Patent Publication Number: US-2020303617-A1

Title: Charge output device, assembly method and piezoelectric acceleration sensor

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to Chinese Patent Application No. 201910223120.0, filed on Mar. 22, 2019, which is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to a technical field of sensor technologies, and particularly relates to a charge output device, an assembly method and a piezoelectric acceleration sensor. 
     BACKGROUND 
     A piezoelectric acceleration sensor, also known as a piezoelectric accelerometer, is an inertial sensor. The principle of the piezoelectric acceleration sensor lies in the piezoelectric effect of a piezoelectric element. When the accelerometer is vibrated, a force applied on the piezoelectric element by a mass changes. When a vibration frequency under measurement is much lower than an inherent frequency of the accelerometer, the change of the force is proportional to an acceleration under detection. A standard piezoelectric acceleration sensor is used to calibrate the acceleration sensor. Therefore, the requirements on performance of the standard piezoelectric acceleration sensor is much higher, for example, a higher sensitivity is required. However, the existing piezoelectric acceleration sensor is generally not sensitive enough to meet the requirements of the standard piezoelectric acceleration sensor. 
     Therefore, there is a dire need for a charge output device with higher sensitivity to meet the requirements of the standard piezoelectric acceleration sensor. 
     SUMMARY 
     Embodiments of the present disclosure provide a charge output device, an assembly method thereof, and a piezoelectric acceleration sensor, which can improve sensitivity of the charge output device. 
     On one aspect, the present disclosure discloses a charge output device, includes a base, including a polygonal connecting member including a plurality of sides; a piezoelectric assembly, including at least two piezoelectric units distributed along a circumferential direction of the connecting member and spaced apart from each other, the at least two piezoelectric units are disposed corresponding to at least two of the plurality of sides of the connecting member, and each piezoelectric unit includes at least one piezoelectric crystal, wherein the respective piezoelectric crystals of the at least two piezoelectric units are connected in parallel; and a mass assembly, disposed on an outer circumferential side of the piezoelectric assembly such that the piezoelectric assembly is located between the connecting member and the mass assembly, wherein the connecting member, the piezoelectric assembly and the mass assembly are interference-fitted with each other. 
     According to one aspect of the present disclosure, each piezoelectric crystal is formed as a bent sheet-like member, a shape of which matches a shape of the side of the connecting member; or each piezoelectric crystal is formed as a straight sheet-like member, a shape of which matches a shape of the side of the connecting member, and on each side of the connecting member, one piezoelectric unit is disposed correspondingly. 
     According to one aspect of the present disclosure, each of two surfaces of each piezoelectric crystal opposite to each other in a normal direction of a circumferential surface of the connecting member is provided with a conductive film, and each piezoelectric unit includes two or more piezoelectric crystals stacked in the normal direction, wherein two surfaces of two adjacent piezoelectric crystals adjacent to each other have the same polarity. 
     According to one aspect of the present disclosure, the charge output device further includes a plurality of electrode plates, the plurality of electrode plates and the piezoelectric crystals of respective layers are alternately stacked in the normal direction, and the number of layers of the plurality of electrode plates is one more than the number of layers of the piezoelectric crystals, wherein each electrode plate includes a fitting portion and a connecting portion, the fitting portion is disposed corresponding to the piezoelectric crystal, and the connecting portion is electrically connected to the fitting portion so that each electrode plate is formed as an annular member that is discontinuous in a circumferential direction; and wherein the respective electrode plates of odd-numbered layers are electrically connected by a wire segment, and the respective electrode plates of even-numbered layers are electrically connected by another wire segment, so that the respective piezoelectric crystals of the at least two piezoelectric units are connected in parallel. 
     According to one aspect of the present disclosure, the fitting portion has a size greater than or equal to that of the piezoelectric crystal, so that the piezoelectric crystal can completely fit to the fitting portion; and/or the connecting portion has a width in an axial direction of the connecting member smaller than that of the fitting portion. 
     According to one aspect of the present disclosure, the wire segment electrically connects the electrode plates of the respective odd-numbered layers in the circumferential direction at discontinuous positions of the electrode plates; and the another wire segment electrically connects the electrode plates of the respective even-numbered layers in the circumferential direction at discontinuous positions of the electrode plates. 
