Apparatus and method for measuring speed of a moving object

[0001] This application claims priority under 35 U.S.C. § 119 to an application entitled “Apparatus and Method for Measuring Speed of Moving Object” filed in the Korean Intellectual Property Office on May 13, 2005 and assigned Serial No. 2005-40359, the contents of which are incorporated herein by reference.

[0002] 1. Field of the Invention

[0003] The present invention generally relates to an apparatus and method for measuring the speed of a moving object, and in particular, to an apparatus and method for measuring the speed of these moving objects based on a roll angle.

[0004] 2. Description of the Related Art

[0005] Generally, moving objects such as vehicles, ships, and aircrafts have an embedded navigation system that determines the position of the moving object (positioning), routes a path to a given destination (routing), and provides the routing results.

[0006] In order to determine the position of a moving object and provide a path to the destination, navigation systems should be able to determine the exact position of a vehicle. Therefore, navigation systems generally include a positioning device for position determination. Such positioning devices are classified into two types, one for determining the position using an outside source and the other for determining the position using an inside sensor. A Global Positioning System (GPS) is an example of the former type of positioning device. A Dead Reckoning (DR) system using an inertial sensor is an example of the latter type of positioning device.

[0007] A DR system calculates the speed and position of a moving object using a gyroscope for detecting a rotational motion of the moving object and an accelerometer for detecting a straight-line motion of the moving object. In particular, the speed of the moving object can be calculated using both speed information acquired from an acceleration measured by the accelerometer and moving direction information acquired from the gyroscope.

[0008] In general, the DR system measures the moving direction angle of a vehicle on a road and an acceleration in the moving direction of the vehicle, as well as calculates the moving speed vector of the vehicle using the moving direction angle of the vehicle and the acceleration in the moving direction of the vehicle. In order to measure the moving direction of the vehicle, the DR system requires a gyroscope installed on an axis perpendicular to a plane on which wheel axles (axis of axles) are placed and In order to measure the acceleration in the moving direction of the vehicle, the DR system requires the measurement value of a road inclination angle in addition to an accelerometer installed in the direction of the wheel axle (axis of axle).

[0009] The road inclination angle measurement value is required because a specific force component proportional to gravitational acceleration is included in the output of the accelerometer and the specific force component may be calculated from the road inclination angle. Since gravitational acceleration works perpendicularly to the surface of the earth spheroid (a spherical surface perpendicular to the directions of the gravitational acceleration) at all times, the angle of the axis of the accelerometer mounted in the vehicle (fixed in a particular direction within the vehicle) with respect to the surface of the earth spheroid changes, thereby resulting in a change in the specific force component included in the output of the accelerometer.

[0010] In other words, if the road inclination angle changes, the direction of the axis of the accelerometer mounted in the vehicle is not perpendicular to the direction of gravitational acceleration. Thus, the accelerometer measures a rate of change in the actual speed of motion (an actual motional acceleration) including a component of gravitational acceleration.

[0011] FIG. 1 is a view explaining a component of the gravitational acceleration included in the acceleration of a moving object. Referring to FIG. 1, a road inclination angle is inclined with respect to a plane perpendicular to the direction (±g) of the gravitational acceleration. In FIG. 1, an angle between a plane 20 perpendicular to the direction (±g) of the gravitational acceleration and a plane 10 extending in the moving direction of a vehicle 30 is a road inclination angle θ. When the vehicle 30 travels on the plane 10 inclined at the road inclination angle θ with respect to the plane 10 perpendicular to the direction (±g) of the gravitational acceleration as shown in FIG. 1, a measurement value {right arrow over (a)} of an accelerometer mounted in the vehicle 30 includes an actual acceleration and a component of a gravitational acceleration {right arrow over (g)}. Thus, the component of the gravitational acceleration {right arrow over (g)} is also measured together with a rate of change in the actual speed of motion and may cause a big error in the measurement of speed.

[0012] Thus, for accurate speed measurement, a vehicle DR system must subtract the gravitational acceleration {right arrow over (g)} from the measurement value {right arrow over (a)} of the accelerometer and measures the road inclination angle θ to measure the gravitational acceleration {right arrow over (g)}.

