An inner stator type hollow shaft harmonic wave loose tooth reduction motor with a compliant structure

Abstract

The application relates to a harmonic loose-tooth reduction motor with a flexible structure and an inner stator, and relates to the technical fields of motors, harmonic transmission and the like. Main parts for realizing functions include a stator, a flexible mechanism, a loose-tooth frame and a center wheel. The application controls a magnetic field through a coil wound on the stator in combination with a controller and a control program, thereby attracting a flexible wheel with ferromagnetism to generate deformation, so that the loose tooth in contact with the flexible wheel moves along a center wheel tooth profile, finally drives the loose-tooth frame to rotate and generates output. The application combines the reduction gear, the flexible hinge and the motor, reduces the size of the transmission device, makes the working machine more controllable, simultaneously weakens the impact generated by the loose tooth in the traditional loose-tooth reduction gear, improves the transmission stability, and designs the fixed shaft of the inner stator as a hollow shaft, so that the application can be better applied to a robot transmission arm.

Description

Technical Field

[0001] This invention relates to the fields of harmonics, live gear transmission and motor technology, and in particular to an inner stator type hollow shaft harmonic live gear reducer motor with a compliant structure. Background Technology

[0002] Harmonic drive (strain-wave gear drive) is a new type of transmission developed based on elastic deformation. It utilizes the difference in the number of teeth between the inner and outer teeth of the meshing flexible and rigid gears to achieve a large transmission ratio. The principle of live gear drive is similar to that of harmonic drive to some extent, and it also has characteristics such as center-to-center transmission and transmission using tooth difference.

[0003] With the continuous development of mechanical transmission, production and daily life have placed higher demands on transmission devices. Transmission machines with limited functions and characteristics cannot meet the needs of some special working scenarios. In response, many researchers have conducted extensive research and improvements in transmission-related fields in recent years, enabling gear reducers, harmonic reducers, and even motors to replace some traditional gear transmissions in certain scenarios and independently undertake production tasks. However, in harmonic reducers, the machining of the flexspline teeth is a major problem in harmonic transmission, and the precision and strength of the flexspline teeth affect the performance and stability of the transmission. Traditional motors need to be used in conjunction with reducers in most production processes, which increases the overall size of the working machine. To solve the above problems and achieve the combination of harmonic reducers, gear reducers, and motors, some researchers have proposed an electromagnetic harmonic geared motor. By utilizing the attraction between the stator and the flexspline, the machining process of the flexspline is simplified to some extent, the overall size of the transmission machine is reduced, and overload protection is also provided. However, due to the bottom-fixed method, it is constrained by size effects, resulting in a still relatively large axial dimension of the flexspline, which also prevents the working machine from achieving a better reduction in axial dimension. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention obtains an inner stator type hollow shaft harmonic geared motor with a compliant structure by having the motor stator attract a flexible ferromagnetic material, and then using the flexible material to drive the live teeth in the reducer to move along the tooth profile of the central wheel.

[0005] The technical solution adopted in this invention is as follows:

[0006] The present invention discloses an internal stator-type hollow shaft harmonic geared motor with a compliant structure, comprising a left end cover, a central wheel, a compliant mechanism, a stator, ball bearings, a hollow stepped shaft, a gear carrier, and a right end cover; the left end cover is coaxially fixed to the left end face of the central wheel; the compliant mechanism is coaxially disposed inside the central wheel and its left end face is fixed to the left end cover; the stator is coaxially assembled inside the compliant mechanism; the gear carrier is coaxially assembled on the right side of the compliant mechanism, and the side of the gear carrier assembled with the compliant mechanism has evenly distributed openings circumferentially corresponding to the number of ball bearings. The ball bearings are respectively assembled in the openings; after the ball bearing frame is assembled, the ball bearings are respectively fitted with the outer wall of the compliant mechanism and the inner wall of the central wheel; the right end cover is coaxially assembled on the outside of the ball bearing frame and connected to the right side of the ball bearing frame through a bearing, and the left end face of the right end cover is correspondingly fixed to the right end face of the central wheel; the hollow stepped shaft is coaxially assembled inside the central wheel from one side of the left end cover, and its left shaft section has through holes evenly distributed around its circumference for passing through the stator conductors, the middle shaft section is coaxially interference-fitted with the stator, and the right shaft section is connected to the ball bearing frame through a bearing.

