US2808522A - Accelerometer - Google Patents

Description

United States Patent ACCELEROMETER Abraham I. Dranetz, Metuchen, N. J., assignor to Gulton Industries, Inc., a corporation of New Jersey Application February 26, 1953, Serial No. 339,113

19 Claims. (Cl. 310--8.2)

This invention relates to accelerometers for producing a voltage in accordance with vibration or the like.

The principal object of this invention is to provide an improved accelerometer which has smallest possible volumetric size and weight for a given combination of electrical impedance, sensitivity and resonant frequency, which has the highest natural frequency for a given combination of sensitivity and electrical impedance, which has the highest sensitivity for a given combination of resonant frequency and electrical impedance, which is rugged in construction, which reduces high stress concentration, and which is simple and inexpensive to manufacture.

Briefly, the accelerometer of this invention includes a supporting rod which is secured at one end to a vibrating member so as to be longitudinally vibrated or moved by the vibrating member. A substantially disc shaped piezoelectric member, having planar dimensions substantially greater than the transverse dimensions of the rod, is carried by the other end of the rod in a plane substantially perpendicular to the longitudinal axis of the rod and extending radially in all directions beyond the rod so as to be flexed by vibration of the rod to produce a voltage in accordance with the vibration thereof. The vibrating rod affords a one point suspension for the piezoelectric member, and since the distributed mass of the piezoelectric member tends to maintain the outer peripheral edge thereof stationary, the piezoelectric member is radially flexed from its inner portion to its outer portion by the rod vibration. The radial flexing of the piezoelectric member, as into and out of an umbrella shape, produces a voltage in accordance with the rod vibration and yet localized or concentrated stresses in the piezoelectric member are eliminated or materially reduced. These uniform stresses in the piezoelectric member extend substantially radially in all directions from the center thereof to the outer edge thereof and provide maximum transducing efliciency.

The piezoelectric member may take various forms, a particularly satisfactory one including one or more titanate ceramic sheets provided with electrodes and preferably permanently polarized, the flexing of the polarized titanate ceramic sheets producing the voltage. In one form of this invention the piezoelectric member includes a substantially disc shaped member of metal or the like formed on the end of the rod and a titanate ceramic sheet having electrodes and overlying and secured to the disc shaped member. This form of the invention is capable of withstanding impacts and is particularly useful where the withstanding of high impacts is of more importance than high voltage sensitivity.

In another form of this invention the piezoelectric member includes at least one substantially disc shaped titanate ceramic sheet which is provided with electrodes and which is secured to the end of the rod as by soldering. This form will not withstand as high impacts as the aforementioned form but will provide higher voltage sensitivity. Preferably two titanate ceramic sheets are bonded together, as by soldering, to provide a rugged construc- 2,808,522 Patented Oct. 1, 1957 tion and increase the impact withstanding characteristics. The exposed faces of the titanate ceramic sheets are provided with electrodes. The exposed electrodes may be conductively coupled together during polarization and the ceramic sheets polarized in opposite directions from the soldered junction. After polarization this connection is removed, and upon flexing, a voltage is produced between these electrodes of a polarity depending upon the direction of flexing. A high voltage sensitivity is thus produced. If double the capacitance is desired at the expense of one half the voltage sensitivity, the polarizing voltage is applied between the outer electrodes. After polarization the outer electrodes are connected electrically, the center electrode is grounded. Flexing of the titanate ceramic sheets thus produce a voltage between the inner electrodes and the conductively coupled outer electrodes with a polarity depending upon the direction of flexing. If higher voltage sensitivities are desired at the expense of capacitance, the electrodes may be formed of concentric electrode rings and the radial voltage used. Two or more rings may be used on either or both titanate ceramic sheets in order to obtain proper capacitance.