[0013] The DR system for vehicles can measure the road inclination angle θ using a rotational angle with respect to the forward direction of a vehicle, a rotational angle with respect to the lateral direction of the vehicle perpendicular to the forward direction of the vehicle, and a rotational angle and a roll angle φ with respect to the lower direction of the vehicle perpendicular to the forward direction and the lateral direction of the vehicle. The roll angle φ means the amount of inclination of the vehicle with respect to the forward direction of the vehicle.

[0014] FIG. 2 illustrates coordinate axes defined in a moving object. In FIGS. 2A and 2B, an axis along the forward direction of a vehicle is defined as an X axis, an axis perpendicular to the X axis and passing through the lateral sides of the vehicle is defined as a Y axis, and an axis perpendicular to an XY plane along the lower direction of the vehicle is defined as a Z axis.

[0015] Referring to FIG. 2, a rate of change in the road inclination angle θ can be expressed in Equation (1) as follows:

[0016] $\begin{array}{cc}\underset{\theta }{E}={\omega }_Y\cos \varphi -{\omega }_Z\sin \varphi ,& \left(1\right)\end{array}$

[0017] where ω_Y is an angular speed along the Y axis, ω_Z is an angular speed along the Z axis, and φ is the roll angle of the vehicle. At this time, the roll angle φ means the angle of inclination of the vehicle along the X axis.

[0018] The change rate of the roll angle φ can be expressed in Equation (2) as follows:

[0019] $\begin{array}{cc}\underset{\varphi }{E}={\omega }_X+{\omega }_Y\sin \mathrm{\varphi tan\theta }-{\omega }_Z\cos \mathrm{\varphi tan}\theta ,& \left(2\right)\end{array}$

[0020] where ω_X is an angular speed along the X axis. Equations (1) and (2) are well-known relational expressions related to the change rate of an Euler angle.

[0021] Referring to Equation (2), to accurately calculate the change rate

[0022] $\underset{\varphi }{E}$
of the roll angle φ, three axis gyroscopes are required for measuring the angular speed ω_X along the X axis, the angular speed ω_Y along the Y axis, and the angular speed ω_Z along the Z axis.

[0023] However, generally, a roll motion that is a rotational motion with respect to a wheel axle (axis of axle) (the X axis) connecting the front and rear sides of the vehicle and a straight line motion with respect to an axis (the Z axis) perpendicular to the ground surface is negligible during driving of the vehicle. Thus, conventionally, the road inclination angle θ is calculated only using the angular speed ω_X along the X axis and the angular speed ω_Y along the Y axis, irrespective of the roll angle φ and the angular speed ω_Z along the Z axis in Equation (2).

[0024] When the roll angle φ and the angular speed ω_Z along the Z axis are neglected, i.e., they are assumed to be 0, Equation (1) is

[0025] $\underset{\theta }{E}={\omega }_r\cos \theta -\theta E\sin \theta$
and the change rate

[0026] $\begin{array}{cc}\underset{\theta }{E}={\omega }_r,& \left(3\right)\end{array}$
of the roll angle φ can be given as in Equation (3) by:

[0027] $\underset{\varphi }{E}$

[0028] where ω_r can be calculated from the output of a gyroscope that measures an angular speed along an axis (the Y axis) passing through the lateral sides perpendicular to the forward direction of the vehicle and the road inclination angle θ is obtained by integrating ω_r.

[0029] However, when there are many curves on the road and thus the roll angle of the vehicle increases, the roll angle of the vehicle has a significant influence upon the road inclination angle. In addition, when the angular speed ω_Z along the Z axis is large in Equation (1), even if the roll angle of the vehicle is not large, the roll angle of the vehicle has a significant influence upon the road inclination angle. As a result, a conventional calculation of the road inclination angle θ, which neglects the roll angle of the vehicle, has a significant error.

