Linear driving electric cylinder based on reverse ball screw pair

Abstract

The invention discloses a linear driving electric cylinder based on a reverse ball screw pair. The linear driving electric cylinder comprises a shell, a motor, the reverse ball screw pair, an encoder, two angular contact ball bearings and two wave springs. The shell comprises a shell body, a shell body front end cover and a shell body rear end cover. A stator of the motor is fixedly mounted on the inner wall of the inner convex ring of the shell; the reverse ball screw pair comprises a ball nut fixed on the inner cavity wall of the motor rotor, a ball screw screwed on the inner wall of the ball nut and a plurality of rows of balls; the encoder is installed on the front end face of the shell rear end cover, and a feedback magnetic sheet of the encoder is installed on the rear end face of the nut end cover. The two angular contact ball bearings are installed on the front portion and the rear portion of the ball nut in a back-to-back mode. And the two wave springs are sleeved at the front part and the rear part of the ball nut and are respectively positioned between the two angular contact ball bearings and the front end surface and the rear end surface of the inner convex ring of the shell. The transmission efficiency can be improved, pre-tightening force can be provided, and expansion and shrinkage of parts influenced by temperature can be compensated.

Description

Technical Field

[0001] The invention relates to a linear drive electric cylinder based on a reverse ball screw pair. Background Art

[0002] Most of the existing linear drive electric cylinders use reverse planetary roller screws, especially those commonly used in humanoid robot joints. Although reverse planetary roller screws have strong load-bearing capacity, they are complex in structure and have high design and processing costs. In addition, within the range of small and medium-sized screws, the load-bearing capacity gap between ball screws and planetary roller screws is not large.

[0003] Common ball screw pairs are driven by motors to rotate the ball screws and drive the ball nuts to make linear motion. They are commonly used in machine tools, guide rails and other equipment. This type of ball screw pair is a positive ball screw pair. The length of the effective external thread raceway of the ball screw in the positive ball screw pair is greater than the sum of the length of the effective internal thread raceway of the ball nut and the effective stroke. Therefore, it is necessary to set the ball circulation return device on the ball nut. This structural feature causes the positive ball screw pair to be relatively large in size, making it difficult to use in miniature and lightweight occasions.

[0004] Existing linear drive electric cylinders generally do not take into account the axial preload and the large amount of heat generated during operation, which causes the elongation and contraction of components such as the housing, lead screw, and nut. Once the components are heated and elongated, resulting in jamming or increased friction torque, their operating accuracy and use accuracy will be affected, causing energy loss and increased parts wear. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a linear drive electric cylinder based on a reverse ball screw pair, which can increase the transmission efficiency, compensate for the expansion and contraction of parts due to temperature, and adapt to various occasions.

[0006] The object of the present invention is achieved as follows: A linear drive electric cylinder based on a reverse ball screw pair comprises a housing, a motor, a reverse ball screw pair, an encoder, two angular contact ball bearings and two wave springs; wherein,

[0007] The housing comprises a housing and a housing front end cover and a housing rear end cover which are mounted on the front end and the rear end of the housing in a one-to-one correspondence; an inner convex ring is provided on the inner wall of the housing;

[0008] The stator of the motor is fixedly mounted on the inner wall of the inner convex ring of the housing, and the rotor of the motor is a cavity structure and is coaxially arranged in the inner cavity of the stator;

[0009] The reverse ball screw pair comprises a ball nut, a ball screw and a plurality of rows of balls; an internal thread groove is provided on the inner wall of the ball nut, the ball nut is fixed on the inner cavity wall of the rotor of the motor, the front end face of the ball nut is against the rear end face of the front end cover of the shell, and a nut end cover is installed on the rear end of the ball nut; a load-bearing raceway and a plurality of ball return channels are provided on the outer wall of the ball screw, the load-bearing raceway is an external thread groove meshing with the internal thread groove of the ball nut, so that the ball screw is screwed on the inner wall of the ball nut, and the plurality of ball return channels are connected between two adjacent external thread grooves, and the plurality of ball return channels are evenly distributed along the circumference of the outer surface of the ball screw, so that the two adjacent external thread grooves and the ball return channels form a row of circulating raceways; a plurality of rows of balls are arranged in a plurality of circulating raceways in a one-to-one correspondence;