A distributed or peripheral mass may be located on the piezoelectric member at a distance from the center thereof for controlling the stress of the piezoelectric member. The piezoelectric member may also be enclosed in a housing for shielding the same. The housing may be carried by the rod and preferably it is resiliently supported thereon so as substantially to reduce the mechanical coupling therebetween to isolate housing resonances from the rod. If desired, damping means may be provided for the piezoelectric member. The damping means may take several forms, such as, fluid damping material located in the housing about the piezoelectric member, or a magnetic damping arrangement including a magnetic member carried by the housing for producing a magnetic field and a conducting ring member carried by the piezoelectric member in the magnetic field.

Further objects of this invention reside in the details of construction of the accelerometer and in the cooperative relationships between the component parts thereof.

Other objects and advantages of this invention will become apparent to those skilled in the art upon reference to the accompanying specification, claims and drawings in which:

Figure l is a vertical sectional view through one form of the accelerometer of this invention and taken substantially along the line 1-1 of Figure 2.

Figure 2 is a horizontal sectional View taken substantially along the line 2-2 of Figure 1.

Figure 3 is a vertical sectional view similar to Figure l but illustrating another form of the invention.

Figure 4 is a perspective view of the piezoelectric member utilized in the form of the invention illustrated in Figure 3.

Figure 5 is a vertical sectional view similar to Figure 1 but illustrating a further form of the invention.

Figure 6 is a perspective view of the piezoelectric member utilized in the form of the invention illustrated in Figure 5.

Figure 7 is a vertical sectional view similar to Figure 1 but illustrating still another form of the invention.

Figure 8 is a perspective view of the piezoelectric member utilized in the form of the invention illustrated in Figure 7.

Figure 9 is a perspective view of a further form of the piezoelectric member.

Referring first to Figures 1 and 2, one form of the accelerometer of this invention is generally designated at 10. It includes a supporting rod 11 which is provided with screw threads 12 at one end for securing the same to a vibrating member 13 so as to be longitudinally vibrated by the vibrating member. The supporting rod 11, if desired, may be of substantially uniform cross sectional dimension or it may have an upwardly extending portion 14 of reduced diameter. A substantially disc shaped member 15 is formed on the upper end of the reduced portion 14 of the supporting rod 11 and preferably is formed integrally therewith. The substantially disc shaped member 15 may be provided with a distributed or peripheral mass 16 at a distance from the center thereof for the purpose of controlling the stress of the substantially disc shaped member 15. The substantially disc shaped member 15 may be substantially circular or it may be square, triagonal, hexagonal, octagonal or other similar shape. The peripheral mass 16, which is shown to be integral with the substantially disc shaped member 15 is located at the outer edge of the substantially disc shaped member 15 although it may be located inwardly therefrom if so desired.

Overlying the substantially disc shaped member 15 and secured thereto is a substantially disc shaped piezoelectric member. The piezoelectric member may be of any suitable construction but preferably it is formed from a titanate ceramic material. Here, the piezoelectric member is formed from a sheet of substantially pure barium titanate ceramic 18. This titanate ceramic sheet 18 has a pair of electrodes 19 and 20 secured to opposite faces thereof. The electrodes 19 and 20 may be formed on the titanate ceramic sheet 18 by applying silver paste to the opposite faces thereof and then firing the paste to form a good bond between the electrodes and the titanate ceramic sheet. The electrode 20 of the titanate ceramic sheet 18 is secured to the substantially disc shaped member 15 in any suitable manner, such as by soldering the same thereto. Thus, the electrode 20 in addition to being bonded to the substantially disc shaped member 15 is also electrically conductively coupled thereto. The titanate ceramic disc 18 is preferably permanently polarized to make the same piezoelectric. In this connection one terminal of a D. C. voltage source is connected to the electrode 19 and the other terminal thereof is connected to the electrode 20, such as through the substantially disc shaped member 15 which is preferably made of metal. A sufliciently high D. C. voltage is applied for a sufficiently long time so as permanently to polarize the titanate ceramic sheet 18. Since the substantially disc shaped member 15 is secured to the titanate ceramic sheet 18 through the electrode 20, it may be considered as a part of the piezoelectric member.

