Abstract:
A mobile navigation system gyro module comprises: first and second gyro sensors outputting angular velocities ω 1 , ω 2  around first and second axes intersecting at an acute angle θ 12 ; a sign determination circuit determining a sign of ω 1 ; a correction circuit correcting the first and second gyro sensor outputs; and a computation circuit computing ω′=√(ω 1′   2 +SA 2 ) and SA=(ω 2′ −ω 1 ′ cos θ 12 )/sin θ 12  using angular velocities ω 1 ′, ω 2′  from the correction circuit, and outputting angular velocity ω by multiplying ω′ by the sign of ω 1 , wherein the correction circuit includes: first and second offset adjustment circuits outputting ω 1 ″ and ω 2 ″ by respectively subtracting from ω 1  and ω 2 , corrections B 1  and B 2  corresponding to the first and second gyro sensor outputs when the mobile unit stops; and the angular velocity ω is around an axis coplanar with and between the first and second axes.

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a gyro sensor module for detecting an angular velocity to know an azimuth and an angular velocity detection method. 
     2. Related Art 
     A gyro sensor is used in a navigation system mounted in a vehicle or the like. The angular velocity to be detected by the gyro sensor when the vehicle makes a turn is used to know the azimuth of the vehicle. In order to detect the angular velocity accurately, the angular velocity detection axis and the detected axis of the gyro sensor must be matched. The detected axis to be used to know the azimuth is an axis perpendicular to the horizontal ground surface. A match between the detection axis and the detected axis increases the detection sensitivity, thereby increasing the signal-to-noise ratio to increase the detection accuracy. On the other hand, an orthogonality between the detection axis and the detected axis reduces the detection sensitivity, thereby reducing the signal-to-noise ratio to reduce the detection accuracy. 
     A gyro sensor mounting angle adjustment device is known that matches the detection axis and the detected axis by detecting the inclination angle of a vehicle and mechanically adjusting the mounting angle of a gyro sensor relative to the vehicle so that the mounting surface of the gyro sensor is in parallel with the horizontal ground surface (see JP-A-2001-153658, pp. 3 to 5, FIGS. 1 and 2). 
     Also, a navigation system is known that obtains the angular velocity around the vertical axis from the square sum average of an output of a first gyro sensor and an output of a second gyro sensor having a detection axis orthogonal to the detection axis of the first gyro sensor without having to determine the inclination angle of the road surface and those of the mounted gyro sensors. Further, a navigation system is known that computes a correction factor from an error outputted from a control circuit and a vehicle speed signal so as to correct the angular velocity around the vertical axis (see JP-A-2002-213959, pp. 8, paragraphs [0067] and [0068]). 
     Furthermore, a multi-axis gyro sensor is known that determines whether or not a failure has occurred therein according to outputs of a first gyro sensor and a second gyro sensor (see JP-A-2004-286529 (ABSTRACT)). 
     In order to mechanically adjust the mounting angle of a gyro sensor, the gyro sensor must include an adjustment component. Dedicated space is needed to substantially change the mounting angle. Therefore, the movable range of the mounting angle of the detection axis is limited. Also, if a mechanical adjustment is made such as when the angle of the detection axis is rapidly changed on an upward or downward slope, or the like, it takes a time to match the detection axis and the detected axis. This makes it difficult to increase the detection accuracy. For these reasons, as disclosed in JP-A-2002-213959, a related art technology has been proposed that obtains the angular velocity around the vertical axis from the square sum average of an output of a first gyro sensor and an output of a second gyro sensor having a detection axis orthogonal to the detection axis of the first gyro sensor without having to determine the inclination angle of a road surface and further increases the detection accuracy using a so-called correction factor. However, the inventors have found that a detection error occurs due to the first and second gyro sensors both having undergone no offset process. 
     SUMMARY 
     An advantage of the invention is to provide a gyro sensor module and an angular velocity detection method that each increases the detection accuracy regardless of to what extent the mounting angle of the detection axis changes. 
