Patent Application
20250207578
The technical field of the invention is a peristaltic pump configured for actuation by a piezoelectric transducer.
Most pumps utilize movable parts, which can generate problems relating to reliability, wear and footprint. Peristaltic pumps are commonly used in the field of health. However, the repeated deformation of a hose, which causes the displacement of the liquid, can result in premature wear of the hose.
Patent application WO2013/41700 describes a non-peristaltic pump, which can be implantable, having piezoelectric actuation. A sleeve, arranged in the centre of a resonator, undergoes flexure under the effect of rotating deformation of the resonator, caused by piezoelectric transducers activated according to an ultrasonic frequency. The flexure of the sleeve generates a pumping effect, which results in the expulsion of the fluid. A reduction in the transverse cross-section of the resonator, in the vicinity of the sleeve or along said sleeve, makes it possible to amplify the vibrations propagating up to the sleeve. Such a pump is effective. However, it has been observed that the sleeve undergoes repeated flexure, which can result in wear. In addition, the pump is intended to be coupled to a fluid circuit. Control of the flow rate depends on the amplitude of vibration of the sleeve, which must be governed by the mechanical load of the fluid circuit, which is not easy.
In particular, the aim is for the pumping principle, the frequency and the amplitude of the ultrasonic vibration for pumping to be less dependent on the mechanical coupling between the pump and the fluid circuit.
Another aim is to design a peristaltic pump that makes it possible to perform pumping at a controlled flow rate with optimized energy expenditure, and which can be particularly compact.
One object of the invention is a peristaltic pump, intended to pump a liquid along a capillary, the pumping resulting from a stress exerted on the capillary, successively along a pumping direction, the pump comprising:
The stress can notably be a compression and/or a displacement along the central axis.
The modulation frequency can notably be greater than 20 kHz.
According to one option:
According to one option, the flat face along which each peripheral transducer extends is delimited by a shoulder, the piezoelectric transducer being force-fitted against the shoulder, so that the shoulder encircles the piezoelectric transducer.
According to one option, each resonator is coupled to at least one annular piezoelectric transducer, the annular piezoelectric transducer extending around the resonator, so as to cause a radial compression of the resonator, in the direction of the central axis.
Each piezoelectric transducer can be force-fitted around the resonator to which it is connected.
According to one option, each resonator is coupled to two annular piezoelectric transducers, extending around the resonator, and offset along a direction parallel to the central axis, the central unit being configured to power the piezoelectric transducers so as to cause a displacement of the sleeve along the central axis and/or a compression of the sleeve perpendicular to the central axis.
According to one option, each piezoelectric transducer having a dipole moment:
According to one option, each piezoelectric transducer having a dipole moment:
According to one option, the control unit is configured to power said piezoelectric transducers according to a predetermined phase shift, of between 0° and 180°, so as to obtain a predetermined ratio between the displacement of the sleeve along the central axis and the compression of the sleeve.
The pump can comprise the capillary, the capillary being for example force-fitted between each sleeve. The capillary can be rigid.
The invention will be more clearly understood on reading the description of the examples of embodiments given hereinafter, with reference to the figures listed below.
The pump comprises K resonators 10k, k being a rank assigned to each resonator. The minimum number of resonators is two, and the optimum number of resonators is between three and five. In the example shown, K=4. Four identical resonators 101, 102, 103, 104 are thus provided, aligned along the central axis. Each resonator extends in an annular shape, between a peripheral part comprising flat portions, having a constant thickness, and a part that becomes thinner towards the central axis. Each resonator becomes thinner, preferably progressively, up to a cylindrical sleeve 3k that extends about the central axis. The progressive thinning makes it possible to increase the deformation forces transferred to the sleeve.
The capillary 2 is arranged along the central axis, between each sleeve. Preferably, the capillary 2 is rigid so that it can be force-fitted into the sleeves. Force-fitting minimizes the losses at the interfaces in the form of parasitic reflection of the mechanical energy or dissipation through friction. In addition, force-fitting does not require clamping means. The capillary can be formed from the same material as the resonator.
Each resonator comprises a shoulder 15k, making it possible to grip the transducer to which it is coupled, so as to exert prestressing. Each shoulder encircles the piezoelectric transducer that it grips. Each piezoelectric transducer can thus be held without adhesive, through simple mechanical stress. This makes it possible to avoid the degradation over time of an adhesive due to ageing.
