JP2005065452A - Electric actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric actuator that is reduced in the number of part items by making a bearing for rotatably supporting a rotor of a motor that constitutes the electric actuator serve both as a screw mechanism, is low in cost and is improved in environment resistance and reliability. <P>SOLUTION: The electric actuator comprises the screw mechanism that converts rotational movement to linear movement and a rotating motor that imparts a rotational force to the screw mechanism. The screw mechanism is composed of a screw shaft formed with a screw at its external periphery and a nut that engages with the screw. The rotor of the rotating motor is integrally and rotatably arranged at the screw shaft. There is arranged a screw mechanism that makes the rotor movable in the axial direction in accordance with the rotation of the rotating motor by fixing the nut together with a stator of the rotating motor, and arranged a bearing that rotatably supports the rotor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electric actuator for positioning an axial direction (linear motion direction) of a motor rotor or the like by a rotary motor and a screw mechanism, and in particular, an automobile that is required to have low cost and environmental resistance and reliability. This is useful for electric actuators.

Conventionally, in an electric actuator that performs axial positioning of a motor rotor or the like using a rotary motor and a screw mechanism, a feed amount per rotation of the screw mechanism and a detection signal from a rotation angle detector such as a rotary encoder Positioning in the axial direction has been performed by angle control of the motor rotor based on the above. For example, as shown in Patent Document 1, a rotary encoder is arranged coaxially with an output shaft of a motor, and the motor is controlled based on an angle detection signal from the rotary encoder.
Japanese Utility Model Publication No. 01-086457

  However, when the electric actuator as described above is applied to an automobile, it is desired to reduce the number of parts regardless of mechanical parts and electrical parts in order to reduce cost and improve reliability.

  Further, in the above conventional apparatus, the axial position of the motor rotor or the like is recognized by the rotation angle detector such as the rotary encoder and the feed amount per rotation of the screw mechanism. If the power is turned off, the position in the axial direction cannot be recognized even if the power is turned on again or the current angle of the motor rotor can be recognized. Therefore, it is necessary to search for an origin sensor installed at an arbitrary position in the axial stroke, and to perform an origin return operation for setting the position as a reference position in the axial direction (linear motion direction).

  This is a serious problem when the electric actuator is used for an automobile, particularly when used as an electric actuator for a transmission system or a brake system. For example, noise may intrude while driving and the drive unit of the electric actuator will be reset, or a large amount of power may be consumed instantaneously in other systems while driving, causing an abnormality in the power line, When a voltage drop occurs in the line and the electric actuator driving device momentarily goes into a power failure state, the current position cannot be recognized, resulting in a problem that the transmission and the brake cannot be operated.

  In view of this, a method has been proposed in which the position at the time of system reset or power-off, particularly the axial position, is stored in a semiconductor memory or the like so that it is not necessary to perform a home return operation when the power is turned on again. However, in this case, if some axial external force is applied to the electric actuator at the time of system boot or power failure, the screw mechanism may be forcibly rotated by the external force and the position may be shifted. Accumulate as a position error. For this reason, an origin return operation and an origin sensor therefor are indispensable and not an essential solution.

  On the other hand, there is a linear motion position detector such as a linear scale, a linear potentiometer, and a rotary potentiometer with a cam mechanism. However, there was a problem that high cost and reduced reliability were inevitable.

  Accordingly, an object of the present invention is to reduce the number of parts while reducing the number of parts by using a screw mechanism that also serves as a bearing for rotatably supporting a rotor of a motor constituting an electric actuator. It is to provide an electric actuator with high performance.

  An object of the present invention is to provide an electric actuator having a screw mechanism that converts a rotational motion into a linear motion and a rotary motor that applies a rotational force to the screw mechanism. The shaft includes a nut and a nut that is screwed onto the screw. The rotor of the rotary motor is rotatably provided integrally with the screw shaft, and the nut is fixed together with the stator of the rotary motor. By configuring a screw mechanism that allows the rotor to move in the axial direction according to the rotation of the rotary motor, and configuring a bearing for rotatably supporting the rotor, Achieved.

  Further, the object is to form the rotary motor in a form in which the stator and the rotor are opposed to each other in the circumferential direction, and the rotor is pivoted together with the screw portion according to the rotation of the rotor. This is achieved effectively by making it movable in the direction.