     According to one aspect of the present disclosure, the mass assembly includes a plurality of masses distributed along the circumferential direction and spaced apart from each other, and on an outer circumferential side of each piezoelectric unit, at least one mass is disposed correspondingly. 
     According to one aspect of the present disclosure, the charge output device further includes a heat shrink ring, disposed surrounding the mass assembly and interference-fitted with the mass assembly; and an insulating plate, disposed surrounding the connecting member and located between the connecting member and each piezoelectric unit. 
     On a second aspect, the present disclosure discloses an assembly method of a charge output device, including steps of: performing a heat treatment on a base to eliminate processing stress in the base, wherein the base includes a polygonal connecting member including a plurality of sides; disposing at least two piezoelectric units spaced apart from each other along a circumferential side of the connecting member, wherein the at least two piezoelectric units are disposed corresponding to at least two sides of the plurality of sides of the connecting member, and each piezoelectric unit includes at least one piezoelectric crystal; connecting the respective piezoelectric crystals of the at least two piezoelectric units in parallel by electrode plates; disposing a mass assembly on an outer circumferential side of the at least two piezoelectric units; and disposing a heat shrink ring to surround the mass assembly on an outer side of the mass assembly and heating the heat shrink ring to shrink it, so that the heat shrink ring, the mass assembly, the at least two piezoelectric units and the connecting member are interference-fitted with each other. 
     On a third aspect, the present disclosure discloses a piezoelectric acceleration sensor, including: a charge output device according to any of the above embodiments; a case, surrounding the charge output device and disposed on the base; and a signal output element, electrically connected to the piezoelectric assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to illustrate the technical solutions of the embodiments of the present disclosure more clearly, the drawings to be used in the embodiments of the present disclosure will be briefly described below. It is obvious that the drawings described below are only some embodiments of the present disclosure, and the person skilled in the art can obtain other drawings based on these drawings without paying any creative work. 
         FIG. 1  is a schematic top view showing a configuration of a charge output device according to an embodiment of the present disclosure; 
         FIG. 2  is a schematic cross-sectional view showing a configuration of a charge output device according to an embodiment of the present disclosure; 
         FIG. 3  is a schematic top view showing a configuration of a charge output device according to another embodiment of the present disclosure; 
         FIG. 4  is a schematic view showing a configuration of an electrode plate according to an embodiment of the present disclosure; 
         FIG. 5  is a schematic view showing electrical connection of electrode plates of odd-numbered layers or even-numbered layers according to an embodiment of the present disclosure; 
         FIG. 6  is a flow chart showing an assembly method of a charge output device according to an embodiment of the present disclosure; and 
         FIG. 7  is a cross-sectional view showing a configuration of a piezoelectric acceleration sensor according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Features and exemplary embodiments of various aspects of the present disclosure will be described in detail below. In the following detailed description, numerous specific details are set forth to provide a full understanding of the present disclosure. However, it shall be apparent to the person skilled in the art that the present disclosure may be implemented without some of the details. The following description of the embodiments is made merely to provide a better understanding of the present disclosure by showing examples of the present disclosure. In the drawings and the following description, at least some of well-known structures and techniques are not shown to avoid unnecessarily obscuring the present disclosure. Further, for clarity, size of part of the structure may be exaggerated. Furthermore, features, structures, or characteristics described hereinafter may be combined in any suitable manner into one or more embodiments. 
     Orientations in the following description refer to directions as shown in the drawings, and are not intended to define specific structure of the embodiments of the present disclosure. In the description of the present disclosure, it shall be noted that, unless otherwise clearly stated and defined, the terms such as “installation”, “connection” shall be understood broadly, and may be, for example, a fixed connection, a disassemble connection, or an integral connection, and may be a direct connection or an indirect connection through an intermediate medium. The specific meaning of the above terms in the present disclosure can be understood by the person skilled in the art according to actual circumstance. 