Each resonator 10k is coupled to an annular piezoelectric transducer 11k.
In this configuration the piezoelectric transducers have a small thickness, typically of between 0.05 mm and 5 mm, preferably 0.5 mm for a radius r of 25 mm and 0.2 mm for a radius r of less than 10 mm, which maximizes the electric field, which can be of the order of 300 V/mm. This makes it possible to increase the mechanical stress, which is directly proportional to the electric field.
Each layer of piezoelectric material 13k can be formed from a PZT (lead zirconate titanate) material, in particular product references PZ26, PZ27, PZ46 and PZ29 made by Ferroperm. Preferably, the coefficients d33 and d31, which reflect the coefficient of the deformation observed for an electric field applied (also perceived as a density of charges collected for a stress applied) are respectively:
The outer radius R of each resonator 10k, defined about the central axis Δ, can extend up to 50 mm, or more. The flat portion of each resonator extends beyond a first radius R1, smaller than the outer radius R defined above. Inside the first radius R1, each resonator has a portion that becomes thinner in the direction of the central axis Δ. The first radius R1 is for example equal to 50% of the outer radius R of the resonator.
Each resonator can extend along a thickness preferably less than 5 mm, for example 1 or 2 mm. The thickness is defined parallel to the longitudinal axis.
The resonator 10k extends up to a cylindrical first sleeve 3k that is coaxial with the central axis Δ. The diameter D of the sleeve 3k is for example between approximately 0.2 mm and 2 mm and preferably close to 1 mm. The sleeve 3k is preferably formed by an extension of the resonator 10k, the resonator and the sleeve forming a monolithic part. The radius of the sleeve forms an inner radius of the first resonator 10k. The height of each sleeve 3k is preferably smaller than a wavelength of the waves propagating in the sleeve. The height of each sleeve 3k is preferably equal to a half wavelength. The wavelength depends on the thickness of the sleeve and the resonance frequency. In practice, the height of the sleeve is less than 1 mm and preferably less than or equal to the thickness of the resonator in the portion applied against the piezoelectric transducer.
This makes it possible for the sleeve of each resonator to be as close as possible to the sleeve of another resonator, without being in direct contact. The spacing between two adjacent sleeves can be at least 0.05 mm.
Each resonator is formed from a deformable solid material, which can be a metal (titanium, stainless steel, aluminium or aluminium alloy, brass or another copper-based alloy, or a nickel-based alloy), an inorganic material (glass), an organic material (PEEK), or alumina.
The pump comprises a control unit 20, connected to each first electrode 12k so as to apply a frequency-modulated polarization voltage to them. The modulation frequency depends on the dimension and on the material forming each resonator. The frequency is the same for each piezoelectric transducer. When the radius of each resonator is 25 mm, the modulation frequency can be approximately 25 kHz. When the radius of each resonator is 12.5 mm, the modulation frequency can be approximately 50 kHz. When the radius of each resonator is 6.5 mm, the modulation frequency can be approximately 100 kHz. In any event, the modulation frequency is preferably ultrasonic, so as to avoid the generation of an audible sound.
Each counter electrode 14k is connected to a fixed potential, which can be common to all of the counter electrodes (for example an earth), or independent from the potential to which another electrode is connected, each independent potential being for example a floating earth.
Each resonator 10k is configured to be deformed by a compression wave acting on each sleeve, so as to radially compress the capillary. Under the effect of the compression, the inner diameter of each sleeve oscillates according to a compressive radial resonance frequency. According to one option, each sleeve can be displaced parallel to the axis of the capillary according to a flexural radial resonance frequency.
More specifically, as the dimensions of the resonator are finite, a surface element situated on the inner wall defining each sleeve oscillates, describing an ellipse on each resonance period. The major axis sz of the ellipse is parallel to the central axis Δ according to a flexural radial resonance frequency. A slight rolling effect is therefore imparted to the capillary. The resonator 10k can vibrate at its fundamental frequency or at a harmonic frequency. In this latter case, the ratio between the major axis sz and the minor axis sr of the ellipse travelled along becomes closer to one. The movement becomes more circular for a higher harmonic frequency.
