Industrial robot RV reducer

Abstract

The present invention discloses an RV reducer for an industrial robot. After the cycloid wheel is reshaped, a reasonable clearance (radial clearance Δj and side clearance Δc) is generated between the needle pin and the cycloid wheel tooth groove. This prevents the meshing parts from getting stuck when the cycloid wheel thermally expands under rated load. Furthermore, the reducer does not require very high manufacturing precision and is interchangeable with RV reducers on the market, thereby improving the adaptability and practicality of the product.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial robot reducers, and in particular to an industrial robot RV reducer with good dynamic characteristics, which solves the defects of heat generation and short life in the background technology by using thermal expansion theory. Background Art

[0002] On September 18, 2019, Professor Zhang Yueming, chief scientist of Beijing Zhitong Technology, said: The biggest gap between domestic reducers and Japanese Nabtesco reducers lies in accuracy retention and lifespan.

[0003] On November 23, 2019, the inventor of No. 2019111606018 of Ningbo Zhongda Lide Company stated: The invention "Cycloidal Pinwheel Transmission Structure" is used to solve the problem of unsatisfactory RV transmission accuracy in the current domestic stage.

[0004] On December 17, 2019, Yigong Technology, a source of innovative driving technology, pointed out in its promotion of the localization of RV reducers: "Despite several years of development, domestic RV reducers still face pain points: high heat generation, high noise, insufficient rigidity, and insufficient precision retention."

[0005] It shows that by the end of 2019, there is still a large gap between domestic RV reducers and Japan's Nabo. The reasons are analyzed as follows:

[0006] (1) Domestic researchers lack theoretical research on the reasonable meshing clearance of cycloid gear modification

[0007] The Gear Transmission Design Manual, page 804, states: "The reasonable modification of the cycloid gear tooth profile should meet the following requirements:

[0008] a. A reasonable meshing backlash and radial clearance can be formed to compensate for actual manufacturing and installation errors while ensuring a sufficient number of simultaneously meshing teeth; b. The working portion of the tooth profile should be as close to the conjugate tooth profile as possible to ensure smooth transmission; c. The grinding process is simple.

[0009] Both theory and practice have proved that the above-mentioned ideal tooth shape can be obtained by adopting the positive equal distance-positive shift optimization combined modification method.

[0010] When grinding a cycloidal wheel with positive offset profile modification, the arc radius of the grinding wheel (equivalent to the pin tooth profile radius) is increased from the standard rz to rz + Δrz; positive offset profile modification moves the grinding wheel a small distance ΔRz away from the center of the worktable. This means that during grinding, the radius of the pin tooth center circle Rz is increased to Rz + ΔRz.

[0011] The literature search shows that there is no research on the theoretical values ​​of reasonable side clearance and radial clearance of cycloid gear modification in China.

[0012] (2) Physics explains that reasonable meshing clearance is closely related to the thermal expansion of the cycloid gear

[0013] North China University of Technology "RV reducer thermal-structural coupling analysis": "Domestic research on RV reducer thermal-structural coupling

[0014] The reducer is grease lubricated, which has poor heat dissipation conditions. Various conditions during operation are closely related to heat.

[0015] The impact of temperature on the volume of parts to prevent expansion and jamming due to excessive temperature. (2016.06)

[0016] Researchers have done little research on the thermal-structural coupling of RV reducers. Various operating conditions are closely related to heat, and the cycloid gear is the main source of heat. If the gap is too small, it will inevitably get stuck due to excessive temperature. The following is an analysis of the thermal expansion of the cycloid gear:

[0017] Physics explains that solids expand in the same way in all directions. Therefore, the linear expansion law of a solid in one direction can be used to characterize its expansion. That is, the linear expansion coefficient αt = (d- d0) / (d0Δt) = Ω / (d0·Δt), so:

[0018] Thermal expansion Ω=(αt·Δt)d0;

[0019] (3) Domestic researchers have determined that the eccentric axis phase difference ΔΨ=180°, so only negative shift-negative equal distance modification can be used

