Static stiffness modeling and sensitivity analysis for geared system used for rotary feeding

The positioning accuracy of rotary feed system under load greatly depends on the static stiffness of mechanical transmission system. This paper proposes a unified static stiffness model of rotary feed system with geared transmission system. Taking the torsional stiffness of transmission shaft and mesh stiffness of gear pairs into account, the motion equations of the whole transmission system are presented. Based on the static equilibrium, a unified expression for the relationship between torsional angles of two adjacent elements is derived. Then a unified static stiffness model is presented. Furthermore, analytical expressions for sensitivity analysis of the static stiffness on the individual element’s stiffness and design parameters are derived. The presented model is verified by a traditional model, and a good agreement is obtained. The influence of phase angle of meshing gear pairs on the resultant static stiffness is investigated. An example transmission system is employed to perform the sensitivity analysis and the results are analyzed. The proposed model provides an essential tool for the design of rotary feed system satisfying requirement of static stiffness

Reliability Technology Based on Meta-Action for CNC Machine Tool

Computer numerical control (CNC) machines are a category of machining tools that are computer driven and controlled, and are as such, complicated in nature and function. Hence, analyzing and controlling a CNC machine’s overall reliability may be difficult. The traditional approach is to decompose the major system into its subcomponents or parts. This, however, is regarded as not being an accurate method for a CNC machine tool, since it encompasses a dynamic working process. This chapter proposes a meta-action unit (MU) as the basic analysis and control unit, the resulting combined motion effect of which is believed to optimize the CNC’s overall function and performance by improving each meta-action’s reliability. An overview of reliability technology based on meta-action is introduced

Mathematical Model of Helical Gear Topography Measurements and Tooth Flank Errors Separation

During large-size gear topological modification by form grinding, the helical gear tooth surface geometrical shape will be complex and it is difficult for the traditional scanning measurement to characterize the whole tooth surface. Therefore, in order to characterize the actual tooth surfaces, an on-machine topography measurement approach is proposed for topological modification helical gears on the five-axis CNC gear form grinding machine that can measure the modified gear tooth deviations on the machine immediately after grinding. Combined with gear form grinding kinematics principles, the mathematical model of topography measurements is established based on the polar coordinate method. The mathematical models include calculating trajectory of the centre of measuring probe, defining gear flanks by grid of points, and solving coordinate values of topology measurement. Finally, a numerical example of on-machine topography measurement is presented. By establishing the topography diagram and the contour map of tooth error, the tooth surface modification amount and the tooth flank errors are separated, respectively. Research results can serve as foundation for topological modification and tooth surface errors closed-loop feedback correction

