ELECTRICAL INCLINATION SENSOR AND METHOD FOR ITS MANUFACTURE

Abstract: The sensor comprises a body (1) formed by first and second elements (2, 3) of which at least one (2) has a ca­ vity (4), the elements being sealed together to form a cham­ ber (12). The chamber contains an electrically-conductive liquid (14) which fills it almost completely so as to form a bubble (15). At least one main electrode (6) and at least one pair of auxiliary electrodes (5, 9; 7, 10) extend into the cham­ ber (12) through the body (1) and are accessible on the ex­ terior thereof, so that any variation in the inclination of the body relative to at least one predetermined direction causes a movement of the bubble (15) and a corresponding variation in the electrical resistance measurable between each auxili­ ary electrode and the main electrode. The electrodes are constituted by strips of electrically-conductive material de­ posited by screen printing on at least one of the said ele­ ments by the thick film deposition method.

Description: The present invention relates to an electrical inclination sensing device. In particular the invention relates to a sensor of the kind defined in the introduction of Claim 1. An inclination sensor of this kind is described in AT-B-349 776. This prior sensor includes a hollow body formed by two glass members. The characteristics of the known sensor depend very much on the shape of the body. The latter, as stated, is of glass and is shaped when the glass is at a high temperature and in the plastic state. The body shapes of two sensors which are nominally identical may thus be noticeably different. This is reflected to an appreciable extent in the electrical characteristics of the sensor. A further disadvantage of the known sensor lies in the fact that it is not readily adaptable to low-cost, production - line manufacture. US-A-3 843 539 discloses a similar inclination sensor comprising a hollow body filled with a conductive liquid. The body of this sensor includes a glass cover member having an undulated surfaces which forms a central cavity and in which radial grooves are provided for receiving respective S-shaped electrodes. Also this prior sensor is not readily adaptable for low-cost, production-line mass manufacture. The object of the present invention is to provide an improved version of an electrical inclination-sensing device of the type specified at the beginning, which avoids the disadvantages of the known sensors. According to the invention this object is achieved by means of a device of the previously specified type, the main features of which are defined in Claim 1. The invention also relates to a method for the manufacture of an inclination sensor of the said type, the method having the features defined in Claims 12-18. Further characteristics and advantages of the invention will become apparent from the detailed description which follows, given with reference to the appended drawings, provided purely by way of non-limiting example, in which: Figure 1 is a perspective view of an inclination sensor according to the invention, Figure 2 is a section taken on the line II-II of Figure 1, Figure 3 is a section taken on the line III-III of Figure 2, Figure 4 is a section taken on the line IV-IV of Figure 2, Figure 5 is a section similar to Figure 2 but with the sensor inclined to the horizontal, Figure 6 is an electrical circuit diagram of a bridge circuit which can be used, in which the sensor according to the invention is connected to measure inclination, Figure 7 is a schematic perspective view of an alternative arrangement of the electrodes of the sensor according to the invention for enabling the detection of the inclination of the sensor relative to a plane or relative to two axes, Figure 8 shows an alternative arrangement of the electrodes of the sensor according to the invention for measuring inclination relative to a plane or relative to two axes, and Figure 9 shows a variant of the sensor according to the invention in which the amplification and/or compensation circuits for the electrical signal output by the sensor in use are incorporated in a single support. With reference to Figures 1 to 5, a sensor according to the invention includes a body 1 comprising two elements 2, 3 joined together. In the embodiment illustrated, the element 2 is generally cylindrical and has a cavity 4 in the shape of a hemisphere or a segment of a sphere. The element 3 acts as a base and, in the embodiment illustrated, is substantially parallelepipedal shaped and of modest thickness. The elements 2 and 3 may be made from ceramic, alumina (Al₂O₃), zirconium oxide(Zr₂0₃), beryllium oxide (BeO), Forsterite (2MgO-SiO₂), steatite (MgO-SiO₂), or of metals whether enamelled, vitrified or even anodised to obtain an insulating surface layer, or of yet other insulating materials. As is apparent in particular from Figure 3, three electrically conductive strips 5, 6 and 7 are applied to the face of the base plate 3 facing the hollow element 2. These conductive strips are applied to the support plate 3 by screen printing followed by firing according to the well known