<p>The optical design of a compact 2 × zoom lens in a lens barrel for miniature cameras is reported. The magnification in the optical system is achieved by means of changing positions of lens elements inside the lens barrel. Six lens elements are employed in the optical system, where up to four elements are actuated. Maximum travel distances for the moving parts are determined as 1.67 mm to reach a magnification of 2.06 × , and the total track length for the telephoto zoom lens state is 9.16 mm at its most extended configuration. Manufacturability of the proposed system is also discussed using a tolerance analysis. The designed optical system is suitable for use with image sensors up to 13 MP, and it can be employed in an endoscopic camera, where the optical zoom and compact design are beneficial. It is also suitable for smartphone cameras with further enhancements and integration of voice-coil-motors and/or MEMS actuators.</p>
Adhesion between micro parts, also referred to as stiction, is a major failure mode in MEMS. Undesirable stiction, which results from contact between surfaces, can severely compromise the reliability of MEMS. In this paper, a model is developed to predict the dry stiction between uncharged micro parts in MEMS. In dry stiction, the interacting surfaces are assumed to be either hydrophobic or placed in dry environment. In this condition, the van der Waals (vdW) and asperity deformation forces are dominant. Here, a model is developed for the vdW force between rough micro surfaces and the new model is combined with a newly developed multiple asperity point model for the elastic/plastic deformation of rough surfaces in contact to solve for the equilibrium condition of the forces. This, in turn, will yield the equilibrium distance between micro surfaces, using which the apparent work of adhesion can be found. The result of the theory is compared with the available experimental data from literature. The developed model can be easily used for design purpose. If the topographic data and material constants are known, the adhesion parameters can be quickly calculated using the model.
In this paper, a novel repulsive force based rotary micromirror is proposed. A repulsive force is produced in the rotary micromirror and the mirror plate is pushed up and away from the substrate. Therefore the rotation angle of the micromirror is not limited to the space underneath the mirror plate and thus the "pull-in" effect is completely circumvented. The novel rotary micromirror can achieve a large rotation angle with a large mirror plate. In addition the novel micromirror has a very simple structure and can be fabricated by standard surface micromachining technology. Numerical simulation is used to verify the working principle of the novel micromirror. A prototype of the novel rotary micromirror is fabricated by a commercially available surface microfabrication process called MUMPs. The prototype has a mirror size of 300μm x 300μm. The experimental measurements show that the prototype can achieve a mechanical rotation of 2.25 degrees (an optical angle of 4.5 degrees) at a driving voltage of 170 volts. A conventional surface micromachined attractive force based rotary micromirror of the same size can only achieve an angle of 0.1~0.2 degree.
An inchworm actuator is described which uses complementary configurations for the two clamping sections. In one configuration clamping and release are achieved using high and low voltage respectively while for the other clamping and release are achieved using low and high voltage respectively. The resulting inchworm actuator can be driven by a two-channel controller with the two clamps sharing the first channel and the extender piezoelectric actuator using the second channel. In the coarse positioning mode the direction of motion is determined by whether the extender voltage pulse overlaps the leading or trailing edge of the common clamp pulse. A fine positioning mode can be realized with the common clamp voltage set to 0V and continuous feedback control applied to the extender actuator. The paper also describes a diode-shunted delay circuit that causes unclamping to occur more slowly than clamping. It is shown that by using the delay circuit in series with each clamp, the overall force drive capability of the actuator is increased. The paper presents simulated and experimental results of clamp surface displacement and force vs. time during the switching transient.
Conventional translation micromirrors for adaptive optics use attractive electrostatic force and therefore have two limitations: 1) the stroke is limited to less than one third of the initial gap distance between the mirror plate and the substrate. Normally the stroke is in the range of submicrometers; 2) stiction happens during operation. A novel translation micromirror, which uses a repulsive electrostatic force, is presented in this paper. This novel translation micromirror completely overcomes the limitations associated with conventional translation micromirrors and its stroke is not limited by the initial gap distance between the mirror plate and the substrate and therefore is able to achieve a much larger vertical stroke to modulate lights over a wider spectrum than that achieved by conventional translation micromirrors. The novel translation micromirror has no stiction problem and is highly compatible with mature surface micromachining technology. An analytical model is derived for the novel translation micromirror and prototypes are fabricated. The prototype of the novel translation micromirror, which is deliberately not optimized so it could be fabricated using MUMPS, achieved a vertical stroke of 1.75μm using a driving voltage of 50 volts, which is three times the stroke of conventional MUMPS translation micromirrors. It is expected that if standard surface micromachining is used instead of MUMPs, the design of the novel translation micromirror can be optimized and a much larger vertical stroke can be achieved.
A discrete-time Preisach model that captures hysteresis in a piezoceramic actuator is developed. The model is implemented using a numerical technique that is based on first order reversal functions and is presented in a recursive form that is amenable for real-time implementation. The first order reversal functions are experimentally obtained using a piezoceramic actuator in a stacked form. The development model shows good agreement with actual measured data. A hysteresis compensation scheme based on the developed discrete-time Preisach model is also developed and used in order to obtain a linear voltage-to-displacement relationship.