WO2001014889A9 - Low-cost accelerometer - Google Patents
Low-cost accelerometerInfo
- Publication number
- WO2001014889A9 WO2001014889A9 PCT/US2000/040729 US0040729W WO0114889A9 WO 2001014889 A9 WO2001014889 A9 WO 2001014889A9 US 0040729 W US0040729 W US 0040729W WO 0114889 A9 WO0114889 A9 WO 0114889A9
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- transducer
- acceleration
- providing
- signal
- flexes
- Prior art date
Links
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
- G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
- G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
- G01P15/09—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by piezoelectric pick-up
- G01P15/0922—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by piezoelectric pick-up of the bending or flexing mode type
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K1/00—Printed circuits
- H05K1/02—Details
- H05K1/0213—Electrical arrangements not otherwise provided for
- H05K1/0216—Reduction of cross-talk, noise or electromagnetic interference
- H05K1/023—Reduction of cross-talk, noise or electromagnetic interference using auxiliary mounted passive components or auxiliary substances
- H05K1/0231—Capacitors or dielectric substances
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K1/00—Printed circuits
- H05K1/02—Details
- H05K1/0213—Electrical arrangements not otherwise provided for
- H05K1/0237—High frequency adaptations
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K1/00—Printed circuits
- H05K1/18—Printed circuits structurally associated with non-printed electric components
- H05K1/181—Printed circuits structurally associated with non-printed electric components associated with surface mounted components
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
- H05K2201/10—Details of components or other objects attached to or integrated in a printed circuit board
- H05K2201/10431—Details of mounted components
- H05K2201/10507—Involving several components
- H05K2201/10545—Related components mounted on both sides of the PCB
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
- H05K2201/10—Details of components or other objects attached to or integrated in a printed circuit board
- H05K2201/10613—Details of electrical connections of non-printed components, e.g. special leads
- H05K2201/10621—Components characterised by their electrical contacts
- H05K2201/10636—Leadless chip, e.g. chip capacitor or resistor
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Definitions
- the present invention is directed to methods and devices for monitoring the acceleration of obj ects .
- Piezoelectric materials are commonly used in transducer and actuator applications.
- a piezoelectric material generates an electric field in response to applied mechanical force, and generates mechanical force in response to an applied electric field.
- Transducer applications take advantage of the former of these properties, and actuator applications take advantage of the latter.
- Examples of piezoelectric materials include quartz crystal (which is a naturally occurring crystal commonly used in oscillators), and certain polycrystaline ceramics, e.g., barium titanate, lead metaniobate, lead [Pb] zirconate titanate (PZT), and the like. These types of ceramics are commonly referred to as piezoceramics.
- Piezoceramic elements for use as actuators or transducers may be fabricated by precasting and firing a quantity of piezoceramic material into a desired shape, e.g., a rectangle or circle. After being formed, each element is typically subjected to a treatment called prepolarization during which the dipoles of the element are aligned in a chosen direction. This polarization of the element's dipoles causes the element to exhibit its piezoelectric properties.
- One way to prepolarize a piezoceramic element is to attach a pair of electrodes to opposing surfaces of the element, and to apply a strong electric field across the electrodes while keeping the element at a temperature just below its Curie point.
- the element When a piezoceramic element is prepolarized in this manner, the element experiences a permanent increase in dimension in the direction of the applied electric field, i.e., between the electrodes, and experiences a permanent decrease in dimension perpendicular to the direction of the applied electric field, i.e., parallel to the surfaces on which the electrodes are disposed.
- a piezoceramic element After a piezoceramic element has been prepolarized, when a dc voltage of the same polarity as the prepolarizing voltage (but of a lesser magnitude) is applied between the element's electrodes, the element experiences further expansion in the direction of the applied voltage and further contraction perpendicular to the direction of the applied voltage. Conversely, when a dc voltage of the opposite polarity (but of a lesser magnitude) as the prepolarizing voltage is applied between the element's electrodes, the element experiences contraction in the direction of the applied voltage and expansion perpendicular to the direction of the applied voltage. In either case, the piezoceramic element returns to its original shape after the dc voltage is removed from the electrodes. Therefore, such a piezoceramic element can be used as an actuator insofar as the voltage applied across the element's plates cause the element's physical shape to undergo corresponding changes.
- This phenomenon also works in reverse. That is, after a piezoceramic element has been prepolarized, when a tension force is applied to the element in a direction parallel to the prepolarization field and/or a compression force is applied to the element perpendicular to the direction of the prepolarization field, the element is caused to expand in the perpendicular direction and contract in the parallel direction. This expansion and contraction, in turn, causes a voltage of the same polarity as the prepolarizing voltage (but of a lesser magnitude) to appear between the electrodes.
- FIG. 1 An example of a prior art acceleration-sensing device 100 which employs a pair of piezoceramic elements as a transducer is shown in Fig. 1.
- the acceleration-sensing device 100 includes a pair of support members 102a and 102b, a piezoceramic beam 104, and a pair of electrodes 106a and 106b.
- the piezoceramic beam 104 includes two distinct piezoceramic portions 104a and 104b, with a bottom surface 114 of the portion 104a being mated with a top surface 116 of the portion 104b.
- the beam 104 is sandwiched between the pair of support members 102a and 102b, and the electrodes 106a and 106b are attached, respectively, to a top surface 112 of the portion 104a and a bottom surface 118 of the portion 104b.
- Each of the portions 104a and 104b is polarized vertically in a direction perpendicular to the top and bottom surfaces of the portions 104a and 104b, but the two portions 104a and 104b are polarized in opposite directions.
