JPH0799161B2 - Electric / hydraulic servo cylinder - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric / hydraulic servo cylinder, and in particular, controls the position of a piston in a cylinder body according to an input of a rotation direction applied from the outside. It relates to a servo cylinder.

Related Art Regarding the above, for example, No. 45 of "Hydraulic Technology, VoL.18, No18" (Nippon Kogyo Publishing Co., Ltd.) issued on November 1, 1979
Pages 50 to 50 disclose an example of an electro-hydraulic stepping cylinder in which the piston rod of the hydraulic cylinder is linearly displaced stepwise based on the rotational displacement of the step motor. That is, the electro-hydraulic stepping cylinder is a digital hydraulic cylinder driven by a time-series pulse signal. As shown in FIG. 11, the piston 2 and the piston 2 are provided inside the cylinder body 1. An integral piston rod 3 is slidably inserted, and a fluid chamber A and a fluid chamber B are formed inside the cylinder body 1 by the piston 2. Here, the supply pressure P _S is applied to the fluid chamber A via the supply port 10. Further, inside the piston 2 is an elongated hollow portion 5 along the longitudinal direction.
Is formed, and a spool 6 having a cylindrical shape is slidably inserted into the hollow portion 5. An annular groove 7 is formed on the surface side of the spool 6, while a female screw 6a is engraved on the inner surface side of the spool 6. Reference numeral 8 is a liquid passage formed between the fluid chamber A and one end of the spool 6 on the front surface side, and 9 is a liquid passage formed between the fluid chamber B and the annular groove 7. An annular groove 11 is formed between the piston 2 and the cylinder body 1, and a liquid passage 12 is formed between the annular groove 11 and one end of the spool 6 on the front surface side. Reference numeral 20 is a discharge port that connects the annular groove 11 and a hydraulic tank (not shown).

On the other hand, 14 is a step motor.
A screw shaft 15 is fixed to the output shaft 14a. Outer screw shaft 15
Extends to the inside of the spool 6, and an external thread 15a that meshes with the internal thread 6a formed on the inner surface of the spool 6 is engraved on the outer peripheral portion thereof. Reference numerals 16 and 17 are O-rings that seal the screw shaft 15 and the cylinder body 1 in a liquid-tight manner.

According to the structure of the electro-hydraulic stepping cylinder, when one electric pulse is applied to the step motor 14 now, the rotational force of the step motor 14 is transmitted from the output shaft 14a to the screw shaft 15, and the screw shaft 15 is moved. Rotate a given angle. Then, on the basis of the screw engagement between the male screw 15a engraved on the screw shaft 15 and the female screw 6a engraved on the inner surface side of the spool 6, the spool 6 is moved from the neutral position shown in FIG. As shown in, move leftward by a certain stroke. Then, the liquid passage 8 formed in the piston 2 slightly opens to the fluid chamber B side at the port (a), so that the supply pressure P _S sent from the hydraulic pressure source (not shown) to the supply port 10 passes through the liquid passage 8. Is supplied to the fluid chamber B, the pressure in the fluid chamber B becomes larger than the pressure in the fluid chamber A, and the piston 2 moves toward the low-pressure side fluid chamber A due to the pressure difference between the fluid chambers A and B. . That is, the movement of the piston 2 follows the movement of the spool 6 to the left. When the pressures of the fluid chamber A and the fluid chamber B are balanced by such movement of the piston 2, the piston 2 stops at that position.

When the sign of the electric pulse applied to the step motor 14 is opposite, the spool 6 moves to the right as shown in FIG. 13, the port (a) is closed, and the annular groove 7 and the liquid passage 12 are closed. The port (b) between them is slightly opened, and the hydraulic pressure in the fluid chamber B flows to the tank (not shown) via the liquid passage 9, the annular groove 7, the liquid passage 12, the annular groove 11 and the discharge port 20. At this time, fluid chamber A
Since the hydraulic pressure on the side remains the same, fluid chamber B
Becomes lower than the pressure in the fluid chamber A, and the piston 2 moves toward the low pressure side fluid chamber B due to the pressure difference between the fluid chambers A and B.

Due to the movement of the piston 2 as described above, the fluid chamber A and the fluid chamber B are
When the pressure is balanced, the piston 2 stops at that position again.

Therefore, by using the above-mentioned electro-hydraulic stepping cylinder, the piston 2 driven by the fluid pressure supplied to the left and right fluid chambers A and B is applied to the input of the rotational direction externally applied by the step motor 14. Accordingly, a stepping cylinder is provided in which a pressure difference is generated between the left and right fluid chambers A and B to move the piston 2 toward the low pressure side fluid chamber.

