WO2023043419A1

WO2023043419A1 - A method for proper mounting grouping of planetary gearbox components with a low backlash value target

Info

Publication number: WO2023043419A1
Application number: PCT/TR2022/051005
Authority: WO
Inventors: Bahadir KARBA; Nihat Yildirim
Original assignee: Gaziantep Universitesi Rektorlugu
Priority date: 2021-09-20
Filing date: 2022-09-19
Publication date: 2023-03-23
Also published as: TR2021014676A2

Abstract

The invention relates to a method developed to estimate the actual backlash and to mount planetary gearboxes with a low backlash taking the production and operating conditions of the planetary gearbox components into account.

Description

A METHOD FOR PROPER MOUNTING GROUPING OF PLANETARY GEARBOX COMPONENTS WITH A LOW BACKLASH VALUE TARGET

Field of the Invention

The invention relates to a method developed to perform low backlash mounting of planetary gearbox components .

State of the Art

Gears are machine components commonly used for power transmission through torque and motion drive . In applications where the main purpose is to transmit torque , the gears usually rotate in one direction, while in applications where the main purpose is to transmit motion, the gears usually rotate in two directions . In either case , whether the rotation is unidirectional or bidirectional , a certain amount of clearance (usually free angular motion called "backlash" ) between the flanks of the meshing teeth is al lowed for functional reasons . As much as backlash is necessary for proper gear meshing, it is a defect when not carefully controlled .

A planetary gearbox is one of the gear drive types used in critical applications such as robots and radars . Thus , creating a kickback value in planetary gearboxes is a practical problem for critical industries .

Especially when motion changes direction within servo motorbased bi-directional motion plat forms , the system that is driven does not move temporarily for a very short period, thereby creating a loss of motion . This loss of motion may prevent the correct ful fillment of the task depending on the amount . The tolerance/ limits of this loss of motion may vary from application to application, and di f ferent loss of motion limits are determined for di f ferent applications . Loss of motion in bidirectional rotation or motions is usually caused by backlash in gear systems in front of servo motors .

Although many non-critical and non-sensitive applications allow more than 20 arcminutes of motion loss (backlash) , relatively critical manufacturing, mounting and many applications require less than 20 arc-minutes of motion loss (backlash) . While this value is requested in the range of 5- 10 arcminutes in some devices in the medical sector, motion loss of less than 3 arc-minutes is requested in the defense industry and aviation sector . Even though this value is considered acceptable for many non-critical applications , it is quite large and can be rej ected for many applications for targeting and defense purposes .

Considering the current design, manufacturing, and quality control technologies , one can observe that there is not enough solid background and experience in cycloid and harmonic converters yet . However, despite the insuf ficient background and experience in planet converters , it is clear to those skilled in the art that the currently producible planet converters have deficiencies to be used in precise positioning applications and in meeting the required backlash values . A minimum/ speci f ic clearance is intended to minimi ze motion loss in traditional design processes . Accordingly, production processes that are forced to minimi ze production tolerances and errors increase the cost of the production and control process , resulting in an increase in the cost of the gearbox .

There are solutions developed in the art to achieve low- backlash targets/values . Low backlash targets can be achieved with the design and manufacturing technologies of cycloid and harmonic-type converters with better performances . Backlash can be eliminated with the production of very sensitive gear and gearbox components or with specially designed gear (beveloid etc . ) designs . Backlash reduction mechanisms can be used by means of externally or internally integrated special design components on gears . Pre-tensioned, plastic fillers , split-shaped or center distance adj ustment solutions are also used . In addition, appropriate motion can be imparted with models that can accurately predict system feedback by controllers .

