JP2015117787A - Electric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric actuator which can perform high-resolution position detection, and enhances position detection accuracy without using a multistage gear, is low in cost, and improved in reliability.SOLUTION: An electric actuator comprises a reduction mechanism 6 which transmits a rotating force of an electric motor 3 via a motor shaft 3a, and a ball screw mechanism 8 which converts the rotational motion of the electric motor 3 into the linear motion of a drive shaft 7 in an axial direction via the reduction mechanism 6. The reduction mechanism 6 comprises an input gear 4 which is externally fit to the motor shaft 3a, and an output gear 5 which is geared with the input gear 4, and fixed to an outside diameter of a nut 16. A plurality of vicinity sensors 9a, 9b and 9c are arranged at an end face side of the input gear 4, and these vicinity sensors 9 are arranged in a center of a tooth 4a of the input gear 4, between the tooth 4a and a tooth 4b adjacent thereto of the input gear 4, and on a pitch circle at an end side of the tooth 4b of the input gear 4, respectively.

Description

  The present invention relates to an electric actuator for general industrial use, an electric actuator having a ball screw mechanism used in a drive unit of an automobile, a ship transporting machine, and the like, and more specifically, rotation input from an electric motor in an automobile transmission, a parking brake, etc. The present invention relates to an electric actuator that converts a linear motion of a drive shaft through a ball screw mechanism.

  In electric actuators used in various drive units, a gear mechanism such as a trapezoidal screw or a rack and pinion is generally used as a mechanism for converting the rotational motion of the electric motor into a linear motion in the axial direction. Since these conversion mechanisms involve a sliding contact portion, the power loss is large, and it is necessary to increase the size of the electric motor and increase the power consumption. Therefore, a ball screw mechanism has been adopted as a more efficient actuator.

  As an actuator using a ball screw mechanism, a system for operating a transmission switching, a clutch, and a brake with an electric motor has been developed in an automobile or the like for the purpose of saving a driver's labor and improving vehicle controllability. In order to position the output shaft in the axial direction in an electric actuator used for such applications, a linear motion sensor or a rotation sensor may be installed inside the actuator to detect the axial position of the output shaft.

  For example, in an electric actuator for a ship, it must be considered that it is used on the open ocean, and it is desired to develop it with a concept different from that of a general actuator. In general linear actuators, axial displacement detection is often performed and controlled. Therefore, a limit switch is provided at a portion that is axially displaced. In many cases, the electric motor serving as the drive source of the actuator is assembled in a state of being exposed on the outer wall of the housing.

  However, if the stroke position of the linear actuator is detected with the limit switch, the axial displacement is detected at two positions. In this case, since the position in the middle cannot be detected, there is a problem that when the actuator stops between two positions for some reason, the drive circuit cannot determine in which direction it should be moved.

  As an electric actuator that solves such a problem, one shown in FIG. 8 is known. The electric actuator 100 includes a cylindrical housing 101, an electric motor 102 attached to the housing 101, a first power transmission mechanism including a plurality of gears for transmitting the rotational force of the electric motor 102, and a measurement shaft 113a. And a second power transmission mechanism that includes a plurality of gears and that transmits the rotational force of the electric motor 102 to the measurement shaft 113a of the potentiometer 113.

  The housing 101 includes a housing main body 101A, a cover member 101B assembled to an end surface thereof, and a motor bracket 101C. The housing body 101A has a motor chamber 101a and a screw shaft chamber 101b, and a motor 102 is disposed in the motor chamber 101a. The electric motor 102 is fixed to a plate-like motor bracket 101C. The motor bracket 101C is attached so that the outer ring of the ball bearing 114 is sandwiched between the housing main body 101A and the motor chamber 101a and the screw shaft chamber 101b of the housing main body 101A are closed.

  A rotating shaft 102a of the electric motor 102 protrudes from the motor bracket 101C, and a first gear 103 is attached to the end of the rotating shaft 102a so as not to be relatively rotatable by press-fitting. A second gear 105 is rotatably disposed around the long shaft 104 whose one end is press-fitted into the bag hole of the motor bracket 101C, and meshes with the large gear portion 106a of the first gear 103 and the third gear 106. Yes.

