JPH012845A - precision positioning device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to precision positioning devices, and more particularly to precision positioning devices using piezoelectric elements.

BACKGROUND OF THE INVENTION Precision positioning devices that use piezoelectric elements as actuators are used in, for example, semiconductor manufacturing equipment, inspection equipment, magnetic disk devices, optical disk devices, and ultra-precision mirror processing devices. This utilizes the expansion and contraction of a piezoelectric element due to changes in applied voltage, and has a fast response.
It has the characteristic that high positioning accuracy can be obtained only by controlling the applied voltage. However, the piezoelectric element has low strength in the tensile direction, and in order to use the piezoelectric element to position a member to be positioned, such as a moving table, it is necessary to take measures to prevent tensile force from acting on the piezoelectric element. For this reason, a method is widely used in which an elastic hinge, a spring, or the like is interposed between the piezoelectric element and the member to be positioned, and a preload is applied so that no tensile force is applied to the piezoelectric element.

However, this approach not only complicates the structure of the device, but also raises the issue of the rigidity of the entire system, as the piezoelectric element tends to have high rigidity in the compression direction and low rigidity in the opposite direction. There are many. Furthermore, the preload once applied by an elastic hinge or spring cannot be adjusted to suit the requirements.

An object of the present invention is to provide a precision positioning device that solves the above problems.

Means for Solving the Problems The precision positioning device according to the present invention is characterized in that piezoelectric elements are attached to opposing parts of a fixed base, and a member to be positioned is directly attached between these piezoelectric elements. It is.

Since the member to be positioned is sandwiched between the piezoelectric elements attached to the opposing parts of the fixing table, the preload of the piezoelectric element can be easily adjusted by controlling the voltage applied to the piezoelectric element. Positioning can be performed with a preload applied to the piezoelectric element at all times. This eliminates the need for conventional elastic hinges and springs, simplifying the structure.

In addition, since the object to be positioned is held between the piezoelectric elements, there is no need to attach the object to be positioned directly to a fixed base and allow it to slide, and there is no need to consider mechanical stick-slip or backlash. This enables extremely smooth and precise positioning. Also,
Since the preload can be adjusted, it is also possible to perform positioning that quickly responds to changes in preload due to thermal expansion of the member to be positioned or the fixing base. Furthermore, since the natural frequency of the member to be positioned can be adjusted by adjusting the preload, it is also effective as a countermeasure against vibration and noise.

Example FIG. 1 shows a first embodiment of the invention.

The vertically opposing surface (lOa) of the fixed stand (lO) with a U-shaped vertical cross section
) (fob) A pair of piezoelectric elements (11) and (12) are arranged facing each other, and a horizontally moving table (13) is held between these piezoelectric elements (11 and 12).

After incorporating the table (13) between the piezoelectric elements (11) and (12), both or one of the piezoelectric elements (11)
By applying a voltage to (12), piezoelectric element (11
) (12) to hold the table (13) by applying preload. Alternatively, after inserting the table (13) slightly between the piezoelectric elements (11) and (12) from the beginning, applying a voltage to the piezoelectric element oD (12), an even larger preload can be applied to the piezoelectric element (1t). ) (12). By changing the voltage applied to each piezoelectric element (11) and (12), these elements are expanded and contracted to move the table (13). At this time, two piezoelectric elements (
11) Adjust the applied voltage so that the amount of expansion and the amount of contraction in (12) are approximately equal, so that the magnitude of the preload does not change due to movement of the table (13).

FIG. 2 shows an example of the principle of a piezoelectric element drive circuit that performs the above-described control. This drive circuit includes a power source (14), a preload adjustment variable resistor (15), and a precision positioning variable resistor (16), and is operated as follows.

First, after assembling the table (13) between the piezoelectric elements (11) and (12), turn on the power (14) and set the variable resistor (1B) for precision positioning in the neutral position. Operate the resistor (15). As a result, an equal voltage EO is applied to the two piezoelectric elements (11) and (12),
A preload is applied to these. At this time, the forces generated by the two piezoelectric elements (11) and (12) are equal, and this position is taken as the origin position of the table (13) (see FIG. 3).

From this state, operate the variable resistor (1B) to
When the applied voltage of the piezoelectric element (11) is set to Eo+Ea,
The voltage applied to the second piezoelectric element (12) becomes Eo-Ea. At this time, since the amount of expansion and contraction of the piezoelectric element (m) (12) is approximately proportional to the amount of increase and decrease in the applied voltage, the amount of expansion and contraction of the first piezoelectric element (11) and the amount of contraction of the second piezoelectric element (
12) The amount of shrinkage is equal. For this reason, table (13)
moves by +a, and the preload acting on the piezoelectric elements (11) and (12) does not change. Similarly, when the variable resistor (1B) is operated to make the voltage applied to the first piezoelectric element (11) Eo-Eb, the voltage applied to the second piezoelectric element (12) becomes Eo+E.
b, and the table (13) moves by -b.

