Variable Gear Research Articles

Variable gearing at the ankle during walking in adults and young children: implications for foot development and evolution

Introduction: The human foot has evolved over the past seven million years from a relatively mobile, grasping appendage to a highly derived structure with a heel pad and longitudinal arch that can absorb shock at heel strike and weight-bearing yet also function as a powerful lever at toe-off. It has been proposed that the modern human foot evolved to allow our species to use “variable gearing” during walking and running. In this model, the gears of the human foot are defined relative to the ankle center of rotation as R, the distance from the ground reaction resultant vector, and r, the distance from the calf muscle vector. The gear ratio defines the torque generated to propel the body or stretch the triceps surae muscles. We test the hypothesis that variable gearing is associated with modern human pedal anatomy and a heel-to-toe rollover that allows a shift from “low gear” to “high gear” during stance.Methods: Using force plate and video analysis, we examined variable gearing in adults and children engaging in adult heel strike (AHS = 35), flat foot contact (FFC = 39), or initial heel contact (IHC = 26).Results and Discussion: Our hypothesis was partly supported. Although variable gearing was observed in IHC steps and was greater than in FFC steps, it was not as developed as in AHS steps. This may be related to anatomical and motor control differences between juvenile and adult feet, suggesting that adult anatomy, including a high arch, and neural control are critical for full use of variable gearing and that this feature would have evolved in later hominins around two million years ago with the appearance of a fully modern foot.

Soft skeletons transmit force with variable gearing.

A hydrostatic skeleton allows a soft body to transmit muscular force via internal pressure. A human's tongue, an octopus' arm and a nematode's body illustrate the pervasive presence of hydrostatic skeletons among animals, which has inspired the design of soft engineered actuators. However, there is a need for a theoretical basis for understanding how hydrostatic skeletons apply mechanical work. We therefore modeled the shape change and mechanics of natural and engineered hydrostatic skeletons to determine their mechanical advantage (MA) and displacement advantage (DA). These models apply to a variety of biological structures, but we explicitly consider the tube feet of a sea star and the body segments of an earthworm, and contrast them with a hydraulic press and a McKibben actuator. A helical winding of stiff, elastic fibers around these soft actuators plays a critical role in their mechanics by maintaining a cylindrical shape, distributing forces throughout the structure and storing elastic energy. In contrast to a single-joint lever system, soft hydrostats exhibit variable gearing with changes in MA generated by deformation in the skeleton. We found that this gearing is affected by the transmission efficiency of mechanical work (MA×DA) or, equivalently, the ratio of output to input work. The transmission efficiency changes with the capacity to store elastic energy within helically wrapped fibers or associated musculature. This modeling offers a conceptual basis for understanding the relationship between the morphology of hydrostatic skeletons and their mechanical performance.

An efficient and accurate measurement method of tooth flank variations for face gears

Traditional measurement method for face gear variations is time-consuming, for it is based on a complex procedure to establish the measurement coordinate system (MCS). Moreover, errors induced by misalignment between the design coordinate system (DCS) and the MCS are not properly processed in measurement. Therefore, this work proposes an efficient and accurate method to measure face gear flank variations using the coordinate measurement machine (CMM). Firstly, the MCS establishment without the need for an iterative process, which saves measurement time. Secondly, the measurement error compensation model (MECM) relies on the MCS and utilizes the four-parameter representation, which reduces variables in the nonlinear equation system. Finally, experiments demonstrated the effectiveness and repeatability of this method, successfully reducing misalignment errors. The tooth flank normal variation improved by 3.33%, the pitch variation improved by 26.28%, and the total cumulative pitch variation improved by 19%.

Guest Editorial Design and Optimisation of Electric Motors for Transport Electrification

Electric traction drives have seen increased application for road, rail, marine and aerospace transportation to provide improved performance and to reduce emissions. They generally consist of a dc power source, a power electronic converter and an electric motor. The electric motors used in such applications require high power density to achieve small size and weight, high efficiency to reduce energy consumption, high reliability to reduce maintenance and a wide constant power speed range to minimize the need for variable gearing between the motor and the wheels.