     According to a first aspect of the invention, a gyro sensor module built into a navigation system mounted into a mobile unit includes: a first gyro sensor detecting and outputting a first angular velocity ω 1  around a first detection axis; a sign determination circuit for determining a sign of the first angular velocity ω 1 ; a second gyro sensor detecting and outputting a second angular velocity ω 2  around a second detection axis intersecting the first detection axis at an acute angle θ 12 ; a sensor output correction circuit for correcting outputs of the first and second gyro sensors; and a computation circuit for computing ω′ by equations ω′=√(ω 1 ′ 2 +SA 2 ) and SA=(ω 2 ′−ω 1 ′ cos θ 12 )/sin θ 12  using a first angular velocity ω 1 ′ and a second angular velocity ω 2 ′ obtained by a correction performed by the sensor output correction circuit, and outputting an angular velocity ω obtained by multiplying the ω′ by the sign of the first angular velocity ω 1  obtained by the sign determination circuit. The sensor output correction circuit includes: a first offset adjustment circuit for outputting a value ω 1 ″ obtained by subtracting from the ω 1  a correction value B 1  corresponding to an output value of the first gyro sensor at a time when the mobile unit in which the gyro sensor module is disposed is stopping; and a second offset adjustment circuit for outputting a value ω 2 ″ obtained by subtracting from the ω 2  a correction value B 2  corresponding to an output value of the second gyro sensor at a time when the mobile unit in which the gyro sensor module is disposed is stopping. The angular velocity ω is an angular velocity around an axis located in a plane including the first and second detection axes and in a range between the first and second detection axes. 
     According to the first aspect of the invention, the first and second angular velocities ω 1  and ω 2  are converted into the first and second angular velocities ω 1 ″ and ω 2 ″ by the first and second offset adjustment circuits included in the sensor output correction circuit, by subtracting the output value B 1  of the first gyro sensor and the output value B 2  of the second gyro sensor at a time when the mobile unit is stopping from the first and second angular velocities ω 1  and ω 2 . Thus, the more accurate first and second angular velocities ω 1 ″ and ω 2 ″ at a time when the vehicle  102  is moving are obtained. 
     Also, the angular velocity ω around the detected axis perpendicular to the horizontal ground surface is detected by synthesizing the angular velocities measured on the two detection axes regardless of to what extent the mounting angle of each detection axis changes or to what extent the angle that each detection axis forms with the horizontal ground surface changes. 
     The angle formed by the first and second detection axes is an acute angle, and the angular velocity ω is detected in the acute angle. Therefore, the angle formed by the detection axes and the detected axis is reduced. This allows a gyro sensor module having a good detection accuracy to be obtained. 
     The acute angle is preferably 20° to 60°, more preferably 30° to 50°. Variations in inclination of a vehicle or the like are on the order of 40° at maximum even if upward slopes and downward slopes of a road are considered. If the acute angle is less than 20°, the detected axis easily gets out of the range between the first and second detection axes, thereby making it difficult to obtain a high detection accuracy. Also, variations in inclination of a vehicle or the like on an ordinary road are rarely 60° or more. 
     The gyro sensor module according to the first aspect of the invention preferably further includes: a vehicle position measurement circuit for outputting an error Δθ between a traveling azimuth obtained by integrating the angular velocity ω outputted from the computation circuit and a traveling azimuth of the mobile unit computed by the navigation system; and an adjustment factor computation circuit for computing and outputting sensitivity adjustment signals A 1  and A 2  from the error Δθ, the angular velocity ω outputted from the computation circuit, and a vehicle speed pulse outputted from the vehicle. The sensor output correction circuit preferably includes: a first sensitivity adjustment circuit for outputting an value ω 1 ′ obtained by multiplying the ω 1 ″ outputted from the first offset adjustment circuit by the sensitivity adjustment signal A 1 ; and a second sensitivity adjustment circuit for outputting an value ω 2 ′ obtained by multiplying the ω 2 ″ outputted from the second offset adjustment circuit by the sensitivity adjustment signal A 2 . 
     According to the first aspect of the invention, the sensitivity adjustment signals A 1  and A 2  are computed from the error Δθ between the traveling azimuth obtained by integrating the angular velocity ω and the traveling azimuth of the mobile unit computed by the navigation system, the angular velocity ω, and the vehicle speed pulse. Then, sensitivity adjustments are performed by multiplying the ω 1 ″ and ω 2 ″ by the sensitivity adjustment signals A 1  and A 2 , and the ω 1 ′ and the ω 2 ′ are outputted from the sensor output correction circuit. Thus, a gyro sensor module that detects the angular velocity ω′ more accurately is obtained. 
