Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L19/00—Details of, or accessories for, apparatus for measuring steady or quasi-steady pressure of a fluent medium insofar as such details or accessories are not special to particular types of pressure gauges
  • G01L19/14—Housings
  • G01L19/148—Details about the circuit board integration, e.g. integrated with the diaphragm surface or encapsulation
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
  • G01L9/0001—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means
  • G01L9/0005—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means using variations in capacitance

Definitions

• the present invention concerns a digital pressure sensor of the capacitive type, suitable for application in domestic appliances, such as for example, but not only, washing machines or dishwashers, in order to detect pressure values with the purpose of conditioning the activation of pre- determined functions and cycles of the electric appliance.
• the invention also concerns a domestic appliance provided with the sensor.
• Capacitive sensors are known, which are normally provided with a flexible conductive membrane kept by a spacer at a determinate distance from a conductive plate connected to a printed circuit, or PCB (Printed Circuit Board).
• PCB printed Circuit Board
• Capacitive sensors can be used in various fields in the state of the art, to measure different quantities, such as for example pressure, displacements, chemical composition, electric or magnetic field, acceleration, level or composition of a fluid.
• the sensors can also be of micrometric sizes and have very high sensitivity and resolution, and operate with variations in capacity even in the order of 5 aF.
• MEMS Micro Electro-mechanical Systems
• electrical, electronic and mechanical devices integrated into the same silicon substrate.
• capacitive sensors provide them to be used as high- resolution proximity sensors.
• one or more pressure sensors are used in order to detect particular and defined values of a pressure and to determine the activation or de-activation of a particular function or functioning cycle of the appliance, based on the commands of an electronic or electro- mechanical programmer.
• pressure sensors comprise for example pressure switches of the electro-mechanical type, which can be activated when the pressure reaches a predetermined level.
• known pressure switches have the further disadvantage that they are not very versatile, since they are generally calibrated only to detect a predetermined pressure and do not perform any measuring of the quantity.
• capacitive sensors have a disadvantage due to a possible measurement hysteresis that can affect the precision and accuracy thereof.
• the hysteresis is mainly due to the fact that the coupling of the conductive membrane and the spacer can cause a reciprocal movement between these two components of the sensor, which movement can be added to or subtracted from the flection of the conductive membrane, affecting the repeatability of the measurement.
• this reciprocal movement can recur with every measurement, but with a random amplitude, or it can be partly or completely recoverable or can be permanent, giving rise to a residual displacement.
• the reciprocal movement introduces a dependency of one measurement on the previous ones, based on its amplitude or the residual displacement that the corresponding stresses have induced between the membrane and the spacer.
• Another problem is to satisfy different requirements in terms of output signal with the same sensor, in order to be able to install the same sensor, possibly modifying only its programming, in applications that manage different output signals.
• JP 2007 225344 A and JP 201 1 007499 A describe solutions where a membrane is applied on a support body in a position opposite to a conductor plate.
• JP 2005 283354 A describes a pressure sensor in which a flexible membrane is made on a support body, an insulating layer and a layer of monocrystalline silicon being interposed between the support body and the vitreous substrate in which the conductor plate is disposed.
• One purpose of the present invention is to obtain a digital pressure sensor which is precise and inexpensive but not bulky, and is also able to measure at least a pressure in a domestic appliance, with maximum resolution, also accurate and able to quickly supply repeated measurements, and not affected by hysteresis.
• Another purpose of the invention is to obtain a digital pressure sensor where the measurement of the pressure is independent from the connection constraint between the conductive membrane and the spacer.
• the Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.
• a digital pressure sensor configured to measure at least a pressure in a domestic appliance and, according to a characteristic feature of the invention, it is of the capacitive type and comprises at least a pressure detection unit with a conductive plate of a printed circuit and a conductive membrane provided with a deformable zone disposed parallel to each other and distanced by a spacer.
• the conductive plate and the conductive membrane define in this way the plates of a variable capacity capacitor.
• the conductive membrane and the spacer are made in a single body as parts of a single sensitive element.