     It should be noted that, the embodiments in the present application and the features in the embodiments may be combined with each other when there is no conflict. The embodiments will be described in detail below with reference to the accompanying drawings. 
     For a better understanding of the present disclosure, a charge output device, an assembly method, and a piezoelectric acceleration sensor of the present disclosure will be described in detail below with reference to  FIGS. 1 to 7 . 
     Referring to  FIG. 1  and  FIG. 2  together, wherein  FIG. 1  is a schematic top view of a configuration of a charge output device according to an embodiment of the present disclosure, and  FIG. 2  is a cross-sectional view of a configuration of a charge output device according to an embodiment of the present disclosure. The charge output device of the present embodiment includes a base  10 , a piezoelectric assembly and a mass assembly  30 . The base  10  includes a polygonal connecting member  11 , which includes a plurality of sides. For convenience of processing and assembly, the connecting member  11  may have a cross section perpendicular to an axial direction of the connecting member  11  in a shape of a regular polygon, that is, the plurality of sides of the connecting member  11  have the same shape. The piezoelectric assembly includes at least two piezoelectric units  20  distributed along a circumferential direction of the connecting member  11  and spaced apart from each other, and the at least two piezoelectric units  20  are disposed corresponding to at least two sides of the plurality of sides of the connecting member  11 . Each piezoelectric unit  20  includes at least one piezoelectric crystal  21 , and the piezoelectric crystals  21  are connected in parallel. The mass assembly  30  is disposed on an outer circumferential side of the piezoelectric assembly, such that the piezoelectric assembly is located between the connecting member  11  and the mass assembly  30 . In the above configuration, the connecting member  11 , the piezoelectric assembly and the mass assembly  30  are interference-fitted with each other to ensure an overall rigidity of the charge output device. 
     In the present embodiment, the connecting member  11  includes a plurality of sides, for facilitating the arrangement of the piezoelectric unit  20  including at least one piezoelectric crystal  21  on a circumferential side of each side of the connecting member  11 . As a result, the number of the piezoelectric crystals  21  on a circumferential side of the connecting member  11  can be increased, and space can be saved. Further, by connecting the respective piezoelectric crystals  21  in parallel, a sensitivity of the charge output device can be improved, thereby improving a sensitivity of the piezoelectric acceleration sensor. Further, the connecting member  11 , the piezoelectric assembly and the mass assembly  30  are interference-fitted with each other, and are rigidly contact with each other without need of adhesive layers. Thus, the overall rigid of the charge output device can be increased, and thus frequency response characteristics and resonance characteristics of the piezoelectric acceleration sensor can be improved. 
     In some alternative embodiments, please refer to  FIG. 3 .  FIG. 3  is a schematic top view of a configuration of a charge output device according to another embodiment of the present disclosure. The piezoelectric crystal  21  of the charge output device in the present embodiment is formed as a bent sheet-like member, a shape of which matches a shape of the side of the connecting member  11 . The specific number of bent portions of the bent sheet-like member is not limited in the present disclosure, as long as the shape formed by the bending can match the side of the connecting member  11 . In the drawings, as an example, the bent sheet-like member has one bent portion, the connecting member  11  includes four sides, and each bent sheet-like member is correspondingly disposed on two sides of the connecting member  11 . It should be understood that the piezoelectric crystals  21  are symmetrically disposed on the circumferential side of the connecting member  11  in order for a better charge output. 
     In some other alternative embodiments, referring to  FIG. 1 , the piezoelectric crystal  21  may be formed as a straight sheet-like member, a shape of which matches a shape of the side of the connecting member  11 , and each side of the connecting member  11  is correspondingly provided with one piezoelectric unit  20 . Since the piezoelectric crystal  21  is formed as a straight sheet-like member, it is convenient for the piezoelectric crystal  21  in such shape to be disposed on each side of the connecting member  11 , and further stacking multiple piezoelectric crystals  21  on each side. By connecting the respective piezoelectric crystals in parallel, the sensitivity of the charge output device can be effectively increased. Moreover, the straight sheet-like piezoelectric crystal  21  has a simple structure, is easy to process, and is easy to stack. 
