Patent Application
20170205440
Piezoelectric transducers are used to convert between mechanical deformations and electrical signals. Piezoelectric transducers can produce a voltage, a current, or a charge in response to changes in pressure, acceleration, temperature, strain, or force, etc. Such transducers are used to monitor processes or deformable members. Piezoelectric transducers can be used in the opposite fashion, producing mechanical movement in response to an actuating signal. Such piezoelectric transducers can be used to perform mechanical actuation of movable members. Micro sized piezoelectric transducers are used in miniature sized devices and systems to perform precise mechanical operations or to sense mechanical conditions.
For piezoelectric accelerometer applications, a built-in self-test capability can be helpful. For example, in aerospace application, the built-in test capability can permit the pilot to check if the accelerometer is in working condition before an airplane takes off. Piezoelectric transducers may have mechanical deformation/sense signal relations or excitation/response relations. Such relations may change over time and/or temperature etc. Built-in test capability can detect changes in the excitation/response relation of a piezoelectric transducer. Bulk-mode piezoelectric accelerometers typically require large actuation voltage to cause measurable deformations. Micro Electro Mechanical System (MEMS) piezoelectric accelerometers, however, can produce measureable mechanical deformations using relatively modest voltages.
An accelerometer includes a substrate having a proofmass and at least one coupling member. The coupling member(s) is configured to mechanically couple the accelerometer to a device to be tested. The accelerometer includes a first MEMS piezoelectric transducer mounted to one of the one coupling member(s) of the substrate. The first MEMS piezoelectric transducer is configured to deform the at least one coupling member in response to a first electrical signal received by the piezoelectric transducer. The accelerometer includes a second MEMS piezoelectric transducer mounted to one of the coupling member(s) of the substrate. The second MEMS piezoelectric transducer is configured to provide a second electrical signal in response to deformation of the at least one coupling member of the substrate. The accelerometer also includes a self-test module configured to generate the first electrical signal and to receive the second electrical signal. The self-test module is configured to compare the received second electrical signal to a reference signal and configured to generate a test result based upon the comparison.
In some embodiments, an accelerometer includes a substrate having a proofmass and an elastically deformable coupling member. The accelerometer includes a first MEMS piezoelectric transducer configured to induce a mechanical deformation of the elastically deformable coupling member in response to an electrical excitation signal received by the first MEMS piezoelectric transducer. The accelerometer includes a second MEMS piezoelectric transducer electrically isolated from but mechanically coupled to the first piezo electric transducer via the elastically deformable coupling member. The second MEMS piezoelectric transducer is configured to generate an electrical response signal in response to mechanical deformation of the elastically deformable coupling member. The accelerometer also includes a self-test module configured to generate the electrical excitation signal and to receive the electrical response signal. The self-test module is further configured to generate a sensor test result based upon a comparison between the received electrical response signal and a reference signal.
Mechanical motion and/or vibration of a device can be measured using an accelerometer. An exemplary accelerometer may have a proofmass coupled to an elastically deformable coupling member. The elastically deformable coupling member may then couple the accelerometer to the device to be tested for vibration and/or mechanical motion. Vibration and/or mechanical motion of the device to which the accelerometer is coupled can be measured by measuring an amount of deformation of the elastically deformable coupling member. Using Micro Electro Mechanical System (MEMS) process technologies, thin-film piezoelectric transducers can be deposited on the elastically deformable coupling member. Such MEMS piezoelectric transducers can be used to actuate a mechanical deformation of the elastically deformable coupling member to which it is attached and/or to sense an amount of deformation of that same elastically deformable coupling member. By attaching two MEMS piezoelectric transducers—one to actuate deformation and one to sense deformation—to an accelerometer, built-in self testing of the accelerometer can be facilitated. Built-in self testing can be performed by using an actuating MEMS piezoelectric transducer to generate a dynamic movement of the proofmass using a low voltage actuation signal, while using a sensing MEMS piezoelectric transducer to electrically sense such movement.
Using MEMS processing techniques, thin film piezoelectric films such as AN and/or PZT can be deposited using various deposition techniques such as sputtering, Chemical Vapor Deposition (CVD), and/or sol-gel coating. Such thin piezoelectric films can have thicknesses ranging from submicrons to tens of microns. These thin piezoelectric films and corresponding electrodes can be patterned to create piezoelectric transducers for mechanical actuation and/or electrical sensing of mechanical deformations.
Both actuating and sensing MEMS piezoelectric transducers can be mounted on a coupling member that can function as a spring of a spring-mass system. One or more coupling members may be used, each coupling member connected to the proofmass. These coupling members can be isolated from each other, semi-isolated from each other, or connected to one another. The actuating MEMS piezoelectric transducer and the sensing MEMS piezoelectric transducer can be located either on the same coupling member or on different coupling members. When located on different coupling members, an electric sensing signal might be better isolated from an electrical activation signal resulting in a sensing signal that is purely induced by the proofmass motion. MEMS piezoelectric transducers and their associated coupling member configurations can be distributed symmetrically around the proofmass to reduce cross-talk noise between actuating and sensing MEMS piezoelectric transducers.
