Rigid wheel, machining method thereof and harmonic speed reducer

Abstract

The invention discloses a rigid wheel and a machining method thereof and a harmonic speed reducer, and relates to the technical field of harmonic speed reducers, the rigid wheel comprises a body and a nitriding layer, the nitriding layer is formed on the surface of the body, the body of the rigid wheel is made of a nodular cast iron material with the tensile strength smaller than or equal to 700 MPa, the cutting performance of the nodular cast iron with the tensile strength is better, and the cutting performance is better. Machining is convenient, tool abrasion can be reduced, the machining efficiency is improved, and the production cost is reduced. The nodular cast iron has smaller specific gravity than quenched and tempered steel, so that the weight of the rigid wheel can be reduced; the nodular cast iron has a self-lubricating function, friction force can be reduced, and the service life of the rigid wheel is prolonged. In order to guarantee that the rigid wheel has certain strength and meets corresponding use requirements, the nitriding layer is formed on the surface of the body through nitriding treatment, the surface hardness of the nitriding layer ranges from 250 HV to 450 HV, the hardness and abrasion resistance of the rigid wheel can be improved, and then the service life of the rigid wheel is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of harmonic reducers, and in particular to a rigid wheel and a processing method thereof, and a harmonic reducer. Background Art

[0002] In the related technology, the harmonic reducer has the advantages of large transmission ratio, high load-bearing capacity, high transmission accuracy, high efficiency, small size, and light weight. Therefore, it can be used in the rotating joints of industrial robots to reduce speed. The harmonic reducer includes three basic components: a rigid wheel, a flexible wheel, and a wave generator. The inner teeth of the rigid wheel mesh with the outer teeth of the flexible wheel. The wave generator is arranged inside the flexible wheel to deform the flexible wheel. Traditional rigid wheels are usually made of quenched and tempered steel, which has poor cutting performance, resulting in difficult machining, severe tool wear, and low machining efficiency. Summary of the invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a rigid wheel, the body of which is made of ductile iron, which has good cutting performance, is easy to process, reduces tool wear, and improves processing efficiency.

[0004] The present invention also provides a method for processing the above-mentioned rigid wheel, and a harmonic reducer having the above-mentioned rigid wheel.

[0005] According to the first aspect of the present invention, the rigid wheel comprises: a main body, comprising an annular portion and an inner tooth portion, the inner tooth portion is arranged on the inner wall of the annular portion, the annular portion and the inner tooth portion are made of ductile iron material with a tensile strength less than or equal to 700 MPa; a nitriding layer is formed on the surface of the annular portion and the inner tooth portion, and the surface hardness of the nitriding layer is 250HV to 450HV.

[0006] The rigid wheel according to the embodiment of the present invention has at least the following beneficial effects:

[0007] By using ductile iron material with a tensile strength less than or equal to 700MPa to make the annular part and the inner tooth part, the ductile iron with this tensile strength has better cutting performance, so it is easy to process, can reduce tool wear and improve processing efficiency. The relative density of ductile iron is smaller than that of quenched and tempered steel, which can reduce the weight of the steel wheel; ductile iron has a self-lubricating function, which can reduce friction and extend the service life of the steel wheel. In order to ensure that the steel wheel has a certain strength and meets the corresponding use requirements, a nitriding layer is formed on the surface of the annular part and the inner tooth part through nitriding treatment, and the surface hardness of the nitriding layer is 250HV to 450HV, which can improve the hardness and wear resistance of the steel wheel, thereby improving the service life of the steel wheel. Using ductile iron material with better processing performance to replace the material with a hardness requirement of 250HV to 450HV after surface nitriding, the processing efficiency is high and the production cost is low.

[0008] According to some embodiments of the present invention, the yield strength of the rigid wheel is less than or equal to 600 MPa.

[0009] According to some embodiments of the present invention, the elongation of the rigid wheel is greater than or equal to 3%.

[0010] According to some embodiments of the present invention, a white bright layer is further provided on the surface of the nitriding layer, and the hardness of the white bright layer is greater than the hardness of the nitriding layer.