  Moreover, the said objective is effectively achieved by making the axial direction length of the said rotor more than the axial direction length of the said stator.

  In addition, the object of the present invention is to dispose the member between the stator of the rotary motor and the rotor by providing a member that magnetically changes the motor winding in accordance with the axial position of the rotor. This is effectively achieved by making it possible to detect the absolute position of the child in the axial direction.

  Further, the object is to dispose a member between the stator of the rotary motor and the rotor for magnetically changing the motor winding according to the axial position and the rotation angle of the rotor. This is achieved effectively by making it possible to detect the absolute position and rotation angle of the rotor in the axial direction.

  Furthermore, the object is achieved more effectively by configuring the screw mechanism with a ball screw.

  As described above, in the electric actuator according to the present invention, the screw mechanism is formed by forming the screw portion on the output shaft of the rotary motor and screwing the nut portion to the screw portion, and the screw mechanism as a bearing. To play a role. Thereby, the number of machine parts of the apparatus can be reduced. In addition, since a member that magnetically changes the motor winding according to the axial position of the rotor or the axial position and angle is provided between the stator and the rotor of the motor, the motor winding In addition to the voltage used to pass torque current to the coil, the absolute position of the screw in the axial direction can be detected simply by applying a high-frequency excitation voltage and detecting the current flowing through the coil winding in accordance with the high-frequency excitation voltage. Can do. Therefore, the number of parts of mechanical parts and electrical parts can be greatly reduced, the cost is low, no axial position detector or origin sensor is required, and troublesome work such as return to origin is unnecessary. An electric actuator having high environmental resistance and high reliability can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an electric actuator according to a first embodiment of the present invention, in which a three-phase brushless DC motor is used as a motor for applying a rotational force to a screw mechanism, and a ball screw is provided as a screw mechanism on its output shaft. is there. Here, as a brushless DC motor, in order to reduce cogging torque and torque ripple, a fraction slot format of 8 poles and 9 slots is adopted. However, the present invention is not limited to this format, and the number of slots is a multiple of 3 and 2 in electrical angle. A three-phase brushless DC motor of a type having motor windings with an interval of / 3π may be used.

  FIG. 1A shows the overall configuration of the brushless motor 1, and the motor housing 2 is formed by a cylindrical center housing 2A and a sealing lid 2B for closing the opening end of the center housing 2A. . A screw shaft 3 is rotatably arranged in the housing 2, and a cylindrical rotor 4 is disposed around the screw shaft 3 as shown in FIG. . The rotor 4 is formed of a permanent magnet, and a conical magnet cover 5 having a thickness different in the axial direction is fitted on the outer periphery thereof. The magnet cover 5 is made of austenitic stainless steel, which is a nonmagnetic metal, in order to protect the rotor 4 and to give a magnetic change to the motor winding 7 in accordance with the axial position of the rotor 4. .

  Further, a core 6 is attached to the inner peripheral surface of the center housing 2A, and for example, a three-phase motor winding 7 is wound around the core 6 so as to surround the rotor 4. The stator 6 of the brushless motor 1 is constituted by the core 6 and the motor winding 7, and an alternating current is passed through the motor winding 7 in accordance with the angle of the rotor 4 to drive the rotor 4 in the rotational direction. Is supposed to give.

  Further, a screw portion 9 is formed on the outer side (left side in FIG. 1) of the screw shaft 3, and a nut portion 10 is screwed to the screw portion 9, and a screw mechanism 11 is configured by the screw portion 9 and the nut portion 10. The This screw mechanism 11 uses a ball screw with a lead length of 10 mm, is an 8-pole 9-slot brushless DC motor, and the nut portion 10 is fixed, so that the screw portion 9 has an electrical angle corresponding to one cycle. Each time the rotor 4 rotates, it moves in the axial direction by 2.5 mm. In addition, since the axial length of the rotor 4 is longer than the axial length of the stator 8 by a stroke or more, no matter which axial position the rotor 4 is in the axial stroke, the torque A driving force in the rotation direction according to the current can be applied to the rotor 4.

  And the screw mechanism 11 comprised by the screw part 9 and the nut part 10 enables the movement of the rotor 4 to the axial direction, and is a bearing required for supporting the rotor 4 of the motor 1 rotatably. Also serves as a role. As a result, the rotor 4 of the motor can be supported by the ball screw, and conventionally required parts such as a bearing can be omitted, and the number of parts of the electric actuator can be greatly reduced.