The systems/methods in the art are not suf ficient to achieve low-backlash targets and involve many technical problems . Distance adj ustment solutions between centers complicate the system and capacity reductions up to 1 / 4 degree ( 15 arcminute ) occur . In addition, these solutions are costly . The fact that systems with low-load hysteresis (up to 0 arcminute ) are the only suitable option for arc and split gear methods is a current problem . Multiple-gear shaft solutions , which are called group gears , are costly, require the use of extra elements to solve the problem, and cause high wear . In the methods related to plastic fillers , due to the plastic material properties , low speed, and low load conditions are required and at what level the tooth clearance is provided cannot be predicted . In specially designed gears such as beveloid gears , challenges arise in production such as high machining costs , development of a design to work constantly under control to continuously close the backlash along with surface wear problem due to 0-degree clearance . For controller-based solutions , since the gearbox behaviour is not stable and each system installation is di f ferent , there is di f ficulty in reaching the actual values .

The document titled "A study on prediction & validation of meshing gear pair backlash under various manufacturing and assembly errors" (Karba, Bahadir & Yildirim, Nihat & Erdogan, Fatih & Vardar, Mert . ( 2019 ) ) may be mentioned as an example for the state of the art . The said document deals with the estimation and veri fication of mating gear-pair backlash under various manufacturing and assembly error conditions . The study of the document describes software developed to estimate the maximum and minimum backlash values of randomly selected and assembled gear pairs . A special test setup was created to veri fy the values obtained with the software , and the backlash of the gear pair operating under various manufacturing and assembly errors was measured experimentally . In the document , the validity of the gear pair backlash estimation software has been proven with the backlash measurement test conducted on only a one-step spur outer gear pair by considering the ef fect of production and assembly errors of phase angle change di f ferences manually . The software of the said document does not provide the optimum installation configuration for the planetary gearbox, which consists of the kinematic behavior of the external gear pair and the internal gear pair, and therefore , the production and assembly errors for the planetary gearbox cannot be determined with the said software .

Patent document No . WO21037448A1 may be referred to as another example of the state of the art . Said document is a patent file describing a method developed for adj usting backlash value in rack and pinion gear systems and positioning/assembly thereof such that the system would produce actual/minimum backlash values . The documented method is directed to rack and pinion systems and does not of fer a speci fic solution to mount planetary gearbox components with a low-backlash value . Therefore , to solve the above-mentioned problems , a method has been developed to estimate/minimi ze the actual backlash and to mount thereof with a low backlash, taking the production and operating conditions of the planetary gearbox components into account . Detailed Description of the Invention

The invention relates to a mounting method developed to position planetary gearbox components with a low backlash .

An obj ect of the invention is to convert , by using the quality-control reports of the produced gears , the tooth backlash values calculated and predicted over the system operating requirement during the design into values emerging in actual conditions .

An obj ect of the invention is to obtain the actual operating clearance values by considering the design and manufacture of essential components that are merely a part of the installation, as well as parameters such as manufacturing defects , deformations under load, di f ferences caused by thermal expansion during operation, theoretical backlash, etc .

An obj ect of the invention is to classi fy the gearbox components , which are not produced and measured with very strict tolerances , for a minimum/ targeted backlash condition and to sort them into di f ferent mounting subgroups . Thereby, a correct/ smart mounting method has been developed for each gearbox to exhibit a higher quality behavior in case the gears are of high quality to dampen their individual faults , regardless of random or target behavior during the mounting phase of the gearbox and for each of it to act as to meet the target design criteria in case they are produced in low quality .

The method of the invention is based on the principle of minimi zing, optimi zing, and estimating the backlash value through three di f ferent algorithms over the sun, planet , and ring gears that have spur or helical gear groups with the ring gear being fixed, and thereafter obtaining the mounting configurations .