[0011] According to some embodiments of the present invention, the thickness of the white bright layer is less than or equal to 0.03 mm.

[0012] According to some embodiments of the present invention, the thickness of the nitriding layer is greater than or equal to 0.1 mm.

[0013] According to some embodiments of the present invention, the chemical composition of the body is, in mass percentage, C: 3.0%-3.6%, Si: 2.0%-3.0%, Mn: ≤1.0%, P: ≤0.1%, S: ≤0.06%, Mg: 0.03%-0.06%, Ce: 0.02%-0.04%, and the remainder is Fe.

[0014] According to the second aspect of the present invention, the harmonic reducer comprises a flexible wheel, a wave generator and the rigid wheel described in the above embodiment, wherein the rigid wheel is provided with an internal tooth portion; the flexible wheel comprises a cylinder portion, and the cylinder portion is provided with an external tooth portion meshing with the internal tooth portion; the wave generator is installed in the inner hole of the cylinder portion.

[0015] The harmonic reducer according to the embodiment of the present invention has at least the following beneficial effects:

[0016] The rigid wheel of the first aspect embodiment is adopted, and the main body of the rigid wheel is made of ductile iron material with a tensile strength less than or equal to 700MPa. The ductile iron with this tensile strength has better cutting performance, so it is easy to process, can reduce the wear of the tool, and improve the processing efficiency. The relative density of ductile iron is smaller than that of quenched and tempered steel, which can reduce the weight of the rigid wheel; ductile iron has a self-lubricating function, can reduce friction, and extend the service life of the rigid wheel. In order to ensure that the rigid wheel has a certain strength and meets the corresponding use requirements, a nitriding layer is formed on the surface of the main body through nitriding treatment, and the surface hardness of the nitriding layer is 250HV to 450HV, which can improve the hardness and wear resistance of the rigid wheel, thereby improving the service life of the rigid wheel. The ductile iron material with better processing performance is used for surface nitriding to replace the material with a hardness requirement of 250HV to 450HV, which has high processing efficiency and low production cost.

[0017] According to some embodiments of the present invention, the wave generator includes a cam and a flexible bearing, wherein the flexible bearing is sleeved on an outer peripheral wall of the cam and has an interference fit with the cam.

[0018] According to some embodiments of the present invention, the harmonic reducer further includes a cross roller bearing, and an inner ring and an outer ring of the cross roller bearing are respectively connected to the rigid wheel and the flexible wheel.

[0019] According to the method for processing a rigid wheel according to the third aspect of the present invention, the method is used to process the rigid wheel of the first aspect, and includes the following steps: using a ductile iron substrate to process a rigid wheel semi-finished product; performing low-temperature nitriding treatment on the rigid wheel semi-finished product; wherein the surface hardness of the rigid wheel semi-finished product after low-temperature nitriding is 250HV to 450HV.

[0020] The method for processing a rigid wheel according to an embodiment of the present invention has at least the following beneficial effects:

[0021] By nitriding the main body of the steel wheel, a nitriding layer is formed on the surface of the main body. The surface hardness of the nitriding layer is 250HV to 450HV, so the surface hardness of the steel wheel can be improved, the wear resistance of the steel wheel can be increased, and the service life of the steel wheel can be improved. Compared with the scheme of using materials with hardness meeting the corresponding requirements to make the main body, this scheme can use materials with lower hardness to make the main body, and then nitriding treatment is performed to increase the surface hardness of the main body to meet the corresponding performance requirements. Materials with low hardness are easy to process, with short processing time, high precision, high work efficiency, and can reduce production costs. Low-temperature nitriding can improve the deformation of the steel wheel semi-finished product caused by excessive temperature during nitriding treatment, thereby ensuring the accuracy of the steel wheel semi-finished product.

[0022] According to some embodiments of the present invention, the process of using a ductile iron substrate to form a semi-finished rigid wheel comprises the following steps: using a ductile iron substrate to form the semi-finished rigid wheel through casting, rough turning, and fine turning.