[0010] The encoder is mounted on the front end surface of the rear end cover of the housing, and the feedback magnetic sheet of the encoder is mounted on the rear end surface of the nut end cover opposite to the encoder;

[0011] Two angular contact ball bearings are mounted back to back and one-to-one at the front and rear of the ball nut; the large end face of the inner ring of the angular contact ball bearing mounted at the front of the ball nut contacts the rear end face of the outer convex ring of the ball nut head; the large end face of the inner ring of the angular contact ball bearing mounted at the rear of the ball nut contacts the front end face of the nut end cover;

[0012] Two wave springs are sleeved on the front and rear parts of the ball nut and are located one by one between the two angular contact ball bearings and the front and rear faces of the inner convex ring of the housing.

[0013] In the above-mentioned linear drive electric cylinder based on the reverse ball screw pair, the nut end cover is threadedly connected to the rear end portion of the ball nut.

[0014] In the above-mentioned linear drive electric cylinder based on the reverse ball screw pair, the profile of the external thread groove on the ball screw is a double arc, and the contact point is in the direction of 30 to 60 degrees.

[0015] The above-mentioned linear drive electric cylinder based on the reverse ball screw pair, wherein the linear drive electric cylinder also includes two rod end joint bearings, one rod end joint bearing is installed at the front end of the ball screw passing through the center hole of the front end cover of the shell; the other rod end joint bearing is coaxially installed on the rear end surface of the rear end cover of the shell through a tension sensor.

[0016] The linear drive electric cylinder based on the reverse ball screw pair of the present invention is characterized by:

[0017] 1. The present invention adopts a reverse ball screw pair as a transmission component, which reduces the processing difficulty, increases the transmission efficiency, and improves the linear travel distance.

[0018] 2. The present invention adopts a reverse ball screw pair, which is small in size and light in weight.

[0019] 3. The present invention adopts a reverse angular contact bearing and a wave spring, and can apply different preloads through the wave spring, which can not only provide a suitable preload force, but also compensate for the expansion and contraction of parts due to temperature, and is suitable for a variety of occasions.

[0020] 4. The present invention reduces the number of parts, reduces the transmission gap, improves the compactness of the mechanism, can achieve better rotation accuracy and rotation coaxiality, and improves the recognition accuracy of the encoder. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is an axial cross-sectional view of the linear drive electric cylinder based on the reverse ball screw pair of the present invention;

[0022] Figure 2 It is a detailed structural diagram of the ball screw in the linear drive electric cylinder of the present invention. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with the accompanying drawings.

[0024] See also Figure 1 and Figure 2 The linear drive electric cylinder based on the reverse ball screw pair of the present invention includes a housing 1, a motor, a reverse ball screw pair, an encoder 4, two angular contact ball bearings 5, two wave springs 6, two rod end joint bearings 7 and a tension sensor 8.

[0025] The housing comprises a housing 10 and a housing front end cover 11 and a housing rear end cover 12 which are mounted at the front end and the rear end of the housing 10 in a one-to-one correspondence; an inner convex ring is provided on the inner wall of the housing 10 .

[0026] The stator 21 of the motor is fixedly mounted on the inner wall of the inner convex ring of the housing 10 , and the rotor 22 of the motor is a cavity structure and is coaxially disposed in the inner cavity of the stator 21 .

[0027] The reverse ball screw pair includes a ball nut 31, a ball screw 32 and six rows of balls 33; wherein, an internal thread groove is provided on the inner wall of the ball nut 31, the ball nut 31 is fixed on the inner cavity wall of the rotor 22 of the motor, the front end face of the ball nut 31 is against the rear end face of the housing front end cover 11, the outer surface of the rear end of the ball nut 31 is provided with an external thread, and a nut end cover 34 is installed through the external thread; a bearing raceway 321 and a plurality of ball return channels 322 are provided on the outer wall of the ball screw 32, and the bearing raceway 32 1 is an external thread groove meshing with the internal thread groove of the ball nut 31, the profile of the external thread groove is a double arc, and the contact point is in the direction of 30-60 degrees, so that the ball screw 32 is screwed on the inner wall of the ball nut 31, and the six ball return channels 322 are connected between two adjacent external thread grooves, and the six ball return channels 322 are evenly distributed along the circumference of the outer surface of the ball screw 32, so that the two adjacent external thread grooves and the ball return channels 322 form a circulating raceway; six rows of balls 33 are arranged in the six circulating raceways in a one-to-one correspondence.

