording media (sheets) 2 stacked in a cassette 1 are picked up and supplied one by one by a pick-up roller 3, the supplied recording sheet is fed by a sheet feeding means 4, a carriage 6 is scanned along the recording sheet 2 backed-up by a platen 5 (in directions perpendicular to the plane of Fig. 1), the recording is performed by activating a recording head (recording means) 7 mounted on the carriage 6, and the recorded sheet 2 is ejected onto an ejection tray 8. Next, each of the constructural elements of the recording system will be fully explained. (Sheet feeding means) As shown in Fig. 1, the sheet feeding means 4 is constituted by a feed roller 4a and a pinch roller 4b which cooperate to feed the recording sheet 2 to a recording area, and an ejector roller 4c and a pinch roller 4d which cooperate to eject the recorded sheet 2 onto the ejection tray 8. The feed roller 4a and the ejector roller 4c are connected to a feed motor (not shown) to be driven thereby, and the pinch rollers 4b, 4d are mounted on one ends of respective arms 4f pivotally mounted on respective shafts 4e. These pinch rollers 4b, 4d are urged against the feed roller 4a and the ejector roller 4c, respectively, by respective springs 4g connected to the other ends of the respective arms 4f. With this arrangement, when the feed motor is driven, the recording sheet 2 is fed in a direction shown by the arrow a in Fig. 1. Incidentally, a driving force is transmitted to the ejector roller 4c in such a manner that the latter is rotated at a speed faster than that of the feed roller 4a by about 2 - 3 %, so that a moderate tension force is applied to the recording sheet 2 being fed. (Carriage shifting apparatus) The carriage 6 is shiftably and rotatably mounted on a guide rail 9 shown in Fig. 2. Now, a mechanism for reciprocally shifting the carriage 6 along the guide rail 9 be described. A driving pulley 11 and a driven pulley 12 are mounted on a chassis 10 by which both ends of the guide rail is supported. An endless timing belt 13 acting as a suspension member extends between and is wound around the pulleys 11, 12. The timing belt 13 is connected to the carriage 6 by a fastening member 14, and a carriage motor 15 serving as a drive source for shifting the carriage 6 is connected to the driving pulley 11. Further, as shown in Fig. 3, a heading or positioning roller 6a is mounted on a lower end of the carriage 6. This roller 6a is contacted with the recording sheet 2 supported on the platen 5 to keep a distance between an ink discharge surface of the recording head 7 and the recording sheet 2 constant. Further, a constant tension force is applied to the timing belt 13 by a tension applying means 16. More particularly, as shown in Figs. 2 and 4, a tensioner plate 16b is pivotally mounted on the chassis 10 via pin 16a, and the driven pulley 12 is rotatably mounted on an upper end of the tensioner plate 16b. Further, a tension spring 16c is arranged between a lower end of the tensioner plate and a locking hook 10a of the chassis 10. With this arrangement, the driven pulley 12 is biased toward a direction shown by the arrow b, thus applying a tension force to the timing belt 13. Further, as shown in Fig. 4, a viscoelastic member 17 is attached to the tensioner plate 16b, and a weight body 18 is attached to the viscoelastic member 17. Incidentally, in this embodiment, the viscoelastic member 17 comprises a vibration suppressing sheet (made by Nihon Tokushu Toryo Co., Ltd. as EASYKEL M5000) having a thickness of about 2 mm and a weight of about 3 grams and adhered to the tensioner plate 16b, and a lead block having a weight of about 60 grams is adhered to this sheet by a both-sided adhesive tape as the weight body 18. (Recording means) A recording means serves to record an ink image on the recording sheet 2 fed by the sheet feeding means 4. In this recording system, an ink jet recording means is used as the recording means. In this embodiment, as shown in Fig. 2, four recording heads 7 integrally including respective ink tanks are mounted on the carriage 6, and a color image is recorded on the recording sheet 2 by discharging yellow, magenta, cyan and black ink droplets from the recording heads in response to image signals in synchronous with the scanning of the carriage 6. Each recording head 7 is provided with fine liquid discharge openings (orifices), liquid passages, energy acting portions associated with portions of the corresponding liquid passages, and energy generating means for generating liquid droplet forming energy which acts on the liquid contacting with the corresponding acting portion. Such discharge energy generating means may be, for example, an energy generating means using electrical/mechanical converters such as piezo-electric elements, an energy generating means for discharging liquid droplet by heating the liquid by the electro-magnetic wave such as laser, or an energy generating means for discharging liquid by heating the liquid by means of electrical/thermal converters. Among them, the ink jet recording heads for discharging the liquid by means of the thermal energy can form the image with high resolving power, since the discharge openings can be arranged with high density. Further, among them, the recording head using the electrical/thermal converters as the energy generating means is advantageous, since it can be small-sized, the merits of IC techniques and/or micro-working techniques which have recently been remarkably progressed and been more reliable in the semi-conductor field can be effectively utilized, it can be assembled with high density, and the manufacturing cost of the head can be reduced. (Noise reduction function) Next, the vibration decreasing and noise reducing function during the recording operation of the recording system having