Vibration driven actuator

A vibration driven motor has a rail-like stator secured to a bottom plate and a vibration member for generating a travelling vibration wave in an elastic member to which an electro-mechanical energy conversion element is fixed due to an application of AC electric field to the electro-mechanical energy conversion element so as to bring a portion of the elastic member into press-contact with the rail-like stator. In the vibration driven motor a surface area of the bottom portion of the rail-like stator which comes in contact with the bottom plate is less than the a surface area of the top portion of the rail-like stator.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a vibration driven motor, and, more 
particularly, to a vibration driven motor of a type arranged in such a 
manner that an elastic member for generating a travelling vibration wave 
is moved along a rail-like stator. 
2. Related Background Art 
Hitherto, there has been disclosed a structure of a vibration driven motor 
of the type described above, for example, constituted as shown in FIGS. 6 
and 7. 
Referring to the drawings, reference numeral 1 represents an elastic member 
in the form of an ellipse and having a projection 1a formed on the moving 
side thereof, a piezo-electric element 2 bonded to the elastic member 1 on 
the top surface thereof for the purpose of generating a travelling 
vibration wave. Reference numeral 8 represents a rail-like stator for 
frictionally coming in contact with the elastic member 1, the rail-like 
stator 8 being brought into press-contact with an elastic spring 3 via a 
vibration insulating material 5 (for example felt). 
Reference numeral 6 represents a comb shaped stopper having a comb portion 
6a inserted into a slit formed in the portion of the elastic member 1 
which is not positioned in contact with the rail-like stator 8. The comb 
portion 6a supports the elastic member 1 via a felt 7 placed in the bottom 
portion of the slit. 
The elastic member 1 is supported on a frame 4 via the stopper 6 and the 
elastic spring 3. The frame 4, to which a printing head (omitted from 
illustration) is fixed is supported by a restricting member 9 for 
restricting the displacement except for that in direction By which is the 
predetermined direction of movement. 
When the travelling vibration wave is formed in the elastic member 1 by a 
known method, the elastic member 1 moves on the rail-like stator 8 due to 
the frictional force generated by the rail-like stator 8 and the elastic 
member 1. In accordance with this, the frame 4 and the other elements 3, 
5, 6 and 7 move in the direction BY along the restricting member 9. The 
frictional driving force generated at this time acts on a portion of the 
elastic member 1. Since the frictional driving force does not act on the 
supporting portion of the elastic member 1, a moment is generated in the 
elastic member 1, causing the elastic member 1 to be shifted in directions 
BX and BY. 
The comb portion 6a of the stopper 6 is, as shown in FIG. 7, inserted into 
the slit portion (omitted from illustration) formed in the elastic member 
1. As a result, the displacement of the elastic member 1 in the direction 
By is restricted and the dead weight of the elastic member 1 is supported 
by the comb portion 6a via the felt 7. Restricting portions 6b and 6c 
restrict the displacement of the elastic member 1 in the direction Bx, 
while a restricting member 6d restricts the displacement of the elastic 
member 1 in the direction By on the side to which the pressure is applied. 
As a result of the actions of the restricting members 6a to 6d, shake of 
the elastic member 1 can be prevented so that it can be moved smoothly and 
linearly together with the frame 4. 
However, according to the above-described conventional structure, since the 
bottom surface of the rail-like stator 8 is positioned in full contact 
with the bottom plate 10, the stator 8 cannot with completely contact with 
the bottom plate 10 if the accuracy of the flatness of the bottom surface 
is insufficient, causing a partial gap to be generated. As a result, the 
rail-like stator 8 and the bottom plate 10 undesirably beat each other due 
to the movement of the elastic member 1, causing noise to be generated. 
An object of the present invention is to provide a vibration driving motor 
which is capable of overcoming the above-described conventional problem 
and in which the rail-like stator can be reliably secured to the bottom 
plate by a simple structure. 
Other and further objects, features and advantages of the invention will be 
appear more fully from the following description. 
SUMMARY OF THE INVENTION 
In order to achieve the above-described object of the present invention, an 
aspect of the present invention lies in a vibration driven motor having a 
rail-like stator secured to a bottom plate and a vibration member for 
generating a travelling vibration wave in an elastic member to which an 
electro-mechanical energy conversion element is fixed due to an 
application of AC electric field to the electro-mechanical energy 
conversion element so as to bring a portion of the elastic member into 
press-contact with the rail-like stator, the vibration driven motor being 
characterized in that the width of the portion of the rail-like stator 
which comes in contact with the bottom plate is arranged to be smaller 
than the width of the rail-like stator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiments of the present invention will be described with 
reference to the drawings, where the same elements as those according to 
the conventional structure are given the same reference numerals and their 
description is omitted here. 
FIG. 1 is a schematic view which illustrates an essential portion of a 
bubble jet printer to which the present invention is applied. 
The bubble jet printer is a printer of a type disclosed in U.S. Pat. No. 
4,723,129 and that in U.S. Pat. No. 4,740,796. 
Then, the structure of the bubble jet printer will be described briefly. 