• the present invention also has the advantage that it makes the measurement more precise, accurate and fast, and therefore more reliable compared to known capacitive sensors where the conductive membrane and the spacer are separate bodies.
• the spacer in a direction orthogonal to the conductive membrane, defines an end part of the sensitive element and the conductive membrane is positioned at the opposite end of the sensitive element, in said direction, with respect to that defined by the spacer.
• said membrane in a direction orthogonal to the conductive membrane, said membrane is made substantially at the center of the sensitive element, and the spacer is essentially symmetrical with respect to the conductive membrane and in the same direction.
• the spacer has a shape defined by a profile with a continuous development, disposed externally with respect to the plan bulk of the deformable zone of the conductive membrane and configured to peripherally surround an interspace comprised between the conductive membrane and the conductive plate.
• the spacer has a shape defined by a discontinuous profile formed by a plurality of spacer bodies disposed symmetrically, in order, or according to any disposition whatsoever that is suitable to guarantee the parallelism of the conductive membrane and the conductive plate, outside the plan bulk of the deformable zone of the conductive membrane and around an interspace comprised between the conductive membrane and the conductive plate.
• the present invention also comprises a domestic appliance provided with a capacitive digital pressure sensor made as described above.
• FIG. 1 and 2 are schematic representations of a washing machine provided with a digital pressure sensor according to the present invention
• FIG. 3 and 4 are schematic views, in section, of forms of embodiment of a digital pressure sensor according to the present invention.
• - figs. 5 and 6 are three-dimensional views of forms of embodiment of a component of the digital sensor in fig. 3.
• a digital pressure sensor is indicated in its entirety by the reference number 10 and is shown schematically, assembled on a domestic appliance, such as for example a washing machine 1 1.
• a domestic appliance such as for example a washing machine 1 1.
• the present description is referred by way of example to a washing machine 1 1 , but can easily be adapted to any domestic appliance in which it is necessary to measure one or more internal pressures.
• Fig. 1 is used to describe by way of example a washing machine 1 1 of the known type and its corresponding functioning.
• the washing machine 1 1 is provided with at least a drum 12 in which the garments to be washed are contained and with an electric motor 13 configured to supply the desired rotatory motion to the drum 12.
• the digital pressure sensor 10 is connected to the drum 12 through a measuring pipe 18 that allows it to measure the pressure of the water contained in the drum 12 in an indirect way.
• the measuring causes some steps of the washing cycle, which depend on the amount of water in the drum 12, to start and/or stop.
• the washing cycles are managed by a command and control unit 19 to which the digital pressure sensor 10, the electric motor 13, the electrovalve 15 and the discharge pump 16 are connected, for example by means of electric feed and signal transmission cables.
• the command and control unit 19 can include a memorization module 20, in which programs containing all the operations connected to the execution of each of the steps of the washing cycles can be memorized, and an electronic processor 21, configured to execute such programs.
• the memorization module 20 and the electronic processor 21 can both be integrated into a programmable card, or motherboard 22.
• command and control unit 19 can also include a user interface 23, by means of which a user can select the desired washing cycle and the desired functions of the washing machine 1 1 , or control the progress of the cycle.
• the digital pressure sensor 10 measures the pressure of the water contained in the drum 12, which causes some steps in the washing cycle to start and stop, for example the start of the filling of the drum 12 at the beginning of the cycle, the stop of said filling and the start of the washing step, the start of the partial discharge step and the subsequent further filling of the drum 12 during the washing cycle and the start of the spinning step.
• the digital pressure sensor 10 sends a signal relating to the pressure of the water in the drum 12 to the command and control unit 19.
• the electronic processor 21 processes the signal in order to obtain the value of the pressure and to compare it to a threshold value contained in the program to be executed and memorized in the memorization module 20. Based on this comparison, the command and control unit 19 selectively commands the electrovalve 15 to open or close.
• the digital pressure sensor 10 can be configured to send the signal corresponding to the pressure measurement to the command and control unit 19 continuously, in order to optimize and accelerate the response times of the command and control unit 19.