  Further, there is a gap a along the circumferential direction between the stator 8 and the rotor 4, and the radial thickness of the magnet cover 5 is the shaft end side (right side in FIG. 1 (a)). ), And the gap of the gap a increases. Therefore, when the rotor 4 moves in the axial direction along with the rotation, the average gap between the rotor 4 and the inner diameter portion of the stator 8 changes depending on the axial position of the rotor 4.

  As a result, when a high frequency excitation voltage of about 1 kHz to 100 kHz is applied to the motor winding 7 separately from the voltage for passing the torque current, the magnitude of the eddy current for the AC magnetic flux induced in the magnet cover 5 is It changes with the average clearance between the inner diameter part of 8. And the magnitude | size changes the inductance of the motor winding 7, and the inductance of the motor winding 7 changes according to the axial direction position of the rotor 4. FIG. Thus, the absolute position of the rotor 4 in the axial direction can be detected by detecting the amplitude of the current flowing through the motor winding 7 by the high-frequency excitation voltage as a change in inductance, that is, the axial position of the rotor 4. .

  Next, drive control of the apparatus will be described based on the block diagram of FIG.

  In the brushless DC motor, a rectified torque current, that is, a necessary torque current flows through the motor winding 7 of each phase according to the angle of the rotor 4. For this reason, the angular position of the rotor 4 is detected by the pole position detector 32 as a magnetic detector using the Hall element 31 and is sent to the current waveform generator 33 to generate a necessary current waveform signal. Yes.

  The current waveform generator 33 has a function of superimposing a high-frequency excitation waveform having a constant amplitude and a constant frequency on a current command value for each phase, while a current detector for each phase is supplied to the motor winding 7 for each phase. The high frequency excitation component is removed by the low pass filter 35 and fed back to the amplifier 36. That is, since the high frequency excitation component is removed in the amplifier 36, the amplifier 36 functions as a voltage amplifier without performing current control in the frequency band where high frequency excitation is performed.

  Here, the current flowing through the motor winding 7 is detected by the current detector 34, and in the speed / position control loop, the speed signal fed back by the proportional integral control (PI control) unit 38 via the speed detector 37 and the like. And the speed command value are controlled so as to eliminate the deviation between the position signal fed back by the proportional control (P control) unit 39 and the position command value.

  In this position control, a three-phase sine wave current flows through the motor winding 7 of each phase (see FIG. 3A). The detection signal from the current detector 34 functions as a band-pass filter that passes only the same frequency component as the high-frequency excitation frequency of each phase and an absolute value calculator that outputs the absolute value of the passed signal. As shown in FIG. 3 (b), the current component (U phase, V phase, W phase) of the motor winding 7 by the high frequency excitation voltage of each phase is extracted by the detector 40 provided. This current component is smoothed by the smoothing low-pass filter 41 and sent to the adder 42 as shown in FIG. In the adder 42, as shown in FIG. 3 (d), the output values of the respective phases are synthesized and added, whereby the axial absolute position signal of the rotor 4 is obtained from the output values.

  As a result, for controlling the absolute position of the rotor 4 in the axial direction, it is not necessary to provide a linear motion position detector or an origin sensor, or to perform an origin return operation, and the rotor 4 can be controlled according to the input position command value. Axial position and moving speed can be controlled.

  In the first embodiment, in order to reduce errors in the absolute position in the axial direction of the rotor 4 due to mechanical error factors such as eccentricity of the magnet cover 5 with respect to the stator 8 and misalignment, current detection is performed for all three phases. If the absolute position of the rotor 4 in the axial direction is detected based on the signal obtained by the detector 34, but the cause of the mechanical error is small, the axial direction is determined using the current generated by high-frequency excitation for only one phase of the current detector 34. The absolute position may be detected. Further, although the Hall element is used to detect the pole position of the rotor 4, other types of magnetic detectors such as a semiconductor magnetoresistive element sensor (MR sensor) may be used.

