Force sensitive element and axial force sensor

Abstract

A force-sensitive element and an axial force sensor, the force-sensitive element comprising: an annular or circular force-bearing member having a first force-bearing portion, a second force-bearing portion and a boss protruding upward from the first force-bearing portion; the boss is annular or circular and corresponds to the stress piece in shape. The outer wall of the boss protrudes outwards in the radial direction to form a plurality of peninsula-shaped protruding parts which are separated in the circumferential direction. The four sets of strain resistors are attached to the upper side surface of the stress piece in the whole circumferential direction of the stress piece at intervals in an insulating mode and located on the radial inner side of the first stress part, the number of the strain resistors in each set is the same, and at least one strain resistor is arranged in each set; and the strain resistors of the second group of strain resistors and the fourth group of strain resistors are distributed on the upper side surfaces of a plurality of peninsula-shaped protruding parts which are formed by outwards protruding the outer wall of the boss along the radial direction and are separated in the circumferential direction in a one-to-one correspondence manner. By means of the protruding parts which are distributed at intervals in the circumferential direction, a proper area of the stress piece can have negative stress, so that the measurement accuracy of the Wheatstone bridge is improved.

Description

Technical Field

[0001] The present application relates to the field of sensor technology, and in particular to a force sensitive element and an axial force sensor. Background Art

[0002] CN115931188A and CN116576998A disclose a force sensor, which is provided with four circumferentially spaced varistors on the upper surface of a metal base as a force sensitive element. These four varistors form a Wheatstone full bridge to measure the deformation degree of the metal base, and then obtain the magnitude of the axial force. Since the thick film resistors are all arranged on the upper surface, the bending stress on the surface is positive (i.e., tensile stress), which also leads to poor theoretical accuracy. In order to improve its theoretical accuracy, two fixed resistors can be arranged in the electronic module assembly together with the varistor to form a Wheatstone full bridge, but doing so will cause the temperature of the fixed resistor and the varistor to be different, thus causing temperature drift.

[0003] In addition, due to the mechanical matching deviation caused by the processing accuracy (flatness, surface roughness) of the metal base itself and the coaxiality with the force-applying member, the increase or decrease degree of the resistance value on the relative bridge arm is usually different, which has a very adverse effect on the measurement accuracy and greatly hinders practical application. Utility Model Content

[0004] In view of the deficiencies of the prior art, the present application is dedicated to providing a force sensitive element to improve its measurement accuracy.

[0005] To achieve the above objectives, this application provides the following technical solutions:

[0006] A force sensitive element, comprising:

[0007] A force-bearing member arranged axially in the up-down direction and in an annular or circular shape comprises an annular first force-bearing portion arranged on the upper side thereof, an annular second force-bearing portion arranged on the lower side thereof, and a boss protruding upward from the first force-bearing portion; the second force-bearing portion is concentrically arranged on the radial outer side of the first force-bearing portion and the radial outer side of the boss, and the boss is an annular or circular shape corresponding to the shape of the force-bearing member; the outer wall of the boss protrudes radially outward to form a plurality of peninsula-shaped protrusions separated in the circumferential direction;

[0008] Four groups of strain resistors are attached to the upper surface of the force-bearing member in an insulated manner at intervals throughout the circumference of the force-bearing member and are located radially inside the first force-bearing portion, each group of strain resistors has the same number and has at least one strain resistor, the first group of strain resistors and the third group of strain resistors are distributed circumferentially at intervals in a first annular area on the upper surface of a boss protruding upward from the first force-bearing portion, the second group of strain resistors and the fourth group of strain resistors are distributed circumferentially at intervals in a second annular area on the upper surface of the force-bearing member, and the second annular area is located outside the first annular area; the strain resistors of the second group of strain resistors and the four groups of strain resistors are distributed one by one on the upper surfaces of a plurality of peninsula-shaped protrusions separated in the circumferential direction formed by the outer wall of the boss protruding radially outward;

[0009] Among them, the four groups of strain resistors are respectively combined into four bridge arm resistors of the Wheatstone full bridge, and the bridge arm resistors corresponding to the first group of strain resistors and the third group of strain resistors are located on the two bridge arms on opposite sides; each group of strain resistors is combined into a corresponding bridge arm resistor individually or in parallel, series or mixed series-parallel manner.

[0010] Preferably, a tangentially extending groove is provided at the lower portion of the outer wall of the protrusion.

[0011] Preferably, the protrusion itself is symmetrically arranged about a symmetrical center line extending radially along the force-bearing member, and the strain resistor arranged on the protrusion is arranged on the symmetrical center line of the protrusion.

