Merve Acer

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 prototypes mechanical and functional capacities are promising for applications in biomedical systems where soft, wearable and high precision sensors are needed.

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. Its 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 its 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.

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.

Comparison of circular flexure hinge compliance modeling methods

This paper presents the analytical in-plane compliance calculation methods for single axis circular flexure hinges and compares the methods with Finite Element Analysis (FEA). These comparisons are also made for varying geometric parameters not only for “b” (the width of the flexure) but also “t” (the shortest distance of the flexure) parameter. The analyses give us the selectable calculation methods for certain “b” and “t” parameters besides they show which geometric parameter (b or t) have more influence on in which direction of compliances. Thus, while designing a flexure based mechanism this work gives us the advantage of selecting right in-plane compliance calculation methods which are less time consuming and easier than FEA and it also helps us to choose the right geometric parameters by showing the effects of them on the compliances.

Micro position control of a 3-RRR compliant mechanism

A planar parallel compliant mechanism based on 3-RRR kinematic structure is designed to be used as a micro positioning stage. The position of the center is measured by using a laser position sensor and the mechanism is actuated by piezoelectric actuators. The stage displacements are analyzed by using structural Finite Element Analysis (FEA). However the experimental displacement results for the manufactured mechanism are not compatible with the FEA which means that we have errors due to manufacturing, assembly etc. A position control using Sliding Mode Control with Disturbance Observer is proposed for the reference tracking of the center of the stage. Piezoelectric actuator linear models are used for disturbance rejection. Finally, the position control of the mechanism is succeeded although it has inadmissible errors compared to FEA.

Design, kinematic modeling and sliding mode control with sliding mode observer of a novel 3-PRR compliant mechanism

Compliant mechanisms have great advantages to be used as micropositioning stages for high-precision applications but they are very sensitive to manufacturing tolerances and assembling errors. In this work, a novel compliant stage having 3-PRR kinematic structure and actuated by piezoelectric actuators is introduced. A kinematic modeling based on compliance of the flexible elements and finite element analysis based model have been extracted. It is found out that the experimental results are not compatible with the theoretical results due to the manufacturing, actuator assembly errors. The position control of the mechanism has been achieved using sliding mode control which is a great method for unpredictable varying parameters in the system. Sliding mode observer has also been used for the hysteresis and nonlinearities of the piezoelectric actuators. Experimental models for each actuation axis have been used as the nominal models for the sliding mode observer. In order to see the advantage of the control method simple PID control has also been implemented. It is seen that sliding mode control with sliding mode observer using experimental models reduces the position tracking errors to the range of the accuracy of our available measurement. Graphical Abstract

Upravljanje gibanjem redundantnog mehanizma temeljenog na savijanju korištenjem piezoelektričnih aktuatora

A 3-PRR flexure based mechanism which is used as a redundant mechanism providing only x-y micro positioning is designed and controlled in this paper. The aim of this work is to eliminate the unpredictable motions due to manufacturing and assembling errors by implementing sliding mode control (SMC) with disturbance observer (DOB) using piezoelectric actuator models. 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 is implemented for 2 piezoelectric actuators and the remainder piezoelectric actuator is treated as a fixture. Then the position control is implemented for 3 piezoelectric actuators. As a result, our redundant mechanism tracks the desired trajectory accurately and its workspace is bigger. Finally we have compared the proposed position control with the conventional PID control. It is seen that SMC with DOB gives better results. We have achieved to make the position control of our mechanism, which has unpredictable position errors due to rough manufacturing, assembly, piezoelectric actuator hysteresis etc. The designed 3-PRR flexure mechanism can be used as a micro positioner with the available measurement in the laboratory.

Force Localization Estimation Using a Designed Soft Tactile Sensor

Wearable tactile sensors are significant in biomedical robotic applications where force feedback is important. In this work, a soft tactile sensor is proposed for force localization. The tactile sensor was manufactured by using layer-by-layer technique that enables flexibility. The sensor has 9 lead zirconate titanate (PZT) elements placed in 3 × 3 matrix form which are 4 × 4 mm2 and the spatial resolution is 3 mm. The voltage values gathered from the sensor were conditioned by a charge amplifier circuit. A human inspired machine learning procedure called Neural Networks was used for force localization. The success rates with respect to different network structures were presented and the maximum success was realized as 80.71%.