[0007] Furthermore, the compliant mechanism includes a flange, an elastic element, and a thin-walled cylinder; the elastic element is radially arranged evenly around the circumference of the flange and is integrally formed with the flange; the thin-walled cylinder is coaxially arranged around the circumference of the flange, and its inner circumferential end face is connected to the outer end of the elastic element respectively, and adjacent elastic elements do not contact each other during deformation, so that they can complete the deformation without interference.

[0008] Furthermore, the ball bearing teeth are ceramic microspheres made of a low-density, high-precision, high-hardness, and non-ferromagnetic material.

[0009] Furthermore, the movable gear frame is made of aluminum and is designed as a hollow drive shaft structure.

[0010] Furthermore, the hollow stepped shaft is a five-segment stepped shaft, with the second segment having through holes evenly distributed around its circumference for passing through wires; the third segment having an interference fit with the stator; and the fifth segment being connected to the movable gear frame via a bearing, with a bearing sleeve installed between the bearing and the fourth segment for axial positioning.

[0011] Compared with the prior art, the present invention has the following advantages:

[0012] This invention features direct power input. Due to the incorporation of a compliant mechanism, the deformed part of the flexure is positioned axially with the movable teeth, making it easier to drive the movable teeth. It also boasts a smaller axial dimension. The planar movable tooth transmission section is tightly integrated with the motor's power input section. The design of the flexure deforming to replace the stator's rotation and simultaneously drive the movable teeth significantly reduces the axial dimension, eliminating the need for a connection between the reducer and the motor output shaft, thus saving considerable space. It is also easy to adjust precision. Since the stator windings can employ various winding methods besides the two-pole type, the flexure can be deformed as needed. This, combined with the advantages of a stepper motor, makes it easier for the transmission system to achieve the desired motion. Furthermore, it offers smooth and continuous transmission. Traditional movable tooth reducers always have some movable teeth in the lift phase and others in the return phase during transmission, affecting transmission stability. However, in this invention's transmission structure, all movable teeth are in contact with the flexure and subjected to contact force. This implicitly restricts the position of the movable teeth that are not actively involved in the operation, reducing system vibration and thus providing better transmission smoothness and continuity. In summary, compared with previous transmission systems, the present invention has the advantages of small size, strong transmission continuity, high degree of automation and high transmission accuracy. Attached Figure Description

[0013] Figure 1 This is a three-dimensional exploded structural diagram of the present invention;

[0014] Figure 2 This is a schematic diagram of the three-dimensional half-section structure of the present invention after assembly;

[0015] Figure 3 This is a three-dimensional structural diagram of the input side of the movable gear frame of the present invention;

[0016] Figure 4 This is a three-dimensional structural diagram of the output side of the movable gear frame of the present invention;

[0017] Figure 5 This is a two-dimensional structural schematic diagram of the compliant mechanism of the present invention;

[0018] Figure 6 This is a three-dimensional structural schematic diagram of the compliant mechanism of the present invention;

[0019] Figure 7 This is a two-dimensional structural schematic diagram of the hollow stepped shaft of the present invention;

[0020] Figure 8 This is a three-dimensional structural schematic diagram of the hollow stepped shaft of the present invention;

[0021] Figure 9 This is the stator winding diagram provided by the present invention;

[0022] Figure 10 This is a schematic diagram showing the deformation of the compliant mechanism at different angles during the operation of this invention.

[0023] In the attached drawings, the following reference numerals are used: 1-left end cover; 2-center wheel; 3-compliant mechanism; 31-flange; 32-elastic element; 33-thin-walled cylinder; 4-stator; 5-ball bearing; 6-hollow stepped shaft; 7-gear frame; 8-right end cover. Detailed Implementation

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] It should be noted that in the description of this invention, the terms "upper", "lower", "top", "bottom", "one side", "the other side", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention and simplifying the description, and do not mean that the device or element must have a specific orientation, or be constructed and operated in a specific orientation.