Furthermore, when it is necessary to increase the preload, the variable resistor (15) is operated to increase the voltage applied to the two piezoelectric elements (11) and (12), for example, E, as shown by the broken line in FIG.
All you have to do is raise it so that .

The magnitude of the preload depends on the weight of the table (13) or what is mounted on it, the deformation characteristics of the table (13) and the fixed base (10), the friction coefficient of the surface receiving the preload, the adjustment range of the preload, and the piezoelectric element. It is determined as appropriate in consideration of the characteristics of (11) and (12).

In the above precision positioning device, two piezoelectric elements (11)
(12) By controlling the applied voltage, the piezoelectric element (
11) The preload of (12>) can be easily adjusted, and the table (13) can be precisely positioned while always applying preload to these piezoelectric elements (11) and (12).For this reason, Even if the moving direction of the table (13) is reversed, the rigidity can be easily made equal, and the structure is simple because special mechanisms such as conventional elastic hinges and springs are not required. In addition, since the table (13) moves without contacting the fixed base (lO), the table (13)
3) There is no need to consider mechanical stick-slip or backlash caused by movement, and extremely smooth precision positioning operations are possible.

Note that if the preload changes due to the shape accuracy of each member or the characteristics of the piezoelectric element, an uneven load will be applied to the member to be positioned, as shown in (a) or (b) in Figure 4.
A mechanism can be provided to reduce the generation of moment between the fixed base (lO) and the piezoelectric elements (11, 12) or between the piezoelectric elements (11, 12) and the table (13), which is the positioning target member. . In the case of FIG. 4(a), an intermediate member (17) is sandwiched between the fixing base (10) and the piezoelectric element (12), and the fixing base (10) is placed on the spherical surface of the groove formed on this member (17). ) is pressed against a hemispherical protrusion formed on the opposing surface (10b). In addition, in the case of FIG. 4(b),
The piezoelectric element receiver is located on the opposite surface (tab) of the fixed base (10).
A piezoelectric element (12) is pressed against the side surface of the receiver (10c).

It is effective to use such a mechanism when it is desired to apply a uniform holding force to both end faces of the member to be positioned without placing emphasis on rigidity.

FIG. 5 shows a second embodiment of the invention.

The fixing base (20) of the precision positioning device is equipped with a pair of mutually parallel facing parts (20a) (20b), and these facing parts (20a) (20b) are provided with through-stepped holes located on one straight line. Holes (21) (22) are large diameter parts (21a)
(22a) are opened so that they face each other. Large diameter portions (21a) (22a) of each stepped hole (21) (22)
are ring-shaped piezoelectric elements (23) and (24), respectively.
and the outer ring (25a) of the anginilla ball bearing (25) (2B)
) (28a> is fitted in order from the annular step part (21e) (22c) side with the small diameter part (21b) (26b).The large diameter part (21a) of each stepped hole (21) (22)
An annular stopper (27) (28) is fixed to the end of (22a), and this stopper (27) (28) and a bearing (2
5) Ring-shaped piezoelectric elements (29) and (30) are further sandwiched between the outer rings (25a and 28a) of (2B), respectively, to form the stepped portions (21c) of the stepped holes (21) and (22).
(22c) and the stoppers (27) and (28), the outer rings (25a) and (28a) are connected to the piezoelectric elements (28a) on both sides, respectively.
23) (29) and (24) are sandwiched through (30).

Inner ring (25b) (26b) of each bearing (25) (2B)
) are fixed to portions near both ends of one ball screw (31) by appropriate means. A pair of nuts (32) (33) are attached to the threaded portion (31a) of the ball screw (31).
(double nuts) are installed and these nuts (32
) (33), a ring-shaped piezoelectric element (34) is clamped in such a way that the nuts (32) and (33) can be preloaded. Further, a movable table (85) is fixed to an appropriate location of the nut <32) (33).

Although not shown, the fixing base opposing part (20a) (20b
) are connected to the same drive circuit as in the first embodiment, for example. Then, the preload of the bearing (25) (2B) is adjusted by adjusting the voltage applied to these piezoelectric elements (23), (24), (29), and (30). In addition, by stretching one of the piezoelectric elements (21) (29) and contracting the other by the same amount, the bearing (25) moves a minute amount to the left and right, stretching one of the piezoelectric elements (24) (30) and contracting the other by the same amount. By contracting the same amount, the bearing (2
G) moves a minute amount left and right. Then, install the left and right bearings (2
5) By slightly moving (26) by the same amount in the same direction, the ball screw (31), that is, the table (35
) moves a minute amount left and right. The piezoelectric elements (34) of the nuts (32, 33) are connected to a suitable drive circuit that controls the applied voltage. In addition, an appropriate preload is applied to the piezoelectric element (34) by tightening the nuts (32) and (33) with springs, etc., and by increasing the applied voltage and stretching the piezoelectric element (34), the nut (32) ) (33
) becomes wider, the preload on the nuts (32) and (33) increases, and by lowering the applied voltage and compressing the piezoelectric element (34), the space between the nuts (32) and (33) narrows, and the nuts (32) and (33) become more preloaded. 32) The preload in (33) becomes lower.