- a center portion 108 of the beam 104 is held stationary by the support members 102a and 102b, and ends 110a and 110b of the beam 104 are permitted to move freely in response to acceleration of the support members 102a and 102b.
- the beam 104 is therefore caused to flex when an object (not shown) to which the support members 102a and 102b are attached is subjected to acceleration.
- the ends 110a and 110b of the beam 104 flex upward in such a situation, the portion 104a of the beam 104 is subjected to compression forces and is caused to contract (i.e., shorten), and the portion 104b is subjected to tension forces and is caused to expand (i.e., lengthen).
- the portions 104a and 104b are polarized in opposite directions, however, the voltage generated (in response to these compression and tension forces) between the top and bottom surfaces of the respective portions is of the same polarity. Therefore, the voltage produced between the electrodes 106a and 106b when the ends 110a and 110b of the beam 104 flexes upward is equal to a sum of the voltages generated between the top and bottom surfaces of the respective portions 104a and 104b.
- the portions 104a and 104b are polarized in opposite directions, the voltage produced between the electrodes 106a and 106b when the ends 1 10a and 110b of the beam 104 flex downward is also equal to a sum of the voltages generated between the top and bottom surfaces of the respective portions 104a and 104b, but is of an opposite polarity as the voltage produced when the ends 110a and 110b flex upward.
- Fig. 2 is a diagram showing another example of a prior art acceleration-sensing device 200 which employs a pair of piezoceramic elements as a transducer.
- the device of Fig. 2 is disclosed in U.S. Patent No. 5,063,782, which is hereby incorporated herein by reference. As shown in Fig.
- the acceleration-sensing device 200 includes an annular, electrically- conductive support member 202; a pair of circular piezoceramic elements 204a and 204b; a circular conductor 212; and a pair of electrodes 206a and 206b.
- the support member 202 supports an inner section 208 of each of the piezoceramic elements 204a and 204b and the circular conductor 212, such that an outer perimeter 210 of these components is permitted to flex upward and downward with respect to the inner section 208 (forming a spherical shape) when an object (not shown) to which the support member 202 is attached is accelerated.
- the electrode 206a is electrically connected to both a top surface 214 of the piezoceramic element 204a and a bottom surface 220 of the piezoceramic element 204b via the electrically conductive support member 202
- the electrode 206b is electrically connected to both a bottom surface 216 of the piezoceramic element 204a and a top surface 218 of the piezoceramic element 204b via the circular conductor 212.
- An annular insulating ring 222 is positioned between the support member 202 and the circular conductor 212 to electrically isolate each from the other.
- each of the piezoceramic elements 204a and 204b of the acceleration sensing device 200 is polarized in a direction perpendicular to its top and bottom surfaces so that each element generates a respective voltage between its top and bottom surfaces when the outer perimeter 210 of the device 200 is flexed.
- the elements 204a and 204b are polarized in the same direction.
- the expansion and contraction, or vice versa, of the respective top and bottom piezoceramic elements 204a and 204b causes voltages of the same polarity to appear (in parallel) between the electrodes 206a and 206b (via the circular conductor 212 and the support member 202).
- This configuration is disclosed as being advantageous because the piezoelectric effects of the two piezoceramic elements 204a and 204b are caused to cancel one another.
- acceleration sensors such as those shown in Figs. 1 and 2 function satisfactorily for their intended purposes, they tend to be relatively difficult and expensive to produce, and can easily become damaged. That is, because a relatively large quantity of piezoceramic material is required to produce the piezoceramic components of these devices, the cost of the piezoceramic material itself tends to make these types of acceleration sensors prohibitively expensive to use for many applications. Additionally, the process of producing and properly polarizing the relatively large piezoceramic elements required by such devices can be quite difficult and expensive. Further, because the shapes of the piezoceramic components used in these prior art acceleration sensors are required to be large in order to generate an appreciable voltage, these components tend to be fragile and can become damaged easily. What is needed, therefore, is an improved method for measuring acceleration.
- a method for monitoring acceleration of an object involves providing an apparatus including a non-conductive structure that flexes in response to acceleration of the object, and at least one transducer supported by the structure so as to generate a signal responsive to flexing of the structure.
- the apparatus is mounted to the object, and the acceleration of the object is monitored based upon the signal.
- a method for monitoring acceleration of an object involves providing an apparatus including a structure that flexes in response to acceleration of the object, and a first transducer supported by the structure so as to generate a signal responsive to flexing of the structure, wherein the structure and the first transducer are constructed and arranged such that a neutral axis passes through the structure when the structure flexes, and such that the neutral axis would still pass through the structure when the structure flexes if the first transducer was removed from the structure.
- the apparatus is mounted to the object, and the acceleration of the object is monitored based upon the signal.
- a method for monitoring acceleration of an object involves providing an apparatus including a structure that flexes in response to acceleration of the object, and at least one transducer supported by the structure so as to generate a signal responsive to flexing of the structure, the at least one transducer including first and second electrodes, each of the first and second electrodes being connected to a respective pair of conductors, the pair of conductors connected to the first electrode being alternately interdigitated with the pair of conductors connected to the second electrode, the apparatus further including a piezoelectric material disposed between adjacent ones of the conductors.
- the apparatus is mounted to the object, and the acceleration of the object is monitored based upon the signal.
- a method for monitoring acceleration of an object involves providing an apparatus including a structure, having a surface area, that flexes in response to acceleration of the object, and at least one transducer supported by the structure so as to generate a signal responsive to flexing of the structure, the at least one transducer covering less than one fourth of the surface area of the structure.
