JP4187433B2 - Linear actuator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a linear actuator including a rotation / linear motion conversion mechanism.
[0002]
[Prior art]
Rotation / straight motion conversion mechanism and linear actuator that converts and transmits rotational motion to straight motion, such as robot arm and finger motion, manipulators used for gene manipulation, etc. The demand for high performance microactuators is high. Conventionally, as a rotation / straight motion conversion mechanism, for example, in a micrometer, a screw and a nut are used, a key and a key groove are provided between the housing and the nut, the rotation of the nut is restricted, and the rotational motion of the screw is coupled to the nut. Those that convert the output shaft into linear motion are known. In this case, backlash, friction loss between the key and the key groove, and the like were problems. Japanese Patent Application Laid-Open No. 2000-161461 provides rotational motion to a ball screw, and a sliding bearing is provided between the outer periphery of the ball nut that is screwed to the ball screw via a plurality of balls, and the rotation of the ball nut. A technique for converting to a straight-ahead motion by restraining the movement is disclosed.
[0003]
[Problems to be solved by the invention]
The prior art using ball screws, ball nuts, and sliding bearings reduces the problem of linear actuator backlash. However, the problem of friction loss still remains in the prior art. In addition, high-precision feeding requires a high-resolution drive method and a high-accuracy displacement sensor, but the normally used deceleration mechanism, laser measurement, etc. require a large actuator or an external device, and are small. It is difficult to reduce the weight.
[0004]
The present invention solves the problems of the prior art, and provides a linear actuator including a high-performance rotation / linear motion conversion mechanism that can reduce backlash and friction loss, and is small, light, large in torque, and capable of high-precision feed. It is.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, a linear actuator according to the present invention includes a motor attached to a housing, a rotation / linear motion conversion mechanism that converts the rotational motion of the motor output shaft into a linear motion, and transmits the linear motion. a displacement sensor for detecting the amount of displacement, the linear actuator including the rotary-linear motion conversion mechanism, the rotational movement, a rotational-linear motion conversion mechanism for converting transmitted into linear motion, rectilinear of the linear motion A housing having a first groove provided in the linear axis direction of the output shaft inside, and a second groove provided in the linear axis direction on the outer periphery, the first groove and the second groove A ball nut means that moves linearly with respect to the housing via a plurality of first balls that are supported in a rolling manner, and a plurality of the ball nut means that are rotatably supported by the housing. Screw through the second ball of And includes a ball screw shaft for rotational motion, the displacement sensor includes an excitation coil and a detection coil disposed in a predetermined positional relationship, an amplifier whose input terminal to the output terminal of the detection coil are connected, an amplifier provided between the output end and the input end of the exciting coil, when the phase difference occurs in the output waveform from the input waveform and the detection coil to the excitation coil, shifted to zero the phase difference by changing the frequency A phase shift circuit, frequency measuring means for detecting a frequency deviation caused by the phase shift, and inserted in at least one air core of the excitation coil or the detection coil provided on the linear output shaft, are cut in the longitudinal axis direction. includes a rod-shaped probe of a magnetic material which area is changed, and while maintaining the resonant state of the closed loop including the space between the exciting coil and the detection coil, the rod-shaped probe longitudinal axis direction From the frequency deviation caused by displacement, and detects the displacement amount of the linear output shaft.
[0007]
In the linear actuator according to the present invention, the motor is preferably an ultrasonic motor. Moreover, the linear actuator which concerns on this invention WHEREIN: It is preferable that said 1st groove | channel and 2nd groove | channel were provided by the in-oil electric discharge machining.
[0011]
The rotation / linear motion conversion mechanism and the linear actuator according to the present invention use a ball screw and ball nut means, and further provide linear axial grooves on the inner side of the casing and the outer periphery of the ball nut means. Roll and support one ball. That is, by using the ball screw and the ball nut means, the problem of backlash at the time of motion transmission is reduced, and further, the rotation of the ball nut means is restrained by the housing and the first ball, and the rolling motion of the first ball is performed. Since the ball nut means moves linearly with respect to the housing, the problem of friction loss associated with rotation restraint is reduced.
[0012]
In addition, since these linearly extending axial grooves are provided by electric discharge machining in oil, for example, wire electric discharge machining in oil, small grinding can be performed unlike grinding and the like, and smoother than abrasive wear marks. The surface roughness is reduced, friction loss is further reduced, and compact, lightweight, and high accuracy can be realized.