[0030] In other words, in the case where the roll angle of the vehicle has a large influence upon the road inclination angle, the road inclination angle calculated using Equation (3) neglecting the roll angle of the vehicle has a difference with the actual road inclination angle, which increases over time. As a result, there are large differences between measured speed and position and actual speed and position. Thus, the road inclination angle should be calculated based on the roll angle of the vehicle.

[0031] In Equation (2), gyroscopes for the X axis, the Y axis, and the Z axis are required to calculate the change rate

[0032] $\underset{\varphi }{E}$
of the roll angle φ based on the roll angle

[0033] φ. However, to use the gyroscope for three axes, additional gyroscopes must be mounted in a DR system, increasing the manufacturing cost of the DR system for measuring the speed of the vehicle.

[0034] It is, therefore, an object of the present invention to provide an apparatus and method for measuring the speed of a moving object based on roll movement.

[0035] It is still another object of the present invention to provide an apparatus and method for measuring the speed of a moving object based on roll movement by using an accelerometer, instead of additionally mounting gyroscopes.

[0036] To achieve one aspect of the present invention, there is provided an apparatus for measuring the speed of a moving object. The apparatus includes accelerometers, gyroscopes, a roll angle calculator, an inclination angle calculator, and a speed calculator. The accelerometers measure a first acceleration along the moving direction of the moving object and a second acceleration along the lateral direction of the moving object. The gyroscopes measure a first angular speed along the lateral direction of the moving object and a second angular speed along the lower direction of the moving object. The roll angle calculator calculates the roll angle of the moving object using the second acceleration, the second angular speed, a previous speed of the moving object in the moving direction of the moving object, and a previous road inclination angle with respect to the moving direction of the moving object. The inclination angle calculator calculates a road inclination angle using the calculated roll angle, the first angular speed, and the second angular speed. The speed calculator calculates pure motion acceleration in the moving direction of the moving object using the calculated road inclination angle and calculates the speed of the moving object using the pure motion acceleration of the moving object.

[0037] To achieve another aspect of the present invention, there is also provided a method for measuring the speed of a moving object. The method includes the steps of measuring a first acceleration along the moving direction of the moving object and a second acceleration along the lateral direction of the moving object, measuring a first angular speed along the lateral direction of the moving object and a second angular speed along the lower direction of the moving object, calculating the roll angle of the moving object using the second acceleration, the second angular speed, a previous speed of the moving object in the moving direction of the moving object, and a previous road inclination angle with respect to the moving direction of the moving object, calculating a road inclination angle using the calculated roll angle, the first angular speed, and the second angular speed, and calculating a pure motion acceleration in the moving direction of the moving object using the calculated road inclination angle and calculating the speed of the moving object using the pure motion acceleration of the moving object.

[0045] A preferred embodiment of the present invention will now be described in detail with reference to the annexed drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for conciseness.

[0046] An apparatus for measuring the speed of a moving object according to the present invention calculates the roll angle of the moving object using two axis gyroscopes and two axis accelerometers and measures the speed of the moving object based on the calculated roll angle.

[0047] FIG. 3 is a view explaining an arrangement of a gyroscope and an accelerometer in a moving object according to the present invention. In FIG. 3, a moving object is a vehicle.

[0048] Referring to FIG. 3, an X axis is a wheel axis connecting the front and rear sides of the vehicle and is in parallel with the moving direction of the vehicle. A Y axis is perpendicular to the moving direction of the vehicle and passes through the lateral sides of the vehicle. A Z axis is perpendicular to the X axis and the Y axis and connects the top and the bottom of the vehicle.

[0049] According to the present invention, the apparatus for measuring the speed of a moving object includes two gyroscopes that are located on the Y axis and the Z axis perpendicularly to each other, and two accelerometers located on the X axis and the Y axis also perpendicularly to each other.

[0050] A Y-axis gyroscope located on the Y axis measures the angular speed ω_Y along the Y axis and a Z-axis gyroscope located on the Z axis measures the angular speed ω_Z along the Z axis. An X-axis accelerometer located on the X axis measures an acceleration f_X along the X axis and a Y-axis accelerometer located on the Y axis measures an acceleration f_Y along the Y axis.