The invention, in its most general form, is a method of mounting planetary gearbox components with a low-backlash value by means of software , comprising the following process steps :

Inputting the information contained in the quality-control reports on the gears and components thereof during the measurement , starting from the tooth and tooth backlash of the machine and all the teeth of the gear, respectively, or in the order of measurement ,

- Numbering every tooth of the gears to ensure correct placement during mounting,

- Determining macro dimensions of gears ,

- Determining minimum and maximum values of the gear backlash value for each combination based on tooth-tooth contact according to the production and operating parameters in the software ' s data repository in case of contact with the gears to work with each other,

- Drawing graphs showing the determined tooth backlash values ,

- Determining the mounting configurations of the numbered gears giving the lowest tooth backlash value according to whether they have a minimum tooth backlash value or the smallest maximum tooth backlash value or a gear backlash di f ference value between the smallest maximum and the minimum at any one or more than one time relative to the condition of placement between said graphs .

In one embodiment of the invention, the production and operating parameters are the tooth thickness , adj acent pitch error, runout , cumulative pitch error, thermal conditions to which the gear and gear components will be exposed during operation, the direction of rotation, the dimensional and geometric dimensions of the gearbox housing .

In an embodiment of the invention, the gears are sun, planet , and ring gears .

In one embodiment of the invention, sun-planet and planetring gear meshing configurations are determined .

Using the method of the invention, the ef fect of both productions , mounting errors , and manually phase dif ferences on the planetary gearbox, which consists of the kinematic behaviour of the external gear pair and the internal gear pair is identi fied and using the software algorithm, the optimum mounting configurations are determined . Thereby, the mechanical gap can be estimated, and results can be obtained that will enable mounting personnel to reduce the mechanical gap . In addition, both the spur and the helical gear characters can be considered within the planetary gearbox . In the method of the invention, quality control reports are requested from individual files for sun, planet , and ring gears , and the data are collected for every tooth-tooth contact of each sun-planet and planet-ring gear meshing configuration .

A diagram of the detailed process steps of the method of the present invention is shown in Figure- 1 . The processes are described in the following order .

In step 1 ( a ) , the maximum and minimum values of the sun, planet , and ring gear macro geometry, the tooth thickness measurement methods for each gear , and the relevant measured parameters according to the beam or pin top measurement methodology are read and processed respectively . The circumferential constant maximum and minimum backlash between the sun-planet gear pair is calculated . Maximum and minimum normal tooth thickness deviations of sun and planet gears are calculated . In the case of thermal expansion contribution, the runout values of sun, planet , and ring gears , the intercenter tolerance values of sun, planet , and ring gears , and the thermal characteristics of sun, planet , and ring gears are read and processed respectively . In the absence of thermal expansion contribution, the runout values of the sun, planet , and ring gears , and the center distance tolerances values of sun, planet , and ring gears are read and processed respectively .

In step 2 (b ) , i f the rotation direction is counter-clockwise , the adj acent pitch error of the left flank of sun and planet gears and in case of clockwise , the adj acent pitch error of the right flank of sun and planet gears are calculated . All tooth-tooth meshing combinations are calculated for the sun & planet gears through 1 rotation . Every backlash value are determined for each sun-planet gear pair . The smallest backlash value i s determined and recorded under 3 mounting types of configurations for the sun-planet gear-pair through 1 cycle of rotation .

In step 3 ( c ) , the smallest backlash values are typed and plotted under 3 mounting type configurations for the sunplanet gear pair . Planet and ring gear-pair are calculated . For planet and ring gear-pair, maximum and minimum tooth thickness deviations are calculated . The circumferential constant maximum and minimum backlash between the planet and ring gear pair is calculated . In the case of sun-planet rotation, the reverse rotation of Planet & Ring gear group is determined . In the case of counter-clockwise rotation, the left flank adj acent pitch error of planet and ring gears and in the case of clockwise rotation, the right flank adj acent pitch error of planet and ring gears are calculated . All tooth-to-tooth mesh combinations are calculated for the planetary-ring gear pair through 1 rotation .

