JP2000341904A - Motor-driven cylinder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized short-stroke motor-driven cylinder which can be actuated smoothly, when such an external load that accompanies an impact is applied to a thrust rod. SOLUTION: In a motor-driven cylinder 100, a female screw 4c is engraved in a motor shaft 4. A male screw which is meshed with the female screw 4c is engraved on a thrust rod 15. Elastic blocks 17 and 19 are arranged on the internal faces of brackets 6 and 7 holding a motor frame 5 in between from the front side and the rear side. A transmission ring is arranged making contact with the blocks 17 and 19. The outer ring of the bearing 25 of the motor shaft 4 is pressed via the transmission ring.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric cylinder capable of converting a rotational output of an electric motor by a built-in linear motion conversion mechanism and outputting a linear motion similar to a hydraulic cylinder.

[0002]

2. Description of the Related Art Conventionally, there has been known an electric actuator capable of converting the rotation output of an electric motor by a linear motion conversion mechanism and outputting a linear motion. Since such an electric actuator mainly operates a work or the like using its linear motion output, it has many uses similar to a fluid pressure cylinder.

However, in a general electric cylinder for the purpose of feeding, the rotation output of a drive motor is transmitted to a thrust shaft of a linear motion conversion mechanism via drive transmission means such as a sprocket wheel and a timing belt. Is simultaneously transmitted to the thrust nut as a rotational force. The thrust nut is screwed into a thrust rod whose rotation is restricted, and converts the rotational force into a thrust to generate a thrust. Due to the serial combination of the thrust shaft, the thrust nut and the thrust rod, the linear motion conversion mechanism had to be long. Moreover, the electric motor is mounted on the side of the frame in which such a linear motion conversion mechanism is accommodated. Therefore, it was not easy to make the electric cylinder as small as a hydraulic cylinder.

[0004] Rather, the electric cylinder is utilized because it is suitable for applications having a long linear movement distance, that is, a long stroke, and has been recognized as disadvantageous for applications having a short stroke. This is because, for example, to obtain an output stroke of only several tens of mm, the installation space of the electric cylinder body is occupied several times as large. When this is a hydraulic cylinder, a half of the main body installation space is sufficient.

[0005] However, the electric cylinder has an advantage that no additional equipment such as a fluid pressure source such as a fluid pressure cylinder is required. Therefore, if a short stroke can be obtained with a short electric cylinder, it is useful in many fields.

As a prior art related to miniaturization of this type of apparatus, a female screw is provided inside a hollow shaft of an electric motor, and a male screw is incorporated therein so as to enter and exit in the axial direction. Electric operating devices are already provided.

Further, "Yaskawa Electric" Technical Report No. 1970
On pages 4 and 256, a motor finger in which an electric motor and a rotary linear motion conversion mechanism are integrated and a rotary inertia energy of the electric motor is absorbed by a thrust damper is presented. FIG. 12 shows a main part MF of the electric operation device. This device is provided with a screw I of a motor shaft responsible for the linear motion of the rotary linear motion conversion mechanism and a screw J of a thrust rod. When the screw J comes into contact with an external work or the like and the movement is suddenly stopped, the motor shaft moves forward and backward because of the engagement of the screw I and the screw J by the rotational inertia energy of the electric motor rotor P interlocked with the screw. The thrust damper W is a coil spring disposed between the front and rear ball bearings and the rotor on the motor shaft. The moat finger is not intended for general feeding operation, but has a structure suitable for a work clamp.

However, in these prior arts, a long coil spring is required inside the motor, so that the size of the electric cylinder could not be further reduced. In addition, if a coil spring is arranged as a thrust damper in the electric motor, the resilience of the coil spring applies a load in the thrust direction to both ball bearings on the motor shaft, and the life of the ball bearings is shortened. there were. Another problem is that the linearly moving thrust rod is displaced by an external force applied in the axial direction of the rod, and the stop position is changed. Therefore, there is a need for a new structure as a short stroke electric cylinder suitable for both the feeding operation and the work clamp.

[0009]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above problems, and has as its object to provide a small-sized electric cylinder suitable for short stroke applications.

[0010]

In order to solve such a problem, an electric cylinder according to the present invention has the following configuration.

According to the first aspect of the present invention, there is provided an electric cylinder comprising a frame, a bracket for clamping the frame from front and rear, a stator fixed in the frame, a rotor rotating inside the frame, And a motor shaft that carries the rotation of the motor shaft. The motor shaft is provided with bearings at both ends, and a female screw is carved inside the thrust rod, and a male screw is carved on the latter half of the thrust rod. In the electric cylinder engaged with the female screw of the motor shaft, an elastic block is disposed on the inner surface of the bracket, a transmission member is disposed in contact with the elastic block, and the bearing is disposed via the transmission member. And the thrust rod has a co-rotation prevention guide mechanism.

Therefore, according to the present invention, even if the thrust of the thrust rod receives a reaction force from the outside, it is not converted into reverse rotation by the automatic stop action of the screw, and the motor shaft is formed in the form of thrust. Transmitted to the bearings. The bearing presses the transmission member by its outer ring, and the transmission member presses and compresses the elastic block.

The amount of compression of the elastic block is determined by the efficiency of the screw such as a thrust rod, the torque generated by the motor, the rotational inertia energy of the motor rotor, or the rigidity of the external mechanism. Then, when the elastic block is compressed, the restoring force becomes a thrust, and a state in which the work can be performed outside even when the motor is not energized. The amount of compression corresponds to thrust, but the value is not excessive, not shocking, and is moderate. As a result, the external thread of the thrust rod and the internal thread of the motor shaft are prevented from being tightened with excessive torque beyond the predetermined performance. Therefore, these screws do not bite and fix (lock) or damage the screws. In addition, the work clamping force can be maintained even when the motor is not energized.

According to a second aspect of the present invention, there is provided an electric cylinder comprising the above-described frame, a bracket for clamping the frame from front and rear, a stator fixed in the frame, a rotor rotating inside the frame, A motor shaft coupled to the rotor for supporting the rotation of the motor shaft. Bearings are combined at both ends of the motor shaft, and a female screw is engraved on the inner rear side of the motor shaft. In an electric cylinder in which a screw is cut and engaged with a female screw of the motor shaft, a bearing bracket is provided inside the bracket, and a bearing and a preload plate are axially moved in a central hole of the bearing bracket. And the elastic block is compressed and arranged on the inner surface of the bracket, and the elastic block can press the outer ring of the bearing via the preload plate. Te, always is in contact with the bearing bracket and has a zero or very small clearance between the outer ring of the bearing, 該推 force rod is characterized by having a co-rotation prevention guide mechanism.