Coupling members 14a and/or 14b are configured to mechanically couple Accelerometer 10 to a device to be tested, such as a fan blade of an aircraft engine. When the fan blade is accelerated, points of attachment of coupling members 14a, 14b are substantially identically accelerated. But proofmass, having inertia, may respond to such acceleration in a lagging manner. The difference in motion between the point of attachment of coupling members 14a, 14b and proofmass 12 may cause deformation of coupling members 14a, 14b therebetween, as coupling members 14a, 14b have vertical thickness dimension 32 that is relatively small. Thus the geometry of Accelerometer 10 can be configured to measure acceleration in either direction of vertical axis 20 or transverse axis 18. Coupling members 14a, 14b may behave as a spring, for example, and may have a spring coefficient that characterizes their deformations.
Piezoelectric transducers 28a, 28b, 30a, 30b may be either single purpose of dual purpose transducers. For example, for vertical axis 20 direction sensing and actuation, piezoelectric transducers 28a, 28b may be dedicated to producing mechanical deformation of coupling members 14a, 14b, respectively, in response to excitation signals received by piezoelectric transducers 28a, 28b. And piezoelectric transducers 30a, 30b may be dedicated to generating electrical response signals in response to the induced deformation of coupling members 14a, 14b, respectively. In some embodiments, piezoelectric transducers 28a, 28b and piezoelectric transducers 30a, 30b may have the opposite roles as described above.
For transverse axis 18 direction built-in testing, piezoelectric transducers 28a, 30b may be dedicated to producing mechanical deformation of coupling members 14a, 14b, respectively, in response to excitation signals received by piezoelectric transducers 28a, 30b. Piezoelectric transducers 28b, 30a may be dedicated to generating electrical response signals in response to the induced deformation of coupling members 14a, 14b, respectively. In some embodiments, piezoelectric transducers 28a, 30b and piezoelectric transducers 28b, 30a may have the opposite roles than those described above. And in some embodiments, transducers 28a, 28b, 30a, 30b can each be used at different times in both of the manners as described above.
Piezoelectric transducers 80a, 80b, 78a, 78b may also be either single purpose or dual purpose transducers in a similar manner as described for depicted embodiment of
Self-testing and measurement system 104 includes microprocessor 116, memory 118, response reference library 120, signal generator 122 and input/output interface 124. Memory 118 includes program memory 126 and data memory 128. Microprocessor 116 is in bidirectional electrical communication with memory 118, reference library 120, input/output interface 124 and signal generator 122. Signal generator 122 is also in electrical communication with input/output interface 124. Input/output interface 124 is in electrical communication with accelerometer element 102.
Piezoelectric transducers 110, 112 are mechanically coupled to one another via coupling member 108. Coupling member 108 may also be used to couple accelerometer element 102 to a body to be monitored by accelerometer element 102. If coupling member 108 is deformed, both piezoelectric transducers 110, 112 may generate an electrical response signal. These electrical response signals may correlate one to another. In a test mode, self-testing and measurement system 104 may generate an excitation signal. The excitation signal may be output to a first one of piezoelectric transducers 110, 112. The first one of piezoelectric transducers 110, 112 may then deform in response to the received excitation signal.
Coupling member 108 may deform in response to the deformation of the first one of piezoelectric transducers 110, 112, due to an intimate mechanical connection therebetween. A second one of piezoelectric transducers 110, 112 may deform in response to the deformation of coupling member 108, due to an intimate mechanical connection therebetween. The second of piezoelectric transducers 110, 112 may then generate an electrical response signal in response to its own deformation. Self-testing and measurement system 104 then receives the electrical response signal generated by the second one of piezoelectric transducers 110, 112.
Self-testing and measurement system 104 may then retrieve a reference signal and compare the received electrical response signal with the retrieved reference signal. Self-testing and measurement system 104 may then generate a pass/fail flag in response to the comparison between the received electrical response signal with the retrieved reference signal. This testing operation can be repeated, using each of piezoelectric transducers 110, 112 in the opposite manner as described above.
At step 210, microprocessor 116 retrieves reference signal REF(I) from reference signal library 120. Then at step 212, microprocessor compares received response signal R(I) with retrieved reference signal REF(I). If received response signal R(I) is not within predetermined limits of retrieved reference signal REF(I), then method 200 proceeds to step 214. At step 214, microprocessor sets pass/fail flag P/F to zero and the method ends. If, however, at step 212, received response signal R(I) is within predetermined limits of retrieved reference signal REF(I), then method 200 proceeds to step 216. At step 216, microprocessor 116 increments index I. Then at step 218, microprocessor compares index I with a maximum index IMAX. If index I is equal to IMAX, then method 200 proceeds to step 220. At step 22, microprocessor sets pass/fail flag P/F to one and the method ends. If, however, at step 218, index I is not equal to IMAX, then method returns to step 204, at which step microprocessor 116 retrieves new amplitude E(I) and frequency f for use in generating a next excitation signal.
In some embodiments, an excitation/response relation will be substantially independent of frequency between a minimum frequency and a maximum frequency. In some embodiments the maximum frequency will be, for example, about 10 kHz, 100 kHz, or about 1 MHz.