[0023] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0025] Figure 1 A schematic diagram of the structure of a rigid wheel according to an embodiment of the present invention;

[0026] Figure 2 A schematic diagram of a partial structure of a rigid wheel according to an embodiment of the present invention;

[0027] Figure 3A flowchart of a method for processing a rigid wheel according to an embodiment of the present invention;

[0028] Figure 4 The present invention is a flowchart of a method for processing a rigid wheel according to an embodiment of the present invention.

[0029] Figure 5 A schematic diagram of the structure of a harmonic reducer according to an embodiment of the present invention;

[0030] Figure 6 The figure is an exploded view of a harmonic reducer according to an embodiment of the present invention.

[0031] Figure Number:

[0032] Harmonic reducer 100; rigid wheel 110; body 111; nitriding layer 112; white bright layer 113; inner tooth portion 114; first inner hole 115; annular portion 116; flexible wheel 120; outer tooth portion 121; cylinder portion 122; second inner hole 123; partition 124; flange 125; wave generator 130; flexible bearing 131; cam 132; cross roller bearing 140. DETAILED DESCRIPTION

[0033] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0034] In the description of the present invention, it should be understood that descriptions involving orientation, such as orientation or positional relationship indicated as up, down, etc., are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0035] In the description of the present invention, "a plurality" means more than two. If there is a description of "first" or "second", it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0036] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0037] The main structure of the harmonic reducer includes three basic components: wave generator, flexwheel and rigid wheel. The flexwheel is a flexible external gear, the rigid wheel is a rigid internal gear ring, and the wave generator is composed of a flexible bearing and a cam. The harmonic reducer has the advantages of compact structure, small size, light weight, large transmission ratio and load capacity, and high transmission accuracy, making it widely used in electronics, aerospace, robotics, automation and other industries.

[0038] The harmonic reducer transmits motion through the meshing between the outer teeth of the flex spline and the inner teeth of the rigid wheel. During the entire motion process, the number of meshing tooth pairs accounts for about 30%, and the inner teeth of the rigid wheel mesh with the outer teeth of the flex spline. The number of meshing teeth is related to the working conditions. The greater the torque, the more meshing teeth there are. Since the flex spline is a thin-walled structure, it presents the same shape as the cam after the wave generator is assembled, and the end face of the flex spline exhibits periodic deformation during the operation of the wave generator. There is meshing relative motion between the outer teeth of the flex spline and the inner teeth of the rigid wheel, that is, the tangential relative motion and the tooth movement caused by the deformation of the flex spline. The meshing bearing of the outer teeth and the inner teeth realizes the transmission of force and motion of the harmonic reducer. The contact between the outer teeth and the inner teeth is similar to line contact. The lubrication state between the teeth of the rigid wheel and the flex spline is mixed lubrication, so both the rigid wheel and the flex spline need to have high wear resistance. Since the rigid wheel is made of high-strength ductile iron, the machining performance of ductile iron with good mechanical properties, high tensile strength and surface hardness is poor, so the wear of the gear shaping tool is large and the cost is high.

[0039] Based on this, a rigid wheel in one embodiment of the present invention has a body made of ductile iron with a tensile strength less than or equal to 700 MPa. The ductile iron with this tensile strength has good cutting performance and is easy to process. It can reduce tool wear and improve processing efficiency.

[0040] The following is further described with reference to the accompanying drawings:

[0041] Reference Figure 1 and Figure 2 As shown, a rigid wheel 110 according to an embodiment of the present invention includes a body 111 and a nitriding layer 112, wherein the body 111 includes an annular portion 116 and an inner tooth portion 114, and the inner tooth portion 114 is arranged on the inner wall of the annular portion 116. The annular portion 116 and the inner tooth portion 114 are made of ductile iron material with a tensile strength less than or equal to 700 MPa. The nitriding layer 112 is formed on the surface of the annular portion 116 and the surface of the inner tooth portion 114, and the surface hardness of the nitriding layer 112 is 250HV to 450HV, for example, 300HV, 350HV, 400HV.

