Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/80—Constructional details
  • H10N30/88—Mounts; Supports; Enclosures; Casings
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/20—Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators
  • H10N30/204—Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators using bending displacement, e.g. unimorph, bimorph or multimorph cantilever or membrane benders
  • H10N30/2041—Beam type
  • H10N30/2042—Cantilevers, i.e. having one fixed end

Definitions

• the invention relates to a micrometric displacement device and to a method of implementation.
• Piezoelectric actuators are used in many technical fields.
• piezoelectric actuators are used for performing precise movements, of the order of one micrometer to one hundred micrometers, of an object of low inertia.
• the displacement of electronic actuators of the type of flexors can only be done for frequency ranges from 0 to 100 Hertz (100 beats per second). Above 100 Hertz, the flexor actuators of the state of the art come into resonance and are no longer usable because their movement is not controlled and the controls of the actuator are not reproducible. Indeed, there is an amplification, or attenuation depending on the case, of certain frequencies.
• One solution envisaged is to filter the control of the actuator by its inverse transfer function.
• a transfer function is a mathematical representation of the relationship between the input signal (or command) and the output signal (the movement of the actuator) of the micrometer displacement device.
• This frequency correction technique is conventional for linear invariant systems (that is to say without moving element).
• the principle of this technique is to acquire the transfer function of the actuator (gain and phase shift to the first resonance frequency) to pre-filter the signal by the inverse of this transfer function.
• the micrometric displacement device must be adjustable in position along the X, Y and Z axes (see Figure 3a).
• the piezoelectric actuator must therefore be integral with movable mechanical elements.
• the measurement of the transfer function of the actuator should be updated after each adjustment of the positioning.
• This constraint is very heavy because it involves installing a device for measuring the movement of the actuator (for example a laser range finder), and subjecting the actuator to a long measurement of the transfer function. (about two minutes for the entire process), which led to the abandonment of this method.
• a first object of the present invention is to provide an adjustable positioning flexor type actuator having a resonant frequency greater than 1000 Hertz.
• a second objective of the present invention is to propose such an actuator whose gain is constant.
• the subject of the invention is a micrometric displacement device comprising:
• a decoupling means comprising: o an inertial mass
• This micrometric displacement device has a resonance frequency greater than 1000 Hertz.
• the material with a high vibration absorption capacity may be a viscoelastic urethane polymer such as sorbothane;
• the inertial mass may be made of a material chosen from lead, copper, steel and an alloy with a density greater than 5000;
• the support and adjustment structure may comprise:
• the adjustable means for compressing the pad against the ball joint may comprise a spring whose end, intended to be in contact with the pad during the locking of the ball joint, is fixed to a threaded shaft engaged with a screw thread carried by a adjusting wheel, so that when the position of the ball joint is to be changed, the tightening of the band wheel the spring so that it stops exerting its pressure on the rubber pad, and when the ball joint is to be blocked, Completely loosening the adjustment knob fully releases the spring which compresses the rubber pad against the patella with a force substantially equal to the stiffness constant of the spring.
• This micrometric displacement device has a resonant frequency greater than 1000 Hertz and a constant gain;
• the support and adjustment structure may comprise a micromanipulator in monoaxial translation; and or
• the monoaxial translation micromanipulator may comprise a ball bearing provided with at least two balls biocable in rotation by clamping by means of clamping screws.
• the invention also relates to a method for implementing the preceding micrometric displacement device, said method comprising an activation phase of the piezoelectric actuator comprising the transmission to the actuator of a control signal at a frequency of between 5 and 1000 Hertz, preferably between 100 and 1000 Hertz.
• a control signal at a frequency of between 5 and 1000 Hertz, preferably between 100 and 1000 Hertz.