The piezoelectric member may be enclosed by a housing for shielding purposes, the housing including a bottom wall 22, a side wall 23 and a removable cover 24. The bottom wall 22 may be made integral with the supporting rod 11 and is preferably provided with a groove 25 adjacent the supporting rod 11 in order to provide a resilient connection between the housing and the supporting rod to reduce the mechanical coupling therebetween. The housing may also be provided with a quick disconnect cable junction having an outer sleeve portion 26 secured and conductively coupled thereto and an insulated inner terminal 27. The outer sleeve 26 is therefore conductively coupled with the electrode 20 and the inner terminal 27 is connected by a lead 28 to the electrode 19.

The supporting rod 11 affords a one point suspension for the piezoelectric member. When the vibrating member 13 vibrates, the supporting rod 11 correspondingly vibrates in a longitudinal direction and since the distributed mass of the piezoelectric member tends to maintain the outer peripheral edge thereof substantially stationary, the piezoelectric member is radially flexed from its inner portion to its outer portion by the vibration of the supporting rod. This radial flexing of the piezoelectric member, as into and out of an umbrella shape, produces a voltage in accordance with the vibration of the supporting rod. Uniform stresses are produced in the piezoelectric member which extend substantially radially in all directions from the center thereof to the outer edge thereof to provide maximum transducing efliciency and to eliminate or materially reduce localized or concentrated stresses. The voltage produced in this manner by the piezoelectric member in accordance with the vibration of the vibrating member 13 appears across the elements 26 and 27 of the quick disconnect cable junction and these voltages are in direct accordance with the vibration of the vibrating member 13. The distributed or peripheral mass 16 controls the stress of the piezoelectric member. Because the titanate ceramic sheet 18 is carried and backed by the substantially disc shaped member 15 it may withstand high impacts and is particularly useful where the withstanding of high impacts is of more importance than high voltage sensitivity. Because the housing provided with the groove 25 is resiliently carried by the supporting rod 11, housing resonances are substantially isolated from the supporting rod. If desired, damping means may be provided for the piezoelectric member, and in this connection the housing may be provided with a fluid damping material about the piezoelectric member. This fluid damping material effectively operates to dampen the movement of the piezoelectric member.

The form of the invention illustrated in Figures 3 and 4 and generally designated at 30 is very much like that illustrated in Figures 1 and 2, the essential difference between the two forms of the invention residing in the manner of damping the piezoelectric member. In Figures 3 and 4 a magnet 31 is located in the housing for the purpose of producing a magnetic field. The magnet 31 may be located in the housing by the use of a plastic material 32 such as pitch or the like. The peripheral mass 16 which is a conducting ring member is located within the magnetic field produced by the magnet 31. Thus, motion of the piezoelectric member is magnetically retarded and damped. Outside of this difference the accelerometer 30 of Figures 3 and 4 operates in the same manner as the accelerometer 10 of Figures 1 and 2. In Figures 1 to 4 like reference characters have been utilized for like parts.

The accelerometer generally designated at 35 in Figures 5 and 6 is very much like the accelerometers 10 and 30 of Figures 1 to 4 and like reference characters have been utilized for like parts. The essential difference between the accelerometer 35 and the accelerometers 10 and 30 resides in the construction of the piezoelectric member. Here, the piezoelectric member includes a pair of substantially pure barium titanate ceramic sheets 36 and 37. The titanate ceramic sheet 36 is provided with a pair of electrodes 39 and 4t and the titanate ceramic sheet 37 is provided with a pair of electrodes 38 and 40, the electrodes being applied to the sheets in the manner described above. The two titanate ceramic sheets 36 and 37 are secured together as by soldering together the electrodes 40 thereof. The piezoelectric member thus includes an inner electrode 40 and a pair of outer electrodes 38 and 39. The piezoelectric member including the titanate ceramic sheets 36 and 37 is substantially disc shaped and may take the various shapes as described above in connection with Figures 1 and 2. The center of the piezoelectric member is secured to the end of the reduced portion 14 of the supporting rod 11 as by soldering to a small enlargement 41 thereon. Thus, here as the supporting rod 11 is longitudinally vibrated, the piezoelectric member is flexed in the same manner as described above, but here the flexing is more pronounced.