Therefore, according to the present invention, even if the thrust of the thrust rod receives a reaction force from the outside, it is not converted into reverse rotation by the automatic stop action of the screw, and the motor shaft is formed in the form of thrust. Transmitted to the bearings. The bearing presses the preload plate by its outer ring, and the preload plate presses and compresses the elastic block. The amount of compression of the elastic block is determined by the efficiency of the screw such as the thrust rod, the generated torque of the motor, the rotational inertia energy of the rotor of the motor, or the rigidity of the external mechanism. Then, when the elastic block is compressed, the restoring force becomes a thrust, and a state in which the work can be performed outside even when the motor is not energized. The amount of compression corresponds to thrust, but the value is not excessive, not shocking, and is moderate. This prevents the male screw of the thrust rod and the female screw of the motor shaft from being tightened with excessive torque. Therefore, these screws do not bite and fix (lock) or damage the screws. In addition, even when the motor power is off, the work clamping force can be maintained using the thrust generated by the compression of the elastic block.

On the other hand, when performing the feed operation, the external reaction force via the thrust rod is a limited amount determined by the load weight and the frictional force. It is set larger than the reaction force value. Therefore, after the completion of the feeding operation, the elastic block is not compressed beyond the preload amount. Also, the screw does not reversely rotate due to the automatic stopping action of the screw. Therefore, the thrust rod is not displaced by the external load and the stop position does not fluctuate, and the feeding operation can be performed accurately.

According to a third aspect of the present invention, there is provided an electric cylinder, comprising: a frame; a bracket for clamping the frame from front and rear; a stator fixed in the frame; a rotor rotating inside the frame; And a motor shaft that carries the rotation of the motor shaft, and the motor shaft is provided with a bearing at both ends thereof, and a female screw is formed on the inner side of the motor shaft. In an electric cylinder which is engraved and engages with an internal thread of the motor shaft, an elastic block is disposed in a compressed state between the bearing bracket and the bracket, and the bearing bracket moves the bearing in the axial direction to zero. The bearing bracket is constrained with a small gap, and the outer periphery of the disk portion of the bearing bracket is moved toward the center of the motor by a retaining ring disposed inside the outer peripheral cylindrical portion of the bracket. It is regulated movement of, and 該推 force rod is characterized by having a co-rotation prevention guide mechanism.

Therefore, according to the present invention, it is possible to dispose the elastic block without increasing the overall length of the electric cylinder. In the electric cylinder according to the fourth aspect of the present invention, the elastic block is a rubber block.

Therefore, according to the present invention, the rotational inertia energy of the motor rotor and the shock applied to the thrust rod from the outside can be absorbed by the elastic deformation of the rubber block. In addition, since the rubber block is used, the energy absorbing mechanism can be made much smaller and less expensive than a metal spring. Further, the rubber block is arranged at a position distant from the stator coil or the rotor where the temperature becomes high. For this reason, the temperature rise is suppressed, and the spring characteristics are kept good for a long period of time. An electric cylinder according to a fifth aspect of the present invention is characterized in that the female screw of the motor shaft and the male screw of the thrust rod are slide screws having a small lead angle, which are formed by a plurality of threads.

Therefore, according to the present invention, the load applied to the thrust rod can be increased. In addition, the automatic stop action of the screw obtained by reducing the lead angle of the screw does not cause reverse rotation of the motor due to an external load, and can maintain the thrust and the position without having to provide an electromagnetic brake. Therefore, the size and cost of the electric cylinder can be reduced.

The electric cylinder according to the present invention is characterized in that a scraper is disposed in the through hole of the thrust rod at the center of the bracket. Therefore, according to the present invention, it is possible to prevent dust and the like from entering the gap between the thrust rod inside the electric cylinder and the engagement screw portion of the motor shaft. Therefore, failure of the electric cylinder can be prevented.

In the electric cylinder according to the present invention, a sliding bearing for the thrust rod is provided in a through hole of the thrust rod at the center of the bracket, and the sliding bearing is a thrust rod. At the same time as carrying a load acting in the direction perpendicular to the thrust rod.

Therefore, according to the present invention, the co-rotation prevention guide mechanism for the thrust rod can be miniaturized. In the electric cylinder according to the eighth aspect of the present invention, the co-rotation prevention guide mechanism connected to the thrust rod has a support arm, a plurality of guide shafts, and a bearing for the guide shaft.

Therefore, according to the present invention, the co-rotation prevention guide mechanism for the thrust rod can be miniaturized. In the electric cylinder according to the ninth aspect of the present invention, at least one of the plurality of guide shafts coupled to the thrust rod via the support arm is provided with a limit switch dog for position detection. A limit switch is arranged on the frame side corresponding to the limit switch dog.

Therefore, according to the present invention, the guide shaft also serves as the thrust rod position detecting means, and does not require a separate limit switch dog mechanism. Therefore, the size and cost of the electric cylinder can be reduced.

In the electric cylinder according to the present invention, the bearing of the guide shaft of the support arm connected to the thrust rod is disposed at the edge of the bracket, and the bearing of the guide shaft is a limit for position detection. The switch and dog are housed inside the outer shape of the motor bracket.

Therefore, according to the present invention, the outer shape of the electric cylinder can be reduced. An electric cylinder according to an eleventh aspect of the present invention is characterized in that a rotary disk of a rotary encoder is connected to a motor shaft, and a detector thereof is arranged on an outer surface of a bracket.

Therefore, according to the present invention, the electric cylinder can be accurately controlled by detecting and utilizing the number of pulses corresponding to the rotation of the motor shaft. In the electric cylinder according to the present invention, a brake plunger is provided in a cylinder provided outside the center hole of the bracket, and a constant sliding brake for pressing the brake plunger against a sliding surface on a rotor side surface is provided. It is characterized by the following.

