EP0577376B1

EP0577376B1 - Printing apparatus having vibration driven linear type actuator for carriage

Info

Publication number: EP0577376B1
Application number: EP19930305050
Authority: EP
Inventors: Atsushi C/O Canon Kabushiki Kaisha Kimura; Hiroyuki C/O Canon Kabushiki Kaisha Seki
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1992-06-29
Filing date: 1993-06-28
Publication date: 1997-12-10
Anticipated expiration: 2013-06-28
Also published as: DE69315628D1; DE69315628T2; EP0577376A2; EP0577376A3; JPH0614567A

Description

The present invention relates to printing apparatus incorporating at least one vibration driven linear type actuator.
The present applicant proposed a printing apparatus which uses a vibration driven actuator as a carriage driving source and a driving source for feeding a printing sheet. For example, a printing apparatus of this type is disclosed in Japanese Laid-Open Patent Application Nos. 2-209335 and 3-93481.
Figs. 6A and 6B show the structure of the printing apparatus disclosed in the above-mentioned patent applications (preamble of claim 1). The structure of the printing apparatus as the prior art related to the present invention will be described below.
Referring to Figs. 6A and 6B, a carriage driving vibration driven actuator 1 is used for moving a carriage 4 in the direction of an arrow A in Fig. 6A, and sheet feeding vibration driven actuators 2 and 3 are used for feeding a printing sheet 16 in the direction of an arrow B. Since these vibration driven actuators 1 to 3 driven by an ultrasonic wave are the same ones, they will be collectively referred to hereinafter. As shown in Fig. 7, each of the actuators 1 to 3 has a pseudo elliptic outer appearance constituted by a pair of parallel linear portions, and a pair of semi-circular portions connecting the two-end portions of these linear portions. Each of the actuators 1 to 3 is constituted by adhering a piezoelectric element group 1b (2b or 3b) having the above-mentioned shape to an elastic member 1a (2a or 3a) having the same shape.
The principle of power generation of the vibration driven actuators 1 to 3 has already been disclosed in the above-mentioned patent applications and the like, and will be briefly described in the present specification. More specifically, when a plurality of AC voltages having different phases are applied to the piezoelectric element group 1b (2b or 3b), a travelling wave, which cyclically moves in the direction of an arrow C in Fig. 7, is generated on the surface of the elastic member 1a (2a or 3a). As a result, a thrust parallel to one linear portion 1ab (2ab or 3ab) of the elastic member 1a (2a or 3a) and in the direction of an arrow D opposite to the arrow C acts on a to-be-driven object M (indicated by an alternate long and short dashed line in Fig. 7) two-dimensionally contacting the linear portion 1ab (2ab or 3ab), thereby driving the object M in the direction of the arrow D (or driving the vibration driven actuators 1 to 3 in the direction opposite to the arrow D).
Note that the tooth-shaped surface of each of the elastic members 1a to 3a of the vibration driven actuators 1 to 3 is employed for increasing components in the feeding direction of the amplitude of a vibration on the elastic member surface, and eliminating interference of vibrations at the respective points, thereby reducing a mechanical energy loss.
The carriage driving vibration driven actuator 1 is fixed facing down on the lower surface of the carriage 4, so that its linear portions extend parallel to the moving direction A of the carriage 4. Thus, the tooth-shaped surface of the elastic member 1a of the actuator 1 faces down, as shown in Fig. 6B. The tooth-shaped surface of one linear portion of the elastic member 1a is pressed against the upper surface of a side projecting portion 8a of a vibrating rail 8, as shown in Fig. 6B.
The entire lower surface of a main body 8b of the vibrating rail 8 for moving the vibration driven actuator 1 in the direction of the arrow A contacts and is fixed to a first bottom plate 10a of the printing apparatus, and the vibrating rail 8 extends parallel to the moving direction A of the carriage 4. The side projecting portion (or actuator engaging portion) 8a, which has a small thickness, and contacts only the surface of one linear portion of the elastic member 1a of the actuator 1, is formed on the upper end of the main body 8b of the vibrating rail 8.
As is apparent from the above arrangement, when the vibration driven actuator 1 is driven (i.e., when AC voltages having different phases are applied to the piezoelectric element group 1b, and a cyclic vibration is generated on the tooth-shaped surface of the elastic member 1a), the vibrating rail 8 vibrates as well, and a relative thrust in the direction of the arrow A acts between the surface of one linear portion of the elastic member 1a and the upper surface of the side projecting portion 8a of the vibrating rail 8. Thus, the movable vibration driven actuator 1 moves along the vibrating rail 8, thereby moving the carriage 4 in the direction of the arrow A. More specifically, the vibration driven actuator 1 and the vibrating rail 8 constitute a vibration driven linear type actuator.
A carriage guide rail 9 is used for guiding the carriage 4, and supports the weight of the carriage 4. The guide rail 9 extends parallel to the vibrating rail 8, and its entire lower surface is fixed to the first bottom plate 10a of the printing apparatus in the same manner as the vibrating rail 8, as shown in Fig. 6B.