  The third gear 106 has a large gear portion 106a and a small gear portion 106b formed coaxially, and is attached to the end portion of the screw shaft 107 so as not to be relatively rotatable by serration coupling. A support member 108 is attached to the motor bracket 101C so as to cover a part of the third gear 106. Here, the first gear 103, the second gear 105, and the third gear 106 constitute a first power transmission mechanism.

  A fourth gear 109 disposed adjacent to the second gear 105 is rotatably supported around the long shaft 104. In the fourth gear 109, a large gear portion 109a and a small gear portion 109b that are meshed with the small gear portion 106b of the third gear 106 are formed coaxially.

  The small gear portion 109 b of the fourth gear 109 meshes with the large gear portion 111 a of the fifth gear 111 that is rotatably supported with respect to the short shaft 110 implanted in the support member 108 in parallel with the long shaft 104. ing. The fifth gear 111 has a large gear portion 111a and a small gear portion 111b formed coaxially. The small gear portion 111 b meshes with a sixth gear 112 that is disposed adjacent to the fifth gear 111 and rotatably supported around the long shaft 104.

  The potentiometer 113 as a sensor is fitted and disposed in the hole of the cover member 101B. The measurement shaft 113a of the potentiometer 113 is connected to the sixth gear 112 and rotates integrally. The tip of the long shaft 104 extending in a cantilever manner is supported by the potentiometer 113 via the sixth gear 112 and the measurement shaft 113a. Here, the first gear 103, the second gear 105, the third gear 106, the fourth gear 109, the fifth gear 111, and the sixth gear 112 constitute a second power transmission mechanism.

  The right end side of the screw shaft 107 is rotatably supported by a ball bearing 114 with respect to the housing main body 101A. The screw shaft 107 penetrates the cylindrical nut 115 and forms a male screw groove 107a on the left end side. A female screw groove 115a is formed on the inner peripheral surface of the nut 115 so as to face the male screw groove 107a, and a large number of balls 116 are arranged to roll in a spiral space formed by both the screw grooves 107a and 115a. Has been. The nut 115 is provided with a detent with respect to the housing main body 101A, and is relatively movable in the axial direction within the screw shaft chamber 101b, and is not relatively rotatable. A nut 115 as an axial movement element, a screw shaft 107 as a rotation element, and a ball 116 as a rolling element constitute a ball screw mechanism, and the ball screw mechanism and the drive shaft 117 constitute a drive mechanism. To do.

  The left end of the screw shaft 107 penetrates into a bag hole 117a formed in the round shaft-shaped drive shaft 117. The right end of the drive shaft 117 is coaxially fitted to the nut 115 and is connected by a pin so as to move integrally. The drive shaft 117 is supported by the bush 118 so as to be movable in the axial direction with respect to the housing main body 101A. A hole 117b for connecting to a link member (not shown) is formed at the end of the drive shaft 117 protruding from the housing main body 101A.

  The rotational force of the rotating shaft 102a is transmitted to the measuring shaft 113a of the potentiometer 113 via the first gear 103, the second gear 105, the third gear 106, the fourth gear 109, the fifth gear 111, and the sixth gear 112. The A signal corresponding to the rotation of the measuring shaft 113a is input from the potentiometer 113 to a drive circuit (not shown). If it is determined that the screw shaft 107 has rotated by a predetermined rotation amount based on this signal, the drive circuit stops the power supply to the electric motor 102. On the other hand, when reverse polarity power is supplied to the electric motor 102, the rotating shaft 102a rotates in the reverse direction, so that the drive shaft 117 of the electric actuator 100 moves in the retracting direction by the reverse operation. To do.

  As described above, the centers of the second gear 105, the fourth gear 109, and the sixth gear 112 coincide with each other and are rotatably disposed around the same long shaft 104, so that a reduction ratio with a high gear ratio can be obtained. A compact configuration can be achieved while using a five-stage gear train. In this way, in the electric actuator 100 in which a plurality of gears are built in, the three gears have the same rotation center axis. This means that the number of center axes is reduced, and support holes for housings that support the center axes. Therefore, there are many merits such as reduction of processing man-hours and reduction of the number of shaft parts.

