Evaluation of Electromechanical Performance of Microactuator Designs

By AZoNano.com Staff Writers

Topics Covered

Introduction
Experimental Setup
Standard Bending Test
Microactuator Deflection Measurement
Measurement of Pre-loaded Actuator Force
Conclusion
About FemtoTools

Introduction

Conducting or conjugated polymers are increasingly gaining interest as smart materials for sensors or actuators for use in innovative microfabricated devices. Although the most commonly reported actuators in the literature are bilayer actuators, a new type of actuator called trilayer has recently evolved. This actuator is made by isolating two electroactive polymer (EAP) films by means of an insulating soft and porous film. Unlike bilayer acutators, trilayer actuators are capable of operating in dry as well as wet environments, thus widening the scope of potential applications.

This article discusses the mechanical characterization of the various kinds of EAP microactuators to assess the electromechanical performance of the microactuator designs. The Laboratoire de Physico-chimie des Polymères et des Interfaces at the University of Cergy-Pontoise, France has developed and created the microactuators.

Experimental Setup

The FT-RS1000 Microrobotic System from FemtoTools, shown in Figure 1, is specially engineered to perform the mechanical characterization of microactuators, microcantilevers, and other miniaturized systems, is used to test the electroactive polymer microactuators.

Figure 1. FT-RS1000 mounted on stereo-microscope

The beam-shaped microactuators to be tested are clasped between two electrodes, as depicted in Figure 2, to enable the application of the actuation signal to drive the microactuator. A function generator is used to supply the driving voltages of +-1V to drive the polymer actuator. Then a FT-S1000 Microforce Sensing Probe is placed horizontally on the FT-RS1000 Microrobotic System. The sensor tip and the sample are placed under a stereomicroscope. This setup ensures the precise alignment of the Microforce Sensing Probe tip to the microactuators and allows sample observation during testing.

Figure 2. Close-up view of the EAP microactuator clamped between electrodes

Standard Bending Test

A standard bending test is carried out to measure the stiffness of the EAP microactuator. First, the positioning joysticks are used to roughly align the FT-S1000 Microforce Sensing Probe tip relative to the end of the cantilever. Then, the FT-WFS01 Micromechanical Testing Software’s automated ‘Find Contact’ functionality is used to determine the contact point between the EAP microactuator and the sensor probe tip to start the horizontal, automated bending test, as illustrated in Figure 3.

Figure 3. Microscope view of the micro-actuator during bending test

The FT-RS1000 Microrobotic System is sampling the force signal of the FT-S1000 Force Sensing Probe as well as the position data of the integrated optical encoders. Figure 4 depicts the resultant measurement data. The slope of the curve shown in Figure 4 provides details about the stiffness of the elastic structure, which is also shown on the FT-WFS01 Graphical User Interface.

Figure 4. Force-deformation measurement data and stiffness extraction

Microactuator Deflection Measurement

The application of an actuation voltage to the EAP microactuators results in their deformation and generates a displacement, which is a key factor to assess their performance. The displacement is accurately measured using the FT-RS1000 Microrobotic System, which performs a series of 9 ‘Find Contact’ tasks while applying variable actuation voltage on the EAP microactuator. The built-in optical encoders in the FT-RS1000 system record the actual position and provide a high-resolution feedback of the point where the contact was established. The position recorded is relative to the deflection of the EAP microactuator. The highest deflection of 188 µm was recorded at an actuation voltage of 2 V.

Measurement of Pre-loaded Actuator Force

The EAP microactuator generates a force which plays a key role in the performance evaluation and the optimization of the device design and material. Hence, for a pre-loaded microactuator, the force output is determined while applying a cyclic actuation voltage and a step actuation voltage. A signal generator is used to supply the actuation voltage to the FT-RS1000 system controller and the resultant actuation force is concurrently measured. The force is measured by means of a FT-S100 Microforce Sensing Probe.

The input signals with a 2 V step and a 0.5 Hz cyclic input are illustrated in Figures 6 and 7, while the corresponding force response created by the EAP microactuator is depicted in Figures 8 and 9.

Figure 5. Voltage input signal – step

Figure 6. Voltage input signal – cyclic

Figure 7. Step force response

Figure 8. Cyclic force response

These data are helpful in analyzing the static as well as the dynamic behavior of the EAP microactuator. About 1.6 seconds are needed to achieve 90% of the actuation force. The actuator is able to achieve only 79% of the full scale force with 0.5 Hz actuation frequency.

Conclusion

From the results, it is evident that the FT-RS1000 Microrobotic System from FemtoTools is effective in the mechanical characterization of the EAP microactuator. The system has been used to realize four different types of measurements: bending test (stiffness measurement), deflection measurement, static force response measurement and dynamic force response measurement.

About FemtoTools

FemtoTools is a Swiss high-tech company that offers award-winning, ultra high-precision instruments for mechanical testing and robotic handling in the micro- and nanodomains. This new generation of instruments meets the challenging requirements of semiconductor technology microsystem development, materials science, micromedicine and biotechnology.

FemtoTools’ microrobotic handling and measurement instruments feature highly sensitive microforce sensing probes and force sensing microgrippers that are the result of a specially developed microelectromechanical system (MEMS)-based manufacturing process. The unmatched sensitivity and accuracy of our innovative systems redefines the standards for true quantitative investigations in the micro- and nanodomains.

FemtoTools’ easy-to-use microrobotic handling and measurement instruments have exceeded customer’s expectations and create exciting new possibilities, as demonstrated by numerous recent scientific advancements that have used our instruments.

This information has been sourced, reviewed and adapted from materials provided by FemtoTools.

For more information on this source, please visit FemtoTools.

Date Added: Jun 29, 2013 | Updated: Aug 29, 2013
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