Stress composite sensor and stress measuring device using the same for structure

Abstract: The invention is intended to provide a stress measuring device for a structure, wherein a plurality of stress sensors are composited or integrated to provide an integrated single-packaged stress composite sensor, the latter being used to deliver X-axis, X- and Z-axis or X-, Y- and Z-axis direction stress signals produced in the structure or deliver stress signals in selected directions, so as to make it possible to measure stresses. A hole 3 is formed in the stress concentration region of a structure 2 whose stresses are to be measured, and a 1-direction stress composite sensor P adapted to deliver stress signals in one direction alone, a 2-direction stress composite sensor adapted to deliver in two directions, or a 3-direction stress composite sensor adapted to deliver stress signals in three directions is selectively installed in the hole, whereby X-axis, X- and Z-axis or X-, Y- and Z-axis direction shearing strains produced in the structure or stresses corresponding to the selected stress composite sensor can be selectively measured.

Description: BACKGROUND OF THE INVENTION Field of Technical Applicability The present invention relates to a stress composite sensor and a stress measuring device using the same for a structure, for measuring stresses, such as shearing stresses, or shearing strains, produced in a structure such as an automobile, airplane, railroad vehicle, crane, robot or the like. Prior Art As for methods for measuring stresses, such as shearing stresses, or shearing strains, produced in a structure such as an automobile, airplane, railroad vehicle, crane, robot or the like, mention may be made of the photoelasticity method, brittle coating method, acoustic method, holographic method and strain gauge method, of which generally the strain gauge method has been used most frequently. Such mechanical quantity sensors are various in kind and easy to handle but when used for measuring stresses, they have to be equipped with transducers. Further, in the strain gauge method, the strain gauge is subjected to stresses in every direction and hence analysis is required. Further, a stress sensor comprising a conventional mechanical quantity sensor such as a strain gauge, when singly used on a structure, receives greater amounts of other stress than the main stress, depending upon the position where it is attached; thus, a plurality of stress sensors have to be used and a stress sensor has to be attached to the neutral point where stress other than the main stress is not transmitted or reduced, which makes it necessary to find the neutral point of the structure and to attach a stress sensor accurately to that neutral point. GB-A-1 088 872; AUTOMATIK, vol. 14, no. 1, January 1969 Bad Worishofen DE, pages 10-17, K. Hoffmann "Die Auswahl geeigneter Dehnungsmeßstreifen (DMS)"; ELECTRONICS & COMMUNICATIONS IN JAPAN, Part II - ELECTRONICS, vol. 73, no. 11, November 1990, New York US, pages 97-104, XP 000229561 M. Esashi et al. "Fabrication of Semiconductor Tactile Imager"; and EP-A-0 611 959 disclose stress composite sensors with a plurality of stress sensors comprising strain gauges fixed on the same base plate for delivering stress signals in one direction. EP-A-0 162 565; JP-A-60-158327; and GB-A-1 088 972 describe measurements of stress in more than one dimension. US-A-5 186 042 discloses a stress composite sensor which has the features included in the first part of claim 1. SUMMARY OF THE INVENTION It is the object underlying the present invention to provide a stress composite sensor array that is capable of accurate stress measurement and can be accommodated in a small space. This object is met by each of claim 1. Preferred embodiments are disclosed in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a 1-direction sensor segment which is not covered by the present invention; Fig. 2 is a perspective view of a 1-direction stress composite sensor which is not covered by the present invention; Fig. 3 is a perspective view of a 2-direction sensor segment; Fig. 4 is a perspective view of a 2-direction stress composite sensor; Fig. 5 is a perspective view of a laminated 2-direction stress composite sensor; Fig. 6 is a perspective view of a 3-direction sensor segment; Fig. 7 is a perspective view of a 3-direction stress composite sensor; Fig. 8 is a perspective view of a laminated 3-direction stress composite sensor; Fig. 9 is a view showing an example of a signal processing circuit using 1-direction sensor elements; Fig. 10 is a view showing an example of a signal processing circuit using two rows of interconnected sensor segments; Fig. 11 is a perspective view showing an example in which a 1-direction stress composite sensor is installed in a hole in a vehicle axle; Fig. 12 is an enlarged view of the region of Fig. 11 where the stress composite sensor is installed; Fig. 13 is a view showing a disk-type 1-direction stress composite sensor installed in a hole in a vehicle axle, which is not an embodiment of the present invention; Fig. 14 is a view showing a plurality of 1-direction stress composite sensors installed in the same hole in a vehicle axle, which is not an embodiment of the present invention; Fig. 15 is a view showing a 2-direction stress composite sensor installed in a hole in an axle; Fig. 16 is a view showing a 1-direction and 2-direction stress composite sensors installed in the same hole in a vehicle axle; Fig. 17 is a view showing a 3-direction stress composite sensor installed in a hole in an axle; Fig. 18 is a view showing a 2-direction stress composite sensor installed in an angular hole in an axle; and Fig. 19 is a view showing a stress composite sensor installed in a hole in an axle and fixed in position by a filler. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described with reference to preferred embodiments showing examples of a stress measuring device applied to a vehicle, particularly an automobile. The invention is not limited to these embodiments. Fig. 1 shows an example of the basic arrangement of a 1-direction stress composite sensor which is not covered by the present invention, wherein strain gauges a, b, c, d formed of metal resistance foil are fixed, in pairs with the two in each pair crossing each other, on opposite surfaces of a base plate made of a plastic material such as epoxy resin, metal or silicon material so as to form a stress sensor (sensor element) S. A plurality of such sensor elements are integrally interconnected on the same plane to form a sensor segment g; each stress sensor S or a selected sensor segment g is used to measure stress in one direction. In Fig. 2, a plurality of rows of sensor segments g as shown in Fig. 1 are prepared and signal processing circuits G such as bridge circuits and amplifying circuits are integrally formed on the same base plate into a single package to provide a stress composite sensor P, so that each stress sensor S in the sensor segments g or the stress sensors S in selected sensor segments g alone are used to measure stresses in one direction. Fig. 3 shows an example of the basic arrangement of a 2-direction stress composite sensor, wherein sensor elements e1 and e2 which have stress sensors S fixed thereto and which are integrally connected together at right angles to form a sensor segment g, so that stresses in two directions, X- and Z-axis directions, can be measured. In Fig. 4, a plurality of sensor segments (in 4 lateral rows and 3 longitudinal rows) as shown in Fig. 3 are integrally connected together to form a 2-direction stress composite sensor P, so that stresses in two directions can be measured by each sensor element e in the sensor segments in the X- and Z-axis directions or by the stress sensors S in selected sensor elements e. In Fig. 5, 2-direction stress composite sensors shown in Fig. 4 are laminated in multilayer (in two layers) and connected together, whereby 2-direction stress composite sensors are formed into a single package. Fig. 6 shows an example of the basic arrangement of a 3-direction stress composite sensor, three sensor elements having stress sensors S fixed on base plates 1 are integrally connected in the three directions of the X-, Y- and Z-axes to form a sensor segment g, so that individual stresses are measured by the individual stress sensors S, whereby stresses in three directions can be measured. In Fig. 7, a plurality of sensor segments g (in 4 lateral rows and 3 longitudinal rows) as shown in Fig. 6 are integrally connected together to form a 3-direction stress composite sensor P, so that stresses in three directions can be measured by each sensor element in the sensor segments in the X-, Y- and Z-axis directions or by the stress sensors in selected sensor elements e. In Fig. 8, 3-direction stress composite sensors shown in Fig. 7 are laminated in multilayer (in two layers) and connected together, are formed into a single packaged 3-direction stress composite sensor P. The aforesaid 2-direction sensor segment g, 2-direction stress composite sensor P, 3-direction sensor segment g and 3-direction stress composite sensor P may be produced by semiconductor process or made of ceramic or other material, and a signal processing circuit G such as a bridge circuit or amplifying circuit for the stress sensor S can be easily integrally formed on the same base plate such as a metal base or semiconductor base into a single package, in the same manner with that shown in Fig. 2. Further, in the case where a signal processing circuit is to be integrally formed on the base plate 1 of the sensor segment g shown in Fig. 2, the strain gauges a, b, c, d in each sensor element e together with adjusting resistors r, as shown in Fig. 9, constitute bridge circuits, which are connected to arithmetic circuits A and B through amplifying circuits AP to form a logic circuit L1, the respective outputs from the logic circuits L1 - L3 being connected to arithmetic circuits C and C' so as to derive stress signals. Fig. 10 shows an example of the arrangement of a signal processing circuit comprising for a 1-direction stress composite sensor comprising two rows of sensor segments g connected together. A signal processing circuit for 2- and 3-direction stress composite sensors can be formed by applying the same idea of forming said signal processing circuit for 1-direction stress composite sensor. In addition, strain gauges for the stress sensor S have been shown as using metal resistance wire strain gauges, but the invention is not limited thereto and strain gauges based on piezoelectric effect, strain gauges based on crystalline structure, and semiconductor strain gauges may be used. Fig. 11 shows an example of the stress measuring device of the present invention applied to an automobile (structure) K, wherein a hole 3 is formed in an axle 2 in the X-axis direction which is the direction of travel of the vehicle and a stress composite sensor P capable of measuring stresses in one direction alone or two or three directions is selectively mounted in said hole, thereby constituting the stress measuring device. In this case, the friction force F can be measured in the X-axis direction which is the direction of travel of the vehicle, the transverse force can be measured in the Y-axis direction which is the transverse direction, and the vertical reaction (vertical load) N can be measured in the Z-axis direction which is the vertical direction. Fig. 12 is an enlarged view of stress measuring means comprising a stress composite sensor P installed in a hole 3 in an axle 2 for measuring stresses in one direction alone shown in Fig. 2, said stress composite sensor P being embedded with the longitudinal edge of its base plate 1 brought into contact with the peripheral wall of the hole 3. If necessary, a filler may be charged into the empty space to provide a waterproof construction. In this stress measuring device, each stress sensor S of a plurality of rows of equispaced coplanar sensor segments g effects sensing corresponding to shearing strains in the X-axis direction alone produced in the axle 2 to deliver a stress signal; thus, the friction force F can be