     In some alternative embodiments, each piezoelectric crystal  21  is provided with a conductive film on each of two surfaces opposite to each other in a normal direction of a circumferential surface of the connecting member  11 , to facilitate electrical connection of the respective piezoelectric crystals  21 . Further, the piezoelectric unit  20  includes two or more piezoelectric crystals  21  stacked in the normal direction, and two surfaces of adjacent two piezoelectric crystals  21  adjacent to each other have the same polarity, to facilitate the parallel connection of the respective piezoelectric crystals  21 . The piezoelectric crystal  21  of the present embodiment may be made of a quartz single crystal. The quartz single crystal has good thermal stability and temperature drift characteristics, and has high sensitivity, excellent linearity, and high dielectric constant. Moreover, a connection of a plurality of quartz single crystals in parallel can increase the sensitivity of the charge output device and improve an anti-interference ability of the charge output device. The conductive film provided on each of the two surfaces of the piezoelectric crystal  21  opposite to each other may be a gold plating film. It should be understood that the polarities of the two surfaces opposite to each other and provided with the conductive films are different, after polarization of the piezoelectric crystal  21 . 
     In some alternative embodiments, the charge output device further includes a plurality of electrode plates  80 . The plurality of electrode plates  80  and the piezoelectric crystals  21  of respective layers are stacked alternately in the normal direction of the circumferential surface of the connecting member  11 , and the number of layers of the electrode plates  80  is one more than the number of layers of the piezoelectric crystals  21 . Referring to  FIG. 4 , wherein  FIG. 4  is a schematic view of a configuration of an electrode plate according to an embodiment of the present disclosure. The electrode plate  80  of the present embodiment includes a fitting portion  81  and a connecting portion  82 . The fitting portion  81  is disposed corresponding to the piezoelectric crystal  21 . The connecting portion  82  is electrically connected to the fitting portion  81 , such that each electrode plate  80  is formed into an annular member that is discontinuous in a circumferential direction. It can be understood that the annular member of the present embodiment is formed as a polygonal annular member, which includes three, four or five sides. The number of sides of the annular member is not limited in the present disclosure, but is consistent with the number of the sides of the connecting member  11 . In the present embodiment, the annular members of odd-numbered layers are electrically connected by a wire segment  83 , and the annular members of even-numbered layers are electrically connected by another wire segment  83 , thereby achieving parallel connection of the respective piezoelectric crystals  21 . In the present embodiment, regarding the odd-numbered layers and the even-numbered layers, a layer of the piezoelectric crystal  21  closest to the connecting member  11  may be a first layer, and layers arranged sequentially outwardly are a second layer, a third layer, etc.; or, a layer of the piezoelectric crystal  21  farthest away from the connecting member  11  is a first layer, and layers arranged sequentially inwardly are a second layer, a third layer, etc. In the present disclosure, a connection position of the wire segment  83  is not limited. However, in order to reduce a height of the charge output device, preferably, the wire segment  83  is disposed at a discontinuous position in the circumferential direction of the electrode plates  80 , to electrically connect the electrode plates  80  of the odd-numbered layers or the even-numbered layers in the circumferential direction as shown in  FIG. 5 , wherein  FIG. 5  is a schematic view of an electrical connection of odd-numbered or even-numbered layers of electrode plates according to an embodiment of the present disclosure. Each of the fitting portion  81 , the connecting portion  82 , and the wire segment  83  of the present embodiment may be made of at least one of pure nickel and a nickel-chromium alloy. 
     As an example, the connecting member  11  has a square cross section perpendicular to the axial direction and includes four sides, and two layers of the piezoelectric crystals  21  formed as a straight sheet-like member are disposed on each side. In this case, three layers of electrode plates  80  are disposed on the circumferential side of the connecting member  11 . As shown in  FIGS. 1 and 5 , by taking the connecting member  11  as a center and counting from inside to outside, a first layer of the electrode plates  80  and a third layer of the electrode plates  80  are discontinuous at the same position on the circumferential side of the connecting member  11 , and are connected at ends on the same side in the circumferential direction by the wire segment  83 , so that the first layer of the electrode plates  80  and the third layer of the electrode plates  80  are connected to form an integral member with two free ends. 