thick film method. The material constituting the strips may be any one of the materials used in the thick film method, for example a conductor based on noble metals (silver, palladium, platinum, gold etc.) or other metals (copper, nickel, aluminium etc.) or a polymeric type conductor. In the embodiment shown in Figure 3, the strips 5 and 7 have respective first ends 5a, 6a and 7a adjacent each other on one and the same side of the support plate 3 to facilitate their connection to external circuits. These strips, as will become apparent below, act essentially as electrodes of the sensor. The conductive strip 6 acts as the main or common electrode and its extent is such that, when the elements 2 and 3 are joined together, it extends into the chamber defined between them to an extent almost equal to the diameter of the circumference of the mouth of the cavity 4. In the embodiment shown in Figures 1 to 5, the conductive strip,or auxiliary electrode, 5 has a second end 5b facing the end of the main electrode 6 opposite the end 6a. A circular ring of a dielectric bonding material 8 (Figure 3), of a shape substantially corresponding to the annular face of the body 2 surrounding the mouth of the cavity 4, is also deposited on the support plate 3 again by the thick film deposition method. The dielectric ring 8 is deposited over the end 5b of the conductive strip 5, over an intermediate portion of the main strip 6 and over the end 7b of the strip 7 opposite the end 7a (Figure 3). The hollow element 2 also bears conductive strips 9, 10 deposited thereon by the thick film deposition method. These conductive strips, as is apparent from Figures 2, 4 and 5, extend along arcs of a great circle of the spherical surface to which the surface of the cavity 4 belongs. These strips have respective ends 9a, 10a which extend over the edge of the cavity onto the cylindrical outer surface of the hollow element 2. The end 10a (Figure 4) extends away from the diametral plane of the cavity 4 passing through the rest of the contact 10 and through the contact 9. A ring 11 (Figure 4) of dielectric bonding material is subsequently deposited on the annular surface of the hollow body 2 surrounding the mouth of the cavity 4. The dimensions of this ring correspond to those of the ring 8 applied to the support plate 3. The hollow element 2 is joined to the support plate 3 in the following manner. The element 2 is placed on the support plate 3 so that the rings 11 and 8 face each other and the strips 10 and 9 also face the strip 6 on the support. The dielectric rings 11 and 8 are then welded together by firing. The material constituting these rings may for example be glass or an insulating resin. As stated above, the end 10a of the conductive strip 10 deviates from the remaining part of this strip so that this end faces the conductive strip 7 on the support. The ends of the strip 10 and of the strip 7 are electrically interconnected by a weld (indicated 14 in Figure 1) formed by a eutectic alloy or by an epoxy resin filled with particles of electrically- conductive material such as silver, gold or copper. The ends 9a of the strip 9 and the end 5b of the strip 5 are similarly welded together. A predetermined quantity of conductive liquid 14 is introduced into the chamber 12 defined between the plate and the hollow body 2 through a hole 13 formed in the support plate 3. The hole 13 is then sealed for example by sealing with a eutectic alloy or with an epoxy resin. The quantity of conductive liquid introduced into the chamber 12 is such as not to fill the chamber completely so that a "bubble", indicated 15 in Figures 2 and 5,is formed. The sensor illustrated in Figures 1 to 5 acts as follows. If the sensor is disposed with the plate 3 horizontal, the bubble 15 is disposed symmetrically between the conductive strips 9 and 10. In this condition the electrical resistance measurable between the strips 5 and 6 and the resistance measurable between the strips 6 and 7 are substantially equal. If the support plate 3 is inclined, for example in the manner illustrated in Figure 5,so as to be at an angle α to the horizontal plane, the bubble 15 moves. In this position it is possible to detect a reduction in the resistance measurable between the strips 6 and 7 and an increase in the resistance between the strips 5 and 6. These variations in resistance are indicative of the angle α. The sensor described above may thus be connected in a bridge circuit to detect the said variations in resistance and hence the inclination of the sensor. Figure 6 shows one possible circuit usable for this purpose. In this Figure the resistances between the strips 6 and 7 and the strips 5 and 6 respectively are indicated R₁ and R₂, these resistances varying in accordance with the inclination as a result of the movement of the bubble 15 described above. The resistances R₃ and R₄ are those of resistors connected to the sensor in the manner illustrated so as to form a bridge. If a constant voltage is applied between the terminal 18 common to these resistors and the end 6a of the strip 6, the voltage V between the ends 5a and 7a of the