[0012] Preferably, an axially extending inner concave portion is formed between each two circumferentially adjacent protrusions.

[0013] Preferably, one end of the inner recessed portion sinks to the lower side of the first force-bearing portion.

[0014] Preferably, the strain resistors are electrically connected via an external circuit or a conductive trace disposed on the upper surface of the force-bearing member to form corresponding bridge arm resistors.

[0015] Preferably, the strain resistors of the first group of strain resistors and the third group of strain resistors are distributed at equal angular intervals in the circumferential direction, and the strain resistors of the second group of strain resistors and the fourth group of strain resistors are distributed at equal angular intervals in the circumferential direction.

[0016] The utility model also claims protection for an axial force sensor, which includes:

[0017] The force sensitive element mentioned above;

[0018] An electronic module assembly disposed on an upper side of the force sensitive element and electrically connected to the strain resistor; and

[0019] A shell is provided outside the electronic module assembly and the strain resistor from the upper side, and the first force-bearing part is located outside the shell.

[0020] Preferably, the force-bearing member and the boss are annular, and an axial hole penetrating up and down is provided at the center of the force-bearing member; the shell includes an outer cylinder shell, an inner cylinder shell and a cover plate connecting the upper ends of the outer cylinder shell and the inner cylinder shell, which are coaxial inside and outside and axially arranged up and down, and the lower end of the outer cylinder shell is sealingly fixed to the force sensitive element; the lower end of the inner cylinder shell extends into the axial hole and is sealingly connected to the axial hole.

[0021] Preferably, the force-bearing member and the boss are circular; the axial force sensor also includes a stepped conductive coil spring whose one end is in electrical contact with the electronic module assembly, and the conductive coil spring is held in a terminal retaining seat; the upper part of the shell is rolled inward to form a clamping portion, and the clamping portion presses the terminal retaining seat downward. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a top view of the force sensitive element of the first embodiment;

[0023] Figure 2 The force sensor of the first embodiment is Figure 1 A cross-sectional view of AA is shown;

[0024] Figure 3 A circuit diagram of a Wheatstone bridge composed of strain resistors according to the first embodiment;

[0025] Figure 4 is a longitudinal sectional view of the axial force sensor of the first embodiment;

[0026] Figure 5 is a top view of a force sensitive element of a second embodiment;

[0027] Figure 6 The force sensor of the second embodiment is Figure 5 A cross-sectional view of BB shown;

[0028] Figure 7 A circuit diagram of a Wheatstone bridge composed of strain resistors according to a second embodiment;

[0029] Figure 8 , Fig. 9 The stress simulation calculation results of the radial stress σr and the tangential stress σt on the symmetric midline M of the upper surface of the protrusion of the force sensor of the second embodiment in the groove-free structure;

[0030] Fig.10 , Fig.11The stress simulation calculation results of the radial stress σr and the tangential stress σt on the symmetric midline M of the upper surface of the protrusion of the force sensitive element of the second embodiment under the groove structure;

[0031] Fig.12 is an exploded view of the axial force sensor of the second embodiment;

[0032] Fig.13 is a longitudinal sectional view of an axial force sensor according to a second embodiment;

[0033] Fig.14 is a three-dimensional diagram of a force sensitive element according to a third embodiment;

[0034] Fig.15 , Fig.16 The stress simulation calculation results of the radial stress σr and the tangential stress σt on the symmetric midline M of the upper surface of the protrusion of the force sensor of the third embodiment in the non-porous structure;

[0035] Fig.17 , Fig.18 The stress simulation calculation results of the radial stress σr and the tangential stress σt on the symmetric midline M of the upper surface of the protrusion of the force sensitive element of the third embodiment under the hole structure;

[0036] Fig.19 is an exploded view of the axial force sensor of the third embodiment;

[0037] Fig. 20 is a longitudinal sectional view of an axial force sensor according to a third embodiment;

[0038] Fig.21 is a three-dimensional diagram of a force sensor according to a fourth embodiment;

[0039] In the figure: 11a, 11b, 11c, 11d, 21a, 21b, 21c, 21d, 21e, 21f, first strain resistor; 21a, 21b, 21c, 21d, 22a, 22b, 22c, 22d, 22e, 21f, first strain resistor; 11, 21, force sensitive element; 100, 200, axial force sensor; 110, 210, force bearing member; 111, 211, first force bearing part; 112, 212, second force bearing part; R1, first bridge arm resistor; R2, second bridge arm resistor; R3, third bridge arm resistor; R4, fourth Bridge arm resistor; 119, conductive trace; 115, boss; 113, 213, protrusion; 118, 218, insulating layer; 114, circumferential positioning portion; Z1, first annular area; Z2, second annular area; 116, 216, recessed portion; 13, 23, support member; 14, 24, electronic module assembly; 15, 25, housing; F1, F2, axial force; 24a, flexible circuit board; 12, 22, sealing ring; 110, 220, force-bearing member; 113a, sealing groove; 19, pin; 16, 26, terminal; 115a, groove; 115b, hole. DETAILED DESCRIPTION

