JP3610241B2 - Ultrasonic motor for stage equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic motor, and more particularly to an ultrasonic motor for a stage suitable as a drive source for a stage such as a table in a measuring apparatus or a processing apparatus .
[0002]
[Prior art]
Conventionally, ultrasonic motors having various structures have been proposed, but the basic structure is as shown in FIG. The ultrasonic motor 21 is fixed to a vibrating body 22 composed of a piezoelectric element 24 that vibrates when an alternating voltage is applied, and an end face of the vibrating body 22 with an adhesive or the like, and an elliptical orbit along with the vibration of the vibrating body 22. And a frictional member 23 having a rectangular parallelepiped shape, and a flat tip surface of the friction member 23 is used as a contact surface 23a with a driven body (not shown). Reference numeral 25 denotes an electrode for energizing the piezoelectric element 24 to vibrate.
[0003]
In order to drive the driven body by the ultrasonic motor 21, as shown in FIG. 11, after positioning the contact surface 23a of the ultrasonic motor 21 against the side surface of the driven body 28, When an AC voltage is applied to the sonic motor 21, the friction member 23 draws an elliptical orbit along with the vibration of the vibrator 22, and the driven body 28 is moved in the direction of the arrow by the frictional force generated between the friction member 23 and the driven body 28 at this time. Was supposed to be moved to.
[0004]
[Problems to be solved by the invention]
However, even if the ultrasonic motor 21 shown in FIG. 10 is used to control the movement of the driven body 28, the contact surface 23 a of the ultrasonic motor 21 is offset against the driven body 28, and the short axis of the elliptical orbit is changed. Since it cannot be asymmetrically brought into contact with the center as a center, the frictional force with the driven body 28 fluctuates during driving. As a result, the speed of the driven body 28 varies within the stroke, and the speed varies depending on the moving direction. There was a problem that stable control was not possible.
[0005]
In other words, there is a limit in trying to increase the flatness accuracy so that the entire contact surface 23a contacts the driven body 28 evenly. Further, the degree of fixation of the friction member 23 to the vibrating body 22 and the ultrasonic motor 21 are limited. Since the pressure contact state with the driven body 28 is likely to change depending on the state of attachment to the apparatus or the like, in the ultrasonic motor 21 in which the entire contact surface 23a is a flat surface, the contact surface 23a is not aligned with the driven body 28. It was extremely difficult to adjust so as not to hit.
[0006]
In addition, if there is uneven contact, the contact surface 23a of the ultrasonic motor 21 is unevenly worn as shown in FIG. 11, so that the frictional force with the driven body 28 is further greatly changed, and the wear powder is generated by the ultrasonic motor. If it enters between the contact surface 23a of 21 and the to-be-driven body 28, it will slip, the control state of the ultrasonic motor 21 will become further unstable, and if it is severe, the drive of the ultrasonic motor 21 will be stopped. There was also fear.
[0007]
In addition, if uneven wear occurs, the original life of the ultrasonic motor 21 cannot be maintained, and there is a disadvantage that it must be replaced after a short period of use.
[0008]
[Means for Solving the Problems]
The present invention has been made in view of the above problems, a vibrating body made of piezoelectric element, provided on the end face of the vibrating body consists of a friction member for drawing an elliptical orbit in accordance with the vibration of the vibrating body, of the friction member tip In the ultrasonic motor for a stage device that can move the driven body to the left and right with respect to the pressed part by pressing the surface while drawing the ellipse drive, ceramics mainly composed of alumina is used as the friction member. together is, in the friction members have a width of 3 mm, forms an abutment surface of that center line average roughness (Ra) 0.4 .mu.m hereinafter, the convex shape consisting of a curvature radius 100mm or more spherical, and the characterized by being configured to abut pressure stage substantially symmetrical about the minor axis of the ellipse driving friction member.
[0010]
Furthermore, the present invention is characterized in that the contact surface is a convex shape having a curved surface, and the radius of curvature is 100 mm or more.
[0011]
Further, the present invention is characterized in that the contact surface of the friction member has a center line average roughness (Ra) of 0.4 μm or less.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0013]
FIG. 1 is a perspective view showing an example of the ultrasonic motor of the present invention, and FIG. 2 is an enlarged perspective view of a friction member which is a main part thereof.
[0014]
An ultrasonic motor 1 shown in FIG. 1 has a vibrating body 2 composed of a piezoelectric element 4 and a friction that is fixed to the end face of the vibrating body 2 by adhesion or the like and has a rectangular parallelepiped that draws an elliptical orbit along with the vibration of the vibrating body 2. It consists of member 3, and the front end surface is made into the contact surface 3a with a to-be-driven body (not shown). And the contact surface 3a of the said friction member 3 is formed in the convex form which consists of a curved surface, as shown in FIG. Reference numeral 5 denotes an electrode for energizing the piezoelectric element 4 to vibrate.