The printing apparatus shown in Figs. 6A and 6B also includes a known bubble jet type printing head 13 fixed to one end of the carriage 4, a position detection photointerrupter 18 fixed to the other end of the carriage 4, a position detection encoder plate 15 fixed on the bottom plate 10a to extend parallel to the vibrating rail 8 and the carriage guide rail 9, and arranged to pass a slit of the position detection photointerrupter 18, as shown in Fig. 6B, a sheet feeding actuator support plate 6 extending parallel to the rails 8 and 9 to pass under the carriage 4, a bearing block 5 attached to the support plate 6 to allow the support plate 6 to be movable in the direction of the arrow B (a guide bar or a screw shaft (not shown) extending in the direction of the arrow B is inserted in a shaft hole of the bearing block 5), a sheet feeding amount detection roller 17 pressed against the upper surface of a printing sheet 16 (to be simply referred to as a sheet hereinafter), and rotated upon movement of the sheet 16 in the direction of the arrow B, and a sheet feeding amount detection rotary encoder 7 coupled to the roller 17, and rotated by the roller 17.
The sheet feeding vibration driven actuators 2 and 3 vertically oppose each other to sandwich the sheet 16 therebetween (i.e., the tooth-shaped surfaces of the elastic members 2a and 3a of the actuators face each other). As shown in Figs. 6A and 6B, the vibration driven actuator 2 is fixed facing down to the lower surface of the support plate 6, and the vibration driven actuator 3 is fixed facing up to the upper surface of a third bottom plate 10c of the printing apparatus. These actuators 2 and 3 are arranged, so that their linear portions extend parallel to the sheet feeding direction B. Only one pair of tooth-shaped surfaces of the opposing linear portions of the actuators 2 and 3 are respectively pressed against the upper and lower surfaces of the sheet 16, and the remaining actuator surfaces do not contact the sheet 16. Therefore, when the vibration driven actuators 2 and 3 are simultaneously driven, and cyclic vibrations in the same direction are generated on the tooth-shaped surfaces of the two actuators, a thrust in the direction of the arrow B acts on the sheet 16 sandwiched between the actuators 2 and 3, and as a result, the sheet 16 is fed in the direction of the arrow B. As shown in Fig. 6B, the sheet 16 is placed on a second bottom plate 10b of the printing apparatus, and is conveyed by using the bottom plate 10b as a convey path.
The above-mentioned conventional printing apparatus requires the first bottom plate 10a for supporting and fixing the vibrating rail 8 and the carriage guide rail 9, the second bottom plate 10b serving as the sheet feeding convey path, and the third bottom plate 10c for supporting the sheet feeding actuator 3.
In the conventional apparatus, the side projecting portion 8a of the vibrating rail 8 (rail-like stationary member) is designed to have a lowest resonance frequency sufficiently larger than the driving frequency of the actuator 1 so as to follow the vibration on the vibration driven actuator 1.
In the above-mentioned conventional printing apparatus, since the sheet 16 must be inserted below the first bottom plate 10a, the bottom plate portion must have a three-layered structure (the first, second, and third bottom plates 10a, 10b, and 10c), and as a result, the thickness of the printing apparatus is undesirably increased.
In the conventional apparatus, since the carriage 4 is supported by the single carriage guide rail 9 alone, it may vertically swing. In addition, since the carriage 4 and the carriage guide rail 9 have a slide structure, if the carriage speed is high, the carriage may swing horizontally. Therefore, the carriage has poor stability, and the above-mentioned structure is not suitable for a high-speed operation.
A concern of the present invention is to provide an improved printing apparatus which can eliminate the above-mentioned drawbacks.
It is another concern of the present invention to provide a feeding apparatus with a simple structure.
According to the present invention there is provided a printing apparatus having the features as recited in claim 1. Preferred features of the invention are set out in the dependent claims. Embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

Fig. 1A is a perspective view showing a printing apparatus comprising a vibration driven linear type actuator according to the first embodiment of the present invention;
Fig. 1B is a sectional view of the printing apparatus shown in Fig. 1A;
Figs. 2A and 2B are graphs showing the frequency characteristics of a main body of a vibrating rail as a constituting element of the vibration driven linear type actuator;
Fig. 3 is an enlarged view showing movement of contact portions between a vibration driven actuator and the vibrating rail in the apparatus shown in Figs. 1A and 1B;
Fig. 4 is an enlarged view showing movement of contact portions between the vibration driven actuator and the vibrating rail in the apparatus shown in Figs. 1A and 1B;
Fig. 5A is a perspective view showing a printing apparatus according to the second embodiment of the present invention;
Fig. 5B is a sectional view of the printing apparatus shown in Fig. 5A;
Fig. 6A is a perspective view showing a conventional printing apparatus;
Fig. 6B is a sectional view of the printing apparatus shown in Fig. 6A; and
Fig. 7 is a perspective view showing a known vibration driven actuator used in the vibration driven linear type actuator and the printing apparatus of the present invention, and in the conventional printing apparatus.

