Comb Fingers Research Articles

A Micromachined Silicon-on-Glass Accelerometer with an Optimized Comb Finger Gap Arrangement.

This paper reports the design, fabrication, and characterization of a MEMS capacitive accelerometer with an asymmetrical comb finger arrangement. By optimizing the ratio of the gaps of a rotor finger to its two adjacent stator fingers, the sensitivity of the accelerometer is maximized for the same comb finger area. With the fingers' length, width, and depth at 120 μm, 4 μm, and 45 μm, respectively, the optimized finger gap ratio is 2.5. The area of the proof mass is 750 μm × 560 μm, which leads to a theoretical thermomechanical noise of 9 μg/√Hz. The accelerometer has been fabricated using a modified silicon-on-glass (SOG) process, in which a groove is pre-etched into the glass to hold the metal electrode. This SOG process greatly improves the silicon-to-glass bonding yield. The measurement results show that the resonant frequency of the accelerometer is about 2.05 kHz, the noise floor is 28 μg/√Hz, and the nonlinearity is less than 0.5%.

Behavior analysis of comb-drive actuators operating in near-zero-overlap configuration

Comb structures are widely used in micro-electromechanical systems as basic components of electrostatic actuators, capacitive sensors, resonators and energy harvesters. Typically, they are operated with a large overlap of the comb fingers, in the linear region. Here we study the behavior of comb-drive actuators during the displacement along the axis of the fingers in the unconventional regime where the fingers are slightly overlapping (around the width d of the fingers), which has recently gained attention in the MEMS community. In the intermediate region where the overlap approaches zero, fringing electric fields induce a non-linear variation of the capacitance, yielding a significant electrostatic force between the combs even without finger overlap with a maximum gradient occurring in this region. The comb capacitance variation with overlap was calculated using analytical and FEM modeling and confirmed with experimental results. We explored the implications of this condition in both static and dynamic modes, highlighting the effect of spring softening arising from the second derivative of the capacitance. These findings introduce new operational possibilities for actuators and sensors and substantial tunability in frequency for resonators.

Development of a Bionic Picking Device for High Harvest and Low Loss Rate Pod Pepper Harvesting and Related Working Parameter Optimization Details

Addressing the issues of low harvesting efficiency and high losses in current pod pepper harvesters, this study presents the design of a bionic comb finger pod pepper picking device and an inclined double-spiral bell pepper harvester to improve the harvest rate and reduce loss rate. Through the utilization of discrete element simulation software EDEM, a discrete element model for pod peppers is established. Additionally, a simulation platform for ground drop loss during pod pepper picking is developed, enabling exploration of the movement trajectory and velocity changes of the pod pepper elements. The study also conducts an analysis on the impact of the speed of the picking rollers X1, the feeding speed of pod peppers X2, and the spacing between the two picking rollers X3 on ground drop losses. Based on the results of the single-factor test, the Box–Behnken response surface test was used to optimize the working parameters of the picking device, which resulted in the optimal combination of the working parameters of the picking device: the speed of the picking rollers was 680.41 rpm, the feeding speed of the pod peppers was 0.5 m/s, and the spacing between the two picking rollers was 12 mm, which resulted in the loss rate of pod peppers on the floor of the ground being 3.526%.

Design and simulation of a tunable comb-drive actuator with a wide frequency tuning range and low pull-in voltage

