Bearing sensor and bearing-distance sensor

Abstract: A small and inexpensive bearing-distance sensor (1) capable of detecting a travel bearing and a travel distance of a vehicle is provided. The bearing-distance sensor (1) includes a rectangular parallelepiped case (2) for example. A first acceleration sensor (10a) and a second acceleration sensor (10b) are mounted within the case (2). The first acceleration sensor (10a) detects an acceleration in one direction, e.g. the longitudinal direction of the case (2), to obtain a signal related to the acceleration and the second acceleration sensor (10b) detects a force applied in the width direction of the case (2), which is perpendicular to said one direction, to obtain a signal related to that force. The travel distance of the vehicle is found from the output signal of the first acceleration sensor (10a) and the travel bearing of the vehicle is found from the output signals of the first and second acceleration sensors (10a) and (10b).

Description: The present invention relates generally to a bearing sensor and a bearing-distance sensor and more particularly to a bearing sensor and a bearing-distance sensor used for a car navigation system for example and capable of detecting a travel bearing of a vehicle and of detecting a travel bearing and a travel distance of the vehicle, respectively. Hitherto, there exists a car navigation system using a bearing sensor for detecting travel bearing and a distance sensor for detecting travel distance. There are also two types of bearing sensors; one using a vibratory gyroscope and another wherein two acceleration sensors are disposed horizontally with a wide space therebetween. The bearing sensor using the vibratory gyroscope detects an angular velocity of rotation by the vibratory gyroscope and finds a travel bearing from the angular velocity of rotation. The bearing sensor in which two acceleration sensors are disposed horizontally detects accelerations of two parts by those two acceleration sensors and finds a travel bearing from a difference of those accelerations. However, because the vibratory gyroscope is expensive, the whole system of the navigation system having the bearing sensor using the vibratory gyroscope becomes also expensive. Meanwhile, a size of the navigation system having the bearing sensor in which two acceleration sensors are disposed horizontally becomes large because those two acceleration sensors have to be disposed horizontally with an adequate space within the system. US-A-4,393,709 concerns a direction detection apparatus comprising a velocity detector for determining the velocity of an object, a centrifugal force detector for detecting the centrifugal force acting on a vehicle, a pulse generator for defining determined periods of time, and a detection device performing arithmetic calculation of the travelling bearing or travelling angle on the basis of the measured velocity, the period of time and the acceleration. GB-2020019A concerns a navigational instrument including a two-access gyro and a rotary accelerometer corresponding to a rotary movement of a vehicle, and accelerometers which respond to linear accelerations. Further, velocity sensors for sensing the velocity of the vehicle over ground are provided, and on the basis of the signals output by the sensors vector components from the vehicle-fixed coordinate system are transformed into a coordinate system which is fixed-relative to the earth. It is the object of the present invention to provide a small and inexpensive bearing sensor which can detect a travel bearing of a vehicle. This object is achieved by a bearing sensor according to claim 1 and claim 2. A bearing sensor of the present invention comprises a first acceleration sensor for detecting an acceleration in one direction to obtain a signal related to the acceleration in said one direction and a second acceleration sensor for detecting a force applied in a direction perpendicular to said one direction to obtain a signal related to the force applied in the direction perpendicular to said one direction and finds a travel bearing of a vehicle from the output signals of the first and second acceleration sensors. In the bearing sensor of the present invention, the travel bearing of the vehicle is found from the output signals of the first and second acceleration sensors by using a first integrating circuit for integrating the output signal of the first acceleration sensor over time to obtain a signal related to a velocity in one direction; a first arithmetic circuit for obtaining a signal related to a radius of curvature from the output signal of the second acceleration sensor and the output signal of the first integrating circuit; a second arithmetic circuit for obtaining a signal related to an angular velocity from the output signal of the first arithmetic circuit and the output signal of the first integrating circuit; and another integrating circuit for integrating the output signal of the second arithmetic circuit over time to obtain a signal related to the travel bearing of the vehicle. Or, it is found by using the first integrating circuit for integrating the output signal of the first