Gear Unit Research Articles

Kinematics Analysis of Incomplete Gear and Rack Pumping Unit

A pumping unit with incomplete gear and rack reversal was designed for smooth motion and low energy consumption. This paper first describes the working principle of the pumping unit. The kinematical equation of the pumping unit is established on the basis of analyzing the kinematic relationship between the first tooth meshing area, the normal meshing area and the final tooth meshing area of incomplete gear and rack. The kinematic relationship curve of the pumping unit is obtained by ADAMS simulation. The simulation results show that the theoretical model is correct. By comparing the results with the conventional pumping unit, it can be seen that: the pumping unit has a smooth movement of the up-down strokes, with fluctuations of movement only in the process of changing directions. The incomplete gear and rack drive is smooth, which can improve the kinestate of the pumping unit.

Modeling of the motion control system of an unmanned tracked vehicle with onboard gear units

The results of a study of the control processes of an automated transmission and internal combustion engine of a transport unmanned tracked vehicle when the speed of movement is set by an external control device are presented. Keywords: unmanned tracked vehicle, algorithm, motion control, onboard gear unit, programmable logic controller, cruise control. tanksv@mail.ru

Design and implementation of a diagnostic system for measuring high-precision reducers

At present, the industry is in a phase where there is an effort to maximize the automation of production processes. In many places, human power is being replaced by automated machines and industrial robots. Automation makes it possible to increase work efficiency, significantly reduce production costs and also increase the quality of the final product. A precondition for increasing the quality of production is to achieve high accuracy of specialized machines and industrial robots, resp. the accuracy of positioning of individual parts. Due to the drive system and the achieved speed, the gear unit includes a gearbox. Reducers used in robotic joints are the most complex subsystems of robots. For very precise applications, the designers will reach for the so-called backlash-free reducers for their characteristic properties (minimum values of backlash in teeth, angular transmission errors, hysteresis and others). Despite many positive properties, high-precision reducers also show their characteristic nonlinearities, which influence the behavior of the whole system and it is so important to know their behavior. Given these facts, this article deals with the design and implementation of mechatronic diagnostic equipment for the identification of nonlinearities, static and dynamic parameters, vibrodiagnostic measurements and measurements of the efficiency of bearing reducers.

Advanced calculation of the deflection of worm shafts with FEM

Worm gears are gear units with a shaft angle of mostly 90°. They are used in a variety of industrial applications due to large gear ratios and high transmittable torques. The high sliding ratio in the tooth contact requires a hard/soft material combination that is insensitive to scuffing. Worm shafts usually are made of case-hardened steel and worm wheels of a copper-tin-bronze alloy. Since damage predominantly occurs at the wheel (pitting, wear, tooth fracture, etc.), a wide range of calculation methods for load capacity and service life were developed. Regarding the worm shaft, only the deflection is examined, because high displacements of the shaft shifts the contact pattern, which leads to transmission errors and may lead to increased wear. Common calculation methods, e.g. according to DIN 3996 and ISO/TS 14521 provide a good approximation of the deflection. However, simplifications are made in favour of the manageability of the calculation method. Geometric modifications on the worm such as reduced tooth thickness or different lead angles cannot be taken into account with common methods. In order to close this gap, a new approach was presented by Norgauer in 2021, however, significantly overestimating the stiffening effect of the gearing in some cases by neglecting the helical winding of the worm teeth. For efficiency-optimal design of minimally thin worm shafts, approaches that go beyond the deflection are also missing. Investigations by the authors on worm gears using the finite element method (FEM) show a deviation of the bending line of worm shafts from the common calculation methods. The FEM calculations simulate the tooth meshing under load by a driving torque on the shaft, whereas the standard calculations simplify the load distribution on the worm shaft as a radial force introduced at a point. In addition to the magnitude of the radial forces, the axial tooth force component was identified as an influence factor on the bending line since it causes a displacement of the maximum bending location. Especially for increasing diameter factors the displacement of the bearings under load must be taken into account since they may be in the same range as the deflection. Furthermore, the helical winding of the teeth around the shaft leads to an average stiffening effect of the gearing. The cross-section depends on the gear meshing position and causes a periodic fluctuation of the area moment of inertia and a wobbling motion of the shaft. The changing load distribution on several teeth causes a periodic change of the lever arms and an additional dependence of the deflection from the mesh position. An analytical calculation method for the deflection of worm shafts is proposed. It aims at the precise calculation of the spatial expression of the bending line, extends the commonly used simplified model and takes the newly identified factors into account. The bending lines in both radial directions are considered separately. The values of the new introduced factors are derived from the FEM results. Finally, the calculated bending lines are compared with the FEM results and verified.