[0042] It is understandable that the annular portion 116 and the inner tooth portion 114 are made of ductile iron material with a tensile strength less than or equal to 700MPa. The ductile iron with this tensile strength has good cutting performance, is easy to process, can reduce the wear of the tool, and improves the processing efficiency. However, due to the low tensile strength of ductile iron, the hardness, strength, and wear resistance of the annular portion 116 and the inner tooth portion 114 are insufficient, so nitriding treatment is required to form a nitriding layer 112 on the surface of the annular portion 116 and the inner tooth portion 114, and the surface hardness of the nitriding layer is 250HV to 450HV, thereby improving the surface hardness, strength and wear resistance of the rigid wheel 110, and then improving the service life of the rigid wheel 110. Using ductile iron material with better processing performance to perform surface nitriding instead of materials with a hardness requirement of 250HV to 450HV, the processing efficiency is high and the production cost is low. The rigid wheel 110 can be used in some occasions with small loads, low speeds, and low requirements.

[0043] In an embodiment of the present invention, the yield strength of the rigid wheel 110 is less than or equal to 600 MPa, for example, the yield strength of the rigid wheel 110 may be 550 MPa, 500 MPa, or 450 MPa. Yield strength is the yield limit of a metal material when yielding occurs, that is, the stress that resists micro plastic deformation. For metal materials without obvious yielding, the stress value that produces 0.2% residual deformation is specified as its yield limit, which is called conditional yield limit or yield strength. For example, the yield strength of the rigid wheel 110 is 600 MPa, and stress below 600 MPa will not cause large plastic deformation or permanent deformation of the rigid wheel 110, while stress exceeding 600 MPa may cause plastic deformation of the rigid wheel 110, and the rigid wheel 110 cannot be restored to its original state after the stress is removed. The yield strength of the rigid wheel 110 is limited to less than or equal to 600 MPa, so the rigid wheel 110 can be made of low-grade ductile iron, such as ductile iron with grades of QT500, QT600, and QT700. Using low-grade ductile iron can reduce costs and improve processing efficiency.

[0044] In an embodiment of the present invention, the elongation of the rigid wheel 110 is greater than or equal to 3%, for example, the elongation may be 4%, 5%, 8%, or 10%. Elongation is an indicator for measuring the plastic deformation ability of a material, which indicates the ductility of the material before tensile fracture. Elongation refers to the degree of deformation of a material before it breaks during the stretching process, that is, the ratio of the length increased before the tensile fracture to the original length during the stretching process. Before tensile fracture, the rigid wheel 110 can undergo a certain plastic deformation without immediately breaking. A rigid wheel 110 with a higher elongation generally exhibits good ductility and toughness, can absorb a certain amount of energy when subjected to a load, reduce stress concentration, and improve durability. During operation, the rigid wheel 110 can better withstand impact loads, resist stress concentration, and avoid sudden fracture, thereby improving the reliability and service life of the rigid wheel 110.

[0045] Reference Figure 2 As shown, in the embodiment of the present invention, the surface of the nitriding layer 112 is provided with a white bright layer 113, and the hardness of the white bright layer 113 is greater than the hardness of the nitriding layer 112. The white bright layer 113 refers to a compound layer composed of the ξ phase, ε phase and γ′ phase or one or two phases of the surface of the nitriding workpiece, so it is also called a compound layer or a compound layer. It is named because it is not easily colored by ordinary corrosive agents and appears white and bright under a microscope. The white bright layer 113 has high hardness, wear resistance and corrosion resistance. The white bright layer 113 can provide additional protection to enhance the performance of the surface of the rigid wheel 110 and extend the service life of the rigid wheel 110.