acceleration sensor over time to obtain the signal related to the velocity in one direction; an arithmetic circuit for obtaining a signal related to an angular velocity from the output signal of the second acceleration sensor and the output signal of the first integrating circuit; and another integrating circuit for integrating the output signal of the arithmetic circuit over time to obtain a signal related to the travel bearing of the vehicle. A bearing-distance sensor of the present invention comprises a first acceleration sensor for detecting an acceleration in one direction to obtain a signal related to the acceleration in said one direction and a second acceleration sensor for detecting a force applied in a direction perpendicular to said one direction to obtain a signal related to the force applied in the direction perpendicular to said one direction. The sensor finds a travel distance of a vehicle from the output signal of the first acceleration sensor and finds a travel bearing of the vehicle from the output signals of the first and second acceleration sensors. In the bearing-distance sensor of the present invention, the travel distance of the vehicle is found from the output signal of the first acceleration sensor by using a first integrating circuit for integrating the output signal of the first acceleration sensor over time to obtain a signal related to a velocity in one direction and a second integrating circuit for integrating the output signal of the first integrating circuit over time to obtain a signal related to the travel distance of the vehicle. Further, in the bearing-distance sensor of the present invention, the travel bearing of the vehicle is found from the output signals of the first and second acceleration sensors by using the first integrating circuit for integrating the output signal of the first acceleration sensor over time to obtain the signal related to the velocity in one direction; a first arithmetic circuit for obtaining a signal related to a radius of curvature from the output signal of the second acceleration sensor and the output signal of the first integrating circuit; a second arithmetic circuit for obtaining a signal related to an angular velocity from the output signal of the first arithmetic circuit and the output signal of the first integrating circuit; and a third integrating circuit for integrating the output signal of the second arithmetic circuit over time to obtain a signal related to the travel bearing of the vehicle. Or, it is found by using the first integrating circuit for integrating the output signal of the first acceleration sensor over time to obtain the signal related to the velocity in one direction; the arithmetic circuit for obtaining the signal related to the angular velocity from the output signal of the second acceleration sensor and the output signal of the first integrating circuit; and the third integrating circuit for integrating the output signal of the arithmetic circuit over time to obtain the signal related to the travel bearing of the vehicle. In the bearing sensor and the bearing-distance sensor of the present invention, an acceleration in one direction is detected and a signal related to the acceleration in said one direction is obtained by the first acceleration sensor. A force applied in a direction perpendicular to said one direction is detected and a signal related to the force applied in the direction perpendicular to said one direction is obtained by the second acceleration sensor. In the bearing sensor of the present invention, a travel bearing of the vehicle is found from the output signals of the first and second acceleration sensors. In the bearing-distance sensor of the present invention, a travel distance of the vehicle is found from the output signal of the first acceleration sensor and a travel bearing of the vehicle is found from the output signals of the first and second acceleration sensors. Accordingly, the present invention can realize a small and inexpensive bearing sensor capable of detecting the travel bearing of the vehicle because no expensive vibratory gyroscope needs to be used and two acceleration sensors need not to be disposed with a wide space therebetween to detect the travel bearing of the vehicle. Further, the present invention can realize a small and inexpensive bearing-distance sensor capable of detecting the travel bearing and travel distance of the vehicle because no expensive vibratory gyroscope needs to be used and two acceleration sensors need not to be disposed with a wide space therebetween to detect the travel bearing and the travel distance of the vehicle. Therefore, the present invention allows a miniaturization and reduction of cost of a system such as a navigation system which requires the bearing sensor and the distance sensor. The above and other related objects and features of the present invention will be apparent from a reading of the following detailed description of preferred embodiments made with reference to the accompanying drawings. FIG. 1 is a diagrammatic plan view illustrating one preferred embodiment of the present invention; FIG. 2 is a block diagram of the embodiment shown in