measured. Further, as shown in Fig. 13, a 1-direction stress composite sensor P may be made in the form of a disk and if it is installed in a hole 3 in an axle at right angles with the X-axis direction, it delivers a stress signal in the vertical direction alone to make it possible to measure the vertical load N. Fig. 14 shows an example of a stress measuring device comprising three 1-direction stress composite sensors P installed at intervals in a hole 3 in an axle 2. In this case, the main sensor P1 and sub-sensors P2 and P3 effect sensing in the X-axis direction alone corresponding to shearing strains formed in axle 2 to deliver stress signals, of which 1-direction stress signals optimum for use as brake control parameters are selected to measure the friction force F. If the 2-direction stress composite sensor P shown in Figs. 4 and 5 is installed in the hole 3 in the axle 2 to constitute a stress measuring device, the stress sensors S of many sensor elements effect sensing to deliver stress signals corresponding to shearing strains produced in two directions, the X- and Z-axis directions, in the axle 2, and selected out of said stress signals are those stress signals in the X- and Z-axis directions which are optimum for use as brake control parameters to enable measurement of the friction force F and vertical load N, and the road surface friction coefficient µ can be easily obtained by arithmetically processing their output values. If the 3-direction stress composite sensor P shown in Figs. 7 and 8 is installed in the hole 3 in the axle 2 to constitute a stress measuring device, the stress sensors S of many sensor elements effect sensing to deliver stress signals corresponding to shearing strains produced in three directions, the X-, Y- and Z-axis directions, in the axle 2, and selected out of said stress signals are those stress signals in the X-, Y- and Z-axis directions which are optimum for use as brake control parameters to enable measurement of the friction force F, vertical load N and transverse force. Furthermore, stresses in particular directions can be measured, namely their directions and values can be measured by sorted stress signals in the X- and Y-axis or X-, Y- and Z-axis directions, and the optimum road surface friction coefficient µ can be easily obtained by arithmetically processing the selected friction force F and vertical load N. In the case where the 1-, 2- or 3-direction stress composite sensor P is selected to constitute a stress measuring device, the 2-direction stress composite sensor P2, as shown in Fig. 15, may be installed in the hole 3 in the axle to selectively measure stress signals in the X- or Z-axis direction, or as shown in Fig. 16, the 1- and 2-direction stress composite sensors P1 and P2 may be installed in the hole 3 in the axle with a distance therebetween so that the 1-direction stress composite sensor P1 is used to measure the friction force F which is associated with stress signals in the X-axis direction alone, while the 2-direction stress composite sensor P2 is used to measure the load surface friction coefficient µ. Alternatively, as shown in Fig. 17, a 3-direction stress composite sensor P3 may be installed in the hole 3 in the axle to separately or selectively use all or some of the stress signals in the X-, Y- and Z-axis directions so as to measure all or some of the friction force F, vertical load N and transverse force. Thus, 1-, 2- and 3-direction stress composite sensors P1, p2 and P3 may be used singly or in combination to constitute stress measuring means for obtaining stress signals. Stress composite sensors each obtained by forming into a single package a plurality of stress sensors capable of measuring stresses in one direction or a plurality of directions may be used singly or in combination to effect sensing by stress sensors of a plurality of selected sensor segments alone in the X-axis, X- and Y-axis and X-, Y- and Z-axis directions of the structure, the resulting stress signals being separated according to the X-, Y- and Z-axis directions, and the separated stress signals are respectively added to provide addition stress signals which are then used for comparative computation. In addition, the hole 3 in the axle may not necessarily be circular; it may be polygonal as shown in Fig. 18, in which case the contact between the stress composite sensor and the peripheral wall of the polygonal hole becomes more intimate, facilitating transfer of shearing strains produced in the axle to the stress composite sensor, ensuring accurate measurement of stresses. In addition, in the case where a stress composite sensor P is formed into a small-sized single package, as shown in Fig. 19, the stress composite sensor P is inserted in the hole 3 in the axle and fixed therein by charging filler H such as epoxy resin into the empty space, thus constituting a waterproof stress measuring device. Further, a hole 3 of different shape may be formed and a stress composite sensor P may be embedded in said hole in any desired posture to make it possible to measure stresses in a selected direction. Embodiments in which the stress composite sensor of the present invention is embedded in an axle of a vehicle have been described so far; however, the same functions and effects can be obtained when it is embedded in a strut portion of a vehicle. Further, the invention is not limited to vehicles and is applicable to other structures. According to the present invention, a stress composite sensor for measuring 1-dimensional, 2-dimensional and 3-dimensional stress directions and stress values can be realized by a single sensor, and when this stress composite sensor is embedded in a structure where 2-dimensionally or 3-dimensionally complicated stresses occur, necessary stress directions and stress values can be measured. Particularly, if the stress composite sensor according to the invention is applied to an axle where 3-dimensionally complicated stresses occur, it is possible to measure selected stresses not influenced by cross talks; thus, a highly safe brake control system can be provided.