     Further, in order to ensure a good fit of the piezoelectric crystal  21  and the electrode plate  80 , the fitting portion  81  of the electrode plate  80  has a size greater than or equal to that of the piezoelectric crystal  21 . Alternatively, the size of the fitting portion  81  is the same as the size of the piezoelectric crystal  21 , and the fitting portion  81  and the piezoelectric crystal  21  fit to each other completely, to avoid interference of signals between the fitting portions  81  of adjacent layers. The connecting portion  82  of the electrode plate  80  has a width in the axial direction of the connecting member  11  smaller than that of the fitting portion  81  of the electrode plate  80 , to reduce an electric resistance of the entire electrode plate  80 . 
     In some alternative embodiments, the mass assembly  30  includes a plurality of masses  31  spaced apart from each other in a circumferential direction, and at least one mass  31  is disposed correspondingly on an outer circumferential side of each piezoelectric unit  20 . The respective masses  31  are disposed on an outer circumferential side of the outermost electrode plate  80 . The masses  31  are fitted to the outermost electrode plate  80  and are interference-fitted with the electrode plate  80 . The respective masses  31  are disposed on the outer circumferential side of the electrode plate  80 , that is, the entire mass assembly  30  is discontinuous in a circumferential direction, which facilitates to adjust positions of the respective masses  31  to realize the interference fit between the respective masses  31  and the electrode plate  80 . The mass assembly  30  of the present embodiment may be made of 316L stainless steel, and has strong corrosion resistance and heat resistance. 
     In some alternative embodiments, the charge output device further includes a heat shrink ring  40  that is disposed surrounding the mass assembly  30  and interference-fitted with the mass assembly  30 . The heat shrink ring  40  may be made of a nickel-titanium memory alloy, which is treated by cold expansion and is heat shrinkable. The heat shrink ring  40  of the present embodiment can increase a preload force on the circumferential side of the mass assembly  30  such that the connecting member  11 , the piezoelectric assembly and the mass assembly  30  are interference-fitted with each other, thereby enhancing the overall rigidity of the charge output device. 
     Further, the charge output device of the present embodiment further includes an insulating plate  50 , which is disposed surrounding the connecting member  11  and located between the connecting member  11  and the piezoelectric units  20 . The arrangement of the insulating plate  50  can prevent an electric charge of the piezoelectric assembly from moving to the connecting member  11 , thereby improving a measurement accuracy of the piezoelectric acceleration sensor. The insulating plate  50  may be made of 95 alumina ceramic and has good insulating property. The specific shape of the insulating plate  50  is not limited in the present disclosure, as long as the insulation between the electrode plate  80  of the piezoelectric assembly and the connecting member  11  can be achieved. For example, the insulating plate  50  may be formed as an annular member, and is disposed surrounding the connecting member  11  and located between the connecting member  11  and the piezoelectric assembly. Further, the insulating sheet  50  may be formed as a sheet-like member, and on each side of the connecting member  11 , one insulating plate  50  is disposed correspondingly and is located between the connecting member  11  and the innermost electrode plate  80 . 
     The present disclosure further provides an assembly method for a charge output device. Please refer to  FIG. 6 .  FIG. 6  is a flow chart of an assembly method for a charge output device according to an embodiment of the present disclosure. The assembly method of the present embodiment includes the steps as below. 
     In step  601 , a heat treatment is performed on a base to eliminate processing stress in the base. 
     The base  10  in this step includes a polygonal connecting member  11  including a plurality of sides. The material of the base  10  is selected from α+β titanium alloy, with a density from 3 g/cm −3  to 5 g/cm −3  and an elastic modulus from 1.0×10 5  MPa to 1.2×10 5  MPa, which has a high strength-to-weight ratio. Specifically, α+β titanium alloy of TC4 type can be used. The heat treatment of the formed base  10  can eliminate the processing stress in the base  10 , stabilize a size of the base  10 , increase a strength of the base  10 , and remove harmful elements (for example, hydrogen) added to the base  10  during processing. The specific heat treatment may include one or more of annealing, solution treatment, and failure treatment. The heat treatment of the present embodiment is performed under vacuum. 
