Sensors and Actuators最新文献

Three-dimensional miniature structures may be fabricated from crystalline quartz using photolithographic processes. Crystalline quartz has an-istropic etching properties in buffered HF solutions and etch rates can vary by factors of 200 along different crystal axes. Although the prevalent application of this technology has been for miniature frequency-control timebases, other applications are beginning to emerge. Sensors for force, strain, acceleration, temperature, pressure and gas density have been developed as well as miniature actuators, precision springs and flow-control devices, to name a few. This paper will focus upon the use of precision quartz resonators in sensing applications. The primary intent is to demonstrate the unique characteristics of crystalline quartz and promote its use for new fields of application.

Miniature quartz resonators that change frequency with a single predominant physical effect are typically used in sensor applications. Thin metal film electrodes deposited on the surface of the miniature quartz structure couple electrical field energy to strain energy in the bulk of the quartz structure through the piezoelectric effect. The quartz crystal unit controls the frequency of an oscillator circuit, which is designed to excite the sensor's resonant mode. The resonant mode to which coupling takes place depends upon the electrode configuration, the shape of the quartz structure and the mechanical and piezoelectric properties of the quartz for the orientation of the crystal axes. Each of these effects must be well understood through a variety of analytical techniques prior to the development of a quartz resonator. In addition, the range over which the desired frequency of the quartz resonator changes in sensor applications indicates that the mode spectrum of the sensor and the surrounding structure must be well understood to avoid interfering modes. Piezoelectric coupling, fabrication techniques and the design of quartz resonators for sensing applications will each be discussed at length.

This paper describes two microactuators used to align fiber optics. One, an actuator using a thin strand of shape memory alloy, is used to align an input fiber with one of two output fibers. This component is useful for switching fiber-optic signals. The second is an electrostatic actuator capable of switching optical fibers, and also of making fine adjustments to correct for misalignments.

A millimeter-sized actuator for driving a rotary joint for a small robot is designed and fabricated using a shape memory alloy (SMA); it has the advantages of a strong force/weight ratio and can be extended down to micron size. The actuator is of push-pull type composed of two 0.05 mm × 0.5 mm × 3 mm SMA sheets. First, a theoretical model of the dynamics of the SMA actuator is derived based on an experimental analysis of the dynamics of large SMA sheets. Using this model, the design method of the above type of SMA actuator is established. Finally, the theoretical torque versus angular displacement of a millimeter-sized rotary joint driven by the above millimeter-sized SMA actuator is obtained, with a maximum torque of 4 gf mm.

As microelectromechanical systems become more complex, designers will find it useful to derive models of the geometry of their device structures directly from the process description and planar mask patterns. OYSTER simulates the geometric effects of sequential IC process stages, including patterning of photoresists with planar masks, in order to produce three-dimensional polyhedral representations of all material structures in a design cell after each process stage. The polyhedral models may be used with various analytic procedures as sources of geometric data for finite-element calculations, or they may be subjected to interference calculations, or inspected to detect structural anomalies. OYSTER has been developed for IC simulation, but is applicable to microelectromechanical systems manufactured using similar processes. In addition, because it uses basic functions of a solid modeling program developed for mechanical systems, it provides access to features like dimensioning and tolerancing and kinematics.

This paper studies the steady-state operation of the electroquasistatic induction micromotor (IM). A rotary pancake IM compatible with surface micromachining serves as an example. A model is developed to predict the electric potential, field and free charge within the IM. The model also predicts the motive torque and transverse force of electric origin acting on its rotor. The torque is balanced against bushing friction and windage to determine rotor velocity. Here, the bushing friction is modeled as a function of the transverse force acting on the rotor. Finally, an equivalent circuit model is developed, which described important aspects of the electromechanical operation of the IM.

The model is used to study IM performance and its dependence on IM dimensions and material properties. For example, IM performance is predicted to be a complex function of axial IM dimensions and a strong function of rotor conductivity. The study also reveals that IM performance can differ significally from that of the variable-capacitance micromotor (VCM). For example, the dependence of motive torque and transverse force on axial dimensions can be significanly different in some IM operating regimes, allowing the possibility of improved performance over the VCM. IM and VCM dependences on micromotor geometry, velocity and material properties can also be significanlty different. The excitation and control requirements reflect the difference between a synchronous (VCM) and an asynchronous (IM) motor, as well as the possibility of obtaining an axially stable rotor position for certain IM material parameters.