  FIG. 4 shows a second embodiment of the present invention. The same members as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The second embodiment differs from the first embodiment shown in FIG. 1B in that the cross-sectional shape of the magnet cover 5 is different, the number of pole pairs is four, and there are four electrical angles per mechanical angle. did. That is, the magnet cover 5 is given a sinusoidal change of four electrical angles per mechanical angle period to the inductance of the motor winding 7, and the amplitude is changed according to the axial position of the rotor 4. It was shaped like this.

  Thereby, the axial position and electrical angle of the rotor 4 can be detected as a change in inductance of the motor winding 7. Therefore, since it is possible to perform the necessary commutation when a torque current is applied to the brushless DC motor without using a magnetic detector, the magnetic detector and its wiring can be omitted. Environmental resistance and reliability can be improved.

  Next, drive control of the apparatus in the second embodiment will be described based on the block diagram of FIG.

  In the second embodiment, the absolute position of the rotor 4 in the axial direction can be obtained by the same method as in the first embodiment. However, each phase is different from the first embodiment in that a four-cycle sinusoidal change in electrical angle per mechanical angle period is superimposed, but this sine wave-like change has an electrical angle of 2 in each phase. Since the phase differs by an interval of / 3π, it is canceled by the adder 42 and is not affected. Using the absolute position of the rotor 4 in the axial direction, a position deviation and a speed deviation with respect to time change are detected, and a torque command signal to the motor 1 is generated.

  In the position control, a three-phase sine wave current flows in each phase of the motor winding 7 (see FIG. 6A), but output signals from the detector 40 and the low-pass filter 41 (FIG. 6B). )) Is sent to the adder 42. In the adder 42, after the addition process is performed, the output signal (FIG. 6C) is sent as a position signal to the proportional control (P control) unit 39 to eliminate the deviation from the position command value. Control is performed. Further, the output signal from the adder 42 is sent to the correction coefficient multiplier 51, and the axial absolute position of the rotor 4 is not changed so that the median value and amplitude do not change regardless of the axial position of the rotor 4. From the output signal obtained by multiplying the signal of each phase by the correction coefficient calculated by the correction coefficient calculator 52, a three-phase sine wave corresponding to the electrical angle of the rotor 4 is generated (FIG. 6 ( d)). This three-phase sine wave is converted into a two-phase sine wave of sin θ, cos θ (θ: electrical angle) by a three-phase / two-phase converter 53, and then an electrical angle of the rotor 4 by a resolver / digital converter 54. A parallel or serial digital signal corresponding to the signal is generated.

  In the second embodiment, the electrical angle and the mechanical angle need not be converted by matching the number of pole pairs of the motor 1 with the number of inductance change periods per one mechanical angle of the motor winding 7 by the magnet cover 5. The generation of the current command signal for each phase in the current waveform generator 33 is simplified. However, if conversion of the electrical angle and the mechanical angle is performed, the motor winding 7 by the magnet cover 5 per cycle of the mechanical angle is provided. The number of inductance change cycles may be a divisor of the number of pole pairs of the brushless DC motor (4, 2, 1 when the number of pole pairs is 4). In this case as well, the same effect as in the first embodiment can be obtained.

  Incidentally, the drive control shown in the block diagrams used in each of the above embodiments is not limited to this, and if the same effect can be obtained, the circuit configuration of the drive device of the electric actuator and the interface with the outside You may change suitably by various circumstances, such as. An analog circuit may be configured using an analog waveform in a method of detecting the absolute position of the rotor 4 in the axial direction and the electrical angle, but processing is performed using digital signals using a microcomputer, a DSP (Digital Signal Processor), or the like. It may be configured. Further, in order to detect abnormal overheating of the motor winding 7, the absolute position in the axial direction of the rotor 4 and the value of the electrical angle are corrected using information from sensors such as a temperature detector and other devices. Thus, the detection accuracy may be increased.

  FIG. 7 shows a third embodiment of the present invention. The same members as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the third embodiment, the stator 8 of the motor 1 is matched with the shape of the magnet cover 5 and the inner diameter of the stator 8 is changed along the axial direction. That is, the inner diameter of the stator 8 was reduced as it proceeded to the shaft end side (right side in FIG. 7) of the screw shaft 3. Thereby, the change of the inductance of the motor winding 7 with respect to the change of the absolute position of the rotor 4 in the axial direction can be increased, and the position resolution is increased. In this case as well, it is possible to obtain the same effects as in the above embodiments.