[0026] See appendix Figure 1-8 The present invention discloses an inner stator type hollow shaft harmonic geared motor with a compliant structure, comprising a left end cover 1, a central wheel 2, a compliant mechanism 3, a stator 4, ball bearing gears 5, a hollow stepped shaft 6, a gear carrier 7, and a right end cover 8. The left end cover 1 is coaxially fixed to the left end face of the central wheel 2. The compliant mechanism 3 is coaxially assembled inside the central wheel 2, and its left end face is coaxially fixed to the left end cover. The stator 4 is coaxially assembled inside the compliant mechanism 3. The gear carrier 7 is coaxially assembled on the outside right side of the compliant mechanism 3, and the gear carrier 7 is circumferentially evenly distributed on the side where it is assembled with the compliant mechanism 3. There are openings corresponding to the number of ball teeth 5, and the ball teeth 5 are respectively fitted into the openings on the tooth holder; after the tooth holder 7 is assembled, the ball teeth 5 are respectively fitted with the outer wall of the compliant mechanism 3 and the inner wall tooth profile of the center wheel 2, and the part of the inner wall of the center wheel 2 that contacts the ball teeth 5 is designed with a certain roughness. The machining method is to use a milling cutter with the same radius as the ball teeth 5 to mill along the ball center path formula. The material can be acrylic sheet or other common steel. The selection depends on the requirements of the working environment and the physical properties and cost considerations of the material itself.

[0027] In this embodiment, the ball bearing 5 is a ceramic ball. Since the transmission system involved in this invention involves the application of electromagnetic induction, and considering that the self-weight of the ball bearing and the friction generated by contact with other components in planar ball bearing transmission will affect the energy transfer efficiency, the ball bearing 5 is made of a low-density, high-precision, high-hardness, and non-ferromagnetic material. The material of the ball bearing frame 7 is aluminum, and two hollow transmission shafts extend outward from the right side in a coaxial manner, so that the transmission system can transmit torque while internally embedded. The right end cover 8 is coaxially mounted on the outside of the ball bearing frame 7 and cooperates with the external rotating pair of the second hollow transmission shaft of the ball bearing frame 7 through a bearing for axial positioning. The left end face of the right end cover 8 is correspondingly and fixedly connected to the right end face of the center wheel 2.

[0028] The hollow stepped shaft 6 is coaxially assembled inside the central wheel 2. In this embodiment, the hollow stepped shaft 6 is a five-segment stepped shaft. The first segment is coaxially rotated with the left end cover 1, the second segment is coaxially rotated with the compliant mechanism 3, and has through holes evenly distributed around its circumference for the insertion of the stator winding conductors. The third segment is interference-fitted with the stator 4, and the fifth segment is rotated with the first-stage hollow transmission shaft of the movable gear 7 via a bearing. A bearing sleeve is provided between the bearing and the fourth segment at this location. The hollow stepped shaft 6 is a stepped shaft that can be connected to other components, allowing the conductors of the stator winding or other necessary leads in the transmission system to pass through the hollow shaft. This allows the stator 4 to control the magnetic field generated in the winding through an external controller and to achieve remote wired connection between two non-adjacent parts in the transmission system.

[0029] The compliant mechanism 3 includes a flange 31, elastic elements 32, and a thin-walled cylinder 33. The thin-walled cylinder 33 is coaxially disposed on the outer circumference of the flange 31. The elastic elements 32 are radially distributed evenly around the outer circumference of the flange 31 and are integrally formed with the flange 31. The thin-walled cylinder 33 is coaxially disposed on the outer circumference of the flange 31, and its inner circumferential end face is fixedly connected to the outer end of the elastic element 32. The elastic element 32 can be a snap ring or a bent elastic thin wall. The number and thickness of the elastic elements 32 can be adjusted as needed. In this embodiment, the elastic elements 32 are regularly bent thin walls, with a total of six, each 0.5 mm thick. The axial inner walls of adjacent thin walls differ by a certain angle, ensuring that adjacent elastic elements 32 do not contact each other when the compliant mechanism 3 deforms, thus completing the deformation function without interference. The elastic elements 32 and the thin-walled cylinder 33 together form the flexible wheel of the compliant mechanism. By deforming the flexure of the compliant mechanism 3 to simulate the rotor in the stator-rotor structure of an internal stator motor, the flexure is attracted by the magnetic field generated by the stator winding, thus deforming instead of rotating like a traditional rotor. Through a microcontroller or other control methods, pulse signals are manually controlled to generate a corresponding magnetic field in the winding, causing the flexure to deform. This pushes the live gear to contact the center wheel and generates a circumferential contact force, thereby driving the live gear frame 7 to rotate. The thin-walled cylinder is assembled in an elliptical posture, applying pressure to the ball bearing live gear 5. Compared with a live gear reducer, this effectively improves the problem of radial runout of the live gear.