The outer electrodes 38 and 39 are conductively coupled together as by means of a lead 42 and they are conductively coupled to the sleeve member 26 of the quick disconnect cable junction through the supporting rod 11 and the housing. The inner or central electrode 40 is connected by a lead 43 to the terminal 27 of the quick disconnect cable junction. The titanate ceramic sheets 36 and 37 of the piezoelectric member are preferably permanently polarized. During polarization, electrodes 38 and 39 are not connected, and one terminal of a D. C. voltage source is applied to the electrode 38 and the other terminal is applied to the electrode 39. A sufliciently high D. C. voltage is applied for a sufliciently long time so as permanently to polarize the titanate ceramic sheets 36 and 37. These sheets are therefor polarized in series. After polarization, electrodes 38 and 39 are connected together and to the case ground, so that flexing of the piezoelectric member produces voltage across the sleeve 26 and terminal 27 in accordance with the vibrations of The vibrating member 13. This electrode arrangement and manner of polarizing the piezoelectric member provides a relatively high capacitance and a thoroughly satisfactory voltage sensitivity. The manner of operation of the accelerometer is substantially the same as the. described above in connection with the accelerometer 10, the essential difference being that high voltage sensitivity is here provided although the accelerometer 35 is not capable of withstanding as high impacts. Here also the piezoelectric member may be damped with a suitable fluid damping material as described above in connection with the accelerometer 10.

The accelerometer generally designated at 45 in Figures 7 and 8 is very much like the accelerometer 35 of Figures 5 and 6 and like reference characters have been utilized for like parts. The essential differences between the two accelerometers are in the manner of polarizing the piezoelectric member and in controlling the flexing thereof. Here, the electrode 39 is conductively coupled to the sleeve 26 of the quick disconnect cable junction through the supporting rod and the housing and the electrode 38 is connected by a lead 46 to the terminal '27 of the quick disconnect cable junction. The electrode has no external electrical connection. The piezoelectric member of Figures 7 and 8 is polarized by first electrically connecting electrodes 38 and 39 and then applying a sufliciently high D. C. voltage across this junction and electrode 40 for a sufliciently long period of time so that the titanate ceramic sheets 36 and 37 are permanently polarized oppositely. Then this connection to electrode 40 is removed and the connection to electrodes 38 and 39 are separated. After this electrode 39 is connected to sleeve 26 and electrode 38 is connected to terminal 27. In this arrangement therefor the voltage sensitivity is substantially doubled at the expense of substantially one half of the capacitance. A distributed mass 47 which may be in the form of a ring is suitably secured to the piezoelectric member as by soldering the same to the electrode 39. This mass 47 operates to control the stressing of the piezoelectric member. This mass 47 may be located at any desired position with respect to the piezoelectric member either below or above or at the periphery or at a place within the periphery, depending upon the amount of stress control desired. Outside of the aforementioned differences the accelerometer of Figures 7 and 8 operates in substantially the same manner as the accelerometers 1t), 3t) and 35 of Figures 1 to 6. Here, again the housing may contain a fluid damping material for damping the piezoelectric member or it may utilize the electromagnetic damping arrangement illustrated in Figures 3 and 4. In this latter event the mass 47 may be a conducting ring cooperating with the magnet.

If still higher voltage sensitivities are desired at the expense of capacitance, the electrodes of the various piezoelectric members may be formed of concentric electric rings and the radial voltage used, as is illustrated in Figure 9. Here, by way of example, the piezoelectric member includes titanate ceramic sheets 36 and 37 soldered together at 40 and concentric electrodes 50 and 51 on the upper surface of the titanate ceramic sheet 37. In permanently polarizing this piezoelectric member one terminal of a D. C. voltage source is applied to the electrode 50 and the other terminal to the electrode 51. When a suificiently high D. C. voltage is thus applied for a sufficiently long time the piezoelectric member is permanently polarized and the radial voltage thereof is utilized for producing the signal voltage. Two or more concentric rings may be used on either or both of the titanate ceramic sheets in order to obtain proper capacitance at these higher voltage sensitivities. If concentric electrodes are utilized in the accelerometers 10 and 30 of Figures 1 to 4, the ceramic sheets 18 are secured to the member 15 by electrically insulating cement or the members 15 are made of an insulating material.