  FIG. 8 shows a fourth embodiment of the present invention. The same members as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the fourth embodiment, the cylindrical protrusion 56 is formed by extending the vicinity of the center of the sealing lid 2B of the housing 2 to the outside (right side in FIG. 8A), and the screw shaft 3 is formed in the protrusion 56. The outer extension 3a is accommodated. In the projecting portion 56, a rolling bearing 57 that is rotatable and linearly represented by a ball bush is provided. As a result, the allowable moment load at the shaft end of the ball screw 11 on the operation side (left side in FIG. 8A) can be increased, the rotor 4 can be prevented from shaking when the stroke is lengthened, and the critical speed can be prevented. Can be prevented. Further, even when an inexpensive ball screw having a gap between the rolling element and the raceway surface is used, the swirl of the threaded portion can be reduced. In this case as well, it is possible to obtain the same effects as in the above embodiments.

In this embodiment, a rolling bearing 57 is provided in the protrusion 56 so as to be freely rotatable.
As shown in FIG. 8 (b), on the outer end surface of the screw shaft 3 (right side in FIG. 8 (a)), a hole is formed in the axial direction to form a groove 3b, and a sealing lid is formed in the groove 3b. A cylindrical member 3c attached to the central opening of 2B is disposed. Then, a rolling bearing 57 may be fitted between the concave groove 3 b and the cylindrical member 3 c so that the screw shaft 3 can be rotated and moved freely by the rolling bearing 57. In this case as well, the same effects as in the above embodiments can be obtained.

  FIG. 9 shows a fifth embodiment of the present invention. The same members as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

In the first embodiment, the ball screw 11 is provided only on one side of the motor 1, whereas in the fifth embodiment, screw portions 58 are formed at both ends of the ball screw 11, respectively. Nut portions 59 and 59 to be screwed to 58 are provided. In this case, at least one nut portion 59 can be attached and fixed at an arbitrary phase when attached to the motor 1. With such a configuration, even if an inexpensive ball screw with a gap between the rolling element and the raceway surface is used,
The gap can be finely adjusted and fixed position preload can be applied, enabling highly accurate positioning.

  In this embodiment, since the diameter of the attachment portion of the rotor 4 is made smaller than the diameter of the screw groove in the screw portion 58, the radially divided permanent magnets are attached to the attachment portion of the rotor 4 of the screw portion 58. The rotor 4 is configured by being bonded and fixed to the cylinder. However, if the diameter of the attachment portion of the rotor 4 is the same as or larger than the diameter of the thread groove, a cylindrical permanent magnet can be used. In addition, when one nut portion 59 is fixed to the motor 1 at an arbitrary phase, the gap is finely adjusted or a fixed position pressure is applied. A spring mechanism such as a disc spring, a wave washer, or a coil spring may be inserted in the axial direction to apply a constant pressure.

  FIG. 10 shows a sixth embodiment of the present invention. The same members as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the sixth embodiment, the spherical portion 61 is formed by subjecting the end of the screw shaft 9 on the operation side (left side in FIG. 10) of the ball screw 11 to spherical processing. Thereby, the increase in the rotational torque of the threaded portion 9 can be reduced even under high load conditions.

  In this embodiment, the spherical portion 61 is provided at the end of the screw shaft 9 on the operation side (left side in FIG. 10) of the ball screw 11, but the screw shaft 9 on the operation side (left side in FIG. 10) of the ball screw 11 is provided. A counterbore may be provided in a spherical shape at the end, and the ball may be attached thereto by gap fitting or tight fitting, and another part that is partly spherically processed is connected to the operation side of the ball screw 11 (FIG. 10). You may provide in the edge part of the screw shaft 9 of the (left side).

  FIG. 11 shows a seventh embodiment of the present invention. The same members as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the seventh embodiment, a rotatable pusher 66 using a deep groove ball bearing 65 as a rolling bearing is provided at the end of the screw shaft 9 on the operation side (left side in FIG. 11) of the ball screw 11. Thereby, the increase in the rotational torque of the screw part 9 can be made small under high load conditions.

  In this embodiment, a deep groove ball bearing is used as a rolling bearing for making the pusher 66 rotatable. However, a thrust bearing may be used under a high load condition that cannot be endured by this bearing. In addition, when both pushing and pulling loads are applied in the axial direction, or when used for high-accuracy positioning, a combined angular ball bearing or a multi-point contact ball bearing may be used to eliminate the bearing gap.