  Moreover, since the rotational displacement of the screw shaft 107 is detected by the potentiometer 113 instead of detecting the displacement position by a limit switch or the like, arbitrary position control is possible. When the rotation of the screw shaft 107 is directly detected, since the screw shaft 107 is multi-rotation, the rotational displacement decelerated via the gear train of the second power transmission mechanism is detected by the potentiometer 113. On the other hand, the rotational motion output from the electric motor 102 is decelerated through the gear train and transmitted to the screw shaft 107. By providing a common rotation center shaft in a part of the two gear trains, a compact layout is possible, and there is a great contribution in terms of cost (for example, see Patent Document 1).

JP 2008-228557 A

  In such a conventional electric actuator 100, the potentiometer 113 can generally set an effective detection angle in a range of 80 ° to 170 °, and although it is a highly accurate sensor, it is between the screw shaft 107 and the potentiometer 113. In order for the electric actuator 100 having multi-stage gears (spur gears) to achieve a large reduction, it is necessary to increase the difference in the number of teeth between the small gear and the large gear. This not only increases the number of parts and the number of parts, but also increases the size of the electric actuator 100 that accommodates each gear.

  In addition, although the mechanism detects the position of the linear movement of the drive shaft 117, the drive shaft 117 and the potentiometer 113 are used to convert the rotation amount of the screw shaft 107 into the detection angle of the potentiometer 113 through the reduction of the spur gear. As the number of parts interposed between the screw shaft 107 and the potentiometer 113 increases, the position detection accuracy decreases, and the rotation angle decelerated from the rotation of the screw shaft 107 is measured. Therefore, the resolution is lowered, and a high-resolution sensor is required to compensate for this. Furthermore, since three gears that are not necessary for driving the actuator are arranged for angle detection, there are problems in terms of cost and assembly.

  The present invention has been made in view of such problems of the prior art, and can detect a position with high resolution, improve position detection accuracy without using a multi-stage gear, and improve reliability at low cost. An object of the present invention is to provide an electric actuator.

  In order to achieve such an object, the invention according to claim 1 of the present invention includes a housing, an electric motor attached to the housing, and a speed reduction mechanism that transmits the rotational force of the electric motor via a motor shaft. And a ball screw mechanism that converts the rotational motion of the electric motor into a linear motion in the axial direction of the drive shaft via the speed reduction mechanism, and the ball screw mechanism is connected to the speed reduction mechanism and is attached to the housing. A nut that is rotatably supported via a mounted rolling bearing and is not axially movable, and is inserted into the nut via a large number of balls and is coaxially integrated with the drive shaft to form the housing. A screw shaft that is supported so as to be non-rotatable and movable in the axial direction, and the speed reduction mechanism is meshed with the input gear that is externally fitted and fixed to the motor shaft. In the electric actuator having an output gear fixed to the outer diameter of the nut, a plurality of proximity sensors are disposed on the pitch circle of one of the gears, and one of the proximity sensors When the length X1 of the arc on the pitch circle connecting the other proximity sensor is α, the tooth thickness of the gear is α, the pitch is β, and n is an integer equal to or less than the number of gear teeth, nβ <X1 < The relationship of α + nβ (n = 1, 2, 3,...) is satisfied.

  As described above, the ball screw mechanism includes a speed reduction mechanism that transmits the rotational force of the electric motor, and a ball screw mechanism that converts the rotational motion of the electric motor into a linear motion in the axial direction of the drive shaft via the speed reduction mechanism. Is connected to the speed reduction mechanism, is rotatably supported via a rolling bearing mounted on the housing, and is supported so as not to move in the axial direction, and is inserted into the nut via a large number of balls, An input gear, which is composed of a screw shaft that is coaxially integrated and supported so as to be non-rotatable with respect to the housing and movable in the axial direction, and in which the speed reduction mechanism is externally fitted and fixed to the motor shaft, and the input gear In the electric actuator having an output gear fixed to the outer diameter of the nut, a plurality of proximity sensors are arranged on the pitch circle of one of the gears, and among these proximity sensors When the length X1 of the arc on the pitch circle connecting one proximity sensor and one other proximity sensor is α, the gear tooth thickness is α, the pitch is β, and n is an integer equal to or less than the number of gear teeth, nβ Since the relationship <X1 <α + nβ (n = 1, 2, 3,...) Is satisfied, the position of the drive shaft can be detected with high resolution by measuring the pulse output of the gear, and the rotation direction of the gear can be determined. It is possible to provide an electric actuator that can detect at the same time and has improved position detection accuracy without using a multi-stage gear.