     According to a second aspect of the invention, a method for detecting an angular velocity using a gyro sensor module built into a navigation system mounted into a mobile unit includes: detecting a first angular velocity ω 1  around a first detection axis; determining a sign of the first angular velocity ω 1 ; detecting a second angular velocity ω 2  around a second detection axis intersecting the first detection axis at an acute angle θ 12 ; performing sensor output corrections including a first offset adjustment in which a correction value B 1  corresponding to an output value of the first gyro sensor at a time when the mobile unit in which the gyro sensor module is disposed is stopping is subtracted from the ω 1  and a second offset adjustment in which a correction value B 2  corresponding to an output value of the second gyro sensor at a time when the mobile unit in which the gyro sensor module is disposed is stopping is subtracted from the ω 2 ; and computing an angular velocity ω by computing ω′ by equations ω′=√(ω 1 ′ 2 +SA 2 ) and SA=(ω 2 ′−ω 1 ′ cos θ 12 )/sin θ 12  using a first angular velocity ω 1 ′ and a second angular velocity ω 2 ′ obtained in the sensor output corrections and then multiplying the ω′ by the sign of the first angular velocity ω 1 . The angular velocity ω is an angular velocity around an axis located in a plane including the first and second detection axes and in a range between the first and second detection axes. 
     According to the second aspect of the invention, the first and second angular velocities ω 1  and ω 2  are offset-adjusted by subtracting, from the first and second angular velocities ω 1  and ω 2 , the output value B 1  of the first gyro sensor and the output value B 2  of the second gyro sensor at a time when the mobile unit is stopping. Thus, the more accurate first and second angular velocities ω 1 ′ and ω 2 ′ at a time when the mobile unit is moving are obtained. 
     Also, the angular velocity ω around the detected axis perpendicular to the horizontal ground surface is detected by synthesizing the angular velocities measured on the two detection axes regardless of to what extent the mounting angle of each detection axis changes or to what extent the angle that each detection axis forms with the horizontal ground surface changes. 
     The angle formed by the first and second detection axes is an acute angle, and the angular velocity ω is detected in the acute angle. This reduces the angle formed by the detection axes and the detected axis, thereby increasing the detection accuracy. 
     The method for detecting an angular velocity according to the second aspect of the invention preferably further includes: computing an error Δθ between a traveling azimuth obtained by integrating the angular velocity ω and a traveling azimuth of the mobile unit computed by the navigation system; and computing sensitivity adjustment signals A 1  and A 2  from the error Δθ and the angular velocity ω. In the sensor output corrections performing step, a first sensitivity adjustment in which an value ω 1 ′ is computed by multiplying a value ω 1 ″ after the first offset adjustment by the sensitivity adjustment signal A 1  and a second sensitivity adjustment in which an value ω 2 ′ is computed by multiplying a value ω 2 ″ after the second offset adjustment by the sensitivity adjustment signal A 2  are preferably performed. 
     According to the second aspect of the invention, besides the offset adjustments, the sensitivity adjustments are performed by multiplying the ω 1 ″ and ω 2 ″ by the sensitivity adjustment signals A 1  and A 2  computed from the error Δθ between the traveling azimuth obtained by integrating the angular velocity ω and the traveling azimuth of the mobile unit computed by the navigation system, the angular velocity ω, and the vehicle speed pulse. Thus, the angular velocity ω is detected more accurately. 
     In the method for detecting an angular velocity according to the second aspect of the invention, the sensor output corrections performing step is preferably performed by a sensor output correction circuit. 
     According to the second aspect of the invention, the sensor output corrections are performed by a sensor output correction circuit. Therefore, the gyro sensor module is able to include the sensor output correction circuit. 
     In the method for detecting an angular velocity according to the second aspect of the invention, one or more of the sensor output corrections, the angular velocity ω computation, the error Δθ computation, and the sensitivity adjustment signals A 1  and A 2  computations are preferably performed using software. 
     According to the second aspect of the invention, one or more of the sensor output corrections, the angular velocity ω computation, the error Δθ computation, and the sensitivity adjustment signals A 1  and A 2  computations are performed using software. Therefore, such processing is performed by a central processing unit (CPU) of the navigation system including the gyro sensor module. This allows downsizing of the gyro sensor module. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a schematic drawing showing a state in which a navigation system including a gyro sensor module according to a first embodiment of the invention is mounted into a vehicle that is a mobile unit. 
         FIG. 2  is a schematic perspective showing the gyro sensor module. 
         FIG. 3  is a diagram showing a positional relation among first and second detection axes, a detected axis, and a horizontal ground surface. 
         FIG. 4  is a block diagram of signal processing to be performed by a circuit. 