[0040] The technical solution of the present application will be clearly and completely described below in conjunction with the accompanying drawings. The following embodiments are exemplary and are only used to explain the present application, and cannot be interpreted as limiting the present application. In the following description, the same symbols are used to represent the same or equivalent elements, and repeated descriptions are omitted.

[0041] In the description of the present application, it should be understood that the terms "upper", "lower", "inside", "outside", "left", "right", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the products of the present application are conventionally placed when in use, or are the orientations or positional relationships conventionally understood by those skilled in the art. They are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0042] In addition, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0043] It should be further understood that the term “and / or” used in the specification and corresponding claims of this application refers to any and all possible combinations of one or more of the listed items.

[0044] like Figure 1 to Figure 3 As shown. The first embodiment of the utility model provides a force-sensitive element 21. The force-sensitive element 21 includes a circular force-bearing member 210, and the axial direction of the force-bearing member 210 extends up and down. The force-bearing member 210 has an annular first force-bearing portion 211 arranged on its upper side, and an annular second force-bearing portion 212 arranged on its lower side, and the second force-bearing portion 212 is concentrically arranged on the radial outside of the first force-bearing portion 211. The first force-bearing portion 211 is used to receive a downward axial force F1, and the second force-bearing portion is used to receive a downward axial force F2. In a state of static force balance, F1 and F2 are reaction forces to each other, which are equal in magnitude and opposite in direction. Under the action of the axial force F1 and the axial force F2, bending stress is generated on the upper surface of the force sensitive element 21. Since the first strain resistors 21a~21f and the second strain resistors 22a~22f are located at different radial distances, the changes in resistance are different under the action of the axial force. Therefore, it can also be said that the first strain resistor and the second strain resistor are arranged at radial distances of different deformation amounts of the force-bearing member 210.

[0045] The force sensitive element 21 further includes twelve strain resistors which are insulatedly attached to the upper surface of the force bearing member 210 and are located radially inward of the first force bearing portion 211. The twelve strain resistors are composed as follows: Figure 2 The Wheatstone full bridge shown. The six first strain resistors 21a-21f are sequentially and spaced apart in the first annular region Z1 on the relatively radial inner side, and the other six second strain resistors 22a-22f are sequentially and spaced apart in the second annular region Z2 on the relatively radial inner side. The six first strain resistors 21a-21f and the six second strain resistors 22a-22f are staggered in the circumferential direction. The upper surface of the force-bearing member 210 may be covered with an insulating layer 218, and the strain resistors are arranged on the upper surface of the insulating layer 218.

[0046] Among them, the three first strain resistors 21a, 21c and 21e are the first group, which are connected in parallel to form the first bridge arm resistor R1; the three second strain resistors 22a, 22c and 22e are the second group, which are connected in parallel to form the second bridge arm resistor R2; the three first strain resistors 21b, 21d and 21f are the third group, which are connected in parallel to form the third bridge arm resistor R3; the three second strain resistors 22b, 22d and 22f are the fourth group, which are connected in parallel to form the fourth bridge arm resistor R4. Among them, the first bridge arm resistor R1 and the second bridge arm resistor R2 are located on the bridge arms on opposite sides, and the second bridge arm resistor R2 and the fourth bridge arm resistor R4 are located on the bridge arms on opposite sides. The Wheatstone full bridge is provided with voltage by the Vc and Vd terminals, and under the balancing action of F1 and F2, the corresponding voltage signals are output by the V1 and V2 terminals, thereby measuring the magnitude of the axial force.

[0047] In the force sensitive element 21 of the embodiment, since each bridge arm resistor of the Wheatstone full bridge serving as the measuring circuit is composed of three circumferentially distributed strain resistors, for a certain degree of matching deviation (such as coaxiality deviation), although the resistance value of a certain strain resistor of the bridge arm on the opposite side changes differently, the overall difference in the bridge arm resistance composed of the above three strain resistors is much smaller. Therefore, the measurement deviation caused by mechanical matching factors such as coaxiality deviation can be eliminated to a large extent, thereby improving the measurement accuracy; and since they are all in the same temperature environment, the temperature drift caused by this is avoided.