- the apparatus is mounted to the object, and the acceleration of the object is monitored based upon the signal.
- a method for monitoring acceleration of an object involves providing an apparatus including a structure that flexes in response to acceleration of the object, and at least one transducer having first and second ends and a middle portion therebetween, wherein the first and second ends of the at least one transducer are mechanically coupled to respective first and second locations on a surface of the structure, without the middle portion being mechanically coupled to the structure, so that the at least one transducer generates a signal responsive changes in a distance between the first and second locations that occur as the structure flexes.
- the apparatus is mounted to the object, and the acceleration of the object is monitored based upon the signal.
- a method for monitoring acceleration of an object involves providing an apparatus including a non-circular structure that flexes in response to acceleration of the object, and at least one transducer supported by the structure so as to generate a signal responsive to flexing of the structure.
- the apparatus is mounted to the object, and the acceleration of the object is monitored based upon the signal.
- a method for monitoring acceleration of an object involves providing an apparatus including a structure that flexes in response to acceleration of the object, and at least one capacitor having first and second plates, the at least one capacitor being configured and arranged on the structure to generate a signal between the first and second plates responsive to flexing of the structure.
- the apparatus is mounted to the object, and the acceleration of the object is monitored based upon the signal.
- a device for monitoring acceleration of an object includes an apparatus including a non-conductive structure that flexes in response to acceleration of the object, and at least one transducer supported by the structure so as to generate a signal responsive to flexing of the structure.
- the device further includes a controller, coupled to the apparatus to receive the signal therefrom, that monitors the acceleration of the object based upon the signal.
- a device for monitoring acceleration of an object includes an apparatus including a structure that flexes in response to acceleration of the object, and a first transducer supported by the structure so as to generate a signal responsive to flexing of the structure, wherein the structure and the first transducer are constructed and arranged such that a neutral axis passes through the structure when the structure flexes, and such that the neutral axis would still pass through the structure when the structure flexes if the first transducer was removed from the structure.
- the device further includes a controller, coupled to the apparatus to receive the signal therefrom, that monitors the acceleration of the object based upon the signal.
- a device for monitoring acceleration of an object includes an apparatus including a structure that flexes in response to acceleration of the object, and at least one transducer supported by the structure so as to generate a signal responsive to flexing of the structure, the at least one transducer including first and second electrodes, each of the first and second electrodes being connected to a respective pair of conductors, the pair of conductors connected to the first electrode being alternately interdigitated with the pair of conductors connected to the second electrode, the apparatus further including a piezoelectric material disposed between adjacent ones of the conductors.
- the device further includes a controller, coupled to the apparatus to receive the signal therefrom, that monitors the acceleration of the object based upon the signal.
- a device for monitoring acceleration of an object includes an apparatus including a structure, having a surface area, that flexes in response to acceleration of the object, and at least one transducer supported by the structure so as to generate a signal responsive to flexing of the structure, the at least one transducer covering less than one fourth of the surface area of the structure.
- the device further includes a controller, coupled to the apparatus to receive the signal therefrom, that monitors the acceleration of the object based upon the signal.
- a device for monitoring acceleration of an object includes an apparatus including a structure that flexes in response to acceleration of the object, and at least one transducer having first and second ends and a middle portion therebetween, wherein the first and second ends of the at least one transducer are mechanically coupled to respective first and second locations on a surface of the structure, without the middle portion being mechanically coupled to the structure, so that the at least one transducer generates a signal responsive changes in a distance between the first and second locations that occur as the structure flexes.
- the device further includes a controller, coupled to the apparatus to receive the signal therefrom, that monitors the acceleration of the object based upon the signal.
- a device for monitoring acceleration of an object includes an apparatus including a non-circular structure that flexes in response to acceleration of the object, and at least one transducer supported by the structure so as to generate a signal responsive to flexing of the structure.
- the device further includes a controller, coupled to the apparatus to receive the signal therefrom, that monitors the acceleration of the object based upon the signal.
- a device for monitoring acceleration of an object includes an apparatus including a structure that flexes in response to acceleration of the object, and at least one capacitor having first and second plates, the at least one capacitor being configured and arranged on the structure to generate a signal between the first and second plates responsive to flexing of the structure.
- the device further includes a controller, coupled to the apparatus to receive the signal therefrom, that monitors the acceleration of the object based upon the signal.
- FIG. 1 is a diagram showing an example of a prior art accelerometer that employs a piezoceramic transducer
- Fig. 2 is a diagram showing another example of a prior art accelerometer that employs a piezoceramic transducer
- Figs. 3A-B are illustrations showing how measurable characteristics of a beam can change when the beam is flexed
- Figs. 4A-C are illustrations of a transducer mounted on a flexible beam according to one embodiment of the present invention.
- Figs. 5A-C are illustrations of a transducer mounted on a flexible beam according to another embodiment of the present invention
- Figs. 6A-C are illustrations showing how transducers may be supported by a structure so as not to substantially affect the flexibility of the structure
- Fig. 7 is an illustration of a capacitor serving as a transducer mounted on a section of a circuit board according to another embodiment of the invention.
- Fig. 8 is a perspective view of a circuit board that incorporates an accelerometer according to one embodiment of the invention.