Influences on the excitation behavior of lightweight planetary gearboxes

One of the main cost drivers in mechanical engineering is material. In order to reduce costs, but also to reduce CO2 emissions in mobile applications, increasing efforts are being made to reduce the mass of components. In gear development, power density as the ratio of transmittable power to gear weight has become one of the key quality criteria. However, saving material usually also leads to lower stiffness of the components. In combination with higher specific powers and the associated higher forces, higher deformations and displacements occur in the gear unit. The gear unit is more elastic overall.Within this paper a measuring cell is presented which allows to measure the influence of elastic deformations and additional misalignments on the excitation behavior. By means of this measuring cell, the influence of certain misalignments and different ring gear rim thicknesses are investigated. The results show modulated excitations and sidebands which are excited depending on the misalignment.

Multi-objective optimization of gear unit design to improve efficiency and transmission error

This study aims to implement multi-objective optimization of a gear unit in order to minimize the power loss and the vibrational excitation generated by the meshing, via a multi-scale approach that extends from gear contact to the complete transmission. All these indicators are closely linked to the macro and micro-geometry definition of the gear pair. The optimization is carried out using a genetic algorithm, namely the Non-Dominated Sorting Genetic Algorithm II (NSGA-II). The design variables chosen for the problem are the pressure angle and the helix angle, as macro-geometry characteristics of the gear, and/or the length and the amount of tooth profile modifications, as micro-geometry characteristics of the gear. Constraints are imposed in order to not exceed a maximum bending stress at the tooth root of the gear and to not fall below a minimum total contact ratio. From the results obtained, it is found that the multi-objective optimization with both micro and macro-geometry parameters simultaneously gives different results than those obtained with macro-geometry first and then micro-geometry parameters. In order to study the importance, or not, to take into account the complete gear unit, a comparison is made between the local power loss generated by gear tooth friction and the total power loss in the single stage gear unit in terms of design variables values.

Design and Development of Lanyard Printing Machine

A Lanyard is an essential part of preparing any company or Organization’s office supplies or stationery. As an ID card holder, Lanyard provides identity and respectability to different organizations. While a simple lanyard is surely practical, a printed and specialized one will undoubtfully leave an enduring effect. To get attractive, brand-relevant satin lanyards to give your company just the right kind of exposure it needs and if employees are participating in conferences and exhibitions, wearing a branded lanyard will help them increase brand awareness. The work involved the design, development, and testing of a Lanyard Printing machine which overcomes the drawback of existing costly printing machines. The design and developmental stages include the gear and chain drive along with the rack and pinion method and their generation mechanisms. Details of a simple, sturdy, and efficient gear and chain unit, financially beneficial to laborers and producers are considered. The unit can print about 80 impressions per minute compared to 30 impressions per minute of existing machines.

