Sliding-mode control of a flexure based mechanism using piezoelectric actuators

The position control of designed 3 PRR flexure based mechanism is examined in this paper. The aims of the work are to eliminate the parasitic motions of the stage, misalignments of the actuators, errors of manufacturing and hysteresis of the system by having a redundant mechanism with the implementation of a sliding mode control and a disturbance observe. x-y motion of the end-effector is measured by using a laser position sensor and the necessary references for the piezoelectric actuators are calculated using the pseudo inverse of the transformation matrix coming from the experimentally determined kinematics of the mechanism. The effect of the observer and closed loop control is presented by comparing the results with open loop control. The system is designed to be redundant to enhance the position control. In order to see the effects of the redundant system firstly the closed loop control for active 2 piezoelectric actuators experiments then for active 3 piezoelectric actuators experiments are presented. As a result, our redundant mechanism tracks the desired trajectory accurately and its workspace is bigger

Micro position control of a 3-RRR compliant mechanism

A 3-RRR compliant mechanism is designed to be used as a micro positioning stage. The stage displacements are analyzed by using structural FEA. However the experimental results for the manufactured mechanism are not compatible with the FEA which are mostly accepted as ideal while designing. A position control using Sliding Mode Control with Disturbance Observer is proposed for the reference tracking of the center of the stage. The motion of the center is measured by using a laser position sensor and the necessary references for the piezoelectric actuators are calculated using the pseudo inverse of the transformation matrix coming from the experimentally determined kinematics of the mechanism. Piezoelectric actuator linear models are used for disturbance rejection. Finally, the position control of the mechanism is succeeded although it has big errors in manufacturing, assembly etc

Design and modeling of a compliant mechanism

Compliant mechanisms are widely used in high precision systems, because they provide high resolution, frictionless, smooth and continuous motion. These kinds of mechanisms are also cheaper than the other types of high precision mechanisms. The main idea of this kind of mechanism is that no additional joints are used for creating the motion, the deflection of the flexible elements are used to create the desired motion. In this thesis, a planar parallel compliant mechanism is designed. The mechanism is actuated from three ends by using piezo mike micromotors to create motion in XY plane. The mathematical model of the mechanism is derived by using Euler Bernoulli dynamic equation for the three beams on the mechanism. The separation of variables technique is used to solve the dynamic equations. Necessary transformations are calculated for defining the center position of the stage in terms of the deflections of the beam. The mathematical model is represented in state space form and it is simulated in MATLAB Simulink. The position results are compared with another simulation called COMET. The mathematical model is reduced to two input and two output system in order to make the XY position control of the mechanism by using PID control. Finally, the mechanism is manufactured by using laser cutting and water jet cutting techniques, open loop experiments of the mechanism are verified by actuating the piezo motors manually and by giving voltage signal

Micro motion stages with flexure hinges-design and control

The developments in micro and nano technologies brought the need of high precision micropositioning stages to be used in micro/nano applications such as cell manipulation, surgery, aerospace, micro fluidics, optical systems, micromachining and microassembly etc. Micro motion stages with flexible joints called compliant mechanisms are built to provide the needed accuracy and precision. This thesis aims to build compliant planar micro motion stages using flexure hinges to be used as micropositioning devices in x-y directions by applying new control methods. First 3- RRR planar parallel kinematic structure is selected which is also popular in the literature. Then the mechanism is developed to have a new structure which is a 3-PRR mechanism. The necessary geometric parameters are selected by using Finite Element Analysis (FEA). The displacement, stress and frequency behaviors of the mechanisms are compared and discussed. Modeling of the flexure based mechanisms is also studied for 3-PRR compliant stage by using Kinetostatic modeling method which combines the compliance calculations of flexure hinges with kinematics of the mechanism. Piezoelectric actuators and optical 2d position sensor which uses a laser source are used for actuation and measurement of the stages. After the experimental studies it's seen that the results are not compatible with FEA because of the unpredictable errors caused by manufacturing and assembly. We have succeeded to eliminate those errors by implementing a control methodology based on Sliding Mode Control with Disturbance Observer which is also based on Sliding Mode Control using linear piezoelectric actuator models. Finally, we have extracted experimental models for each actuation direction of the stage and used those models instead of piezoelectric actuator models which lowered our errors in the accuracy of our measurement and ready to be used as a high precision micro positioning stage for our micro system applications

Tasarlanan düzlemsel paralel esnek bağlantılı mekanizmanın kayan kipli kontrolü

Günümüzde mikro/nano teknolojileri geliştikçe bildiğimiz rijit mekanizmaların yerini esnekliği ayarlanabilir, yeniden yapılandırılabilir yüksek hassasiyetli konum kontrollerine elverişli esnek bağlantılı mekanizma tasarımları öne çıkmıştır. Bu mekanizmalar malzemelerin esnekliğinden yararlanarak yer değişim ve kuvvet transferlerini sürekli, kararlı ve mikron seviyede yapılmasını sağlamaktadır. Bu çalışmada da yeni bir düzlemsel paralel esnek bağlantılı mekanizma tasarlanıp konum kontrolü yapılmıştır. Esnek bağlantılı mekanizma tasarımında göz önünde bulundurulması gereken önemli noktalar sunulmuştur. Hassas konum kontrolü için kayan kipli bozan etken gözlemleyicisi ile kayan kipli konum kontrolü metoduyla hassas konum kontrolü metodu sunulmus¸ deney sonuçları açık çevrim kontrol ve bilinen PID kontrol yöntemleriyle karşılaştırılmıştır. Sonuç olarak önerilen kontrol yöntemi ile mekanizmanın mikron seviyede kontrolü sağlanmıştır