[0046] Continue to refer to Figure 2 As shown, in the embodiment of the present invention, the thickness of the white bright layer 113 is less than or equal to 0.03 mm, for example, it can be 0.02 mm, 0.01 mm, 0.005 mm. It should be noted that the white bright layer 113 has a certain brittleness. When the thickness of the white bright layer 113 is greater than 0.03 mm, the surface brittleness of the rigid wheel 110 will increase, and the white bright layer 113 is prone to cracking, peeling, etc., affecting the reliability and durability of the rigid wheel 110. Since the nitriding process is usually carried out before processing the inner tooth portion 114 of the rigid wheel 110, the excessive thickness of the white bright layer 113 is also prone to cause processing difficulties. The processing process requires the use of stronger and more wear-resistant cutting tools, which increases costs. At the same time, the heat generated by the processing will also be concentrated on the surface of the rigid wheel 110, which is difficult to dissipate, causing the rigid wheel 110 to deform and affect the surface quality. Therefore, the white bright layer 113 should not be too thick, and needs to be controlled within an appropriate range to take into account the strength, toughness and processing performance of the rigid wheel 110.

[0047] Continue to refer to Figure 2 As shown, in an embodiment of the present invention, the thickness of the nitriding layer 112 is greater than or equal to 0.1 mm, for example, the thickness of the nitriding layer 112 may be 0.2 mm, 0.3 mm, or 0.5 mm. It is understandable that if the thickness of the nitriding layer 112 is too small, it will not provide sufficient hardness and wear resistance to the rigid wheel 110, resulting in increased wear of the rigid wheel 110, affecting the service life of the rigid wheel 110, and an overly thin nitriding layer 112 will easily cause the rigid wheel 110 to be corroded by liquid and reduce its strength. Therefore, a reasonable design of the thickness of the nitriding layer 112 can improve the overall hardness, wear resistance, and service life of the rigid wheel 110.

[0048] In an embodiment of the present invention, the chemical composition of the body 111 is calculated in mass percentage as follows: carbon C: 3.0%-3.6%, silicon Si: 2.0%-3.0%, manganese Mn: ≤1.0%, phosphorus P: ≤0.1%, sulfur S: ≤0.06%, magnesium Mg: 0.03%-0.06%, cerium Ce: 0.02%-0.04%, and the balance is iron Fe.

[0049] It is understandable that too low carbon content is likely to produce free cementite, which reduces the mechanical strength of the rigid wheel 110, increases brittleness, and increases casting defects such as shrinkage cavities and shrinkage. Too high carbon content is likely to cause graphite to float and reduce mechanical properties. Therefore, a reasonable design of carbon content can increase the volume expansion of graphitization, compensate for shrinkage, increase the density of the casting, and improve mechanical properties.

[0050] Silicon can promote graphite crystallization and cementite decomposition. When the silicon content is greater than 3.0%, brittleness increases and plasticity decreases. When the silicon content is less than 2.0%, it is not conducive to improving the roundness of the graphite ball and affects the overall performance of the rigid wheel 110.

[0051] Manganese can improve the strength and hardness of the steel wheel 110 and reduce the plasticity and toughness. Too much manganese content will increase the toughness-brittleness transition temperature of the steel wheel 110, so the manganese content is generally not more than 0.4% to 0.6%, but in order to improve the wear resistance of the steel wheel 110, the manganese content can be appropriately increased to be less than or equal to 1.0%.

[0052] Phosphorus and sulfur are impurities in the rigid wheel 110. Too high a phosphorus content will make the rigid wheel 110 brittle, reducing its toughness and impact strength. Too high a sulfur content will cause thermal cracks and brittleness, reducing the reliability and load-bearing capacity of the rigid wheel 110. Therefore, the lower the phosphorus and sulfur content, the better.

[0053] When magnesium is used as a spheroidizing agent, its residual amount is related to parameters such as sulfur content and the wall thickness of the steel wheel 110, and is generally controlled at 0.03%-0.06%. Too high a magnesium content can easily deteriorate the shape of graphite, and in severe cases, cause distortion. The reason is that magnesium atoms are adsorbed on the surface of graphite. Magnesium is a surface active element. Excessive magnesium atoms will close the spiral dislocation steps of graphite and promote the growth of graphite along the crystal direction. Excessive magnesium will also increase the tendency of cast iron to form white cast iron and increase the amount of magnesium oxide, thereby increasing the possibility of casting defects in the steel wheel 110.