         FIG. 5  is a schematic perspective view showing a gyro sensor module according to a second embodiment of the invention. 
         FIG. 6  is a schematic perspective view showing a gyro sensor module according to a third embodiment of the invention. 
         FIG. 7  is a schematic perspective view showing a gyro sensor module according to a fourth embodiment of the invention. 
         FIG. 8  is a block diagram of signal processing using software according to a fifth embodiment of the invention. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Embodiments of the invention will now be described with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a schematic drawing showing a state in which a navigation system  101  including a gyro sensor module  100  according to a first embodiment of the invention is mounted in a vehicle  102  that is a mobile unit. In  FIG. 1 , the navigation system  101  is mounted in the front part of the vehicle  102 . The vehicle  102  moves toward the left side of the paper surface. The navigation system  101  is mounted at an angle θ formed by a bottom thereof  103  and a horizontal ground surface  70 . The gyro sensor module  100  is mounted on the bottom  103  of the navigation system  101 . 
       FIG. 2  is a schematic perspective view showing the gyro sensor module  100  according to this embodiment. In  FIG. 2 , the gyro sensor module  100  includes a first gyro sensor  10 , a second gyro sensor  20 , a circuit  30 , a box-shaped package  40 , and a lid  50 . The first gyro sensor  10 , the second gyro sensor  20 , and the circuit  30  are disposed on a rectangular bottom  41  of the package  40 . 
     The first gyro sensor  10  is a tuning fork-shaped gyro sensor having a first detection axis  11  and is disposed on a slope of a base  91  provided on the bottom  41 . The slope is at an angle θ 24  with the bottom  41 . Therefore, the first detection axis  11  is at the angle θ 24  with the bottom  41 . 
     The second gyro sensor  41  is a double T-shaped gyro sensor that is a combination of two T-shaped vibrators. The second gyro sensor  20  is disposed so that a second detection axis  21  thereof is orthogonal to the bottom  41 . 
     Since the first detection axis  11  is at the angle θ 24  with the bottom  41 , the angle formed by the first and second detection axes  11  and  22  is an acute angle θ 12  (the direction of the second detection axis  21  is shown on an extension of the first detection axis  11  using a dotted line in the drawing). 
       FIG. 3  is a diagram showing a positional relation among the first and second detection axes  11  and  21 , a detected axis  60 , and the horizontal ground surface  70 . In  FIG. 3 , the horizontal ground surface  70  is orthogonal to the paper surface, and the detected axis  60  around which an angular velocity ω is to be detected is directed perpendicular to the horizontal ground surface  70 . The navigation system  101  including the gyro sensor module  100  shown in  FIG. 1  is mounted in the vehicle so that a plane including the first and second detection axes  11  and  21  is approximately perpendicular to the horizontal ground surface  70 . 
     The first detection axis  11  and the horizontal ground surface  70 , and the second detection axis  21  and the horizontal ground surface  70  form an angle θ 22  and an angle θ 23 , respectively. If the bottom  41  of the gyro sensor module  100  is parallel with the bottom  103  of the navigation system  101  shown in  FIG. 1 , the angle θ 22  is equal to the angle θ formed by the bottom  103  and the horizontal ground surface  70  plus an angle θ 24 . 
     In order to detect the azimuth of the vehicle accurately, the navigation system  101  is mounted and used in the vehicle so that the detected axis  60  does not get out of the plane including the first and second detection axes  11  and  21  even if the mounting angle of the gyro sensor module  100  or the like changes. 
     Specifically, the mounting angle θ that the navigation system  101  forms with the horizontal ground surface  70  changes relative to the traveling azimuth of the vehicle due to an upward or downward slope of a road surface. Therefore, the navigation system  101  is disposed so that the plane including the first and second detection axes  11  and  21  is parallel with the traveling azimuth of the vehicle. In  FIG. 3 , the vehicle moves toward the right or left side of the paper surface. 
     Also, the navigation system  101  is disposed in the vehicle so that the detected axis  60  is located between the first and second detection axes  11  and  21  even if the angles θ 22  and θ 23  change. Since a road has upward slopes and downward slopes by the same number, the navigation system  101  is preferably mounted so that the angles θ 22  and θ 23  are equal with the vehicle being horizontal. 
     In this embodiment, the navigation system  101  is preferably mounted in the vehicle in a manner that the bottom  41  of the package  40  shown in  FIG. 2  is inclined so that the angle θ 22  and the angle θ 23  are equal relative to the horizontal ground surface  70  with the vehicle being horizontal. 