It seems clear that small robots which take advantage of recent reductions in packaging size and costs of microelectronics can potentially be very useful; even more so if similar savings could be achieved in the actuation and power supply areas. Typically, the computational power required in a robotic system that connects perception to action is enormous, but if the organization of the sensors, actuators and computing elements is carefully laid out, the actual silicon area required for the intelligence system becomes quite small. A viable avenue of pursuit, then, is to aim towards scaling down the rest of the subsystems in a robot to the same scale as the control system, integrating motors, sensors, computation and power supplies onto a single piece of silicon; the advantages being mass productibility, lower costs and the avoidance of the usual connector problems encountered in combining discrete subsystems. By rethinking implementation strategies with this new form of robotic technology (i.e., the application of many very small robots), it may be possible to solve many problems more cost effectively, albeit in novel ways.

As the completely integrated robot faces many technology hurdles, it seems necessary to focus on just one or two of the problem areas at a time. It turns out that many of the cost-saving benefits still accrue at small, but macroscopic scales. This paper describes an exercise of building a complete system, aimed at being as small as possible, but using off the shelf components exclusively. The result is an autonomous mobile robot slightly larger than one cubic inch, which incorporates sensing, actuation, onboard computation and on-board power supplies. Nicknamed Squirt, this robot acts as a ‘bug’, hiding in dark corners and venturing out in the direction of last heard noises, only moving after the noises are long gone.

This paper establishes a theoretical framework for analyzing and classifying actuators that generate their output by rectifying small-amplitude mechanical vibrations, such as might be generated by piezoelectric elements. These ideas are of special interest when designing for microfabrication, because motors based on these principles: (a) can generate translational output directly without use of rotary bearings; (b) appear to be scalable over several orders of magnitude of the length scale; and (c) appear to be capable of generating mechanical power proportional to driving frequency over one to two orders of magnitude of frequency. In order to achieve this performance, it is necessary to be able to farbricate features, or at least control surface irregularities, on the scale v/w where v is velocity of the actuator and w is the operating frequency.

A new type of superconducting actuator of the order of 100 μm in size called a Meissnac is proposed. It utilizes magnetic levitation using the Meissner effect to remove the friction between the slider and the stator. The slider and the stator of the actuator consist of linear arrays of vertically magnetized permanent magnet strips and superconductor strips, respectively. The pitch of the stator and that of the slider are different and the driving force is obtained by providing this difference between them and controlling the state of the superconductors by applying a current having a value of more than a critical current density, Jc, to some of the superconductor strips. The lateral continuous movement of the slider is obtained by switching appropriate superconductors to the normal state. The magnetic field and the force in the actuator are analysed by a numerical method called the discrete surface current method. When the pitch size and and the levitation height are of the order of 100 μm, maximum values of the driving force and the levitating force are 0.26 and 1.7 N m ⁻² A⁻², respectively. The movement of the slider in a particular direction (right or left) is obtained by choosing a driving mode. A scale model (about ten times larger) or the micro Meissnac is fabricated using YBCO high-T_c bulk superconductors. The width of the superconductor strips and the pitch are of the order of 1 mm. The levitating force and the driving force of the scale model are experimentally measured and the levitating force is compared with that calculated numerically for the micro Meissnac.

Micromechanical devices such as bearings require smooth surfaces. Fine-grained polysilicon can be produced with a surface roughness near 8Årms. The ability to anneal films of this type into tension eliminates size restrictions due to compressive buckling.

The use of these films in micromechanical devices has been restricted because hydrogen fluoride-etched structures are covered by an etch residue that leads to contact welding. Contact between opposing surfaces is induced mainly by surface tension effects. This problem may be avoided by removing the deflection mechanism. Thus, freezing of a water-methanol rinse after sacrifical ethcing all but eliminates surface tension. Removal of the ice mixture via sublimation at 0.15 millibar occurs readily. Free-standing structures with smooth surfaces and small gaps are next passivated by silicon deposition or other techniques.

Micromotors having rotors with a diameter of 120 μm have been fabricated and driven electrostatically to continuous rotation. These motors are built using processes derived from IC micro-circuit fabrication techniques. Initial tests on the motors show that friction plays a dominant role in their dynamic behavior. Observed rotational speeds have thus far been limited to several hundred rpm, which is a small fraction of what should be achievable if only natural frequency were to limit the response. Experimental starting voltages (60 V at minimum and above 100 V for some structures) are at least an order of magnitude larger than had been expected. Continuous motor motion has been observed for as long as one minute under three-phase bias at 200 V. Observations of reverse as well as forward rotor rotation with respect to the driving fields can be explained in terms of the torque/rotor-angle characteristics and friction for the motors.