In step 4 ( d) , each backlash value is determined for each planet-ring gear pair . The smallest backlash value is determined and recorded under 3 mounting type configurations for the planet-ring gear pair through 1 cycle of rotation . The smallest backlash values are typed and plotted under 3 mounting type configurations for planetary-ring gear pairs . I f the sun gear is driving or i f the carrier gear i s driving, the smallest backlash values are typed under 3 mounting type configurations for planetary gearbox considering the driving element and graphs thereof are plotted and the most appropriate planetary gearbox mounting information is given .

With the method of the invention, a technique has been developed to estimate the actual tooth backlash value for all operating combinations where the backlash value in the gearboxes is not the only value and each tooth of the mating gears being within their own tolerances and bonuses and in the cases that they remain within the limits or do not remain within the limits after the production of the machine .

Thanks to the method of the invention, the actual backlash of the planetary gearbox with the spur and helical gear group is estimated and minimi zed by considering the actual operating response . Actual operating backlash values are obtained by considering the design and manufacturing of essential components that are part of the assembly along with manufacturing defects and deformations under load, di f ferences caused by thermal expansion during operation as well as theoretical backlash, etc . parameters .

To ensure design validity according to the quality class for each gear, there are minimum parameters to be measured and post-production values of measurements such as inter-bearing distance tolerances determined as critical measurements over technical drawings . Examples of these parameters include tooth thickness measurements , adj acent pitch error, runout , and cumulative pitch error .

Among the parameters mentioned in the method of the invention, the most important ones of the sources that make up the backlash value can constitute the inputs of the software . Estimation of sun gear-planet gear pair backlash value and an estimate of the planetary gear-ring gear pair backlash value after mounting configurations that can generate a minimum backlash value and the mounting configurations that can create the minimum backlash value are calculated and the desired mounting configurations and backlash values for the entire planetary gear group are provided .

Information on gear and gear components from GMI , GMS , and/or CMM reports is inputted through software starting from the tooth and tooth backlash of the machine during measurement , in such a way that all the teeth of the gears are the same , respectively or in the order of measurement , and numbering is made for the correct placement of the gears during the installation .

Information on the thermal conditions to which the gears will be exposed during operation, the direction of rotation, and the dimensional and geometric dimensions of the steering box housing are included in the software repository .

In case of contact with the gears to work with each other, the tooth backlash values according to the relevant parameters are determined for the entire operating period as minimum and maximum for each combination based on tooth-tooth contact . In the method of the invention, graphs are drawn for the tooth backlash values that will occur during all combinations of gears that will work with each other . Then, in all the graphs , information is given about which mounting conditions the gear backlash value will be the lowest compared to the 3 main configurations .

The said 3 configurations may be described according to the following .

- Whether they have a minimum backlash value at any one or more than one time relative to the condition of placement between the graphs ,

- Whether they have the smallest maximum backlash value at any one or more than one time relative to the condition of placement between the graphs : and

- Whether they have the di f ference between the smallest maximum and minimum backlash value at any one or more than one time relative to the condition of placement between the graphs and the method of the invention further elaborates on the said configurations .

The advantages of the method of the invention and the technical ef fects it provides over existing systems are described below .

By using the quality-control reports of the gears produced, the method of the invention provides that the tooth backlash values are calculated and estimated over the system operating requirement during the design and converted into values that emerge in real conditions .

Through the software in the method of the invention, the macro dimensions of the gears added with quality-control reports can be determined . The tooth clearance values during mounting can be calculated based on the ef fects of parameters that emerge during production and loading . The backlash value during operation through 1 rotation can be estimated and the optimum distance between the centers can be calculated to reduce the tooth clearance by considering the entry conditions of the mating gears . The algorithm enables the individual characteristics of the gears that will work with phase methodology can be automatically minimi zed . Information on the change of tooth clearance values can be given manually in the installation of the gears that will work with phase di f ference as desired by the user . In addition, the amount of output backlash in the gearbox can be determined by considering the direction of rotation .

Under the calculation of the algorithms of three di f ferent configurations that can guide the mounting personnel to minimi ze the backlash, a reduction ef fect even below the desired target backlash value is achieved .