While for purposes of illustration several forms of this invention have been disclosed other forms thereof may become apparent to those skilled in the art upon reference to this disclosure, and, therefore, this invention is to be limited only by the scope of the appended claims.

I claim as my invention:

1. An accelerometer for producing a voltage in accordance with vibration imparted thereto comprising a supporting rod, means for securing the supporting rod to a vibrating member so as to be longitudinally vibrated by the vibrating member, a substantially disc shaped piezoelectric member having planar dimensions substan tially greater than the transverse dimensions of the rod, and means for centrally securing the piezoelectric member to the rod in a plane substantially perpendicular to and with its planar center in substantial alignment with the longitudinal axis of the rod and extending radially in all directions beyond the rod so as to be radially flexed substantially uniformly about the axis of the rod, as into and out of umbrella shape, by vibration of the rod to produce a voltage in accordance with the vibration thereof.

2. An accelerometer for producing a voltage in accordance with vibration imparted thereto comprising a supporting rod, means for securing the supporting rod to a vibrating member so as to be longitudinally vibrated by the vibrating member, a substantially disc shaped piezoelectric member having planar dimensions substantially greater than the transverse dimensions of the rod and including at least one titanate ceramic sheet provided with electrodes, and means for centrally securing the piezoelectric member to the rod in a plan substantially perpendicular to and with its planar center in susbtantial alignment with the longitudinal axis of the rod and extending radially in all directions beyond the rod so as to be radially flexed substantially uniformly about the axis of the rod, as into and out of umbrella shape, by vibration of the rod to produce a voltage across the electrodes in accordance with the vibration thereof.

3. An accelerometer for producing a voltage in ac cordance with vibration imparted thereto comprising a supporting rod, means for securing the supporting rod to a vibrating member so as to be longitudinally vibrated by the vibrating member, a substantially disc shaped piezoelectric member having planar dimensions substantially greater than the transverse dimensions of the rod and including at least one titanate ceramic sheet provided with electrodes and permanently polarized, and means for centrally securing the piezoelectric member to the rod in a plane substantially perpendicular to and with its planar center in substantial alignment with the longitudinal axis of the rod and extending radially in all direc tions beyond the rod so as to be radially flexed substantially uniformly about the axis of the rod, as into and out of umbrella shape, by vibration of the rod to produce a voltage across the electrodes in accordance with the vibration thereof.

4. An accelerometer for producing a voltage in accordance with vibration imparted thereto comprising a supporting rod, means for securing the supporting rod to a vibrating member so as to be longitudinally vibrated by the vibrating member, a substantially disc shaped piezoelectric member having planar dimensions substantially greater than the transverse dimensions of the rod and including at least one titanate ceramic sheet provided with electrodes on the opposite faces thereof, and means for centrally securing the piezoelectric member to the rod in a plane substantially perpendicular to and with its planar center in substantial alignment with the longitudinal axis of the rod and extending radially in all directions beyond the rod so as to be radially flexed substantially uniformly about the axis of the rod, as into and out of umbrella shape, by vibration of the rod to produce a voltage across the electrodes in accordance with the vibra tion thereof.

5. An accelerometer for producing a voltage in accordance with vibration imparted thereto comprising a supporting rod, means for securing the supporting rod to a vibrating member so as to be'longitudinally vibrated by the vibrating member, a substantially disc shaped piezoelectric member having planar dimensions substantially greater than the transverse dimensions of the rod and including at least one titanate ceramic sheet having a pair of spaced apart substantially annular electrodes on one side thereof, and means for centrally securing the piezoelectric member to the rod in a plane substantially perpendicular to and with its planar center in substantial alignment with the longitudinal axis of the rod and extending radially in all directions beyond the rod so as to be radially flexed substantially uniformly about the axis of the rod, as into and out of umbrella shape, by vibration of the rod to produce a voltage across the electrodes in accordance with the vibration thereof.

