Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02N—ELECTRIC MACHINES NOT OTHERWISE PROVIDED FOR
  • H02N2/00—Electric machines in general using piezoelectric effect, electrostriction or magnetostriction
  • H02N2/10—Electric machines in general using piezoelectric effect, electrostriction or magnetostriction producing rotary motion, e.g. rotary motors
  • H02N2/14—Drive circuits; Control arrangements or methods
  • H02N2/142—Small signal circuits; Means for controlling position or derived quantities, e.g. speed, torque, starting, stopping, reversing

Definitions

• a rotary piezoelectric motor also referred to as a traveling wave rotary motor
• the driving of a rotor is due to the friction of the stator teeth on the contact surface of the rotor, the motor comprising own piezoelectric excitation means of the stator. to excite it and cause the rotational movement of the rotor.
• FIG. 1 of the accompanying drawings there is shown very schematically a simplified structure of a rotary piezoelectric motor limited to the main bodies concerned by the invention.
• the rotor 1 is in the general form of a wheel having an annular contact pad 2 joined by a web 3 to a central hub 4.
• the stator 5 is in the general form of a fixed annular structure comprising an annular stator ring 6 which has a toothed surface 9 on which the contact pad 2 bears and which is supported cantilevered towards the outside on an annular base 7 via a stator rim 8 of substantially radial extent; the piezoelectric ceramic material 10 is fixed under the stator ring 6 opposite the toothed surface 9.
• the drive of the rotor is by friction of the teeth of the stator 5 on the contact surface of the rotor 1.
• Each excitation sector comprises a plurality of piezoceramic segments ai-a ⁇ , bi-b ⁇ polarized alternately.
• the excitation sectors A, B each allow the generation of a standing wave with the same wavelength ⁇ .
• the transmission of the rotational movement of the progressive wave to the rotor is based on the friction of the toothed surface 9 on the rotor 1, this friction, having a yield of 30 to 40%, favors the temperature rises, the rise in temperature playing in particular on the internal stresses of the stator resulting from the bonding of the piezoelectric material on the stator.
• the piezoelectric material reacts differently depending on whether its temperature is higher or lower.
• the speed control means do not automatically take into account the temperature rise of the piezoelectric material and the actual speed of rotation of the piezoelectric motor is different from the requested rotation speed. Indeed, in a current manner, the control of the motor is achieved by controlling the excitation voltages of the two excitation sectors.
• variable parameters of the excitation voltages are commonly modified, in particular by modifying, independently or in combination, the frequency and amplitude of the excitation voltages. and / or the phase and amplitude of the excitation voltages.
• the present invention proposes to solve this problem by means of a method for regulating the speed of rotation of a piezoelectric motor taking into account the temperature of the piezoelectric material and thus making it possible to automatically modify the control parameters of the piezoelectric motor. depending on the required rotation speed and the actual rotation speed.
• the present invention relates to a method for controlling the rotational speed of a rotor of a piezoelectric motor powered by at least two voltages excitation circuit each exciting an excitation sector of the piezoelectric material, the two excitation voltages being variable using variable physical parameters comprising the frequency, the amplitude and the phase shift of the two excitation voltages, characterized in that that it includes at least the following successive stages:
• the method comprises the following additional steps: "determining the difference between the actual temperature and the reference temperature;” determining the variation of the speed of rotation according to said variable physical parameter for the actual temperature; modifying said variable physical parameter, and
• variable physical parameter is the frequency of the excitation voltages.
• the variation of the speed of rotation of the piezoelectric motor as a function of said variable physical parameter follows a Gaussian type law.
• the temperature variation of the speed of rotation of the piezoelectric motor as a function of the frequency of the excitation voltages is linear, for an amplitude and a phase shift of the fixed excitation voltages.
• the present invention also relates to a device for controlling the speed of rotation of a piezoelectric motor rotor operating according to the method having the characteristics mentioned above.
• FIG. 2 is a schematic representation of the arrangement of the excitation sectors of a piezoelectric ring used according to the prior art
• FIG. 3 is a graph showing the variation of the rotational speed of a piezoelectric motor as a function of the frequency of the excitation voltages
• FIG. 4 is a block diagram of the main steps of the control method according to the prior art of the speed of rotation of a piezoelectric motor as a function of the frequency of the excitation voltages;
• FIG. 5 is a graph showing the variation of the speed of rotation of a piezoelectric motor as a function of the frequency of the excitation voltages and for two temperatures of the piezoelectric material;
• FIG. 6 is a block diagram of the main steps of the method for regulating the speed of rotation of a piezoelectric motor according to the invention.
• FIG. 7 illustrates theoretically a portion of the means for implementing the method according to the invention using a graph of variation of the speed of rotation as a function of the frequency of the excitation voltages for a temperature.
• FIG. 3 is a graph of variation of the rotational speed of a piezoelectric motor of known type as a function of the frequency of the excitation voltages.
• the speed of rotation of the piezoelectric motor it is determined, for a given speed value, the corresponding frequency of the excitation voltages of the excitation sectors A, B of the piezoelectric ring.
• the modification of the control voltage by varying the amplitude of the excitation voltages by fixing the phase shift and the frequency or by acting on the phase shift of the excitation voltages by setting the amplitude and frequency.
• the variation of the rotation speed ⁇ as a function of the amplitude of the excitation voltages also follows a Gaussian type law for a fixed phase and frequency as well as the variation of the rotation speed ⁇ as a function of the phase shift of the excitation voltages for a fixed frequency and amplitude.