[0030] The left end cap 1 has six countersunk holes evenly distributed on its outer side and six threaded through holes evenly distributed on its inner side. Six of these through holes are coaxial with the countersunk holes, facilitating screw insertion and connection to the center wheel 2. Additionally, the six through holes on the inner side correspond to the through holes on the flange 31, allowing connection with them via screws. Furthermore, an additional cable outlet hole exists among the six inner through holes, positioned between any two through holes and within the same circumference. A limiting structure is designed at the connection end to ensure coaxiality. A groove is provided on the end face connecting to the compliant mechanism 3 for connection and positioning.

[0031] The center wheel 2 is the part that connects to many other parts. It has internal threads of appropriate depth evenly distributed at its small diameter end and a positioning structure at its large diameter end to ensure the coaxiality of the center wheel 2 after it is assembled with other parts.

[0032] The compliant mechanism 3 is made of a deformable material. A countersunk hole is formed in its central flange 31, allowing it to be connected to the left end cover 1 with screws. Coaxiality is ensured by the engagement of the flange 31 boss with the groove of the left end cover 1. The outer wall of the flange 31 has circumferentially distributed grooves into which one end of elastic elements 32, such as snap rings or thin-walled cylinders, can be inserted. Simultaneously, a ferromagnetic, deformable thin-walled cylinder 33 is welded between the other ends of each elastic element 32. When the flexure is attracted by the magnetic field generated by the stator 4, it deforms, simultaneously causing the compliant mechanism 3 itself to deform as well. If the flexure shaft diameter ratio is too small, it will strongly affect the deformation of the flexure under magnetic attraction. Furthermore, its dimensions also affect the dimensions of the stator 4 and the central wheel 2 nested within it, as well as the tooth profile of the central wheel 2.

[0033] The stator 4 is a stacked silicon steel sheet product, and its stator winding method is a concentrated winding with eighteen poles. After calculating the electromagnetic force, a three-phase, two-pole winding method was selected. Two adjacent sets of coils of the same phase are reverse-wound to form a magnetic circuit. After completing half of the winding, the same winding method is used at the negative phase end. After the three sets of windings are completed, a Y-connection method is used to connect the tail wires. The other end enters the hollow shaft through a through hole opened on the second section of the hollow stepped shaft 6, which facilitates external control.

[0034] The material of the movable gear frame 7 is aluminum, which is chosen to improve efficiency and reduce weight and system friction. At the same time, the part is designed as a hollow drive shaft, so it can be used in transmission systems that require the use of hollow shafts.

[0035] The right end cover 8 has six countersunk holes evenly distributed at the screw insertion positions. The design dimensions conform to national standards such as GB / T 152. The screw insertion holes are through holes and do not require internal threading. A positioning structure is provided at the end that contacts the center wheel 2 to ensure the coaxiality of the right end cover 8 and its contacting parts.

[0036] The location where electromagnetic induction occurs, the location where the compliant mechanism 3 deforms, and the location where the ball bearing tooth 5 moves are all on the same axial axis, rather than the design in previous studies where the deformation positions of the bearing tooth and the flexure were staggered. The structure disclosed in this invention greatly reduces the axial dimension of the flexure when the same pressure is applied, while making the force more direct and the output torque more stable.

[0037] To achieve control over the output motion characteristics and torque, the stator 4 is assembled onto the hollow stepped shaft 6 via an interference fit. Prior to assembly, [the following steps are taken]. Figure 9The winding method is shown, connecting the ends of each coil group, and then connecting the input ends of the windings to phases A, B, and C of the controller respectively, forming a Y-type three-phase two-pole connection for a three-phase motor. This controls the rotational direction, intensity, and speed of the magnetic field generated by the windings, thereby controlling the output speed. Simultaneously, the wires wound on stator 4 extend through a hollow shaft and connect to the controller, ultimately creating the physical conditions for controlling and generating the rotating magnetic field.

[0038] To improve transmission smoothness, the compliant mechanism 3, after assembly, has a flexible wheel portion that is round at one end and elliptical at the other. Utilizing the physical properties of the flexible wheel portion itself, it applies pressure to the ball bearing teeth 5, ensuring they remain in contact with the tooth profile of the central wheel 2 at all times. This avoids the situation in traditional gear reducers where the teeth are partially free during the return stroke, thereby improving transmission smoothness. Furthermore, to facilitate deformation of the flexible wheel, this invention does not use the traditional cylindrical flexible wheel with a bottom end face structure found in conventional harmonic reducers. Instead, a bottomless flexible wheel is used, making deformation easier. The compliant mechanism 3 is fixed to the left end cover 1 using screws, thus restricting the degree of freedom. Additionally, the compliant mechanism 3 can be adapted to different shapes or materials by considering various working or environmental factors; alternatively, other products with elasticity and limiting functions could also be used.