     If the navigation system  101  is not mounted in a manner that the bottom of the package  40  is inclined toward the horizontal vehicle, the second detection axis  21  may also be inclined toward the bottom  41  in  FIG. 2 , provided that the first and second detected axes  11  and  21  form the acute angle θ 12 . Specifically, the gyro sensor  20  may be disposed on a slope of a base similar to the base  91  and the angle that the second detection axis  21  forms with the bottom  41  may be adjusted. 
     As described above, the inclinations of the first and second detection axes  11  and  21  toward the bottom  41  are adjusted in accordance with the angle at which the package  40  is mounted in the vehicle. 
     A first angular velocity ω 1  around the first detection axis  11  is measured on the first detection axis  11 , and a second angular velocity ω 2  around the second detection axis  21  is measured on the second detection axis  21 . 
       FIG. 4  is a block diagram of signal processing to be performed by the circuit  30 . In  FIG. 4 , the circuit  30  includes a sensor output correction circuit  32 , a computation circuit  33 , a sign determination circuit  34 , and a control circuit  35 . 
     The first angular velocity ω 1  is detected in the first gyro sensor  10  and the second angular velocity ω 2  is detected in the second gyro sensor  20 . Signals representing the detected velocities are transmitted to the sensor output correction circuit  32 . The sensor output correction circuit  32  includes a first offset adjustment circuit  36 , a second offset adjustment circuit  37 , a first sensitivity adjustment circuit  38 , and a second sensitivity adjustment circuit  39 . 
     The first offset adjustment circuit  36  obtains a value ω 1 ″ by subtracting an output value B 1  of the first gyro sensor  10  in a state in which the vehicle  102  is stopping, from the detected first angular velocity ω 1 , and outputs the value ω 1 ″. 
     The second offset adjustment circuit  37  obtains a value ω 2 ″ by subtracting an output value B 2  of the second gyro sensor  20  in a state in which the vehicle  102  is stopping, from the detected second angular velocity ω 2 , and outputs the value ω 2 ″. 
     The first sensitivity adjustment circuit  38  obtains a value ω 1 ′ by multiplying the ω 1 ″ by a sensitivity adjustment signal A 1 , and outputs the value ω 1 ′. The second sensitivity adjustment circuit  39  obtains a value ω 2 ′ by multiplying the ω 2 ″ by a sensitivity adjustment signal A 2 , and outputs the value ω 2 ′. The output values B 1  and B 2  and the sensitivity adjustment signals A 1  and A 2  are previously outputted from the control circuit  35 . Signals representing the ω 1 ′ and ω 2 ′ are transmitted to the computation circuit  33 . The signal representing the ω 1 ′ is also transmitted to the sign determination circuit  34 . 
     The computation circuit  33  includes a circuit for obtaining an SA represented by the equation below, a square sum average circuit, and a multiplication circuit  332 .
 
 SA= (ω2′−ω1′ cos θ 12 )/sin θ 12  
 
     First, as a step of obtaining the SA, the acute angle θ 12  between the first and second detection axes  11  and  21  is converted into a signal representing cos θ 12  by inputting a voltage V 1  corresponding to the acute angle θ 12  into a cosine computation circuit. This is because the acute angle θ 12  is determined according to the disposition of the first gyro sensor  10  and that of the second gyro sensor  20 . Similarly, the acute angle θ 12  is converted into a signal representing sin θ 12  by inputting a voltage V 2  corresponding to the acute angle θ 12  into a sine computation circuit. 
     Then, the multiplication circuit converts the analog signal representing ω 1 ′ and the signal representing cos θ 12  into a signal representing ω 1 ′ cos θ 12 . 
     Then, a subtraction circuit converts the analog signal representing ω 2 ′ and the signal representing ω 1 ′ cos θ 12  into a signal representing ω 2 ′−ω 1 ′ cos θ 12 . 
     Then, a division circuit converts the signal representing ω 2 ′−ω 1 ′ cos θ 12  and the signal representing sin θ 12  converted in the sine computation circuit, into a signal representing (ω 2 ′−ω 1 ′ cos θ 12 )/sin θ 12 . The obtained signal serves as a signal representing the SA. 