[0020] It was found that domestic researchers determined that the phase difference of the eccentric shaft of the RV reducer is 180 degrees. The following table is a list of more than 80 examples in the literature. Small part

[0021]

[0022] However, theoretical calculations have shown that the negative offset-negative offset combination has a fatal characteristic: the side clearance ΔC is too small, which not only fails to compensate for thermal expansion and manufacturing errors caused by temperature rise, but also cannot prevent seizure due to temperature rise and expansion. Examples are as follows:

[0023] (Example 1) Dalian Jiaotong University, "Research on Meshing Stiffness of Cycloidal Gears in RV Transmissions," April 2017: RZ = 77, e = 1.50, Za = 39, K1 = 0.7792, Δrz = - 0.022, ΔRZ = - 0.027: Backlash Δc = 0.003 (mm) (too small);

[0024] (Example 2) Harbin Institute of Technology's "Design Research on Small and Medium-Power Shell-Fixed RV-E Reducers" RV-450E: RZ=155, e=3.0, Za=37, K1=0.7355, Δrz=-0.015, ΔRZ=-0.03, side clearance Δc=0.007 (mm) (too small);

[0025] (Example 3) Professor × of Tongji University, "Research on Gear Clearance of High-Precision RV Reducer Based on..." RV-40E parameters: RZ=64,

[0026] e=1.30, Za=39; K1= 0.8125, Δrz= - 0.002, ΔRZ= - 0.008, side clearance Δc= 0.003 (mm) (too small). Summary of the Invention

[0027] The present invention aims to solve the defects of the background technology such as heat generation and short life by using thermal expansion theory and anti-backlash cycloid, and to provide an industrial robot RV reducer with good dynamic characteristics and interchangeable with Japanese Nabtesco products.

[0028] In order to solve the above technical problems, the present invention adopts the following technical features:

[0029] Provided is an industrial robot RV reducer, comprising a pinion housing and a two-stage reduction component disposed therein: the first stage comprises an input shaft, a sun gear, and planetary gears; the second stage comprises a uniformly distributed eccentric shaft, a cycloid gear, a pinion, a bearing, and a planetary carrier, wherein: the cycloid gear comprises a first cycloid gear and a second cycloid gear, the planetary carrier comprises a left planetary disk and a right planetary disk, the eccentric shaft extension end is connected to the planetary gear, eccentric shaft bearings for supporting the cycloid gear are provided on the two eccentric sections of the eccentric shaft, the shaft extensions on both sides of the eccentric section of the eccentric shaft are supported in the peripheral holes of the left and right planetary disks by tapered roller bearings, the left and right planetary disks are supported on both sides of the pinion housing by main bearings, the input shaft is supported in the center holes of the left and right planetary disks by input bearings, the flange on the left planetary disk passes through the corresponding hole of the cycloid gear and is connected to the right planetary disk to form a rigid body, and after the cycloid gear is modified:

[0030] (A) Create a reasonable radial clearance Δj between the pin and the cycloid tooth groove to ensure that under rated torque, the thermal expansion of the cycloid wheel does not cause the meshing parts to be in interference friction. Therefore, the reasonable radial clearance Δj must be related to the thermal expansion Ω:

[0031] Radial clearance Δj = (0.18~0.5)Ω (mm),

[0032] Thermal expansion Ω=(αt·Δt)d0,

[0033] Where: temperature rise Δt = 45℃, d0 is the average diameter of the cycloid gear tooth top circle and tooth root circle, if the thermal expansion coefficient of the cycloid gear bearing steel is αt =1.379·10 -5 (1 / ℃),

[0034] Then the thermal expansion is: Ω=(αt·Δt)d0=0.00062·d0,

[0035] The relationship between radial clearance and thermal expansion is: Δj = (0.18~0.5)Ω (mm);

[0036] (B) The cycloid wheel adopts positive equidistance-positive displacement combination shaping, and its shaping amount depends on the radial gap Δj:

[0037] Positive isometric modification amount Δr z =Δj / (1-K), positive displacement correction amount ΔR z =KΔr z , Δr z -ΔR z =Δj, where:

[0038] K=(1-K1 2 ) 0.5 , short amplitude coefficient K1=e Z b / Rz, e is the eccentricity, Z b is the number of needle teeth, R z is the radius of the center circle of the needle teeth,

[0039] (C) The positive equidistant shaping amount Δrz and the positive displacement shaping amount ΔRz determine the size of the side clearance Δc, which represents the size of the backlash. According to the anti-backlash gear principle, the first eccentric section of the eccentric shaft of the RV reducer deviates by a small angle θ, so that one of the cycloid wheels approaches the needle pin clockwise; the second eccentric section deviates by a small angle θ in the opposite direction, so that the other cycloid wheel approaches the needle pin counterclockwise. At this time, the phase difference between the two eccentric sections of the eccentric shaft of the RV reducer is ΔΨ=180°-2θ or ΔΨ<179°, so as to reduce or eliminate the backlash.

[0040] In a preferred embodiment of the present invention, the radial gap Δj between the needle pin and the cycloid tooth groove is (0.183-0.4) Ω (mm).

[0041] In a preferred embodiment of the present invention, the radial gap Δj between the needle pin and the cycloid tooth groove is: 0.186Ω≤Δj≤0.3Ω (mm).

[0042] In a preferred embodiment of the present invention, corresponding to the size of the side clearance Δc values ​​of various RV models, according to the principle of anti-backlash gears, the phase difference ΔΨ between the two eccentric sections of the eccentric shaft is 177.7°~178.9°.

[0043] In a preferred embodiment of the present invention, corresponding to the size of the side clearance Δc values ​​of various RV models, according to the principle of anti-backlash gears, the phase difference between the two eccentric sections of the eccentric shaft is: 177.8°≤ΔΨ≤178.8°.

[0044] The beneficial effects of the present invention are as follows: after the cycloid wheel is reshaped, a reasonable gap (radial gap Δj and side gap Δc) is generated between the needle pin and the cycloid wheel tooth groove, so that when the reducer is under rated load and the cycloid wheel thermally expands, the meshing parts will not be stuck, and high manufacturing precision is not required. It can also be interchangeable with Japan Nabo RV reducer, thereby improving the adaptability and practicality of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive work, among which:

[0046] Figure 1 This is a structural diagram of a preferred embodiment of the industrial robot RV reducer of the present invention;

[0047] In the figure: 1. Pinion housing, 2. Main bearing, 3. First cycloid gear, 4. Pin, 5. Second cycloid gear, 6. Eccentric shaft, 7. Tapered roller bearing, 8. Eccentric shaft bearing, 9. Input shaft, 10. Input shaft bearing, 11. Left planetary disk flange, 12. Right planetary disk, 13. Left planetary disk, 14. Sun gear, 15. Planetary gears. DETAILED DESCRIPTION

[0048] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0049] See also Figure 1 , embodiments of the present invention include:

[0050] An industrial robot RV reducer adopts the Japanese Nabo RV structure to facilitate interchangeability. The specific structure includes pin gear

[0051] The housing 1 and the two-stage reduction components placed therein: the first-stage reduction component includes an input shaft 9, a sun gear 14 and a planetary gear 15; the second-stage reduction component includes 2 to 3 evenly distributed eccentric shafts 8, a cycloid wheel, a needle pin 4 and a planetary carrier, the cycloid wheel includes a first cycloid wheel 3 and a second cycloid wheel 5, the planetary carrier includes a left planetary disk 13 and a right planetary disk 12, the eccentric shaft 6 is connected to the planetary gear 15 at its extended end, and the two eccentric sections of the eccentric shaft 6 are provided with eccentric shaft bearings 8 for supporting the cycloid wheel. The shaft extensions on both sides of the eccentric section of the eccentric shaft are supported by tapered roller bearings 7 in the peripheral holes of the left planetary disc 13 and the right planetary disc 12 respectively. The left planetary disc 13 and the right planetary disc 12 are supported by main bearings 2 in the inner holes on both sides of the pin gear housing 1 respectively. The input shaft 9 is supported by input shaft bearings 10 in the center holes of the left planetary disc 13 and the right planetary disc 12 respectively. The flanges 11 evenly distributed on the left planetary disc 13 pass through the corresponding holes of the cycloid wheel and are connected to the right planetary disc 12 with screws and positioning pins to form a rigid body.