The resonators can be separated from each other by spacers 4. This makes it possible to stiffen the stack.
The thickness of the stack can be between 5 mm and 10 mm.
The transducers are offset along the longitudinal axis Δ, so that the compression moves along the central axis. The time offset is
where T corresponds to the period in which each transducer was actuated. The resonance frequency is estimated to be at most 150 kHz for a fundamental frequency.
where T corresponds to the period in which each transducer was actuated.
The use of piezoelectric transducers arranged on the periphery of resonators makes it possible to increase the frequency, the resonators having a high thickness resonance frequency, in practice greater than a megahertz, or a lower frequency if a compressive radial resonance of the thin disc is utilized. This makes it possible to use a finer capillary, close to one tenth or a few tenths of a millimetre. Such a configuration is suitable for delivering low doses of active ingredient, or for an implanted pump, or for dispensing low volumes of fluids such as catalysts or costly products, or for slow and well-controlled supply of powders or various products (gas, lubricant, etc.) necessary for a particular production process or for maintenance.
As in the preceding embodiment, the transducers coupled to two adjacent resonators are offset along the longitudinal axis Δ, so as to propagate the shear stress gradually along the capillary. The time offset (or shift) is
where T corresponds to the period in which each transducer was actuated. During the same phase, the first transducer 11k of a resonator 10k is activated, so as to induce a bowing of the resonator in one direction in its central region, while the second transducer 21k of a resonator 10k is activated, so as to induce a bowing of the resonator in the same direction, and must therefore be offset by π, on the central axis. This is obtained if the outer electrodes of the transducers 11k and 21k (respectively) are subjected to the same electric excitation voltage and if the electric dipole moments of the piezoelectric materials of the transducers 11k and 21k are of opposite directions as indicated by the arrows passing through the transducers shown in
Pumping by peristaltic shear effect is thus obtained, due to the progressive shearing of the capillary 2, which causes a displacement of the fluid by viscosity and incompressibility of the fluid along the central axis. The efficiency of pumping is increased by a displacement component sr in the plane of each resonator, corresponding to the minor axis of the displacement ellipse and resulting in a compression of the capillary tube. The symmetric and antisymmetric acoustic modes S0 and A0 initiated at the periphery of the resonators in
The configuration shown in
When the dipole moments of the transducers 11k and 21k are oriented in the same direction, and the excitation voltages are in phase opposition, an antisymmetric vibration mode A0 is obtained as described above. When the excitation voltages are in phase, a symmetric vibration mode S0 is obtained.
A symmetric vibration mode has the effect of compressing the capillary and producing a displacement of the capillary/sleeve interface travelling along an ellipse with a major axis orthogonal to the axis Δ. This vibration is transmitted into the wall of the capillary in the form of a flexural wave having axial symmetry relative to the axis Δ.
An antisymmetric vibration mode has the effect of producing a displacement of the capillary/sleeve interface wherein the major axis of the ellipse is parallel to the axis Δ, which results in a shearing of the capillary in accordance with the axial symmetry relative to the axis Δ.
As a result, if the electrical phase shift between the two transducers 11k and 21k is varied from 0 to 180°, there is a continuous switch from predominant generation of a symmetric deformation mode to predominant generation of an antisymmetric mode relative to the mid-plane of the resonator 10k. The two symmetric and antisymmetric vibration modes are created simultaneously but in different proportions depending on the phase shift and at different phase speeds that are higher for the symmetric mode than for the antisymmetric mode. Given that these vibration modes can coexist simultaneously and elastically in the resonator, a specific electric excitation phase shift of between 0 and 180° C. must simply be imposed in order to obtain a vibration of the wall of the capillary so that each surface element of the capillary moves along an ellipse, the major axis of which can vary from an orientation perpendicular to the axis Δ to an orientation parallel to the axis Δ as a function of the phase shift that has been selected between the two transducers 11k and 21k.
Whatever the configuration, the peak-to-peak polarization voltage can vary for example from a few volts to several hundred volts, the voltage acting on the amplitude of the out-of-plane deformation component of the resonator. The amplitude of this deformation component acts on the volume of fluid at the inner interface of the capillary undergoing the elliptical rolling effect that drives it, and therefore on the pumping pressure.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR2314942 | Dec 2023 | FR | national |
