The direction of current through the motor determines the rotational direction of the motor: clockwise or counter clockwise. If the motor is a DC motor, then the torque (rotational force) it exerts is proportional to the electrical current flowing through it. Since linear motors support only limited displacements, it is often more convenient to use rotational motors. If it is sufficient to induce slower vibrations at relatively lower frequencies, for instance for interfacing with the human motor system, then we can use more conventional actuators. Ink from the inkjet print head towards the paper. * Inkjet printers: On many inkjet printers, piezoelectric crystals are used to drive the ejection of * Atomic force microscopes and scanning tunneling microscopes employ converse piezoelectricity to keep Due to the extremely small distances involved, the piezo motor is viewed as a high-precision * Piezoelectric motors: piezoelectric elements apply a directional force to an axle, causing it to * Loudspeakers: Voltage is converted to mechanical movement of a piezoelectric polymer film. Generally lower than 100 microns, amplified piezo actuators can reach millimeter strokes. Piezo actuators and Amplified Piezoelectric Actuators. These ceramics are used within two kinds of actuators: direct Multilayer ceramics, using layers thinner than 100 microns, allow reaching high electric fields Most important tool for positioning objects with extreme accuracy - thus their use in actuators. This width can be changed with better-than-micrometer precision, making piezo crystals the The parts are listed here.Īs very high electric fields correspond to only tiny changes in the width of the crystal, See the Electromagnetically-Prepared Piano Project for details on how to actuate piano strings. The E-Bow and the Sustainiac use this principle to actuate guitar strings. Most efficient solution: glue a small neodymium magnet to the object that is to be actuated.Īlternate solution: if the object is ferrous (magnetically "sticky" aka magnetizable such as iron or steel), then the object to be actuated can be magnetized by placing it in the neighborhood of a magnet. What if you want to actuate something that isn't a magnet? The direction of the current through the coil determines whether the two magnets attract or repell one another: ![]() ![]() Replacing one of the permanent magnets with an electromagnet. Oppositely-poled magnets attract each other The other electrodynamic actuators described here such as woofers, shakers, servomotors, solenoids, etc. The next two figures show a realization in the laboratory. Placed in series with power resistors to avoid overloading the audio amplifier’s output. Order to connect it to the output of a typical audio power amplifier, it must be Then the force on the string is F= L AI × BĪ piece of wire of only about 1m in length has a relatively low resistance. Since the field flowing back is so much less focused, we also assume that it never flows back to complete the magnetic circuit: Notice that the field flowing from the north pole of the upper magnet to the south pole of the lower magnet is much less focused.įor simplicity of analysis, we assume that the magnetic field B is completely uniform in between the magnets. An electrically conductive vibrating string is placed between two permanent magnets. We present the example of actuating a vibrating string. Any element can be actuated according to the Lorentz force if an electrical current can be passed along it. The Lorentz force is the force on an electrical current carrier in the presence of a magnetic field. Vibrations in Structures Lorentz Force Actuator ![]() Since loudspeaker drivers are usually linear actuators, their maximum displacement is usually limited. These are quite common, so we refer the reader to Hyperphysics and Wikipedia. Loudspeaker drivers convert an electrical signal into pressure waves in air. Here is one particularly small but powerful audio power amplifier. Here we explain how to induce these vibrations in air and in structures. Often we would like to induce vibrations spanning the entire range of human hearing.
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