However, in such a conventional electro-hydraulic stepping cylinder, the male screw 6a for converting the rotation input from the step motor 14 into the piston 2 into a linear movement. Therefore, since the mechanical feedback mechanism such as the female screw 15a is formed, the structure itself is extremely complicated and the number of parts is large, resulting in an increase in man-hours required for production and an increase in cost. have. Further, since the electro-hydraulic stepping cylinder has a structure in which the step motor 14 is arranged on at least one side of the cylinder body 1, it is a so-called double rod type cylinder device in which the piston rod is projected on both sides of the piston 2. It also has the drawback that it cannot be applied.

Therefore, the present invention solves the problem of having such a conventional electro-hydraulic stepping cylinder, and provides a device having a simple structure and easily applicable to the double rod type cylinder device. That is the purpose.

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention, as a basic first invention described in claim 1, is arranged in a cylinder body, and left and right fluid chambers are arranged. A piston that is driven by the fluid pressure supplied to the cylinder, and a spool valve that is arranged between the piston and the cylinder body and that moves in the axial direction in response to an externally applied circumferential input. By controlling the opening and closing of the fluid passage that connects the fluid pressure source and at least one fluid chamber in accordance with the movement of the spool valve, a difference in the pushing force based on the fluid pressure between the left and right fluid chambers is generated. In an electric / hydraulic servo cylinder in which the piston is moved in the axial direction, the spool valve is arranged on the outer circumference of the piston, and a piezoelectric vibrator or a piezoelectric vibrator is provided at a predetermined portion of the cylinder body. An electric / hydraulic servo cylinder having an ultrasonic motor for moving the spool valve in the axial direction by utilizing ultrasonic vibration energy output from an electrostrictive vibrator is provided. As a second invention described, as the ultrasonic motor, a ring-shaped vibrating body, and a slider that is in close contact with the vibrating body and rotates in a certain direction according to flexural vibration or stretching vibration of the vibrating body. According to a third aspect of the present invention, a flat plate-shaped connecting portion made of an elastic body and A pressure-transmitting vibration which is composed of a pair of driving feet made of an elastic body and which protrudes from both ends of the connecting portion in a substantially vertical direction and a moving element which is fixed to the moving element and vibrates the both driving feet. Child or strain transducer Et made are the configuration using an ultrasonic linear motor.

Action According to such a configuration of the electric / hydraulic servo cylinder,
When the piston is in the neutral position, the force due to the fluid pressure supplied to the left and right fluid chambers is equal, so the piston is not moved in either the left or right direction.

Next, when the spool valve is moved to the left or right by a certain stroke by the input from the ultrasonic motor, the supply pressure generated from the hydraulic pressure source is applied to either the left or right fluid chamber based on the action of the spool valve. The piston is moved in the axial direction based on the difference between the forces caused by the pressures in the two fluid chambers.

Therefore, by adjusting the amount of rotation in the circumferential direction applied from the ultrasonic motor to the spool valve, the movement distance of the piston can also be adjusted, and the movement of the piston can be controlled to a desired position. To be

In the above operation, when the annular ultrasonic motor disclosed in the second invention is used as the ultrasonic motor, the flexural vibration or the stretching vibration of the annular vibrating body is transmitted to the slider in close contact with the vibrating body. Thus, the slider can be rotated in a fixed direction, and the spool valve can be moved in the left-right direction based on the action of the slider.

Further, when the ultrasonic linear motor disclosed in the third invention is used as the ultrasonic motor, when a driving voltage having a specific driving frequency is applied to the piezoelectric vibrator or the electrostrictive vibrator constituting the ultrasonic linear motor, The vibrator starts to vibrate according to the frequency, and this vibration is transmitted to both drive feet. However, since the resonance frequencies of the both drive feet are different, the vibration displacement of both is also different, and the tip of the drive foot is also different. Since the portion oscillates in an elliptical manner to rotate the slider, the spool valve can be moved in the axial direction by transmitting this rotational force to the spool valve. Further, selection of leftward movement or rightward movement of the spool valve can be switched by changing the frequency of the drive voltage applied to the vibrator.

Embodiment Hereinafter, a specific structural example of the electric / hydraulic servo cylinder according to the present invention will be described in detail by giving the same reference numerals to the same components as those of the conventional configuration.