[0054] When cerium is used as a spheroidizing agent, in order to obtain a high spheroidization rate and roundness, a hypereutectic carbon equivalent is required. The spheroidization of cerium is also related to the amount of oxygen in the molten iron. Only when the activity of oxygen in the molten iron is low, cerium can mainly combine with sulfur, and the activity of sulfur is low enough, can graphite have good spheroidization. However, excessive cerium will also deteriorate the shape of graphite, increase the tendency of cast iron to white cast iron, and increase inclusions.

[0055] Therefore, reasonable control of the content of each component in ductile iron can obtain excellent ductile iron material, which has good strength, hardness, toughness and wear resistance, as well as appropriate impact resistance and fatigue resistance.

[0056] Reference Figure 3As shown, in the embodiment of the present invention, the processing method of the rigid wheel 110 includes the following steps:

[0057] Step S301: Use ductile iron substrate to process into a semi-finished steel wheel. It is understandable that ductile iron is a cast iron material containing spheroidal graphite. Due to the presence of spheroidal graphite, stress can be absorbed and dispersed, providing good toughness and fracture resistance. This enables ductile iron to withstand dynamic or impact loads in engineering applications and has good deformation resistance. Ductile iron has good processing properties and can be subjected to a variety of processing techniques such as casting, machining and heat treatment, which can meet the production needs of parts of different shapes and sizes. Compared with some high-strength alloy materials, ductile iron has a lower production cost. Therefore, the use of ductile iron to make steel wheel semi-finished products can improve production efficiency, reduce costs, and meet the performance requirements of steel wheel 110.

[0058] Step S302: low-temperature nitriding treatment is performed on the semi-finished steel wheel. The nitriding temperature of the conventional nitriding treatment is usually higher than 500°C. Too high a temperature can easily lead to an increase in the deformation of the semi-finished steel wheel, affecting the product quality. Therefore, the nitriding temperature of the low-temperature nitriding can be controlled between 350°C and 450°C, such as 350°C, 380°C, 400°C, and 450°C. Among them, gas nitriding can be used for nitriding. The low-temperature nitriding method can reduce the deformation risk of the semi-finished steel wheel, protect the surface quality, and improve the toughness of the material. For example, during low-temperature nitriding, due to the low temperature, the thermal expansion coefficient of the material is small, thereby reducing the risk of material deformation and stress accumulation that may be caused during the nitriding process. Problems such as surface oxidation, burning and discoloration caused by excessive temperature can be effectively avoided, and the surface quality of the semi-finished steel wheel can be protected. At the same time, the low-temperature nitriding layer has a good bond with the substrate, so the overall toughness and anti-stripping ability of the semi-finished steel wheel can be improved.

[0059] The surface hardness of the semi-finished steel wheel after low temperature nitriding is 250HV to 450HV. For example, it can be 300HV, 350HV, or 400HV. The hardness of the steel wheel 110 in the related art is usually above 600HV. Compared with the steel wheel in the related art, the steel wheel of the embodiment of the present invention has a shorter manufacturing time and lower cost, and can be applied to some occasions with low requirements such as small load and slow speed.

[0060] Reference Figure 4 As shown, in the embodiment of the present invention, step S301 includes:

[0061] Step S401: A ductile iron substrate is used to form a semi-finished gear wheel through casting, rough turning and fine turning. It is understandable that ductile iron has good machining properties and can be cast, rough turned and fine turned. This allows the semi-finished gear wheel to be flexibly designed and accurately processed according to actual needs to meet the requirements of different sizes, shapes and gear parameters.