[0052] The cycloid wheel of an industrial robot RV reducer must be reshaped:

[0053] (A) When reshaping the cycloid wheel, a reasonable radial clearance Δj needs to be created between the pin and the cycloid tooth groove to ensure that under rated torque, the thermal expansion of the cycloid wheel does not cause interference friction of the meshing parts. Therefore, the reasonable radial clearance Δj must be related to the thermal expansion Ω.

[0054] Physics explains that the expansion law of solids is the same in all directions, and the expansion of solids can be characterized by the linear expansion law in one direction: αt = (d- d0) / (d0Δt) = Ω / (d0·Δt), so the thermal expansion Ω = (αt·Δt)d0,

[0055] The relationship between radial clearance and thermal expansion is: Δj = (0.18~0.5)Ω (mm),

[0056] If the thermal expansion coefficient of bearing steel is αt=1.379·10 -5 (1 / ℃)

[0057] Then the thermal expansion Ω=(αt·Δt})d0= 0.00062·d0 (mm).

[0058] Where, d0 is the average diameter of the cycloid gear tooth top circle and tooth root circle, and the temperature rise Δt is 45°C.

[0059] Although these data may change, they can all be measured using current technical means.

[0060] Furthermore, the radial clearance Δj between the needle pin 4 and the cycloid wheel tooth groove is (0.183-0.4) Ω (mm).

[0061] Furthermore, the radial clearance Δj between the needle pin 4 and the tooth groove of the cycloid wheel is: 0.186Ω≤Δj ≤0.3Ω (mm), which can more accurately control the radial clearance of the cycloid wheel.

[0062] (B) The cycloid wheel adopts positive equidistance-positive displacement combination shaping, and its shaping amount depends on the radial gap Δj:

[0063] Δr z =Δj / (1-K), ΔR z =K Δr z And Δrz - ΔRz = Δj (mm), where:

[0064] K=(1-K1 2 ) 0.5 , short amplitude coefficient K1=eZ b / Rz, e is the eccentricity, Z b is the number of needle teeth, and Rz is the radius of the center circle of the needle teeth.

[0065] The force between the gear teeth and the pins in the positive equidistance-positive displacement modification is 49% of that in the negative equidistance-negative displacement modification; the bearing capacity in the positive equidistance-positive displacement modification is 1.71 times that of the negative equidistance-negative displacement modification. ("Pin Cycloidal Transmission Tooth Profile Optimization and Dynamic Return Error Analysis")

[0066] in,

[0067] Equidistant shaping: the grinding wheel grinding radius increases to positive equidistant; conversely, it decreases to negative equidistant;

[0068] Shifting and shaping: When the grinding wheel moves away from the center of the worktable, it is a positive shift; otherwise, it moves forward, which is a negative shift.

[0069] (C) The positive equidistant shaping amount Δrz and the positive displacement shaping amount ΔRz determine the value of the side clearance Δc, which represents the size of the backlash. To eliminate the backlash, according to the anti-backlash gear principle, the phase difference between the two eccentric sections of the eccentric shaft of the RV reducer cannot be equal to 180°: the first eccentric section deviates by a small angle θ, so that the cycloid wheel approaches the needle pin clockwise; the second eccentric section deviates by a small angle θ in the opposite direction, so that the other cycloid wheel approaches the needle pin counterclockwise. The phase difference between the two eccentric sections ΔΨ=180°-2θ or ΔΨ<179° can reduce or eliminate the backlash.