Therefore, according to the present invention, the motor power supply O
The inertial rotation of the motor shaft from the time of FF is suppressed, and the electric cylinder can be stopped more accurately.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] Next, an embodiment of an electric cylinder 100 according to the present invention will be specifically described. FIG. 1 is a cross-sectional view showing a first embodiment of an electric cylinder 100, and FIG. 2 explains the structure of FIG. 1 in more detail. FIG. 3 explains the operation of the preload plate. 1 and 2
, The electric cylinder 100 has a basic structure including a motor unit that generates a rotational torque, and a motion conversion unit that converts the rotational torque into a linear motion to be used as an axial thrust.

The motor unit includes a stator 2 around which a coil 1 is wound, a rotor 3 rotating inside the stator 2, and a motor shaft 4 coupled to the rotor 3 to carry the rotation. Here, the stator 2 is fixed to the motor frame 5. The motor frame 5 is, for example, cylindrical and both ends are supported by brackets 6 and 7. The brackets 6 and 7 hold the frame 5, and the outer peripheral portions of the brackets 6 and 7 are connected by a plurality of fastening bolts 8.

The motor shaft 4 is supported by a front ball bearing 11 and a rear ball bearing 12. More specifically, the inner race 11a of the front ball bearing 11 is fitted and held in the front small diameter portion 4a of the motor shaft 4, and the inner race 12a of the rear ball bearing 12 is fitted and held in the rear small diameter portion 4b of the motor shaft 4. I have. The central portion inside the front and rear small diameter portions 4a and 4b of the motor shaft 4 is the front and rear small diameter portion 4
The diameter is larger than a and 4b. The front and rear ball bearings 1
The support structure for the outer races 11b and 12b of the first and second 12 will be described later. Further, the ball bearings 11 and 12 can withstand both radial and thrust loads, and are small in size and low in cost.

Next, the motor shaft 4 constituting the motion converter is hollow. A female screw 4c is engraved on the inner rear side of the motor shaft 4. An external thread 15a is engraved on a part of the thrust rod 15, that is, a rear half thereof. The male screw 15a is engaged with the female screw 4c of the motor shaft 4.
The female screw 4c and the male screw 15a are both slide screws. These screws are engraved in a plurality of threads to increase the allowable load. Further, the lead angles of these screws are small so as to have an automatic stop function.

The thrust rod 15 has a cylindrical portion 15b having a smooth surface in the first half thereof. Thrust rod 1
A coupling screw 15c is engraved on the tip portion of 5. Further, the thrust rod 15 penetrates a through hole at the center of the bracket 6, and a scraper 16 is disposed in the through hole. The scraper 16 maintains the smooth surface of the cylindrical portion 15b of the thrust rod 15 by the dust sealing action. Then, dust and the like are prevented from entering the gap between the motor shaft 4 inside the electric cylinder 100 and the engagement screw portion of the thrust rod 15.

A so-called double-armed support arm 21 having a pair of arms is fixed near the tip of the thrust rod 15. A retaining ring 22 is fitted in a fixing groove provided in the thrust rod 15. The retaining ring 22 reinforces the axial holding of the thrust rod 15 and the support arm 21. Therefore, even when the thrust rod 15 is pressed toward the electric cylinder 100 by a large external load such as an abnormal impact, the support arm 21 of the thrust rod 15 is prevented from moving in the axial direction. A cushioning member 23 is fixedly provided on the front surface of the bracket 6. By installing the cushioning member, the support arm 21 and the bracket 6
Can reduce the impact when the collision occurs. Note that the cushioning member 2
3 is preferably made of an elastic material such as a rubber plate.

On the other hand, guide shafts 24 are fixed to symmetrical ends of the support arm 21, respectively. Guide shaft 24
Are guided by a bearing 25 provided on a peripheral portion of the bracket 6. Therefore, the thrust rod 15 is
1 to a bearing 25. Therefore, the rotation of the thrust rod 15 is restricted and can be moved only in the axial direction. Further, the thrust rod 15 can carry a vertical load.

Accordingly, the support arm 21, the guide shafts 24 fixed to both symmetrical ends thereof, and the bearing 25 provided on the peripheral edge of the bracket 6 form a co-rotation prevention guide mechanism for the thrust rod 15. .

Furthermore, not only can the bearings 25 be arranged in pairs or more to increase the load bearing capacity, but also can be arranged in parallel with the thrust rods 15, so that the overall length of the electric cylinder 100 is reduced. In this case, the bearing 25 is a female screw 4 of the motor shaft 4.
Since it is provided at a position forward of c, the bearing 25 can share the lateral moment acting on the thrust rod 15. In addition, the thrust rod 15
Since the eccentric stress is prevented from acting on the motor shaft 4, the screw surfaces of the motor shaft 4 and the thrust rod 15 are evenly brought into contact with each other, so that the desired function can be exhibited.

Referring to FIG. 2, the support structure of the outer race of the front and rear ball bearings 11, 12 will be described. Outer ring 1 of front ball bearing 11
1b is loosely fitted in the cylindrical central hole 13a of the front bearing bracket 13, and similarly, the outer ring 12b of the rear ball bearing 12 is loosely fitted in the cylindrical central hole 14a of the rear bearing bracket 14. In addition, the ball bearings 11 and 12 are slidably supported in the axial direction of the motor shaft 4 on the outer peripheral surfaces of the outer races 11b and 12b. The front and rear bearing brackets 1
The reference numerals 3 and 14 are fixed inside the motor frame 11 in a state of being in close contact with the brackets 6 and 7.

The bracket 6 and the front bearing bracket 1
A circular hole 6 a is formed in the center of the bracket 6 as a space between the bracket 6 and the bracket 3. A circular hole 7a is formed in the center of the bracket 7 as a space between the bracket 7 and the rear bearing bracket 14. The circular hole 6
A circular front elastic block 17 and a preload plate 18 are arranged in a, and an annular rear elastic block 19 and a preload plate 20 are arranged in a circular hole 7 a of the bracket 7. One surface of the preload plate 18 is in contact with the front elastic block 17, and the other surface is in contact with the front bearing bracket 13. Similarly, one surface of the preload plate 20 is in contact with the rear elastic block 19, and the other surface is in contact with the rear bearing bracket 14. A rubber material is suitable for the front and rear elastic blocks 17 and 19. The rubber material is low in cost and can be elastically deformed according to the load, and when formed in a block shape, it can be compact and have the required load-bearing performance. Therefore, the elastic block 1
Suitable as 7 and 19.