When an electro-mechanical energy conversion member, disposed so as to 
correspond to a sheet or a liquid passage which encloses liquid (ink), is 
applied with at least one operation signal corresponding to the recording 
information and capable of rapidly raising the temperature of the 
electro-mechanical energy conversion member exceeding the nuclear boiling, 
thermal energy is generated in the electro-mechanical energy conversion 
member. The surface of the recording head experiences film boiling, 
causing an air bubble corresponding to the above-described operation 
signal to be formed in the liquid (ink). The enlargement and the 
contraction of the air bubble cause the liquid (ink) to be discharged 
through the discharge port so that at least one droplet is formed. The 
thus formed droplet is sprayed against the sheet so that characters are 
formed. 
According to an embodiment shown in FIG. 1, a rectangular-shape groove 80 
is formed at the lower end of the rail-like stator 8 so that the area of 
the rail-like stator 8 which is positioned in contact with the bottom 
plate 10 of the printer is reduced. 
FIG. 2 illustrates a second embodiment of the present invention in which 
the area of the rail-like stator 8 which is positioned in contact with the 
bottom plate 10 is reduced by forming an inverted V-shape groove 81 in the 
surface of the rail-like stator 8 which is secured to the bottom plate 10. 
Furthermore, according to a third embodiment shown in FIG. 3, a U shape 
groove 82 is formed in the surface of the rail-like stator 8 which comes 
in contact with the bottom plate 10. 
The rail-like stator 8 according to the respective embodiments shown in 
FIGS. 1 to 3 is integrally formed by a resin or by an elastic member. 
However, as shown in FIG. 4, the rail-like stator 8 may be made of an 
elastic member to which a resin 8b is fixed to the top surface of the 
rail-like true stator 8a thereof in such a manner that the area of contact 
is reduced similarly to the above-described embodiments. As a result, a 
structure capable of overcoming the above-described problem can be 
realized. 
Another structure shown in FIG. 5 may be employed which has a flange 8c and 
which is arranged in such a manner that the area of contact with the 
bottom plate 10 is reduced. In general, the rail-like stator 8 made of a 
material such as an elastic material having a large Young's modulus 
generates noise when subjected to vibrations generated in the elastic 
member 1. However, the vibration of the elastic member 1 is absorbed by 
virtue of the elasticity created by a structure arranged in such a manner 
that the flange 8c as shown in FIG. 5 is provided so as to bring the 
elastic member 1 into contact with the flange 8c. 
FIG. 8 illustrates another embodiment of the present invention, which is 
applied to the above-described bubble jet printer. According to this 
embodiment, a rectangular-shape rail-like projection portion 11a is formed 
by bending the bottom plate 11 of the printer so as to make is serve as 
the rail-like stator. Thus, the elastic member 1 is able to move on the 
rail-like projection portion 11a. As a result, the number of the necessary 
parts can be reduced in addition to the effects obtainable from the 
above-described embodiments. 
In the case when the thickness of the rail-like stator as shown in FIG. 1 
is reduced for the purpose of reducing its weight, the rigidity of the 
rail-like stator deteriorates and the flatness of the rail-like stator 
also deteriorates. As a result, undesirable noise may be generated when 
the elastic member 1 moves on the stator due to the presence of a gap 
between the elastic member and the stator. The above-described problem can 
be overcome according to this embodiment since the rigidity of the stator 
having the projection portion 11a is not deteriorated. 
FIG. 9 illustrates another embodiment of the present invention in which the 
wear resistance is improved by fixing a resin 11b to the top surface of 
the rail-like projection portion 11a shown in FIG. 8. 
FIG. 10 illustrates a still further embodiment of the present invention in 
which the rail-like projection portion 11a is arranged to be in the form 
of a semicircular shape. 
According to this embodiment, the elastic member 1 is able to smoothly move 
since the rough surface of the edge portion of the elastic member 1 does 
not come in contact with the rail-like projection portion 11a even if the 
elastic member 1 is tilted considerably. 
As described above, according to the present invention, the width of the 
contact portion between the rail-like stator and the bottom plate can be 
made smaller than the width of the rail-like stator by forming any of the 
rectangular-shape, inverted V-shape and inverted rectangular-shape grooves 
at the lower end portion of the elastic member, that is the stator which 
supports the vibration member. Therefore, the rail-like stator and the 
bottom plate can be brought into hermetical contact with each other, 
causing noise to be prevented. 
According to the above-described embodiments, the travelling vibration wave 
generated in the vibration member including the elastic member 1 and the 
piezo-electric element 2 serving as the electro-mechanical energy 
conversion element is utilized as the power. However, a structure 
disclosed in U.S. Pat. No. 4,562,374 may be employed in which vibrations 
generated in vibration members 13, 18 and 19 shown in FIG. 2 thereof are 
utilized. 
Although the invention has been described in its preferred form with a 
certain degree of particularly, it is understood that the present 
disclosure of the preferred form has been changed in the details of 
construction and the combination and arrangement of parts may be resorted 
to without departing from the spirit and the scope of the invention as 
hereinafter claimed.