Antibacklash Nut

In another possible configuration, the nut may be fixed and the lead screw rotation is converted to its translation together with other connected parts (i.e., motor, frame, payload, etc.). This configuration is shown in Fig. 5.6. 

The equation of motion of this system is also given by (5.18). 

3 Basic Model with Fixed Lead Screw 

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The velocity-dependent friction model used in this work is discussed in Sect. 5.1. The dynamics of a pair of meshing lead screw and nut threads is studied in Sect. 5.2. Based on the relationships derived in this section, the basic 1-DOF lead screw drive model is developed in Sect. 5.3. This model is used in Chaps. 6 and 8 to study the negative damping and kinematic constraint instability mechanisms, respectively. A model of the lead screw with antibacklash nut is presented in Sect. 5.4, and the role of preloaded nut on the increased friction is highlighted. Additional DOFs are introduced to the basic lead screw model in Sects. 5.5 to 5.8 in order to account for the flexibility of the threads, the axial flexibihty of the lead screw supports, and the rotational flexibility of the nut. These models are used in Chaps. 7 and 8 to investigate the mode coupling and the kinematic constraint instability mechanisms, respectively. Finally, in Sect. 5.9, srane remarks are made regarding the models developed in this chapter. 

As mentioned in Chap. 1, antibacklash nuts are commonly used to counter the effects of backlash and wear in a lead screw drive. An antibacklash nut is usually made of two parts that are connected together by a preloaded spring. Figure 5.8 shows a schematic model of a lead screw drive with a two-part nut. The spring kn is preloaded such that a force P = knSn acts between the two halves of the nut. Sn is the initial compression of the spring. Neglecting the mass of the nut, the Newton s second law gives... 

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