FIG. 1; FIG. 3 is an exploded perspective view illustrating an acceleration sensor used in the embodiment shown in FIG. 1; FIG. 4 is a side view of the acceleration sensor used in the embodiment shown in FIG. 1; FIG. 5 is a graph showing a relationship among a velocity V at moving part of a mass m, a radius of curvature r, an angular velocity ω, a centrifugal force F and a travel bearing ; and FIG. 6 is a block diagram illustrating another embodiment of the present invention. Preferred embodiments of the present invention will be explained below with reference to the drawings. FIG. 1 is a diagrammatic plan view illustrating one embodiment of the present invention and FIG. 2 is a block diagram of the embodiment shown in FIG. 1. A bearing-distance sensor 1 includes a rectangular parallelepiped case 2 for example. In the figure, a first acceleration sensor lOa and a second acceleration sensor lOb are mounted within the case 2. The first acceleration sensor 10a detects an acceleration in one direction, e.g. a longitudinal direction of the case 2, to obtain a signal related to that acceleration. The second acceleration sensor lOb detects a force applied in a width direction of the case 2, which is perpendicular to said one direction, to obtain a signal related to that force. While the first acceleration sensor 10a and the second acceleration sensor 10b have the same structure, they have a special structure. Then, the first acceleration sensor 10a will be explained in detail with reference to FIGs. 3 and 4. The first acceleration sensor 10a includes a vibrator 12 which vibrates in the longitudinal direction and which includes a strip vibrating member 14 which is created by an elastic invariable metal such as nickel, iron, chrome and titanium or an alloy of them such as an elinver and an iron-nickel alloy. Note that the vibrating member 14 may be created by a material such as silica, glass, quartz and ceramic, other than metals which generally generate mechanical vibration. Two piezoelectric elements 16a and 16b are formed so as to face from each other on both main surfaces of a part on the side of one end from the center in the longitudinal direction of the vibrating member 14. One piezoelectric element 16a includes a piezoelectric layer 18a composed of ceramic for example and electrodes 20a and 22a are formed respectively on both main surfaces of the piezoelectric layer 18a. The electrode 20a is adhered on one main surface of the vibrating member 14 by an adhesive for example. Similarly, the other piezoelectric element 16b includes a piezoelectric layer 18b composed of ceramic for example and electrodes 20b and 22b are formed respectively on both main surfaces of the piezoelectric layer 18b. The electrode 20b is adhered on the other main surface of the vibrating member 14 by an adhesive for example. The piezoelectric layers 18a and 18b of those piezoelectric elements 16a and 16b are polarized from the electrodes 22a and 22b to the electrodes 20a and 20b, i.e. in a thickness direction toward the vibrating member 14 from the outside thereof. Further, two piezoelectric elements 16c and 16d are formed so as to face from each other on both main surfaces of a part on the side of the other end from the center in the longitudinal direction of the vibrating member 14. One piezoelectric element 16c includes a piezoelectric layer 18c composed of ceramic for example and electrodes 20c and 22c are formed respectively on both main surfaces of the piezoelectric layer 18c. The electrode 20c is adhered on one main surface of the vibrating member 14 by an adhesive for example. Similarly, the other piezoelectric element 16d includes a piezoelectric layer 18d composed of ceramic for example and electrodes 20d and 22d are formed respectively on both main surfaces of the piezoelectric layer 18d. The electrode 20d is adhered on the other main surface of the vibrating member 14 by an adhesive for example. The piezoelectric layers 18c and 18d of those piezoelectric elements 16c and 16d are polarized from the electrodes 20c and 20d to the electrodes 22c and 22d, i.e. in a thickness direction from the vibrating member 14 toward the outside thereof. The vibrator 12 vibrates in the longitudinal direction thereof when driving signals having a same phase are applied to the piezoelectric elements 16a through 16d. In this case, because the piezoelectric elements 16a and 16b and the piezoelectric elements 16c and 16d are polarized in the opposite direction each other, they are displaced in the opposite direction each other. Due to that, when a part on the side of one end from the middle of the vibrating member 14 expands in the longitudinal direction, a part on the side of the other end from the middle of the vibrating member 14 in the longitudinal direction contracts as shown by solid line arrows in FIG. 4. Contrary to that, when the part on the side of one end from the middle of the vibrating member 14 contracts in the longitudinal direction, the part on the side of the other end from the middle of the vibrating member 14 in the longitudinal direction expands as shown by dashed line arrows in FIG. 4. A distance between the both ends of the vibrating