  Preferably, as in the invention according to claim 2, one of the plurality of proximity sensors is further disposed between the gears, and an arc on a pitch circle connecting the proximity sensor and the one proximity sensor. If the length X2 satisfies the relationship X2 ≠ X1 ≠ β, the resolution of the detection output is improved approximately twice.

  If the proximity sensor is arranged on the input gear as in the third aspect of the invention, it becomes a gear on the side where the number of teeth to be reduced is small, and the axial position of the drive shaft can be obtained with high resolution. Can be detected.

  Further, as in the invention according to claim 4, if a bush that slidably supports the drive shaft is mounted on the housing, and the bush comprises an end ring having a slit at an end, the housing The change in sliding clearance caused by the difference in coefficient of linear expansion caused by the difference in material between the bush and the drive shaft can be allowed when the drive shaft slides at low or high temperatures. It is possible to prevent an increase in the load on the electric motor without increasing the force and hindering the smooth movement of the drive shaft.

  Further, as in the invention according to claim 5, if the bush is set so that the width of the slit is not less than 0 and the fitting shimiro is not less than 0 in the low temperature or high temperature region, In the region, even if the housing with a large linear expansion coefficient contracts more than the bush, the slit of the bush has a gap, and in the high temperature operating temperature range, even if the housing with a large linear expansion coefficient expands beyond the bush, A fitting shimiro between the housing and the bush remains.

  In addition, as in the invention described in claim 6, if the bush has a slit inclined with respect to the axis, even if a radial load is applied to the bush, any part in the axial direction is applied to the slit portion. Can be received at.

  An electric actuator according to the present invention includes a housing, an electric motor attached to the housing, a reduction mechanism that transmits the rotational force of the electric motor via a motor shaft, and the electric motor via the reduction mechanism. A ball screw mechanism that converts rotational motion into linear motion in the axial direction of the drive shaft, and the ball screw mechanism is connected to the speed reduction mechanism and is rotatable via a rolling bearing mounted on the housing. A nut that is supported so as not to move in the axial direction, and is inserted into the nut via a large number of balls, and is integrated with the drive shaft so as to be non-rotatable and axially movable. The speed reduction mechanism is engaged with and fixed to the motor shaft and is fixed to the outer diameter of the nut. In the electric actuator provided with the output gear, a plurality of proximity sensors are arranged on the pitch circle of one of the gears, and one of the proximity sensors is connected to the other proximity sensor. When the length X1 of the arc on the pitch circle is α, the gear tooth thickness is α, the pitch is β, and n is an integer equal to or less than the number of gear teeth, nβ <X1 <α + nβ (n = 1, 2, 3)), the high-resolution position of the drive shaft can be detected by measuring the pulse output of the gear, and the rotational direction of the gear can be detected simultaneously. An electric actuator with improved position detection accuracy can be provided without using it.

It is a longitudinal section showing one embodiment of an electric actuator concerning the present invention. It is a longitudinal cross-sectional view which shows the actuator main body of FIG. It is the III arrow directional view which fractured | ruptured a part which shows the arrangement | positioning location of the sensor of FIG. It is a principal part enlarged view of FIG. It is a graph which shows the pulse waveform of the output of a sensor. (A) is a front view which shows the bush of FIG. 1, (b) is a side view of (a). (A) is a front view which shows the modification of the bush of FIG. 6, (b) is a side view of (a). It is a longitudinal cross-sectional view which shows the conventional electric actuator.

  A housing, an electric motor attached to the housing, a reduction mechanism that transmits the rotational force of the electric motor via a motor shaft, and the rotational movement of the electric motor via the reduction mechanism in the axial direction of the drive shaft A ball screw mechanism that converts the linear screw motion into a linear motion, and the ball screw mechanism is connected to the speed reduction mechanism and is supported by a rolling bearing mounted on the housing so as to be rotatable and not axially movable. And a screw shaft that is inserted into the nut via a large number of balls, is coaxially integrated with the drive shaft, and is supported so as to be non-rotatable and axially movable with respect to the housing. An electric actuator comprising: an input gear configured to be externally fitted and fixed to the motor shaft; and an output gear meshed with the input gear and fixed to the outer diameter of the nut. A plurality of proximity sensors are arranged on the pitch circle of the input gear, and the length X1 of the arc on the pitch circle connecting one proximity sensor and the other proximity sensor among these proximity sensors is the input circle. When the gear tooth thickness is α, the pitch is β, and n is an integer equal to or smaller than the number of gear teeth, the relationship of nβ <X1 <α + nβ (n = 1, 2, 3,...) Is satisfied.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1 is a longitudinal sectional view showing an embodiment of an electric actuator according to the present invention, FIG. 2 is a longitudinal sectional view showing an actuator main body of FIG. 1, and FIG. 3 is a partial view showing an arrangement position of the sensor of FIG. FIG. 4 is an enlarged view of the main part of FIG. 3, FIG. 5 is a graph showing a pulse waveform of the output of the sensor, FIG. 6 (a) is a front view showing the bush of FIG. (B) is a side view of (a), FIG. 7 (a) is a front view showing a modification of the bush of FIG. 6, and (b) is a side view of (a).

