Future work

Though the SDA and LVSDA have been studied in analytical or experimental manners, and the simulated results can match the measured results in reasonable accuracy, there still have some works needed to improve the reliability and applicability of this research. The future works can be classified into five topics as following.

1. Further experimental verification:

Further experimental verification on dynamical response is quite necessary in general.

For example, the non-contact length for given input is a lower bound of SDA main plate length, while a SDA with longer plate will still be priming with same non-contact length as implicated by Eq.(2-16). This argument somewhat violates with intuition but it is true. Evidence has been shown in [1], the contact length of three different main plates at same input level are recorded and plotted as shown in Figure 5-1. The contact length values for devices with plate length 60,

70 and 80 µm are 43, 53, and 63 µm respectively. In other words, the values of non-contact length are around 17 µm for these devices. This discovery supports the validity of this work’s result. Why SDA of different plate length produces different force when the non-contact length is same? This problem can be probably simulated by introducing friction into the contact surface. An alternate method is applying the adhesion energy on contact part as done in [36], in which only the release problem is concerned. When taken adhesion effect into energy balance consideration, the adhesion will consume energy and reduce the mechanical displacement.

These above discussions may be verified by fabrication and testing of next-generation design of SDA/LVSDA test structures.

2. Application on other SDA shapes:

Applied the analytical SDA model to plate shape beside rectangle is important in proving the model’s applicability. This is basically routine but time-consuming work. The key point is the governing equation Eq. (2-2) is derived in general meaning, as it can be applied for other type of plate shape in case of the distributed load as Eq. (2-1) is expressed in suitable manner according to its shape as triangular, trapezoidal, or circular. Some previous works [37, 38] were done in pull-in research for these shapes under electrostatic force. Once the governing equation has been constructed, the steps followed are similar as presented in chapter 2 while the solution will be different. As the expressions are often complicated, this process may be somewhat tedious but the expected results will prove its great worth in predicting the device performance.

3. Reliability of SDA/LVSDA:

The load in SDA/LVSDA is basically dynamic. As a result, their life cycles rely on the material, loading/unloading level and geometric factors. To ensure the system be reliable in certain degree for guaranteed life cycles, the reliability design criteria should be introduced.

The S-N curve may be constructed after enough tested data have been collected and analyzed as derived in sections 2.3 and 4.2. Once the maximum and minimum stresses have been calculated from the input level, the expected life cycles can be decided from S-N curve. When the fatigue test data are enough, the endurance limit, yielding stress and ultimate stress of the fabricated devices can be determined from fatigue theory. These results may be utilized to improve the device design and process flow.

4. Analytical modeling of LVSDA:

Since the LVSDA is effective in reducing the threshold voltage than SDA of same width and length. It is worth of an analytical model, while it is more complicated in nature than SDA. The beam model proposed in Eq. (2-2) may be applied for LVSDA and the governing equations increase to three and are rather time-consuming to solve in analytical manner, though it is believed to be solvable. An alternative method is the application of pseudo-rigid-body model as Figure 5-2 for the main plate and scratch plate, while the flexible joint is still a beam.

The main plate and scratch plate are viewed as rigid, while flexibe joint is still a beam. The minimum potential energy principle of the sum of elastic deformation energy and electrostatic energy in capacitor will decide the equilibrium generalized coordinates (θ1, θ2) at given input.

This approach seems easier to derivate an analytical solution. Once the generalized coordinates (θ1, θ2) are determined, the other characteristics can be calculated by routine manner.

5. Optimization design of SDA/LVSDA:

The optimization of SDA/LVSDA on geometrical factors may be handled in two ways.

The first one is the present method, i.e., by fabricating different devices and then testing for optimal geometrical set. For example, for a flexible joint with fixed length and width, the joint location will affect the output force level. The test results will reveal the optimal geometrical set of LVSDA. This approach is effective but expensive. Another one is to form the object function

with suitable constrain conditions by using the results in last topic: Analytical modeling of LVSDA and SDA modeling. These object function and constraint may be used in commercial software as Optimization Toolbox in MATLAB.

6. Latch mechanism for stable step size:

Though the friction effect is the major operation principle of SDA/LVSDA, it also introduce instable step size. To minimize this defect, a rachet mechanism is proposed to fabricated along the trajectory of motion to fix the step size in mechanical manner. However, this design will confine the step size in the pitch of rachet teeth.

Figure 5-1. Contact and Non-contact length for different plate length [1].

Figure 5-2. Pseudo-rigid-body model of LVSDA to find the equilibrium state of generalized coordinates (θ1, θ2) at given input level. The main plate and scratch plate are viewed as rigid, while flexibe joint is still a beam. The minimum potential energy principle of the sum of elastic deformation energy and electrostatic energy in capacitor will decide the equilibrium generalized coordinates (θ1, θ2) at given input.

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Publication List

• Journal papers:

– Shawn Chen, Chiawei Chang and Wensyang Hsu, “Output Force Enhancement of Scratch Drive Actuator in Low-Voltage Region by Using Flexible Joint,” Sensors and Transducers Journal, Vol. 115, Issue 4, April 2010, pp.71-82.

– Shawn Chen, Chiawei Chang and Wensyang Hsu, “Improved Model of Rectangular Scratch Drive Actuator,” Journal of Micro/Nanolithography, MEMS, and MOEMS, (submitted).

– Shawn Chen, Chiawei Chang and Wensyang Hsu, “Design, Fabrication and Testing of a Novel Low Voltage-driving Scratch Drive Actuator with Flexible Joint,” Sensors and Actuators: A, (submitted).

• Conference papers:

– Shawn Chen, Chiawei Chang and Wensyang Hsu, “Output Force Characterization of Scratch Drive Actuators with Flexible Joints”, APCOT, Perth, Australia, July 6-9, 2010.

– Shawn Chen and Wensyang Hsu, “Feasibility study on a novel low-voltage-driven fixed-step-size scratch drive actuator with flexible joint”, EUROSENSORS, Barcelona, Spain, Sep. 11-14, 2005.

– Shawn Chen and Wensyang Hsu, “Reversible stepwise motion by a novel symmetric scratch drive actuator”, ASME IMECE, New Orleans, USA, Nov. 17-22, 2002.

簡歷(Vita)

學歷: 國立交通大學工學博士(民國99年) 國立中央大學工學碩士(民國77年) 國立交通大學工學學士(民國71年) 經歷: 國立勤益科技大學講師

國立勤益技術學院講師 私立勤益技術學院講師 研究方向: 微致動器最佳化設計

創意性機構設計 油壓機械設計