A circular hole 6 in the center of the bracket 6
The thickness of the front elastic block 17 in the natural state is larger than the gap GA between the bottom surface 6b of FIG. Therefore, as shown in FIG. 2, the hole bottom surface 6b of the bracket 6 and the preload plate 1
When the elastic block 17 is disposed between the front elastic block 8 and the front elastic block 8, the front elastic block 17 is in a compressed state. Further, the preload plate 18 constantly presses the front bearing bracket 13 with a predetermined pressure, that is, preloads. Similarly, the rear elastic block 19 constantly preloads the rear bearing bracket 14 at a predetermined pressure.

The motor shaft 4 is supported by front and rear ball bearings 11 and 12. The ball bearings 11 and 12 maintain zero to minute gaps (refer to gaps of about 0.1 μm to 5 mm in the present embodiment) between the respective preload plates 18 and 20. As a result, the ball bearings 11 and 12
The movement is regulated and the position is maintained. Therefore, the rotor 3 fixed to the motor shaft 4 is held at a position facing the stator 2. As described above, the advance positions of the preload plates 18 and 20 are regulated by the front and rear bearing brackets 13 and 14.

Therefore, even if the preload plate 18 always preloads the bearing bracket 13, the ball bearing 11 is not necessarily pressed by the preload plate 18. Therefore, a state in which a thrust load is constantly applied to the ball bearing 11 does not occur, and the durability is maintained.

The electric cylinder 100 according to the present embodiment having such a structure operates as follows. Stator 2
Is energized, the rotor 3 and the motor shaft 4 coupled to the rotor 3 rotate integrally therewith. A thrust rod 1 is attached to the female screw 4c of the motor shaft 4.
5 male screws 15a are engaged. Therefore, when the motor shaft 4 rotates, the thrust rod 1
A thrust is generated to move the 5 forward or backward. Such forward movement or backward movement of the thrust rod 15 can be used as it is for feeding or clamping the work. Also,
Even if a load perpendicular to the axial direction is applied to the thrust rod 15, there is no problem in its operation.

When the thrust rod 15 moves forward, for example, to the left by the rotation of the motor shaft 4 and collides with a large load, the reaction force applied to the thrust rod 15 from the outside causes the rotation of the motor shaft 4 to rotate. It is not converted back to motion.
This is due to the automatic stop effect obtained by the thrust rod 15 and the slide screw of the motor shaft 4. That is, because the screw gradient is small, the frictional resistance component becomes larger than the screw rotation component.

As a result, the rightward reaction force externally applied to the thrust rod 15 is applied to the rear ball bearing 1 via the motor shaft 4.
2 is transmitted. The rear ball bearing 12 is pressed from the preload plate 20 only by the outer ring 12b. The preload plate 20 presses the rear elastic block 19 to absorb the reaction force thereof, thereby reducing the impact. Thereby, the thrust rod 15
Of the male screw 15a of the motor shaft 4 and the female screw 4c of the motor shaft 4 are prevented from deviating from the predetermined performance and being tightened with excessive torque. Therefore, the screws do not cause biting and fixing (locking) or breakage of the screws.

The reaction force externally applied to the thrust rod 15 is transmitted to the rear ball bearing 12 via the motor shaft 4, but the preload plate 20 is preloaded by the rear elastic block 19. Therefore, the external reaction force is
The preload plate 20 does not press the rear elastic block 19 when the load is within the range of the rated load of the internal screw 4a and the female screw 4c. This will be described with reference to FIG. In FIG. 3, the motor shaft 4
Presses the preload plate 20 and is displaced by x amount because of + F
This is a case where a reaction force of 0 or more or a tensile force of -F0 or more acts on the thrust rod 15. In addition, the front and rear elastic block 1
The spring constant S = k of 7, 19 is.

Further, by setting the preload F0 to be equal to or higher than the rated load Fr, no displacement is caused by the elastic block 19 under a load equal to or lower than the rated load Fr. To summarize, when F0 is the preload and F is the external load, the following equation x = 0 in the range of | F | ≦ | F0 |. In the range of | F |> | F0 |, the relationship | x | = | (F−F0) / k | is established. As described above, when the load is equal to or less than the rated load Fr, the displacement by the elastic block 19 does not occur, and the position of the motor shaft 4 does not move back and forth.

Therefore, when the load is equal to or less than the rated load Fr, the linearity of the displacement is maintained during the feeding operation. In addition, since the preload by the elastic block 19 does not act on the ball bearing 12, the ball bearing 12 is not always in a state where a thrust load is applied, and its durability can be maintained. The ball bearing 1
Since only the external load 2 needs to receive the external load, a small-sized, low-cost one is good and economical.

As described above, the automatic stop action of the slide screw by the thrust rod 15 and the motor shaft 4 causes
When the power supply to the motor is cut off and the motor shaft 4 stops rotating, the thrust rod is kept in its position. Therefore, a brake device or the like for maintaining rotation is not required.

Next, the return of the electric cylinder 100 will be described. FIG. 4 shows that the motor rotates in the reverse direction and the thrust rod 15
Is retracted, and the workpiece is clamped at a position α before the buffering member 23 at the feed end. Assume that the clamped thrust rod 15 stops at the position of α. Immediately before reaching the position α, the motor power supply is stopped by the operation of a limit switch (not shown). At this time, since the rotor and the like have the moment of inertia I, if the rotational kinetic energy is Em, the relationship Em = (1/2) · I · ω ² is established. Further, even if the thrust rod 15 stops at that position, the inertia energy E
Due to m, the motor shaft 4 rotates the female screw 4c on the inner rear side thereof, advances on the male screw 15a of the thrust rod 15, and presses and deforms the front elastic block 17 by x length.

The relationship between the amount of deformation and the strain energy Es of the front elastic block 17 is as follows. The spring constant of the elastic block 17 is k, the initial compression amount of the elastic block 17 is x ₀ , and the efficiency in the screw tightening direction is When _{y 1, Es = (1/2)} · k · {(x + x 0) 2 - (x 0) 2] = relation _{Em × y 1 = (1/2)} · I · ω 2 × y 1 is Natsutsu. Here, assuming that the tightening thrust in the clamping operation is F1, k · x ₂ (1 + 2x ₀ / x) = y ₁ × I · ω ² , so that the following equation is obtained: F1 = k · (x + x ₀ ) . Then, the thrust F1 generates a screw tightening force in a non-energized state.