[0013]
In addition, since an ultrasonic motor is used as the rotation drive source of the linear actuator, high-resolution rotation drive can be performed. Furthermore, since a displacement sensor that detects the displacement of the straight output shaft is built in, high-accuracy feeding can be realized. Especially when combined with an ultrasonic motor, the high-resolution rotation drive performance of the ultrasonic motor is sufficient. Small size, light weight and high accuracy can be realized.
[0014]
In addition, using a light-emitting element and a light-receiving element, light is incident on a displacement detector provided on the linear output shaft of the actuator, the reflected wave is detected, and the light-receiving element, amplifier, phase shift circuit, and light-emitting element are connected in this order. The configuration. In this configuration, when the displacement detector is displaced, a frequency deviation is generated according to the displacement amount while maintaining a closed loop resonance state including a space between the light emitting element and the light receiving element. Can be detected. Since a frequency deviation of 10 kHz or more is produced with a displacement amount of 1 mm, the displacement amount can be detected with a resolution of nanometer order, and a small size, light weight and high accuracy can be realized.
[0015]
Further, as a displacement sensor, a detection rod, an amplifier, a phase shift circuit, and an excitation coil are connected in this order, and a magnetic rod-shaped probe whose cross-sectional area changes in the longitudinal axis direction is provided in at least one air core of the detection coil or excitation coil. The configuration is to be inserted. The rod-like probe is provided on the straight output shaft of the actuator. With this configuration, when the rod-shaped probe is displaced in the longitudinal axis direction, a frequency deviation is generated according to the amount of displacement while maintaining a closed loop resonance state including a space between the excitation coil and the detection coil. The amount of displacement can be detected. Since a frequency deviation of several kHz occurs with a displacement of 1 mm, the displacement can be detected with a resolution of 0.1 to 0.01 micrometers , and a small size, light weight and high accuracy can be realized.
[0016]
The exciting coil is assumed to be a series of two coils wound in opposite directions. In this case, the magnetic field cancels out near the connection point of the two coils, and when the two coils have the same characteristics, the magnetic field is almost zero and balanced. By adopting a configuration in which a magnetic probe is inserted and arranged in the air core, the sensitivity to the displacement is increased, and a frequency deviation of 10 kHz or more is generated with a displacement amount of 1 mm, so that the displacement amount can be detected with a resolution of micrometer level. Small size, light weight and high accuracy can be realized.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of the linear actuator 1 in the linear axis direction, and FIG. 2 is a radial cross-sectional view along AA of FIG. The cylindrical housing 3 supports the outer periphery of the support member 6 that moves integrally with the ball nut 5 so as to be able to advance linearly, and is connected to the other end of the ball screw 7 that is screwed to the inner periphery of the ball nut 5. 9 is supported rotatably. The housing 3 fixes the ultrasonic motor 11, the motor output shaft 13 of the ultrasonic motor 11 is coupled to the rotary shaft 9, and the support member 6 that moves integrally with the ball nut 5 is a linear output shaft 15. Combined with. The ultrasonic motor 11 is connected to a drive control device (not shown). A small motor other than the ultrasonic motor can also be used. The outer shape of the housing 3 may be a rectangular parallelepiped other than a cylindrical shape, an elliptical cross-sectional shape, or the like.
[0018]
The ball nut 5 is fitted into a deformed D-shaped inner window of the support member 6 to restrict rotation, and its longitudinal direction is also fixed to the support member 6 by an appropriate fixing means such as a stopper. Therefore, the support member 6 and the ball nut 5 move as a unit.
[0019]
A first groove 21 is provided in the housing 3 in the longitudinal direction of the linear actuator 1, that is, in the linear axis direction of the linear output shaft 15, and is integrated with the ball nut 5 corresponding to the first groove 21. A second groove 23 is also provided on the outer periphery of the support member 6 that moves in the straight axis direction. The first groove 21 and the second groove 23 support the first ball 25 so as to roll freely. A spiral groove 27 is provided on the inner periphery of the ball nut 5, and a corresponding spiral groove 29 is provided on the outer periphery of the ball screw 7. The second ball 31 is supported by the spiral groove 27 and the spiral groove 29 so as to roll freely. A ball bearing 33 is provided between the rotating shaft 9 and the housing 3.
[0020]
The operation of this configuration will be described. When the ultrasonic motor 11 is driven by a drive control device (not shown), the motor output shaft 13 rotates and the rotating shaft 9 and the ball screw 7 rotate. The rotational kinetic energy of the ball screw 7 is transmitted to the ball nut 5 through the rolling friction of the second ball 31. Since the support member 6 that moves integrally with the ball nut 5 is restricted in rotation with the housing 3, the kinetic energy transmitted to the ball nut 5 is supported by the rolling friction of the first ball 25. The support member 6 is linearly moved along the first groove 21 provided in the housing, and the linear output shaft 15 is displaced linearly accordingly.