Power-Flow and Mechanical Efficiency Computation in Two-Degrees-of-Freedom Planetary Gear Units: New Compact Formulas

The mechanical efficiency is a computed value for comparing the performance of the multi degrees-of-freedom geared transmissions of hybrid vehicles. Most of the current methods for estimating gear trains mechanical efficiency require the decomposition of gear transmissions in basic structural elements or planetary gear units (PGU). These are two degrees-of-freedom components whose mechanical efficiency has a deep influence on the overall device. The authors (E.L.E., E.P.) already evidenced that, under certain kinematic conditions, the classic Radzimovsky’s formulas, widely accepted for computing the mechanical efficiency of PGUs, are not adequate. In this paper, more general and reliable formulas for computing the mechanical efficiency are deduced. The proposed formulas herein, exploiting the concept of potential or virtual power, evidence the dependency between kinematics and efficiency. A numerical example compares our results with previous work on the subject.

Design and modeling of an in-wheel two-speed AMT for electric vehicles

To improve the performance of the electric vehicles (EVs), significantly reduce unsprung mass, and improve system reliability, in the present paper, the authors propose a novel in-wheel two-speed automatic manual transmission (WH-AMT) structure which weighs only 16.8 kg. The proposed WH-AMT is composed of a high-speed drive motor unit, gear transmission unit, and shift actuator unit. The gear transmission system has no free planet carrier and ring gear, which improves the reliability of the WH-AMT in the harsh working environment within the wheel. Owing to the integrated design in the wheel, the free space in the wheel is increased, and unsprung mass is greatly reduced. In this study, kinematic analysis of the WH-AMT, derivation of its dynamic equations, and development of a simulation model of the shifting process are carried out. The results indicate that there is no power interruption in the WH-AMT during gear shifting, and the shift quality is high, which considerably enhances the power performance of EVs.

Development of a small-sized electromechanical steering gear unit by simulation modeling

In this paper the results of the development of an electromechanical steering gear based on waveform reductor that provides rotary motion of the working surfaces of small-sized aerial munition are presented. Calculations of the design parameters of the components of the steering gear, the formation of the desired dynamic properties of the product are implemented by the method of simulation modeling in the Matlab Simulink environment. The model is fully parametrized. The Simulink-model contains blocks that implement signal conversion in accordance with the physical model of real equipment. The article presents the results of laboratory and flight tests of a prototype of steering gear confirming the success of the adopted circuitry solutions and the adequacy of the developed simulation model. The developed simulation model can be used as universal design tool for electromechanical steering gears.

A Rational Numerical Method for Simulation of Drop-Impact Dynamics of Oleo-Pneumatic Landing Gear

Oleo-pneumatic landing gear is a complex mechanical system conceived to efficiently absorb and dissipate an aircraft’s kinetic energy at touchdown, thus reducing the impact load and acceleration transmitted to the airframe. Due to its significant influence on ground loads, this system is generally designed in parallel with the main structural components of the aircraft, such as the fuselage and wings. Robust numerical models for simulating landing gear impact dynamics are essential from the preliminary design stage in order to properly assess aircraft configuration and structural arrangements. Finite element (FE) analysis is a viable solution for supporting the design. However, regarding the oleo-pneumatic struts, FE-based simulation may become unpractical, since detailed models are required to obtain reliable results. Moreover, FE models could not be very versatile for accommodating the many design updates that usually occur at the beginning of the landing gear project or during the layout optimization process. In this work, a numerical method for simulating oleo-pneumatic landing gear drop dynamics is presented. To effectively support both the preliminary and advanced design of landing gear units, the proposed simulation approach rationally balances the level of sophistication of the adopted model with the need for accurate results. Although based on a formulation assuming only four state variables for the description of landing gear dynamics, the approach successfully accounts for all the relevant forces that arise during the drop and their influence on landing gear motion. A set of intercommunicating routines was implemented in MATLAB® environment to integrate the dynamic impact equations, starting from user-defined initial conditions and general parameters related to the geometric and structural configuration of the landing gear. The tool was then used to simulate a drop test of a reference landing gear, and the obtained results were successfully validated against available experimental data.

