| The gear is in the modern machinery applies the most widespread one transmission mechanism. It may use for to transmit the movements and the forth between the spatial willfully two axes, moreover the transmission is accurate, steady, the mechanical efficiency is high, the service life is long and the job safety is reliable. Worm mechanism is evolved from cross helical gear transmission. Usually angle between two intersecting axes is90 . The advantages of worm drive are: 1) can be a lot of single-stage transmission ratio. 2) Due to the continuity of the worm gear to drive a smooth, noise small. 3) When a worm helix angle less than the equivalent friction angle of the meshing surface, the worm can self-locking. The shortcoming is: Worm drive's efficiency is low, when specially self-locking, is high to the heat dissipation request, when manufacture the worm gear one needs to use the precious anti-attrition material bronze. The limitations of worm gear materials as well as worm drive fuzzy contact region are limiting the widespread application of worm drive. Worm gear's processing manufacture difficulty, the process is complex, causes the traditional worm gear precision to further enhance with difficulty. So, the development of a high-precision, and worm wheel to facilitate processing of the worm drive deputy must.The new precision worm drive, the basic principle is under the special condition:Cross-axis helical gear drive, contact form by point contact into line contact , the use of this principle to the evolution of a helical gear as the worm, and the other the same as a worm helical gear form a line contact as instantaneous contact with the worm gear transmission, Deputy. The advantages are: high-precision transmission can be achieved; worm helical gear is common simple processing; worm alloy materials can be used, saving valuable non-ferrous metals.Meet the conditions of the crossed axes helical gear drive, base helix angleβb1of a helical gear gets large, approach 90°.Reduce the base circle radius, longer axes length. The helical gear teeth will gradually evolved into small, and teeth in the base to keep the rotating cylinder, the shape will be as the same as the worm, the helical gear evolution is a worm. Let another helical gear's base helix angle get small, andβb1 +βb2=90,so will be staggered to achieve 90°angle of the worm (in real terms are helical gear) transmission. Contact any one of the instantaneous tooth meshing point of the relative velocity, use vector analysis, which concluded that: the tooth face line of contact's instantaneous relative velocity in the tooth line direction or in the tooth profile direction is not zero; speed depends on the angular velocity, base circle radius, and diameter of the worm, Worm Center Distance. Proven the new type of precision worm drive meet the tooth profile meshing basic law, the worm and worm gear tooth surface for instantaneous conjugate tooth surface, can be given in accordance with the transmission gear ratio.New type of precision worm because of its nature is helical gear, so the selection and design parameters are similar with helical gear. However, the basic principle is center distance equal to the base circle radius add, leading to the size of base circle as the new standard of new precision worm size (pitch circle as the size of the existing gear standard size). The derivations of main parameter formula imitate helical gear's formula. Determine the shape and the specific size, grasp the principle that in the non-interference conditions, the worm tooth surface with sufficient stiffness, strength, life. That is, with the best value for money.Worm gear is round shape, and the worm in the worm gear on both sides of contact with the special circumstances, at the same time in order to save materials, designed new precision cone-shaped worm. The size of cone angle is not only, it can be determined in accordance with specific circumstances, generally 10 ? 20, so worm can be better to avoid interference with the worm gear. According to the principle, we can see that worm can only be one-way transmission, worm and worm gear is only one side of tooth contact, need two-way transmission of two worm split on both sides of the worm gear, so the overall shape of the worm as a combination of two single worms. According to the shape and force analysis of the worm, Fn denotes the force of any instantaneous contact point in the worm. it's size changes with theα. The largest force in the big worm, according to the force analysis carried out the contact fatigue strength check of the worm:Concluded that:The impact of tooth surface contact fatigue strength most main parameter is the diameter of the worm. Larger diameter, point of contact tooth profile radius of curvature increases, reducing the contact stress, improve contact strength. Conversely, if we do not change the diameter, the module with different combination and number of teeth, have little effect on the contact strength.New precision worm drive's meshing efficiency, taking into account the essence of which is cross-axis helical gears transmission. Therefore, estimates the meshing efficiency with the cross-axis helical gear pair's formula. Impact on the efficiency of worm drive factors are the worm helix angleβ1 and friction coefficient f . Worm helix angleβ1 and helix angleλof the relationship is Specific design of the worm helix angle will be determined by specific conditions, very little room for change, then only to improve efficiency by changing the friction coefficient.The modeling and simulation of the new precision worm drive, design a new type of precision worm transmission pair, to replace the traditional worm transmission pair, installation and using in the fixed conditions. Use CATIA modeling precision worm and worm gear, assembly and simulation of movement. through CATIA visual expression, and continuously modify the worm and worm gear design inappropriate size, eventually to be specific and detailed the size of the worm and worm gear, and plans were made for the processing of parts to use.Cutting method of tooth surface of the new precision worm, the use of CNC machine tools, using its high precision and high efficiency can be very complex surface machining, etc. Worm tooth surface is divided into three different surfaces, one involute helicoid surface, two straight grained helicoid. They have the same pitch. Tool starting position is different, the use of three knives, three times the processing of these three surface. Processing order is working surface first, involute helicoid surface first.In this study, not only in theory for this new type of precision worm drive to the various aspects of, but also gives a specific example of the transformation. And the use of CATIA CAD software, ultimately, makes a worm and worm gear parts entities. For the new precision worm drive further research provides a theoretical basis and foundation. The new precision worm drive because of its high-precision, processing and manufacturing convenience, save materials. It will be to develop a wide range of applications. And this new theory can be applied to other aspects of gear, such as gears precision grinding finishing, etc.
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