A 2 degree-of-freedom SOI-MEMS translation stage with closed loop positioning

This research contains the design, analysis, fabrication, and characterization of a closed loop XY micro positioning stage. The XY micro positioning stage is developed by adapting parallel-kinematic mechanisms, which have been widely used for macro and meso scale positioning systems, to silicon-based micropositioner. Two orthogonal electrostatic comb drives are connected to moving table through 4-bar mechanism and independent hinges which restrict unwanted rotation in 2-degree-of-freedom translational stage. The XY micro positioning stage is fabricated on SOI wafer with three photolithography patterning processes followed by series of DRIE etching and HF etching to remove buried oxide layer to release the end-effector of the device. The fabricated XY micro positioning stage is shown in Fig1 with SEM images. The device provides a motion range of 20 microns in each direction at the driving voltage of 100V. The resonant frequency of the XY stage under ambient conditions is 811 Hz with a high quality factor of 40 achieved from parallel kinematics. The positioning loop is closed using a COTS capacitance-to-voltage conversion IC and a PID controller built in D-space is used to control position with an uncertainty characterized by a standard distribution of 5.24nm and a approximate closed-loop bandwidth of 27Hz. With the positioning loop, the rise time and settling time for closed-loop system are 50ms and 100ms. With sinusoidal input of ω=1Hz, the maximum phase difference of 108nm from reference input is obtained with total motion range of 8μm

Elastodynamic Effects of Mass-Balancing: Experimental Investigation of a Four-Bar Linkage

This paper deals with static balancing of closed-loop mechanisms. The long-term goal of the research is enhancing the performance of parallel robots by means of effective static balancing strategies that take into account the system dynamic behaviour. In this contribution, the influence of mass-balancing on the elastodynamic performance of a four-bar linkage, intended as the simplest example of closed-loop mechanism, is experimentally investigated. The design of the experimental apparatus is discussed and the results of tests on both an unbalanced linkage and its balanced variant are presented. Base-transmitted forces and vibrations are monitored for constant-speed operations and for velocity ramp tests in order to characterize the elastodynamic behaviour of the linkages. The analysis is supported by implementing a flexible multibody model of the experimental apparatus that enhances the interpretation of the experimental data

A Systematic Procedure for the Elastodynamic Modeling and Identification of Robot Manipulators

International audienceThis paper presents a systematic procedure for the elastodynamic modeling of industrial robots that is applicable to either serial or parallel manipulators. This procedure is based on a 3-D space generalization of the equivalent rigid link system (ERLS) description, the finite-element method (FEM), and the Lagrange principle. It considers flexible links and joints, and leads to generic equations of motion expressed according to the angles of the actuated joints and the independent elastic degrees of freedom. An efficient identification process through modal analysis is detailed, and the description of damping and joint behavior according to the model application is discussed. The method is applied to a 3-D delta-like parallel structure and successfully validated through an experimental impact testing-based modal analysis

Modal analysis of a parallel kinematic machine: Freehex.

Parallel Kinematic Machines (PKM) are mechanical systems utilized to produce precise operations at high speeds compared to serial machines. Its applications cover a wide range of operations in the automotive and aerospace industry. These machines can be affected by oscillatory effects such as resonant frequencies, which can produce adverse effects on the performance and the useful life of the systems. Therefore the determination of these characteristics is an important element in the design and operation of these machines. The research developed in this thesis addresses the identification of these resonant frequencies in the possible working volumes of a PKM called FreeHex. This machine is used to perform high speed machining operations and in situ rapair of aerospace equipment. Two methods are developed and described to estimate the resonant frequencies.The first is formulated through the Finite Element Method (FEM), and given the initial configuration of the FreeHex is capable to estimate the resonant frequencies within the working volume of that configuration. The second method is intended to validate the model described by the FEM. As the FreeHex is able to achieve a several configurations the analysis is performed to a single one and then the experimental and the finite element analysis model are compared. The experimental results are obtained by impact testing trough Multiple Input Single Output (MISO) method on the structure. The average error between the FEA models and experimental results lies in a value of 3.94 % showing a good correlation between both methods and making possible to implement the algorithms here developed

Investigation of the effects of Stewart platform-type industrial robot on stability of robotic milling