The following are non-exclusive descriptions of possible embodiments of the present invention.
An accelerometer includes a substrate having a proofmass and at least one coupling member. The at least one coupling member is configured to mechanically couple the accelerometer to a device to be tested. The accelerometer includes a first MEMS piezoelectric transducer mounted to one of the at least one coupling member of the substrate and configured to deform the at least one coupling member in response to a first electrical signal received by the piezoelectric transducer. The accelerometer includes a second MEMS piezoelectric transducer mounted to one of the at least one coupling member of the substrate and configured to provide a second electrical signal in response to deformation of the at least one coupling member of the substrate. The accelerometer also includes a self-test module configured to generate the first electrical signal and to receive the second electrical signal. The self-test module is configured to compare the received second electrical signal to a reference signal and configured to generate a test result based upon the comparison.
The accelerometer of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: i) a third MEMS piezoelectric transducer mounted to one of the at least one coupling member of the substrate and configured to deform the at least one coupling member in response to a first electrical signal received by the piezoelectric transducer; and ii) a fourth MEMS piezoelectric transducer mounted to one of the at least one coupling member of the substrate and configured to provide a second electrical signal in response to deformation of the at least one coupling member of the substrate.
A further embodiment of the foregoing accelerometer, wherein the proofmass of the substrate may be substantially cylindrical, and the at least one coupling member of the substrate may be formed as a single annular coupling member projecting radially outward from the proofmass of the substrate. A further embodiment of any of the foregoing accelerometers, wherein the first and second MEMS piezoelectric transducers may be substantially circular. A further embodiment of any of the foregoing accelerometers, wherein the at least one coupling member of the substrate may include two coupling members. The first MEMS piezoelectric transducer may be located on a first one of the two coupling members. The second MEMS piezoelectric transducer may located on a second one of the two coupling members.
A further embodiment of any of the foregoing accelerometers, wherein the first and second MEMS piezoelectric transducers may be located on a same one of the at least on coupling member. A further embodiment of any of the foregoing accelerometers, wherein the first and second MEMS piezoelectric transducers may be located on a first one and second one of the at least one coupling member, respectively. A further embodiment of any of the foregoing accelerometers, wherein the proofmass of the substrate may have a substantially orthorhombic shape, and the at least one coupling member of the substrate may include two coupling members projecting from opposite sides of the orthorhombic shaped proofmass.
A further embodiment of any of the foregoing accelerometers, wherein the at least one coupling member of the substrate may be configured to permit motion of the proofmass in a unidirectional manner. A further embodiment of any of the foregoing accelerometers, wherein the accelerometer may have an excitation/response relation that is substantially independent of frequency between a low-frequency limit and a high-frequency limit. A further embodiment of any of the foregoing accelerometers, wherein the first and second MEMS piezoelectric transducers comprise aluminum nitride. A further embodiment of any of the foregoing accelerometers, wherein the second MEMS piezoelectric transducer may be adjacent to the first piezoelectric transducer.
In some embodiments, an accelerometer includes substrate having a proofmass and an elastically deformable coupling member. The accelerometer includes a first MEMS piezoelectric transducer configured to induce a mechanical deformation of the elastically deformable coupling member in response to an electrical excitation signal received by the first MEMS piezoelectric transducer. The accelerometer includes a second MEMS piezoelectric transducer electrically isolated from but mechanically coupled to the first piezo electric transducer via the elastically deformable coupling member. The second MEMS piezoelectric transducer is configured to generate an electrical response signal in response to mechanical deformation of the elastically deformable coupling member. The accelerometer also includes a self-test module configured to generate the electrical excitation signal and to receive the electrical response signal. The self-test module is further configured to generate a sensor test result based upon a comparison between the received electrical response signal and a reference signal.
A further embodiment of the foregoing accelerometer, wherein the electrical excitation signal is a first electrical excitation signal, and the second MEMS piezoelectric transducer may be further configured to induce a mechanical deformation of the elastically deformable coupling member in response to a second electrical excitation signal received by the second MEMS piezoelectric transducer. A further embodiment of any of the foregoing accelerometers, wherein the electrical response signal is a first electrical response signal, and the first MEMS piezoelectric transducer is further configured to generate a second electrical response signal in response to mechanical deformation of the elastically deformable coupling member.
A further embodiment of any of the foregoing accelerometers, wherein the sensor test result is a first sensor test result and the reference signal is a first reference signal. The self-test module may be further configured to generate the second electrical excitation signal and to receive the second electrical response signal. The self-test module may be further configured to generate a second sensor test result based upon a comparison between the received second electrical response signal and a second reference signal.
A further embodiment of any of the foregoing accelerometers, wherein the elastically deformable coupling member may be configured to permit motion of the proofmass in a unidirectional manner. A further embodiment of any of the foregoing accelerometers, wherein the accelerometer may have an excitation/response relation that is substantially independent of frequency between a low-frequency limit and a high-frequency limit. A further embodiment of any of the foregoing accelerometers, wherein the second MEMS piezoelectric transducer may be adjacent to the first piezoelectric transducer.
While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