[0048] In a further preferred embodiment of this embodiment, the twelve strain resistors are arranged on the upper surface of the force bearing member 210 at an angle interval of 30° in the circumferential direction, and preferably have the same or similar initial resistance values. Figure 2 It is only shown that each of the three strain resistors mentioned above is connected in parallel to form a corresponding bridge arm resistor, but in some other variant embodiments, each of the three strain resistors mentioned above can also be connected in series to form a corresponding bridge arm resistor; in more complex variant embodiments, the three resistors can also be connected in mixed series-parallel, for example, two of the strain resistors can be connected in series and then connected in parallel with the remaining strain resistor, or two of the strain resistors can be connected in parallel and then connected in series with the remaining strain resistor. In some other more complex variant embodiments, each bridge arm resistor can also be composed of four or more strain resistors in the same manner. In short, configuring the total resistance of each bridge arm resistor to depend on a combination of strain resistors arranged at the same radial distance but evenly distributed at multiple circumferential angles formed in the same manner is very beneficial to improving the error of the force sensitive element caused by mechanical matching deviation.

[0049] The strain resistors of each bridge arm resistor may be connected by means of an external circuit to form a parallel connection, a series connection, or a mixed series-parallel connection.

[0050] The upper surface of the force sensitive element 21 may be lifted upward relative to the first force receiving portion 211 to form a circular boss 215 .

[0051] like Figure 4 As shown, this embodiment also provides an axial force sensor 200 using the above-mentioned force sensitive element 21. In addition to the above-mentioned force sensitive element 21, the axial force sensor 200 also includes a shell 25. The lower part of the shell 25 can be cylindrical, and its lower end can be welded to a first support step surface 217 formed on the force sensitive element 21 and located on the inner side of the first force-bearing part 211. The shell 25 is arranged around the periphery of the boss 215, and the first force-bearing part 211 is located on the outer side of the shell 25. An electronic module assembly 24 is also arranged inside the shell 25, and the electronic module assembly 24 can be electrically connected to the strain resistor through a flexible circuit board 24a. The electronic module assembly 24 can be fixedly supported on a cylindrical support seat 23. The support seat 23 is located inside the shell 25, and its lower end can also be supported on the first support step surface 217. The electronic module assembly 24 is electrically led out through a number of terminals 26. Among them, the terminal 26 can be a stepped conductive coil spring, which is held on a terminal retaining seat 26a and one end of which is electrically in contact with the electronic module assembly 24. The upper part of the shell 25 can be rolled inward to form a pressing portion (not marked), and the pressing portion presses the terminal retaining seat 26a downward to the electronic module assembly 24 or the support seat 23. A sealing ring 22 can be provided between the terminal retaining seat 26a and the pressing portion. In addition to being fixedly supported on a cylindrical support seat 23, in some other schemes, the electronic module assembly 24 can also be alternatively directly bonded to the upper surface of the force-bearing member 110, or directly fixed to the lower end of the terminal retaining seat 26a.

[0052] like Figure 5 to Figure 7 As shown. The second embodiment of the utility model provides another force sensitive element 11 with a different structure. Similar to the first embodiment, the force sensitive element 11 includes a force-bearing member 110, and the axial direction of the force-bearing member 110 extends up and down. Compared with the force sensitive element 11 of the first embodiment, the force sensitive element 21 of this embodiment is annular rather than circular, and a shaft hole 131 is provided in the center thereof, which passes through the shaft hole 131 up and down.

[0053] The force-bearing member 110 has an annular first force-bearing portion 111 disposed on its upper side, and an annular second force-bearing portion 112 disposed on its lower side, and the second force-bearing portion 112 is concentrically disposed radially outside the first force-bearing portion 111. The first force-bearing portion 111 is used to receive the downward axial force F1, and the second force-bearing portion is used to receive the downward axial force F2. In a state of static force equilibrium, F1 and F2 are reaction forces to each other, which are equal in magnitude and opposite in direction. Under the action of the axial force F1 and the axial force F2, bending stress is generated on the upper surface of the force sensitive element 11. Since the first strain resistors 11a~11d and the second strain resistors 12a~12d are located at different radial distances, the resistance value changes differently under the action of the axial force. Therefore, it can also be said that the first strain resistor and the second strain resistor are arranged at radial distances of different deformation amounts of the force-bearing member 110.