FIG. 1 shows a first invention of the present application, in which 1 is a cylinder body, and a piston 2 and piston rods 3a, 3b integral with the piston 2 are slidable inside the cylinder body 1. Has been inserted into. That is, the present embodiment has a so-called double rod type cylinder structure in which the piston rods 3a and 3b project on both sides of the piston 2. Therefore, the inside of the cylinder body 1 is divided into the fluid chamber A and the fluid chamber B by the piston 2 and the cylinder body 1.
In the case of this embodiment, the pressure receiving areas of the fluid chambers A and B are different, and if the pressure receiving area of the fluid chamber A is a and the pressure receiving area of the fluid chamber B is b, then a <b.

Here, the fluid chamber A is supplied to the hydraulic pump 30 via the supply port 10.
The supply pressure P _{S from} is given. In addition, the other part of the cylinder body 1 has a supply port for receiving the same supply pressure P _S.
21 and a discharge port 20 are formed.

An annular groove 25 is formed in the inner wall portion of the cylinder body 1, and a cylindrical spool valve 26 is axially slidably inserted in the annular groove 25. The spool valve 26 is prevented from rotating in the circumferential direction by spline means (not shown). A fluid passage 27 for the working fluid is provided at a predetermined portion of the spool valve 26, and the fluid passage 27 serves as the supply port 21.
Is in communication with. A discharge passage 28 for the hydraulic fluid is provided at another predetermined portion of the spool valve 26, and the discharge passage 28 is communicated with the discharge port 20 communicating with the tank T.

Inside the piston 2, there are a liquid passage 31 extending from the fluid chamber B to the spool valve 26 near the liquid passage 27, and a liquid passage 32 extending from the fluid chamber B to the spool valve 26 near the discharge passage 28. Has been formed.

On the other hand, a hollow portion 35 is formed inside the cylinder body 1 in the vicinity of the outside of the spool valve 26, and an annular piezoelectric body 41 and an elastic body 42 are mainly formed inside the hollow portion 35. And a slider 44 which is in close contact with the vibrating body 43 and rotates in a fixed direction.
And a spring 45 that presses the slider 44 toward the vibrating body 43.
And are provided.

A tooth portion 44a is provided on the inner surface side of the slider 44, and a slide screw 53 that meshes with the tooth portion 44a is formed on the surface side of the spool valve 26.

As an example of the above ultrasonic motor M, for example, a ring-shaped ultrasonic motor M ₁ shown in FIG. 2 can be used. That is, as shown in the drawing, a slider 44 similarly formed in an annular shape is closely contacted in parallel with a vibrating body 43 having an annular shape, and the vibrating body 43 is excited by exciting the vibrating body 43. The flexural vibration a shown in FIG. 3 is induced at the position, and the flexural vibration a causes the slider 44 to start rotating in the direction indicated by B. The rotational force of the slider 44 is transmitted to the sliding screw 53 via the tooth portion 44a.

FIG. 4 shows an example of another annular ultrasonic motor M ₂ .
In the case of this example, the slider 44 is closely attached so as to cover the outer peripheral surface of the vibrating body 43 having an annular shape. According to such a configuration, as in the above-described example, by exciting the vibrating body 43, the stretching vibration d shown in FIG. 5 is induced in the vibrating body 43, and the stretching vibration d causes the slider 44 to move in the direction shown in C. The rotation force of the slider 44 is applied to the teeth 44
It is transmitted to the sliding screw 53 via a.

In the case of the present invention, the ultrasonic linear motor M ₃ shown in FIG. 6 can be used as the ultrasonic motor M in addition to the annular ultrasonic motors M ₁ and M ₂ . That is, the ultrasonic linear motor M ₃ is mainly composed of a piezoelectric vibrator or an electrostrictive vibrator 51 (hereinafter simply referred to as a vibrator 51) and a moving element 52 fixed to the vibrator 51. 51 to lead wire
55,56 have been derived. Further, the moving element 52 has a flat plate-like connecting portion 52a made of an elastic body, and a pair of driving feet 52b made of an elastic body protruding vertically from both ends of the connecting portion 52a,
Made of 52c and. Further, friction members 57 and 58 are fixed to the tip ends of the drive feet 52b and 52c so as to abut against the annular slider 44 with a proper friction force.

The drive legs 52b and 52c differ in thickness, that is, the dimension S ₁ and the dimension S ₂ shown in the figure, so that the resonance frequencies of the drive legs 52b and 52c also differ, and the vibration displacement also differs.