The kinematic analysis and metrology of cylindrical worm gearing

PhD ThesisWorm gearing is very widely used, especially in heavy industry, but due to the complexity of worm gear geometry, worm gear research has lagged behind that for spur and helical gears. In the last decade, however, the potential for significant improvement in worm gearing has dramatically increased: computers have given greater freedom to analyse worm gearing; CNC machines make it possible to aim for optimised worm gear geometries with very high accuracy and the development of synthetic lubricants has substantially improved lubrication conditions. In the UK, over the last few years, research effort in the field of worm gearing has increased considerably. As a part of this recent activity in the UK, the author has been involved mainly in developing the analytical mechanics and metrology of worm gears. A method for the generalised 3D non-elastic worm gear mesh analysis and associated software have been developed and worm wheel metrology software has been implemented on a CNC measuring machine in the UK National Gear Metrology Laboratory, to allow, for the first time, analytical measurement of worm wheel tooth flanks. Combination of the mesh analysis software and CNC measurement of worm wheels has assisted in the design and manufacture of worm gears with modified tooth profiles. Two methods of 3D non-elastic worm gear analysis have been developed for conjugate action and non-conjugate action respectively. The conjugate analysis determines the lines of contact, sliding and rolling velocities, limitations of the working area (the envelope of contact lines on a worm surface and singularities on a wheel surface), principal relative curvatures and the orientations of contact lines. It is based on the B-matrix method [Zhang and Hu, 1989]. The non-conjugate analysis predicts entry and exit gaps, contact ratio, wear marking on the worm flank, instantaneous contact topology on all the engaged tooth flanks, total contact area, contact pattern and transmission error. This is based on numerical simulation of the actual worm gear running process under no-load. Although the non-elastic analysis models have been designed for any type of worm gearing, and have been used to study Cavex (ZC) wormgears and the meshing of a ZA Abstract worm with a helical gear, most of the work has been on involute (ZI) worm gearing, since this is, by far, the most commonly produced type in the UK. This thesis presents the work as follows: 1) The development of the B-Matrix kinematic method for conjugate analysis. The B-Matrix method, presented in chapter 2, elegantly simplifies the derivation and calculation procedures, since the geometric parameters and the motional parameters can be arranged in separate matrices. As a result, the models can be applied to different geometries and coordinate systems with no need for further difficult derivations. The method leads to an easier way of integrating the theory of various types of worm gearing into compact generalised models. It is much more convenient and reliable to let the computer formulate and solve matrix equations numerically, treating each matrix as a simple variable, than to develop analytically the corresponding long tedious non-linear equations. 2) The development of mathematical equations to allow CNC measuring machines to measure cylindrical worm wheels with respect to their mating worms. The measurements are 3-dimensional and absolute, in the sense that the results are the deviations from the theoretical geometries rather than comparative measurements relative to a (necessarily imperfect) master worm wheel. The measurement theory has been implemented on a particular CNC measuring machine. This is presented in chapters 3 and 5. 3) The development of the non-conjugate analysis. The fundamental basis of the non-conjugate analysis presented in this thesis is to rotate the worm wheel to bring its tooth flank into contact with the worm flank at each given angle of worm rotation, so that the no-load transmission error and gap contours can be determined. This method is suitable for both cylindrical and globoidal worm gears, since the rotation angles of worm and wheel are used to simulate the running process directly. Abstract The method also allows the wheel tooth flank to be obtained either by conjugate analysis of the hobbing process, or by analytical measurements or other methods (for example, when a theoretically-generated involute helical gear is used to mesh with a worm). This work is presented in chapter 4. 4) implementation of the non-elastic analysis theory. The non-elastic analysis software has been written for personal computers. In addition, dimensional calculations specified by BS 721 and commonly used hob design methods have been added to the non-elastic analysis software to increase user-friendliness. The software has been used to investigate the effects on the worm gear contact and performance of machining errors and profile deviations or modifications. The structure of this analysis software allows for the inclusion of new modules for other types of worm gearing without in any way disturbing the integrity of the program's existing abilities. The non-elastic analysis software is user-friendly with a "Windows" graphical user interface. Software reliability and error tolerance have been of particular concern during program development. This work is presented in chapter 5. 5) The software has been thoroughly validated against other published results and/or actual production. The software has been used extensively for both research and commercial purposes, and the user interface developed further in response to user feedback. Examples of these applications are given in chapter 7

Design and Characterization of a Low-Cost and Efficient Torsional Spring for ES-RSEA

The design of torsional springs for series elastic actuators (SEAs) is challenging, especially when balancing good stiffness characteristics and efficient torque robustness. This study focuses on the design of a lightweight, low-cost, and compact torsional spring for use in the energy storage-rotary series elastic actuator (ES-RSEA) of a lumbar support exoskeleton. The exoskeleton is used as an assistive device to prevent lower back injuries. The torsion spring was designed following design for manufacturability (DFM) principles, focusing on minimal space and weight. The design process involved determining the potential topology and optimizing the selected topology parameters through the finite element method (FEM) to reduce equivalent stress. The prototype was made using a waterjet cutting process with a low-cost material (AISI-4140-alloy) and tested using a custom-made test rig. The results showed that the torsion spring had a linear torque-displacement relationship with 99% linearity, and the deviation between FEM simulation and experimental measurements was less than 2%. The torsion spring has a maximum torque capacity of 45.7 Nm and a 440 Nm/rad stiffness. The proposed torsion spring is a promising option for lumbar support exoskeletons and similar applications requiring low stiffness, low weight-to-torque ratio, and cost-effectiveness