Even if the remaining inertial energy Em of the rotor 3 or the like is released, the slide screw is kept pressed even in a non-energized state by the automatic stop function of the slide screw. It does not naturally reverse open.

On the other hand, when the motor current in the loosening direction, the thrust F2, when the lead screw L, and motor starting torque T, the loosening direction of the efficiency of the screw and _{y 2, F2 = (2π /} L) × T × y ₂ . Here, if F2> F1, the female screw 4c of the motor shaft 4 can be started in the reverse rotation by the starting torque of the motor. That is, F
By selecting a small value of the spring coefficient of the elastic block 17 so that 2> F1, it is possible to prevent the screw from being stuck and fixed, and to resume reverse rotation.

On the other hand, if the spring coefficient of the elastic block 17 is set to a large value, F2 <F1, and the female screw 4c of the motor shaft 4 is fixed, and the reverse rotation cannot be resumed. When the required output of the motor is determined, the outer diameter and length of the motor are determined. If the main body length of the motor is Lo, the motor shaft 4
The engagement length between the female screw 4c of the thrust rod 15 and the male screw 15a of the thrust rod 15 must not be shorter than the minimum engagement length A determined from the PV (allowable load) value of the contact surface.

Assuming that the effective shaft length of the female screw 4c of the motor shaft 4 is L and the amount of distortion of the elastic block 17 is δ, the stroke S is S = (１ ／) · (LA−δ) δ ≒ 0 Therefore, S ≒ (1/2) · (LA). Therefore, the effective shaft length L of the female screw 4c of the motor shaft 4 can be ensured to be large near the main body length Lo of the motor.

Therefore, according to the present embodiment, the following effects can be obtained. (1) According to the electric cylinder 100 of the present embodiment, the female screw 4c of the motor shaft 4 has the male screw 15a of the thrust rod 15
Are engaged and the male screw 15a is built in the motor, so that the whole is downsized. In such a case, the inertia energy of the rotor 3 of the motor is absorbed by the small elastic block 17, so that the electric cylinder 100
Can be operated stably without increasing the size.

(2) The thrust rod 15 is guided by a support arm 21 as a co-rotation prevention guide mechanism, and a guide shaft 24 and a bearing 25 at the end of the support arm 21, so that a radial load can be obtained. Is carried. In addition, since the co-rotation of the thrust rod 15 that rotates with the load is prevented, there is no limitation in connecting the thrust rod 15 to the work. Therefore, the use of the electric cylinder 100 can be expanded.

(3) The rated load F of the thrust rod 15
Even if a load of r or more is applied, the engagement screw is not fixed by the preload ring and the elastic block 19. Therefore, the operation of the work clamp and the like can be performed stably. In addition, when the load is equal to or less than the rated load Fr, the linearity of the displacement is maintained during the feeding operation.

(4) The scraper 16 maintains the smooth surface of the cylindrical portion 15b of the thrust rod 15 by the dust sealing action. Therefore, dust does not enter the screw engaging portion, and failure of the screw engaging portion is prevented.

(5) The thrust rod 15 and the motor shaft 4
When the power to the motor is cut off and the motor shaft 4 stops rotating,
The thrust rod 15 is kept in its position. Therefore, a brake device or the like for holding the rotation is not required, and the cost of the electric cylinder 100 can be reduced. [Second Embodiment] Next, a second embodiment of the electric cylinder 110 of the present invention will be described with reference to the drawings. FIG. 5 is a sectional view showing the electric cylinder 110 of the present embodiment. The electric cylinder 110 of the present embodiment
The basic structure of the motor unit, the motor shaft, the motion conversion unit, and the like is the same as that of the first embodiment, and a sliding bearing 31 for the thrust rod 15A is added. Therefore,
Detailed description of the common part is omitted.

This embodiment is characterized in that the thrust rod 15A
A sliding bearing 31 is provided in the center hole of the bracket 6A. The sliding bearing 31 guides the linear motion of the thrust rod 15A and, at the same time, carries a load acting in a direction perpendicular to the thrust rod 15A. Therefore, the thrust rod 15A is connected to the bearing 2 of the guide shaft 24A of the support arm 21A.
It is guided by 5A and the sliding bearing 31. This guide prevents the thrust rod 15A from rotating together with the load and prevents the thrust rod 15A from rotating in a direction perpendicular to the thrust rod 15A. Therefore, one bearing 25A for the guide shaft 24A is sufficient, and the support arm 21A may be one-armed. In the case where the anti-rotation function of the thrust rod 15A is provided in the counterpart load device, the support arm 2
1A, the guide shaft 24A, and the bearing 25A can be omitted.

Therefore, according to the electric cylinder 110 of the present embodiment, the structure of the co-rotation prevention guide mechanism including the support arm 21A, the guide shaft 24A, and the bearing 25A thereof can be simplified and downsized. [Third Embodiment] Next, a third embodiment of the electric cylinder 120 of the present invention will be described with reference to the drawings. FIG. 6 is a sectional view showing the electric cylinder 120 of the present embodiment. The electric cylinder 120 according to the present embodiment
The basic structure of the motor unit, the motor shaft, the motion conversion unit, and the like is the same as that of the first embodiment, and the front elastic block 17B
Is changed to a smaller size.

The feature of this embodiment is that the front elastic block 1
7B is disposed between the front bearing bracket 13B and the front bracket 6B. The front bearing bracket 13B has a disk portion 13Ba and a cylindrical hole 13Bc. A ball bearing 11B is held in the cylindrical hole 13Bc, and the outer peripheral portion of the cylindrical hole 13Bc is loosely fitted to the cylindrical central hole 6Ba of the bracket 6B so as to be movable in the axial direction.

An annular front elastic block 17B is arranged between the bracket 6B and the disk portion 13Ba on the outer peripheral side of the front bearing bracket 13B. The front elastic block 17B is compressed by an amount corresponding to a necessary preload. Therefore, the front bearing bracket 13B is constantly pressed inside the motor by the front elastic block 17B. On the other hand, the outer circumference 13Ba of the disk portion of the front bearing bracket 13B is restricted from moving in the center direction of the motor by a retaining ring 41 disposed inside the outer cylindrical portion of the bracket 13B. That is, in the electric cylinder 120 of the present embodiment, the front bearing bracket 13B acts as a preload plate. Therefore, the motor shaft is connected to the front and rear ball bearings 11.
It is held at a position between B and 12B.