[0015]
In order to drive the driven body by the ultrasonic motor 1, as shown in FIG. 3, the ultrasonic motor 1 is positioned in a state where the contact surface 3 a of the ultrasonic motor 1 is pressed against the side surface of the driven body 8. When an AC voltage is applied to the ultrasonic motor 1, the friction member 3 draws an elliptical orbit along with the vibration of the vibrating body 2, and the driven body 8 is indicated by an arrow due to the frictional force generated between the driven body 8 and the driven body 8. It moves in the direction (left and right direction with respect to the pressed part) .
[0016]
According to the ultrasonic motor 1 of the present invention, the contact surface 3a of the friction member 3 is formed in a convex shape, and the friction member 3 is configured to contact the driven body 8 at the center of the contact surface 3a. For this reason, even if there is a bias, it can be brought into substantially symmetrical contact about the minor axis of the elliptical orbit. As a result, the fluctuation of the frictional force with the driven body 8 can be reduced, and the driven body can be controlled stably. In addition, since the contact surface 3a is a curved surface, wear during sliding with the driven body 8 can be reduced, and durability can be increased.
[0017]
The shape of the abutting surface 3a is not limited to a convex shape having a curved surface as shown in FIGS. 2 and 3. For example, a flat surface at the center as shown in FIGS. Chamfering is applied to at least both edges of the contact surface 3a of the friction member 3, such as a convex shape with chamfered surfaces such as a C surface and an R surface at both ends, or a convex shape consisting of a spherical surface as shown in FIG. Any convex shape may be used.
[0018]
In addition, since the friction member 3 always slides with the driven body 8, it is important to form the friction member 3 with a material having excellent wear resistance. Examples of such a material include alumina, zirconia, silicon carbide, silicon nitride. Such ceramics as the main component, TiC-based, TiN-based, TiC-TiN-based cermets, and cemented carbide can be used.
[0019]
Furthermore, if the surface roughness of the contact surface 3a is too rough, the contact surface 3a is greatly worn by sliding with the driven body 8. Therefore, it is necessary to finish the surface roughness of the contact surface 3a as smoothly as possible, and the center line average roughness (Ra) is preferably 0.4 μm or less.
[0020]
In addition, as a method of forming the friction member 3 in which the contact surface 3a has a convex shape by the above-described material, machining is performed on each sintered material or a flat surface pressed against a mold having a concave portion corresponding to the convex shape. A desired convex shape is formed by grinding. Or it can also obtain by sintering what formed the convex shape integrally in the stage of press molding. After that, the convex surface can be obtained by forming the contact surface 3a by polishing with free abrasive grains or fixed abrasive grains or by buffing.
[0021]
【Example】
Example 1
The ultrasonic motor of the present invention and a conventional ultrasonic motor were incorporated in a stage apparatus, and an experiment was conducted to examine the drive characteristics of each ultrasonic motor.
[0022]
In this experiment, the stage apparatus shown in FIG. 5 was used. 1 and 21 are ultrasonic motors, 9 is a moving stage, 10 is a base board, 11 is a guide guide made of alumina for transmitting the driving force of the ultrasonic motors 1 and 21 to the moving stage 9, and 12 is for guiding the moving stage 9. A cross roller guide 13 is a pressing means for pressing the ultrasonic motors 1 and 21 against the guide guide 13, and the stroke of the moving stage 9 is 220 mm.
[0023]
In addition, for the vibrators 2 and 22 constituting the ultrasonic motors 1 and 21, a piezoelectric element (form SP-1) manufactured by Israel Nanomotion Co. is used, and the end face of the vibrators 2 and 22 is made of alumina ceramic. The friction member 3 was fixed with an epoxy adhesive. The shape of the friction members 3 and 23 is a cube having a side of 3 mm. In the present invention, the contact surface 3a is a convex shape having a curved surface with a radius of curvature of 200 mm, and in the conventional example, the contact surface 23a is a flat surface. It was used.
[0024]
Then, each ultrasonic motor 1 and 21 was driven, and the speed of the moving stage 9 when the moving stage 9 was reciprocated by open loop control (the load voltage to the vibrating bodies 2 and 22 was constant) was measured. .
[0025]
FIG. 6 shows the speed of the moving stage 9 when the ultrasonic motor 1 of the present invention is used, and FIG. 7 shows the speed of the moving stage 9 when the conventional ultrasonic motor 21 is used.
[0026]
The speed was calculated by measuring the distance traveled by the moving stage 9 with a linear encoder (not shown) and dividing the value by the moving time.
[0027]
As a result, as shown in FIG. 7, in the case where the conventional ultrasonic motor 21 is used, there is a difference in the speed of the moving stage 9 between going and returning, and the speed in the stroke also fluctuates greatly. I understand.
[0028]
On the other hand, as shown in FIG. 6, when the ultrasonic motor 1 of the present invention is used, the speed of the moving stage 9 is almost the same on the way back and forth, and there is almost no speed variation within the stroke. It was.
[0029]
As a result, if the ultrasonic motor 1 of the present invention is used, the speed variation within the stroke in the open loop control and the speed difference in the moving direction can be reduced, so that stable closed loop control of the moving stage 9 becomes possible. I understand that.
