Electric actuator expanded with sensor and electronic brake

An electric actuator that is capable of driving a motor in a cylindrical structure, such that the electric actuator itself can be expanded. The electric actuator includes: a motor for driving the electric actuator and a screw cylinder for connecting a shaft of the motor to a connecting part and for surrounding the external surface of the motor. The screw cylinder has right-handed and left-handed screw recesses formed thereon, and has first and second ball screw nuts. The first ball screw nut has a first electronic brake mounted thereon and the second ball screw nut has a second electronic brake mounted thereon, thereby enabling a non-stop reciprocating linear movement. An outside cylinder is provided with thrust bearings that are in contact with the first and second ball screw nuts, and is provided with a sensor that is disposed on the surface of a fixed part thereof for measuring the movement distance of the screw cylinder, thereby enabling the first and second electronic brakes to control the operations of the first and second ball screw nuts.

RELATED APPLICATIONS

This is a U.S. National Phase Application under 35 USC 371 of International Application PCT/KR03/00171, filed on 27 Jan. 2003.

FIELD OF THE INVENTION

The present invention relates to an electric actuator, and more particularly, to an electric actuator that is capable of driving a motor in a cylindrical structure, such that the electric actuator itself can be expanded.

BACKGROUND OF THE INVENTION

A conventional electric actuator is moved on a fixed frame by using convey equipment that is attached thereon, within the length of the frame, such that it has no function of self-expanding like an oil hydraulic cylinder or pneumatic cylinder.

Moreover, the conventional electric actuator should stop by the application of the load according to the performance of its own motor, at the time of rotating in a backward direction.

SUMMARY OF THE INVENTION

One object of the present invention is to provide an electric actuator that has a function of self-expanding, driven by an electric motor and carries out a reverse rotation at a high speed without any stop.

This and other objects are attained in accordance with one aspect of the invention directed to an electric actuator that includes: a motor for driving the electric actuator and a screw cylinder for connecting a shaft of the motor to a connecting part and for surrounding the external surface of the motor. The screw cylinder has right-handed and left-handed screw recesses formed thereon and first and second ball screw nuts. The first ball screw nut has a first electronic brake mounted thereon, and the second ball screw nut has a second electronic brake mounted thereon, thereby enabling a non-stop reciprocating linear movement. An outside cylinder is provided with thrust bearings that are in contact with the first and second ball screw nuts and is provided with a sensor that is disposed on the surface of a fixed part thereof for measuring the movement distance of the screw cylinder, thereby enabling the first and second electronic brakes to control the operations of the first and second ball screw nuts.

DETAILED DESCRIPTION OF THE DRAWINGS

Now, an explanation of the preferred embodiment of the present invention will be given with reference to accompanying drawings.

As shown inFIG. 1, a motor1on which a fixed part17is mounted is connected to a screw cylinder3with the help of a connecting groove5coupled with the shaft thereof. Mounting the bearings15on the both sides of the outer surface of the motor1enables a motor case and the screw cylinder3to be all moved.

The screw cylinder3is provided with a ball bearing14on the both sides of the one end thereof for the purpose of smoothly moving an outside cylinder2.

The screw cylinder3is also provided with screw recesses4formed thereon, through each of which a ball is guided. In this case, the screw recesses4are formed in such a manner that they start from the one end of the screw cylinder3and arranged in the directions of right-handed and left-handed screws in the condition where they are twice crossed to each other in the directions of the right-handed and left-handed screws during one rotation.

The outside cylinder2is provided with a first ball screw nut6that has the ball in the direction of the right-handed screw in the inner diameter thereof and a second ball screw nut9that has the ball in the direction of the left-handed screw in the inner diameter thereof. The first ball screw nut6includes a first electronic brake8mounted thereon, and the second ball screw nut9includes a second electronic brake7mounted thereon.

As shown inFIG. 5, the first electronic brake8is provided with sliding rods22and springs10on the lower portion of the sliding rods that are disposed to be separated at intervals of 90°, and the first ball screw nut6is formed in such a manner that the ball19is endlessly rotated in the size of one rotation.