  The electric actuator 1 includes a housing 2, an electric motor 3 attached to the housing 2, and a speed reduction mechanism including a pair of spur gears 4 and 5 that transmit the rotational force of the electric motor 3 via a motor shaft 3 a. 6, a ball screw mechanism 8 that converts the rotational motion of the electric motor 3 to the axial motion of the drive shaft 7 via the speed reduction mechanism 6, and a proximity sensor 9 disposed on the end face side of the spur gear 4, It has.

  The housing 2 is formed by die-casting from an aluminum alloy such as A6063TE or ADC12, and includes a first housing 2a and a second housing 2b assembled to an end surface thereof. An electric motor 3 is disposed inside the first housing 2a. A small spur gear 4 serving as an input gear is attached to the motor shaft 3a of the electric motor 3 so as not to be relatively rotatable. The large spur gear 5 serving as an output gear is attached to the outer diameter of a nut 16 constituting a ball screw mechanism 8 described later so as not to rotate relative to the small spur gear 4.

  A rolling bearing 14 is attached to the outer diameter of the nut 16. The rolling bearing 14 is formed of a deep groove ball bearing, and an outer ring thereof is attached while being sandwiched between the first housing 2a and the bearing bracket 10.

  The drive shaft 7 is integrally formed with a screw shaft 15 constituting the ball screw mechanism 8, and a circular hole 7 a for connecting to a link member (not shown) is formed at the left end portion of the drive shaft 7 in the drawing. At the same time, a cylindrical through hole 2c for accommodating the drive shaft 7 is formed in the first housing 2a, and a bag hole 2d is formed in the second housing 2b. The outer periphery of the drive shaft 7 is slidably supported by the bush 11 with respect to the first housing 2a. The bush 11 is fitted in a collar 12 with a flange that is press-fitted into the opening side of the through hole 2c of the first housing 2a. In addition, the collar 12 is positioned and fixed by a retaining ring 13, and a space between the drive shaft 7 and the first housing 2a is sealed as a labyrinth seal by a collar 12 to prevent entry of dust and the like from the outside. .

  As shown in an enlarged view in FIG. 2, the ball screw mechanism 8 has a screw shaft 15 having a spiral thread groove 15a formed on the outer periphery thereof, and is opposed to the screw groove 15a of the screw shaft 15, and has a spiral shape on the inner periphery thereof. The nut 16 is formed with a thread groove 16a, and a large number of balls 17 are rotatably accommodated in a spiral space formed by the thread grooves 15a and 16a. The nut 16 is press-fitted and fixed to the outer periphery of the large spur gear 5 via a key 19 and the rolling bearing 14 fitted to the first housing 2 a and the bearing bracket 10 is positioned and fixed via a retaining ring 18. Thus, relative movement in the axial direction is impossible, and relative rotation is possible.

  The cross-sectional shape of each thread groove 15a, 16a may be a circular arc shape or a Gothic arc shape, but here, it has a Gothic arc shape that allows a large contact angle with the ball 17 and a small axial clearance. Is formed. Thereby, the rigidity with respect to an axial load becomes high and generation | occurrence | production of a vibration can be suppressed.

  The nut 16 is made of case-hardened steel such as SCM415 or SCM420, and its surface is subjected to hardening treatment in the range of 55 to 62HRC by vacuum carburizing and quenching. Thereby, the buffing etc. for the scale removal after the heat treatment can be omitted, and the cost can be reduced. On the other hand, the screw shaft 15 is made of medium carbon steel such as S55C or case-hardened steel such as SCM415 or SCM420, and the surface thereof is hardened in the range of 55 to 62 HRC by induction hardening or carburizing hardening.