The drive feet 52b, 52c and the connecting portion 52a are made of an elastic material such as aluminum, brass, stainless steel, iron, glass material, duralumin, or a composite material thereof, which is capable of excellent transmission of vibration.

Further, the vibrator 51 is composed of a laminated piezoelectric element or an electrostrictive element, and in addition to the above, a single plate piezoelectric, an electrostrictive vibrator, or a single plate piezoelectric, an electrostrictive vibrator and an elastic vibration. A so-called Langevin oscillator in which the body is combined can be used. When a drive frequency voltage is applied to this oscillator 51, it expands and contracts at a frequency according to the frequency of the frequency voltage. And this expansion and contraction is transmitted to the drive feet 52b, 52c with different resonance frequencies,
A driving force can be applied to the driving feet 52b, 52c.

The operation mode of such an electric / hydraulic servo cylinder will be described below.

In FIG. 7, all the fluid passages between the fluid chambers A and B are closed by the spool valve 26, so that the piston 2 is stopped in a neutral state. At this time, assuming that the pressure receiving area of the fluid chamber A is a and the pressure receiving area extending from the fluid chamber B is b, as described above, a × P _S = b × P _B P _S : supply pressure P _B : inside the fluid chamber B It can be expressed as hydraulic pressure = (a / b) × P _S.

Next, the operation of moving the piston 2 to the left will be described. That is, when a drive voltage having a specific drive frequency is applied to the vibrating body 43 from a drive source (not shown) to excite the vibrating body 43,
Based on the above-mentioned operation principle, the slider 44 starts rotating in the hollow portion 35. The rotation direction of the slider 44 depends on the vibration body 43.
It can be switched by changing the frequency of the drive voltage applied to the. At this time, the spring 45 moves the slider 44
Since the slider 44 is pressed against the vibrating body 43 side from the back surface side, the slider 44 and the vibrating body 43 are always in proper pressure contact with each other, and the rotation of the slider 44 progresses smoothly.

When the slider 44 rotates, for example, in the counterclockwise direction by a certain angle based on the above operation mode, the meshing action of the tooth portion 44a of the slider 44 and the sliding screw 53 causes the spool valve 26 to move to the left as shown in FIG. Linearly displace by x ₁ . Then, as shown in the figure, the supply pressure P _S generated from the hydraulic pump 30 is introduced into the fluid chamber B from the supply port 21 via the liquid passage 27 and the liquid passage 31. Since the pressure receiving area b of the fluid chamber B is larger than the pressure receiving area of the fluid chamber A, a × P _S <b × P _S , and the piston 2 moves leftward due to the difference in the pressing force.

When the moving distance of the piston 2 reaches x ₁ , the liquid path 27
And the liquid passage 31 are closed to return to the state of FIG. 7, and the movement of the piston 2 is stopped.

Since the movement of the piston 2 is instantaneously and continuously performed, the piston rods 3a and 3b fixed to the piston 2 are freely moved in the axial direction by the input of the rotational direction obtained from the slider 44, and their positions are set. Can be controlled.

The operation of moving the piston 2 to the right from the state shown in FIG. 7 will be described. That is, by changing the frequency of the drive voltage applied to the vibrating body 43, the slider 44 rotates in the clockwise direction at a constant angle contrary to the above. Then, the tooth portion 44 of the slider 44
By the meshing action of a and the sliding screw 53, the spool valve 26 is linearly displaced to the right by a distance x ₂ as shown in FIG. Then, as shown in the same figure, the hydraulic fluid in the fluid chamber B flows from the fluid passage 32 to the tank T via the discharge passage 28 and the discharge port 20, so that the hydraulic pressure in the fluid chamber B decreases and a × P _S > b × P _B , and the piston 2 moves to the right due to this difference in pushing force.

When the moving distance of the piston 2 reaches x ₂ , the liquid passage 32
The discharge passage 28 is closed and the state returns to the state shown in FIG. 7, and the movement of the piston 2 is stopped.