- Fig. 9 is a side view of the accelerometer portion of the circuit board of Fig. 8;
- Fig. 10 is a perspective view of the circuit board of Fig. 8 wherein a shear damper is disposed on a beam of the accelerometer portion of the circuit board according to one embodiment of the invention
- Fig. 11 is a perspective view of the circuit board of Fig. 8 wherein damping foam is disposed on a distal end of the beam of the accelerometer portion of the circuit board according to one embodiment of the invention
- Figs. 12A-B show top and side views of a piezoceramic element typically used in a speaker or microphone that may be used to measure acceleration of an object in accordance with one embodiment of the invention
- Fig. 13 illustrates how the piezoceramic element of Figs. 12A-B may be mounted in a base so as to measure acceleration of the base in accordance with one embodiment of the invention
- Fig 14 is a schematic diagram of a circuit in which a transducer used to monitor the flexing of a structure may be included in accordance with one embodiment of the invention. Detailed Description of the Invention
- a structure e.g., a beam or a disk
- one side of the structure is subjected to compression forces and is caused to contract
- the opposite side of the structure is subjected to tension forces and is caused to expand.
- Prior art accelerometer devices that employ transducers made of piezoceramic materials, e.g., the acceleration-sensing devices of Figs. 1 and 2, exploit this characteristic of flexible structures by using the flexible structures themselves to generate voltages indicative of amounts that the structures are flexed.
- the flexing of a flexible structure is monitored using a transducer that is attached to the flexible structure, rather than the flexible structure itself, to generate a signal indicative of the structure's flexing.
- the transducer when the flexible structure is attached to an object so that the structure flexes in response to acceleration of the object, the transducer generates a signal indicative of the object's acceleration.
- the transducer in such an embodiment may be any of numerous devices or substances capable of monitoring one or more physical characteristics of the structure that change as the structure flexes, and may be supported by the flexible structure in any of a number of ways to achieve this result.
- transducer refers to any device or substance that is capable of converting input energy of one form, e.g., physical energy, into output energy of another form, e.g., electrical energy.
- Figs. 3A-B show an example of a flexible structure that may be secured to an object so that the structure flexes when the object is accelerated.
- the flexible structure is a beam 302.
- the structure may be primarily two- dimensional (i.e., substantially flat), and be of any shape such as triangular, square, rectangular, trapezoidal, rhombic, oval, round, or the like, or may be three-dimensional and have any number of flat or curved surfaces of these or different shapes.
- one or more portions of the beam 302 may be secured to an object (not shown) whose acceleration is to be monitored so that the beam 302 is caused to flex when the object is accelerated.
- one end 308 of the beam 302 may be held by a support (not shown) that is attached to the object, and the other end 310 of the beam 302 may be left unsupported so that it can move with respect to the object when the object is accelerated.
- a middle portion 312 of the beam 302 may be secured to the object in some manner so that the two free ends 308 and 310 of the beam 302 are permitted to move with respect to the object when the object is accelerated.
- the beam 302 (or other structure) may also be flexed upwards, sideways, or in any other direction, and that the same or similar measurable characteristic(s) as those described below may be monitored for changes in such situations.
- One characteristic of the flexible beam 302 that may be monitored for changes when the shape of the beam 302 is altered from its unflexed position (Fig. 3A) to its flexed position (Fig. 3B) is the length of a particular section of one of the top 304 and bottom surfaces 306 of the beam 302. That is, when the beam 302 flexes (Fig.
- the surface 304 on the expanding side of the beam 302 is elongated, and the surface 306 on the contracting side of beam 302 is shortened.
- the length L0 across the middle portion of the beam 302 is identical to the lengths LI and L2 across the bottom and top surfaces 306 and 304, respectively.
- the length L0 across the middle portion of the beam 302 remains the same, but the length L2' across the top surface 304 increases and the length LI' across the bottom surface 306 decreases.
- the length L2' is caused to be longer than the length L0, and the length LI' is caused to be shorter than the length L0. Examples of how transducers may be supported by the beam 302 so as to measure these dimensional changes on the top and bottom surfaces 304 and 306 are described below.
- dimensional changes also take place internal to the beam 302 when the beam 302 flexes, and that, in alternative embodiments, such dimensional changes may be monitored by one or more properly placed transducers. However, the most significant dimensional changes occur on the top and bottom surfaces 304 and 306 of the beam 302.
- Another characteristic of the flexible beam 302 that may be monitored for changes when the shape of the beam 302 is altered from its unflexed position (Fig. 3A) to its flexed position (Fig. 3B) is the amount of tension or compression that is exerted at a particular location within the beam. Therefore, in some embodiments, one or more transducers may be strategically placed within the beam 302 so as to measure stress changes within the beam 302 that occur when the beam 302 flexes. Yet another characteristic of the flexible beam 302 that may be monitored for changes when the shape of the beam 302 is altered from its unflexed position (Fig. 3 A) to its flexed position (Fig. 3B) is the curvature of a particular section of one of the beam's surfaces.
- Figs. 4A-C show an example of how a transducer 404, e.g., a piezoceramic element, piezoresistive element, or the like, may be supported by a flexible structure, e.g., the beam 302 or any other suitable structure, so as to generate a signal responsive to changes in one or more characteristic of the structure that occur when the structure flexes. Therefore, when the beam 302 of the embodiment of Figs. 4A-C is attached to an object (not shown) so that the beam 302 is caused to flex in response to acceleration of the object, the output of the transducer 404 is indicative of the acceleration of the object.
- a transducer 404 e.g., a piezoceramic element, piezoresistive element, or the like
- a controller may be coupled to the transducer 404 to receive the output signal therefrom, and may monitor the signal to monitor the acceleration of the object.