Study on Health Status Classification of Variable Gear Pump Based on GLCT and CPA-SVM

Study on Health Status Classification of Variable Gear Pump Based on GLCT and CPA-SVM

Effects of rotational speed on the natural frequency of the differential bevel gear

With the development of techniques for the use of gears and their many shapes and types, the mechanical need for them has become great, especially in the use of them in the field of cars, and the most important of these types are bevel gears, as these gears are considered essential in differential gears. The use of differential gears in mechanics in general helps to reduce noise in the movement, but there must be vibration resulting from this movement, and accordingly, bevel gears and the effect of rotating gears on free vibration have been studied. Variable gears were used according to a simulation program and the study of the free vibrations that occur to them. The effect of rotational speed on the natural vibration greatly affects the transmission of movement in the car and increases the fault distortions that occur in the differential gearbox. The result shows the natural vibration reached at the speed of 5000 rpm, and the value of the vibration reached 3564.5 Hz, which is the highest value compared to the remaining speed. The distortion at a speed of 1,000 rpm. The process of rotation and natural vibration affects the deformations and stresses that get on the gears themselves. The natural vibration is greatly reduced when the number of clamping places for the differential gear is increased. Compared to the presence of two spinning tires, the vibration value reduced. At a rotating speed of 5000 rpm, it is known that increasing the rotational speed raises the value 3015.9 Hz with one tire revolution with one tire rotation, the huge strains influence the little gears in the differential gearbox. The greatest value of distortion is 0.00067 m at 5000 rpm, which is the largest value of deformation compared to the rest of the employed rotational rates with one tire revolution.

Contribution of stroke-related changes in neuromuscular factors to gear ratio during isometric contraction of medial gastrocnemius muscle: A simulation study

BackgroundIt is not clear which neuromuscular factors are most closely associated with the loss of variable fascicle gearing after chronic stroke. The purpose of this simulation study is to determine the effects of stroke-related changes in key neuromuscular factors on the gear ratio. MethodsA modified Hill-type model of the medial gastrocnemius was developed to determine the gear ratio for a given muscle activation level and musculotendon length. Model parameters were then systematically adjusted to simulate known stroke-related changes in neuromuscular factors, and the gear ratio was computed for each change in the parameters. A Monte Carlo simulation was performed to understand which neuromuscular factors and fiber behavior-related parameters are most relevant to the loss of variable gearing. Dominance analyses were also conducted to quantify the relative importance of fiber behavior-related parameters on the gear ratio. FindingsThe gear ratio decreases significantly with smaller pennation angle and with shorter optimal fiber length. In addition, muscle thickness and pennation angle at optimal fiber length appear to be the most important muscle architectural parameters. Dominance analyses further suggest that primary determinants of gear ratio include initial pennation angle, fiber rotation-shortening ratio, initial muscle thickness, and fiber rotation. InterpretationOur findings provide insight that the pennation angle may play an important role for efficient muscular contraction, implying that maintaining muscle architecture and/or improving fiber/fascicle rotation could a key goal in rehabilitation interventions. Our findings will help us to better interpret altered gearing behavior in aging and pathological muscles.

Contact stress reliability analysis based on first order second moment for variable hyperbolic circular arc gear

Aiming at the contact strength reliability of variable hyperbolic circular arc gear, a reliability analysis method for contact strength of variable hyperbolic circular arc gear based on Kriging model and advanced first-order and second-moment algorithm is proposed. Kriging model was used to establish the limit state equation of the contact stress reliability analysis of variable hyperbolic circular arc gear, and the advanced first-order second-moment method was used to analyze the contact stress reliability of variable hyperbolic circular arc gear based on the limit state equation of the contact stress. In order to verify the effectiveness of the proposed algorithm, a Markov Chain Monte Carlo reliability analysis method based on Important Sampling was proposed. Markov Chain and Important Sampling were exploited to improve the accuracy of contact reliability analysis based on Monte Carlo method for variable hyperbolic circular arc gear. The comparison between the analysis results of Markov Chain Monte Carlo with Important Sampling method and first order second moment shows that it is feasible to analyze the reliability of variable hyperbolic circular arc gear by first-order second-moment method.

Rattle Dynamic Model and Vibration Behaviors of Noncircular Face Gear

Abstract Noncircular face gear (NFG) is a new type of variable transmission ratio gear mechanism. Based on nonlinear dynamic theory of gear, the rattling behavior of the NFG under multifrequency excitation was studied. The generalized transmission ratio function of the NFG with closed pitch curve was constructed by Fourier series. The nonlinear relative displacement between teeth was described by an analytical expression during the process of time-varying transmission. Considering the factors of time-varying instantaneous center, meshing stiffness, transmission error, and backlash, a nonlinear dynamic model of the gear was established with the rotational angle as the independent variable. The dynamical responses were calculated by Runge–Kutta method to analyze the effects of the input speed, load torque, transmission ratio coefficient, and error on rattling behaviors. The results show that under the action of combined excitation of time-varying instantaneous center and meshing stiffness, the rattle of noncircular gear is more likely to occur. As the increase in input speed, error, and range of transmission ratio variation or the decrease of load, the NFG appears no rattling, unilateral, and bilateral rattle successively and the rattling intensity increases accordingly. The rattling threshold speed can be improved by increasing the accuracy and load of gear or decreasing the range of the transmission ratio.

