Thrust pads in rotary machines are often used to bear the axial load, sometimes part or whole of the rotor weight is also sustained by thrust pads when the machine is not installed horizontally. Static characteristics of gas foil thrust bearing such as bearing load and friction torque play important roles in bearing-rotor system. In this paper, Finite Difference Method (FDM) was adapted to analyze compliant surface thrust gas bearing with viscoelastic support. Considering inclination of the journal, pressure distribution and film thickness between thrust disk and thrust pads were obtained by solving dimensionless governing equations, then nondimensional bearing load and nondimensional friction torque can be calculated subsequently. Based on the results of numerical calculation, effects of structural parameters and operational parameters on static characteristics were discussed. Theoretic analysis denote that: thrust foil bearing in journal inclination have higher load capacity and higher friction torque than that in no tilting condition; the optimum structure parameters for viscoelastic supported foil thrust bearing with the outer radius to inner radius ratio of 3 and dimensionless compliant coefficient of 1 is β = 90° and b = 0.5. Experiment about bearing load also has been implemented in this paper, and the results prove that the theoretical analysis is available.
Energy consumption of machine tool has drawn wide attention in recent years. The additional load losses of machine tools are of great importance for investigating the energy consumption of machine tools because those account for 15-20% of the cutting power and may even be up to nearly 30% of the cutting power in our researches. For lack of adequate understanding of the characteristics of additional load losses in the past, the additional load losses coefficient, defined as the ratio of additional load losses to cutting power, was regarded as a constant while the spindle speed was unchanged. However, it is discovered in our practical measurements that it is not so. In this paper, it proposes an additional load losses model based on power flow model, under the condition of the slip of spindle motor being small, in order to fully understand the characteristics of additional load losses. The characteristics of additional load losses include the relationship between additional load losses and cutting power, the relationship between additional load losses and spindle speed, and the relationship between additional load losses and cutting torque. Further more, an experimental system is developed to acquire the additional load losses through measuring cutting torque, spindle speed and input power of machine tool. As an example, several experiments are carried out on the CNC lathe by adjusting cutting parameters including spindle speed, feed rate and cutting depth. The experimental results show that the additional load losses coefficient varies with spindle speed and cutting torque, which can be fitted by a 1st order polynomial.
This paper presents a method to minimize the task completion time of a manipulator system in a multiple-goal task by considering the existence of position errors of objects that may change the manipulator pose (position and orientation) and cause collisions. In this paper, we propose a method which cannot only reduce this change but also minimize the task completion time of the system. The proposed method resolves the redundancy of the system and the redundancy in the given task using Particle Swarm Optimization under a manipulability restriction. The proposed method is verified through simulations and is shown to be effective.
This paper describes a novel tool path generation for three-axis ball-end milling using a local interpolation. After a modified local interpolation using normal unit vectors is introduced, generation of a parametric offset geometry is presented based on the local interpolation. In tool path generation, determination of a path interval and tool feed planning, which can be applied to both the scanning-line and contour-line machining, are proposed using normal unit vectors. Through their examples, it was verified that the proposed procedures possessed simplicity and flexibility.
Tool design for orbiting EDM process often encounters some difficulties to adjust for EDM orbit and machining overcut concurrently. In orbiting process, the tool sweeps out some extra volume due to the additional orbit motion. Hence, it is compulsory to adjust tool geometry based on the chosen orbit cycle to avoid dimension distortion on the final product. Currently, tool correction is done manually since there is no CAD package which provides a specific assistance to adjust the tool geometry for orbital motion. Therefore, design process becomes lengthy and more prone to error due to manual correction process. The authors have proposed a tool design principle for orbiting purposes. Presented in the paper is continuation of the previous work, which emphasizes an automation strategy of tool design developed inside CAD system. The tool is compensated automatically for overcut and EDM orbit, and checked for its validity. The developed CAD system has been tested for a few EDM applications with complex shapes and proven effective to cut tool design time and human-related failures which are commonly found during manual design processes. Experimental validation for a complex part was executed with a promising result.