• the method may comprise an initialization phase comprising the following steps:
• step b) repeating steps b) and c) until the activation frequency is equal to a first resonant frequency of the actuator; e) establish the transfer function of the activator using the gains and phase shifts acquired in step b);
• the initialization phase being followed by an activation phase of the piezoelectric actuator comprising the transmission to the actuator of a pre-filtered control signal by the inverse of the transfer function;
• the method may comprise a step of adjusting the pressure exerted on each ball of the ball bearing by a screw, in order to equalize the position of a rebound of the transfer function for all the translation positions;
• the method may comprise the following steps:
• the step of measuring the position of the actuator can be performed using a laser range finder connected to an oscilloscope. This method makes it possible to maintain the homogeneous gain and the zero phase shift throughout the range of use of the actuator.
• FIG. 1 is a schematic side view of the micrometric displacement device according to the invention.
• Figure 2 is a schematic longitudinal sectional view of a portion of the support structure of the micrometric displacement device according to the invention.
• FIG. 3a is a diagrammatic perspective view of the piezoelectric actuator of the micrometric displacement device according to the invention.
• FIG. 3b three curves illustrating the filtering of the control by the inverse transfer function of the micrometric displacement device according to the invention
• FIG. 4 six curves showing the phase shift and the gain of the micrometric displacement device according to the invention, with or without filtering the control by the inverse transfer function;
• FIG. 5a a histogram illustrating the Pearson correlation index between the control and the movement of the micrometric displacement device according to the invention, as a function of the number of adjustments in position;
• FIG. 5b a curve illustrating the superimposed movements of the piezoelectric actuator for fifteen different positions of the ball joint and translation with identical control
• FIG. 6a a curve illustrating the linearity of the control / motion gain for a range of amplitude between 10 and 90% of the maximum control amplitude
• FIG. 6b a curve illustrating the reproducibility of the command with several gains
• FIG. 7 is a diagram illustrating the independence of movement between the X axis and the Y axis.
• the present disclosure relates to a flexor type piezoelectric actuator such as CMB-2D manufactured by NOLIAC A / S (Hejreskovvej 18C, DK-3490 Kvistgaard, Denmark).
• a flexor type piezoelectric actuator such as CMB-2D manufactured by NOLIAC A / S (Hejreskovvej 18C, DK-3490 Kvistgaard, Denmark).
• NOLIAC A / S Hejreskovvej 18C, DK-3490 Kvistgaard, Denmark.
• the invention is not restricted to this example of a piezoelectric actuator.
• the CMB-2D actuator has a range of motion of 400 micrometers and a resonance frequency, without coupling, of several thousand Hertz.
• the coupling of the CMB-2D piezoelectric actuator induces a fall in its resonance frequency at 200 Hertz. As a result, no faster motion than 100 Hertz can be performed by the actuator without generating a resonance artifact.
• the actuator 10 is coupled to a support and adjustment structure 20 by a decoupling means 30.
• This decoupling means 30 comprises an inertial mass 31, on which is coupled the actuator 10, and a layer 32 made of material with a high vibration absorption capacity.
• the piezoelectric actuator 10 is connected to the inertial mass 31 by means of a plexiglass piece 11
• Part Plexiglas 11 aims to provide a rigid mounting of the piezoelectric actuator 10 on the inertial mass 31.
• the choice of plexiglass is related to the fact that this part 11 is relatively complex, and that it must be machined to lower cost. Indeed, each time the piezoelectric actuator 10 is used, it is replaced with the piece 11 in plexiglass.
• other rigid assemblies are also possible (other material, other spatial configuration).
• the piezoelectric actuator 10 comprises a piece 12 of steel fixed at its free end. This piece 12 makes it possible to reach an amplitude of movement, at the tip, of 400 ⁇ m.
• this part 12 could be modified (or even replaced) to accommodate a particular tool or sensor.