[0021]
As described above, the conversion of kinetic energy is performed by the rolling friction of the second ball 31 and the first ball 25 that are accurately supported by rolling, so that the problem of backlash during the transmission of motion is reduced and the rotation is also performed. The energy loss in the restraint is greatly improved compared to the sliding friction.
[0022]
1 and 2, the support member 6 and the ball nut 5 have been described as separate members. However, when considering these two members together, a second groove 23 is provided on the outer periphery, and the ball nut is provided on the inner periphery. It is a so-called ball nut means having a helical groove 27. Therefore, these two members can be made into an integral structure, and the second groove 23 can be provided directly on the outer periphery of the ball nut. In this case, the structure becomes simpler.
[0023]
FIG. 3 shows the portion B of FIG. 2, that is, the first ball 25 is supported by rolling in the first groove 21 provided in the housing 3 and the second groove 23 provided in the support member 6. It is an expanded sectional view of the part made. The shape of the first groove 21 and the second groove 23 is a so-called gothic groove, which is known as suitable for rolling support. In the design of the Gothic groove, the first groove 21 has an arc part a that is a part of a circle centered on Oa and an arc part b that is a part of a circle centered on Ob, Oa, Ob is provided at a position offset from the center O of the first ball 25 by a predetermined distance. At this time, assuming that the center of the first ball 25 is O, the first ball 25 is in point contact with the arc portions a and b at one point Pa and Pb, respectively, so that the angle formed by Pa-O-Pb becomes a right angle. A predetermined offset amount is selected. Similarly, the gothic groove is designed for the second groove 23.
[0024]
1 and 2, when the outer diameter of the housing 3 is 10 mm, the diameter of the first ball 25 is selected to be 0.8 mm. As an example of the Gothic groove design at this time, it is required that the positional accuracy of the predetermined offset amount is plus or minus 5 micrometers or less and the surface roughness of the groove inner surface is within 0.8 micrometers . When the outer diameter of the housing 3 is 20 mm, the diameter of the first ball 25 is selected to be about 2 mm or less, but the positional accuracy of the predetermined offset amount of the Gothic groove is plus or minus 5 micrometers or less, and the groove inner surface The surface roughness is preferably within 0.8 micrometer .
[0025]
In order to ensure the high accuracy of the shape of the first groove and the second groove, the present invention appropriately controls the electric current value of the electric discharge machining in the wire electric discharge machining, particularly in oil, regardless of the grinding process. A predetermined gothic groove is provided.
[0026]
4 (a) and 4 (b) are diagrams for explaining the difference in surface roughness between grinding and in-oil electrical discharge machining. As shown in FIG. 4 (a), the surface obtained by grinding is in the form of abrasive wear due to abrasive grains, and the formation of sharp scratch-like wear marks can be confirmed. Depending on various conditions such as the degree of bonding, it is difficult to process the inner surface of the groove having a radius of curvature of about 1 mm or less with a surface roughness within 0.8 micrometers . On the other hand, as shown in FIG. 4 (b), the surface by electric discharge machining in oil takes the form of dissolution removal by the wire electrode line to which a high voltage is applied, and the generation of smooth crater-like low current pulse discharge traces is generated. It can be confirmed that the size of the discharge trace can be controlled by the current value, and the inner surface of the groove having a radius of curvature of about 1 mm or less can be processed with a surface roughness within 0.8 μm .
[0027]
Therefore, by EDM in oil, it is possible to provide the first and second grooves with small dimensions and having a smooth inner surface with a small surface roughness with high dimensional accuracy, and further reduce friction loss. A small, lightweight and highly accurate linear actuator can be realized.
[0028]
FIG. 5 is a block diagram when the optical displacement sensor 41 is provided in the linear actuator. Near the linear output shaft 15 of the linear actuator, a light-emitting element 43 and a light-receiving element 45 are provided inside the housing 3, receive a light incident from the light-emitting element 43, reflect it, and return it to the light-receiving element 45. 47 is provided on the straight output shaft 15. An output terminal from the light receiving element 45 and an input terminal to the light emitting element 43 are connected to the signal processing unit 51. In the signal processing unit 51, an output terminal from the light receiving element 45 is connected to the amplifier 53, and a phase shift circuit 55 is provided between the amplifier 53 and the input terminal of the light emitting element 43. A frequency deviation detector 57 is connected to the phase shift circuit 55, and a displacement amount calculator 59 is connected to the frequency deviation detector 57.