Therefore, according to the electric cylinder 120 of the present embodiment, the front elastic block 17B is
The front elastic block 17B can be installed in parallel with the front ball bearing 11B without being installed in series with B in the axial direction. Therefore, the length in the axial direction can be shortened accordingly, and the electric cylinder 12
0 can be shortened. In addition, since the load in the thrust direction is not normally applied to the two ball bearings 11B and 12B on the motor shaft by the resilience of the elastic block, the life of the ball bearings can be maintained. [Fourth Embodiment] Next, a fourth embodiment of the electric cylinder 130 of the present invention will be described with reference to the drawings. FIG. 7 is a sectional view showing the electric cylinder 130 of the present embodiment. The electric cylinder 130 of the present embodiment
The structures of the motor unit, the motor shaft, and the motion conversion unit are not different from those of the first embodiment, and thus detailed description thereof is omitted. This embodiment is characterized by the elastic block 17, the transmission ring 18, and the ball bearing 1 of the motor shaft 4C.
1C is arranged in the central hole 6Ca of the bracket 6C.

In the electric cylinder 130 of the present embodiment, a ball bearing 11C is provided in the central hole 6Ca of the bracket 6C.
A transmission ring 18C is disposed in contact with the outer race of the vehicle, and an annular front elastic block 17C is disposed in contact with the transmission ring 18C. Similarly, the central hole 7C of the bracket 7C
a has a transmission ring 20C in contact with the outer ring of the ball bearing 12C.
Are disposed, and an annular rear elastic block 19C is disposed in contact with the transmission ring 20C. Front and rear ball bearing 11
C and 12C are loosely fitted in the central holes 6Ca and 7Ca, respectively, and are movable in the axial direction. The annular front elastic blocks 17C, 19C are provided with front and rear ball bearings 11C,
It is arranged so as to sandwich 12C.

A rubber material that elastically deforms in proportion to stress is suitable for the elastic blocks 17C and 19C. Such a rubber block is small in size, has the required load resistance, and is low in cost. Therefore, it is suitable as elastic blocks 17C and 19C.

The rightward reaction force applied to the thrust rod 15C from the outside is transmitted to the rear ball bearing 12C via the motor shaft 4C. The rear ball bearing 12C presses the elastic block 19C via the transmission ring 20C. Thereby, the reaction force of the thrust rod 15C is absorbed, and the impact is reduced. Then, the external thread 15a of the thrust rod 15C and the internal thread 4c of the motor shaft 4C are prevented from deviating from their predetermined performance and being tightened with excessive torque. Therefore, they do not cause the screws to be stuck and fixed or the screws to be damaged.

Therefore, according to the electric cylinder 130 of the present embodiment, the front and rear brackets 6C and 7C need only have a simple one-piece structure, so that the size and cost can be further reduced. Therefore, electric cylinder 130 of the present embodiment
Are particularly suitable for work clamp applications. [Fifth Embodiment] FIG. 8 is a sectional view showing an electric cylinder 140 according to a fifth embodiment, and FIG. 9 is a front view of the electric cylinder 140 as viewed from the thrust rod 15D.

This embodiment is characterized in that the thrust rod 15D
In the structure of the support arm 21D. In the electric cylinder 140 of the present embodiment, the bearing 25D of the guide shaft 24D of the support arm 21D is connected to the edge 6D of the bracket 6D.
a.

Therefore, according to the electric cylinder 140 of the present embodiment, the guide shaft 24D and the bearing 25D are housed in the outer shape of the motor, so that the overall size is reduced.
Further, by providing a limit switch dog 26D for position detection by sharing the guide shaft 24D and arranging the limit switch 27 on the corresponding frame side, a small-sized and low-cost electric signal of the position can be transmitted. Sixth Embodiment FIG. 10 is a cross-sectional view showing an electric cylinder 150 according to a sixth embodiment.

The feature of the present embodiment is that the sliding brake is always incorporated in one of the brackets (7E). Here, a brake plunger 52 is loosely fitted in a cylinder 51 provided outside the central hole 7Ea of the bracket 7E. The end of the cylinder 51 is sealed with a plug 54. A coil spring 53 is interposed in a space defined by the brake plunger 52 and the plug 54. The brake plunger 52 is pressed against the sliding surface 55 on the side surface of the rotor 3E by the urging force of the coil spring 53. The sliding surface 55 is a flat sliding surface on the side surface of the secondary coil of the rotor 3E fixed to the motor shaft 4E. The sliding surface 55 is provided with the brake plunger 52.
, A slight frictional resistance is generated on the sliding surface.

Therefore, according to the electric cylinder 150 of the present embodiment, the braking time after the feeding operation can be shortened, and the stopping accuracy of the thrust rod 15E can be increased. Further, even when it is difficult to hold the position because the external stop does not keep the automatic stop function of the male screw of the thrust rod 15E and the female screw 4c of the motor shaft 4E, the holding force can be compensated. Seventh Embodiment FIG. 11 is a sectional view showing an electric cylinder 160 according to a seventh embodiment. A feature of the present embodiment is that a rotary encoder is integrally mounted on the motor shaft 4F. The rear end of the motor shaft 4F protrudes from the central through hole of the bracket 7F, and the motor shaft 4F
A rotary disk 61 is connected to a rear end of the rotary disk. Also,
The detector 62 is arranged in a groove on the outer surface of the bracket 7F. The detector 62 detects an angle mark printed on the rotary disk 61 and outputs a pulse. In addition,
The rotary disk 61 of the rotary encoder is covered by a protective cover 63.

By counting the number of pulses detected by the detector 62 of the rotary encoder by a control device (not shown), the motor can be controlled to stop at an arbitrary position. In that case, the position of the dog 26F connected to the thrust rod 15F can be detected by a limit switch (not shown) to detect the limit point or the origin of forward and backward movement of the thrust rod 15F.

Therefore, according to the electric cylinder 160 of the present embodiment, the thrust rod 15 of the electric cylinder 160
It becomes easy to control the stop position of F. The present invention is not limited to these embodiments, and various changes can be made without departing from the gist of the present invention. For example, depending on the use of the electric cylinder, it is not necessary to provide the elastic block on both the front and rear brackets. Also, a through hole may be provided in the rear bracket to extend the other end of the thrust rod, and the thrust rod may have a non-circular cross section to prevent its rotation.