[0062] In an embodiment of the present invention, the metallographic structure of the semi-finished steel wheel includes ductile iron, pearlite and ferrite. Ductile iron can provide good toughness and impact resistance. It can form a tough ferrite matrix with fracture toughness under stress, which helps to reduce stress concentration and crack propagation. Pearlite is a phase composed of ferrite and a certain amount of carbon in ductile iron. The formation of pearlite is beneficial to improving the hardness and strength of ductile iron. Pearlite has a layered structure, which can effectively hinder the expansion of cracks and improve fatigue resistance and tensile strength. Ferrite is the matrix phase of ductile iron, which is composed of iron and a small amount of carbon. The presence of ferrite helps to improve the toughness and machinability of ductile iron. The appropriate ferrite content can be used to adjust the mechanical properties of ductile iron by heat treatment, such as strengthening the distribution of pearlite and improving the morphology of pearlite.

[0063] Reference Figure 5 and Figure 6 As shown, a harmonic reducer 100 of an embodiment of the present invention comprises a flexible wheel 120, a wave generator 130 and a rigid wheel 110 of the above embodiment, wherein a first inner hole 115 is provided in the middle of the rigid wheel 110, and an inner tooth portion 114 is provided around the inner wall of the first inner hole 115; the flexible wheel 120 comprises a cylinder 122, a second inner hole 123 is formed in the cylinder 122, and an outer tooth portion 121 is provided in the cylinder 122, and the outer tooth portion 121 is meshed with the inner tooth portion 114. The wave generator 130 is installed in the second inner hole 123 and has an interference fit with the flexible wheel 120. The wave generator 130 is connected to the input shaft of the motor, and the input shaft drives the wave generator 130 to rotate, so that the flexible wheel 120 is deformed. The number of teeth of the outer tooth portion 121 is usually two less than the number of teeth of the inner tooth portion 114. When the outer tooth portion 121 meshes with the inner tooth portion 114 at different positions, it can drive the flexible wheel 120 to rotate, thereby completing the power output.

[0064] The harmonic reducer 100 of the embodiment of the present invention adopts the rigid wheel 110 of the embodiment of the first aspect, and the body 111 of the rigid wheel 110 is made of ductile iron material with a tensile strength less than or equal to 700 MPa. Ductile iron with this tensile strength has good cutting performance and is easy to process, which can reduce tool wear and improve processing efficiency. However, since the tensile strength of ductile iron is not high, the hardness, strength and wear resistance of the body 111 are insufficient, so nitriding treatment is required to form a nitriding layer 112 on the surface of the body 111, thereby improving the surface hardness, strength and wear resistance of the rigid wheel 110, and further improving the service life of the rigid wheel 110. Therefore, the rigid wheel 110 can be used in some occasions with small loads, low speeds and low requirements.

[0065] Reference Figure 6 As shown, in the embodiment of the present invention, the wave generator 130 includes a cam 132 and a flexible bearing 131, the cam 132 is elliptical, and is arranged on the inner ring of the flexible bearing 131 by interference fit. The flexible bearing 131 is flexible and can be elastically deformed, so when the cam 132 is arranged on the flexible bearing 131, the flexible bearing 131 is elliptical. During the rotation of the cam 132, the long axis region can make the outer tooth portion 121 of the flexible wheel 120 and the inner tooth portion 114 of the rigid wheel 110 mesh, and the short axis region can make the outer tooth portion 121 of the flexible wheel 120 and the inner tooth portion 114 of the rigid wheel 110 separate, and the flexible bearing 131 can reduce the rotational friction between the cam 132 and the flexible wheel 120, thereby increasing the service life of the wave generator 130.

[0066] Reference Figure 5 and Figure 6 As shown, in the embodiment of the present invention, the harmonic reducer 100 further includes a cross roller bearing 140, the inner ring of the cross roller bearing 140 is connected to the rigid wheel 110, and the outer ring is connected to the flexible wheel 120, and the cross roller bearing 140 plays the role of transmitting force and bearing load. For example, the flexible wheel 120 also includes a partition 124 and a flange 125, the partition 124 is connected to the end of the barrel 122 away from the outer tooth portion 121, the partition 124 is bent in the direction away from the second inner hole 123 and arranged around the second inner hole 123, and the flange 125 is arranged around the side of the partition 124 away from the barrel 122. The flange 125 is fixedly connected to the outer ring of the cross roller bearing 140, and when the flexible wheel 120 rotates, it can drive the outer ring of the cross roller bearing 140 to rotate to complete the power output. Therefore, the cross roller bearing 140 also has a positioning function, which can effectively reduce the occurrence of offset and dislocation of the flexible wheel 120.