Novel generation method of tooth surface points for variable transmission ratio gears

Variable transmission ratio gears have shown considerable potential as key components of variable speed transmission steering boxes that balance steering portability and sensitivity. The objective of this study is to develop a novel method for designing variable transmission ratio tooth surfaces to circumvent the shortcomings of the meshing theory method. The involute rack of the variable transmission ratio pinion-and-rack pair is considered as a set of countless and infinitely close transverse sections, each of which is referred to as a gear element. Assuming evenly distributed circles in the physical domain of the variable transmission ratio tooth surfaces of the pinion, the problem of generating a tooth surface point is transformed into solving the specific geometric feature intersection point of each circle and corresponding gear element during variable transmission ratio meshing. Thereafter, a mathematical model and algorithm are developed to generate tooth surface points in an approximately even pattern. The normal deviations of the gear-element–generated tooth surface points and the corresponding tooth surface points calculated using meshing theory show that the proposed design method has a sufficiently high accuracy. Finite element models are employed analyzing the contact pattern, contact stress, bending stress, and transmission ratio error. The results indicate that the layout of approximately even tooth surface points using the gear element method is beneficial for improving the fitting precision of tooth surfaces and reducing the contact stress and transmission ratio error. Further, the same derived law of the flank and fillet tooth surfaces is conducive to the continuity of the tooth surfaces, which contributes toward reducing the bending stress. Finally, a prototype is manufactured via CNC end milling. The major contributions lie in a robust and efficient modeling method for variable transmission ratio tooth surfaces, which combined forms a solid foundation for their application.

Simulation and Experimental Research on Electrical Control Anti-backlash Based on a Novel Type of Variable Tooth Thickness Involute Gear Pair

This paper presents an electrical backlash control method based on a novel variable tooth thickness involute gear pair (VTTIGP) through acceleration judgment. First, the principle, characteristics and theoretical tooth surface equation of the novel type of variable tooth thickness involute gear (VTTIG) are proposed. Compared with the traditional variable tooth thickness gear (VTTG), each transverse of the novel type of VTTIG has the same tooth root circle and the addendum circle. Therefore, there will be no interference caused by the excessive axial relative movement distance between the gear pairs when eliminating the backlash. The theoretical calculation equation of no-load transmission error (TE) and time-varying backlash for a dual-eccentric novel type of VTTIGP are deduced. Second, using the theoretical backlash equation and the eccentricities and the initial phases obtained through the experimental TE curve obtained with angular displacement sensors and the developed TE equation, the continuous backlash curve of the gear pair is obtained. Based on the RecurDyn software and its Colink control module, the co-simulation model of the novel type of VTTIGP and its backlash control system is used to explore the electrical backlash control method through acceleration judgment in the case of time-varying backlash. Finally, using angular displacement sensors and linear actuators, the experimental study on the anti-backlash control with different reversed positions under different input speeds is carried out, demonstrating that this novel electrical anti-backlash control method is effective.

Adaptive Transmission for Unmanned Mobile System

The unmanned mobile system of any transport facilities (land, space and underwater) should have high extent of reliability and non-failure operation in process. The elementary mechanical system in a combination to the elementary control system can provide these qualities. Besides the unmanned mobile system of space and underwater transport should have small sizes and weight and self-regulation possibility at origination of non-staff situations. Automatic gearboxes existing now (CVT) are the most complicated mechanical systems and have the most complicated hydro mechanical control system [1]. Such transmissions are absolutely unsuitable for unmanned mobile system because of their low reliability and inadequacy to a changing circumambient.
 Recently adaptive gear variators are developed [2, 3, 4, 5]. The adaptive variator represents the self-controlled gear planetary train with the constant engagement of the toothed wheels. Who’s that was created on the basis of an author's disclosure «Effect of force adaptation in mechanics». The adaptive gear box of the automobile represents a brand-new planetary gear variator in the form of two mobile kinematic chain with the elementary additional original constraints. The adaptive variator has ability to drive the executive tool with a speed which is back - proportional external loading at constant power of an engine. The basic advantages of an adaptive gear variator: absence of the control system, simplicity of a design, full adequacy to working conditions. It seems expedient to use an adaptive gear variator in the transmission of a mobile transport system.
 Adaptive drivetrain based on usage of a gear variator (theoretical bases, tests, characteristics and practical recommendations) is in-process presented.