the above construction will be explained. When the recording operation is performed, the carriage 6 is shifted from a home position at a left end in Fig. 2 in a direction shown by the arrow c to effect the recording (normal scan), then is stopped at a right end of Fig. 2, then is shifted in a direction shown by the arrow d (reverse scan) by reversely rotating the carriage motor 15, and then is returned to the home position. Now, the carriage 6 is driven at a shifting speed on the basis of a speed curve shown in Fig. 5. Generally, when the recording is effected only in the normal scanning direction, the carriage returning speed in the reverss scanning direction is increased more than the carriage speed in the normal scanning direction by serial times to reduce the total recording time. Also in this embodiment, the carriage returning speed is set to have a value more than that of the carriage speed in the normal scanning direction by about three times. In this case, although the carriage 6 is driven so that a building-up speed of the carriage 6 becomes as gentle as possible, as the position of the carriage may be, the timing belt 13 acts like a cord of a bow to generate the tension shock, thus easily causing the vibration. Such vibration is apt to generate at the start of the shifting of the carriage (acceleration for start) in the normal and reverse scans. Particularly, at the start of the reverse scan, since the rapid acceleration generates and a free length (length of the belt portion which is not contacted with any members) of the timing belt 13 is longest when the carriage is at the right end position of Fig. 2, the belt generates the tension shock as the cord of the bow, thus easily causing the vibration and noise. However, when the viscoelastic member 17 and the weight body 18 are attached to the tensioner plate 16b as in the illustrated embodiment of the present invention, as shown in the test result of Fig. 6, the vibration is decreased and the noise is reduced by about 2 dB in comparison with the case where there are no viscoelastic member 17 and weight body 18. The reason seems to be that, by providing the viscoelastic member 17 and the weight body 18, the tensioner plate 16b functions as if a tensioner plate having a vibration absorber comprising "spring and weight mass", so that the vibration transmitted to the tensioner plate 16b is decreased to reduce the noise. Fig. 6 shows a test result wherein an amount of the noise reduction in comparison with the conventional cases was sought as a function of weight of the weight body 18. As apparent from the test result, as the weight of the weight body 18 increased, the noise was decreased, and when the weight of the weight body became more than 150 grams, the noise reduction effect became substantially constant. From the above test result, it is effective that the weight of the weight body 18 is set to 30 - 300 grams. Particularly, when the weight of the weight body 18 becomes more than 50 grams, the noise is decreased more than 2 dB that the noise reduction effect can be audibly noticed or ascertained, and thus, the conventional discordant noise can be clearly decreased. According to the test result, by attaching the viscoelastic member 17 and the weight body 18 to the tensioner plate 16b, the noise reduction effect of about 2 dB can be achieved, and, when a further degree of freedom in design is permitted, the noise reduction effect of about 3 dB can be expected. Incidentally, it was found from the test that, when the weight body 18 was directly secured to the tensioner plate 16b, the noise reduction effect could not be obtained, and, when the weight body 18 was adhered to the tensioner plate 16b by the both-sided adhesive tape, the noise was decreased slightly. Further, when the weight of the weight body 18 was greater than that of the viscoelastic member 17 by several to several hundred times, the noise reduction effect could be obtained. From the above, in the present time, although it is not clear why the noise is decreased, the reason why the noise is decreased by attaching the weight body 18 to the tensioner plate 16b via the viscoelastic member 17 seems to be that the vibration of the tensioner plate 16b is decreased to reduce the noise by the same effect as a tensioner plate having the vibration absorber as mentioned above, rather than that the vibration is decreased by viscous resistance of the viscoelastic member 17 such as a so-called vibration suppressing sheet. Incidentally, in the above-mentioned embodiment, while an example that the vibration suppressing sheet available in the market is used as the viscoelastic member 17 was explained, the viscoelastic member 17 is not limited to the vibration suppressing sheet, but may be made of, for example, vibration isolating rubber material or general rubber material, adhesive tapes such as a both-sided adhesive tape, or polymer material having viscoelasticity, which are grouped as a so-called viscoelastic material or vibration isolating material and which can stably hold the weight body 18. Further, in the illustrated embodiment, while an example that the lead block is used as the weight body 18 was explained, this is the reason why the lead is used as practical metal having high specific gravity in consideration of the installation space, and thus, the weight body 18 is not limited to the lead block, but may be made of, for example, other metals such as stainless steel, copper, brass or aluminium, or non-metallic material such as resin, and may be appropriately selected in consideration of the installation space, cost, usage and the like. Furthermore, in the illustrated embodiment, while an example that the carriage shifting apparatus is used with the serial recording system wherein the recording head 7 is mounted on the