Browsing by Author "Bair, BW"

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Effects of profile shifted factor and pressure angle on the ZK-type dual-lead worm gear drives
(2001-05-03)
Bair, BW
;
Tsay, CB
;
機械工程學系
;
Department of Mechanical Engineering
In the light of a mathematical model of the ZK-type dual-lead worm gear set proposed in the authors' recent work, this study adopts tooth contact analysis to compute the kinematic errors, instantaneous contact teeth (ICT) and average contact ratios (ACR). An elastic deformation of 3 mum is allowed while calculating ICT and ACR. In addition, increasing the ICT from three to four or from four to five reduces the root stress of the gear set due to its multiple contact teeth. Although a worm gear driven with a small pressure angle can increase the ICT. a worm gear with a small pressure angle incurs a more serious undercutting phenomena. Undercutting can also be averted by applying a positive-shifted modification of the hob cutter during the worm gear generation. Moreover, the boundary of conjugate and nonconjugate surface regions appears on the worm gear tooth surface when the worm gear has a low pressure angle. The non-conjugate region also influences the transmission efficiency, operational life time and noise of the worm gear drive. Furthermore, worm gear generation with a negative-shifted modification can decrease the unfavorable non-conjugate region. (C) 2001 Elsevier Science B.V. All rights reserved.
ZK-type dual-lead worm and worm gear drives: Contact teeth, contact ratios and kinematic errors
(1998-09-01)
Bair, BW
;
Tsay, CB
;
機械工程學系
;
Department of Mechanical Engineering
Contact ratio is an important gear design parameter for gear bending and contact stresses. A higher contact ratio may reduce the stresses and kinematic errors of the gear set. In this study, we calculate the kinematic error of the ZK-type dual-lead worm gear set by applying the tooth contact analysis (TCA) method. Two kinds of contact ratios, the instantaneous contact teeth (ICT) and the average contact ratio (ACR), are investigated and calculated by applying TCA method. ICT is an important design parameter for a dual-lead worm gear set when the gear set is used in a machine subjected to large impact forces. ACR is also a useful design factor for assessing gear tooth strength and dynamic load. If gear surface elastic deformation 3 mu m is allowed for the worm gear set, the ICT may have 2, 3 or 4 teeth and the ACR reveals that the ZK-type dual-lead worm gear drive is a high-contact-ratio gear set. It is found that this type of worm gear set with a shorter center distance assembly can increase the value of ACR during the gear meshing. Illustrative examples presented herein demonstrate the effects of gear parameters on contact teeth, contact ratios, average contact ratios and kinematic errors under various conditions.
ZK-type dual-lead worm and worm gear drives: Geometry
(1998-09-01)
Bair, BW
;
Tsay, CB
;
機械工程學系
;
Department of Mechanical Engineering
A dual-lead worm gear set is frequently used for machines to operate without backlash, which cart be adjusted along the worm's axial direction. The ZK-type dual-lend worm is generated by a cone-type straight-edged grinding wheel while an oversize worm-type hob cutter cuts the worm gear. The dual-lead worm gear set has two different axial modules and helix angles for the right- and left-side tooth surfaces. The mathematical model involving ZK-type dual-lead worm and worm gear surface geometries is developed based on the theory of gearing and gear cutting mechanism. According to the proposed mathematical model, computer graphs of the ZK-type dual-lead worm gear drives have been presented. Coordinates of the meshed grid-point on gear drive surfaces can thus be determined by applying the numerical method. Undercutting of the worm gear surface has been investigated based on the theory of gearing and the developed gear set mathematical model. The gear set mathematical model developed herein can facilitate gear set tooth contact analysis, contact teeth, contact ratio and other advanced investigations.