Linear driving electric cylinder based on reverse ball screw pair

Abstract

The utility model 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. According to the utility model, the transmission efficiency can be improved, the pre-tightening force can be provided, and the expansion and shrinkage of parts due to temperature influence can be compensated.

Description

Technical Field

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

[0002] Most existing linear actuators use inverted planetary roller screws, particularly in humanoid robot joints. While inverted planetary roller screws offer high load-bearing capacity, they are complex and expensive to design and manufacture. Furthermore, within the small and medium-sized screw range, the load-bearing capacity gap between ball screws and planetary roller screws is similar.

[0003] Common ball screw pairs are generally driven by a motor to rotate the ball screw, driving the ball nut to perform linear motion. They are commonly used in machine tools, guide rails, and other equipment. This type of ball screw pair is called a forward ball screw pair. In a forward ball screw pair, the effective external thread raceway of the ball screw is longer than the sum of the effective internal thread raceway length of the ball nut and the effective stroke. Therefore, a ball recirculation device must be installed on the ball nut. This structural feature results in a relatively large size for forward ball screw pairs, making them difficult to use in miniature and lightweight applications.

[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, screw, and nut. Once the components elongate due to heat, they may become stuck or the friction torque increases, which will affect their operating accuracy and use accuracy, resulting in energy loss and increased wear of parts. Utility Model Content

[0005] The purpose of the utility model 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 transmission efficiency, compensate for the expansion and contraction of components due to temperature, and adapt to various occasions.

[0006] The purpose of the utility model is achieved as follows: 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; wherein,

[0007] The housing includes 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 includes 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 to 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 housing, and a nut end cover is installed on the rear end portion of the ball nut; a load-bearing raceway and a plurality of return ball 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 return ball channels are connected between two adjacent external thread grooves, and the plurality of return ball 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 return ball 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 piece 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 in one-to-one correspondence 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 between the two angular contact ball bearings and the front and rear ends of the inner convex ring of the housing in a one-to-one correspondence.

[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 characteristics of the linear drive electric cylinder based on the reverse ball screw pair of the utility model are:

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

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

[0019] 3. The utility model adopts reverse angular contact bearings and wave springs, which can apply different preloads through the wave springs. It can not only provide suitable preload forces, but also compensate for the expansion and contraction of parts due to temperature, and is suitable for various occasions.

[0020] 4. The utility model 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 This is an axial cross-sectional view of the linear drive electric cylinder based on the reverse ball screw pair of the utility model;

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

[0023] The present invention will be further described below with reference to 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 on 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 hollow 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 front end cover 11 of the housing, and the outer surface of the rear end of the ball nut 31 is provided with an external thread, through which a nut end cover 34 is installed; the outer wall of the ball screw 32 is provided with a bearing raceway 321 and six ball return channels 322, the bearing raceway 32 1 is an external thread groove that meshes 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 to the inner wall of the ball nut 31. 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 ends 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 withstand push and pull forces in multiple directions.

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

[0033] The utility model discloses a linear drive electric cylinder based on a reverse ball screw pair. During operation, the stator 21 of the motor is energized to generate a magnetic field. The rotor 22 of the motor is made of a 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 plate 40 to rotate through the nut end cap 34. The encoder 4 controls the rotation and reversing of the ball nut 31 and controls the movement and limit of the ball screw 32. At the same time, the rotation of the ball nut 31 drives the balls 33 to rotate in the circulation channel, thereby promoting the axial movement of the ball screw 32. The encoder 4 is set with instructions through an external control system, so that the encoder 4 can accurately measure the rotation speed and relative position of the ball nut 31. The feedback information from the encoder 4 can better set the preload force, the specifications and compression length of the wave spring 6, and the motor speed.

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

[0035] 1. This utility model uses a reversed ball screw pair as the transmission component of the electric cylinder. This pair incorporates a circulation channel on the ball screw 32, consisting of a ball return channel and a load-bearing channel. The motor directly drives the ball nut 31, converting the rotational motion of the ball nut 31 into linear motion of the ball screw 32. When converting the motor's rotational motion into linear motion, the balls 33 act as rolling elements between the ball screw 32 and the ball nut 31, reducing friction and improving transmission efficiency. Its compact size and high transmission efficiency allow the ball screw pair to be integrated into the drive system within limited space, making it suitable for applications such as humanoid robot joints, where installation space is limited but long life and continuous operation are required.

[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 bearing raceway of the ball screw 32 form four-point contact with the ball 33, which can withstand radial loads and increase bidirectional axial loads, so that the ball screw 32 can adapt to higher speeds and complex force situations, and improve operation accuracy and rigidity.

[0037] 3. This utility model optimizes the design of the circulation channel on the ball screw 32. The channel adopts a large arc design, which increases the steering performance of the ball 33 and the safety factor of the ball 33's movement within the circulation channel. The centerline of the circulation channel is 0.01 to 0.5 mm away from the actual motion trajectory of the ball 33, leaving sufficient safety margin for subsequent processing.

[0038] 4. The present invention installs angular contact ball bearings 5 ​​back-to-back on both sides of the ball nut 31, increasing the axial load while also bearing radial loads, supporting the application of preload force inside the electric cylinder. A wave spring 6 is installed between the bearing 5 and the inner convex ring of the housing 10. By compressing the wave spring 6, a preload force is applied to the bearing 5. When the electric cylinder is operating, the cylinder releases heat, causing the temperature to rise. Parts such as the ball nut 31 and the housing 10 will elongate due to the heat. The wave spring 6 can effectively compensate for this elongation, avoiding jamming or excessive friction torque caused by contact between the end faces of internal parts, thereby improving 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 art may make various changes or modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions should also fall within the scope of the present invention and should be defined by the claims.

Claims

1. A linear drive electric cylinder based on an inverted ball screw pair, comprising a housing, a motor, an inverted ball screw pair, an encoder, two angular contact ball bearings and two wave springs; characterized in that: The housing includes 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 includes 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 to 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 housing, and a nut end cover is installed on the rear end portion of the ball nut; a load-bearing raceway and a plurality of return ball 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 return ball channels are connected between two adjacent external thread grooves, and the plurality of return ball 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 return ball 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 piece 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 in one-to-one correspondence 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 between the two angular contact ball bearings and the front and rear ends of the inner convex ring of the housing in a one-to-one correspondence.

2. The linear drive electric cylinder based on the reverse ball screw pair according to claim 1, 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, 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, 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.

Images