Load-dependent Variable Gearing Mechanism of Muscle-like Soft Actuator

Pennate muscle is characterized by muscle fibers that are oriented at a certain angle (pennation angle) relative to the muscle’s line of action and rotation during contraction. This fiber rotation amplifies the shortening velocity of muscle, to match loading conditions without any control system. This unique variable gearing mechanism, which characterized by Architecture Gear Ratio (AGR), is involves complex interaction among three key elements: muscle fibers, connective tissue, and the pennation angle. However, how three elements determine the AGR of muscle-like actuator is still unknown. This study introduces a Himisk actuator that arranges five contractile units at a certain pennation angle in a flexible matrix, the experiment and simulation results demonstrated that the proposed actuator could vary AGR automatically in response to variable loading conditions. Based on this actuator, we present a series of actuators by simulations with the varying pennation angle (P), elastic modulus of the flexible matrix (E), and number of contractile units (N) to analyze their effects on AGR, and their interaction by three-factor analysis of variance. The results demonstrated that P and N effect on the AGR significantly, while E effects on AGR slightly, which supported the idea that the P is the essential factor for the AGR, and N is also an important factor due to the capability of force generation. This provides a better understanding of mechanical behavior and an effective optimizing strategy to muscle-like soft actuator.

Adaptive control and disturbance compensation for gear transmission servo systems with large-range inertia variation

In gear transmission servo systems, backlash effect and inertia variation often generate low precision, oscillations or even affect the stability. Focusing on this issue, an adaptive terminal integral sliding mode control (ATISMC) strategy and a discrete linear extended state observer (DLESO) are proposed in this article. First, different from using traditional dynamic model, a characteristic model is established with online parameter identification to describe inertia variation. Then, a DLESO is proposed to observe and compensate the modeling error caused by parameter identification and backlash effect. An ATISMC is newly designed based on the characteristic model to suppress the uncertainties and stabilize the whole closed-loop system. Both the uniform ultimate boundedness of observation error and the practical finite-time stability of the system is proved. Finally, simulation and experimental results demonstrate that the proposed strategy can adapt to large-range inertia variation and suppress the backlash effect.

Multibody Dynamic Analysis of a Wind Turbine Drivetrain in Consideration of the Shaft Bending Effect and a Variable Gear Mesh Including Eccentricity and Nacelle Movement

Due to the energy crisis and global warming issues, the wind energy is becoming one of the most attractive renewable energy resources in the world. The drivetrains in the wind turbine tend to fail more prematurely than those in any other applications. Gearbox is the subsystem that causes the most downtime for the wind turbines. In the previous research, only the torsional flexibility of the shaft was considered in the drivetrain model. However, because the shaft is longer than other parts, and components connected by the shaft affect each other via shaft bending, the flexibility of the shaft cannot be ignored. In this study, a spherical joint that consists of three rotational springs was used to define the shaft bending. This shaft bending will affect the drivetrain rotation, the translational motion and the gear mesh contact force. Additionally, the eccentricity and the nacelle movement are analyzed due to the coupled motion. In this paper, a mathematical model of the drivetrain is proposed, which is a three-dimensional dynamic model that includes flexible bearings, a gear mesh model, shaft flexibility, eccentricity, and nacelle movement. The equation of motion of the drivetrain is derived using Lagrange's equation. The governing equation is solved numerically via direct numerical integration. The dynamic responses of the system and contact forces between the gear tooth in the time and frequency domains are calculated numerically. The study shows that this dynamic model of the drivetrain will be highly useful for subsequent studies on the wind turbine condition monitoring.

Loss of variable fascicle gearing during voluntary isometric contractions of paretic medial gastrocnemius muscles in male chronic stroke survivors.