  If the parallelism or perpendicularity between the axial center of the threaded portion 9 and the object to be axially positioned cannot be maintained, a spherical washer is provided between the pusher 66 and the bearing 65, or automatic alignment is performed. An angular error may be absorbed by using a bearing, or the misalignment may be absorbed by providing a gap in the radial direction without fitting the pusher 66 to the raceway of the bearing 65 on the pusher 66 side.

  FIG. 12 shows an eighth embodiment of the present invention. The same members as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the eighth embodiment, a bellows-like boot 67 is provided at a portion where the screw portion 9 is exposed to the outside. Thereby, the airtightness and waterproofness of the whole apparatus are improved, and it can be used even in an environment where there is a lot of dust or water or oil. At this time, the material of the boot 67 can be rubber or resin for use in a room temperature state, and metal can be used for use in a high temperature state.

  In addition, it is good to seal | stick to parts into which dust, water, oil, etc. may penetrate | invade, such as the rolling bearing used for a pushing element, and the joint of a housing.

  FIG. 13 shows a ninth embodiment of the present invention. The same members as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the ninth embodiment, a cylindrical magnet cover 5 having a constant wall thickness made of austenitic stainless steel, which is a nonmagnetic metal, is subjected to drilling (drilling), and a large number of holes 71, 71 are formed in the magnet cover 5. , ... are provided. Thereby, the magnitude of the eddy current caused by the high frequency excitation differs depending on the axial position or the axial position and the rotation angle. In this case, the magnet cover 5 may have a cylindrical shape with a constant thickness as long as it has been subjected to mechanical processing such as drilling (hole processing) or slit processing or surface treatment such as etching.

  In each of the above embodiments, the material of the magnet cover 5 is austenitic stainless steel, which is a nonmagnetic metal, but is not limited thereto. For example, nonmagnetic materials that generate eddy currents by high-frequency excitation, such as aluminum alloys, can be applied, and not only eddy currents by high-frequency excitation, but also magnetic materials that change the amount of magnetic flux flowing through the magnetic material. Can do.

  In each of the above-described embodiments, the current detectors 34 are all provided in the three-phase motor windings 7, and the axial absolute position and electrical angle of the rotor 4 are determined based on the signal obtained by the current detector 34. Although detected, the current detector 34 may be provided only in two of the three phases, and signal processing may be performed by estimating the remaining one phase. Further, the absolute position and electrical angle of the rotor 4 in the axial direction are detected using the amplitude of the current flowing in the motor winding 7 by the high frequency excitation voltage. The high frequency excitation voltage and the current flowing in the motor winding 7 by the high frequency excitation are The change in inductance, that is, the axial position and electrical angle of the rotor 4 may be detected by the phase difference.

  In addition, when a load is always applied in the direction of the output shaft of the motor 1 or when it is necessary to maintain the position even when the electric actuator control device is turned off, an electromagnetic brake or the like is used. By providing an anti-rotation mechanism for the threaded portion 9, the copper loss of the non-movable motor winding 7 after positioning can be reduced, and the position can be maintained even when the power supply of the control device of the electric actuator is turned off. become.

  Furthermore, the rotor 4 is provided with a smaller diameter of the attachment portion of the rotor 4 than the diameter of the screw groove in the screw portion 9, but the diameter of the attachment portion of the rotor 4 is the same as or larger than that of the screw groove. Also good. In this case, it is not always necessary to process the thread groove in the attachment site of the rotor 4. By the way, when a thread groove is machined in this part, a cylindrical back yoke made of a magnetic material for preventing the magnetic path of the rotor 4 from being interrupted by the thread groove is inserted between the rotor 4 and the attachment part. Also good.

  Further, in each of the above embodiments, the rotor 4 is configured by providing a permanent magnet divided into a cylindrical shape or a radial shape at an attachment site of the rotor 4, but when the stroke is long, a long permanent magnet is integrally formed. For example, a plurality of short permanent magnets may be arranged in the axial direction. The permanent magnet may be magnetized before the magnet is disposed on the rotor 4.

