Sino Howo Truck Co Ltd. , https://www.sinotruk-howo.com
1. Floating support 2. Guide mechanism 3. Gland 4. Screw fixed support 5. Bearing 6. Screw nut 7. Screw bushing Fig. 1 Motor direct drive P joint 1 Introduction The parallel mechanism is mainly composed of rods. , Light weight, so the speed of the end effector can be very high. The use of a parallel mechanism for a numerically controlled machine tool can greatly increase the feed rate of its moving parts. This is one of the important reasons why parallel machine tools have attracted attention in recent years. However, the damping of the parallel mechanism itself is very small, which is unfavorable for vibration suppression. On the other hand, while utilizing the advantages of light weight, high speed, etc., it also brings about problems of vibration force due to great acceleration and deceleration. In addition, because the parallel mechanism is composed of a plurality of rods, the vibration thereof is relatively complicated. Therefore, the vibration problem of the parallel mechanism is an urgent problem to be solved. The P-joint (linear motion) of the parallel mechanism has a variety of drive forms. For example, the hydraulic drive rod moves axially: the motor drives the screw, and then the rod is moved by the joint installed on the slide table: the motor drives the screw to rotate and passes through. The nut drives the rod to move linearly. The P-joint drive form of Fig. 1 belongs to the latter: the support of the lead screw is a fixed support, and it bears radial and axial loads. The screw nut couple and the screw sleeve fixed on the nut and its guide mechanism together make up the P joint. In this structure, on the one hand, the screw rotates at a high speed and the lead screw sleeve moves linearly along the guide mechanism without rotation: on the other hand, the lead screw sleeve is relatively long, and the cylindricity error thereof is relatively large. Therefore, there is no fixed support between the end of the lead screw and the lead screw sleeve. Therefore, only one end of the screw is supported. When the overhanging long lead screw (the nut in the nut lead screw in Fig. 1 moves to the upper side), high lateral vibration may occur during high speed rotation and acceleration and deceleration. In this paper, we propose and design a floating support that can suppress lateral vibration from the standpoint of enhancing damping and improving lateral stiffness. 
1. Lead screw sleeve 2. Damping sleeve bearing seat 3. Screw 4. Bearing 5. Damping sleeve 6. Steel ball 7. Clip cover 8. Lock nut 9. Bearing inner ring 10. Bearing outer ring 11. Spring Figure 2 Vibration-suppressed floating support structure 2 Structure of vibration-suppressing and floating support The form of vibration-suppressing floating support structure is shown in Figure 2. It is mainly composed of screw, bearing, damping sleeve, spring, screw sleeve, clamp cover, and steel ball. , damping sleeve bearing seat, lock nut, bearing inner retaining ring and bearing outer retaining ring and other components. During the movement, the inner ring of the bearing rotates with the screw, and rolling friction occurs between the floating bearing and the screw sleeve. 3 Working principle of spring damper The steel ball, spring and damping sleeve in Fig. 2 can be considered as a spring damper. A plurality of such spring dampers can be arranged in the circumferential direction of the damping sleeve bearing seat, where m is the spring damper The mass, k is the spring stiffness, c is the damping, as shown in Figure 3. The vibration equation is
Mx ̈(t)+cx.(t)+kx(t)=f(t) (1) 
The damping of the damper of the vibration damping system is mainly the tangential contact damping between the damping sleeve and the floating bearing support. The magnitude of the damping force is mainly related to the contact state between the material of the damping sleeve, the damping sleeve and the support seat, and the lateral vibration speed of the screw. The spring acts as a self-supporting bearing. On the one hand, it supports the mass m, and at the same time it makes the floating bearing self-positioning for the mechanical model: When the sleeve moves axially with respect to the screw, even if the bore in the sleeve has a cylindricity Inaccuracy, the balls of each spring damper of the floating bearing can also maintain contact with the inner bore of the sleeve: When the screw has lateral vibration, the center of the floating bearing is forced to return to the equilibrium position. 4 Design principle of floating bearing parameters When the screw has a lateral vibration force Fejwt, it will produce lateral bending vibration. The purpose of setting the floating support is to reduce or suppress the effect of Fejwt. When the screw diameter is determined, the radial size of the floating support is also limited. In order to maximize the effective stroke, the axial dimension of the floating support should be as compact as possible. Therefore, the following principles should be taken into account when designing the floating bearing: (1) The overall bending stiffness of the floating bearing should be high. The overall bending stiffness of a floating bearing includes the spring stiffness of the spring damper, the bearing stiffness of the floating bearing, and the bending stiffness of the screw shaft end. Note that the flexural rigidity of the screw shaft end cannot be reduced by increasing the spring rate. (2) Select the appropriate damping sleeve contact state. The damping of the spring damper mainly comes from the contact damping between the damping sleeve and the floating bearing. The contact damping per unit area is c=apnb (2) where: c is the tangential contact damping: pn is the normal contact pressure of the contact surface: a, b are coefficients related to contact surface materials, processing methods, vibration frequencies, and the like. In general, the greater the contact pressure, the greater the damping. However, the contact pressure is large and friction and wear are also great. Therefore, while increasing the damping, the damping sleeve cannot be excessively worn or stuck. 5 Concluding remarks This paper presents the structure and design principles of a floating mechanism supported by a screw in a parallel mechanism. The design must be based on the specific design conditions (structural size constraints, the size of the vibration force, the bending stiffness of the structure itself, etc.) for rational design. In order to improve the effect of damping and damping, damping sleeves in different materials and structures can be designed.
Parallel floating screw support design of drive screw