- the term "controller” is intended to refer to any circuitry or component(s) used to monitor the signal from a transducer to monitor the acceleration of an object. The invention is not limited to the use of any particular type of controller to perform this monitoring function.
- the controller which is used to monitor the acceleration of the object may, for example, comprise a simple peak detection circuit. Alternatively, the controller used may comprise a microcontroller chip, or a personal computer, which receives the signal from the transducer.
- the transducer 404 is supported by the beam 302 so as to monitor changes in a surface dimension of the beam 302 (i.e., a distance between locations 406a and 406b on a top surface 410 of the beam 302), as well as changes in the curvature of the top surface 410, that occur when the beam 302 flexes.
- Figs. 4A-C (1) when the beam 302 is unflexed (Fig. 4A), there is a distance D2 between the locations 406a and 406b; (2) when the beam 302 is flexed downward (Fig. 4B), there is a distance D2' (which is longer than the distance D2) between the locations 406a and 406b; and (3) when the beam 302 is flexed upward (Fig. 4C), there is a distance D2" (which is shorter than the distance D2) between the locations 406a and 406b.
- D2 when the beam 302 is unflexed (Fig. 4A), there is a distance D2 between the locations 406a and 406b; (2) when the beam 302 is flexed downward (Fig. 4B), there is a distance D2' (which is longer than the distance D2) between the locations 406a and 406b; and (3) when the beam 302 is flexed upward (Fig. 4C), there is a distance D2" (which is shorter than the distance
- supports 408a and 408b e.g., metal or plastic members used to support the transducer 404 on the beam 302
- supports 408a and 408b are disposed on opposite ends of the transducer 404 and are fixedly secured to the locations 406a and 406b, respectively, so that the changes in the dimension D2 that occur when the beam 302 flexes also cause the length D3 of a lower portion 416 of the transducer 404 to change accordingly.
- the supports 408a and 408b when used, can take on any of numerous forms, and that the invention is not limited to any particular type of supports.
- Figs. 4A-C (1) when the beam 302 is unflexed (Fig. 4A), the lower portion 416 of the transducer 404 has a length D3; (2) when the beam 302 is flexed downward (Fig. 4B), the lower portion 416 of the transducer 404 has a length D3' (which is longer than the length D3); and (3) when the beam 302 is flexed upward (Fig. 4C), the lower portion 416 of the transducer 404 has a length D3" (which is shorter than the length D3).
- the transducer 404 in the embodiment of Figs. 4A-C therefore generates a signal responsive to such changes in the length D3 of its lower portion 416.
- the supports 408a and 408b and/or the transducer 404 are constructed and arranged so that a bottom surface 412 of the transducer 404 is held in direct contact with the top surface 410 of the beam 302 when the beam 302 flexes.
- the supports 408a and 408b are rigid enough and are secured to the top surface 410 in such a manner that the physical relationship between each of the supports 408a and 408b and the top surface 410 of the beam 302 is not altered when the beam 302 flexes. This configuration forces the curvature of the bottom surface 412 of the transducer 404 to mimic the curvature of the top surface 410 of the beam 302.
- an upper portion 414 of the transducer 404 elongates from a length D4 (Fig. 4A) to a length D4' (Fig. 4B) when the beam 302 is flexed downward, and shortens from the length D4 (Fig. 4A) to a length D4" (Fig. 4C) when the beam 302 is flexed upward. Therefore, in the embodiment of Figs. 4A-C, the signal generated by the transducer 404 also is responsive to changes in the length D4 of its upper portion 414 that occur as a result of the curvature of the bottom surface 412 of the transducer 404 mimicking the curvature of the top surface 410 of the beam 302.
- the curvature of the bottom surface 412 of the transducer 404 may also be caused to mimic the curvature of the top surface 410 of the beam 302 in a number of other ways.
- the entire bottom surface 412 of the transducer 404 may be fixedly secured, e.g., using an adhesive, to the top surface 410 to achieve such a result.
- the supports 408a and 408b may or may not also be used to secure the transducer 404 to the top surface 410.
- Figs. 5A-C show another example of how a transducer 404, e.g., a piezoceramic element, a piezoresistive element, or the like, may be supported by a flexible structure, e.g., the beam 302 or another suitable structure, so as to generate a signal responsive to changes in one or more characteristic of the structure that occur when the structure flexes. Therefore, when the beam 302 of the embodiment of Figs. 5A-C is attached to an object (not shown) so that the beam 302 is caused to flex in response to acceleration of the object, the output of the transducer 404 is indicative of the acceleration of the object.
- a transducer 404 e.g., a piezoceramic element, a piezoresistive element, or the like
- a controller may be coupled to the transducer 404 to receive the output signal therefrom, and may monitor the signal to monitor the acceleration of the object.
- the transducer 404 primarily monitors changes in a surface dimension of the beam 302, i.e., a distance between the locations 406a and 406b on the top surface 410 of the beam 302.
- the transducer 404 may be secured to the locations 406a and 406b on the top surface 410 of the beam 302 using the supports 408a and 408b, respectively, so that a gap 502 is formed between the bottom surface 412 of the transducer 404 and the top surface 410 of the beam 302.
- the supports 408a and 408b are made of a material that is flexible enough that the supports 408a and 408b are allowed to deform slightly when the beam 302 flexes.
- the change in the distance D2 along the top surface 410 of the beam 302 causes corresponding changes in the lengths of both the top 414 and bottom portions 416 of the transducer 404 (i.e., from D3 to D3', and from D4 to D4'), with the lengths of the top 414 and bottom portions 416 remaining substantially equal to one another when the beam 302 flexes (i.e., D3 ⁇ D4; D3' ⁇ D4').