The preferred embodiment of the present invention will be described below with reference to Figs. 1A to 3.
Figs. 1A and 1B show a bubble jet type printing apparatus according to the first embodiment of the present invention. The same reference numerals in Figs. 1A and 1B denote the same parts as in the conventional apparatus shown in Figs. 6A and 6B, and a detailed description thereof will be omitted unless needed.
In the bubble jet type printing apparatus according to the first embodiment of the present invention shown in Figs. 1A and 1B, posts 8c and 9a are respectively provided to only two end portions of a vibrating rail 8 and only two end portions of a carriage guide rail 9. The rail 8 is supported on a bottom plate 10c via the posts 8c, and the rail 9 is supported on the bottom plate 10c via the posts 9a. Therefore, the vibrating rail 8 and the carriage guide rail 9 extend over the moving path of a sheet 16, and portions other than the two end portions of the rails 8 and 9 float in the air. Since the rails 8 and 9 are supported on the bottom plate 10c at their two end portions via the posts 8c and 9a, the first bottom plate 10a required in the conventional apparatus can be omitted, and hence, the thickness of the printing apparatus of this embodiment can be decreased as compared to the conventional apparatus.
In this embodiment, since the portion, other than the two end portions, of the vibrating rail 8 is suspended in the air, many resonance points are formed on a main body 8b of the rail 8, and some resonant frequencies of these resonance points are lower than the driving frequency of a vibration driven actuator 1 in a lower-order mode. (All resonant frequencies of vibration modes in which only a side projecting portion 8a of the vibrating rail 8 vibrates are sufficiently larger than the driving frequency of the actuator 1.)
Figs. 2A and 2B show the frequency characteristics of the main body 8b of the vibrating rail 8. Fig. 2A shows the relationship between the applied vibration frequency (the driving frequency of the actuator 1) to the vibrating rail 8, and the vibration amplitude of the main body 8b of the vibrating rail 8, and Fig. 2B shows the relationship between the applied vibration frequency to the vibrating rail 8 and the phase delay of the vibration of the main body 8b with respect to the applied vibration. In Figs. 2A and 2B, f₁, f₂, and f₃ indicate the resonant frequencies of the main body 8b of the vibrating rail 8. At this time, the vibration of the side projecting portion 8a is increased under the influence of the vibration of the main body 8b (since the mass of the main body 8b is larger than that of the side projecting portion 8a), and the phase is delayed by 90°. In this state, the side projecting portion 8a interferes with the wave on the actuator 1 or contacts the valleys of the wave, and cannot smoothly feed the carriage 4. Therefore, the resonant frequency of the main body 8b must not become equal to the driving frequency of the actuator 1.
When the main body 8b has a low rigidity, if the vibration frequency of the main body 8b is shifted from the resonance frequency, the vibration amplitude of the main body 8b is considerably large, and that of the side projecting portion 8a becomes large accordingly. For example, when the applied vibration frequency in Figs. 2A and 2B is fa, although it is shifted from the resonance point f₂, the vibration amplitude of the main body 8b is considerably large, and the phase delay is also large. Thus, the vibration state of the side projecting portion 8a in this mode is as shown in Fig. 3. The actual vibration state of the side projecting portion 8a is complicated since it corresponds to superposition of the components shown in Fig. 3 and components of a mode for vibrating the side projecting portion 8a alone, i.e., the components of a mode having a phase delay of almost 0° for the vibration of the actuator 1 (almost no phase delay occurs since the resonance frequency of the side projecting portion 8a is sufficiently large), as shown in Fig. 4. As a result, the carriage 4 cannot be smoothly fed. When the applied vibration frequency in Figs. 2A and 2B is fb, the vibration amplitude of the main body 8b is small, and almost no phase delay occurs. For this reason, the actual vibration state of the side projecting portion 8a is as shown in Fig. 4, and the carriage 4 can be smoothly fed. Therefore, when the temporal phase delay of the vibration of the main body 8b of the vibrating rail 8 with respect to the vibration of the actuator 1 is selected near 0°, the carriage 4 can be smoothly fed even when the main body 8b has a low rigidity.
Fig. 5A is a perspective view of a bubble jet type printing apparatus according to the second embodiment of the present invention, and Fig. 5B is a side view showing main part of Fig. 5A. In this embodiment, only the two end portions of a main body 8'b of a vibrating rail 8' are fixed to the bottom plate 10c via fixing members 8'c. The vibrating rail 8' also serves as a guide for the carriage 4, and is formed with a groove along which rollers 19 provided to the carriage 4 roll. Thus, even when the main body 8'b of the vibrating rail 8' is slightly bent or warps, the vibration driven actuator 1 and a side projecting portion 8'a of the vibrating rail 8 can maintain a stable contact state, and a further low-profile structure of the apparatus can be expected. A roller 20 provided to a projecting portion 4a of the carriage 4 rolls along a carriage guide rail 9' upon reception of the weight of the carriage 4. Thus, the carriage 4 is supported by the vibrating rail 8' and the carriage guide rail 9' via the rollers 19 and 20.
As described above, according to the printing apparatus of the present invention, only the two end portions of the vibrating rail are attached to the bottom plate to form a gap between the vibrating rail and the bottom plate, and a sheet is fed in the gap, thus providing a low-profile printer. When the driving frequency of the vibration driven actuator 1 is set to be different from the resonance frequency of the main body of the vibrating rail, the side projecting portion (actuator engaging portion) can follow the vibration of the actuator, and the carriage can be smoothly fed.
Furthermore, when the temporal phase delay of the vibration of the main body of the vibrating rail with respect to the vibration of the actuator is selected near 0°, the side projecting portion can follow the vibration of the actuator even when the main body has a low rigidity. Thus, the carriage can be smoothly fed.
In each of the above embodiments, the bases for supporting the vibrating rail and the guide rail are separated from these rails. However, the vibrating rail and its support bases may be integrated, and the guide rail and its support bases may be integrated. The sheet feeding actuators 2 and 3 comprise travelling wave driven actuators.
In each of the above embodiments, the actuator 1 moves along the rail 8. However, the end portion of the actuator 1 may be fixed to the bottom plate 10c, and the rail 8 may be fixed to the carriage 4, thereby moving the rail 8.
The rails 8 and 9 may be attached to the second bottom plate 10b to extend over the sheet convey path in place of attaching them to the bottom plate 10c.