• the digital pressure sensor 10 is provided with great precision and sensitivity, and also great accuracy and reliability, indispensable for making the washing conditions of each washing cycle repeatable and to optimize consumption, in particular of water.
• the components of the digital pressure sensor 10 can be miniaturized, it is possible that the overall volumetric bulk of the digital pressure sensor 10 can also be in the order of a few millimeters. Forms of embodiment, shown for example in fig. 2, are therefore possible in which the digital pressure sensor 10 is integrated in the motherboard 22 of the command and control unit 19.
• This solution gives the advantage of reducing the internal bulk of the washing machine 1 1 and the advantage of simplifying the production process thereof, thus reducing the number of independent components.
• the digital pressure sensor 10 can be made in the same production cycle as the command and control unit 19.
• figs. 3 and 4 are used to describe preferential forms of embodiment of a digital pressure sensor 10, in which it is the capacitive type.
• the digital pressure sensor 10 comprises a container 24, in this case with a box-like shape defined by a first part, or lid 25, and by a second part, or closing body 26, said parts 25, 26 being attached to each other for example by means of gluing, welding or joining means.
• a printed circuit or PCB 27 rests, on one surface of which a conductive plate 28 is made, which can also be a few microns thick, for example if defined by a metal coating of the PCB 27 surface itself, or by part of it.
• the lid 25 can be provided, in example forms of embodiments, with housing seatings 29 in which peripheral ends of the PCB 27 can be housed, in order to keep the latter firmly in position after the assembly of the container 24.
• the digital pressure sensor 10 also includes a sensitive element 30, made of a conductor material such as metal, for example copper, aluminum or steel, contained inside the lid 25.
• a sensitive element 30 made of a conductor material such as metal, for example copper, aluminum or steel, contained inside the lid 25.
• the shape of the sensitive element 30 is defined by a flexible central part consisting of a conductive membrane 31 and a peripheral part that functions as a support for the conductive membrane 31, and that consists of a spacer 37.
• the spacer 37 is configured to keep the conductive membrane 31 at a desired distance from the conductive plate 28 of the PCB 27.
• the shape of the sensitive element 30 is such that, once the digital pressure sensor 10 is assembled, the conductive membrane 31 is parallel to the conductive plate 28, so that between conductive membrane 31 and conductive plate 28 an interspace I is created, of a known value, and defined, in the absence of external stresses.
• a desired difference in potential is set between the conductive membrane 31 and the conductive plate 28, and in the interspace I there is a dielectric material, normally air, they define the plates of a capacitor.
• the distance between the conductive membrane 31 and the conductive plate 28 can even be a few hundredths of a millimeter, in order to obtain a desired value of sensitivity of the digital pressure sensor 10 that can be also extremely low.
• the conductive membrane 31 is provided, substantially at the center of its plan bulk, with a deformable zone 33 which is less thick than the rest of the conductive membrane 31.
• the deformable zone 33 is configured to bend if subjected to a pressure P (figs. 3 and 4) due to the presence of water in the drum 12 of the washing machine 11, thus increasing the capacity of the capacitor formed by the conductive membrane 31 and the conductive plate 28.
• the lid 25 in correspondence with the central zone 33 of the conductive membrane 31, the lid 25 is provided with an aperture 35 communicating with the measuring pipe 18 and with the function of transmitting the pressure P of the water contained in the drum 12 to the deformable zone 33 of the conductive membrane 31, deforming it.
• This deformation due to the pressure P, causes the central zone 33 and the conductive plate 28 to approach each other, which causes an increase in the capacity of the capacitor of which they are the plates.
• This increase in capacity like other possible reductions in capacity which occur, for example, following the increase in said pressure P, are detected by a micro-controller 34, for example a microchip.
• the microcontroller 34 is integrated in the PCB 27.
• the micro-controller 34 is configured to process the measurement of the capacity variations and provide an output signal to the command and control unit 19 with which it is electronically connected.
• the PCB 27 and the sensitive element 30 define a pressure detection unit 36.
• the measuring pipe 18 can be connected to the lid 25 by means of a removable type connection, for example jointed or threaded, or the irremovable type, such as gluing or welding.