strips 5 and 7 is indicative of the angle of inclination. The embodiment illustrated in Figures 1 to 5 obviously allows the inclination of the sensor to be detected solely with respect to one axis. Even if the shapes of the elements 2 and 3 of the sensor are left substantially unchanged, it is possible to form a sensor which can detect inclination relative to a plane or relative to a pair of non-parallel coplanar axes by a simple modification of the conductive strips deposited on the elements 2 and 3. Figure 7 shows schematically one possible shape and arrangement of the conductive strips for this purpose. As is apparent from Figure 7, it suffices to provide a main electrode or strip 6 shaped so that the part thereof enclosed within the chamber 12 effectively forms three arms 6b, 6c, 6d at 120°. Three conductive strips 109, 110, 111, also at 120° to each other, are correspondingly deposited on the cavity 4 of the hollow element 2. If the resistances between these strips and the three arms of the main strip 6 are measured it is possible to obtain an indication of the inclination of the plane of the support plate 3 to a reference plane. An alternative arrangement of the conductive strips is shown in Figure 8 in which two main strips 6 and 106 (superimposed and insulated from each other) form four arms at 90° within the chamber 12. Four conductive strips 109 to 112 equiangularly spaced from each other are correspondingly deposited on the wall of the cavity 4 of the hollow body 2. Clearly it is necessary to provide a suitable number of conductive strips on the support plate 3 for variants of Figures 7 and 8. As shown in Figure 9, a hybrid circuit 100 may to advantage be formed on the support plate 3, still by the thick film method, this circuit including both supply circuits for the sensor and amplification and processing circuits for the signal output by the sensor and, optionally, calibration and thermal compensation circuits. This solution enables the formation both of the inclination sensor proper and the electronic circuit associated therewith in a single monolithic structure. The sensor according to the invention has numerous advantages. It is easy to manufacture on a production line with good consistency of the geometric and electrical characteristics. It may be made from extremely cheap materials and with the use of highly automated, and hence low cost, technology. The structure of the sensor is extremely strong and hence suited for use even in the presence of strong vibrations.

Claims: Electrical inclination sensing device comprising a body (1) in which there is formed a closed chamber (12) containing a quantity of an electrically conductive liquid (14) which almost fills it so as to form a bubble (15), at least one main electrode (6) and at least one first and one second auxiliary electrode (5, 9; 7, 10) extending into the chamber (12) through the body (1) and accessible from the exterior of the body, so that any variation in inclination of the body (1) relative to at least one predetermined direction causes a movement of the bubble (15) and a corresponding variation in the electrical resistance measurable between each auxiliary electrode (7, 10; 5, 9) and the main electrode (6); the body (1) comprising two elements (2, 3) of which a first one (2) has a cavity (4), the elements being sealed together to form the said chamber; characterised it that the second one (3) of the elements (2, 3) forming the said chamber (13) is planar while the first one (2) has a cavity (4) in the form of a spherical segment, and in that at least a main electrode (6) is applied to the second planar element (3) while the auxiliary electrodes (9, 10) are applied at least partly to the first hollow element (2); the auxiliary electrodes (9, 10) being deposited at least partly along arcs of the same great circle of the sphere to which the said spherical segment belongs, the main electrode (6) extending along a line lying in the plane identified by the said arcs. A device according to Claim 1, characterised in that the strips (5, 6, 7, 9, 10) are formed by the thick film deposition method. A device according to Claim 2, characterised in that the first and second elements (2, 3) are joined together by a dielectric bonding material (8, 11). A device according to Claim 3, characterised in that the dielectric bonding material (8, 11) is deposited on at least one of the elements (2, 3) by the thick film deposition method. A device according to Claim 3 or Claim 4, characterised in that the first and second auxiliary electrodes (9, 10) extend outside the chamber (12) across the bonding material (8, 11) which joins the first and second elements (2 and 3) and onto the outer surface of the hollow element (2), and in that the planar element (3), on its face carrying the main electrode (6), and outside the chamber (4), also carries further first and second electrically conductive strips (5, 7) electrically connected to the first and second auxiliary electrodes (9, 10). A device according to any one of the preceding claims, characterised in that it includes at least three auxiliary electrodes (109, 110, 111) cooperating with at least one main electrode (6) to allow the detection of the inclination of the body (1) relative to a plane. A device according to any one of the preceding claims, characterised in that it includes first and second main electrodes (6, 106) cooperating respectively with first and second pairs of auxiliary electrodes (110, 112; 111, 109). A device according to Claims 1 and 7, characterised in that the auxiliary electrodes of the first and second pairs (110, 112; 109, 111) respectively are disposed along arcs of respective first and second great circles of the spherical surface on which the surface of the cavity (4) lies. A device according to any one of the preceding claims, characterised in that the said elements (2, 3) forming the body (1) are made of ceramic material. A device according to any one of claims 1 to 9, characterised in that the elements (2, 3) forming the body (1) are made of metal with a surface layer of electrically insulating material. A device according to any one of the preceding claims, characterised in that hybrid amplification and/or measuring and/or thermal compensation circuits are deposited on one (3) of the elements (2, 3) outside the chamber (4) by the thick film deposition method. Method for the manufacture of an inclination sensor according to one or more of the preceding claims, including the steps of: providing first and second elements (2, 3) which are electrically insulating at least on the surface, of which at least one (2) has a cavity (4) for forming the said chamber (4) together with the other element (3); applying at least first and second members (5, 7) of electrically-conductive material to at least one of the said elements (2, 3) to act as auxiliary electrodes and at least one further electrically-conductive member (6) for acting as a main electrode, and sealing the first and second elements (2, 3) together so that the electrically-conductive members (5, 6, 7) are at least partly within the chamber; characterised in that one (3) of the said elements (2, 3) forming the chamber (3) is given a planar shape while the other one (2) is provided with a cavity (4) in the form of a spherical segment and in that the at least one main electrode is applied to the planar element (3) while the auxiliary electrodes are applied to the hollow element 2; at least two conductive strips (9, 10) being deposited on the hollow element (2) to act as auxiliary electrodes, these extending partly over the surface of the cavity (4) and partly over the surface of the hollow element (2) outside the chamber (4); a first conductive strip (6) which will serve as the main electrode and at least one pair of supplementary strips (5, 7) are deposited on the planar element (3), the supplementary strips extending over a portion of the surface of the planar element (3) which will remain outside the chamber (12) up to zones which will be adjacent the outer ends (10 a , 9 a ) of the strips (10, 9) of the hollow element (2), and in that, after joining of the elements, the outer ends (10 a , 9 a ) of the strips (10, 9) of the hollow element (2) and the corresponding ends of the supplementary strips (5, 7) of the planar element (3) are electrically connected by welding with an electrically conductive material. A method according to Claim 12, characterised in that the conductive liquid (14) is introduced into the chamber (4) through a hole (13) formed in one (3) of the elements (2, 3) forming the body (1) and in that the hole (13) is sealed hermetically after the introduction of the conductive liquid (14). A method according to Claim 12, characterised in that the liquid is poured into the cavity (4) of one (2) of the elements (2, 3); the elements then being sealed together. A method according to Claim 13 or Claim 14, characterised in that the first and second elements (2, 3) are joined together by a dielectric bonding material (8, 11). A method according to Claim 15, characterised in that a layer (8, 11) of dielectric material which can become adhesive as a result of heating, is applied to regions of the elements (2, 3) intended to be joined together, and in that the elements (2, 3) are joined together so that these regions mate, and are then heated sufficiently to weld the layers (8, 11) of dielectric material together. A method according to Claim 16, characterised in that the conductive strips (5, 6, 7, 9, 10) and the layers (8, 11) of dielectric bonding material are applied in succession to the elements (2, 3) by the thick film deposition method. A method according to any one of the preceding claims, characterised in that a hybrid supply and/or amplification and/or measuring and/or thermal compensation circuit (100) is formed on at least one of the elements (2, 3) constituting the body (1) by the thick film method; this circuit (100) being connected to the main and auxiliary electrodes by conductive strips formed by the thick film deposition method on one or both of the elements (2, 3).

Inventors: DELL'ACQUA ROBERTO
Applicants: MARELLI AUTRONICA S.P.A.
Application year: 1985
Main classification: G01C9
IPC codes: G01C9, G01B7