Teeth deformation of non-circular gears

In practice, gear units whose transmission number is not constant during one revolution are used. Such gears include the proposed elliptical transmission. Its application can be (missing a word?) and the automotive industry. The gears set consists of a pair of identical elliptical gears. The transmission ratio of the designed elliptical gear is not constant. The basic kinematic characteristics of this transmission are described in this work. The deformation in contact point of non - circular gears is determined by the finite element method in this paper. The results are compared with the deformation of the teeth of the spur gears.

Suitable Material Selection for Large Size Cylindrical Gears*

Abstract Globalization and international supply chains constantly challenge gear- and steel manufacturers. In the case of large gear units in particular, expensive alloy contents have a direct impact on the material price. Steels with lower alloy contents and therefore cheaper steels are therefore becoming the focus of attention in order to further improve competitiveness. This article therefore compares two materials with different alloying elements and contents and thus different hardenability behaviour. For this purpose, extensive material characterizations as well as pulsator tests were carried out on case-hardened large gears. The aim of these tests was to determine the tooth root load-bearing capacity of the two material variants. Finally, the results are compared, discussed and recommendations for industrial application are derived, taking into account the hardenability of large gears. ◼

Modified Stacked Autoencoder Using Adaptive Morlet Wavelet for Intelligent Fault Diagnosis of Rotating Machinery

Intelligent fault diagnosis techniques play an important role in improving the abilities of automated monitoring, inference, and decision making for the repair and maintenance of machinery and processes. In this article, a modified stacked autoencoder (MSAE) that uses adaptive Morlet wavelet is proposed to automatically diagnose various fault types and severities of rotating machinery. First, the Morlet wavelet activation function is utilized to construct an MSAE to establish an accurate nonlinear mapping between the raw nonstationary vibration data and different fault states. Then, the nonnegative constraint is applied to enhance the cost function to improve sparsity performance and reconstruction quality. Finally, the fruit fly optimization algorithm is used to determine the adjustable parameters of the Morlet wavelet to flexibly match the characteristics of the analyzed data. The proposed method is used to analyze the raw vibration data collected from a sun gear unit and a roller bearing unit. Experimental results show that the proposed method is superior to other state-of-the-art methods.

Development of a precision drive unit at K.K.K. 99 Ltd. to be universally used as robot joints with high powerdensity and modular construction

A highly innovative gear unit set has been developed and manufactured to be widely used in medical industry, manufacturing robots or high precision manipulators. The main elements of the drive unit are the gear ratio reducing strain wave gear, the torque-motor and the force-torque measuring sensor, which can be combined arbitrarily. In one unit the motor series size is given but its power output (longer motor) and the gear reduction ratio can be varied. Assembling these parts, the result of this RnD project is a high precision drive with minimal dimensions, which, on itself, is able to position rotating movement precisely and while at halt it can also keep that position with high torsional stiffness. What makes the modular precision drive unit whole, is the controlling system. The above-mentioned machine elements can be assembled into different configurations so it can become part of a SCARA, humanoid or Delta robot. As a result of this project the created precision drive prototypes could provide tests and results that may influence the mechatronic and mechanical engineering profession.

Improvement of Gear Unit Load and Noise Reduction by Optimal Design of Tooth Surface Using Principal Component Analysis

Improvement of Gear Unit Load and Noise Reduction by Optimal Design of Tooth Surface Using Principal Component Analysis

Development and manufacturing of an experimental flat wheel strain wave gear unit at K.K.K. 99 Ltd.

The functions of the main components of a flat-wheel harmonic drive are similar to the functions of a traditional harmonic drive, but the features of the flexible and the solid wheels are different. This paper reports the development and investigation of the experimental flat wheel harmonic drives. The development project was sponsored by Ministry for National Economy.