[0070] The backlash Δc value is dependent on factors such as the accuracy of the needle pin spacing, needle diameter accuracy, clearance between the needle pin and the semi-buried hole, cycloidal gear pitch deviation, assembly deviation, and the RV machine model. If the backlash Δc is too small, thermal expansion of the cycloidal gear causes interference friction between components, leading to increased noise, wear, vibration, and shortened service life. If the backlash Δc is too large and the input speed is too high, vibration is more likely to occur.

[0071] The principle of anti-backlash gears is described in the doctoral thesis "Anti-backlash gear systems... and their impact on dynamic performance":

[0072] "Relying on methods to improve processing accuracy to ensure transmission accuracy will significantly increase processing costs. ... Effective backlash elimination methods should be used to control transmission errors and improve the transmission accuracy of the mechanism,..."

[0073] "The spring-loaded double-piece gear anti-backlash mechanism (abbreviated as anti-backlash gear) can not only eliminate the tooth clearance caused by gear manufacturing errors, but also eliminate the idle motion caused by temperature changes. Therefore, it is widely used in industrial robots, precision servo mechanisms, radar antennas and inertial stabilized platforms. Inertial stabilized platforms (ISPs) are used in mobile carrier systems such as satellites and missiles."

[0074] "Anti-backlash gear mechanisms not only require high-speed, high-precision, and high-stability dynamic characteristics, but their gear systems also operate under load conditions involving frequent starting, braking, and forward and reverse rotation, resulting in significant variations in operating conditions."

[0075] Furthermore, corresponding to the size of the side clearance Δc value of various RV models, according to the principle of anti-backlash gear,

[0076] The phase difference between the two eccentric sections of the eccentric shaft is ΔΨ=177.7°~178.9°.

[0077] Furthermore, corresponding to the size of the side clearance Δc value of various RV models, according to the principle of anti-backlash gear,

[0078] The phase difference between the two eccentric sections of the eccentric shaft is: 177.8°≤ΔΨ≤178.8°.

[0079] The phase difference ΔΨ≠180° between the two eccentric segments of the eccentric shaft of the present invention forms an anti-backlash gear similar to that of a high-precision CNC machine tool, an anti-backlash cycloid gear structure, which has the effect of eliminating backlash. The required shaping accuracy is much lower than the 0.001 (mm) of RV-250AⅡ.

[0080] Theoretical calculations confirm that when the eccentric segment phase difference is 177.8°≤ΔΨ≤178.8°, the unbalanced centrifugal force is very small because the eccentric segment deflects clockwise and counterclockwise around the center of mass of the rotor (i.e., the eccentric segment) in a thin crescent shape and has a very small mass, as shown in the following table:

[0081]

[0082] Further calculations confirmed that when the eccentric phase difference is 177.8°≤ΔΨ≤178.8°, the maximum allowable unbalance reaches G1. There are 11 levels of balance quality: G0.4, G1, G2.5, G6.3, G1600, and G4000.

[0083] Take RV-80E as an example: the mass of the second eccentric section is m=192 (g), the speed is n=1000rpm,

[0084] Permissible unbalance degree eper=1.0(60·10 3 / 2π·1000) = 9.55 (g·mm / kg),

[0085] Permissible unbalance Uper = m· eper = (192 / 1000)·9.55 = 1.834·10 3 (g mm),

[0086] Uper Ⅰ=1.834·10 3 (0.5L / L) = 0.917·10 3 (g·mm), UpeⅡ= UpperⅠ,

[0087] Therefore, Uper Ⅰ+Upe Ⅱ=0.917·10 3 +0.917·10 3 =1.834·10 3 (g·mm).