  Further, in each of the above embodiments, a ball screw is used to support the output shaft of the motor 11, but the present invention is not limited to this. For example, a screw using a roller as a rolling element or a slide screw not using a rolling element is used. Although it may be used, a ball screw using a ball as a rolling element is preferable in terms of torque performance and the like. The ball screw is preferably a pressurizing type that does not have a gap between the rolling element and the raceway surface, but an electric actuator can be configured at low cost even if it is a type that has a gap between the rolling element and the raceway surface.

(A) is a fragmentary sectional view which shows the inside of the motor of the electric actuator which concerns on 1st Example of this invention, (b) is sectional drawing in the AA of (a). It is a block diagram which shows the drive control of 1st Example. In the first embodiment, (a) is the relationship between the motor winding current and the electrical angle, (b) is the relationship between the detector output and the electrical angle, (c) is the relationship between the output of the low-pass filter and the electrical angle, (D) is a figure which shows the relationship between the output of an adder, and an electrical angle. It is sectional drawing corresponding to FIG.1 (b) which shows 2nd Example of this invention. It is a block diagram which shows the drive control of 2nd Example. In the second embodiment, (a) shows the relationship between the motor winding current and the electrical angle, (b) shows the relationship between the output of the detector and the low-pass filter and the electrical angle, and (c) shows the output of the adder and the electrical angle. (D) is a figure which shows the relationship between the output of a correction coefficient multiplier, and an electrical angle. It is a fragmentary sectional view which shows the inside of the motor of the electric actuator which concerns on 3rd Example of this invention. (A) is a fragmentary sectional view which shows the inside of the motor of the electric actuator which concerns on 4th Example of this invention, (b) is principal part sectional drawing which shows the modification of (a). It is a fragmentary sectional view which shows the inside of the motor of the electric actuator which concerns on 5th Example of this invention. It is a fragmentary sectional view which shows the inside of the motor of the electric actuator which concerns on 6th Example of this invention. It is a fragmentary sectional view which shows the inside of the motor of the electric actuator which concerns on 7th Example of this invention. It is a fragmentary sectional view which shows the inside of the motor of the electric actuator which concerns on 8th Example of this invention. It is a fragmentary sectional view which shows the inside of the motor of the electric actuator which concerns on 9th Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric motor 2 Housing 3 Screw shaft 4 Rotor 5 Magnet cover 7 Motor winding 8 Stator 9 Screw part 10 Nut part 11 Screw mechanism 33 Current waveform generator 34 Current detector 35 Low pass filter 36 Amplifier 40 Detector 41 Low pass filter 42 Adder 51 Correction Coefficient Multiplier 52 Correction Coefficient Calculator 56 Projecting Part 57 Rolling Bearing 58 Screw Part 59 Nut Part 61 Spherical Part 65 Ball Bearing 66 Pusher 67 Boot

Claims (6)

In an electric actuator having a screw mechanism that converts rotational motion into linear motion, and a rotary motor that applies rotational force to the screw mechanism,
The screw mechanism includes a screw shaft having a screw portion formed on the outer periphery and a nut portion screwed into the screw portion, and a rotor of the rotary motor is provided so as to be rotatable integrally with the screw shaft. By fixing the nut portion together with the stator of the rotary motor, a screw mechanism is provided that enables the rotor to move in the axial direction in accordance with the rotation of the rotary motor, and the rotor can be rotated freely. An electric actuator comprising a bearing for supporting. The rotary motor is configured in a form in which the stator and the rotor are opposed to each other in the circumferential direction, and the rotor is movable in the axial direction together with the screw portion according to the rotation of the rotor. The electric actuator according to claim 1. The electric actuator according to claim 2, wherein the axial length of the rotor is equal to or greater than the axial length of the stator. In the rotary motor, a member that gives a magnetic change to the motor winding according to the axial position of the rotor is disposed between the stator and the rotor, so that the axial direction of the rotor is increased. The electric actuator according to claim 1, wherein an absolute position can be detected. In the rotary motor, a member that magnetically changes a motor winding in accordance with an axial position and a rotation angle of the rotor is disposed between the stator and the rotor, thereby the rotor. The electric actuator according to any one of claims 1 to 3, wherein the absolute position in the axial direction and the rotation angle can be detected. The electric actuator according to claim 1, wherein the screw mechanism is a ball screw.

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