查看更多>>摘要：Power skiving is currently an efficient machining process to manufacture gears. In practical applications, uneven gear profile deviations caused by the asymmetric cutting edge of a skiving cutter affect gear profile accuracy and finishing cost. Therefore, this paper proposes a novel method to attain the even grinding allowance on both gear flanks in the CNC skiving. A quadratic polynomial function is adopted to correct an asymmetric rack profile, which is used to generate the skiving cutter profile. Pressure angles, protuberances, and polynomial coefficients on two sides of the rack are determined analytically according to the requisite grinding allowance and the conjugation relationship between the gear and the cutter. Skived tooth profiles for internal/external gears are simulated based on the CNC machine motion, and its normal deviation can be estimated. As the numerical results demonstrate, the profile deviations on both gear flanks are close to the required settings, and the even grinding allowance is achieved on the active involute sections. Additionally, a radial basis function (RBF) regression model is constructed to conveniently determine the design parameters of the skiving cutter.
查看更多>>摘要：The cumulative pitch errors of the left and right helical gears are the main source of the asymmetry error for the double helical gear. In this paper, a new three-dimensional loaded tooth contact analysis (3-DLTCA) model of double helical gear considering long period asymmetry error is proposed. The desired error (modification), undesired error (cumulative pitch error) and the change of normal clearance increment of left and right helical gear pairs caused by the axial shift of the driving pinion are considered in the model. Based on the new 3-DLTCA model, combined with the equivalent gap of the current meshing tooth pair, the meshing impact force (MIF) of the current meshing tooth pair in each meshing period is calculated. The results show that the proposed model can quickly and accurately calculate the long period end loaded transmission error (ELTE) and pinion axial displacement (PAD) of double helical gear with asymmetry error. Moreover, the long period asymmetry error of double helical gear has great effect on the MIF for left and right helical gears.
查看更多>>摘要：In the present work, the analytical expressions for engagement process and contact line of the involute helical gears were developed in the Cartesian coordinate system, for obtaining comprehensive understanding of particular mechanism in helical gear process; a profound analysis of the engagement process of the involute helical gears was made in the Cartesian coordinate system and then an equation of the contact line, some parameters and analytic relations between them were obtained. Based on those expressions, the change process of total length of the contact lines was investigated and the total length and its change interval were determined. The engagement mode further was divided into three types and the formula for obtaining the maximum and minimum value of each type was derived. A formula of the condition necessary for total length of the contact lines to be constant was also derived so as to assist engineers when determining a reasonable helix angle.
查看更多>>摘要：In order to investigate the dynamic characteristics of the straight bevel gear drive system, its torsional-bending-axial dynamics model considered the multi-state meshing characteristics is established. The time-varying load distribution ratio and meshing stiffness of the system are calculated by micro element method according to the performance of the straight bevel gear. Three different Poincaré sections are defined to study the dynamic characteristics of the system. The mechanism of tooth disengagement and back-side contacting is studied according to the time history diagram of the total normal force. The nonlinear dynamics equation of the system is solved by the variable step fourth-order Runge-Kutta method when the bevel gear drive system in automobile reducer is taken as the research object. The transition process of system dynamic characteristics and the influences of the meshing frequency, load coefficient and the comprehensive transmission error are studied by using the time history diagram of the total normal force, phase portraits, Poincaré maps, bifurcation diagrams and the corresponded top Lyapunov exponent (TLE). The chaotic motion found in the research is unfavorable from a practical point of view which can be avoided by adjusting the value of parameters or the initial value of state variables in engineering. The research can provide a theoretical basis for the parameter design and dynamic characteristic control of straight bevel gear drive system.
查看更多>>摘要：This paper aims to establish a rich and complete meshing theory of the toroidal surface enveloping cylindrical worm drive with arc-toothed worm and obtain the meshing performance of the proposed worm drive. The arc-toothed worm is machined by a disc-shaped grinding wheel whose formulae of the installation position parameters are determined according to differential geometry. The characteristic of the contact line on the worm helicoid during cutting engagement is analyzed by establishing the Frenet frame. Then the relative motion model and some important results of the worm pair are acquired using the meshing theory of gearing. Based on this, the locus features of the knot of meshing are analyzed in different coordinate systems. In addition, the meshing points which determine the conjugated zone and instantaneous contact lines are classified according to their different positions on the tooth surface of the worm gear. Utilizing the methods of eliminating and geometric construction, the nonlinear equations are solved. Finally, a numerical example is implemented and the result shows the proposed worm drive has favorable meshing performance.
查看更多>>摘要：Tensegrity robots, which are famous for their lightweight and capability of sustaining massive loads, have unique potential applications in task execution in complex environments. In this paper, a quadruped robot with tensegrity legs is proposed. By combining the tensegrity structure with a rigid mechanism, a 3-DOF tensegrity leg is developed. Necessary theoretical basis of the tensegrity leg including kinematics, statics, force space and force-workspace have been derived and proposed for design and control. A quadruped prototype based on tensegrity legs is manufactured and shows unique walking ability in different morphologies. The high load performance and terrain adaptability based on dynamic morphologies of the quadruped robot is verified by experiments.
NSTL
Elsevier