- the beam 302 flexes upward (Fig.
- the amplitude of the voltage generated by the transducer 404 is affected primarily by the stretching and compression forces exerted on the ends of the transducer 404, and is affected only secondarily, if at all, by any bending forces exerted thereon.
- a relatively small transducer 404 may be mounted on a beam 302 (or another structure) having a relatively large surface area so that the transducer 404 covers only a small portion (e.g., one fourth, one tenth, one one-hundredth, or even one one-thousandth) of the surface area of the beam 302.
- the flexibility of the beam 302 may not be affected substantially by the presence of the transducer 404 thereon, and the flexibility of the unit including both the transducer 404 and the beam 302 is determined primarily by the flexibility of the beam 302. It should be appreciated that a similar result may also be accomplished in other ways.
- a transducer 404 may be employed which is substantially more flexible that the beam 302 (or another structure) on which it is mounted.
- the effect that each of a transducer 404 and a beam 302 (or another structure) has on the flexibility of a unit including both elements can be appreciated by examining the position of the so-called neutral axis (explained below) of the unit which passes through the unit when the unit flexes.
- Figs. 6A-C illustrate an example of how a flexible structure (e.g., the beam 302) and one or more transducers 404a-b may be configured and arranged such that mounting of each transducer 404 on the beam 302 does not substantially affect the position of a neutral axis 418 which passes through a unit 600 (including both the beam 302 and the transducer(s) 404) when the unit 600 is flexed.
- the neutral axis 418 of the unit 600 is the axis that (when the unit 600 is flexed) separates the portion 602 of the unit 600 that is subjected to tension forces from the portion 604 of the unit 600 that is subjected to compression forces.
- the location of the neutral axis 418 may be affected, for example, by the relative sizes, positions, and flexibilities of the beam 302 and the transducer(s) 404, and/or the manner in which such elements are interconnected.
- the position of the neutral axis 418 of the unit 600 is located at substantially the same location: (a) when both of the transducers 404a and 404b are attached to the beam 302 (Fig. 6A); (b) when only the transducer 404b is attached to the beam 302 (Fig. 6B); and (c) when neither of the transducers 404a and 404b is attached to the beam 302 (Fig. 6C). Therefore, the attachment or removal of either (Fig. 6B) or both (Fig. 6C) of the transducers 404a and 404b to or from the beam 302 does not substantially affect the position of the neutral axis 418 that passes through the unit 600.
- the neutral axis 418 passes only through the beam 302, and does not pass through either of the transducers 404a and 404b, regardless of whether either or both of the transducers 404a and 404b are attached to the beam 302.
- the other embodiments of the invention described herein may also incorporate this aspect of the invention.
- the transducer 404 and the beam 302 may be constructed and arranged such that the position of the neutral axis 418 passes only through the beam 302, regardless of whether the transducer 404 is mounted thereto.
- Fig. 7 shows an example of how a specific type of transducer, i.e., a multi-layer capacitor 708 having a piezoceramic dielectric 706, may be attached to a specific type of flexible structure, i.e., a section 710 of an organic-laminate circuit board material, so as to generate a signal responsive to changes in a specific characteristic of the circuit board section 710 (i.e., a distance between locations 706a and 706b on the circuit board's top surface 712) that occur when the circuit board section 710 flexes.
- a specific type of transducer i.e., a multi-layer capacitor 708 having a piezoceramic dielectric 706, may be attached to a specific type of flexible structure, i.e., a section 710 of an organic-laminate circuit board material, so as to generate a signal responsive to changes in a specific characteristic of the circuit board section 710 (i.e., a distance between locations 706a and 706
- the piezoceramic dielectric 706 of the capacitor 708 may generate a signal between pole conductors 714a-b of the capacitor 708 when it is compressed and/or stretched as the circuit board section 710 flexes. Therefore, when the circuit board section 710 is attached to an object (not shown) so that the circuit board section 710 is caused to flex in response to acceleration of the object, the signal generated between the pole conductors 714a and 714b of the capacitor 708 is indicative of the acceleration of the object.
- a controller (not shown) may be coupled to the capacitor 708 to receive the output signal therefrom, and may monitor the signal to monitor the acceleration of the object.
- a capacitor suitable for use as the capacitor 708 in the Fig. 7 embodiment may, for example, be selected from the GRM series of monolithic ceramic capacitors available from Murata Electronics Distributors. Such capacitors are on the order of two millimeters (mm) long, one millimeter wide, and one millimeter thick, and may be mass-produced at a very low cost (e.g, one-tenth of one cent each). It should be appreciated, of course, that other capacitors having the desired piezoelectric characteristics may alternatively be used, and that the invention is not limited to the particular type of capacitor shown and described. As shown in Fig.
- each of the plates PI and P2 of the capacitor 708 may include multiple layers of conductors PI A-P1C and P2A-P2B, with the conductors P1A-P1C of one plate PI being interdigitated with the conductors P2A-P2B of the other plate P2. While the capacitor 708 of Fig. 7 may function satisfactorily in the form in which it is originally produced by its manufacturer, it may be desirable to prepolarize the piezoceramic dielectric 706 of the capacitor 708 by placing a high, but non-destructive voltage (e.g., just below the capacitor's maximum voltage rating) between the capacitor's plates while maintaining the capacitor 708 at a temperature just below the Curie point of its ceramic dielectric 706.