  Here, as shown in FIG. 3, a proximity sensor 9 is disposed on the end face side of the small spur gear 4 constituting the speed reduction mechanism 6. In this embodiment, the proximity sensor 9 includes three sensors 9a, 9b, and 9c. As shown in an enlarged view in FIG. 4, the teeth 4a, 4b, 4c, 4d, 4e, 4f,.・ It is arranged to face. Here, the arrangement of the sensors will be described. The sensors 9a and 9b are arranged with a certain width. Specifically, if the sensor 9a is arranged in a range where the irradiation point Pa of the sensor 9a is irradiated on the teeth 4a of the small spur gear 4 when the gear is viewed from the axial direction, that is, the tooth thickness α of the gear, the irradiation of the sensor 9a. The sensor 9b is arranged so that the length X1 of the arc on the pitch circle connecting the point Pa and the irradiation point Pb of the sensor 9b satisfies the relationship nβ <X1 <α + nβ (n = 1, 2, 3,...). ing. Here, α is the gear tooth thickness, β is the gear pitch, and n is an integer equal to or less than the number of gear teeth. Note that FIG. 4 shows an arrangement when n = 2.

  Further, since the irradiation points Pa, Pb, Pc of the three sensors 9a, 9b, 9c are arranged on the pitch circle of the small spur gear 4, the rotation angle of the small spur gear 4 can be detected with high accuracy. .

  The proximity sensor 9 is an alternative to a mechanical switch such as a limit switch or a micro switch, and is a sensor that detects that a detection object is approaching in a non-contact manner, and uses electromagnetic induction including a laser type due to a difference in operation. There are a high-frequency oscillation type, a magnetic type using a magnet, a capacitance type using a change in capacitance, and the like. In this embodiment, a laser displacement sensor is used as the proximity sensor 9. This laser displacement sensor is a system that applies triangulation, and is composed of a combination of a light emitting element and a light receiving element, and a semiconductor laser is used as the light emitting element. The light of the semiconductor laser is condensed through a light projecting lens and irradiated to a detection object (here, a small spur gear 4). A part of the light beam diffusely reflected from the detection object forms a spot on the light receiving element through the light receiving lens. Specifically, the small spur gear 4 is irradiated with laser light, and the pulse output of the small spur gear 4 is measured. Here, “1” is output when the laser beam hits the small spur gear 4, and “0” is output when it does not hit.

  In addition, for example, a proximity sensor of a magnetic type using a magnet, a capacitance type using a capacitance, or a high-frequency oscillation type using electromagnetic induction may be used. In this high-frequency oscillation type, a high-frequency magnetic field is generated from the detection coil, and when a detection object made of a magnetic material approaches the magnetic field, an induction current (eddy current) flows to the detection object due to electromagnetic induction. It is detected when the impedance changes and oscillation stops.

  Next, the operation of the electric actuator and the operation of the proximity sensor 9 according to the present invention will be described in detail with reference to FIGS. First, as shown in FIG. 1, when the electric motor 3 is driven, the rotation of the electric actuator 1 is reduced and transmitted to the nut 16 of the ball screw mechanism 8 via the speed reduction mechanism 6, and the screw shaft 15. Moves linearly in the axial direction. And it is interlocked with the linear motion of the drive shaft 7 formed integrally with the screw shaft 15 on the same axis.

  As for the proximity sensor 9, as shown in FIG. 4, the sensor 9c is disposed between the teeth 4e and the adjacent teeth 4f as compared with the case where one sensor 9a is disposed on the end face of the small spur gear 4. The resolution is improved approximately twice. Here, although the example which has arrange | positioned the sensor 9c in the approximate center of the tooth | gear 4e and the tooth | gear 4f was shown, it is not restricted to this. The sensor 9c may be arranged in any position that does not overlap the sensors 9a and 9b. That is, it is only necessary that the arc length X2 on the pitch circle connecting the sensors 9c of the sensor 9a satisfies the relationship of X2 ≠ X1 ≠ β. As described above, the position of the drive shaft 7 can be detected at a high resolution by measuring the rotation angle with the proximity sensor 9 including the two sensors 9a and 9c at an arbitrary position in the linear motion range of the drive shaft 7. The electric actuator 1 with improved position detection accuracy can be provided without using any gear.