[0054] The force sensitive element 11 also includes eight strain resistors insulatedly attached to the upper surface of the force-bearing member 110 and located radially inside the first force-bearing portion 111. The eight strain resistors form a Wheatstone full bridge. The four first strain resistors 11a to 11d are sequentially and spaced apart in the first annular area Z3 on the relatively radial inside, and the other four second strain resistors 12a to 12e are sequentially and spaced apart in the second annular area Z4 on the relatively radial inside. The four first strain resistors 21a to 21d and the four second strain resistors 12a to 12d are staggered in the circumferential direction. The upper surface of the force-bearing member 110 may be covered with an insulating layer 118, and the strain resistors are arranged on the upper surface of the insulating layer 118. A circumferential positioning portion 114 for relative positioning with an external setting may be provided on the outer wall of the force-bearing member 110.

[0055] like Figure 7 As shown, two spaced-apart first strain resistors 21a and 21c are the first group, which are connected in parallel to form the first bridge arm resistor R1; two spaced-apart second strain resistors 22a and 22c are the second group, which are connected in parallel to form the second bridge arm resistor R2; two spaced-apart first strain resistors 21b and 21d are the third group, which are connected in parallel to form the third bridge arm resistor R3; two spaced-apart second strain resistors 22b and 22d are the fourth group, which are connected in parallel to form the fourth bridge arm resistor R4. The first bridge arm resistor R1 and the second bridge arm resistor R2 are located on the bridge arms on opposite sides, and the second bridge arm resistor R2 and the fourth bridge arm resistor R4 are located on the bridge arms on opposite sides. The Wheatstone full bridge is provided with voltage by the Vc and Vd terminals, and under the balancing action of F1 and F2, the corresponding voltage signals are output by the V1 and V2 terminals, thereby measuring the magnitude of the axial force. Among them, each strain resistor of the bridge arm resistors R2 and R4 is provided with voltage by an external circuit (for example, through Fig.12The strain resistors of the bridge arm resistors R1 and R3 are connected in parallel through the conductive traces 119 arranged on the upper surface of the force sensitive element 11. In some other variant embodiments, the two strain resistors constituting each bridge arm resistor can be connected in series to form a corresponding bridge arm resistor.

[0056] In the force sensitive element 11 of the embodiment, since each bridge arm resistor of the Wheatstone full bridge as the measuring circuit is composed of two strain resistors distributed circumferentially, for a certain degree of matching deviation (such as coaxiality deviation), although the resistance value of a certain strain resistor of the bridge arm on the opposite side changes differently, the overall difference in the bridge arm resistance composed of the above two strain resistors is much smaller. Therefore, the measurement deviation caused by mechanical matching factors such as coaxiality deviation can be eliminated to a large extent, thereby improving the measurement accuracy; and since they are all in the same temperature environment, the temperature drift caused by this is avoided.

[0057] In a further preferred implementation of this embodiment, the eight strain resistors are arranged on the upper surface of the force-bearing member 110 at an angular interval of 45° in the circumferential direction, and preferably have the same or similar initial resistance values.

[0058] The force sensitive element 11 in this embodiment can also have a more optimized structure. Specifically, the upper surface of the force sensitive element 21 can be lifted upward relative to the first force-bearing part 211 to form a boss 115. The first strain resistors 11a~11d are located on the upper surface of the boss 115 that protrudes upward from the first force-bearing part 111, and the second strain resistors 12a~12d are arranged one by one on the upper surface of a plurality of peninsula-shaped protrusions 113 formed by the outer wall of the boss 115 protruding radially outward. Two circumferentially adjacent protrusions 113 are separated in the circumferential direction by an axially extending inner recess 116. A tangentially extending groove 113a is provided on the lower part of the outer wall of the protrusion 113. By providing such a groove 113a, the resistance value of the second strain resistor under the action of the axial forces F1 and F2 can be opposite to that of the first strain resistor, that is, reduced, thereby improving the measurement accuracy.

[0059] In the above embodiments, the strain resistor is preferably an isotropic resistor, such as a thick film resistor, that is, it has the same resistance strain coefficient in all directions.

[0060] It is known from the existing mechanical theory that when the force sensitive element 11 does not have the peninsula-shaped protrusion 113 , the stress at each location on the upper surface thereof is tensile stress, and the tensile stress is greater at locations closer to the radial inner side.