Claims: A stress composite sensor (P) having a plurality of sensor elements (e) and arithmetic circuits (A), wherein each of the sensor elements (e) includes a rectangular base plate (1), a pair of first strain gauges (a, b) disposed on a first main surface of the base plate (1) so as to cross each other, and a pair second strain gauges (c, d) disposed on a second main surface of the base plate (1) so as to cross each other and to be in symmetry to the first strain gauges (a, b) with respect to a centre plane of the base plate (1), wherein the four strain gauges (a, b, c, d) form a bridge circuit, wherein the sensor elements (e) include X-sensor elements (e1) for measuring stress in the X-direction and Y-sensor elements (e2) for measuring stress in the Y-direction, and wherein the arithmetic circuits (A) calculate the stress from outputs of the sensor elements (e), characterised in that all sensor elements (e) are substantially identical with respect to the size of their base plates (1) and the disposition of their strain gauges (a, b, c, d), that one X-sensor element (e1) and one Y-sensor element (e2) have their edge portions orthogonally joined together to form an L-shaped sensor segment (g) capable of outputting X- and Y-direction stress signals, and that a plurality of such sensor segments (g) are edgewise joined together to form one homogeneous assembled body in a matrix form and are integrated into a single package. The stress sensor (P) of claim 1, wherein each sensor segment (g) includes a Z-sensor element (e3) measuring stress in the Z-direction, with the X-, Y- and Z-sensor elements (e1, e2, e3) forming the three contiguous faces of a parallelepiped, to output X-, Y- and Z-direction stress signals. A stress measuring device comprising the stress sensor (P) of claim 1 or 2 and a signal processing circuit, wherein said bridge circuit or an amplifying circuit is integrally formed on the same base plate (1). A stress measuring device having a stress sensor (P) according to claim 1 or 2 installed in a hole formed in a stress concentration region of the structure whose stress is to be measured, for measuring shearing stress in the X- and Y-axis or X-, Y- and Z-axis directions. The device of claim 4, wherein at least one or more sensor elements (e) or sensor segments (g) of the stress composite sensor (P) are selected for stress measurement. A stress measuring device having a stress sensor (P) according to claim 1 or 2 installed in a hole formed in a stress concentration region of the structure whose stress is to be measured, for measuring summed stress signals in the X- and Y-axis or X-, Y- and Z-axis directions of the structure. A stress measuring device having a stress sensor according to claim 1 or 2 installed in a hole formed in a stress concentration region of the structure whose stress is to be measured, wherein the stress sensor elements (e) of a plurality of sensor segments aligned in the X- and Y-axis or X-, Y- and Z-axis directions of the structure are employed, the stress signals of said stress sensor elements being taken separately according to the X-, Y- and Z-axis directions, added together and subjected to comparative computation. The device of claim 7, wherein when a sensor segment (g) is selected for stress measurement, a plurality of stress signals are derived from sensor segments disposed in a stress layer having relatively little mixing of other stresses produced in the structure, and combined. The device of claim 7 or 8, wherein stresses in the X- and Y-axis or X-, Y- and Z-axis directions are selected to measure stress in a plurality of directions, the resulting stress signals being used as control parameters.

Inventors: MIYAZAKI NAGAO, MIYAZAKI, NAGAO, Miyazaki, Nagao, c/o Japan Elec. Ind. Ltd.
Applicants: JAPAN ELECTRONICS IND LTD, JAPAN ELECTRONICS INDUSTRY, LTD.
Application year: 1995
Main classification: G01L1
IPC codes: G01L5, G01L1