6. An accelerometer for producing a voltage in accordance with vibration imparted thereto comprising a supporting rod, means for securing the supporting rod to a vibrating member so as to be longitudinally vibrated by the vibrating member, a substantially disc shaped piezoelectric member having planar dimensions substantially greater than the transverse dimensions of the rod and including a pair of titanate ceramic sheets secured together and provided with electrodes, and means for centrally securing the piezoelectric member to the rod in a plane substantially perpendicular to and with its planar center in substantial alignment with the longitudinal axis of the rod and extending radially in all directions beyond the rod so as to be radially flexed substantially uniformly about the axis of the rod, as into and out of umbrella shape, by vibration of the rod to produce a voltage across the electrodes in accordance with the vibration thereof.

7. An accelerometer for producing a voltage in accordance with vibration imparted thereto comprising a supporting rod, means for securing thesupporting rod to a vibrating member so as to be longitudinally vibrated by the vibrating member, a substantially disc shaped piezoelectric member having planar dimensions substantially greater than the transverse dimensions of the rod and including a pair of titanate ceramic sheets, each having electrodes on opposite faces, and secured together to provide electrodes on the outer faces of the piezoelectric member, and means for centrally securing the piezoelectric member to the rod in a plane substantially perpendicular to and with its planar center in substantial alignment with the longitudinal axis of the rod and extending radially in all directions beyond the rod so as to be radially flexed substantially uniformly about the axis of the rod, as into and out of umbrella shape, by vibration of the rod to produce a voltage across the electrodes in accordance with the vibration thereof.

8. An accelerometer for producing a voltage in accordance with vibration imparted thereto comprising a supporting rod, means for securing the supporting rod to a vibrating member so as to be longitudinally vibrated by the vibrating member, a substantially disc shaped piezoelectric member having planar dimensions substantially greater than the transverse dimensions of the rod and including a pair of titanate ceramic sheets, each having electrodes on opposite faces thereof, and secured together to provide an inner electrode and outer electrodes on the piezoelectric member, and means for centrally securing the piezoelectric member to the rod in a plane substantially perpendicular to and with its planar center in substantial alignment with the longitudinal axis of the rod and extending radially in all directions beyond the rod so as to be radially flexed, as into and out of umbrella shape, by vibration of the rod to produce a voltage across the inner electrode and the outer electrodes in accordance with the vibration thereof.

9. An accelerometer for producing a voltage in accordance with vibration imparted thereto comprising a supporting rod, means for securing the supporting rod to a vibrating member so as to be longitudinally vibrated by the vibrating member, a substantially disc shaped piezoelectric member having planar dimensions substantially greater than the transverse dimensions of the rod and having a mass spaced outwardly from the center thereof, and means for centrally securing the piezoelectric member to the rod in a plane substantially perpendicular to and with its planar center in substantial alignment with the longitudinal axis of the rod and extending radially in all directions beyond the rod so as to be radially flexed substantially uniformly about the axis of the rod, as into and out of umbrella shape, by vibration of the rod to produce a voltage in accordance with the vibration thereof.

10. An accelerometer for producing a voltage in accordance with vibration imparted thereto comprising a supporting rod, means for securing the supporting rod to a vibrating member so as to be longitudinally vibrated by the vibrating member, a substantially disc shaped piezoelectric member having planar dimensions substantially greater than the transverse dimensions of the rod and including at least one titanate ceramic sheet provided with electrodes, a mass secured to and spaced outwardly from the titanate ceramic sheet, and means for centrally securing the piezoelectric member to the rod in a plane substantially perpendicular to and with its planar center in substantial alignment with the longitudinal axis of the rod and extending radially in all directions beyond the rod so as to be radially flexed substantially uniformly about the axis of the rod, as into and out of umbrella shape, by vibration of the rod to produce a voltage across the electrodes in accordance with the vibration thereof.