[0061] Figure 8 , Fig. 9The stress simulation calculation results of the radial stress σr and the tangential stress σt on the symmetric center line M of the upper surface of the protrusion 113 without the groove 113a are shown respectively under the condition that the size of the shaft F1 and F2 are both 35KN. The results show that: under the condition that the protrusion 113 is provided and there is no groove on the protrusion 113, its radial stress σr has negative stress (i.e., compressive stress) in a relatively limited radial distance range of the radial outer edge, and its minimum value is about -3MPa. At the same time, the minimum value of the tangential stress σt is about 8Mpa, which also appears at the radial outer edge. This shows that the stress distribution is changed by providing the protrusion 13, so that the total bending stress within a certain radial distance range close to the edge is reduced. The symmetric center line M extends along the radial direction of the force-bearing member 110.

[0062] Fig.10 , Fig.11 They are shown respectively Figure 6 The stress simulation calculation results of the radial stress σr and tangential stress σt of the force sensitive element 11 shown in FIG. 1 on the symmetric midline M of the upper surface of the protrusion 113 with the groove 113a under the condition that the axis F1 and F2 are both 35KN, the results show that: under the condition that the protrusion 113 is provided and the groove structure is provided, the absolute value of the negative stress of the radial stress σr at the radial outer edge increases, and its minimum value is -13MPa, but at the same time, the tangential stress σt has a minimum value of about -24Mpa at the radial distance of the non-edge (5.7mm to 6.1mm radially outward from the inner edge of the boss as the starting point), and the change is faster than σr. Therefore, when the radial distance is in the appropriate range (for example, about 5.8mm), the radial stress σr is about 13Mpa, and the tangential stress σt is about -18MPa. When the isotropic second strain resistor is provided here, its resistance value will decrease compared with the initial resistance value. Furthermore, by reducing R2 and R4 composed of the second strain resistor (while R1 and R3 composed of the first strain resistor are still increased), the measurement accuracy is greatly improved.

[0063] It can be seen from the above simulation calculation results that by setting a groove 113a at the lower part of the outer wall of the protrusion 113, the stress distribution on the upper surface of the protrusion 113 can be changed, and the resistance value of the second strain resistor thereon can be reduced within a certain radial distance range, thereby greatly improving the measurement accuracy.

[0064] like Figures 12-13As shown, this embodiment also provides an axial force sensor 100 using the above-mentioned force sensitive element 11. In addition to the above-mentioned force sensitive element 11, the axial force sensor 100 also includes a housing 15. The lower part of the housing 15 can be an inner and outer double-cylindrical shell structure, including an outer cylindrical shell 151 and an inner cylindrical shell 152 that are coaxial inside and outside and axially arranged up and down, and a cover plate 153 connecting the upper ends of the outer cylindrical shell 151 and the inner cylindrical shell 152. Among them, the lower end of the outer cylindrical shell 151 can be sealed and fixed to a first supporting step surface 117 formed on the force sensitive element 21 and located on the inner side of the first force-bearing part 111, and the lower end of the inner cylindrical shell 152 extends into the shaft hole 131 and can be sealed and connected to the inner wall of the shaft hole 131 through a sealing ring 12. The sealing ring 12 can be arranged in a sealing groove 131a formed on the inner wall of the shaft hole 131. The first force-bearing part 111 is located outside the outer cylindrical shell 151.

[0065] The housing 15 and the force sensitive element 11 form a mounting cavity (not marked). An electronic module assembly 14 is arranged in the mounting cavity, and the electronic module assembly 14 can be electrically connected to the strain resistor through a lead (not shown). A support seat 13 for supporting the electronic module assembly 14 can also be arranged in the mounting cavity. The electronic module assembly 14 can be electrically led outward through a plurality of terminals 16. The terminal 16 can be a pin, one end of which is electrically connected to the electronic module assembly 14 after passing through the housing 15 inward. Among them, the inner side of the terminal 16 can be assisted by a terminal fixing member 16a fixed to the upper end of the electronic module assembly 14. The electronic module assembly 14 can be positioned between the force sensitive element 11 through a vertical pin 19. For example, a positioning blind hole (not shown) can be provided on the force sensitive element 11, and a positioning hole 19a can be provided on the electronic module assembly 14. The upper and lower ends of the pin 19 are plugged into the positioning hole 19a and the positioning blind hole.

[0066] An axially extending inner concave portion 116 is formed between each two circumferentially adjacent protrusions 113 , and one end of the inner concave portion 116 can sink to the lower side of the first force-bearing portion 111 . A positioning blind hole can be provided at the bottom of the inner concave portion 116 .

[0067] like Fig.14 As shown, the third embodiment of the utility model provides a force sensor 11 obtained by changing the second embodiment. Compared with the second embodiment, the force sensor 11 of this embodiment is provided with a tangentially extending hole 113b on its protrusion 113 to replace the groove 113a. At the same time, the inner concave portion 116 can be selectively omitted. In order to facilitate processing, the hole 113b is preferably a straight hole.