[0029]
In this manner, a closed loop resonance circuit is formed including the space between the light emitting element 43 and the light receiving element 45, that is, the light path of the light emitting element 43-displacement detecting unit 47-light receiving element 45, and is illustrated. Resonance can be maintained by supplying energy from a non-power source and appropriately setting the frequency-gain / phase characteristics of the phase shift circuit 55. The internal configuration and operation of the phase shift circuit 55 in such a closed-loop resonance circuit is described in detail in Japanese Patent Laid-Open No. 9-146991.
[0030]
In FIG. 5, when the linear output shaft is displaced and a change occurs in the space between the light emitting element 43 and the light receiving element 45, that is, the length of the light path of the light emitting element 43 -displacement detecting unit 47 -light receiving element 45. Accordingly, a phase difference is generated between the input signal to the light emitting element 43 and the output signal from the light receiving element 45, and the phase shift circuit 55 changes the frequency so that the phase difference becomes zero. The frequency deviation at this time is detected by a frequency deviation detector 57, and the displacement amount is output by a displacement amount calculator 59 that performs a relational expression process between the frequency deviation and the displacement amount. Since a frequency deviation of 10 kHz or more is produced with a displacement amount of several mm, the displacement amount can be detected with a resolution of nanometer order. The signal processing unit 51 may be integrated with the linear actuator 1 or may be configured as a separate external type.
[0031]
FIG. 6 is a block diagram when the inductance type displacement sensor 71 is provided in the linear actuator. In the vicinity of the linear output shaft 15 of the linear actuator, an excitation coil 73 is provided inside the housing 3, and a detection coil 75 is concentrically disposed on the outer periphery of the excitation coil 73. A part of the linear output shaft 15 includes a conical probe portion 77 whose cross-sectional area changes in the longitudinal direction. The probe portion 77 is made of a magnetic material. The probe portion 77 is arranged in a state of being inserted into the air cores of the excitation coil 73 and the detection coil 75. An output terminal from the detection coil 75 and an input terminal to the excitation coil 73 are connected to the signal processing unit 51. The configuration and operation of the signal processing unit 51 are the same as those in FIG.
[0032]
Thus, a closed loop resonance circuit is formed including the space between the excitation coil 73 and the detection coil 75, that is, the magnetic circuit of the air core portion-detection coil 75 including the excitation coil 73-probe portion 77.
[0033]
In FIG. 6, when the linear output shaft 15 is displaced and the magnetic probe portion 77 moves in the air core portion of the excitation coil 73 and the detection coil 75, the magnetic material probe portion 77 is conical. The volume of changes. As a result, the inductances of the excitation coil 73 and the detection coil 75 change, and change to the space between the excitation coil 73 and the detection coil 75, that is, the magnetic circuit of the air core portion-detection coil 75 including the excitation coil 73-probe portion 77. Happens. Accordingly, a phase difference occurs between the input signal to the excitation coil 73 and the output signal from the detection coil 75, and the phase shift circuit 55 changes the frequency so that the phase difference becomes zero. The frequency deviation at this time is detected by a frequency deviation detector 57, and the displacement amount is output by a displacement amount calculator 59 that performs a relational expression process between the frequency deviation and the displacement amount. Since a frequency deviation of several kHz or more is produced with a displacement amount of 1 mm, the displacement amount can be detected with a resolution of 0.1 to 0.01 micrometers .
[0034]
FIG. 7 shows a detection portion 72 of a more sensitive inductance type displacement sensor. Components that are the same as those in FIG. 6 are given the same reference numerals, and descriptions thereof are omitted. In this case, an exciting coil 74 in which two coils 74a and 74b wound in opposite directions are connected in series. In this configuration, the magnetic field cancels out in the vicinity of the connection point between the two coils 74a and 74b, and when the two coils 74a and 74b have the same characteristics, the magnetic field is almost zero and balanced. By adopting a configuration in which the magnetic probe portion 77 is inserted and arranged in the air core, a change in balance due to the insertion of the magnetic probe portion 77 can be detected by the detection coil 75, and the sensitivity to displacement is further increased.
[0035]
Since a frequency deviation of 10 kHz or more is generated with a displacement amount of 1 mm, the displacement amount of the moving object can be detected with a resolution of micrometer level with a simple structure.