As shown inFIG. 4, a sensor13connects its output line to a distance output signal unit and a control unit, and the first and second electronic brakes8and7are connected to the control unit, thereby building a command input circuit.

Now, an explanation of the operation embodiment of the electric actuator according to the present invention will be given.

As illustrated inFIG. 3, if the motor1is rotated in the direction of the right-handed screw at the front view of its shaft after the application of power to the first electronic brakes8and7is made, the screw cylinder3is rotated in the direction of the right-handed screw when viewed in the same direction. At this time, the motor1is in the fixed state by the fixed part17.

If the application of the signal to the first electronic brake8stops while the screw cylinder3is being rotated in the direction of the right-handed screw, the first electronic brake8is moved along slide grooves21by means of the springs10thus to brake the first ball screw nut6, with the result that the first ball screw nut6is fixed. Thereby, the first ball screw nut6with the ball in the direction of the right-handed screw receives the load applied according to the rotation of the screw cylinder3to transmit the pressure against a thrust bearing11, such that the screw cylinder3is moved toward the sensor13.

At this time, the sensor13transmits a measured distance signal to the control unit, which is used as next data information. If the screw cylinder3is to be moved in the opposite direction to the sensor13, the power is applied to the first electronic brake8thus to enable an electric current to flow to the second electronic brake7. Thereby, the second electronic brake7is operated by the springs10, such that the second ball screw nut9is stopped. At this time, the screw cylinder3receives the load of the second ball screw nut9with the ball guided in the direction of the left-handed screw during its rotation and thus applies the load to the thrust bearing11that is in contact with the second ball screw nut9, while the second ball screw nut9is stopped by the operation of the ball guided in the direction of the left-handed screw. As a result, the screw cylinder3is moved to the opposite direction to the sensor13. In this case, the first ball screw nut6is freely rotated along with the screw cylinder3, applying somewhat load to the thrust bearing11.

If there is a need for stopping the rotation of the screw cylinder3, the power to each electronic brake is cut off to thereby stop the operation of each ball screw nut.

When the power is cut off, in normal cases, limitations to the expansion of the electric actuator may occur, such that its generally original shape can be kept.

The thrust bearings11are differently arranged in accordance with the rotating directions of the motor1and the directions of the first and second ball screw nuts6and9, which is illustrated inFIGS. 6A to 6C.

As shown inFIG. 6A, in the case where the motor is rotated in the direction of the right-handed screw, when the first ball screw nut6is disposed in the direction of the right-handed screw and the second ball screw nut9is disposed in the direction of the left-handed screw, the thrust bearings11are formed in the both sides of each of the first and second ball screw nuts6and9.

As shown inFIG. 6B, in the case where the motor is rotated in the direction of the right-handed screw, when the first ball screw nut6is disposed in the direction of the left-handed screw and the second ball screw nut9is disposed in the direction of the right-handed screw, the thrust bearings11are formed in the insides of the first and second ball screw nuts6and9.

In the same manner as above, in the case where the motor is rotated in the direction of the left-handed screw, when the first ball screw nut6is disposed in the direction of the right-handed screw and the second ball screw nut9is disposed in the direction of the left-handed screw, the thrust bearings11are formed in the insides of the first and second ball screw nuts6and9, as shown inFIG. 6C.

Also, in the case where the motor is rotated in the direction of the left-handed screw, when the first ball screw nut6is disposed in the direction of the left-handed screw and the second ball screw nut9is disposed in the direction of the right-handed screw, the thrust bearings11are formed in the both sides of each of the first and second ball screw nuts6and9, as shown inFIG. 6D.

As set forth in the foregoing, the electric actuator according to the present invention can eliminate the disadvantages that conventional electric actuators have had to thereby provide a novel one that is capable of self-expanding, which of course can be a part of artificial muscles. That is, the sensor13acts as a sensory nerve and the first and second ball screw nuts6and9act as a motor nerve, which makes nerves fed back. Therefore, the electric actuator of the present invention may be applied easily in the field of a robotics industry.

While the present invention has been described with reference to a few specific embodiments, the description is illustrative of the invention and is not to be construed as limiting the invention. Various modifications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.