Mobile machining with industrial robots is proposed as a cost-effective and portable manufacturing alternative to large scale CNC machine tools in large-scale part manufacturing. Robotic milling, one of the widely used mobile machining approaches, involves several technical challenges and distinct characteristics in terms of machining dynamics and stability due to completely different structural build up. In this paper, distinctive effects of Stewart platform-type of hexapod robot on stability of robotic milling is investigated based on characterisation of its structural dynamics, simulation of stability limits and experimental validation. Three aspects are demonstrated: (1) the position-dependent stability diagrams due to the position-dependent dynamics of the hexapod platform, (2) the effects of cross transfer function due to the complex kinematic chain on milling stability and (3) the role of feed rate direction in stability of robotic milling. The conditions for minimised position-dependent stability through appropriate tooling are also illustrated through simulations and experimental verification. The cases where process stability may be governed by either the hexapod robot or the cutting tool modes are discussed and identified through stability analysis. It is shown that the feed rate direction becomes a significant parameter for stability limits in robotic milling. The conditions at which the cross transfer function becomes significant on milling stability are discussed through simulations and experimental results. It is shown that cross transfer functions may significantly affect milling stability especially when the radial depth of cut is less than 50 % of the tool diameter. As one of the important outcomes of this research, it is found that appropriate tooling may decrease the reliance of milling stability on robot position

Kinematics and Robot Design I, KaRD2018

This volume collects the papers published on the Special Issue “Kinematics and Robot Design I, KaRD2018” (https://www.mdpi.com/journal/robotics/special_issues/KARD), which is the first issue of the KaRD Special Issue series, hosted by the open access journal “MDPI Robotics”. The KaRD series aims at creating an open environment where researchers can present their works and discuss all the topics focused on the many aspects that involve kinematics in the design of robotic/automatic systems. Kinematics is so intimately related to the design of robotic/automatic systems that the admitted topics of the KaRD series practically cover all the subjects normally present in well-established international conferences on “mechanisms and robotics”. KaRD2018 received 22 papers and, after the peer-review process, accepted only 14 papers. The accepted papers cover some theoretical and many design/applicative aspects

Research and development of a reconfigurable robotic end-effector for machining and part handling.