The presented paper describes the design, simulation, and analysis of a novel tunable comb-drive actuator that aims to increase the range of tuning resonance frequency while reducing the pull-in voltage. The conventional comb resonator has a limited resonant frequency tuning range, and hence, modifying the spring stiffness of the structure is crucial to obtaining a tunable comb resonator. The proposed design includes eight flexible beams on each side that support a set of comb finger parts. The actuator achieves the goal of shifting the resonance frequency both downwards and upwards by utilizing Serpentine nested-folded beams. A triangular comb with non-uniform varied finger lengths combined with variable gap fingers is designed to adjust the frequency downwards, while a comb with constant finger lengths combined with variable gap fingers is designed to adjust the frequency upwards. To simulate and design the structure, the IntelliSuite software is utilized. The results show that the actuator has a primary resonant frequency of 3052 Hz, which can be lowered to 335 Hz by applying a tuning voltage of 74 V to the downward tuning part. Similarly, the resonant frequency can be increased to 3159 Hz by applying a tuning voltage of 60 V to the upward tuning part. The resonator achieves a maximum frequency tuning range of 90%, and the simulation results are in good agreement with the theoretical predictions. However, it is worth noting that the size of this resonator is relatively small, approximately 1077 × 328 μm2. This innovative design offers potential applications in various fields, including micro-electromechanical systems (MEMS), micro-optics, and microsensors. Overall, the presented work demonstrates the feasibility of achieving a tunable comb resonator with a significantly improved resonant frequency tuning range and reduced pull-in voltage.

An innovative methodology for monitoring the sacrificial layer removal process in MEMS structures

The sacrificial layer is a key component for the fabrication of a released structure in the MEMS sensors and actuators. Wet etching is a practical microfabrication process that minimizes costs compared to dry etching. Since the sacrificial layer exists between the structural layer and the substrate, characterization of the etching process is unavailable to observe and evaluate directly. This research, for the first time, presents a methodology for monitoring sacrificial layer removal. It takes advantage of using a transparent substrate (during process development) to observe the removal process from the backside. This method can be used as a separate test during surface micromachining to monitor and optimize the release process of the MEMS device. To evaluate the efficiency of the method, the copper sacrificial layer was selected. The removal process was investigated for typical structures used in MEMS sensors and actuators including the etch-holes, the cantilever beams, comb fingers, and the pads. The experimental test showed the removal of the sacrificial layer, the non-uniformity of the etching, and all the veritable chemical reactions and phenomena under the structural layer. In addition, the etch-rate were obtained in the order of 0.35–5.5 μm min−1 for various structural features. The procedure developed in this research is an approach to the process monitoring of the sacrificial layer removal. Therefore, it can be used to organize the quality control in the released structures of MEMS and optimization in batch processing. This method can be adopted for non-metallic sacrificial layers and dry etching as well.

Driving Principle and Stability Analysis of Vertical Comb-Drive Actuator for Scanning Micromirrors.

We have developed a manufacturing process for micromirrors based on microelectromechanical systems (MEMS) technology. The process involves designing an electrostatic vertically comb-driven actuator and utilizing a self-alignment process to produce a height difference between the movable comb structure and the fixed comb structure of the micromirror. To improve the stability of the micromirror, we propose four instability models in micromirror operation with the quasi-static driving principle and structure of the micromirror considered, which can provide a basic guarantee for the performance of vertical comb actuators. This analysis pinpoints factors leading to instability, including the left and right gap of the movable comb, the torsion beams of the micromirror, and the comb-to-beams distance. Ultimately, the voltages at which device failure occurs can be determined. We successfully fabricated a one-dimensional micromirror featuring a 0.8 mm mirror diameter and a 30 μm device layer thickness. The height difference between the movable and fixed comb structures was 10 μm. The micromirror was able to achieve a static mechanical angle of 2.25° with 60 V@DC. Stable operation was observed at voltages below 60 V, in close agreement with the theoretical calculations and simulations. At the driving voltage of 80 V, we observed the longitudinal displacement movement of the comb fingers. Furthermore, at a voltage of 129 V, comb adhesion occurred, resulting in device failure. This failure voltage corresponds to the lateral torsional failure voltage.