- a high, but non-destructive voltage e.g., just below the capacitor's maximum voltage rating
- the circuit board section 710 of the Fig. 7 embodiment may be made of any of numerous types of materials, and the invention in not limited to any particular type of circuit board material.
- the circuit board section 710 is a section of an organic-laminate substrate.
- such a circuit board is considered to be a "non-conductive" structure, even though it may have electrically conductive circuit traces and/or power/ground planes thereon or therein which may or may not be coupled to the capacitor 710 or other transducer used therewith to monitor acceleration.
- the pole conductors 714a-b of the capacitor 708 electrically connect the plates PI and P2 of the capacitor 708 to conductors 704 of the circuit board.
- the pole conductors 714a-b are inserted into vias 702 in the circuit board and are soldered therein so as to make electrical contact with the conductors 704.
- the pole conductors 714a-b may be pins of a surface- mounted device.
- the circuit traces 704 in the Fig. 7 embodiment may be electrically connected to other components in a circuit in which the capacitor 708 is included so that the capacitor 708 is electrically coupled to such components.
- the characteristics of the capacitor 708 and the circuit board section 710, and the physical relationships therebetween, may be similar to the characteristics of and physical relationships between, the beams 302 or other surfaces and the transducers 404 used therewith discussed above in connection with Figs. 4-6.
- the relative flexibilities of the circuit board section 710 and the capacitor 708 are such that the neutral axis of the combination passes through the circuit board section 710 regardless of whether the capacitor 708 is attached thereto.
- Figs. 8 and 9 show perspective and side views, respectively, of an illustrative embodiment of the invention wherein a transducer 404 (e.g., a capacitor having a piezoceramic dielectric such as that described in connection with Fig. 7) is mounted on a section 710 of a circuit board 802.
- the circuit board 802 also includes a section 816 on which additional circuitry 804 is disposed.
- Such a structure may be formed, for example, by cutting or otherwise establishing a gap or slit 820 in the circuit board 802, or by prefabricating the circuit board 802 to include the beam-like section 710.
- a distal end 812 of the circuit board section 710 is permitted to move when the section 816 of the circuit board 802 (or an object to which the section 816 is mounted) is accelerated.
- Figs. 8 and 9 employs a circuit board 802 that includes separate beam-like 710 and circuitry 816 sections
- the portion 816 of the circuit board 802 that has the additional circuitry 804 mounted thereon may itself be used as a structure whose flexing is to be monitored.
- the circuit board (or other structure) whose flexing is to be monitored may, for example, be rectangular, circular, or any other shape.
- the structure whose flexing is to be monitored may, for example, be rectangular, circular, or any other shape.
- a pair of notches 808a and 808b are formed on the sides 818a and 818b of the circuit board section 710 near a location 810 along a longitudinal axis of the circuit board section 710 at which the transducer 404 is mounted.
- This placement of the notches 808a and 808b make the circuit board section 710 more narrow, and therefore more flexible, at the location 810 than at other locations along the circuit board section's longitudinal axis.
- inclusion of the notches 808a and 808b in the circuit board section 710 causes the circuit board section 710 to flex primarily at the location 810 when the section 816 of the circuit board 802 (or an object to which the section 816 is mounted) is accelerated.
- circuit board section 710 may be caused to flex primarily at the location 810 in alternative ways, and that the invention is not limited to the use of notches in the circuit board section 710 to cause such a result.
- a different thickness and/or type of material may be used to form a portion of the circuit board section 710 at the location 810 than is used to form the remainder of the circuit board section 710, or the portion of the circuit board section 710 at the location 810 may otherwise be physically or chemically altered or weakened so as to make that portion 810 more flexible than the remainder of the circuit board section 710.
- a weight 806 is disposed on the distal end 812 of the circuit board section 710 to increase a moment force that is applied about a proximal end 814 of the circuit board section 710 when the section 816 of the circuit board 802 (or an object to which the section 810 to attached) is accelerated.
- This placement of the weight 806 therefore increases the sensitivity of the accelerometer.
- the sensitivity of the accelerometer of Figs. 8 and 9 may also be increased or decreased by adjusting the length of the circuit board section 710 or by altering its flexibility. As illustrated in Fig.
- a pair of transducers 404a and 404b are mounted on opposite sides of the circuit board section 710 so that, whenever the bending of the circuit board section 710 causes one of the transducers 404a and 404b to be stretched, the other transducer 404 is compressed a corresponding amount, and vice versa.
- the transducers 404a and 404b together can generate a differential signal indicative of the acceleration of the portion 816 circuit board 802 (or an object to which the section 816 is attached).
- Fig. 10 shows how the embodiment of Figs.
- the shear damper 1002 may, for example, be made of a material (e.g., plastic, metal, glass, fiberglass, or the like) that is substantially more rigid than the circuit board section 710.
- the use of such a shear damper may, for example, reduce the vibration of the circuit board section 710, and/or cause the circuit board section 710 to flex primarily at the location 810 when the section 816 of the circuit board 802 (or an object to which the section 816 is attached) is accelerated.
- a shear damper 1002 of a particular shape i.e., the same shape as the circuit board section 710) is used in the Fig.
- Fig. 11 illustrates how the embodiments of Figs. 8-10 may be modified by disposing a mass of damping foam 1102, or the like, on the distal end 812 of the circuit board section 710.
- an opening 1104 in the damping foam 1102 surrounds the distal end 812 and the weight 806 such that inner surfaces 1106 and 1108 of the damping foam 1102 exert compression forces on the weight 806 and the distal end 812 to hold the damping foam 1102 in place on the distal end 812 of the circuit board section 710.