member 14 in the longitudinal direction barely changes in this case because the degree of expansion/contraction of the part on the side of one end from the middle of the vibrating member 14 in the longitudinal direction is canceled by the degree of expansion/contraction of the part on the other end from the middle of the vibrating member 14 in the longitudinal direction. The vibrating member 14 vibrates at the middle portion of the piezoelectric elements 16a and 16b and the middle portion of the piezoelectric elements 16c and 16d as its nodal portions. The vibrating member 14 also vibrates at the both ends in the longitudinal direction as its antinodes. Two circular holes 14a for example are created at the two nodal portions of the vibrating member 14 of the vibrator 12. Those two holes 14a increases a deflection of the vibrating member 14 caused by an acceleration and stabilizes the vibration of the vibrating member 14 in the longitudinal direction. Two supporting members 24 are formed on the side of one end in the longitudinal direction of the vibrator 12. In this case, those two supporting members 24 are formed in one body with the vibrating member 14 extending in the width direction from the circumference of the nodal portion on the side of one end of the vibrating member 14 in the longitudinal direction and that extending from the end portion thereof. Those supporting members 24 support the portion of the vibrator 12 on the side of one end thereof. Further, two mounting members 26 are formed projecting from a distal half of the vibrating member 14. In this case, the mounting members 26 extend in the width direction from the circumference of the nodal portion on the side of the other end of the vibrating member 14 and are formed in one body with the vibrating member 14. Weights 28 are mounted on the both main surfaces of those mounting members 26 by welding or soldering. Those weights 28 increase a deflection of the vibrating member 14 caused by an acceleration. In the first acceleration sensor 10a, the vibrator 12 vibrates in the longitudinal direction as shown by the solid line arrows and the dashed line arrows in FIG. 4 when the side of the one end of the vibrator 12 is supported by fixing the two supporting members 24 and when driving signals having a same phase are applied to the four piezoelectric elements 16a through 16d. Then, when an acceleration is applied to the vibrating member 14 of the vibrator 12 in the direction perpendicular to the main surface thereof, the vibrating member 14 deflects together with the piezoelectric elements 16a through 16d corresponding to the acceleration and voltages which correspond with the deflection are generated in the piezoelectric elements 16a through 16d. Due to that, the acceleration may be detected by measuring any of the voltages generated in the piezoelectric elements 16a through 16d. Further, because holes 14a are created respectively at the two nodal portions of the vibrating member 14 in the first acceleration sensor 10a, the deflection of the vibrating member 14 caused by the acceleration is increased and the vibration of the vibrating member 14 in the longitudinal direction is stabilized by keeping the balance of the vibration of the vibrating member 14 in the longitudinal direction. Due to that, an acceleration detecting sensitivity of the first acceleration sensor 10a is improved. Further, because the weights 28 are mounted to the mounting members 26 near the nodal portion of the vibrator 12 in the first acceleration sensor 10a, the deflection of the vibrating member 14 is increased, the acceleration detecting sensitivity is increased and the vibration of the vibrator 12 is not interfered by the weights 28 since almost no vibration of the vibrator 12 is transmitted to the weights 28. Note that although each of the circular holes 14a are created respectively at those two nodal portions of the vibrating member 14 in the first acceleration sensor 10a, the holes created at the nodal portion may have another shape such as a rectangular shape instead of the circular shape and the number of holes created at one nodal portion is not confined to be only one and may be more than two. The first acceleration sensor 10a can detect the acceleration also by detecting a difference of voltages generated by the piezoelectric elements 16a and 16b and a difference of voltages generated by the piezoelectric elements 16c and 16d. Further, the polarizing direction of the piezoelectric layer of more than one piezoelectric element may be reversed and the phase of driving signal applied to the piezoelectric element whose polarizing direction is reversed may be reversed in the first acceleration sensor 10a. The reason why the vibrator is vibrated in the longitudinal direction in the first acceleration sensor 10a is because the vibrator deflects significantly when an acceleration is applied to the vibrator when the vibrator vibrates in the longitudinal direction, thus improving the acceleration detecting sensitivity. The supporting member 24 of this first acceleration sensor 10a is fixed within the case 2 so that the main surface of the vibrating member 14 crosses at right angles