     In step  602 , at least two piezoelectric units are disposed along a circumferential side of the connecting member and spaced apart from each other. 
     In this step, at least two piezoelectric units  20  are disposed corresponding to at least two of the plurality of sides of the connecting member  11 , and each piezoelectric unit  20  includes at least one piezoelectric crystal  21 . 
     In step  603 , the respective piezoelectric crystals are connected in parallel through electrode plates. 
     In this step, the respective piezoelectric crystals  21  are connected in parallel via electrode plates  80 , which can improve a sensitivity of the charge output device. 
     In step  604 , a mass assembly is disposed on an outer circumferential side of the piezoelectric units. 
     In step  605 , a heat shrink ring is disposed surrounding an outer side of the mass assembly and is heated to shrink, so that the heat shrink ring, the mass assembly, the piezoelectric units and the connecting member are interference-fitted with each other. 
     In this step, by heating the heat shrink ring  40  to shrink, a preloading force on a circumferential side of the mass assembly is increased, thereby achieving an interference fit between the mass assembly  30 , the piezoelectric units  20 , the electrode plates  80  and the connecting member  11 . 
     In the present embodiment, the heat treatment is performed on the formed base  10  to eliminate processing stress in the base  10 , which can stabilize the size of the base  10 , increase the strength of the base  10 , and remove the harmful elements (for example, hydrogen) added to the base  10  during processing. The connecting member  11  includes a plurality of sides, and at least two sides are provided with the piezoelectric unit  20 , which includes at least one piezoelectric crystal  21 . Thus, the number of the piezoelectric crystals  21  can be increased and space can be saved. By connecting the piezoelectric crystals  21  in parallel through the electrode plates  80 , the sensitivity of the charge output device can be improved. Further, by increasing a radial preloading force by use of the heat shrink ring  40 , the interference fit between the mass assembly  30 , the piezoelectric units  20  and the connecting member  11  can be achieved, which can increase the overall rigidity of the charge output device, thereby improving the frequency response characteristics and resonance characteristics of the piezoelectric acceleration sensor. 
     The present disclosure further provides a piezoelectric acceleration sensor. Please refer to  FIG. 7  together, wherein  FIG. 7  is a cross-sectional view of a configuration of a piezoelectric acceleration sensor according to an embodiment of the present disclosure. The piezoelectric acceleration sensor of the present embodiment includes the charge output device according to the above embodiments, a case  60 , and a signal output element  70 . The case  60  is disposed surrounding the charge output device and is disposed on the base  10 , which can seal and protect the charge output device. The signal output element  70  is electrically connected to the mass assembly  30  and the piezoelectric assembly. Specifically, the signal output element  70  can be electrically connected to the mass assembly  30  and the piezoelectric assembly through two signal transmission lines. One end of one signal line is connected to the mass assembly  30 , while the other end of the one signal line is connected to the signal output element  70 . Moreover, one end of the other signal line is connected to the electrode plate  80  that is not in electrical contact with the mass assembly  30 , and the other end of the other signal line is connected to the signal output element  70 . Thereby, a signal of the charge output device can be transmitted to an external device through the signal output element  70 . The same heat treatment as the base  10  may be performed on the case  60  of the piezoelectric acceleration sensor of the present embodiment, to eliminate the processing stress in the case  60 , stabilize a size of the case  60 , increase a strength of the case  60 , and remove harmful elements added to the case  60  during the forming process. Thereby, the overall rigidity of the piezoelectric acceleration sensor can be increased. 
     The piezoelectric acceleration sensor according to the embodiment of the present disclosure includes the charge output device of the above embodiment, and thus has the advantageous effects of the charge output device of the above embodiment, which will not be described herein any longer. 
     The above description is only the specific embodiment of the present disclosure, and the scope of the present disclosure is not limited thereto. The person skilled in the art can easily think of various equivalent modifications or substitutions within the technical scope disclosed by the present disclosure, which also fall within the protective scope of the present disclosure. Therefore, the protective scope of the present disclosure is determined by the scope of the claims.