- the damping foam 1102 may, for example, be placed near or in contact with a casing (not shown) in which the circuit board 802 is disposed.
- the damping foam 1102 may contact the casing when the distal end 812 of the circuit board section 710 moves, and thereby dampen the motion of the distal end 812.
- the use of the damping foam 1102, or the like, in this manner may, for example, reduce the ringing in the signal output by the transducer 404.
- a disk-shaped element including a piezoelectric transducer or the like
- a disk-shaped element may be used to monitor acceleration of an object by properly mounting the element to the object and monitoring a signal output by the transducer included therein.
- Top and side-views of an example embodiment of a disk-shaped element 1200 that may be used for this purpose are shown in Figs. 12A-B, respectively.
- An example of one such disk-shaped element is part number CD1 IBB, manufactured by Taiyo Yuden. In the example shown in Figs.
- the disk-shaped element 1200 includes a flat, disk-shaped metal support 1202, and a flat, disk- shaped section of piezoceramic material 1210 concentrically arranged on a top surface 1204 of the support disk 1202.
- conductors 1206a-b may be connected, respectively, to a top surface 1208 of the piezoceramic disk 1210 and to a portion 1212 of the conductive support disk 1202.
- Fig. 13 illustrates an example of how the disk-shaped element 1200 of Fig. 12 may be supported by a base 1302 (i.e., an object whose acceleration is to be monitored) so that a signal generated between the conductors 1206a-b of the element 1200 is indicative of the acceleration of the base 1302 (the object).
- a base 1302 i.e., an object whose acceleration is to be monitored
- an outer portion 1310 of the support disk 1202 is secured to (e.g., using an epoxy or other substance or technique) a circular shelf 1306 of the base 1302.
- a cylindrical ledge 1312 drops off from the circular shelf 1306 to form a cavity 1308 within the base 1302.
- the support disk 1202 When the base 1302 (the object) is accelerated, the support disk 1202 is caused to flex such that a center portion 1304 of the support disk 1202 is caused to move up and down within the cavity 1308 of the base 1302 (as indicated by the arrows in Fig. 13). Because the piezoceramic disk 1210 generates a signal in response to the flexing of the support disk 1202, the signal generated between the conductors 1206a-b when the base 1302 (the object) is accelerated is indicative of the acceleration of the base 1302.
- a controller (not shown) may be coupled to the conductors 1206 to receive the output signal therefrom, and may monitor the signal to monitor the acceleration of the base 1302.
- the characteristics of the piezoceramic disk 1210 and the support disk 1202, and the physical relationships therebetween may be similar to the characteristics of, and the physical relationships between, the beams 302 or other surfaces and the transducers 404 used therewith discussed above in connection with Figs. 4-6.
- the relative flexibilities of the support disk 1202 and the piezoceramic disk 1210 may be such that the neutral axis of the combination passes through the support disk 1202 regardless of whether the piezoceramic disk 1210 is attached thereto.
- FIG. 14 is a schematic diagram showing an illustrative embodiment of an electronic circuit 1400 in which an element 1406 used as a transducer to monitor the flexing or other characteristics of a structure in response to acceleration of an object to which the structure is attached may be included.
- the element 1406 may correspond, for example, to the transducer 404 of Figs. 4-6 and 7-11, to the capacitor 708 of Fig. 7, or the disk-shaped element 1200 of Figs. 12 and 13.
- the components in the circuit 1400 (other than the element 1406) may, for example, be included in the additional circuitry 804 shown in Figs. 8, 10, and 11.
- the element 1406 has a well-defined capacitance associated therewith (e.g., it may be a capacitor having a piezoceramic or another piezoelectric dielectric), and is therefore used as a capacitor Cl in the circuit 1400, in addition to being used as a transducer.
- the circuit 1400 additionally includes an amplifier 1402, a controller 1404, capacitors C2-C5, and resistors R1-R5.
- the amplifier 1402 is coupled to the element 1406 to receive and amplify a signal generated thereby.
- the controller 1404 in the embodiment shown may, for example, include a microprocessor which includes an on-board analog-to-digital converter.
- the controller 1404 in such an embodiment may, for example, convert the output of the amplifier 1402 into a digital signal and analyze the digital signal to monitor the acceleration of an object.
- the purpose and function of each of the other components will be readily understood to one skilled in the art, and therefore will not be discussed further.
- the circuit 1400 is disposed on a circuit board (e.g., the circuit board 802 of
- any circuit board may conceivably be modified to sense acceleration of an object to which it is attached simply by properly placing a transducer on the circuit board so as to generate a signal responsive to the flexing of the circuit board.
Abstract
Description
Claims
Priority Applications (1)
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AU80333/00A AU8033300A (en) | 1999-08-24 | 2000-08-24 | Low-cost accelerometer |
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US09/382,049 US6336365B1 (en) | 1999-08-24 | 1999-08-24 | Low-cost accelerometer |
US09/382,049 | 1999-08-24 |
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WO2001014889A2 WO2001014889A2 (en) | 2001-03-01 |
WO2001014889A3 WO2001014889A3 (en) | 2001-08-30 |
WO2001014889A9 true WO2001014889A9 (en) | 2001-09-20 |
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PCT/US2000/040729 WO2001014889A2 (en) | 1999-08-24 | 2000-08-24 | Low-cost accelerometer |
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AU (1) | AU8033300A (en) |
WO (1) | WO2001014889A2 (en) |
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