[0051] When the constant of the gravitational acceleration is assumed to be g, the acceleration f_X along the X axis calculated by the X-axis accelerometer is expressed in Equation (4) as follows:
f_X=a_X+g sin θ−ω_ZV_Y+ω_YV_Z  (4),

[0052] where a_X is an actual motion acceleration component of a moving object along the X axis, g is the constant of the gravitational acceleration, g sin θ is a gravitational acceleration component, and −ω_ZV_Y+ω_YV_Z is an acceleration component caused by a rotational motion of the moving object. The acceleration f_y along the Y-axis calculated by the Y-axis accelerometer is expressed in Equation (5) as follows:
f_Y=a_Y−g sin φ cos θ+ω_ZV_X+ω_XV_Z  (5);

[0053] where a_Y is an actual motion acceleration component of a moving object along the Y axis, g is the constant of the gravitational acceleration, −g sin θφ cos θ is a gravitational acceleration component, and ω_ZV_X+ω_XV_Z is an acceleration component caused by a rotational motion of the moving object.

[0054] In Equations (4) and (5), ω_X is an angular speed along the X axis, ω_Y is an angular speed along the Y axis, ω_Z is an angular speed along the Z axis, V_X is a speed component along the X axis, V_Y is a speed component along the Y axis, and V_Z is a speed component along the Z axis. “Since the vehicle nearly moves along a straight line in the direction of the X axis Vy and Vz in equation (4) are close to 0. Thus when Vy and Vz are assumed to be 0, the acceleration fx along the X axis is expressed in Equation (6) as follows:.”
f_X=a_X+g sin θ  (6)

[0055] In order to acquire a gravitational acceleration component g sin θ included in the acceleration f_X along the X axis in Equation (6), the road inclination angle θ should be calculated first.

[0056] The road inclination angle θ can be calculated by integrating Equation (1), i.e.,

[0057] $\underset{\theta }{E}={\omega }_Y\cos \varphi -{\omega }_Z\sin \varphi .$

[0058] By integrating Equation (1), the road inclination angle θ at a time instant t is induced and expressed in Equation (7) as follows:

[0059] $\begin{array}{cc}\theta ={\theta }_0+\stackrel{{@}^{\prime }}{A_0}\left({\omega }_Y\cos \varphi -{\omega }_Y\sin \varphi \right)\mathrm{dt},& \left(7\right)\end{array}$

[0060] where θ₀ is the initial value of θ.

[0061] In order to calculate the road inclination angle θ in Equation (7), the roll angle φ should be acquired first. The roll angle φ can be calculated using Equation (5). When the acceleration component a_Y along the Y axis is assumed to be 0 in Equation (5), Equation (5) can be arranged as expressed in Equation (8) as follows:
f_Y=−g sin φ cos θ+ω_ZV_X+ω_XV_Z  (8)

[0062] f_Y can be expressed as in Equation (9) for the roll angle φ as follows:
φ(sin⁻¹[(−f_Y+ω_ZV_X)/g cos θ]  (9),

[0063] where f_Y uses a measurement value of the Y-axis accelerometer, ω_Z uses a measurement value of the Z-axis gyroscope, a speed V_X along the X axis and the road inclination angle θ use their immediately previous estimates. The immediately previous estimates mean previous estimates V_X and θ. When there is no immediately previous estimate, predetermined initial values may be used.

[0064] By using the immediately previous estimates V_X and θ in Equation (9), the roll angle φ can be given by Equation (10) as follows:
{circumflex over (φ)}=sin⁻¹[(−f_Y+ω_Z{circumflex over (V)}_X)/g cos {circumflex over (θ)}]  (10)

[0065] By substituting a calculated roll angle estimate {circumflex over (θ)} into Equation (1), a road inclination angle change rate {circumflex over ({dot over (θ)} is expressed in Equation (11) as follows:
{circumflex over ({dot over (θ)}=ω_Y cos {circumflex over (θ)}−ω_Z sin {circumflex over (φ)}  (11)

[0066] By substituting a measurement value ω_Y of the Y-axis gyroscope and a measurement value ω_Z of the Z-axis gyroscope into Equation (11), the road inclination angle change rate {circumflex over ({dot over (θ)} is calculated and is then integrated with respect to a time axis to acquire the road inclination angle θ.