[0067] Since the harmonic reducer 100 adopts all the technical solutions of the rigid wheel 110 of the above embodiment, it has at least all the beneficial effects brought by the technical solutions of the above embodiment, which will not be described in detail here.

[0068] An industrial robot according to an embodiment of the present invention comprises the harmonic reducer 100 of the above-mentioned embodiment. Since industrial robots usually need to perform complex movements and precise position control, and the harmonic reducer 100 can provide high-precision speed conversion and torque output, the robot can achieve accurate positioning and motion control. Industrial robots usually need to be installed and operated in a limited space. The harmonic reducer 100 adopts a miniaturized and compact design, which can effectively save installation space, make the overall size of the industrial robot smaller, and facilitate operation and movement in a small space. The harmonic reducer 100 has high wear resistance and fatigue resistance, can operate stably for a long time under high load and frequent working conditions, and provides reliable performance and a long service life.

[0069] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. Rigid wheel, used in harmonic reducer, characterized by: include: The body comprises an annular portion and an inner tooth portion, wherein the inner tooth portion is arranged on the inner wall of the annular portion, and the annular portion and the inner tooth portion are made of ductile iron material with a tensile strength less than or equal to 700 MPa; A nitriding layer is formed on the surfaces of the annular portion and the inner tooth portion, and the surface hardness of the nitriding layer is 250 HV to 450 HV.

2. The rigid wheel according to claim 1, characterized in that: The yield strength of the rigid wheel is less than or equal to 600 MPa.

3. The rigid wheel according to claim 1, characterized in that: The elongation of the rigid wheel is greater than or equal to 3%.

4. The rigid wheel according to claim 1, characterized in that: A white bright layer is also provided on the surface of the nitriding layer, and the hardness of the white bright layer is greater than the hardness of the nitriding layer.

5. The rigid wheel according to claim 4, characterized in that: The thickness of the white bright layer is less than or equal to 0.03 mm.

6. The rigid wheel according to claim 1, characterized in that: The thickness of the nitriding layer is greater than or equal to 0.1 mm.

7. The rigid wheel according to claim 1, characterized in that: The chemical composition of the body is calculated in mass percentage: C：3.0％-3.6％， Si: 2.0%-3.0%, Mn:≤1.0%, P：≤0.1％， S：≤0.06％， Mg: 0.03%-0.06%, Ce: 0.02%-0.04%, The balance is Fe.

8. Harmonic reducer, characterized in that: include: The rigid wheel according to any one of claims 1 to 7; A flexible wheel, comprising a cylindrical portion, wherein the cylindrical portion is provided with an external tooth portion meshing with the internal tooth portion; The wave generator is installed in the inner hole of the cylinder.

9. The harmonic reducer according to claim 8, characterized in that: The wave generator comprises a cam and a flexible bearing. The flexible bearing is sleeved on the outer peripheral wall of the cam and is interference fit with the cam.

10. The harmonic reducer according to claim 8, characterized in that: The harmonic reducer also includes a cross roller bearing, and the inner ring and the outer ring of the cross roller bearing are respectively connected to the rigid wheel and the flexible wheel.

11. A method for processing a rigid wheel, characterized in that: The following steps are involved: The semi-finished steel wheel is made of ductile iron base material; Performing low temperature nitriding treatment on the semi-finished steel wheel; Wherein, the surface hardness of the semi-finished steel wheel after low-temperature nitriding is 250HV to 450HV.

12. The method for processing a rigid wheel according to claim 11, characterized in that: The method of using ductile iron substrate to process the semi-finished steel wheel comprises the following steps: The semi-finished steel wheel is made of a ductile iron base material through casting, rough turning and fine turning.

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