[0028] The encoder 4 is mounted on the front end surface of the rear end cover 12 of the housing, and the feedback magnetic piece 40 of the encoder 4 is mounted on the rear end surface of the nut end cover 34 opposite to the encoder 4 .

[0029] Two angular contact ball bearings 5 ​​are installed back to back and one to one at the front and rear of the ball nut 31; the large end face of the inner ring of the angular contact ball bearing 5 installed at the front of the ball nut 31 contacts the rear end face of the outer convex ring of the head of the ball nut 31; the large end face of the inner ring of the angular contact ball bearing 5 installed at the rear of the ball nut 31 contacts the front end face of the nut end cover 34.

[0030] The two wave springs 6 are sleeved on the front and rear parts of the ball nut 31 and are located between the two angular contact ball bearings 5 ​​and the front and rear faces of the inner convex ring of the housing 10 in a one-to-one correspondence.

[0031] One rod end joint bearing 7 is installed at the front end of the ball screw 32 passing through the center hole of the front end cover 11 of the housing; the other rod end joint bearing 7 is coaxially installed on the rear end surface of the rear end cover 12 of the housing; the two rod end joint bearings 7 bear push and pull forces in multiple directions.

[0032] The tension sensor 8 is installed between the rear end surface of the rear end cover 12 of the housing and the rod end joint bearing 7 located on the rear end surface of the rear end cover 12 of the housing.

[0033] The linear drive electric cylinder based on the reverse ball screw pair of the present invention, when working, the stator 21 of the motor is energized to generate a magnetic field, the rotor 22 of the motor is made of magnetic material, the magnetic field drives the rotor 22 of the motor to rotate and drives the ball nut 31 to rotate, the ball nut 31 drives the feedback magnetic sheet 40 to rotate through the nut end cover 34, the encoder 4 controls the rotation and reversal of the ball nut 31, controls the movement limit of the ball screw 32, and at the same time, the rotation of the ball nut 31 drives the ball 33 to operate in the circulation channel, thereby pushing the ball screw 32 to move axially. The encoder 4 is set with instructions through the external control system, so that the encoder 4 can accurately measure the rotation speed and relative position of the ball nut 31, and the feedback information of the encoder 4 can better set the preload force, the specification and compression length of the wave spring 6, and the rotation speed of the motor.

[0034] The linear drive electric cylinder based on the reverse ball screw pair of the present invention has the following characteristics:

[0035] 1. The present invention adopts a reverse ball screw pair as the transmission component of the electric cylinder. The reverse ball screw pair sets the circulation channel on the ball screw 32. A circulation channel includes a return ball channel + a load-bearing channel. The motor directly drives the ball nut 31, and the rotational motion of the ball nut 31 is converted into the linear motion of the ball screw 32. When the rotational motion of the motor is converted into linear motion, the ball 33 is used as a rolling element between the ball screw 32 and the ball nut 31, which reduces friction and improves transmission efficiency. It has a small size and high transmission efficiency. The ball screw pair can be integrated into the drive system in a limited space. It is suitable for application scenarios such as humanoid robot joints with limited installation space but requiring long life and continuous work.

[0036] 2. The thread grooves in the reverse ball screw pair of the present invention all adopt a ceramic double arc profile, and the contact points are in the direction of 30 to 60 degrees. The ball nut 31 and the load-bearing raceway of the ball screw 32 form four-point contact with the ball 33, which can not only withstand radial loads but also increase bidirectional axial loads, so that the ball screw 32 can adapt to higher rotation speeds and complex stress situations, and improve operation accuracy and rigidity.

[0037] 3. The present invention optimizes the design of the circulation channel on the ball screw 32. The circulation channel adopts a large arc design to increase the steering performance of the ball 33 and the safety factor of the ball 33 running in the circulation channel. The center line of the circulation channel is 0.01 to 0.5 mm away from the actual motion trajectory of the ball 33. Considering the difficulty of subsequent processing, sufficient safety space is reserved for processing.