Hydraulic Variable Valve Timing Testing and Validation

This thesis documents the development of a fully continuous, hydraulics-based variable valve timing system. This hydraulics based variable valve timing system is capable of controlling an engine valves lift height and infinitely varying the engine valves lift profile. Along with full valve controllability during normal operation, the variable valve timing system is capable of providing the same operation as a classic cam shaft under engine power loss conditions. This is possible due to the rotating hydraulic spool valves coupled to the engines crank shaft, which are used to actuate the engine poppet valves. The main focus of this thesis is to investigate, alter and implement a new iteration of the hydraulic variable valve timing system on a standalone test bench to validate the systems operating principles. The test bench utilizes servo motors to act as an engines crank shaft which runs the rotating hydraulic spool valves and hydraulic pump. This serves as an intermediate step to full engine implementation of the variable valve timing system. The research begins by analyzing the current mechanical spool valve and hydraulic cylinder design for any potential problems that may occur either during assembly or full operation. The basic system equations are presented to give a glimpse into the working principles of the rotary valves. The mechanical, electrical, and hydraulic subsystems are discussed in terms of what was considered during the design and implementation process. Then design changes that were performed on the rotary valve system to overcome any failures. Lastly the resulting data is presented from the current variable valve timing design to verify proper system functionality

Influence of feed drives on the structural dynamics of large-scale machine tools

Milling is one of the most widely used processes in the manufacturing industry and demands machines with high productivity rates. In large machine tool applications, the cutting capability is mainly limited by the appearance of structural chatter vibrations. Chatter arises from the dynamic interaction of the machining system compliance with the cutting process. For the specific case of large-scale machine tools, the low frequency resonances have modal shapes that generate relative displacements in the machine joints. This thesis presents new approaches to minimize the appearance of chatter vibrations by targeting and understanding the machine tool compliance, in particular, from the feed drive of the machine tool. A detailed model of the double pinion and rack feed drive system and the master-slave coupling improves the large machine tools modeling. As the vibrations are measured by the axes feedback sensors, a new strategy for feed drive controller tuning allows increasing the chatter stability using a judicious selection of the servo parameters. Then, in-motion dynamic characterizations demonstrate the important influence of the nonlinear friction on the machine compliance and improve the chatter stability predictions. Finally, an operational method for characterizing both tool and workpiece side dynamics while performing a cutting operation is developed. All the contributions of the thesis have been validated experimentally and tend to consider the influence of the feed drives on the structural dynamics of large-scale machine tools

System Identification and Adaptive Compensation of Friction in Manufacturing Automation Systems

Industrial demands for more efficient machine tool systems have been significantly increased. In order to obtain high performance machine tool systems, researchers are focused on enhancing functioning of various components of machine tool systems. Feed drives are important component of the most of machine tool systems such as computer numerical control (CNC) machines for achieving desirable performance. An essential research stream of current interest aiming enhancement of feed drive performance is construction of control methods that help to decrease tool positioning errors in the system. An effective approach for mitigation or reduction of positioning errors is modeling, identifying, and compensating friction in appropriate manner. In addition, accurate modeling of feed drive systems is essential in elimination of these positioning errors. In this thesis, the precision control of feed drives is studied using several different control methods. Firstly, the feed drive type that has common use in machine tools is chosen to be main focus for this research, namely ball screw drive. Different dynamic models of ball screw drive are shown in detail. In addition, some of the nonlinearities that affect ball screw dynamics such as friction affects are discussed. Friction modeling needs to be performed realistically and accurately in order to design an effective compensator to cancel friction effects. In general, the friction models are divided into two categories; classic (static) and dynamic friction models. In this thesis, we present details of these models and derive linear parametrization of the key ones. Based on the derived linear parametric models, we design a least-squares on-line friction estimator and adaptive friction compensation scheme. The performance of these designs are verified via simulation and real-time experimental tests. Noting that the parameters of the base rigid body model, i.e., inertia and viscosity constants, need to be known precisely for effective high precision control tasks, including the aforementioned adaptive schemes. The second part of the thesis focuses on off-line identification of these key base model parameters. In this part, we present a real-life case study on identification of plant and built-in controller parameters and a simulator design based on this identification for a grinding CNC machine used in a gear manufacturing company