Micro position control of a designed 3-PRR compliant mechanism using experimental models

A new compliant stage based on 3-PRR kinematic structure is designed to be used as a planar micro positioner. The mechanism is actuated by using piezoelectric actuators and center position of the stage is measured using a dual laser position sensor. It's seen that manufactured mechanism has unpredictable motion errors due to manufacturing and assembly faults. Thus, sliding mode control with disturbance observer is chosen to be implemented as position control in x-y axes of the center of the mechanism. Instead of piezoelectric actuator models, experimental models are extracted for each actuation direction in order to be used as nominal plants for the disturbance observer. The position control results are compared with the previous position control using linear piezoelectric actuator models and it's seen that the implemented control methodology is better in terms of errors in x and y axes. Besides, the position errors are lowered down to ±0.06 microns, which is the accuracy of the dual laser position sensor

Esnek bağlantılı mekanizma modeli ve kontrolü

Bu çalışmada mikro sistem için konumlandırıcı olarak tasarımı yapılmış uyumlu bir mekanizmanın benzetiminin yapılması amacıyla mekanizmanın dinamik modellemesi yapılmıştır. Mekanizmanın kirişlerden oluştuğu düşünülüp, mekanizmaya gelen kuvvetler kirişlerin uçlarında dikey deformasyonlara neden olduğundan, kirişlerin dikey dinamik denklemleri kullanılarak model oluşturulmuştur. Mekanizmanın merkezine bir eksen takımı yerleştirilip, merkezinin hareketi kirişlere dik yönde oluşan deformasyon vektörlerinin mekanizmanın geometrisine bağlı olarak oluşturdukları kinematik transformasyon ile mekanizmanın merkezinin hareketi bulunmuştur. Son olarak da mekanizmanın benzetimi Matlab Simulink ortamında yapılmıştır. Ayrıca PID kontrol uygulanıp sistemin pozisyon kontrolü sağlanmıştır

Development and Integration of Inkjet-Printed Strain Sensors for Angle Measurement of an Origami-Based Delta Mechanism

An origami-based parallel mechanism is an excellent solution for various applications where small-scale, low profile and foldability are needed. These mechanisms are composed of rigid and flexible layers designed according to layer-by-layer fabrication methods. In addition, it becomes important to design functional layers that provide user feedback. Here, the design and fabrication of an origami-based 3 Degree-of-Freedom (DoF) Delta mechanism, which has the same traditional kinematics as a Delta mechanism, are presented. A sensor layer was designed composed of 3 strain gauges to measure the angular position of the actuated arm of the mechanism. The strain-gauge patterns were printed on a special Polyethylene terephthalate (PET) using Silver nanoparticle ink with a commercial desktop printer. The integration of these sensors has been studied by placing them in different locations between rigid layers. The sensors' outputs were presented when subjected to step and sinusoidal inputs of the actuated arm. The experiment results show that the developed sensor layer can track the angular position changes of the actuated lower arm, which is a promising result to be used in a control loop in the feature

Control systems with network delay

In this paper motion control systems with delay in measurement and control channels are discussed and a new structure of the observer-predictor is proposed. The feature of the proposed system is enforcement of the convergence in both the estimation and the prediction of the plant output in the presence of the variable, unknown delay in both measurement and in the control channels. The estimation is based on the available data – undelayed control input, the delayed measurement of position or velocity and the nominal parameters of the plant and it does not require apriori knowledge of the delay. The stability and convergence is proven and selection of observer and the controller parameters is discussed. Experimental results are shown to illustrate the theoretical prediction

Development and characterization of silicone embedded distributed piezoelectric sensors for contact detection

Tactile sensing transfers complex interactive information in a most intuitive sense. Such a populated set of data from the environment and human interactions necessitates various degrees of information from both modular and distributed areas. A sensor design that could provide such types of feedback becomes challenging when the target component has a nonuniform, agile, high resolution, and soft surface. This paper presents an innovative methodology for the manufacture of novel soft sensors that have a high resolution sensing array due to the sensitivity of ceramic piezoelectric (PZT) elements, while uncommonly matched with the high stretchability of the soft substrate and electrode design. Further, they have a low profile and their transfer function is easy to tune by changing the material and thickness of the soft substrate in which the PZTs are embedded. In this manuscript, we present experimental results of the soft sensor prototypes: PZTs arranged in a four by two array form, measuring 1.5–2.3 mm in thickness, with the sensitivity in the range of 0.07–0.12 of the normalized signal change per unit force. We have conducted extensive tests under dynamic loading conditions that include impact, step and cyclic. The presented prototype's mechanical and functional capacities are promising for applications in biomedical systems where soft, wearable and high precision sensors are needed