Maximum fascicle shortening/rotation was significantly decreased in paretic medial gastrocnemius (MG) muscles compared to non-paretic MG muscles. The fascicle gear ratio on both sides decreased as the ankle became dorsiflexed, but the slope of the fascicle gear ratio over ankle joint angle was significantly lower on the paretic side. The side-to-side slope difference was strongly correlated with the relative maximum joint torque and with the relative shear wave speed, suggesting that variable gearing may explain muscle weakness after stroke. The present study aimed to understand variable fascicle gearing during voluntary isometric contractions of the medial gastrocnemius (MG) muscle in chronic stroke survivors. Using ultrasonography, we characterized fascicle behaviour on both paretic and non-paretic sides during plantarflexion contractions at different intensities and at different ankle joint angles. Shear wave speed was also recorded from the MG muscle belly under passive conditions. Fascicle gear ratios were then calculated as the ratio of muscle belly shortening velocity to fascicle shortening velocity, and variable fascicle gearing was quantified from the slope of gear ratio vs. joint angle relations. This slope was used to establish associations with maximum joint torques and with shear wave speeds. At all measured angles, we found a significant reduction in both maximum fascicle shortening and maximum fascicle rotation on the paretic side compared to the non-paretic side on our stroke survivor cohort. The fascicle rotation per fascicle shortening on the paretic side was also significantly smaller than on the non-paretic side, especially at plantarflexed positions. Furthermore, the fascicle gear ratio on both sides decreased as the ankle became dorsiflexed, but the change in the fascicle gear ratio was significantly lower on the paretic side. The side-to-side difference in the gear ratio slope was also strongly correlated with the relative maximum joint torque and with the relative shear wave speed, suggesting that variable gearing may explain muscle weakness after stroke. Further studies are needed to investigate how muscular changes after stroke may impede variable gearing and adversely impact muscle performance.

Optimization-Based Investigation of Bioinspired Variable Gearing of the Distributed Actuation Mechanism to Maximize Velocity and Force

Transmission between high speed and high force motions is a classic, but challenging problem for most engineering disciplines as well as robotics. This study optimizes the performances (i.e., both velocity and force) of the distributed actuation mechanism (DAM) based on the novel concept of continuously variable gearing, which is inspired by muscle movement. To quantify continuously variable gearing in the DAM, the structural gear ratio (defined as joint speed/motor speed) is mathematically derived in terms of the slider position and the joint angle. Then, for a DAM-based three-revolute joint manipulator, a multi-objective optimization problem is formulated to determine the maximum end-effector velocity according to varying payloads. An optimization framework consisting of the analysis and optimization modules is constructed to verify the proposed concept with a comparison of an equivalent joint actuation mechanism (JAM)-based three-revolute joint manipulator. The numerical results demonstrate that the bioinspired variable gearing of the DAM allows for a significant enhancement of end-effector velocity and force, depending on a given task.

Past, present, future of agricultural tractors

The development of tractor design is closely related to its technological updating, improving environmental performance and increasing usability. Study of this problem in a historical context shows the unity in approaches of various agricultural tractor manufacturers to tractor design aimed at increased productivity and reduced operation costs in accordance with the requirements for agronomic and environmental performance. The main task of the first-generation tractors was to develop traction for agricultural work with maximum productivity and cost-effectiveness. Solution of these problems required further development of the tractor theory and the idea of the processes quality, and ensured the optimization of design and performance. As a result, the designs of tractors from different manufacturers developed in the same direction. Modern tractors are equipped with electronically controlled turbocharged diesel engines and have systems reducing toxicity of the exhaust gases. Power transmission of the tractors is implemented either with a robotic gearbox without interrupting the power flow, or in a continuously variable format, which ensures a more optimized operating mode. While for small-traction-class tractors stepless power transmission is provided with a mechanical variable speed gear, the rest of the tractors require electronicallycontrolled hydromechanical transmissions. As the capacity of power stations grows and an extensive power grid based on renewable energy resources is developed, the demand for electric tractors is to be increased. Tractors with hybrid power plants are likely to be produced at the transitional stage of development. They have the advantages of controlling processes in the machine and tools, the ability to provide agricultural implements with electric power for carrying out their work processes and ensuring their active drive to develop traction as well.

Experimental Investigation on Backlash Control of Variable Tooththickness Gear Pair under Varying Load Excitation

Experimental Investigation on Backlash Control of Variable Tooththickness Gear Pair under Varying Load Excitation

Low-Cost, Continuously Variable, Strain Wave Transmission Using Gecko-Inspired Adhesives

In robotics, high gear reductions are often required when using an electromagnetic motor to drive revolute joints, as in a humanoid robot. Strain wave gears (SWGs), also known as harmonic drives, are often used. However, these transmissions are relatively expensive and have a fixed gear ratio. Here, we present a low-cost transmission that maintains the high reduction of the SWG and enables a continuously variable gear ratio. We achieve this by, first, replacing the teeth of an SWG with a smooth frictional contact to enable continuous gear variation and, second, inverting the gear elements to enable high frictional torque transfer with a low preload via the capstan effect. We choose a gecko-inspired dry adhesive as the frictional material because it has high friction at low normal forces, and is not inherently tacky. We present a model describing the transmission, as well as experimental data gathered from a prototype device that verifies this model and establishes a proof of concept. Our transmission expands the possibilities for low-cost robotic systems.