Masters Degree. University of KwaZulu-Natal, Durban.Abstract available in PDF

Dynamic Substructuring for Evaluating Vibro-acoustic Performance

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 기계항공공학부, 2020. 8. 강연준.Generally, a mechanical system consists of various substructures that cause noise and vibration problems. This thesis proposes a dynamic substructuring method for the estimation of the dynamic characteristics of a coupled mechanical system based on substructure characteristics. The first phase of this thesis presents a method for the estimation of rotational stiffness at the coupled points of an assembled system based on a dynamic substructuring method. Conventional test-based rotational stiffness evaluation methods are sensitive to measurement errors and require a specialized jig for testing. In contrast, given that the proposed method uses the natural frequency shift phenomenon that results from the addition of mass, the measurement error is relatively small, and the accuracy is improved by excluding the interference of other modes. In addition, the proposed method solves the problem due to the complexity of the conventional method by changing the fixed condition of the system using frequency response function (FRF)-based substructuring (FBS) modeling; thus, it does not require a specialized jig for fixing parts. In this manuscript, the concepts of trial mass, virtual mass, and virtual spring are introduced to systematically explain the proposed method and its application based on frequency shifts. The results of the experiments conducted on a vehicle shock absorber verify the utility of the proposed method. In the second phase, a novel transfer path analysis (TPA) method based on a dynamic substructuring model is proposed. With the dynamic substructuring model, the FRF information of a base system can be used to evaluate the stiffness addition effect at the measurement points instead of adding the actual stiffness. In the proposed method, a spring with an infinite stiffness is virtually added to a specific transfer path among various possible paths, such that the specific path is removed. Hence, the virtual spring significantly reduces the contribution of the specific path. This method is more implementable and applicable than existing TPA methods (i.e., conventional TPA and operational TPA), as it does require part removal or the correlation information between the signals. To verify the feasibility of the FBS-based TPA method, it was applied to a significant road noise phenomenon. The test results confirm that the proposed method can be applied to the TPA of suspension linkages and vehicle bodies. In the final phase of this thesis, an improved dynamic substructuring model is presented based on the estimated FRF information at a coupling point between substructures. An assembled system generally consists of two or more such substructures, which are typically connected by a bolt. To ensure an accurate estimation of the dynamic characteristics of the assembled system, an accurate measurement of the joint properties is required. However, in most practical cases, physical constraints prevent such measurements at actual coupling points. Accordingly, this study proposes a method that uses generalized coupling properties to estimate the dynamic characteristics of a new coupling system based on the characteristics of the original substructure. In this process, the concept of virtual point transformation was used to estimate accurate FRFs at the coupling points of the assembled system based on convenient measurements. Thereafter, the proposed method was validated using a hard-mount vehicle suspension in a test jig and on an actual vehicle body for estimating the vibration characteristics of the assembled system. This research contributes towards the accurate estimation of the dynamic properties of bolt-assembled systems in several practical applications.일반적으로 기계시스템은 다양한 하위 부분구조물로 구성되며, 이들은 많은 소음 및 진동 문제를 야기한다. 본 논문은 이러한 하위 부분구조물의 동특성 정보만을 사용하여 전체 대상 시스템의 동적 특성을 추정하기 위한 동특성 합성기법을 다루고 있다. 먼저, 본 논문의 첫 장에서는, 동특성 합성기법을 활용한 결합 시스템의 회전 강성 추정 기법을 제시하였다. 기존 시험기반의 회전 강성 평가법들은 측정 오류에 민감 할 뿐 아니라, 측정을 위한 별도의 고정용 지그가 필요하다. 그러나, 본 연구에서 제시된 방법은 시스템에 부가되는 질량에 의한 고유 주파수 편이 현상을 사용하기 때문에 기존 방법에 비해 측정오차가 상대적으로 작고, 다른 모드의 간섭을 배제함으로써 추정 정확도의 향상을 기대할 수 있다. 또한, 본 기법은 주파수 응답함수 기반 합성 모델을 사용하여 실제 고정 지그를 사용하는 대신, 고정 경계조건을 수식적으로 대체함으로써 기존 방법의 복잡성을 해결하였다. 이 과정에서 시험 질량, 가상 질량 및 가상 스프링의 개념이 도입되었으며, 실제 차량의 충격 흡수장치를 이용하여 모델의 검증을 수행하였다. 다음으로, 본 논문의 두 번째 장에서는, 동특성 합성 모델을 이용한 새로운 전달 경로 분석 기법을 제시하였다. 본 연구에서는 대상 시스템의 실제 전달경로를 제거하는 대신, 무한대의 강성을 갖는 가상의 스프링을 주파수 응답 함수의 형태로 반영함으로써, 특정 전달경로의 제거 효과를 구현하였다. 본 기법은 기존의 전달경로 분석법에 비하여 실험적으로 구현이 쉬우며, 측정에 소요되는 작업량과 계산량 또한 획기적으로 줄일 수 있다. 해당 기법은 차량 현가계의 특정 진동 전달 현상을 이용하여 실험적으로 유효성이 검증되었다. 본 논문의 마지막 장에서는, 동특성 합성 모델의 정확도 개선을 위한 연구가 수행되었다. 일반적으로 결합시스템은 두 개 이상의 결합물이 볼트를 이용하여 결합되며, 결합 시스템의 동특성 예측을 위해서는 결합부의 정확한 동특성이 요구된다. 하지만 대부분의 경우, 물리적 공간의 제약으로 인하여 실제 결합 지점에서의 측정이 불가능하기 때문에, 가상 지점의 개념을 도입하여 결합지점에서의 주파수 응답함수를 추정하였다. 해당 방법 역시, 실제 차량과 서스펜션 시험 지그를 이용하여 검증되었다. 본 연구는 많은 실제 응용 분야에서 정확한 시스템의 동특성 추정에 기여하고 있다.CHAPTER 1. GENERAL INTRODUCTION 1 1.1 Research background and motivation of the work 1 1.2 Literature reviews 8 1.3 Overview of the present work 15 1.4 Contributions 17 CHAPTER 2. INTRODUCTION TO DYNAMIC SUBSTRUCTURING 21 2.1 Introduction 21 2.2 Summary 25 CHAPTER 3. VIRTUAL PARAMETERS FOR ESTIMATING ROTATIONAL STIFFNESS 27 3.1 Introduction 27 3.2 Theoretical concepts 34 3.2.1 Concept of trial masses 34 3.2.2 Concept of virtual masses 40 3.2.3 Concept of virtual springs 44 3.3 Experimental validation 47 3.3.1 Validation of trial masses 47 3.3.2 Validation of virtual masses 55 3.3.3 Validation of virtual springs 59 3.4 Summary 64 CHAPTER 4. TRANSFER PATH ANALYSIS USING A VIRTUAL SPRING 69 4.1 Introduction 69 4.2 Conventional TPA 76 4.3 FBS-based TPA 79 4.4 Experimental validation 83 4.4.1 Specific road noise phenomenon 83 4.4.2 Suspension link TPA 89 4.4.3 Body TPA 99 4.5 Summary 104 CHAPTER 5. EXPERIMENTAL METHOD FOR IMPROVED ACCURACY OF DYNAMIC SUBSTRUCTURING MODEL 109 5.1 Introduction 109 5.2 Theoretical concepts 111 5.2.1 Dynamic substructuring model considering generalized coupling properties 111 5.2.2 Virtual point transformation method to improve experimental data 117 5.2.2.1 Virtual point displacement 117 5.2.2.2 Virtual point FRF 125 5.3 Validation of virtual point transformation 128 5.3.1 Target system and system description 128 5.3.2 Validation of virtual point transformation 133 5.3.2.1 Validation of virtual point displacement 133 5.3.2.2 Validation of virtual point FRF 139 5.3.3 Dynamic substructuring with virtual point transformation 143 5.4 Summary 152 CHAPTER 6. CONCLUSIONS AND RECOMMENDATIONS 155 6.1 Conclusions 155 6.2 Recommendations 159 APPENDIX 163 REFERENCES 167 국 문 초 록 177Docto