Investigation of Collision Damage Mechanisms and Reduction Methods for Pod Pepper

This study aims to address the current situation of the late start of mechanized harvesting technology for the pod pepper, the high damage rate of existing pod pepper harvesters, and the lack of theoretical support for key harvesting components. The Hertz theory is employed to investigate the damage mechanism of collisions between pod pepper and comb fingers. The study analyzes the maximum deformation of pod pepper and the critical speed at which damage occurs during the collision process. Furthermore, it explores the critical relative speed that leads to damage in pod pepper. Orthogonal tests are conducted to analyze the effects of rotational speed, hose thickness, and moisture content on the efficiency of pod pepper picking. The experimental results are then subjected to multifactorial ANOVA to identify the optimal test parameters. The structural and motion parameters of the picking device are optimized based on these conditions. It is determined that the critical relative velocity for damage to pod pepper during a collision with the comb finger is V0 = 11.487 m s−1. The collision velocities of pod pepper with different hose thicknesses are analyzed using the i-SPEED TR endoscopic high-speed dynamic analysis system to obtain the corresponding collision velocities for different hose thicknesses. The study finds that rotational speed, hose thickness, and the water content of pod pepper affect the damage rate and stem shedding rate. The optimal experimental parameters are determined to be a rotational speed of 705.04 rpm, hose thickness of 3 mm, and water content of the pepper of 71.27%.

Structural design and analytical study of a new polysilicon tunable microactuator for measurement of different resonance frequencies

This paper presents a novel MEMS tunable resonator that draws inspiration from the folded beam structure in its comb drive resonator design. Conventional electrostatic comb-drive resonators commonly employ folded-beam suspensions to achieve linearity and reduce system stiffness. The proposed design incorporates eight zigzag-shaped meander springs to support the comb finger structure, featuring two central anchors. The objective of this design is to introduce zigzag-shaped nested-folded beam suspensions to the comb parts, thereby reducing the tuning voltage and sensor size. The governing equations are provided to calculate the support springs’ stiffness, and a comparative analysis is conducted to evaluate the stiffness of the proposed design against other parameters. The mathematical analysis demonstrates that Zigzag Nested-Folded beams result in a decreased resonance frequency and a softened electrostatic spring under applied DC voltage. The integration of zigzag-shaped nested-folded beam flexures enables MEMS resonator devices to exhibit reduced stiffness, leading to a lower pull-in voltage. The resonator design and simulation are performed using Intellisuite and SolidWorks software. Results indicate that the resonant frequency of the proposed tunable comb-drive resonator, equipped with 26 finger pairs and a movable part displacement of 21 μm, is reduced by 66% from the original frequency of 2.420 kHz when a tuning voltage of 59 V is applied. Simultaneously, the corresponding effective stiffness decreases by 66% from the initial value of 0.72 N m−1. This compact resonator occupies an area of approximately 1.058×278 (μm)2, demonstrating a smaller size compared to previous works.

Correction: Modeling and analysis of MEMS capacitive pressure sensors with vertical comb fingers

Correction: Modeling and analysis of MEMS capacitive pressure sensors with vertical comb fingers

梳刷式收获装置的研究现状及对物料的损伤机理综述

Mechanized harvesting of crops is very important in the field of agricultural engineering, then the brush harvesting is a common way. The comb brush device is divided into four types: comb tooth type, roller spring finger type, belt comb finger type, and rod comb finger type. The picking rate and breakage rate are the indexes to evaluate the effect of comb brush harvesting devices. How to improve the picking rate and reduce damage rate is of great significance to the popularization of the devices. To improve the picking rate, the design of comb teeth should conform to the growth characteristics of crops. In this study, the application of four comb brush devices in harvesting crops was introduced, then the working principles and results were summarized. Meanwhile, the research status of a variable finger spacing device was summarized. In addition, to study fruit damage caused by brush devices during harvesting, three common analysis methods were summarized. The application situations and key steps were listed, and the modeling methods of material fruit in simulation analysis were analyzed. The study is intended to provide a reference for improving the harvesting effect of comb brush device. In the future, with the deepening combination of agronomy and agricultural machinery technology, comb brush harvesters will be more widely applied.