with the longitudinal direction of the case 2. Accordingly, an acceleration in the longitudinal direction of the case 2 is detected and a signal related to the acceleration is obtained by the first acceleration sensor 10a. The supporting member 24 of the second acceleration sensor 10b having the same structure with the first acceleration sensor 10a is also fixed within the case 2 so that the main surface of the vibrating member 14 thereof crosses at right angles with the width direction of the case 2. Accordingly, a force F applied in the width direction of the case 2 is detected and a signal related to the force F is obtained by the second acceleration sensor 10b. An output terminal of the first acceleration sensor 10a is connected to an input terminal of a first integrating circuit 30a as shown in FIG. 2. The first integrating circuit 30a integrates the output signal of the first acceleration sensor 10a related to the acceleration in the longitudinal direction of the case 2 over time to obtain a signal related to a velocity V in the longitudinal direction of the case 2. An output terminal of the first integrating circuit 30a is connected to an input terminal of a second integrating circuit 30b. The second integrating circuit 30b integrates the output signal of the first integrating circuit 30a related to the velocity V in the longitudinal direction of the case 2 over time to obtain a signal related to a travel distance L of the vehicle. An output terminal of the second acceleration sensor 10b and the output terminal of the first integrating circuit 30a are connected respectively to two input terminals of a first arithmetic circuit 32a. The first arithmetic circuit 32a obtains a signal related to a radius of curvature r from the output signal of the second acceleration sensor 10b related to a centrifugal force F applied in the width direction of the case 2 and the output signal of the first integrating circuit 30a related to the velocity V in the longitudinal direction of the case 2. Note that the first arithmetic circuit 32a may be realized from a relationship of r = mV 2 /F , where m is a mass of a moving part. An output terminal of the first arithmetic circuit 32a and the output terminal of the first integrating circuit 30a are connected respectively to two input terminals of a second arithmetic circuit 32b. The second arithmetic circuit 32b obtains a signal related to an angular velocity ω from the output signal of the first arithmetic circuit 32a related to the radius of curvature r and from the output signal of the first integrating circuit 30a related to the velocity V in the longitudinal direction of the case 2. Note that this second arithmetic circuit 32b may be realized from a relationship of ω = V/r. An output terminal of the second arithmetic circuit 32b is connected to an input terminal of a third integrating circuit 30c. The third integrating circuit 30c integrates the output signal of the second arithmetic circuit 32b related to the angular velocity ω over time to obtain a signal related to a travel bearing Θ of the vehicle. FIG. 5 shows a relationship among the velocity V at the moving part of the mass m, the radius of curvature r, the angular velocity ω, the centrifugal force F and the travel bearing . The bearing-distance sensor 1 is mounted in a automobile 40 so that the longitudinal direction and the width direction of the case 2 run parallel respectively with the longitudinal direction and the width direction of the automobile 40 as shown in FIG. 1. Accordingly, the acceleration α in the longitudinal direction of the automobile 40 is detected and the signal related to the acceleration α is obtained by the first acceleration sensor 10a. The centrifugal force F applied in the width direction of the automobile 40 is detected and the signal related to the centrifugal force F is obtained by the second acceleration sensor 10b. Further, the output signal of the first acceleration sensor 10a related to the acceleration α in the longitudinal direction of the automobile 40 is integrated over time and the signal related to the velocity V in the longitudinal direction of the automobile 40 is obtained by the first integrating circuit 30a. The output signal of the first integrating circuit 30a related to the velocity V in the longitudinal direction of the automobile 40 is integrated over time and the signal related to the travel distance L in the longitudinal direction of the automobile 40 is obtained by the second integrating circuit 30b. The signal related to the radius of curvature r is obtained from the output signal of the second acceleration sensor 10b related to the centrifugal force F applied in the width direction of the automobile 40 and the output signal of the first integrating circuit 30a related to the velocity V in the longitudinal direction of the automobile 40. The signal related to the angular velocity ω is obtained from the output signal of the first arithmetic circuit 32a related to the radius of curvature r and the output signal of the first integrating circuit 30a related to the velocity V in the longitudinal direction of the automobile 40. Then the output signal of the second