[0067] The gravitational acceleration component g sin θ included in the acceleration measurement value f_X along the X axis in Equation (6) can be acquired using the calculated road inclination angle θ.

[0068] By subtracting the gravitational acceleration component g sin θ from the acceleration f_X along the X axis, a pure motion acceleration of the moving object along the X axis is acquired as expressed in Equation (12) as follows:
a_X=f_X−g sin θ  (12)

[0069] By integrating the pure motion acceleration a_X acquired using Equation (12) with respect to the time axis, a pure speed V_X of the moving object along the X axis can be acquired.

[0070] Thus, the apparatus for measuring the speed of a moving object according to the present invention can accurately measure a pure motion speed of the moving object using the principles described above.

[0071] Hereinafter, the configuration of the apparatus for measuring the speed of a moving object according to the present invention will be described in detail below. FIG. 4 is a block diagram of an apparatus for measuring the speed of a moving object according to the present invention. Referring to FIG. 4, the apparatus includes an X-axis accelerometer 110, a Y-axis accelerometer 120, a Y-axis gyroscope 130, a Z-axis gyroscope 140, a sensor data processor 150, a roll angle calculator 160, an inclination angle calculator 170, a speed calculator 180, and a data storage unit 190.

[0072] The X-axis accelerometer 110 measures a first acceleration, i.e., the acceleration f_X along the X axis. The Y-axis accelerometer 120 measures a second acceleration, i.e., the acceleration f_Y along the Y axis. The Y-axis gyroscope 130 measures a first angular speed, i.e., the angular speed ω_Y along the Y axis. The Z-axis gyroscope 140 measures a second angular speed, i.e., the angular speed ω_Z along the Z axis.

[0073] The sensor data processor 150 processes the acceleration measurement values f_X and f_Y output from the X-axis accelerometer 110 and the Y-axis accelerometer 120 and the angular speed measurement values ω_Y and ω_Z output from the Y-axis gyroscope 130 and the Z-axis gyroscope 140. In other words, the sensor data processor 150 corrects the acceleration measurement values f_X and f_Y and the angular speed measurement values ω_Y and ω_Z and provides correction data to the roll angle calculator 160.

[0074] The roll angle calculator 160 calculates the roll angle φ of a moving object using the acceleration measurement value f_Y along the Y axis, the angular speed measurement value ω_Z along the Z axis, a previous speed V_X along the X axis, and a previous road inclination angle θ. In other words, the roll angle calculator 160 arranges Equation (5) for the acceleration f_Y measured by the Y-axis gyroscope 130 to Equation (9) for the roll angle φ. The roll angle calculator 160 calculates the roll angle φ by substituting the acceleration measurement value f_Y along the Y axis, the angular speed measurement value ω_Z along the Z axis, the previous speed V_X along the X axis, and the previous road inclination angle θ into Equation (9). At this time, the previous speed V_X along the X axis and the previous road inclination angle θ are immediately previous estimates. The immediately previous estimates mean previous estimates V_X and θ. When there is no immediately previous estimate, predetermined initial values may be used.

[0075] The inclination angle calculator 170 calculates the road inclination angle θ using the roll angle φ calculated by the roll angle calculator 160, the angular speed ω_Y measured by the Y-axis gyroscope 130, and the angular speed ω_Z measured by the Z-axis gyroscope 140. In other words, the inclination angle calculator 170 acquires Equation (10) for the roll angle φ using immediately previous estimates V_X and θ and calculates a road inclination angle change rate using Equation (11) by substituting Equation (10) into Equation (1). The inclination angle calculator 170 substitutes the calculated roll angle φ, the angular speed ω_Y measured by the Y-axis gyroscope 130, and the angular speed ω_Z measured by the Z-axis gyroscope 140 into Equation (11) and integrates the road inclination angle change rate with respect to the time axis, thereby calculating the road inclination angle θ.