[0068] Fig.15 , Fig.16 They are shown respectively Fig.14The stress simulation calculation results of the radial stress σr and the tangential stress σt of the force sensitive element on the symmetric midline M of the upper surface of the protrusion 113 without a hole under the condition that the magnitudes of the axes F1 and F2 are both 30KN. The results show that: under the condition that the protrusion 113 is provided and there is no hole on the protrusion 113, its radial stress σr appears negative stress (i.e., compressive stress) within a relatively limited radial distance range of the radial outer edge, and its minimum value is about -19MPa. At the same time, the minimum value of the tangential stress σt is about -3.4Mpa, which also appears at the radial outer edge.

[0069] Fig.17 , Fig.18 They are shown respectively Fig.14 The stress simulation calculation results of the radial stress σr and tangential stress σt on the symmetric midline M of the upper surface of the protrusion 113 with the hole 113b under the condition that the axis F1 and F2 are both 30KN, the results show that: under the condition that the protrusion 113 is set and the hole structure is present, the radial stress σr and the tangential stress σt both have a minimum value at the radial distance of the non-edge (4.8mm radially outward from the inner edge of the boss as the starting point), and the minimum values ​​are -15MPa and -67MPa respectively. Since the surface radial stress within the first annular area (about 2mm radially outward from the inner edge of the boss as the starting point) is above 100MPa, in order to make the reduction value of the second strain resistor as close as possible to the increase value of the first strain resistor, the radial stress σr and the tangential stress σt can be maximized as much as possible.

[0070] Combined with the simulation calculation results of the force sensor of the second embodiment, it can be known that providing the hole 113 b on the protrusion 115 can more effectively reduce the resistance of the second strain resistor than providing the groove 113 a, thereby improving the measurement accuracy.

[0071] Please refer to Fig.18 , Fig.19 The third embodiment of the utility model further provides an axial force sensor 100 using the above force sensitive element 11. Compared with the second embodiment, in addition to the different structure of the force sensitive element 11, the overall structure of the axial force sensor 100 can also be selectively changed as follows: the terminal 16 can be replaced by a cable, one end of which is passed through the housing 15 inwardly and then electrically connected to the electronic module assembly; the axial force sensor 100 can also include an annular force transmission member 17, which is downwardly abutted against the first force-bearing portion 111.

[0072] Preferably, the support seat 13 may include a vertical barrel 131 and a horizontal support plate 132 horizontally connected to the proximal end of the upper end of the barrel 131. The electronic module assembly 14 is supported on the horizontal support plate 132 and surrounded by the upper end of the barrel 131. More preferably, a positioning notch 133 is provided at the upper end of the barrel 131, and a part of the electronic module assembly 14 extends into the positioning notch 133 in a circumferentially positioned manner to form a circumferential positioning. The horizontal support plate 132 may be provided with a clearance hole 134 to allow the lead wire to pass through.

[0073] See also Fig. 20 The fourth embodiment of the utility model also provides a relatively inferior force sensitive element 11. Compared with the force sensitive element of the second embodiment, this embodiment includes four strain resistors instead of eight strain resistors, that is, two first strain resistors 11a, 11b and two second strain resistors 12a, 12b are staggered in the circumferential direction of the force-bearing member 110, and these four strain resistors are distributed at 90° angle intervals in the circumferential direction. Each strain resistor is a group of bridge arm resistors of a Wheatstone full bridge, rather than being formed by connecting several strain resistors in parallel, in series, or in parallel and in series. Compared with the solution in the prior art in which all four strain resistors are arranged on the upper surface of the force-bearing member 110, due to the presence of the groove 113a, the stress state of the second strain resistor is opposite to that of the first strain resistor, thereby improving the measurement accuracy.

[0074] The housing 15 is disposed on the outside of the electronic module assembly and the strain resistor from the upper side, and the first force-bearing portion 111 is located outside the housing 15 .

[0075] In the above embodiments, the strain resistor and the conductive trace may be covered with a protective layer such as a protective glaze.

[0076] The scope of the disclosure is defined not by the detailed description but by the claims and their equivalents, and all variations within the scope of the claims and their equivalents are construed as being included in the disclosure.