     Then, the signal representing ω 1 ′ and the signal representing SA are transmitted to the square sum average circuit so as to obtain a square sum average √(ω 1 ′ 2 +SA 2 ). Then, the obtained square sum average √(ω 1 ′ 2 +SA 2 ) is outputted as |ω| therefrom. 
     On the other hand, the sign determination circuit  34  obtains a value sign (ω 1 ′) from the ω 1 ′ and determines whether the sign (ω 1 ′) is positive or negative. If the sign (ω 1 ′) is positive, the sign determination circuit  34  outputs cω. This indicates that an angular velocity ω to be inputted is a clockwise rotation toward the arrow direction shown in  FIG. 3 . If the sign (ω 1 ′) is negative, the sign determination circuit  34  outputs ccω. This indicates that an angular velocity ω to be inputted is a counterclockwise rotation toward the arrow direction shown in  FIG. 3 . 
     The computation circuit  33  obtains an angular velocity value ω by adding a positive or negative sign to what is obtained by multiplying the output of the sign determination circuit  34  by |ω| using a multiplication circuit  332 , and outputs a signal representing the angular velocity value ω. 
     The control circuit  35  includes a vehicle position measurement circuit  351  and an adjustment factor computation circuit  352 . The vehicle position measurement circuit  351  outputs an error Δθ between a traveling azimuth obtained by integrating the angular velocity ω and the traveling azimuth θ of the vehicle  102  computed by the navigation system  101 . Then, the adjustment factor computation circuit  352  computes sensitivity adjustment signals A 1  and A 2  from the error Δθ, the angular velocity ω outputted from the computation circuit  33 , and a vehicle speed pulse outputted from the vehicle  102 , and outputs the computed sensitivity adjustment signals A 1  and A 2  to the first and second sensitivity adjustment circuits  38  and  39 . The sensitivity adjustment signals A 1  and A 2  may always be equal. These signals may be computed by the following equation.
 
 A 1= A 2=1+Δθ/θ=1+(θω−θ)/θ
 
where θω is a value obtained by integrating the angular velocity ω outputted by the multiplication circuit  332  while the traveling azimuth of the vehicle  102  changes from 0 to θ. The θω is determined by the following equation.
 
θω=∫ωdt
 
     Also, the adjustment factor computation circuit  352  outputs the output value B 1  of the first gyro sensor  10  and the output value B 2  of the second gyro sensor  20  at a time when the vehicle  102  is stopping, to the first and second offset adjustment circuits  36  and  37 , respectively. 
     The control circuit  35  determines whether or not the vehicle is stopping, according to the vehicle speed pulse. Alternatively, an offset adjustment may be made, for example, using, as a trigger, the startup of the navigation system  101  or the change of the ignition key from the “off” position to the “accessory-on” or “ignition-on” position. 
     Incidentally, it is sufficient that the first and second sensitivity circuits  38  and  39  are located after the first and second offset adjustment circuits  36  and  37 , respectively. For example, these sensitivity circuits may be located after the square sum average circuit or the multiplication circuit  332 . Also, changes in adjustment amount due to changes in temperature change may previously be stored so that an offset adjustment is automatically made by a temperature sensor. Further, a sensitivity adjustment may be made by detecting a deviation from the map due to the inclination of the vehicle  102  toward the pitch direction using a gravity direction sensor or an acceleration sensor. 
     The advantages of this embodiment will be described below. 
     (1) The first and second angular velocities ω 1  and ω 2  are converted into the first and second angular velocities ω 1 ″ and ω 2 ″ by the first and second offset adjustment circuits  36  and  37  included in the sensor output correction circuit  32  by subtracting the output value B 1  of the first gyro sensor  10  and the output value B 2  of the second gyro sensor  20  at a time when the vehicle is stopping, from the first and second angular velocities ω 1  and ω 2 . Thus, the more accurate first and second angular velocities ω 1 ″ and ω 2 ″ at a time when the vehicle  102  is moving are obtained. 
     Further, the first and second detection axes  11  and  21  forms the acute angle θ 12  and the angular velocity is detected in the acute angle θ 12 . This reduces the angle formed by the detection axes and the detected axis  60 , allowing the gyro sensor  100  having a high detection accuracy to be obtained. 
     (2) The sensitivity adjustment signals A 1  and A 2  are computed from the error Δθ between the traveling azimuth obtained by integrating the angular velocity ω and the traveling azimuth computed by the navigation system  101 , the angular velocity ω, and the vehicle speed pulse. Then, sensitivity adjustments are made by multiplying the ω 1 ″ and ω 2 ″ by the sensitivity adjustment signals A 1  and A 2 . Thus, the ω 1 ′ and ω 2 ′ are outputted from the sensor output correction circuits  32 . As a result, the gyro sensor module  100  and the angular velocity detection method for detecting the angular velocity more accurately are obtained. 