Next, in addition to the technical ideas described in the claims, the technical ideas grasped by the above-described embodiment will be listed below. (1) a frame, a bracket for clamping the frame from front and rear, a stator fixed in the frame, a rotor rotating inside the stator, a hollow motor shaft integrally rotating with the rotor, Bearings provided at both ends of the motor shaft, and a thrust rod inserted into the motor shaft, a female screw provided inside the motor shaft, and a male screw provided at a part of the thrust rod. Is an electric cylinder, wherein an elastic member is disposed on the inner surface of the bracket, a transmission member is disposed in contact with the elastic member, and a part of the bearing is pressed through the transmission member. An electric cylinder configured to be able to move.

(2) A frame, a bracket for holding the frame from front and rear, a stator fixed in the frame, a rotor rotating inside the stator, and a hollow motor shaft integrally rotating with the rotor. And a bearing provided at both ends of the motor shaft, and a thrust rod inserted into the motor shaft, a female screw provided inside the motor shaft, and provided at a part of the thrust rod. An electric cylinder in which a male screw is engaged, wherein said thrust rod has a co-rotation preventing and guiding function mechanism.

(3) A frame, a bracket for holding the frame from front and rear, a stator fixed in the frame, a rotor rotating inside the stator, and a hollow motor shaft integrally rotating with the rotor. And a bearing provided at both ends of the motor shaft, and a thrust rod inserted into the motor shaft, a female screw provided inside the motor shaft, and provided at a part of the thrust rod. An electric cylinder in which a male screw is engaged, wherein a bearing bracket is provided inside the bracket, and the bearing is fitted in a central hole of the bearing bracket so as to be movable in the axial direction. A preload member is arranged between the bracket and a bracket, and an elastic member is compressed and arranged on the inner surface of the bracket. An electric cylinder characterized in that the cylinder is always in contact with the bearing bracket so that the portion can be pressed, and a zero to minute gap is maintained between the elastic block and a part of the bearing.

According to the first aspect of the present invention, the elastic block is disposed on the inner surface of the bracket for holding the motor frame from the front and back, and the transmitting member is disposed in contact with the elastic block, and the transmitting member is disposed via the transmitting member. The outer ring of the bearing can be pressed, and the thrust rod has a co-rotation prevention guide mechanism. Therefore, according to the present invention, the elastic block can absorb the impact due to the external load transmitted from the thrust rod, and can stably operate the electric cylinder to reduce its size.

According to the second aspect of the present invention, a bearing bracket is provided inside a bracket for holding the motor frame from the front and rear, and a bearing and a preload plate are fitted in the center hole of the bearing bracket so as to be movable in the axial direction. The elastic block is compressed and arranged on the inner surface of the bracket for holding the frame from front and rear. The elastic block is capable of pressing the outer ring of the bearing via the preload plate, is always in contact with the bearing bracket, and the thrust rod has a co-rotation preventing guide mechanism. Therefore, according to the present invention, the action of the preload plate prevents the external thread of the thrust rod and the internal thread of the motor shaft from being tightened with excessive torque. Therefore, the screws are not stuck and locked (locked) or the screws are not damaged, and the screw engagement is stabilized. Further, even when the external load fluctuates, the linearity of the operating speed of the thrust rod can be maintained.

According to the third aspect of the present invention, a bearing bracket is provided inside a bracket for holding the motor frame from front and rear, and a bearing and a preload plate are fitted in a central hole of the bearing bracket so as to be movable in the axial direction. The elastic block is compressed and arranged on the inner surface of the bracket for holding the frame from front and rear. The elastic block is capable of pressing the outer race of the bearing via the preload plate, and is always in contact with the bearing bracket. Therefore, according to the present invention, the elastic blocks can be arranged without increasing the overall length of the electric cylinder.

According to the fourth aspect of the present invention, the elastic block is disposed on the inner surface of the bracket for holding the motor frame from front and rear, and the elastic block is a rubber block. Therefore, according to the present invention, the rotational inertia energy of the motor rotor and the shock applied to the thrust rod from the outside can be absorbed by the elastic deformation of the rubber block. Also,
Since the rubber block is used, the energy absorbing mechanism can be made much smaller and less expensive than a metal spring.

According to the fifth aspect of the present invention, the female screw of the motor shaft and the male screw of the thrust rod are slide screws having a small lead angle and formed by a plurality of threads. Therefore, according to the present invention, the load applied to the thrust rod can be increased. In addition, since the screw has an automatic stop function, the motor does not rotate backward due to an external load, and thrust and position can be maintained without installing an electromagnetic brake, and the electric cylinder can be reduced in size and cost. it can.

According to the sixth aspect of the present invention, the scraper is disposed in the through hole of the thrust rod at the center of the motor bracket. Therefore, according to the present invention, it is possible to prevent dust and the like from entering the gap between the thrust rod inside the electric cylinder and the engagement screw portion of the motor shaft, thereby preventing failure of the electric cylinder.

According to the seventh aspect of the present invention, a slide bearing for the thrust rod is provided in the through hole of the thrust rod at the center of the bracket. Therefore, according to the present invention, since the sliding bearing guides the linear motion and at the same time carries the load acting in the direction perpendicular to the thrust rod, the anti-corotating guide mechanism for the thrust rod having the same function is miniaturized. Can be

In the invention according to claim 8, the bearings of the plurality of guide shafts of the support arm of the co-rotation prevention guide mechanism connected to the thrust rod are arranged on the bracket. Therefore, according to the present invention, the co-rotation prevention guide mechanism for the thrust rod can be downsized, and the motor can be downsized.

According to the ninth aspect of the present invention, at least one of the plurality of guide shafts connected to the thrust rod via the support arm is provided with a limit switch dog for position detection. A limit switch is arranged on the frame side corresponding to the limit switch dog. Therefore, according to the present invention, the guide shaft also serves as the thrust rod position detecting means, and a separate limit switch dog mechanism is not required, so that the size and cost of the electric cylinder can be reduced.

According to the tenth aspect of the present invention, the bearing of the guide shaft of the support arm connected to the thrust rod is disposed at the edge of the bracket, and the bearing of the guide shaft is a limit switch for position detection, It is housed inside the outer shape of the motor bracket together with the dog. Therefore, according to the present invention, the outer shape of the electric cylinder can be reduced.