[0088] The beneficial effects of the industrial robot RV reducer of the present invention are:

[0089] (1) After the cycloid wheel of the present invention is modified, a reasonable gap (radial gap Δj and side gap Δc) is generated between the needle pin and the cycloid wheel tooth groove, so that the meshing parts will not be stuck when the cycloid wheel expands thermally under the rated load of the reducer;

[0090] (2) The present invention only requires the use of domestic machine tools and conventional manufacturing precision, and the processing and manufacturing difficulty is low;

[0091] (3) The external dimensions of the present invention are the same as those of the RV reducer of Japan's Nabtesco, and thus the present invention can be interchanged with the RV reducer, thereby improving the adaptability and practicality of the product.

[0092] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. An industrial robot RV reducer, comprising: The pinion gear housing and the two-stage reduction components placed therein: the first-stage reduction components include the input shaft, sun gear and planetary gears; The second-stage reduction component includes 2 to 3 evenly distributed eccentric shafts, cycloid wheels, needle pins and planetary carriers, the cycloid wheels include a first cycloid wheel and a second cycloid wheel, the planetary carrier includes a left planetary disk and a right planetary disk, the eccentric shaft shaft extension end is connected to the planetary wheel, the two eccentric sections of the eccentric shaft are provided with eccentric shaft bearings for supporting the cycloid wheel, the shaft extensions on both sides of the eccentric section of the eccentric shaft are supported by tapered roller shafts in the peripheral holes of the left planetary disk and the right planetary disk respectively, the left planetary disk and the right planetary disk are supported by main bearings on the inner holes on both sides of the pin gear housing respectively, the input shaft is supported by input shaft bearings on the center holes of the left planetary disk and the right planetary disk respectively, the evenly distributed flanges on the left planetary disk pass through the corresponding holes of the cycloid wheel and are connected to the right planetary disk with screws and positioning pins to form a rigid body, characterized in that: (A) Create a reasonable radial clearance Δj between the pin and the cycloid tooth groove to ensure that under rated torque, the thermal expansion of the cycloid wheel does not cause the meshing parts to be in interference friction. Therefore, the reasonable radial clearance Δj must be related to the thermal expansion Ω: Radial clearance Δj = (0.18~0.5)Ω, Thermal expansion Ω=(αt·Δt)d0, Where: temperature rise Δt = 45℃, d0 is the average diameter of the cycloid gear tooth top circle and tooth root circle, if the thermal expansion coefficient of the cycloid gear bearing steel is α t =1.379·10 -5 (1 / ℃), then Ω=(αt·Δt)d0=0.00062·d0; (B) The cycloid wheel adopts positive equidistance-positive displacement combination shaping, and its shaping amount depends on the radial gap Δj: Positive isometric modification amount Δr z =Δj / (1-K), positive displacement correction amount ΔR z =KΔr z , Δr z -ΔR z =Δj, where: K=(1-K1 2 ) 0.5 , short amplitude coefficient K1=e Z b / Rz, e is the eccentricity, Z b is the number of needle teeth, R z is the radius of the center circle of the needle teeth; (C) The positive equidistant shaping amount Δrz and the positive displacement shaping amount ΔRz determine the size of the side clearance Δc, which represents the size of the backlash. According to the anti-backlash gear principle, the first eccentric section of the eccentric shaft of the RV reducer deviates by a small angle θ, so that one of the cycloid wheels approaches the needle pin clockwise; the second eccentric section deviates by a small angle θ in the opposite direction, so that the other cycloid wheel approaches the needle pin counterclockwise. At this time, the phase difference between the two eccentric sections of the eccentric shaft of the RV reducer is 177.8°≤ΔΨ≤178.8°, so as to reduce or eliminate the backlash.

2. The industrial robot RV reducer according to claim 1, characterized in that: The radial clearance Δj between the needle pin and the cycloid wheel tooth groove is: 0.186Ω≤Δj≤0.3Ω.

3. The industrial robot RV reducer according to any one of claims 1-2, characterized in that: Thermal expansion coefficient of cycloid bearing steel: αt = 1.379·10 -5 (1 / °C), Ω = (αt·Δt) d 0 = 0.00062·d0, the units of Δj and Ω are mm.

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