[0038] 4. The present invention installs angular contact ball bearings 5 ​​back-to-back on both sides of the ball nut 31, which can increase the axial load while also bearing the radial load, and support the application of preload inside the electric cylinder. A wave spring 6 is installed between the bearing 5 and the inner convex ring of the housing 10, and a preload can be provided to the bearing 5 by compressing the wave spring 6; when the electric cylinder is working, the electric cylinder releases heat and causes the temperature to rise, and the ball nut 31 and the housing 10 and other parts will elongate due to the heat, and the wave spring 6 can effectively compensate for this elongation, avoid jamming or excessive friction torque caused by the end face contact of internal parts, and improve the operation and positioning accuracy of the electric cylinder; by setting a reasonable preload and designing a wave spring 6 of appropriate specifications, the allowable operating temperature range of the electric cylinder can be effectively increased.

[0039] The above embodiments are only used to illustrate the present invention, rather than to limit the present invention. Those skilled in the relevant technical field may make various changes or modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions should also belong to the scope of the present invention and should be defined by the claims.

Claims

1. A linear drive electric cylinder based on a reverse ball screw pair, comprising a housing, a motor, a reverse ball screw pair, an encoder, two angular contact ball bearings and two wave springs; characterized in that: The housing comprises a housing and a housing front end cover and a housing rear end cover which are mounted on the front end and the rear end of the housing in a one-to-one correspondence; an inner convex ring is provided on the inner wall of the housing; The stator of the motor is fixedly mounted on the inner wall of the inner convex ring of the housing, and the rotor of the motor is a cavity structure and is coaxially arranged in the inner cavity of the stator; The reverse ball screw pair comprises a ball nut, a ball screw and a plurality of rows of balls; an internal thread groove is provided on the inner wall of the ball nut, the ball nut is fixed on the inner cavity wall of the rotor of the motor, the front end face of the ball nut is against the rear end face of the front end cover of the shell, and a nut end cover is installed on the rear end of the ball nut; a load-bearing raceway and a plurality of ball return channels are provided on the outer wall of the ball screw, the load-bearing raceway is an external thread groove meshing with the internal thread groove of the ball nut, so that the ball screw is screwed on the inner wall of the ball nut, and the plurality of ball return channels are connected between two adjacent external thread grooves, and the plurality of ball return channels are evenly distributed along the circumference of the outer surface of the ball screw, so that the two adjacent external thread grooves and the ball return channels form a row of circulating raceways; a plurality of rows of balls are arranged in a plurality of circulating raceways in a one-to-one correspondence; The encoder is mounted on the front end surface of the rear end cover of the housing, and the feedback magnetic sheet of the encoder is mounted on the rear end surface of the nut end cover opposite to the encoder; Two angular contact ball bearings are mounted back to back and one-to-one at the front and rear of the ball nut; the large end face of the inner ring of the angular contact ball bearing mounted at the front of the ball nut contacts the rear end face of the outer convex ring of the ball nut head; the large end face of the inner ring of the angular contact ball bearing mounted at the rear of the ball nut contacts the front end face of the nut end cover; Two wave springs are sleeved on the front and rear parts of the ball nut and are located one by one between the two angular contact ball bearings and the front and rear faces of the inner convex ring of the housing.

2. The linear drive electric cylinder based on the reverse ball screw pair according to claim 1 is characterized in that: The nut end cover is threadedly connected to the rear end portion of the ball nut.

3. The linear drive electric cylinder based on the reverse ball screw pair according to claim 1 is characterized in that: The profile of the external thread groove on the ball screw is a double arc, and the contact point is in the direction of 30 to 60 degrees.

4. The linear drive electric cylinder based on the reverse ball screw pair according to claim 1 is characterized in that: The linear drive electric cylinder also includes two rod end joint bearings, one rod end joint bearing is installed at the front end of the ball screw passing through the center hole of the front end cover of the shell; the other rod end joint bearing is coaxially installed on the rear end surface of the rear end cover of the shell through a tension sensor.

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