The operation when the ultrasonic linear motor M ₃ shown in FIG. 6 is adopted as the ultrasonic motor M is as follows. That difference in the resonant frequency of the drive foot 52b and the drive foot 52c constituting the ultrasonic linear motor M ₃ are, together with the vibration displacement is selected to occur alternately, the resonant frequency itself is the length of each drive foot It can be set to an arbitrary value by changing the height and the material. Further, the rotation speed of the slider 44 can be freely adjusted by changing the drive voltage applied to the ultrasonic linear motor M ₃ . Therefore the oscillator 51
When a drive voltage having a specific drive frequency is applied to the lead wires 55 and 56 derived from the drive power source, the drive voltage is applied to the vibrator 51 of the ultrasonic linear motor M ₃ ,
51 starts the vibration according to the frequency, and this vibration forms the moving element 52 from the connecting portion 52a to both driving feet 52b, 52c.
Be transmitted to. Since the drive feet 52b and 52c have different resonance frequencies, the vibration displacements of the two are also different, and
The tip portions of b and 52c perform elliptical vibration, and the slider 44 can be rotated by the frictional force between the sliders 44 and the friction members 57 and 58 attached to the tip portions.

FIG. 10 is a schematic view showing an example of use of the electric / hydraulic servo cylinder 60 according to the present invention. In this example, when steering the rear wheels 61, 62 of an automobile using the electric / hydraulic servo cylinder 60. Is shown. That is, a control unit that configures the controller 65 with the detection signal θ obtained from the steering angle sensor 63 of the steering wheel and the detection signal v obtained from the vehicle speed sensor 64.
65a, and generate a drive voltage corresponding to the steering angle calculated by the control unit 65a from the ultrasonic motor drive circuit 65b, and generate the drive voltage through the signal line 66 in the electric / hydraulic servo cylinder 60. The ultrasonic motor M disposed in the
By applying to (Fig. 1), the piston rods 3a, 3b integrated with the piston 2 can be moved in the vehicle width direction by the supply pressure obtained from the hydraulic pump 30, and the rear wheel 6
It is possible to carry out 1,62 steering.

That is, since the electric / hydraulic servo cylinder 60 according to the present invention is a double rod type, it is possible to realize such a usage mode, and a low cost rear wheel steering mechanism is provided with a simple structure.

EFFECTS OF THE INVENTION As described in detail above, according to the electric / hydraulic servo cylinder of the present invention, firstly, the electric / hydraulic servo cylinder is arranged in the cylinder body as the basic first invention described in claim 1. , A piston driven by the fluid pressure supplied to the left and right fluid chambers, and a spool valve which is arranged between the piston and the cylinder body and moves in the axial direction in response to an externally applied circumferential input. By controlling the opening and closing of the fluid passage that connects the fluid pressure source and at least one fluid chamber in accordance with the movement of the spool valve, a pressing force based on the fluid pressure between the left and right fluid chambers is provided. In an electric / hydraulic servo cylinder in which a difference is generated to move the piston in its axial direction, the spool valve is arranged on the outer periphery of the piston, and a predetermined portion of the cylinder body is arranged. In the configuration of an electric / hydraulic servo cylinder in which an ultrasonic motor for axially moving the spool valve by utilizing ultrasonic vibration energy output from a piezoelectric vibrator or an electrostrictive vibrator is arranged, As a second invention described in claim 2, as the ultrasonic motor,
The use of an annular ultrasonic motor composed of an annular vibrating body and a slider which is in close contact with the vibrating body and rotates in a certain direction in response to flexural vibration or stretching vibration of the vibrating body. A third aspect of the present invention is characterized in that, as the ultrasonic motor, a flat plate-like connecting portion made of an elastic body and both ends of the connecting portion are provided so as to project in a substantially vertical direction. An ultrasonic linear motor composed of a moving element composed of a pair of driving feet made of elastic body, and a pressure transmission element or a strain transmission element which is fixed to the moving element and vibrates both driving feet. Since the configuration is used, the following operational effects are brought about. That is, the first
According to the invention, when a drive voltage having a specific drive frequency is applied to the ultrasonic motor, the spool valve can be moved in the left-right direction by the ultrasonic vibration energy output from the piezoelectric vibrator or the electrostrictive vibrator. it can. Then, the spool valve moves to the left or right by a certain stroke depending on the magnitude of the energy, guides the supply pressure generated from the hydraulic pressure source to the fluid chamber on either the left or right side, and is based on the pressure in both fluid chambers. The piston can be moved toward the low pressure side fluid chamber by the difference in the pressing force.

Therefore, by adjusting the magnitude of the ultrasonic vibration energy output from the ultrasonic motor, the moving distance of the piston can also be adjusted, and a servo cylinder that can control the movement of the piston in a desired direction and position can be obtained.

Further, when the annular ultrasonic motor disclosed in the second invention is used, the flexural vibration or the stretching vibration of the annular vibrating body is transmitted to the slider in close contact with the vibrating body, and the slider is kept constant. The spool valve can be rotated in the right and left directions, and the spool valve can be moved in the left and right directions based on the action of the slider.