The controllers of the platforms are provided with the tooth backlash value that they will have through the scanning after each degree rotation and correct backlash value estimates are made by considering the dimensional and geometric parameter value di f ferences on the right and left flanks of the teeth of the gear according to the direction of rotation . Therefore , being able to obtain the backlash value correctly for each contact , which is one of the dynamic effects of the gearbox, the gearbox behaviour becomes a predictable phenomenon .

Thanks to the integration of measuring instruments and tools into the software based on the tooth or tooth backlash, when they start to measure the parameters af fecting the tooth backlash while creating reports , the backlash values in each tooth-tooth contact give the necessary conditions for mounting gears with teeth numbered to give the lowest backlash value from all mounting combinations that may occur under three di f ferent configurations . Thus , the tooth backlash value estimation accuracy margin problem resulting from an evaluation solely based on the average value of the parameter received from the measurement report , which itsel f is the cause of any tooth backlash and the unpredictability problem of backlash values for the gears placed randomly on the numbered gears during assembly are eliminated .

As the theoretical tooth backlash value , the minimum and maximum tooth backlash values in each tooth-tooth combination and the tooth backlash values at the time of operation can be estimated instead of a single value in the studies in the literature .

With the data of each backlash value in every tooth-tooth combination by means of the method of the invention, providing information for platforms making a full turn ( 360 ° ) or a hal f turn i . e . , a 180 ° turn, as well as transmitting tooth backlash values correctly to the controller of the system on the rotating platforms become possible , which brings a great advantage compared to the studies in the current art .

Hundreds and thousands of sub-elements such as planetary gear, sun gear, orbital gear and planetary carrier manufactured within ( or partially outside ) manufacturing tolerances , using this method, the mounting of said elements can be planned in the most ef ficient way and by classi fying the backlash values , the production of planetary type converters with guaranteed backlash values becomes possible .

Planetary converters that are produced and quality control measurements thereof are completed but couldn' t meet the required backlash values because of installation can be classi fied as converters having di f ferent backlash values

( from high to low) with this mounting method . I f the quality value determined by the customer in the design during production cannot be obtained for any gear or gears after production, the most compatible counter-produced gear is found by means of the algorithm provided by the method of the invention instead of quali fying the gears as waste , the gearbox that can be located within the target backlash value can be provided with the correct mounting configuration .

In addition to the fact that it ensures the installation of the assembly line in companies that perform main assembly as well as in production companies , there is an advantage that the software is integrated to obtain the correct clearance values with the gears numbered according to the provided quality-control reports during the mounting of the gears .

In summary, the method of the invention enables correct positioning and mounting of planetary gearbox components with a low backlash value , by taking production and operating conditions into account .

Description of the Figures

Figure-1 A diagram of the method of the invention

Description of Reference Numbers in Figures a . Step 1 b . Step 2 c . Step 3 d . Step 4

Claims

1 . A method of mounting planetary gearbox components with a low backlash value , wherein the method comprises the following process steps by means of a software :

Inputting the information contained in the quality-control reports on the gears and components thereof during the measurement , starting from the tooth and tooth backlash of the machine and all the teeth of the gear, respectively or in the order of measurement ,

- Determining macro dimensions of gears ,

- Determining the minimum and maximum values of the gear backlash value for each combination based on tooth-tooth contact according to the production and operating parameters in the software ' s data repository in case of contact with the gears to work with each other,

- Drawing graphs showing the determined tooth backlash values ,

2 . A method according to claim 1 , wherein the production and operating parameters are the tooth thickness , adj acent pitch error, runout , cumulative pitch error, thermal conditions to which the gear and gear components will be exposed during operation, the direction of rotation, the dimensional and geometric dimensions of the gearbox housing . A method according to claim 1 or 2 , wherein the gears are sun, planet , and ring gears . A method according to claim 3 , wherein the sun-planet and planet-ring gear meshing configurations are determined .