Вдосконалення конструкції бітерів дозатора кормів порційної дії

Вдосконалення конструкції бітерів дозатора кормів порційної дії

Parametric Analysis of Electrostatic Comb Drive for Resonant Sensors Operating under Atmospheric Pressure

The microelectrostatic comb resonator’s issues with high driving voltage and strong feed‐through coupling noise limit its practical use. In earlier studies, the design and structural optimization of microcomb resonators generally focused on lowering beam stiffness and raising electrostatic force density to enhance resonance displacement and lower driving voltage. However, for a microresonator that performs high‐speed resonance in the air, it is required to consider the three influencing elements of the electrostatic field, structural mechanics, and fluid mechanics to achieve the best dynamic resonance amplitude. In this paper, the parametric analysis of the comb‐driven resonator is carried out. First, the comb‐driven electrostatic force and all air‐damping terms are investigated using an electrostatic force analytical model considering edge effects, a damping analytical model simplified based on the thin‐film damping model, and the finite element model. The analysis results agree with the simulated results. To more accurately quantify the dynamic electrostatic force and damping coefficient, the electrostatic–structure–fluid three‐field indirect coupling model was used, and the law of the resonant amplitude of the resonator as a function of the structural parameters was obtained. The results show that, for the electrostatic comb resonator that oscillates at atmospheric pressure, to obtain a high‐voltage driving efficiency, a thin polysilicon film can be used to design narrow comb fingers that are dense in the vertical direction and loose in the lateral direction. To validate the accuracy of the model and the results of parameter analysis, an electrostatic comb‐drive resonator with shapes optimized from numerical simulations was fabricated. The results show that the driving efficiency is enhanced by 102%, with the chip area increased by 29%, which shows the superiority of parameter optimization.

Computational analysis of vertical comb-drive microactuator with extended mirror for manipulation of light

Squeeze film damping is a dominant mechanism to examine the losses in the micro-opto-electro-mechanical systems. It plays an important role in understanding the dynamic performance of vertical-comb drive (VCD) microactuator. In the present paper, finite element method is used to estimate the Q factor and damping ratio at varying ambient pressures ranging from atmospheric (105 Pa) to vacuum (0.1 Pa) in COMSOL Multiphysics. The effect of ambient pressure on dynamic performance of the VCD is discussed in detail. Based on the applications, two different VCDs (VCD-L and VCD-SR) with extended micromirrors have been proposed in the current study for the manipulation of light. VCD-L having lower eigen frequency of 670 Hz can be used in laser and biomedical applications. VCD-SR with higher eigen frequency nearly 90 kHz has the potential use in a synchrotron radiation source. In addition, a parametric study is done to understand the performance of VCD for varying process parameters such as variable offset length among the comb fingers, spring dimensions, and orientation of single crystal silicon. For spring design, the von-Mises stress theory is preferred over maximum shear stress theory.

Closed-loop MOEMS accelerometer.

In this paper, a closed-loop micro-opto-electro-mechanical system (MOEMS) accelerometer based on the Fabry-Pérot (FP) interferometer is presented. The FP cavity is formed between the end of a cleaved single-mode optical fiber and the cross-section of a proof mass (PM) which is suspended by four U-shaped springs. The applied acceleration tends to move the PM in the opposite direction. The arrays of fixed and movable comb fingers produce an electrostatic force which keeps the PM in its resting position. The voltage that can provide this electrostatic force is considered as the output of the sensor. Using a closed-loop detection method it is possible to increase the measurement range without losing the resolution. The proposed sensor is fabricated on a silicon-on-insulator wafer using the bulk micromachining method. The results of the sensor characterization show that the accelerometer has a linear response in the range of ±5 g. In the closed-loop mode, the sensitivity and bias instability of the sensor are 1.16 V/g and 40 µg, respectively.