According to the eleventh aspect of the present invention, the rotary disk of the rotary encoder is connected to the motor shaft, and the detector is disposed on the outer surface of the bracket. Therefore, according to the present invention, the electric cylinder is accurately controlled by detecting and utilizing the number of pulses corresponding to the rotation of the motor shaft.

According to the twelfth aspect of the present invention, the brake plunger pressing mechanism is provided in the cylinder provided outside the center hole of the bracket, and the constant sliding brake for pressing the brake plunger against the sliding surface on the side of the rotor is provided. It has become. Therefore, according to the present invention, the motor power is turned off.
The inertia rotation of the motor shaft from the time point is suppressed, and the electric cylinder can be stopped more accurately.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of an electric cylinder according to the present invention.

FIG. 2 is a sectional view illustrating the structure of FIG. 1 in further detail.

FIG. 3 is a table illustrating the operation of a preload plate of the electric cylinder according to the present invention.

FIG. 4 is a sectional view illustrating the operation of the electric cylinder according to the present invention.

FIG. 5 is a sectional view showing a second embodiment of the electric cylinder according to the present invention.

FIG. 6 is a sectional view showing a third embodiment of the electric cylinder according to the present invention.

FIG. 7 is a sectional view showing a fourth embodiment of the electric cylinder according to the present invention.

FIG. 8 is a sectional view showing a fifth embodiment of the electric cylinder according to the present invention.

FIG. 9 is a front view showing an electric cylinder according to a fifth embodiment of the present invention.

FIG. 10 is a sectional view showing an electric cylinder according to a sixth embodiment of the present invention.

FIG. 11 is a sectional view showing an electric cylinder according to a seventh embodiment of the present invention.

FIG. 12 is a sectional view of a main part of a conventional electromagnetic actuator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Coil 2 Stator 3 Rotor 4 Motor shaft 4a Internal screw 5 Motor frame 6 Bracket 7 Bracket 11 Ball bearing 12 Ball bearing 13 Front bearing bracket 14 Rear bearing bracket 15 Thrust rod 15a Male screw 17 Elastic member 18 Preload plate 18A Transmission ring 19 Elasticity Member 20 Preload plate 21 Support arm 24 Guide shaft 25 Bearing 100 Electric cylinder

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Osamu Otani 3005 Hayasaki, Kita-gaiyama, Komaki, Aichi Prefecture Inside (72) Inventor Shin Shin Ito 3005, Hayasaki, Kita-gaiyama, Komaki-shi, Aichi Prefecture KK F term (reference) 5H607 AA04 BB01 BB14 CC01 CC03 DD02 DD03 EE53

Claims (12)

[Claims] 1. A frame, a bracket for holding the frame from front and rear, a stator fixed in the frame, a rotor rotating inside the motor, and a motor shaft coupled to the rotor to carry the rotation. The motor shaft has bearings combined at both ends thereof and a female screw is formed in the inside thereof. In the electric cylinder, an elastic block is disposed on the inner surface of the bracket, a transmission member is disposed in contact with the elastic block, and the outer ring of the bearing can be pressed through the transmission member.
An electric cylinder, wherein the thrust rod has a co-rotation prevention guide mechanism. 2. A frame, a bracket for clamping the frame from front and rear, a stator fixed in the frame, a rotor rotating inside the motor, and a motor shaft coupled to the rotor to carry the rotation. The motor shaft has bearings combined at both ends thereof and a female screw is formed in the inside thereof. In the electric cylinder, a bearing bracket is provided inside the bracket, a bearing is fitted in a central hole of the bearing bracket so as to be movable in the axial direction, and a preload plate is provided between the bracket and the bearing bracket. And an elastic block is compressed and arranged on the inner surface of the bracket, and the elastic block can press an outer ring of the bearing via the preload plate,
An electric cylinder, which is always in contact with the bearing bracket, has a zero to minute clearance with the outer ring of the bearing, and the thrust rod has a co-rotation prevention guide mechanism. 3. A frame, a bracket for holding the frame from front and rear, a stator fixed in the frame, a rotor rotating inside the motor, and a motor shaft coupled to the rotor to carry the rotation. The motor shaft is provided with bearings at both ends thereof, and a female screw is formed on the inner side of the inside thereof. In the engaged electric cylinder, a resilient block is compressed and arranged between the bearing bracket and the bracket, and the bearing bracket restrains the bearing with zero to minute clearance in the axial direction. In addition, the outer periphery of the disk portion of the bearing bracket is restricted from moving in the center direction of the motor by a retaining ring disposed inside the outer peripheral cylindrical portion of the bracket. The electric cylinder has a co-rotation prevention guide mechanism. 4. The electric cylinder according to claim 1, wherein the elastic block is a rubber block. 5. The motor according to claim 1, wherein the female screw of the motor shaft and the male screw of the thrust rod are slide screws having a small lead angle and formed by a plurality of threads.
The electric cylinder according to any one of the above. 6. The electric cylinder according to claim 1, wherein a scraper is provided in a through hole of the thrust rod at a central portion of the bracket. 7. A sliding bearing for a thrust rod is provided in a through hole of the thrust rod at a central portion of the bracket,
4. The sliding bearing according to claim 1, wherein said sliding bearing guides a linear movement through a cylindrical portion of a smooth surface of the thrust rod and carries a load acting in a direction perpendicular to the thrust rod. An electric cylinder according to any of the claims. 8. The electric cylinder according to claim 1, wherein the co-rotation prevention guide mechanism has a support arm, a plurality of guide shafts, and bearings for the guide shafts. 9. A limit switch dog for position detection is provided on at least one of the plurality of guide shafts constituting the co-rotation prevention guide mechanism, and a limit switch is arranged on the corresponding frame side. The electric cylinder according to any one of claims 1 to 3, wherein the electric cylinder is provided. 10. The motor according to claim 1, wherein a bearing of a guide shaft of the support arm connected to the thrust rod is arranged at an edge of the bracket, and the bearing of the guide shaft is housed in an outer shape of the motor. The electric cylinder according to claim 3. 11. The electric cylinder according to claim 1, wherein a rotary disk of a rotary encoder is connected to the motor shaft, and a detector thereof is disposed on an outer surface of the bracket. 12. The brake plunger is provided in a cylinder provided outside the center hole of the bracket, and a constant sliding brake is provided for pressing the brake plunger against a sliding surface on a rotor side surface. 2. The electric cylinder according to 1.