  Further, by arranging the sensor 9b so that the distance X1 between the irradiation point Pa of the sensor 9a and the irradiation point Pb of the sensor 9b satisfies the relationship of nβ <X1 <α + nβ (n = 1, 2, 3...). The rotational direction of the small spur gear 4, that is, the traveling direction of the drive shaft 7 can be detected simultaneously. As a specific example, in FIG. 4, when the irradiation point Pa of the sensor 9a is located at the center of the tooth 4a of the small spur gear 4 when the gear is viewed from the axial direction, the irradiation point Pb of the sensor 9b is the end of the tooth 4c ( The example which has arrange | positioned the sensor 9b so that it may become the edge part in the tooth surface side when a gearwheel is seen from an axial direction is shown. FIG. 5 shows a pulse waveform when rotating in the CW direction as shown in FIG. 4, and shows how the time changes from left to right in the graph of FIG. Here, paying attention to the time when the waveforms of the sensors 9a and 9b become 0 → 1, in the case of the CW direction (moving from the left to the right of the graph) as shown in FIG. 4, the waveforms of the sensors 9a and 9b. Is read in the order of sensor 9a → sensor 9b → sensor 9a → sensor 9b.

  On the other hand, in the case of the CCW direction, the obtained pulse waveform has a time flow opposite to that in the CW direction, so the time in the graph in FIG. 5 may be viewed from right to left. In this state, when the part where the waveforms of the sensors 9a and 9b are 0 → 1 is read, the signals are output in the order of sensor 9b → sensor 9a → sensor 9b → sensor 9a. Therefore, by arranging the sensor 9b, it is possible to read in which direction the small spur gear 4 is rotating. In order to detect the position of the drive shaft 7 in the axial direction with high resolution, the proximity sensor 9 is arranged on the speed-reduced side (the side with a smaller number of teeth, here the small spur gear 4) as in this embodiment. It is preferable to do this. The CW here refers to the clockwise direction (forward rotation) when viewed from the output shaft side, and the CCW refers to the counterclockwise direction (reverse rotation) when viewed from the output shaft side.

  Next, a bush 11 is shown in FIG. 6 as an example of an electric actuator with improved reliability at low cost. As described above, the bush 11 is fitted into the collar 12 with a hook that is press-fitted into the opening side of the through hole 2c of the first housing 2a, and supports the drive shaft 7 so as to be slidable. The bush 11 is formed of a copper alloy such as LBC3 having a small friction coefficient, and is formed of an end ring having slits 11a parallel to the axis. The slit 11a allows a sliding clearance with the drive shaft 7 that changes due to a difference in linear expansion coefficient caused by a difference in material from the first housing 2a. That is, there is a difference of 30 to 40% in the linear expansion coefficient between the first housing 2a made of aluminum alloy and the bush 11 made of copper alloy. For example, in the low temperature operating temperature range, the first linear expansion coefficient is large. The housing 2a contracts to the bush 11 or more. Even in such a situation, the slit 11a of the bush 11 is set to have a clearance (become 0 or more). On the other hand, in the high temperature operating temperature range, even if the first housing 2a having a large linear expansion coefficient expands to the bush 11 or more, the fitting squeezing between the first housing 2a and the bush 11 remains (becomes 0 or more). Is set to

  Thus, in the present embodiment, the bush 11 is constituted by an end ring, and is set so that the width of the slit 11a is 0 or more and the fitting shishiro is 0 or more in a low temperature or high temperature region. When the drive shaft 7 slides, the frictional force between the bush 11 and the drive shaft 7 increases, and the load on the electric motor 3 increases without hindering the smooth movement of the drive shaft 7. Can be prevented. Therefore, since the drive shaft 7 can move smoothly, the gear can be rotated stably, and the reliability of the actuator is improved. As described above, in the electric actuator according to the present embodiment, position detection with high resolution is possible, position detection accuracy can be improved without using a multistage gear, and reliability can be improved at low cost.

  A bush 20 shown in FIG. 7 is a modification of the bush 11 described above. The bush 20 is formed of a copper alloy such as LBC3, and is formed of an end ring having a slit 20a inclined with respect to the axis. Even if a radial load (indicated by an arrow in the figure) is applied to the bush 20 by the inclined slit 20a, it can be received at any part in the axial direction.