carriage 6 was explained, the carriage shifting apparatus may be used with an original reading system wherein a reading means for reading image information on an original is mounted on a carriage, with the same function and advantage. Further, in the illustrated embodiment, while an example that the ink jet recording system is used as the recording means was explained, the recording means is further preferably designed that ink is discharged by the growth of bubble caused by the film boiling of ink generated by selectively energizing a electrical/thermal converters in response to a record signal. It is preferable to employ the typical structure and the principle of structures disclosed in, for example, U.S.P. No. 4,723,129 and U.S.P. No. 4,740,796. This system can be adopted in a so-called "On-Demand" type and "Continuous" type structures. In this system, an electrothermal conversion member disposed to align to a sheet or a liquid passage in which liquid (ink) is held is supplied with at least one drive signal which corresponds to information to be recorded and which enables the temperature of the electrothermal conversion member to be raised higher than a nuclear boiling point, so that thermal energy is generated in the electrothermal conversion member and film boiling is caused to take place on the surface of the recording head which is heated. As a result, bubbles can be respectively formed in liquid (ink) in response to the drive signals. Due to the enlargement and contraction of the bubble, liquid (ink) is discharged through the discharge port, so that at least one droplet is formed. In a case where the aforesaid drive signal is made to be a pulse Signal, a further satisfactory effect can be obtained in that the bubble can immediately and properly be enlarged/contract and liquid (ink) can be discharged while exhibiting excellent responsibility. It is preferable to employ a drive signal of the pulse signal type disclosed in U.S.P. No. 4,463,359 and U.S.P. No. 4,345,262. Furthermore, in a case where conditions for determining the temperature rise ratio on the aforesaid heated surface disclosed in U.S.P. No. 4,313,124 are adopted, a further excellent recording operation can be performed. In addition to the structure (a linear liquid passage or a perpendicular liquid passage) of the recording head formed by combining the discharge ports, the liquid passage and the electrothermal conversion member as disclosed in the aforesaid specifications, a structure disclosed in U.S.P. No. 4,558,333 and U.S.P. No. 4,459,600 in which the heated portion is disposed in a bent portion is included in the scope of the present invention. Further, even when a plurality of electrical/thermal converters are constructed on the basis of the technique disclosed in the Japanese Patent Laid-Open No. 59-123670 describing the construction wherein a common slit is disposed at discharge portions of electrical/thermal converters or the technique disclosed in the Japanese Patent Appln. Laid-Open No. 59-138461 describing the construction wherein openings for absorbing pressure waves due to thermal energy are disposed at the discharge portions, the present invention can be effectively carried out. That is to say, according to the present invention,,regardless of the configuration of the recording head, it is possible to surely perform the recording efficiently. In addition, among the above-mentioned serial types, the present invention is effectively applicable to a recording head secured to the carriage, a removable recording head of chip type wherein, when mounted on the carriage, electrical connection between it and the recording system and the supply of ink from the recording system can be permitted, or to a recording head of cartridge type wherein an ink tank is integrally formed with the recording head as in the above-mentioned embodiment. Further, it is preferable that a head recovering means and an auxiliary aiding means are added to the recording head according to the present invention, since the effect of the present invention is further stabilized. More concretely, these means include a capping means for capping the recording head, cleaning means, pressurizing or suction means, and an auxiliary heating means comprising electrical/thermal converters or other heating elements or the combination thereof. Further, it is effective for the stable recording to perform an auxiliary discharge mode wherein the ink discharge regardless of the recording ink discharge is effected. Further, as to the kind and number of the recording head to be mounted, each recording head may correspond to each different color ink, or a plurality of recording heads can be used for a plurality of ink having different colors and/or different density. That is to say, for example, as recording modes of the recording system, not only a recording mode with a main color such as black alone, but also a combination of plural colors provided by plural recording heads integrally formed. Further, in the illustrated embodiment, while the ink was liquid, the ink may be solid in a room temperature or less, or may be softened at a room temperature. In the above-mentioned ink jet recording system, since the temperature control is generally effected in a temperature range from 30°C to 70°C so that the viscosity of the ink is maintained within a stable discharging range, the ink may be liquidized when the record signal is emitted. In addition, ink having a feature that is firstly liquidized by the thermal energy, such as solid ink which serves to prevent the increase in temperature by absorbing energy in changing the ink from the solid state to the liquid state or which is in the solid state in the preserved condition to prevent the vaporization of ink and which is liquidized into ink liquid to be discharged