• the part 12 must preferably have a high rigidity to transmit the movements of the piezoelectric actuator 10 even at high frequency (Young's modulus - 200000 MPa) while being very light, so as to represent a negligible mass in front of the of the inertial mass (see below). This relative lightness is also useful for limiting the load of the piezoelectric actuator 10, and therefore its premature aging. It is these different reasons that justify the use of a steel tube, both lightweight and very rigid. Other materials such as tungsten or ceramic (pure alumina tubes) are good substitutes, but they are more expensive and more fragile (for ceramics).
• the layer 32 of high vibration absorbing material material is preferably a viscoelastic urethane polymer: sorbano.
• Sorbothane is a viscoelastic elastomer. Each elastomer of this type has a different vibration absorption spectrum.
• Chen & Lakes "Characterization of high-loss viscoelastic elastomers", (Journal of material science, 23 (1988) 3660-3665), a methodology for the quantitative description of various elastomers is proposed.
• tan ( ⁇ ) is an important parameter, because the inertia of the lead mass guarantees a low amplitude of shear at its base: the shear modulus is therefore not a parameter critical.
• Sorbothane has a Shore OO durometer 70 (some rigidity is necessary so that Sorbothane does not bend under the load, so Shore OO 30 is excluded, and Shore OO 50 is acceptable as part of the device shown).
• a material with a high capacity for absorbing vibrations that can be substituted for Sorbothane (of greater or equal durometer) can be envisaged, for example to improve the mechanical strength of the support of the actuator.
• This substitute material must have sufficient energy dissipation factor tan ( ⁇ ).
• the substitution material should have tan ( ⁇ ) values for frequencies above 100 Hz similar to Sorbothane Shore OO 50 or Shore OO 70.
• the material with high vibration absorption capacity has a tan ( ⁇ ) of between approximately 0.4 and 0.7, preferably between 0.53 and 0.6, for any frequency in the frequency range 5 - 1000Hz.
• the inertial mass located at the base of the actuator has the function of providing, by its inertia, a fixed point for the movement of the actuator despite the fact that the assembly is fixed on a viscoelastic material.
• this inertial mass must have a mass "very large” in front of the mass 12 attached to the movable end of the actuator. Indeed, at high oscillation frequencies (greater than 5 Hz), the displacement amplitude of the mobile end resulting from the torsion of the actuator is mainly defined by the ratio between the masses fixed at the two ends of the actuator (the elastomer is not rigid at these frequencies).
• the inertial mass is chosen so that its mass is at least ten times greater than the mass 12 fixed at the end of the mobile piezoelectric actuator.
• the inertial mass is lead.
• the choice of lead as the material of the inertial mass is due to its high density, which reduces the size of the device. This offers two substantial advantages: (1) a reduction of the lever arm exerted on the elastomer decoupling means by the mass due to its short length, and (2) a reduction in the overall size of the device. It would be perfectly feasible to replace lead with copper or steel (which are only slightly less dense) or an alloy with a density greater than 5000 kg. m "3 .
• the values of the various parameters indicated are valid for flexor type actuators 37 mm long. For example, if the actuator is longer, its resonant frequency is lowered; if the actuator is shorter, its resonant frequency is higher and the device must be modified to obtain the same technical effect by adjusting the aforementioned parameters.
• actuators 27 to 47 mm long it is possible to simply adjust the length of the mass inertial so that the actuator / inertial mass system has a resonance frequency equal to that of the system described in detail below.
• the adjustments of the different characteristics of the device will have to be more numerous.
• the layer of material 32 is attached to the support and setting structure 20.
• the decoupling means 30 allows activation of the flexor actuator at a frequency greater than 100 Hertz and up to 1000 Hertz without resonance phenomenon.
• the support and adjustment structure 20 comprises a ball joint
• micromanipulator UL-1C-P manufactured by the company NARISHIGE (27-9, Minamikarasuyama 4-chomen Setagaya-ku, Tokyo 157-0062, Japan).
• NARISHIGE Minamikarasuyama 4-chomen Setagaya-ku, Tokyo 157-0062, Japan.