11. An accelerometer for producing a voltage in accordance with vibration imparted thereto comprising a supporting rod, means for securing one end of the supporting rod to a vibrating member so as to be longitudinally vibrated by the vibrating member, a substantially disc shaped part having planar dimensions substantially greater than the transverse dimensions of the rod and formed on the other end of the rod in a plane substantially perpendicular to and with its planar center in substantial alignment with the longitudinal axis of the rod and extending radially in all directions beyond the rod, and a substantially disc shaped piezoelectric member having planar dimensions similar to those of the substantially disc-shaped part and overlying and secured to the substantially disc shaped part, said substantially disc shaped part and piezoelectric member being radially flexed substantially uniformly about the axis of the rod, as into and out of umbrella shape, by vibration of the rod to produce a voltage in accordance with the vibration thereof.

12. An accelerometer for producing a voltage in accordance with vibration imparted thereto comprising a supporting rod, means for securing one end of the supporting rod to a vibrating member so as to be longitudisc shaped part having planar dimensions substantially greater than the transverse dimensions of the rod and dinally vibrated by the vibrating member, a substantially formed on the other end of the rod in a plane substantially perpendicular to and with its planar center in substantial alignment with the longitudinal axis of the rod and extending radially in all directions beyond the rod and having a mass spaced outwardly from the center thereof, and a substantially disc shaped piezoelectric member having planar dimensions similar to those of the substantially disc-shaped part and overlying and secured to the substantially disc shaped part, said substantially disc shaped part and piezoelectric member being radially flexed substantially uniformly about the axis of the rod, as into and out of umbrella shape, by vibration of the rod to produce a voltage in accordance with the vibration thereof.

13. An accelerometer for producing a voltage in accordance With vibration imparted thereto comprising a supporting rod, means for securing the supporting rod to a vibrating member so as to be longitudinally vibrated by the vibrating member, a substantially disc shaped piezoelectric member having planar dimensions substantially greater than the transverse dimensions of the rod, means for centrally securing the piezoelectric member to the rod in a plane substantially perpendicular to and with its planar center in substantial alignment with the longitudinal axis of the rod and extending radially in all directions beyond the rod so as to be radially flexed substantially uniformly about the axis of the rod, as into and out of umbrella shape, by vibration of the rod to produce a voltage in accordance with the vibration thereof, and means for damping the flexing movement of the piezoelectric member.

14. An accelerometer for producing a voltage in accordance with vibration imparted thereto comprising a supporting rod, means for securing the supporting rod to a vibrating member so as to be longitudinally vibrated by the vibrating member, a substantially disc shaped piezoelectric member having planar dimensions substantially greater than the transverse dimensions of the rod, means for centrally securing the piezoelectric member to the rod in a plane substantially perpendicular to and with its planar center in substantial alignment with the longitudinal axis of the rod and extending radially in all directions beyond the rod so as to be radially flexed substantially uniformly about the axis of the rod, as into and out of umbrella shape, by vibration of the rod to produce a voltage in accordance with the vibration thereof, and means for damping the flexing movement of the piezoelectric member, said last mentioned means including a fluid damping material.

15. An accelerometer for producing a voltage in accordance with vibration imparted thereto comprising a supporting rod, means for securing the supporting rod to a vibrating member so as to be longitudinally vibrated by the vibrating member, a substantially disc shaped piezoelectric member having planar dimensions substantially greater than the transverse dimensions of the rod, means for centrally securing the piezoelectric member to the rod in a plane substantially perpendicular to and with its planar center in substantial alignment with the longitudinal axis of the rod and extending radially in all directions beyond the rod so as to be radially flexed substantially uniformly about the axis of the rod, as into and out of umbrella shape, by vibration of the rod to produce a voltage in accordance with the vibration thereof, and means for damping the flexing movement of the piezoelectric member, said last mentioned means including a magnetic member for producing a magnetic field and a conducting ring member in the magnetic field, one of said members being substantially stationary and the other carried by the piezoelectric member.