     (3) It is sufficient that the first gyro sensor  10  has the first detection axis  11  and the second gyro sensor  20  has the second detection axis  21 . Therefore, the structures of these gyro sensors are made simpler than that of a gyro sensor having two detection axes. 
     (4) The angular velocity ω is outputted by the computation circuit  33 . This allows the circuit  30  to be mounted into the gyro sensor module  100 . 
     Second Embodiment 
       FIG. 5  is a schematic perspective view showing a gyro sensor module  200  according to a second embodiment of the invention. The gyro sensor module  200  includes a first gyro sensor module  12 , a second gyro sensor module  22 , and a base  80  having a rectangular mounting surface  81 . 
     In the first gyro sensor  12 , a tuning fork-shaped vibrator is mounted in a package having a rectangular mounting surface  13 . A first detection axis  11  of the first gyro sensor  12  is mounted on the mounting surface  13  so as to be a longitudinal edge of the mounting surface  13 . The first gyro sensor  12  is disposed on a slope of a base  90  disposed on the mounting surface  81 . Therefore, the first detection axis is inclined toward the mounting surface  81 . 
     In the second gyro sensor  22 , a double T-shaped vibrator that is a combination of two T-shaped vibrators is mounted in a package having a rectangular mounting surface  23 . The double T-shaped vibrator is mounted so that a second detection axis  21  thereof is orthogonal to the mounting surface  23 . The second gyro sensor  22  is mounted on the base  80  so that the mounting surface  23  is parallel with the mounting surface  81 . Since the first detection axis  11  is inclined toward the mounting surface  81 , the angle formed by the first detection axis  11  and the second detection axis  21  is the acute angle θ 12  (the direction of the second detection axis  21  is shown on an extension of the first detection axis  11  using a dotted line in the drawing). 
     As with the first embodiment, as long as the angle θ 12  formed by the first and second detection axes  11  and  12  is an acute angle, the first and second gyro sensors  12  and  22  disposed on the mounting surface  81  may have any positional relation. A circuit similar to that according to the first embodiment may be used as a circuit  31 . 
     Besides the advantages of the first embodiment, this embodiment has the following advantage. 
     (5) The gyro sensor module  200  is easily configured by combining the first and second gyro sensors  12  and  22  and the circuit  31 , which are all already mounted. 
     Third Embodiment 
       FIG. 6  is a schematic perspective view showing a gyro sensor module  300  according to a third embodiment of the invention. In  FIG. 6 , the gyro sensor module  300  includes the first gyro sensor  10 , a second gyro sensor  14 , the circuit  30 , the box-shaped package  40 , and the lid  50 . The first gyro sensor  10 , the second gyro sensor  14 , and the circuit  30  are disposed on a rectangular bottom  41  of the package  40 . 
     The first and second gyro sensors  10  and  14  are tuning fork-shaped gyro sensors and are disposed so that the angle θ 12  formed by a first detection axis  17  of the first gyro sensor  10  and a second detection axis  15  of the second gyro sensor  14  is an acute angle. 
     The gyro sensor module  300  is mounted into a vehicle or the like so that a plane including the first detection axis  17  and the second detection axis  15  is orthogonal to the horizontal ground surface  70  as shown in  FIG. 3 . 
     Specifically, the gyro sensor module  300  is mounted so that the bottom  41  is orthogonal to the horizontal ground surface  70 . As with the first embodiment, if the gyro sensor module  300  is mounted into a vehicle, it is mounted so that the bottom  41  is parallel with the traveling direction of the vehicle, and used. Also, as with the first embodiment, the gyro sensor module  300  is preferably mounted into the vehicle so that the θ 22  and θ 23  shown in  FIG. 3  each form an identical angle with the horizontal ground surface  70  with the vehicle being horizontal. 
     This embodiment has the following advantage. 
     (6) The gyro sensor module  300  need not use the base  91  shown in the first embodiment, in the package  40 . This allows the gyro sensor module  300  to be slimmed. 
     Fourth Embodiment 
       FIG. 7  is a schematic perspective view showing a gyro sensor module  400  according to a fourth embodiment of the invention. The gyro sensor module  400  includes a first gyro sensor  19 , a second gyro sensor  18 , the circuit  30 , and a base  82  having a rectangular mounting surface  83 . 