Claims

1. A force sensitive element (11), characterized in that: include: A force-bearing member (110) is arranged axially in the up-down direction and is annular or circular, and comprises an annular first force-bearing portion (111) arranged on the upper side thereof, an annular second force-bearing portion (112) arranged on the lower side thereof, and a boss (115) protruding upward from the first force-bearing portion (111); the second force-bearing portion (112) is concentrically arranged on the radial outer side of the first force-bearing portion (111) and the radial outer side of the boss (115); the boss (115) is annular or circular corresponding to the shape of the force-bearing member (110); the outer wall of the boss (115) protrudes radially outward to form a plurality of peninsula-shaped protrusions (113) separated in the circumferential direction; Four groups of strain resistors are attached to the upper surface of the force-bearing member (110) at intervals and insulated throughout the circumference of the force-bearing member (110) and are located radially inside the first force-bearing portion (111), each group of strain resistors having the same number and at least one strain resistor, the first group of strain resistors (11a, 11c) and the third group of strain resistors (11b, 11d) are circumferentially spaced and distributed in a first annular area (Z1) on the upper surface of a boss (115) protruding upward from the first force-bearing portion (111), the second group of strain resistors (2 The second group of strain resistors (22a, 22c) and the fourth group of strain resistors (22b, 22d) are circumferentially spaced and distributed in a second annular area (Z2) on the upper surface of the force-bearing member (110), and the second annular area (Z2) is located outside the first annular area (Z1); the strain resistors of the second group of strain resistors (22a, 22c) and the fourth group of strain resistors (22b, 22d) are distributed one by one on the upper surface of a plurality of peninsula-shaped protrusions (113) separated in the circumferential direction and formed by the outer wall of the boss (115) protruding radially outward; Among them, the four groups of strain resistors are respectively combined into four bridge arm resistors (R1, R2, R3, R4) of the Wheatstone full bridge, and the bridge arm resistors corresponding to the first group of strain resistors and the third group of strain resistors are located on the two bridge arms on opposite sides; each group of strain resistors is combined into a corresponding bridge arm resistor individually or in parallel, series or mixed series-parallel.

2. The force sensitive element (11) according to claim 1, characterized in that: A groove (113a) extending tangentially is provided at the lower portion of the outer wall of the protruding portion (113).

3. The force sensitive element (11) according to claim 1, characterized in that: The protrusion (113) itself is symmetrically arranged about a symmetrical center line (M) extending radially along the force-bearing member, and the strain resistors (12a, 12b, 12c, 12d) arranged on the protrusion (113) are arranged on the symmetrical center line of the protrusion (113).

4. The force sensitive element (11) according to claim 1, characterized in that: An axially extending inner recess (116) is formed between each two circumferentially adjacent protrusions (113).

5. The force sensitive element (11) according to claim 4, characterized in that: One end of the inner recess (116) sinks to the lower side of the first force-bearing portion (111).

6. The force sensitive element (11) according to claim 1, characterized in that: The strain resistors are electrically connected via an external circuit or a conductive trace (119) disposed on the upper surface of the force-bearing member (110) to form corresponding bridge arm resistors.

7. The force sensitive element (11) according to claim 1, characterized in that: The strain resistors of the first group of strain resistors (11a, 11c) and the third group of strain resistors (11b, 11d) are distributed at equal angles in the circumferential direction, and the strain resistors of the second group of strain resistors (21a, 21c) and the fourth group of strain resistors (21b, 12d) are distributed at equal angles in the circumferential direction.

8. An axial force sensor, characterized in that: include: A force sensitive element (11) as claimed in any one of claims 1 to 7; An electronic module assembly (14) disposed on the upper side of the force sensitive element (11) and electrically connected to the strain resistor; and A housing (15) is provided outside the electronic module assembly and the strain resistor from the upper side, and the first force-bearing portion (111) is located outside the housing (15).

9. The axial force sensor according to claim 8, characterized in that: The force-bearing member (110) and the boss (115) are annular in shape, and an axial hole (131) penetrating vertically is provided at the center of the force-bearing member (110); the housing (15) comprises an outer cylindrical shell (151) and an inner cylindrical shell (152) which are coaxial inside and outside and axially arranged vertically, and a cover plate (153) connecting the upper ends of the outer cylindrical shell (151) and the inner cylindrical shell (152); the lower end of the outer cylindrical shell (151) is sealedly fixed to the force sensitive element; the lower end of the inner cylindrical shell (152) extends into the axial hole (131) and is sealedly connected to the axial hole (131).

10. The axial force sensor according to claim 8, characterized in that: The force-bearing member (110) and the boss (115) are circular; the axial force sensor also includes a stepped conductive coil spring, one end of which is in electrical contact with the electronic module assembly (14), and the conductive coil spring is retained in a terminal retaining seat (26a); the upper part of the shell is rolled inward to form a pressing portion, and the pressing portion presses the terminal retaining seat (26a) downward.

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