• This micromanipulator allows a monoaxial translation with a travel of 15 millimeters. This translation is based on a ball bearing whose tightening can be adjusted by a series of screws which adjusts the pressure exerted on the balls of the bearing in their cavity.
• the support and adjustment structure 20 is illustrated, in section, in FIG.
• the stylet 22 comprises a tubular body 22a housing an adjustable compression means such as a spring 22b, for compressing a buffer 22c of elastic material against the ball of the ball 21.
• the buffer 22c is, preferably rubber.
• the end of the spring 22b in contact with the buffer 22c is fixed to a threaded shaft 22d in engagement with a screw thread carried by a control wheel 22e.
• the ball of the ball 21 When it is desired to modify the position of the actuator 10 along the X and Y axes (FIG. 3a), the ball of the ball 21 must be released for free rotation. To do so, the user squeezes the adjustment knob 22e which is engaged with the threaded shaft 22d. Tightening the bandwheel the spring so that it stops exerting its pressure on the rubber pad 22c. Once the position of the ball is adjusted along the X and Y axes, the user completely loosens the clamping wheel so that the spring 22b exerts, again, precisely the same pressure on the ball of the ball as that that he exercised before the adjustment. This pressure is constant since it depends solely on the stiffness constant of the spring.
• the pressure exerted on the ball is independent of the tightening of the adjustment wheel: it suffices that it is completely loosened so that the spring exerts the same force against the patella.
• the pressure on the ball of the ball is therefore reproducible and does not cause any change in the transfer function.
• a rotational locking device (not shown) of the threaded shaft is preferably provided in the stylet.
• the position of the actuator can be adjusted along two X and Y axes.
• the position of the actuator along the axis Z is adjustable thanks to the micromanipulator 23.
• the support structure 20 and adjustment of the previous example comprises two elements: a micromanipulator allowing a monoaxial translation (displacement along the Z axis) and a ball joint (rotation in two dimensions along the two axes X and Y). These two elements have the property of being stable for their transfer function in all their positioning range. Their combination in the arrangement illustrated in FIGS. 1 and 2 is given by way of example. However, the invention also covers supports allowing a triaxial translation, that is to say an adjustment of the position of the piezoelectric actuator along the three axes X, Y and Z.
• the support structure and adjustment according to the invention it becomes possible to apply, with great flexibility of use, the prefiltering technique by inverse transfer function, even though the structure comprises movable elements.
• FIG. 4 illustrates the phase shift and the gain of the micrometric displacement device according to the invention, with or without filtering the control by the inverse transfer function. This figure shows that the systematic filtering of the control by the inverse transfer function makes it possible to achieve a constant gain and a zero phase shift over the entire frequency range of the actuator (5 to 1000 Hertz).
• FIG. 5a shows a histogram of the correlation between a control and a movement of the actuator for different positions of the support.
• the hatched histogram bars represent the Pearson correlation index for ten settings at different angles of the patella.
• the shaded histogram bars represent the Pearson correlation index for nine different translation settings of the micromanipulator.
• Figure 5b illustrates the superimposed movements of the piezoelectric actuator for fifteen different positions of the ball joint and translation with identical control.
• the technique of pre-filtering by inverse transfer function comprises, in a first step, a step of acquiring the transfer function of the actuator (gain and phase shift to the first resonance frequency).
• This step is preferably performed using a laser rangefinder, such as the Micro-Epsilon LD1605 Type 0.5 range finder.
• the micrometric displacement device preferably comprises a control software that controls the acquisition of the position of the actuator using the laser range finder while sinusoidal controls scanning the frequency spectrum are transmitted to the actuator. This step calculates the transfer function of the actuator. In a second step, the control software filters commands sent to the actuator using the reverse transfer function (see Figure 3b).
• the method according to the invention comprises an initialization phase comprising the following steps:
• step b) repeating steps b) and c) until the activation frequency is equal to a first resonant frequency of the actuator; e) establish the transfer function of the activator using the gains and phase shifts acquired in step b).