16. An accelerometer for producing a voltage in accordance with vibration impart-ed thereto comprising a supporting rod, means for securing the supporting rod to a vibrating member so as to be longitudinally vibrated by the vibrating member, a substantially disc shaped piezoelectric member having planar dimensions substantially greater than the transverse dimensions of the rod, means for centrally securing the piezoelectric member to the rod in a plane substantially perpendicular to and with its planar center in substantial alignment with the longitudinal axis of the rod and extending radially in all directions beyond the rod so as to be radially flexed sub stantially uniformly about the axis of the rod, as into and out of umbrella shape, by vibration of the rod to produce a voltage in accordance with the vibration thereof, and a housing carried by the rod and enclosing the piezoelectric member.

17. An accelerometer for producing a voltage in accordance with vibration imparted thereto comprising a supporting rod, means for securing the supporting rod to a vibrating member so as to be longitudinally vibrated by the vibrating member, a substantially disc shaped piezoelectric member having planar dimensions substantially greater than the transverse dimensions of the rod, means for centrally securing the piezoelectric member to the rod in a plane substantially perpendicular to and with its planar center in substantial alignment with the longitudinal axis of the rod and extending radially in all directions beyond the rod so as to be radially flexed substantially uniformly about the axis of the rod, as into and out of umbrella shape, by vibration of the rod to produce a voltage in accordance with the vibration thereof, a housing enclosing the piezoelectric member, and provided with means for resiliently supporting the housing on the rod so as substantially to reduce the mechanical coupling therebetween to isolate housing resonances from the rod.

18. An accelerometer for producing a voltage in accordance with vibration imparted thereto comprising a supporting rod, means for securing the supporting rod to a vibrating member so as to be longitudinally vibrated by the vibrating member, a substantially disc shaped piezoelectric member having planar dimensions substantially greater than the transverse dimensions of the rod, means for centrally securing the piezoelectric member to the rod in a plane substantially perpendicular to and with its planar center in substantial alignment with the longitudinal axis of the rod and extending radially in all directions beyond the rod so as to be radially flexed substantially uniformly about the axis of the rod, as into and out of umbrella shape, by vibration of the rod to produce a voltage in accordance with the vibration thereof, a housing enclosing the piezoelectric member, and provided with means for resiliently supporting the housing on the rod so as substantially to reduce the mechanical coupling therebetween to isolate housing resonances from the rod, and a fluid damping material in the housing for damping the flexing movement of the piezoelectric element.

19. An accelerometer for producing a voltage in accordance with vibration imparted thereto comprising a supporting rod, means for securing the supporting rod to a vibrating member so as to be longitudinally vibrated by the vibrating member, a substantially disc shaped piezoelectric member having planar dimensions substantially greater than the transverse dimensions of the rod, means for centrally securing the piezoelectric member to the rod in a plane substantially perpendicular to and with its planar center in substantial alignment with the longitudinal axis of the rod and extending radially in all directions beyond the rod so as to be radially flexed substantially uniformly about the axis of the rod, as into and out of umbrella shape, by vibration of the rod to produce a voltage in accordance with the vibration thereof, a housing enclosing the piezoelectric member, and provided with means for resiliently supporting the housing on the rod so as substantially to reduce the mechanical coupling therebetween to isolate housing resonances from the rod, and means for damping the flexing movement of the piezoelectric element including a magnetic member carried by the housing for producing a magnetic field and a conducting ring member carried by the piezoelectric member in the magnetic field.

11 "12 UNITED STATES PATENTS FOREIGN PATENTS 2,137,188 Whitman Nov. 15, 1938 747,008 Germany SePt- 1944 2,496,293 Kiernan Feb. 7, 1950 OTHER REFERENCES 2,640,165 Howatt May 1953 5 Publication: Radio and Television News, Radio Eng.

2682003 Stubner June 1954 Section, November 1951, page 16.

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