[0036]
The positional relationship between the excitation coil and the detection coil has a fixed positional relationship, such as arranging the detection coil on the outer periphery of the excitation coil shown in FIGS. 6 and 7 and arranging the excitation coil and the detection coil side by side on a straight axis. A fixed arrangement method may be used. The probe portion may be disposed by being inserted into at least one air core portion of the excitation coil and the detection coil. In addition to the conical shape, the probe portion may have another shape whose cross-sectional area changes, such as a part of a cone, a function rotating body having a longitudinal axis as a rotation axis, and a part of a pyramid.
[0037]
As described above, a simple configuration in which a light emitting element, a light receiving element, a displacement detection unit, or an excitation coil, a detection coil, and a probe part are provided inside the linear actuator is 0.1 to 0.01 micrometer , nanometer. The amount of order displacement can be easily detected.
[0038]
【The invention's effect】
The linear actuator including the rotation / straight-motion conversion mechanism according to the present invention reduces backlash and friction loss, and is small and light, and has high torque and high precision feed.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a linear actuator according to an embodiment of the present invention in a linear axis direction.
FIG. 2 is a radial sectional view of a linear actuator according to an embodiment of the present invention.
FIG. 3 is an enlarged cross-sectional view of a portion where the first ball is rolled and supported by the first groove and the second groove 23 according to the embodiment of the present invention.
FIGS. 4A and 4B are diagrams for explaining a difference in surface roughness between grinding and electric discharge machining in oil. FIG. 4A is a conventional grinding process, and FIG. 4B is an electric discharge in oil according to an embodiment of the present invention. This is the case for processing.
FIG. 5 is a block diagram in a case where an optical displacement sensor is provided as a reference example in the linear actuator according to the embodiment of the present invention.
FIG. 6 is a block diagram in the case where an inductance type displacement sensor is provided in the linear actuator according to the embodiment of the present invention.
FIG. 7 is a diagram of a detection portion when a more sensitive inductance displacement sensor is provided in the linear actuator according to the embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Linear actuator, 3 housing | casing, 5 ball nut, 6 support member, 7 ball screw, 9 rotating shaft, 11 ultrasonic motor, 13 motor output shaft, 15 rectilinear output shaft, 21 1st groove | channel, 23 2nd groove | channel 25 First ball, 27, 29 Spiral groove, 31 Second ball, 33 Ball bearing, 41 Optical displacement sensor, 43 Light emitting element, 45 Light receiving element, 47 Displacement detecting part, 51 Signal processing part, 53 Amplifier, 55 phase shift circuit, 57 frequency deviation detector, 59 displacement calculator, 71 inductance displacement sensor, 72 detection part, 73 excitation coil, 74, 75 detection coil, 77 probe part.

Claims (4)

In a linear actuator including a motor attached to a housing, a rotation / linear motion conversion mechanism that converts and transmits the rotational motion of the motor output shaft into a linear motion, and a displacement sensor that detects a displacement amount in the linear motion direction,
The rotation / linear motion conversion mechanism is
A housing provided therein with a first groove provided in the linear axis direction of the linear output shaft of the linear movement;
A second groove provided on the outer periphery in the linear axis direction is provided, and a plurality of first balls supported by rolling between the first groove and the second groove are linearly moved with respect to the housing. Ball nut means to exercise,
A ball screw shaft that is rotatably supported by the housing and is engaged with the ball nut means via a plurality of second balls, and rotates.
Including
The displacement sensor is
An excitation coil and a detection coil arranged in a predetermined positional relationship;
An amplifier having an input terminal connected to the output terminal of the detection coil ;
Provided between the output end of the amplifier and the input end of the excitation coil . When a phase difference occurs between the input waveform to the excitation coil and the output waveform from the detection coil , the phase difference is shifted to zero by changing the frequency. A phase shift circuit to
A frequency measuring means for detecting a frequency deviation caused by the phase shift;
A magnetic rod-shaped probe provided in the linear output shaft, inserted in at least one air core of an excitation coil or a detection coil, and having a cross-sectional area that varies in the longitudinal axis direction;
The amount of displacement of the linear output shaft is calculated from the frequency deviation caused by the displacement of the rod-shaped probe in the longitudinal axis direction while maintaining a closed loop resonance state including a space between the excitation coil and the detection coil. A linear actuator characterized by detecting. The linear actuator according to claim 1, wherein the motor is an ultrasonic motor . 3. The linear actuator according to claim 1, wherein the first groove and the second groove are provided by in-oil electric discharge machining . 4. The linear actuator according to claim 1 ,
The exciting coil is a linear actuator in which two coils wound in opposite polarities are connected in series .

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