[0030]
(Example 2)
Next, using the ultrasonic motor 1 of the present invention, an experiment for examining the degree of wear when the radius of curvature of the contact surface 3a was varied was performed under the same conditions as in Example 1.
[0031]
As shown in FIG. 8, the results show that the wear progresses until the total driving distance of the moving stage 9 is about 3 km, and the progress of the wear stops thereafter. This is because the tip surface of the friction member 3 is formed in a convex shape, so that it can be pressed almost symmetrically about the minor axis of the elliptical orbit, so there is a difference in the initial wear due to the difference in the radius of curvature. However, it seems that the amount of wear after that can be reduced.
[0032]
As a result, the abutment surface 3a can be reduced initial wear by forming as much as possible a smooth curved surface, in particular, if the radius of curvature R and the 100mm or more, it is possible to reduce the initial wear amount, initial wear It was excellent because the time to finish was shortened.
[0033]
(Example 3)
Furthermore, an experiment for examining the initial wear amount when the surface roughness of the contact surface 3a was varied using the ultrasonic motor 1 of the present invention was performed under the same conditions as in Example 1. In this experiment, the contact surface 3a is a convex surface having a curved surface, and its curvature radius R is 100 mm.
[0034]
As shown in FIG. 9, it can be seen that the smoother the surface roughness of the contact surface 3a, the lower the initial wear amount. And when the surface roughness of the contact surface 3a is 0.4 μm and 0.2 μm in the centerline average roughness (Ra), no significant difference was found in the initial wear amount, whereas the centerline average roughness It can be seen that when (Ra) is 0.8 μm, the amount of initial wear increases and the distance until the initial wear ends is also increased.
[0035]
As a result, it is understood that the initial wear amount can be suppressed by setting the surface roughness of the contact surface 3a to 0.4 μm or less in terms of the center line average roughness (Ra).
[0036]
【The invention's effect】
As described above, according to the present invention, the vibration member including the piezoelectric element and the friction member that is provided on the end surface of the vibration member and draws an elliptical orbit along with the vibration of the vibration member, In the ultrasonic motor for a stage apparatus in which the stage can be moved to the left and right with respect to the pressed part by pressing the driven surface while drawing the elliptical drive, the ceramic mainly composed of alumina is used as the friction member. together used in the friction member have a width of 3 mm, forms an abutment surface of that center line average roughness (Ra) 0.4 .mu.m hereinafter, the convex shape consisting of a curvature radius 100mm or more spherical, and, from what has been configured to abut pressure stage substantially symmetrical about the minor axis of the ellipse driving of the friction member, it is possible to greatly reduce the variation of frictional force due to contact polarization of the driven body For this reason, if the ultrasonic motor of the present invention is used as a drive source for a driven body such as a table, the speed change in the stroke of the driven body and the speed difference in the moving direction can be eliminated. In addition, stable control is possible.
[0037]
In addition, since the contact surface of the friction member has a center line average roughness (Ra) of 0.4 μm or less, the present invention reduces wear of the contact surface due to sliding with the driven body, The life of the ultrasonic motor can be improved.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an example of an ultrasonic motor of the present invention.
FIG. 2 is an enlarged perspective view of a friction member that is a main part of FIG.
3 is a plan view showing a state in which the ultrasonic motor of FIG. 1 is brought into contact with a driven body. FIG.
FIGS. 4A to 4C are diagrams showing various shapes of contact surfaces. FIG.
FIG. 5 is a partially cutaway perspective view showing a stage apparatus used in an experiment.
FIG. 6 is a graph showing the relationship between the moving distance and speed of the moving stage when using the ultrasonic motor of the present invention.
FIG. 7 is a graph showing the relationship between the moving distance and speed of a moving stage when a conventional ultrasonic motor is used.
FIG. 8 is a graph showing the relationship between the radius of curvature of a contact surface formed in a convex shape and the amount of wear.
FIG. 9 is a graph showing the relationship between the roughness of the contact surface formed in a convex shape and the initial wear amount.
FIG. 10 is a perspective view showing an example of a conventional ultrasonic motor.
11 is a plan view showing a state in which the ultrasonic motor of FIG. 10 is brought into contact with a driven body. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,21 ... Ultrasonic motor 2,22 ... Vibration body 3,23 ... Friction member 3a, 23a ... Contact surface 9 ... Moving stage 10 ... Base base 11 ... Guide guide 12 ... Cross roller guide 13 ... Pressing means

Claims (1)

A vibrating body composed of a piezoelectric element and a friction member provided on the end face of the vibrating body and which draws an elliptical orbit along with the vibration of the vibrating body. The tip surface of the friction member is pressed against the stage while drawing an elliptical drive. Thus, in the ultrasonic motor for a stage apparatus that can move the driven body to the left and right with respect to the press contact portion, ceramics mainly composed of alumina are used as the friction member, and the friction member has a width of 3 mm. center in the abutting surface center line average roughness of its (Ra) in 0.4μm hereinafter, is formed in a convex shape made of a curvature radius 100mm or more spherical, and the minor axis of the ellipse driving of the friction member ultrasonic motor stage apparatus characterized by being configured to contact pressure stage substantially symmetrical as.

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