[0076] The speed calculator 180 calculates an accurate speed of the moving object using the road inclination angle θ calculated by the inclination angle calculator 170 and the acceleration measurement value f_X along the X axis. In other words, the speed calculator 180 calculates the gravitational acceleration component g sin θ in Equation (6) for the acceleration f_X by using the road inclination angle θ. The speed calculator 180 subtracts the gravitational acceleration component g sin θ from the acceleration measurement value f_X, thereby calculating the pure motion acceleration of the moving object along the X axis as in Equation (12).

[0077] The data storage unit 190 stores the road inclination angle θ calculated by the inclination angle calculator 170 and the pure speed V_X of the moving object calculated by the speed calculator 180 and provides the stored previous road inclination angle θ and the stored previous pure speed V_X of the moving object to the roll angle calculator 160. Thus, the roll angle calculator 160 can calculate the roll angle φ using the acceleration measurement value f_Y, the angular speed measurement value ω_Z, the previous pure speed V_X, and the previous road inclination angle θ.

[0078] Hereinafter, a method for measuring the speed of a moving object according to the present invention will be described in detail. FIG. 5 is a flowchart illustrating a method for measuring the speed of a moving object according to the present invention. Referring to FIG. 5, the acceleration measurement value f_Y is acquired in step 402 of FIG. 5. The acceleration measurement value f_Y is acquired by the Y-axis accelerometer 120 and indicates the amount of change in a speed along an axis (the Y axis) perpendicular to an axis (the X axis) along the forward direction of the moving object and passing through the lateral sides of the moving object.

[0079] In step 404 of FIG. 5, the angular speed measurement value ω_Z is acquired. The angular speed measurement value ω_Z is acquired by the Z-axis gyroscope 140 and indicates an angular speed along an axis (the Z axis) perpendicular to an XY plane along the lower direction of the moving object.

[0080] In step 406 of FIG. 5, the angular speed measurement value ω_Y is acquired. The angular speed measurement value ω_Y is acquired by the Y-axis gyroscope 130 and indicates an angular speed along an axis (the Y axis) passing through the lateral sides of the moving object.

[0081] After the acceleration measurement value f_Y and the angular speed measurement values ω_Z and ω_Y are acquired, the roll angle φ is calculated in step 408 of FIG. 5. Simply, the roll angle φ of the moving object is calculated using the acquired acceleration measurement value f_Y, the angular speed measurement value ω_Y, the previous speed V_X along the X axis, and the previous road inclination angle θ. An equation for the acceleration measurement value f_Y acquired by the Y-axis gyroscope 130 is arranged to an equation for the roll angle φ. The roll angle φ is then calculated by substituting the acceleration measurement value f_Y, the angular speed measurement value ω_Y, the previous speed V_X along the X axis, and the previous road inclination angle θ into the equation for the roll angle φ. At this time, the speed V_X along the X axis and the road inclination angle θ are immediately previous estimates. The immediately previous estimates are the previous estimates V_X and θ. When there is no immediately previous estimate, predetermined initial values may be used.

[0082] After calculation of the roll angle X, the road inclination change rate is calculated in step 410 of FIG. 5. In other words, Equation (10) for the roll angle φ is acquired using the immediately previous estimates V_X and θ and the road inclination change rate is calculated using Equation (11) acquired by substituting Equation (10) into Equation (1).

[0083] In step 412 of FIG. 5, the road inclination change rate is integrated with respect to the time axis, thereby calculating the road inclination angle θ. In step 414 of FIG. 5, pure motion acceleration is calculated by subtracting a gravitational acceleration component from the acceleration measurement value f_X along the X axis. In other words, the gravitational acceleration component g sin θ is calculated using the calculated road inclination angle θ and the pure motion acceleration a_X is calculated by subtracting the gravitational acceleration component from the acceleration measurement value f_X.

[0084] In step 416 of FIG. 5, the pure speed V_X of the moving object along the X axis is calculated by integrating the pure motion acceleration a_X with respect to the time axis.