     In each of the first and second gyro sensors  19  and  18 , a tuning fork-shaped vibrator is mounted in a package having a rectangular mounting surface  16 . The first detection axis  17  of the first gyro sensor  19  and the second detection axis  15  of the second gyro sensor  18  are each packaged so as to be parallel with a longitudinal edge of the mounting surface  16 . The first detection axis  17  and the second detection axis  15  are disposed so that the angle θ 12  formed by these detection axes is an acute angle. 
     As with the third embodiment, the gyro sensor module  400  is preferably mounted into a vehicle so that the angles θ 22  and θ 23  shown in  FIG. 3  each form an identical angle with the horizontal ground surface  70  with the vehicle being horizontal. A circuit similar to that according to the first embodiment may be used as the circuit  30 . 
     Besides the advantage of the second embodiment, this embodiment obtains the advantage of the third embodiment. 
     Fifth Embodiment 
       FIG. 8  is a block diagram of signal processing using software. In a fifth embodiment of the invention, an angular velocity is computed using the gyro sensor  100 ,  200 ,  300 , or  400  according to the above-mentioned embodiments that includes none of the circuits  30  and  31 . 
     The analog signals representing the first and second angular velocities ω 1  and ω 2  detected by the first gyro sensor  10 ,  12 , or  19  and the second gyro sensor  20 ,  14 ,  18 , or  22  are converted into digital signals by an analog digital converter (ADC). The ADC may be provided in the gyro sensor  100 ,  200 ,  300 , or  400  or may be provided in a device including the gyro sensor  100 ,  200 ,  300 , or  400 , for example, in the navigation system  101 . Sensor output corrections, a square sum average computation, a multiplication, a sign determination, an adjustment factor computation, and a vehicle position measurement are performed by processing the converted digital signals by a central processing unit (CPU) using the software. Thus, the angular velocity ω is detected. 
     One or more of the sensor output corrections, the square sum average computation, the multiplication, the sign determination, the adjustment factor computation, and the vehicle position measurement may be performed using the software. In this case, an ADC is provided before performing such processing using the software. 
     This embodiment has the following advantage. 
     (7) One or more of the sensor output corrections, the angular velocity ω computation, the error Δθ computation, and the sensitivity adjustment signals A 1  and A 2  computations are performed using the software. Therefore, such processing is performed by the CPU of the navigation system  101  including the gyro sensor module  100 ,  200 ,  300 , or  400 . This allows downsizing of the gyro sensor modules  100 ,  200 ,  300 , and  400 . 
     The gyro sensor modules and the angular velocity detection method according to the invention may be used in a motorcycle as a vehicle. A case in which these modules and the angular velocity detection method are used in a motorcycle will now be described with reference to  FIG. 2 . 
     For use in a motorcycle, the gyro sensor module  100 ,  200 ,  300 , or  400  is mounted on the motorcycle so that a plane including the first detection axis  11  and the second detection axis  21  is orthogonal to the traveling direction of the motorcycle. 
     The motorcycle is inclined bank angles θ 22  and θ 23  toward the horizontal ground surface  70  and makes a turn. Mounting the gyro sensor module  100 ,  200 ,  300 , or  400  on the motorcycle so that the plane including the first detection axis  11  and the second detection axis  21  is orthogonal to the traveling direction of the motorcycle allows the angular velocity ω′ to be obtained from a synthesis of the first and second angular velocities ω 1 ′ and ω 2 ′ according to the following equations even if the bank angles θ 22  and θ 23  vary.
 
ω′=√(ω1′ 2   +SA   2 )
 
 SA =(ω2′−ω1′ cos θ 12 )/sin θ 12  
 
     As for a portable navigation system that is detachable from a vehicle, its mounting angle changes each time it is re-mounted in the vehicle. Therefore, the gyro sensor modules and the angular velocity detection method according to the invention are effectively used in such a navigation system. 
     The invention is not limited to the above-mentioned embodiments and changes and modifications thereto fall within the invention as long as the advantages of the invention are achieved. 
     For example, one gyro sensor may have a first detection axis and a second detection axis so that a first angular velocity and a second angular velocity are detected in the gyro sensor. 
     The entire disclosure of Japanese Patent Application No. 2007-25138, filed Feb. 5, 2007 is expressly incorporated by reference herein.