• FIG. 4 shows a functional diagram showing the main steps of a method for controlling the rotation of a piezoelectric motor currently used to regulate the speed of rotation over time.
• step 400 the variation of the speed of rotation of the piezoelectric motor is determined as a function of the frequency of the excitation voltages (the amplitude and the phase shift being fixed), this variation being represented on the graph of Figure 3 as an example.
• the user sets the rotational speed that he wants to reach with the aid of the piezoelectric motor (step 410).
• step 400 Since the variation of the speed as a function of the frequency of the excitation voltages in step 400 has been determined, the user can then determine and set the frequency of the excitation voltages which he has to apply. to the piezoelectric motor to have the fixed rotation speed Vreeiie (step 420).
• the rotor of the piezoelectric motor then has a theoretical rotational speed v t heo ⁇ e •
• the only currently known means for compensating the speed of rotation of the piezoelectric motor over time is to measure the actual rotational speed (step 430) and to calculate if there is a difference between the theoretical desired rotation speed v t heo ⁇ e and the actual rotational speed v ree iie (step 440). In the case of a positive response and if the difference between these two speeds exceeds a certain drift acceptability threshold, then the frequency of the theoretical excitation voltages of the excitation sectors should be modified. The process then recommences at step 420.
• the piezoelectric motor is allowed to operate over a period of time t during which the engine operating parameters are not modified (step 450). After this time, the actual rotational speed (step 430) is again measured and the difference between the actual rotational speed and the theoretical rotational speed (step 440) is again calculated.
• FIG. 5 represents a graph illustrating the variation of the speed of rotation of a piezoelectric motor as a function of the variation of frequency of the excitation voltages (the amplitude and the phase shift of the excitation voltages are fixed) and for two temperatures data of the piezoelectric material.
• the change in temperature of the piezoelectric material thus influences in a linear manner the variation of the speed of rotation of the piezoelectric motor as a function of the frequency of the voltages. excitation (the amplitude and the phase shift of the excitation voltages being fixed), which results in a translation of the graph illustrating this variation.
• FIG. 6 is a block diagram showing the main steps of the method according to the invention for controlling the speed of rotation of the piezoelectric motor, the method according to the invention being based on the linear behavior at the temperature of the variation of the speed. of rotation of the piezoelectric motor as a function of the frequency of the excitation voltages.
• the variation of the rotational speed of the rotor of the piezoelectric motor is determined as a function of the frequency of the excitation voltages for a reference temperature (step 600), the amplitude and the phase shift of the voltages. of excitation being fixed.
• the theoretical reference frequency is then determined (step 620).
• the piezoelectric motor is started and it is measured the actual speed v ree iie engine (step 630). It is then calculated the difference between v t heo ⁇ e and v r éeiie (step 640). If the difference between these two values does not exceed an acceptable threshold value, then the motor is allowed to run for a certain period of waiting time t (step 650) and is then again measured rotational speed v ree iie after this lapse of time and therefore returns to the step of measuring the rotational speed of the piezoelectric motor (step 630).
• the waiting time t corresponds to a sampling period.
• Figure 7 shows more precisely the mode of determining the value of this temperature difference.
• FIG. 7 a first curve showing the variation of the rotational speed as a function of the frequency of the excitation voltages for a reference temperature T re f (solid line curve).
• the realization of this curve is carried out during step 600 of determining the speed of rotation of the piezoelectric motor as a function of the frequency of the excitation voltages for a reference temperature with the amplitude and the phase shift of the excitation voltages. set.
• the theoretical rotational speed v t heo ⁇ e (step 610) is then set for this reference temperature.
• the frequency of the theoretical theoretical excitation voltages is determined (step 620).
• the piezoelectric motor By measuring the actual rotational speed v ree iie the piezoelectric motor, it determines the position of point E (step 630) and the difference between the actual temperature T ree iie and the reference temperature T ref (step 640). The position of point F is then determined.
• the resonance modes of the motor are relatively close to the curve of variation of the speed of rotation as a function of the frequency of the excitation voltages for a reference temperature, it is possible, during the determination of the curve at real temperature, to change the resonance mode and in particular, during the translation of the reference temperature curve to interfere with a resonance mode.
• the present invention also relates to a device for controlling the speed of rotation of a piezoelectric motor rotor operating according to the method as previously described.
• the present invention has been described on the basis of the variation of the rotational speed of the rotor of the piezoelectric motor as a function of the frequency of the excitation voltages, the other variable physical parameters of the excitation voltages being fixed, namely the amplitude and phase shift of excitation voltages.
• the variation of the speed of rotation of the piezoelectric motor as a function of the amplitude of the excitation voltages, the phase shift and the frequency then being fixed, or, alternatively as a function of the phase shift of the excitation voltages, the frequency and the amplitude excitation voltages being fixed. It is then possible to apply the principle according to the invention on the basis of these variations.

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• General Electrical Machinery Utilizing Piezoelectricity, Electrostriction Or Magnetostriction (AREA)

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• 2006
  • 2006-07-13 FR FR0606438A patent/FR2903826B1/fr not_active Expired - Fee Related
• 2007
  • 2007-07-10 WO PCT/FR2007/051635 patent/WO2008007017A2/fr not_active Ceased
  • 2007-07-10 EP EP07823558A patent/EP2044680A2/de not_active Withdrawn
  • 2007-07-10 US US12/373,635 patent/US8115424B2/en not_active Expired - Fee Related
• 2009
  • 2009-01-12 IL IL196459A patent/IL196459A0/en unknown

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