Claims

A printing apparatus comprising a base plate member (10b, 10c); first driving means (2, 3) for driving recording material (16) in a first direction along a predetermined feed path; a carriage (4) for supporting a recording head (13); second driving means (1,8,8') for driving said carriage (4) whereby the recording head (13) moves in a second direction transversely of said first predetermined direction for effecting a recording operation on said recording material (16); and guide means (9) to maintain the movement of said carriage (4) in said second direction; said second driving means (1,8,8') including a vibration wave actuator (1) and a contact rail (8,8'), said vibration wave actuator (1) being movable relative to said contact rail (8,8') by vibration caused by said vibration wave actuator (1) and being connected to said carriage (4), said contact rail (8,8') being fixedly supported to extend across a feed path area so that said contact rail (8,8') is spaced at a predetermined distance from the feed path, whereby said recording material (16) is movable in the space formed between the base plate member (10c) and said second driving means (1,8,8')
characterised in that
said contact rail (8,8') is supported at positions laterally beyond the feed path area on said base plate member (10c), and is freely suspended across said feed path area at said predetermined distance from the feed path to bridge the feed path area.
A printing apparatus as claimed in claim 1, characterised in that said guide means (9) is supported at each end on posts (9a, 9b') mounted on said base plate member (10b, 10c) at positions laterally beyond the feed path area.
A printing apparatus as claimed in claim 1 or claim 2, characterised in that said vibration wave actuator (1) includes a loop shaped elastic element (1a) having at least one straight portion in contact with said contact rail (8,8' ) and an electro-mechanical energy conversion element (1b) for generating a travelling wave in said elastic element (1a).
A printing apparatus as claimed in any preceding claim, characterised in that said first driving means (2,3) includes a travelling wave generating element in contact with said recording material (16).
A printing apparatus as claimed in any preceding claim, characterised in that said contact rail (8,8') is adapted so that its resonant frequency is different from a driving frequency of said vibration wave actuator (1).
A printing apparatus as claimed in any preceding claim, characterised in that said carriage (4) is provided with rollers (19, 20) which engage tracks in said contact rail (8,8') to maintain stability of the carriage during movement thereof.
A printing apparatus as claimed in any preceding claim, characterised in that a temporal phase delay of the vibration of said contact rail (8,8') to the vibration of said vibration wave actuator (1) is substantially 0 degrees.