Developing tools and methods for object-oriented mechatronics

Thesis (Ph. D.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. [161]-166).The digital revolution has fundamentally changed our lives by giving us new ways to express ourselves through digital media. For example, accessible multimedia content creation tools allow people to instantiate their ideas and share them easily. However, most of these outcomes only exist on-screen and online. Despite the growing accessibility of digital design and fabrication tools the physical world and everyday objects surrounding us have been largely excluded from a parallel explosion of possibilities to express ourselves. Increasingly, webbased services allow professional and non-professional audiences to access computer-aided manufacturing (CAM) tools like 3D-printing and laser-cutting. Nonetheless, there are few (if any) design tools and methods for creating complex mechanical assemblies that take full advantage of CAM systems. Creating unique mechatronic artifacts or "originalMachines" requires more specific and sophisticated design tools than exist today. "Object-Oriented Mechatronics" is a parametric design approach that connects knowledge about mechanical assemblies and electronics with the requirements of digital manufacturing processes. Parametric instances like gears, bearing and servos are made available as objects within a CAD environment which can then be implemented into specific projects. The approach addresses the missing link between accessible rapid-manufacturing services and currently available design tools thereby creating new opportunities for self-expression through mechatronic objects and machines. The dissertation matches mechanical components and assemblies with rapid manufacturing methods by exploring transferability of conventional manufacturing techniques to appropriate rapid manufacturing tools. I rebuild various gearing and bearing principles like four-contact point bearings, cross roller bearings, spur and helical gears, planetary gears, cycloidal and harmonic gear reducers using the laser cutter, the CNC-mill and the 3D-printer. These explorations lead to more complex assemblies such as the PlywoodServo, 3DprintedClock and 3-DoF (Degree of Freedom) Head. The lessons from these explorations are summarized in a detailed "cook book" of novel mechatronic assemblies enabled by new fabrication tools. Furthermore, I use the results to develop a CAD tool that brings together several existing software packages and plug-ins including Rhino, Grasshopper and the Firefly experiments for Arduino, which will allow animation, fabrication and control of original machines. The tool is an example of an object-oriented design approach to mechatronic assemblies. A user calls a DoF (Degree of Freedom) object (parametric servo) with specific parameters like gearing and bearing types, motor options and control and communication capabilities. The DoF object then creates the corresponding geometry which can be connected and integrated with other actuators and forms. A group of roboticists and designers participated in a workshop to test the tool and make proposals for original machines using the tool. The dissertation has contributions on multiple levels. First, the actuator assembly examples and parametric design tool present a body of novel work that illustrates the benefits of going beyond off-the-shelf actuator assemblies and kit-of-parts for robotic objects. Second, this tool and the accompanying examples enable the design of more original machines with custom actuator assemblies using the latest digital fabrication tools. Finally, these explorations illustrate how new CAD/ CAM tools can facilitate an exchange between more design-oriented users and more engineering-oriented users.by Peter Schmitt.Ph.D

Haptic Feedback for Transesophageal Echocardiogram Transducer

This project focused on developing a haptic feedback control system for a transesophageal echocardiogram probe. The project group researched current haptic technologies available today to create feasible design ideas while focusing on combining simplicity, efficiency, and reliability. A customized haptic feedback sensor system was then designed for our application and a 3D model was developed. The project group built a functional prototype using a combination of self-manufactured parts and parts from several suppliers. Test procedures were then designed and implemented to prove the prototype’s functionality