arithmetic circuit 32b related to the angular velocity ω is integrated over time and the signal related to the travel bearing Θ of the automobile 40 is obtained by the third integrating circuit 30c. Accordingly, this bearing-distance sensor 1 can detect the travel bearing Θ and the travel distance L of the automobile 40. Further, because no expensive vibratory gyroscope is used and two acceleration sensors need not be disposed with a wide space therebetween in the bearing-distance sensor 1, it can be small and inexpensive. FIG. 6 is a block diagram showing another embodiment of the present invention. In the embodiment shown in FIG. 6, one arithmetic circuit 32 is provided instead of the first arithmetic circuit 32a and the second arithmetic circuit 32b provided in the embodiment shown in FIGs. 1 and 2. The output terminals of the second acceleration sensor 10b and the first integrating circuit 30a are connected respectively to two input terminals of the arithmetic circuit 32. An output terminal of the arithmetic circuit 32 is connected to the input terminal of the third integrating circuit 30c as another integrating circuit. The arithmetic circuit 32 obtains a signal related to the angular velocity ω from the output signal of the second acceleration sensor 10b related to the centrifugal force F applied in the width direction of the case 2 and the output signal of the first integrating circuit 30a related to the velocity V in the longitudinal direction of the case 2. This arithmetic circuit 32 is realized from a relationship of ω = F/(mV), where m is a mass of the moving part. The embodiment shown in FIG. 6 can detect a travel bearing and a travel distance of a vehicle such as an automobile and can be small and inexpensive, similarly to the embodiment shown in FIGs. 1 and 2. Note that the circuit structure of the embodiment shown in FIG. 6 may be simplified as compared to the embodiment shown in FIGs. 1 and 2 because one arithmetic circuit is decreased. A bearing sensor which can detect only the travel bearing Θ of the vehicle is constructed by removing the second integrating circuit 30b in each embodiment shown in FIGs. 2 and 6. This bearing sensor can be small and inexpensive because no expensive vibratory gyroscope is used and two acceleration sensors need not be disposed with a wide space therebetween.

Claims: A bearing sensor (1) for detecting a travel bearing (Θ) of a vehicle (40), the sensor (1) comprising: a first acceleration sensor (10a) for detecting an acceleration (α) in one direction to obtain a signal related to the acceleration (α) in said one direction; a second acceleration sensor (10b) for detecting a force (F) applied in a direction perpendicular to said one direction to obtain a signal related to the force (F) applied in the direction perpendicular to said one direction; a first integrating circuit (30a) for integrating the output signal of said second acceleration sensor (10a) over time to obtain a signal related to a velocity (V) in said one direction; a first arithmetic circuit (32a) for obtaining a signal related to a radius (r) of curvature from the output signal of said first acceleration sensor (10b) and the output signal of said first integrating circuit (30a); a second arithmetic circuit (32b) for obtaining a signal related to an angular velocity (ω) from the output signal of said first arithmetic circuit (32a) and the output signal of said first integrating circuit (30a); and a further integrating circuit (30c) for integrating the output signal of said second arithmetic circuit (32b) over time to obtain a signal related to the travel bearing (Θ) of said vehicle (40). A bearing sensor (1) for detecting a travel bearing (Θ) of a vehicle (40), the sensor (1) comprising: a first acceleration sensor (10a) for detecting an acceleration (α) in one direction to obtain a signal related to the acceleration (α) in said one direction; a second acceleration sensor (10b) for detecting a force (F) applied in a direction perpendicular to said one direction to obtain a signal related to the force (F) applied in the direction perpendicular to said one direction; a first integrating circuit (30a) for integrating the output signal of said second acceleration sensor (10a) over time to obtain a signal related to a velocity (V) in said one direction; an arithmetic circuit (32) for obtaining a signal related to an angular velocity (ω) from the output signal of said first acceleration sensor (10b) and the output signal of said first integrating circuit (30a); and a further integrating circuit (30c) for integrating the output signal of said arithmetic circuit (32) over time to obtain a signal related to the travel bearing (Θ) of said vehicle (40). The bearing sensor (1) according to Claim 1 or Claim 2, further comprising: a second integrating circuit (30b) for integrating the output signal of said second integrating circuit (30a) to obtain a signal related to a travel distance (L) of said vehicle (40).

Inventors: NAKAMURA TAKESHI, NAKAMURA, TAKESHI, Nakamura, Takeshi, c/o Murata Man. Co., Ltd.
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1995
Main classification: G01C21
IPC codes: G01C21, G01P15, G01C22