Linear harmonic oscillatory rarefied gas flow with arbitrary frequency in comb finger blocks

The linear oscillatory two-dimensional rarefied gas flow in the zig-zag channel between the shuttle and stator fingers of typical comb elements, due to the harmonic motion of the shuttle finger with arbitrary frequency, is numerically investigated, via the linearized unsteady Shakhov kinetic model equation, subject to purely diffuse boundary conditions. The amplitude and phase distributions of the velocity components, normal and shear stresses, density and temperature are thoroughly investigated in the whole range of the gas rarefaction and oscillation parameters, characterizing the flow. The low, moderate and high flow oscillation regimes are defined by the ratio of the gas rarefaction over the oscillation parameters. It is shown that in the low oscillation regime the flow may be approximated by the corresponding steady-state analysis, while in the high oscillation one by the superposition of the associated oscillatory one-dimensional normal sound propagation and Couette flows. In the former case edge and compressibility effects are considerable and in the latter one the flow is characterized by gas trapping along the shuttle finger. In the moderate oscillation regime the fully oscillatory two-dimensional flow must be analysed. Here, the antiresonance and resonance states of the flow are considered. The ratios of the gas rarefaction over the oscillation parameters, where the average normal and shear stresses acting on the shuttle finger are minimized are computationally specified. Changing the main geometry parameters of the comb finger block, significantly affects the normal and shear stresses acting on the shuttle finger, mainly in the low oscillation regime. The present work may be applied to minimize the damping forces in comb finger blocks, as well as to optimize the design of new generation devices operating in moderate and high frequencies.

Asymmetric phononic frequency comb in a rhombic micromechanical resonator

As an analog of the optical frequency comb, the phononic frequency comb has been demonstrated in mechanical resonators recently. In this Letter, we generate the frequency comb in a rhombic micro-resonator with stiffness parametrically modulated by low-frequency pumping. Interestingly, this comb exhibits the asymmetry in the amplitude, i.e., the amplitudes of comb fingers on either side of the central comb finger decay with different rates. With a parametrically modulated model, we analyzed in detail the asymmetry in the frequency comb and accurately captured the reason for the asymmetry. Furthermore, the asymmetry of the frequency comb can be adjusted experimentally. These results provide a theoretical basis for manipulating the comb fingers and are expected to open the door for potential applications of the frequency comb.

Development of an Electrostatic Comb-Driven MEMS Scanning Mirror for Two-Dimensional Raster Scanning.

Microelectromechanical System (MEMS)-based scanning mirrors are important optical devices that have been employed in many fields as a low-cost and miniaturized solution. In recent years, the rapid development of Light Detection and Ranging (LiDAR) has led to opportunities and challenges for MEMS scanners. In this work, we propose a 2D electrostatically actuated micro raster scanner with relatively large aperture. The 2D scanner combines a resonant scanning axis driven by an in-plane comb and a quasistatic scanning axis driven by a vertical comb, which is achieved by raising the moving comb finger above the fixed comb finger through the residual stress gradient. The analytic formula for the resonant axis frequency, based on the mechanical coupling of two oscillation modes, is derived and compared with finite element simulation. A prototype is designed, fabricated, and tested, and an overall optical Field-of-View (FoV) of about 60° × 4° is achieved. Finally, some possibilities for further improvement or optimization are discussed.

Design and experiment of the comb-brush harvesting machine with variable spacing for oil-tea camellia fruit

Oil-tea camellia tree is an important oil plant in China that has long flexible branches. The most challenging feature for the mechanized harvest of oil-tea fruits is that its flower and fruit grow synchronously. In order to improve the harvesting efficiency and avoid damaging the flower bud, a hand-held fruit harvesting machine with a variable spacing comb brush was proposed. The harvesting machine can generate three kinds of actuation to detach fruit when it runs. The main actuation results from the brushing of multiple comb fingers. The other two kinds of actuation result from the beating of comb fingers on the fruits and the branches. The finger spacing of the comb brush can be adjusted consequently through moving the spacing adjusting crossbar. Hence, when the finger spacing is smaller than the diameter of the oil-tea fruit, the fruit is brushed off, but the flower bud and leaf pass through the finger gap. When the finger spacing is bigger than the fruit diameter, the fruit stuck between the fingers is loosened to ensure the continuous operation of the machine. Nylon was used as the material of the brush finger to avoid damage, which can also reduce the overall weight. The dynamic simulation of the harvesting machine was carried out with ADAMS, and the acceleration of the front end of the comb finger and the variation of the finger spacing were analyzed. The prototype of the harvesting machine was built and tested in the field. Field experiment results showed that when the speed of the comb finger drive shaft was 480 r/min, the average harvesting percentage of oil-tea fruit was 80%, and the flower bud was seldom detached, which met the working requirements of oil-tea fruit harvesting. Keywords: oil-tea camellia fruit, harvesting machine, variable spacing, comb brush, simulation analysis DOI: 10.25165/j.ijabe.20211401.5703 Citation: Du X Q, Shen T F, Zhao L J, Zhang G F, Hu A G, Fang S G, et al. Design and experiment of the comb-brush harvesting machine with variable spacing for oil-tea camellia fruit. Int J Agric & Biol Eng, 2021; 14(1): 172–177.