[0039] To integrate the planar movable gear transmission part with the motor part, this invention designs the center wheel 2, the cage end of the movable gear frame 7, the ball movable gear 5, the stator 4, the flexible wheel part of the compliant mechanism 3, and the hollow stepped shaft 6 in the same axial position. Specifically, the stator 4 is assembled onto the third section of the hollow stepped shaft 6 by interference fit. After the power is turned on, the rated voltage and current are respectively applied to the microcontroller and the stepper motor controller. The windings on the stator 4 are connected to the A, B, and C phases of the stepper motor controller in a Y-type configuration. After receiving the signal from the microcontroller, the controller issues a command to pass current through the stator, energizing the windings and generating electromagnetic induction. This, in turn, creates a magnetic force through the poles of the current-energized windings in the stator 4, attracting the thin-walled cylinder 33 of the compliant mechanism 3. This causes the thin-walled cylinder 33 to deform, and the ball bearings 5 ​​in contact with it at corresponding circumferential positions are simultaneously affected by the deformation of the compliant mechanism 3, the contact force with the central wheel 2 and the tooth carrier 7, and move along the tooth profile of the central wheel 2, thereby driving the tooth carrier 7 to rotate. Figure 10 The deformation of the flexible gear at different angles during operation can be obtained. By combining the motor, gear drive, and harmonic drive in the above manner, the overall size of the machine tool is significantly reduced.

[0040] All matters not covered in this invention are common knowledge.

[0041] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A hollow shaft harmonic geared motor with a compliant internal stator structure, characterized in that: It includes a left end cover, a center wheel, a compliant mechanism, a stator, ball bearings, a hollow stepped shaft, a toothed frame, and a right end cover; the left end cover is coaxially fixed to the left end face of the center wheel; the compliant mechanism is coaxially disposed inside the center wheel and its left end face is fixed to the left end cover; the stator is coaxially assembled inside the compliant mechanism; the toothed frame is coaxially assembled on the right side of the compliant mechanism, and the side of the toothed frame that is assembled with the compliant mechanism has openings evenly distributed circumferentially corresponding to the number of ball bearings, and the ball bearings are respectively assembled in the openings; After the movable gear frame is assembled, the ball bearing movable teeth fit into the outer wall of the compliant mechanism and the inner wall of the central wheel respectively; the right end cover is coaxially assembled on the outside of the movable gear frame and connected to the right side of the movable gear frame through a bearing, and the left end face of the right end cover is correspondingly fixed to the right end face of the central wheel; the hollow stepped shaft is coaxially assembled inside the central wheel from one side of the left end cover, and its left shaft section has through holes evenly distributed around its circumference for passing through the stator conductors, the middle shaft section is coaxially interference-fitted with the stator, and the right shaft section is connected to the movable gear frame through a bearing; The compliant mechanism includes a flange, an elastic element, and a thin-walled cylinder; the elastic element is radially distributed around the circumference of the flange and is integrally formed with the flange; the thin-walled cylinder is coaxially arranged around the circumference of the flange, and its inner circumferential end face is connected to the outer end of the elastic element, and adjacent elastic elements do not contact each other during deformation, so that they can complete the deformation without interference.

2. The inner stator type hollow shaft harmonic geared motor with a compliant structure according to claim 1, characterized in that: The ball bearing teeth are ceramic spheres made of a low-density, high-precision, high-hardness, and non-ferromagnetic material.

3. The inner stator type hollow shaft harmonic geared motor with a compliant structure according to claim 1, characterized in that: The movable gear frame is made of aluminum and is designed as a hollow drive shaft structure.

4. The inner stator type hollow shaft harmonic geared motor with a compliant structure according to claim 1, characterized in that: The hollow stepped shaft is a five-segment stepped shaft. The second segment has through holes evenly distributed around its circumference for passing through wires. The third segment is interference-fitted with the stator. The fifth segment is connected to the movable gear frame through a bearing, and a bearing sleeve is installed between the bearing and the fourth segment for axial positioning.

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