  The embodiment of the present invention has been described above, but the present invention is not limited to such an embodiment, and is merely an example, and various modifications can be made without departing from the scope of the present invention. Of course, the scope of the present invention is indicated by the description of the scope of claims, and further, the equivalent meanings described in the scope of claims and all modifications within the scope of the scope of the present invention are included. Including.

  An electric actuator according to the present invention is used in a drive unit of a general industrial electric motor, an automobile or the like, and includes a ball screw mechanism that converts rotational input from an electric motor into linear motion of a drive shaft via the ball screw mechanism. Applicable to electric actuators.

DESCRIPTION OF SYMBOLS 1 Electric actuator 2 Housing 2a 1st housing 2b 2nd housing 2c Through-hole 2d Bag hole 3 Electric motor 3a Motor shaft 4 Small spur gear 4a, 4b, 4c, 4d, 4e, 4f Small spur gear tooth 5 Large spur gear 6 Deceleration Mechanism 7 Drive shaft 7a Circular hole 8 Ball screw mechanism 9 Proximity sensors 9a, 9b, 9c Sensor 10 Bearing bracket 11, 20 Bush 11a, 20a Slit 12 Collar 13 Retaining ring 14 Rolling bearing 15 Screw shaft 15a, 16a Screw groove 16 Nut 17 Ball 18 Retaining ring 19 Key 100 Electric actuator 101 Housing 101A Housing body 101B Cover member 101C Electric motor bracket 101a Motor chamber 101b Screw shaft chamber 102 Electric motor 102a Rotating shaft 103 First gear 104 Long shaft 105 Second gear 106 Third gear 06a Large gear portion 106b Small gear portion 107 Screw shaft 107a Male screw groove 108 Support member 109 Fourth gear 109a Large gear portion 109b Small gear portion 110 Short shaft 111 Fifth gear 111a Large gear portion 111b Small gear portion 112 Sixth gear 113 Tensiometer 113a Measuring shaft 114 Ball bearing 115 Nut 115a Female thread groove 116 Ball 117 Drive shaft 117a Bag hole 117b Hole 118 Bush n Number of gear teeth P Pitch circle Pa, Pb, Pc Sensor irradiation point X1, X2 Proximity sensor irradiation point Distance α Gear tooth thickness β Gear pitch

Claims (6)

A housing;
An electric motor attached to the housing;
A speed reduction mechanism for transmitting the rotational force of the electric motor via the motor shaft;
A ball screw mechanism that converts the rotational motion of the electric motor to the linear motion in the axial direction of the drive shaft via the speed reduction mechanism, and
The ball screw mechanism is connected to the speed reduction mechanism, and is rotatably supported via a rolling bearing mounted on the housing and is supported so as not to move in the axial direction;
The nut is inserted through a large number of balls, and is composed of a screw shaft that is coaxially integrated with the drive shaft and supported so as to be non-rotatable and axially movable with respect to the housing. In the electric actuator including a reduction mechanism, an input gear externally fitted and fixed to the motor shaft, and an output gear meshed with the input gear and fixed to the outer diameter of the nut,
A plurality of proximity sensors are arranged on the pitch circle of one of the gears, and the arc length X1 on the pitch circle connecting one proximity sensor and the other proximity sensor among these proximity sensors. However, when the tooth thickness of the gear is α, the pitch is β, and n is an integer equal to or smaller than the number of gear teeth, the relationship of nβ <X1 <α + nβ (n = 1, 2, 3,...) Is satisfied. An electric actuator characterized by that.   One proximity sensor among the plurality of proximity sensors is disposed between the gears, and the length X2 of the arc on the pitch circle connecting the proximity sensor and the one proximity sensor has a relationship of X2 ≠ X1 ≠ β. The electric actuator according to claim 1, wherein the electric actuator is satisfied.   The electric actuator according to claim 1, wherein the proximity sensor is disposed on the input gear.   The electric actuator according to claim 1, wherein a bush that slidably supports the drive shaft is mounted on the housing, and the bush includes an end ring having a slit at an end.   5. The electric actuator according to claim 4, wherein the bush is set to have a slit width of 0 or more and a fitting squealing of 0 or more in a low temperature or high temperature region.   The electric actuator according to claim 4, wherein the bush has a slit inclined with respect to an axis.

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