Design and experiment of the comb-brush harvesting machine with variable spacing for oil-tea camellia fruit

Oil-tea camellia tree is an important oil plant in China that has long flexible branches. The most challenging feature for the mechanized harvest of oil-tea fruits is that its flower and fruit grow synchronously. In order to improve the harvesting efficiency and avoid damaging the flower bud, a hand-held fruit harvesting machine with a variable spacing comb brush was proposed. The harvesting machine can generate three kinds of actuation to detach fruit when it runs. The main actuation results from the brushing of multiple comb fingers. The other two kinds of actuation result from the beating of comb fingers on the fruits and the branches. The finger spacing of the comb brush can be adjusted consequently through moving the spacing adjusting crossbar. Hence, when the finger spacing is smaller than the diameter of the oil-tea fruit, the fruit is brushed off, but the flower bud and leaf pass through the finger gap. When the finger spacing is bigger than the fruit diameter, the fruit stuck between the fingers is loosened to ensure the continuous operation of the machine. Nylon was used as the material of the brush finger to avoid damage, which can also reduce the overall weight. The dynamic simulation of the harvesting machine was carried out with ADAMS, and the acceleration of the front end of the comb finger and the variation of the finger spacing were analyzed. The prototype of the harvesting machine was built and tested in the field. Field experiment results showed that when the speed of the comb finger drive shaft was 480 r/min, the average harvesting percentage of oil-tea fruit was 80%, and the flower bud was seldom detached, which met the working requirements of oil-tea fruit harvesting. Keywords: oil-tea camellia fruit, harvesting machine, variable spacing, comb brush, simulation analysis DOI: 10.25165/j.ijabe.20211401.5703 Citation: Du X Q, Shen T F, Zhao L J, Zhang G F, Hu A G, Fang S G, et al. Design and experiment of the comb-brush harvesting machine with variable spacing for oil-tea camellia fruit. Int J Agric & Biol Eng, 2021; 14(1): 172–177.

Nonlinear Vibration Study Based on Uncertainty Analysis in MEMS Resonant Accelerometer.

This paper aims to develop a resonant accelerometer for high-sensitivity detection and to investigate the nonlinear vibration of the MEMS resonant accelerometer driven by electrostatic comb fingers. First, a nonlinear vibration model of the resonator with comb fingers in a MEMS resonant accelerometer is established. Then, the nonlinear and nonlinear stiffness coefficients are calculated and analyzed with the Galérkin principle. The linear natural frequency, tracking error, and nonlinear frequency offset are obtained by multi-scale method. Finally, to further analyze the nonlinear vibration, a sample-based stochastic model is established, and the uncertainty analysis method is applied. It is concluded from the results that nonlinear vibration can be reduced by reducing the resonant beam length and increasing the resonant beam width and thickness. In addition, the resonant beam length and thickness have more significant effects, while the resonant beam width and the single concentrated mass of comb fingers have little effect, which are verified by experiments. The results of this research have proved that uncertainty analysis is an effective approach in nonlinear vibration analysis and instructional in practical resonant accelerometer design.