[0085] In other words, according to the present invention, the speed of a moving object can be accurately measured based on the roll angle of the moving object.

[0086] FIGS. 6A, 6B, 7A and 7B illustrate the speeds of a moving object measured according to prior art and according to the present invention. In FIGS. 6 and 7, the speed of a moving object measured irrespective of the roll angle of the moving object according to prior art and the speed of the moving object measured based on the roll angle of the moving object according to the present invention are compared to the speed (V-GPS) of the moving object measured using a GPS.

[0087] Such comparisons are performed because the speed of the moving object measured using a GPS has a small error when compared to an actual speed of the moving object. Thus, in the present invention, it is assumed that the speed of the moving object measured using a GPS is an actual speed of the moving object.

[0088] As a first comparison result, referring to FIG. 6A, it shows a graph of the speed of a moving object measured irrespective of the roll angle of the moving object according to prior art and a graph of the speed of the moving object measured using a GPS. In FIG. 6A, the horizontal axis indicates a time axis (sec.) and the vertical axis indicates a speed axis (m/s). In FIG. 6A an encircled ‘a’ indicates the speed (V-GPS) of the moving object measured using the GPS and an encircled ‘b’ indicates the speed (V-DR) of the moving object measured irrespective of the roll angle of the moving object according to prior art. Referring to FIG. 6A, when the roll angle of the moving object is neglected according to prior art, the speed (V-DR) measured according to prior art has a large difference from the speed (V-GPS) measured using the GPS. Thus, it can be seen that measurement of the speed of the moving object irrespective of the roll angle has a significant error.

[0089] Referring to FIG. 6B, it shows a graph of the speed of a moving object measured based on the roll angle of the moving object according to the present invention and a graph of the speed of the moving object measured using a GPS. In FIG. 6B, an encircled ‘a’ indicates the speed (V-GPS) of the moving object measured using the GPS and an encircled ‘c’ indicates the speed (V′-DR) of the moving object measured based on the roll angle of the moving object according to the present invention. Referring to FIG. 6B, the speed (V′-DR) measured according to the present invention has a small difference from the speed (V-GPS) measured using the GPS. Thus, a speed that is almost the same as the actual speed of the moving object can be acquired by measuring the speed of the moving object based on the roll angle of the moving object.

[0090] As a second comparison result, referring to FIG. 7A, it shows a graph of the speed of a moving object measured irrespective of the roll angle of the moving object according to prior art and a graph of the speed of the moving object measured using a GPS. In FIG. 7A, an encircled ‘d’ indicates the speed (V-GPS) of the moving object measured using the GPS and (e) (circled-‘e’) encircled ‘e’ indicates the speed (V-DR) of the moving object measured irrespective of the roll angle of the moving object according to prior art.

[0091] Referring to FIG. 7B, it shows a graph of the speed of a moving object measured based on the roll angle of the moving object according to the present invention and a graph of the speed of the moving object measured using a GPS. In FIG. 7B, (d) an encircled ‘d’ indicates the speed (V-GPS) of the moving object measured using the GPS and an encircled ‘f’ indicates the speed (V′-DR) of the moving object measured based on the roll angle of the moving object according to the present invention.

[0092] When FIGS. 7A and 7B are compared, a performance difference between measurement of the speed of the moving object irrespective of the roll angle of the moving object and measurement of the speed of the moving object based on the roll angle of the moving object can be seen. In other words, when the speed of the moving object is measured based on the roll angle of the moving object according to the present invention, a speed measurement error is small and a speed that is almost the same as the actual speed of the moving object can be acquired.

[0093] As described above herein, according to the present invention, the speed of the moving object can be accurately measured based on the roll angle of the moving object.

[0094] In addition, already mounted accelerometers are used without further mounting of expensive and bulky gyroscopes for measurement based on the roll angle of the moving object, thereby reducing the manufacturing cost of a DR system.

[0095] Furthermore, by accurately measuring the speed of the moving object, accuracy in positioning of the moving object using the speed of the moving object can be improved.

[0096] While the present invention has been shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.