Optimum variable input speed for kinematic performance of Geneva mechanisms using teaching-learning-based optimization algorithm

Abstract

An optimum design of variable input speed for the Geneva mechanism is aimed at improving the kinematic performance of the traditional Geneva mechanism by eliminating infinite angular jerks and reducing the peak angular acceleration of the Geneva wheel during the indexing motion. The normalized angular velocity and acceleration of the Geneva wheel corresponding to the normalized time are introduced. A polynomial function of the normalized time is used to describe the normalized angular position of the crank, and therefore, the corresponding polynomial coefficients are considered as the design variables. The optimum design task is very specialized and difficult to solve with some evolutionary and swarm optimization methods because of the extremely large range for the value of the design variable, arising from the utilization of a higher order polynomial for the normalized time parameter with a value between 0 and 1. A new evolutionary algorithm termed teaching-learning-based optimization comprises a teacher phase and a learner phase. In the teacher phase, the entire population can be gradually shifted to a more promising region, which may be very far from the relatively small initial region. The obtained optimal results are compared with those obtained using the length-adjustable deriving link method discussed in the literature. The findings show that the difference in the effectiveness of the variable input speed method and the length-adjustable driving link method for the reduction of the peak angular acceleration of the Geneva wheel is small.

A new indexing motion program for optimum designs of Geneva mechanisms with curved slots

“…Because the differences of the optimum results obtained using 2 elements, 3 elements, and 4 elements are slight, only the optimum results obtained using 2 elements with 3 nodes are shown. Table 5 shows the peak normalized angular acceleration of the Geneva wheel for different lengths of elements, together with the results obtained using the cycloidal and modified sine indexing motion programs and with the optimum results obtained using a variable input speed method for the straight slots 18 and a length-adjustable driving link method for the straight slots. 19 The values of the design variables and the associated peak normalized angular acceleration obtained using the proposed indexing motion program for one element, two elements with lengths of 0.25 and 0.25 and two elements with lengths of 0.19 and 0.31 are shown in Table 6.…”

“…The comparisons of the peak normalized angular velocity, the initial normalized angular acceleration (¯··θw,ini) and the peak normalized angular acceleration of the Geneva wheel for the traditional Geneva mechanism 18,23 and the curved slotted Geneva mechanism using the cycloidal and modified sine motion programs are shown in Table 1. The peak angular acceleration (not shown) of the Geneva wheel obtained using the fifth-order polynomial program is smaller than that obtained using the cycloidal program, while higher than that obtained using the modified sine program.…”

“…Taking advantage of the symmetry with which the mechanism acts with respect to the centerline, 18,19 the problem is formulated in the domain of -θ0≤θ≤0. In this study, the domain of the indexing position function θw=f(θ) is divided into m segments.…”

“…Quite a few valuable studies have been devoted to the issue of improving the afore-mentioned drawbacks, approaching the problem from different ways. The main methods for improvement include four-bar linkage driven Geneva mechanisms, [1][2][3][4] gear driven Geneva mechanisms, 5 Geneva mechanisms with curved slots, [6][7][8][9][10][11][12] conjugate Geneva mechanisms with curved slots, [13][14][15] variable input speed driven Geneva mechanisms, [16][17][18] and length-adjustable driving link method. 19 Fenton et al 6 proposed replacing straight slots with curved slots to eliminate shock forces and reduce the peak acceleration of the Geneva wheel for high speed applications.…”

Experimental kinematic analysis of an intermittent motion planetary mechanism with elliptical gears

“…-mechanisms of a permanent structure with a one-way coupling (anchor mechanisms, ratchets); -variable structure mechanisms (Geneva drives, star wheels, mutilated gears). Today the Geneva drives is extensively used in automatic machinery (the tool changers in CNC machines; the turrets of turret lathes, screw machines, and turret drills; some kinds of indexing heads and rotary tables; and so on) or conveyors [7,8]. In order to reduce shockloading, a basic Geneva mechanism in combination with linkages, gears, and cams is applied as shown in [9].…”