• the initialization phase is then followed by an activation phase of the piezoelectric actuator comprising the transmission to the actuator of a pre-filtered control signal by the inverse of the transfer function.
• the initial frequency may be arbitrary. It can therefore be located within the operating range of the actuator. Thus, it may be necessary during step c) to increment or decrement the activation frequency of the activator to arrive at the first resonance frequency of the actuator and then establish the transfer function.
• the pre-filtering by the inverse transfer function cancels the effects of the transfer function of the actuator (FIG. 3b), which makes it possible to achieve an equal gain and a zero phase shift over the entire range of use of the actuator. actuator.
• the structure of the actuator described in relation to FIGS. 1 and 2 allows mechanical adjustments of the position and rotation of the actuator 10, while ensuring the stability of the transfer function. Since it is no longer necessary to repeat the initialisation previously described for each mechanical adjustment, the use of the filtering technique by the inverse transfer function can be used and the actuator according to the invention has a homogeneous gain and a zero phase shift over its entire range of use, unlike actuators of the state of the art.
• the inventors have realized that an adjustment of the pressure exerted by the adjusting screws on the ball bearing of the micromanipulator allows to modulate the frequency position of the rebound present in the transfer function of the actuator.
• the invention diverts this device from its initial purpose and uses it to obtain the same transfer function of the piezoelectric actuator for the different positions of the translation by modulating the pressure exerted by the screws arranged along the axis.
• the method according to the invention can be applied to any ball-bearing device having a device for exerting an adjustable pressure at multiple points along the ball bearing.
• the method for implementing the micrometric displacement device according to the invention comprises a step of adjusting the pressure exerted by each screw on the balls of the ball bearing in order to equalize the position of the rebound of the transfer function for all translation positions. For this, a sinusoidal control of constant frequency and close to the average frequency of the rebound is sent continuously to the actuator. A continuous measurement of the position of the actuator is performed, for example using the laser range finder connected to an oscilloscope.
• By adjusting the pressure carried by each screw it is possible to set the amplitude of the movement of the actuator for all the positions of the translation, which amounts to setting the position of the rebound over the entire trajectory.
• the transfer function of the actuator / support assembly is thus fixed through its entire adjustment space, namely translation and rotation. Thanks to this method according to the invention, the stability of the reproduction of movements for different translational positions is ensured.
• control / movement relationship of the micrometric displacement device according to the invention is linear, including for a control having very high frequencies (FIG. 6b).
• FIG. 7 shows that the specific use of the CMB-2D actuator (which has two axes of freedom) in the device according to the invention does not influence the independence of the movement of the two axes of the Actuator 10. In other words, movement on one axis does not interfere with movement on the other axis.
• the movement resulting from a single-axis control was compared to the sum of the movement resulting from the same command on the same axis added to a control in phase then in antiphase on the other axis.
• This resulting movement which should be influenced by an interaction between the movements on one and the other of the axes, is very close to the movement resulting from the control on a single axis.
• FIG. 7 illustrates the absence of effect of a movement on the Y axis on the movement recorded on the X axis.
• the two axes of displacement of the micrometric displacement device according to the invention are therefore independent.
• a flexor type piezoelectric actuator is adjustable along the three axes X, Y and Z in a wide frequency band up to 1000 Hertz and having stable characteristics for adjustments.
• micrometric displacement device allows a use for precision positioning: precise movements of the order of one micrometer to the hundred micrometers of an object of low inertia.
• the illustrated embodiment is economical to manufacture and has a small footprint because it requires no position sensor permanently mounted on the actuator

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• 2009
  • 2009-07-30 FR FR0903752A patent/FR2948593B1/fr not_active Expired - Fee Related
• 2010
  • 2010-07-27 EP EP10747923A patent/EP2460199A1/de not_active Withdrawn
  • 2010-07-27 WO PCT/FR2010/000541 patent/WO2011015722A1/fr active Application Filing

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