Design and Manufacturing Strategy of a Back-to-Back Test Rig for Investigation of Ultra High Cycle Fatigue Strength Regarding Tooth Root Strength in Aerospace Applications

Geared turbofans increase the efficiency of aircraft engines. By decoupling the fan and low- ressure turbine, both components can be operated at their optimum speed. Due to the high number of flight hours and the high turbine speeds of n > 10,000 rpm, the number of load cycles at the gear teeth of the planetary gear unit is significantly higher than the conventional fatigue strength of gear teeth. The planetary gears under fully reversed bending load are particularly susceptible to tooth root fractures. Pulsator test rigs are not suitable for testing tooth root load capacity under fully reversed bending load. The concept of a modified 3-shaft backto-back test rig was set up to cope with this challenge. A back-to-back test rig consists of a test and reference gearbox, which are connected by shafts to form a closed power circuit. In order to perform the investigation efficiently, the test rig is operated at a speed of n > 12,000 rpm with a recirculating power of P > 5 MW. This performance class results in special requirements for the test rig design. The roller bearing arrangements normally used for back-to-back test rigs no longer offer sufficient load carrying capacity, so that a changeover to journal bearings is necessary. This leads to high power losses of the bearings of P ≈ 200 kW and oil quantities of Q ≈ 450 l/min on the cooling and bearing lubrication side. The journal bearings of the gearboxes have a decisive disadvantage. Starting under load is not possible. Therefore, a hydraulic load unit was designed which allows load application at operating speed. In the reference gearbox, this unit shifts two helical gears on a spline shaft, which are slanted in opposite directions, towards each other, so that a torsional load is generated in the test gearbox by means of a closed power circuit. The two displaceable helical gears represent the greatest challenge from a manufacturing point of view. In order to achieve an even load distribution on both gears, they must be manufactured very precisely to each other and to the spline profile. In the report, the focus is set on the double helical reference gearbox including the axial load unit. Besides the design of the components the requirements regarding manufacturing are analysed and possible manufacturing chains are discussed.

Reliability analysis of gear rotation meta-action unit based on Weibull and inverse Gaussian competing failure process

In order to analyze the reliability of meta-action unit(MAU) from the perspective of competing failure, this paper proposes a reliability analysis method for gear rotation MAU (GRMAU) subjected to the competing failure process of wear degradation and random shocks. For the traditional competing failure process, Winner process and Gamma process were widely used to describe soft failure, Poisson process was widely used to describe hard failure. In this paper, hard failure is described by the Weibull distribution, which can handle the case that the shocks count data are under-dispersion or over-dispersion, and soft failure is described by the inverse Gaussian(IG) process, which is suitable for the degradation process that is monotonically increasing and that degraded mean and variance have certain randomness. Moreover, a mixed δ-extreme shock model is proposed to extend the traditional shock models. Taking into account the interaction between the two failure forms, the reliability analyses of the mutually dependent competing failure process based on the four shock models, namely extreme shock model, cumulative shock model, δ shock model and mixed δ-extreme shock model, are carried out. Finally, some numerical examples vis-à-vis a GRMAU are illustrated to explain the implementation and effectiveness of the proposed model.

New construction of cycloidal gear unit made of plastics

Cycloidal gears constitute the main working unit of the fluid power gerotor machine. The paper presents a way of increasing the load-carrying capacity of cycloidal unit made of plastic. The aim has been reached through design and material modifications. As a result of those modifications, a design concept of the cycloidal gear system, which is different from the structures previously produced, has been created. The introduced modifications are based on the theoretical analysis of stress and deformations that occur in cycloidal gears during their operation. The analysis was conducted by means of the finite element method. Although the main focus was on analyzing the mechanism behind the deformations, an attempt was also made at extending the application scope for finite element method. The analysis by means of finite element method has been conducted for plastic and steel at the same time. This is result of showed design in which plastics and steel form the construction together one integral part. As a result of the analysis, the maximum value of the working pressure at which hydraulic gerotor machines with plastic cycloidal gears can work was determined. Thanks to the use of the finite element method one can point out the way of introduction of plastics in hydraulic machines construction.