Further, when the ultrasonic linear motor disclosed in the third invention is used as the ultrasonic motor, a drive voltage having a specific drive frequency is applied to the pressure transmission vibrator or the electrostrictive vibrator forming the ultrasonic linear motor. At this time, the vibrator starts to vibrate according to the frequency, and this vibration is transmitted to both driving feet. However, since the resonance frequencies of the both driving feet are different, the vibration displacement of both is also different and the driving feet are also different. Since the tip portion of the rotor rotates elliptically to rotate the slider, the spool valve can be moved in the left-right direction by transmitting this rotational force to the spool valve.

The selection of left or right movement of the spool valve can be switched by changing the frequency of the drive voltage applied to the vibrator.

Further, in the present invention, since the mechanical feedback mechanism for converting the rotational input from the outside into the linear movement is not formed inside the piston, the structure itself is extremely simplified, and the number of parts is reduced. It has the advantage that the number of man-hours required for manufacturing can be reduced and cost can be reduced, and in particular it can be easily applied to a so-called double rod type cylinder device in which the piston rod protrudes on both sides of the piston. To do.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part showing an embodiment of an electric / hydraulic servo cylinder according to the present invention, FIG. 2 is a perspective view showing an example of an annular ultrasonic motor adopted in the present invention, and FIG. Is a schematic view for explaining the same operation mode, FIG. 4 is a perspective view showing an example of another annular ultrasonic motor adopted in the present invention, FIG. 5 is a schematic view for explaining the same operation mode, and FIG. Is a front view showing an example of the configuration of the ultrasonic linear motor adopted in the present invention, FIG. 7, FIG.
FIG. 9 and FIG. 9 are cross-sectional views of essential parts showing the operating state of the present invention,
FIG. 11 is a schematic view showing an application example of the present invention, FIG. 11 is a cross-sectional view of essential parts showing an example of a conventional electric / hydraulic stepping cylinder,
FIG. 12 and FIG. 13 are cross-sectional views of essential parts showing an operation example of a conventional device. 1 ... Cylinder body, 2 ... Piston, 3a, 3b ... Piston rod, 10, 21 ... Supply port, 20 ...
… Exhaust port, 25 …… annular groove, 26 …… spool valve, 28 …… exhaust passage, 30 …… hydraulic pump, 31,32 …… fluid passage, 41 …… piezoelectric body, 42 …… elastic body, 43 ...... Vibrator, 44 ...... slider, 45 ...... spring, 51 ...... vibrator, 52 ...... mover, 52a ...... connection part, 52b, 52c ...... driving foot, 57,58 ...... friction member, 53 …… Slide screw, 60 …… Electric / hydraulic servo cylinder, 63 …… Steering angle sensor, 64 …… Vehicle speed sensor, 65 …… Controller,

Claims (3)

[Claims] 1. A piston disposed in a cylinder body and driven by fluid pressure supplied to left and right fluid chambers, and a circumferential direction applied from the outside disposed between the piston and the cylinder body. A spool valve that moves in the axial direction in response to the input of the control valve, and by controlling the opening and closing of the fluid passage that connects the fluid pressure source and at least one fluid chamber according to the movement of the spool valve, In the electric / hydraulic servo cylinder in which a difference is generated in the pressing force based on the hydraulic pressure between the fluid chambers, and the piston is moved in its axial direction, the spool valve is arranged on the outer circumference of the piston. At the same time, an ultrasonic motor that moves the spool valve in the axial direction by using ultrasonic vibration energy output from a piezoelectric vibrator or an electrostrictive vibrator is provided at a predetermined portion of the cylinder body. Electric / hydraulic servo cylinder characterized by 2. The ultrasonic motor comprises an annular vibrating body and a slider which is in close contact with the vibrating body and rotates in a fixed direction in response to flexural vibration or stretching vibration of the vibrating body. The electric / hydraulic servo cylinder according to claim 1, wherein an annular ultrasonic motor is used. 3. A movement constituted by a flat plate-shaped connecting portion made of an elastic body and a pair of driving feet made of an elastic body protruding substantially vertically from both ends of the connecting portion as the ultrasonic motor. 2. The electric / hydraulic pressure according to claim 1, wherein an ultrasonic linear motor including a child and a piezoelectric vibrator or an electrostrictive vibrator that is fixed to the mover and vibrates both of the driving feet is used. Servo cylinder.