In the precision positioning device of the second embodiment, the ball screw (31
), the nuts (32) and (33), that is, the table (35) are moved left and right to position them. At this time, the piezoelectric element (23) is used to ensure smooth movement of the table (35) and high positioning accuracy.
(24) (29) (30) (34) are controlled as follows.

That is, when rotating the ball screw (31),
The voltage applied to the piezoelectric elements (21) (24) is lowered, and the voltage applied to the piezoelectric elements (29) (30) is increased.
) (26) and reduce the preload of the piezoelectric element (34).
) to lower the preload on the nuts (32) and (33). By lowering the preload of the bearings (25) (2B) and nuts (32) (33) in this way,
The ball screw (31) can be rotated smoothly with low torque. Furthermore, when stopping the ball screw (31), the voltage applied to the piezoelectric elements (23) and (24) is increased.
The voltage applied to the piezoelectric elements (29) (30) is lowered to increase the preload on the bearings (25) (20), and the voltage applied to the piezoelectric element (34) is increased to tighten the nuts (32) (33).
Increase the preload. Bearing like this (25) (2B)
By increasing the preload of the nut (12) ($3), the rigidity of the entire precision positioning device is increased. and,
In this state, each pair of piezoelectric elements (23) (
By expanding and contracting 29), (24), and (30) by an appropriate amount, the entire ball screw (31) can be moved by a minute amount left and right to perform ultra-precise positioning of the table (35).

Note that such piezoelectric elements (23) (24) (29
) The adjustment of the applied voltage in (80) and (34) is performed by the drive control device for the ball screw (31) based on the input voltage of the servo motor that drives the ball screw (31).

In a positioning device using a ball screw, in order to increase the rigidity, the preload on the ball screw's support bearing is increased, or the double nut is preloaded. However, if this preload is too high, the torque of the motor that drives the ball screw becomes large, causing problems such as shortening the life of the ball screw. Conversely, if the preload is reduced, the rigidity will decrease and the positioning accuracy will also deteriorate. For this reason, at present, the preload is set to an appropriate value in consideration of the above matters.
Generally, the positioning accuracy is on the order of p, and the positioning accuracy is about 0.0171717 by operating one ball screw.
cannot be done.

In order to improve positioning accuracy, a fine movement table that moves short strokes using a special actuator is installed on top of a coarse movement table that moves long strokes using a ball screw. First, the ball screw is rotated to move the coarse movement table at high speed on the order of p. After positioning, stopping the ball screw and fixing the coarse movement table to the guide surface, it is conceivable to position the fine movement table with high precision using a special actuator. However, in this case, a fine movement table is required in addition to the coarse movement table, which increases the size of the apparatus.

On the other hand, in the case of the second embodiment, as described above, the rotation of the ball screw (31) and the piezoelectric elements (23) (24) (2
9) By combining the controls in (30) and (34), the ball screw (31) rotates smoothly with low torque, and the table (35) is positioned at zero. 01/171!
This is done with high accuracy on the order of . Further, it is not necessary to fix the moving table to the guide surface or to provide a fine movement table in addition to the moving table, and the moving table can be made lighter and smaller.

Effects of the Invention According to the precision positioning device of the present invention, as described above,
By controlling the voltage applied to the piezoelectric element, the preload acting between the fixing base and the positioning target member can be easily adjusted, and positioning can be performed with the piezoelectric element always applying preload to the positioning target member. . This eliminates the need for conventional elastic hinges and springs, simplifying the structure.

[Brief explanation of drawings]

FIG. 1 is a side view of a precision positioning device showing a first embodiment of the present invention, FIG. 2 is an electric circuit diagram showing an example of a drive control circuit for a piezoelectric element of the device shown in FIG. 1, and FIG. A graph showing the relationship between the applied voltage of the piezoelectric element and the position of the table in Figure 2,
FIG. 4 is a drawing corresponding to FIG. 1 showing a modification of the first embodiment;
FIG. 5 is a vertical cross-sectional view of a precision positioning device showing a second embodiment of the invention, and FIG. 6 is a vertical cross-sectional view showing an enlarged portion of the nut in FIG. 4. (10)--Fixing base, (10a) (10b)--Opposing surface, (ll) (12)...Piezoelectric element, (13)...
・Moving table, (20)...Fixed table, (20a)
(20b) - Opposing part, (23) (24) (29
) (30)...Piezoelectric element, (25) (28)...
・Bearing, (31)...Ball screw, (35)...Moving table. Above Figure 1 Figure 2

Claims (1)

[Claims] A precision positioning device characterized in that piezoelectric elements are attached to opposing portions of a fixed base, and a member to be positioned is directly attached between these piezoelectric elements.