in response to the record signal comprising the thermal energy, or ink which has already been solidified upon reaching the recording medium, can also be applied to the present invention. In such a case, the ink can be held in the liquid state or solid state in recess or holes in porous sheet as disclosed in the Japanese Patent Appln. Laid-Open Nos. 54-56847 and 60-71260, in confronting relation to the electrical/thermal converters. Incidentally, the above-mentioned film boiling principle is most effective for each ink. Further, the above-mentioned ink jet recording head can be used as an image output terminal of an information processing system such as a computer, or with a copying machine combined with a reader, or with a facsimile system having the communication function. Incidentally, while the ink jet recording head was used as the recording means, the recording means according to the present invention is not limited to the ink jet recording system, but may comprise a heat transfer recording means, heat sensitive recording means, or any other recording means other than a wire dot impact recording means. As mentioned above, according to the present invention, since the weight body is attached, via the viscoelastic member, to the tension applying means of the carriage shifting apparatus, it is possible to decrease the vibration generated by the shifting movement of the carriage, thus reducing the noise. Particularly, when the carriage is used in a rapid speed change or rapid acceleration and deceleration condition or when a stepping motor is used as the drive source, the effective noise reduction can be attained Thus, it is possible to attain the speed-up of the apparatus and load bearing ability of the carriage which could not attained in the conventional techniques. Further, since the apparatus does not become complex and there is no need to use the large installation space, it is possible to design the apparatus with a wider degree of freedom, and the present invention can be effectively applied to the existing apparatuses to prevent the vibration and noise therein.

Claims: A carriage mechanism for moving a head member along a sheet member, said mechanism comprising: a carriage (6) for holding the head member; a belt member (13) for moving said carriage (6) in a moving direction; a first pulley member (11) for driving said belt member (13) and being provided at one end of the mechanism relative to the moving direction of said carriage (6); a second pulley member (12) for supporting said belt member (13) at the other end of the mechanism relative to the moving direction of said carriage (6); and a support member (16) for supporting said second pulley member (12), said support member (16) being arranged to move with vibration of said second pulley member (12); characterised by: a vibration absorbing member for absorbing a vibration said vibration absorbing member having a viscoelastic member (17) and a weight member (18), with said weight member (18) being attached to said support (16) member via said viscoelastic member. A carriage mechanism according to claim 1, wherein said vibration absorbing member achieves a noise reduction effect when the weight of said weight member (18) is between a few times and a few hundred times the weight of said viscoelastic member (17), and the noise reduction effect increases as the weight of said weight member (18) increases until the weight reaches a predetermined value, said viscoelastic member (17) being a vibration preventing member capable of holding said weight member relative to said support member (16) stably. A carriage mechanism according to claim 1, wherein the weight of said weight member (18) is between a few times and a few hundred times the weight of the viscoelastic member (17). A carriage mechanism according to any preceding claim, wherein the weight of said weight member (18) is in the range 30-300 grams. A serial recording apparatus comprising a carriage mechanism according to any of the preceding claims and a head member (7) in the form of a recording head for the recording of information formed on the sheet member (2). A serial recording apparatus according to claim 5 wherein said head member (7) comprises an ink jet recording head. A serial recording apparatus according to claim 6, wherein said ink jet recording head (7) has an electric-thermal converter for generating thermal energy to be used discharging ink from an ink discharge opening. A serial recording apparatus according to any of claims 5 to 7, wherein the head member (7) is controlled by a control means. A method for reducing the noise of a belt member, said method comprising the steps of: providing a carriage mechanism for moving a head member along a sheet member, the carriage mechanism comprising: a carriage (6) for holding a head member; a belt member (13) for moving the carriage in a moving direction; a first pulley member (11) for driving said belt member (13) and being provided at one end of the mechanism relative to the moving direction of said carriage (6); a second pulley member (12) for supporting said belt (13) member at the other end of the mechanism relative to the moving direction of said carriage (6); and a support member (16) for supporting the said second pulley member (12), said support member (16) being arranged to move with vibration of said second pully member; and rotating the first pulley (11) to drive the belt member (6); characterised by: providing a vibration absorbing member having a viscoelastic member (17) and a weight member (18), with the weight member (18) being attached to the support member (16) via said viscoelastic member (17).

Inventors: HARADA TOSHIAKI, HARADA, TOSHIAKI, Harada, Toshiaki, c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: B41J19
IPC codes: B41J19