Prezentacja na temat: "PIEZO MOTOR Transverse motion is generally larger, on the order of microns to tens of microns. Piezo materiały: Przyłożone napięcie zmienia ich długość"— Zapis prezentacji:
PIEZO MOTOR Transverse motion is generally larger, on the order of microns to tens of microns. Piezo materiały: Przyłożone napięcie zmienia ich długość i grubość. Vin Fout T T== Thickness Vin Fout TLout L== Length
Free deflection X f refers to displacement attained at the maximum recommended voltage when actuator is not asked to exert any force. Blocked force F b refers to the force exerted when the actuator is not allowed to move. A piezo motor must move a specified amount and exert a specified force. An actuator is considered optimized for a particular application if it delivers the required force at one half its free deflection. All other actuators satisfying the design criteria will be larger, heavier, and consume more power.
Piezo linear motors can be divided into two groups: resonant motors (ultrasonic motors), and quasistatic motors. A great advantage of piezo motors is their intrinsic steady-state auto-locking capability.
High-purity lead, zirconate, and titanate powders are processed, pressed to shape, fired, electroded, polarized, and tested. Polarization is achieved using high electric fields, 2500 V/ mm, to align material domains along a primary axis.
A displacement constant d 33 is equal to 500 pm/ V. Piezoelectric motors are driven at or near a resonant frequency mode of the crystal shape. Exist standing-wave and propagating-wave == travelling-wave == progressing-wave piezoelectric motors.
Element expands Element retracts Axial motion imparts a frictional force
When the sign of the drive voltage swings negative, the same crystal thickness contracts. This action creates a minuscule separation between the motor shoe and the wear strip, allowing the motor to return to its original position without dragging the wear strip backward. As the drive voltage swings positive again, the crystal stroke cycle repeats and the wear strip moves another incremental step to the left. When the crystal driving process is repeated 130,000 times/s, with a resonant frequency amplification factor of 10, the resulting velocity is ~130 mm/s (5 ips) using mid-range control voltage. Faster or slower speeds are achieved by changing control voltage.
Conventional displacement sensors may be used to measure motor travel and position. One example of this is the Model LK-031, a laser-based interferometer made by Keyence Corp. of America, Woodcliff Lake, NJ, that measures motor position over time. Nonlinear start and stop times are a function of system mass (inertia), while resolution of motor position is directly proportional to the voltage across the piezoelectric crystal.
Motor performance is enhanced with the strategic placement and use of additional piezoelectric crystals or structural elements. To meet additional force requirements, several motor elements may be driven in parallel. This process will cumulatively add force.
A travelling flexural wave is generated by several piezoelectric ceramics in a ring that consist in the stator of the motor. A rotor is then prestressed on it and is moved by friction. To amplify the vibrations of the stator, teeth are added on the ring. The tops of teeth are in contact with the rotor and have an elliptical trajectory with an amplitude of 5 to 10 μm.
A voltage V1 at a given frequency excites a flexure mode by a set of electrodes on the piezoelectric layer. A second set of electrode excites with the voltage V2 the same mode at the same frequency but 90 ° shifted on the wavelength. Exciting the 2 sets of electrodes with a phase difference of 90°, a travelling wave is generated on the ring of the stator.
A modal resonance and antiresonance analysis permits first to find precisely the working frequency for a given mode (N# 7).
Zalety piezo-silników Cicha praca Wysoka sprawność Niska prędkość i wysoki moment obrotowy Mała mechaniczna stała czasowa Dobra regulacja prędkości obrotowej Samohamowność Wysoki stosunek mocy do masy Brak wpływu zakłóceń na pracę silnika
Wady piezo-silników Wymaga zasilania generatorem wysokiej częstotliwości Wycieranie się elementów ciernych Spadający moment obrotowy wraz ze wzrostem prędkości obrotowej Wysoki koszt wytworzenia