• the measuring pipe 18 can be integrated in the lid 25 and made for example by molding, in a single body therewith.
• the entity of the flectional deformation of the deformable zone 33 of the conductive membrane 31 depends, as is known, on factors such as the geometry and properties of the material of the conductive membrane 31, the type of constraint that connects it to the spacer 37 and the compressibility of the dielectric material present in the interspace I.
• figs. 3 to 6 are used to describe example forms of embodiment in which the sensitive element 30 includes the conductive membrane 31 and the spacer 37 in a single body. In this way in practice we eliminate the possibility of reciprocal movements being created between the conductive membrane 31 and the spacer 37, other than the flection of the deformable zone 33.
• the flection of the deformable zone 33 and consequently the measurement made by the digital pressure sensor 10 depends only on the physical and geometrical characteristics of the conductive membrane 31, and is independent of the conditions of constraint with the spacer 37.
• the spacer 37 defines one end of the sensitive element 30, that is, the end which, when the digital pressure sensor 10 is assembled, is closest to the conductive plate 28.
• the membrane 31 is positioned in a direction orthogonal to it and to the conductive plate 28, at the opposite end of the sensitive element 30 with respect to the one defined by the spacer 37.
• the spacer 37 is in contact with, and in this case rests on, the PCB 27, but in other implementations it may be provided that it rests on the closing body 26 of the container 24.
• the closing body 26 may not be provided and the PCB 27 can be defined by an area of the motherboard 22 itself. In these cases, the motherboard 22 can perform the function of the closing body 26.
• Fig. 4 can be used to describe forms of embodiment in which the conductive membrane 31 is made in a direction orthogonal thereto, substantially at the center of the sensitive element 30, and the spacer 37 is essentially symmetrical with respect to the conductive membrane 31 in the same direction.
• Variants of the present invention can provide to position the conductive membrane 31 in an intermediate part of the sensitive element 30 and an asymmetrical conformation of the spacer 37 with respect to the conductive membrane 31 in the direction orthogonal thereto.
• the detection unit 36 includes a spacer 37 having a shape defined by a profile with a continuous development.
• the continuous profile is external with respect to the plan bulk of the deformable zone 33 of the conductive membrane 31 and is configured to surround the interspace I between the conductive membrane 31 and the conductive plate 28.
• the spacer 37 of the detection unit 36 has a shape defined by a discontinuous profile and includes a plurality of spacer bodies 137 disposed externally with respect to the plan bulk of the deformable zone 33 of the conductive membrane 31.
• the spacer bodies 137 can be disposed symmetrically with respect to the center of the sensitive element 30 around the interspace I; while in other solutions they can have any disposition whatsoever in the sensitive element 30, provided that they must remain outside the plan bulk of the deformable zone 33 of the conductive membrane 31.
• the sensitive element 30 is shown, to simplify the drawings, with a substantially cylindrical shape; nevertheless it is also possible to make sensitive elements 30 with any three-dimensional shape, for example polyhedral, regular or irregular, without departing from the field of the present invention.
• the solutions shown in figs 5 and 6 differ substantially in that the spacer 37 with the continuous profile (fig. 5) can allow to insulate the interspace I, while the spacer 37 with the discontinuous profile (fig. 6), that is, with separate spacer bodies 137, can allow the dielectric contained in the interspace I to flow toward the outside of the digital pressure sensor 10 due to the effect of the thrust that the deformable part 33 of the conductive membrane 31 exerts on it when it bends.
• the digital pressure sensor equipped with a sensitive element 30 that comprises, in a single body, conductive membrane 31 and spacer 37, can reach a hysteresis value that is substantially zero, or in any case less than the resolution of the digital pressure sensor 10 itself.
• the hysteresis value of the digital pressure sensor 10 can also be advantageously less than 8 Pa.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Measuring Fluid Pressure (AREA)

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Citations (5)

• 2013
  • 2013-05-23 IT IT000071A patent/ITUD20130071A1/it unknown
• 2014
  • 2014-05-23 WO PCT/IB2014/061647 patent/WO2014188381A1/en active Application Filing

Patent Citations (5)

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