Measuring and testing – Instrument proving or calibrating – Angle – direction – or inclination
Reexamination Certificate
2002-11-12
2004-12-28
Moller, Richard A. (Department: 2856)
Measuring and testing
Instrument proving or calibrating
Angle, direction, or inclination
C073S001780, C073S001790, C073S001370
Reexamination Certificate
active
06834528
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority under 35 USC §119(e) to European Patent Application No. 01126973.5-2213 filed on Nov. 13, 2001.
TECHNICAL FIELD
The present invention is related to a method, device and system for calibrating angular measurement sensors. Particularly the present invention is relates to a method, device and system for calibrating angular measurement sensors using an acceleration measurement device to provide a set of calibration steps to calibrate the angular measurement sensors in a cheap, fast and easy manner.
BACKGROUND OF THE INVENTION
Inertial navigation systems are used to track the position of objects, such as vehicles, planes and also for handheld personal systems for personal use. Since navigation is possible using GPS systems the combination of GPS receivers and inertial navigation systems is applied. GPS receivers are able to track a movement path but due to the timely distance of the signal only a coarse grid of the movement can be obtained. Besides, navigational information like current orientation of an object cannot be obtain using GPS systems. Therefore an inertial navigation systems is added to the GPS systems. Data obtained by the GPS systems are used as reference position for the inertial navigation systems. Fine grid of the movement can be determined thereby.
Inertial navigation systems are accomplished by integrating the output of a set of sensors to compute position, velocity and orientation to trace movements beginning at an initialisation point. In order to gain this information, linear acceleration measurements with respect to initial space and angular rate measurements, again with respect to initial space, have to be performed. These measurements allow solving of the inertial differential equations leading to position, velocity and orientation. The assembly of linear acceleration measurement sensors (accelerometers) to measure the linear acceleration and angular rate measurement sensors to measure the angular rate is known as inertial sensor assembly (ISA).
It has to be considered that the most important disadvantage of inertial navigation systems is involved by the procedure of solving a differential equation. The basic measurement data are acceleration and angular rate values obtained by the inertial sensor assembly. These values have to be integrated in time once in case of angular rate and twice in case of acceleration values. Errors due to erroneous calibration, bias, drift or changing environmental influence cause relative high deviation, particularly if the integration time is long.
Current acceleration measurement devices have reached a relatively high accuracy, but angular rate measurement sensors like gyroscopes suffer in accuracy. To calibrate angular rate measurement sensors expensive 3-dimensional turn-rate tables have to be applied. The scale factor of the angular rate measurement sensor is determined by using these turn-rate tables. This calibration measurement is only available in specially equipped laboratories. But the scale factor of angular rate measurement sensors is strongly dependent on the condition of usage, like aging, temperature, humidity etc. Effects influencing the measurement results of angular rate measurement sensors are often compensated in prior devices by using expensive additional electronic equipment which is not able to be accurate at any time. The electronic equipment uses pre-measured calibration data obtained in environment simulation systems to estimate the correct scale factor. Re-calibration of such sensors is necessary to ensure permanent accuracy which is a time and cost-intensive procedure.
A method of easily and quickly calibrating angular measurement sensors is not known hitherto, but it would be desired to provide reliable systems at an acceptable price.
An inertial sensor assembly used in inertial navigation systems comprises angular rate measurement sensors and linear acceleration measurement sensors like those described above. A linear acceleration sensor can not distinguish between acceleration related to change of the velocity of the assembly and acceleration due to gravity of the earth. Therefore, it is often assumed that the gravity is constant or a model is applied using the latitude since the shape of the earth can be modelled as a rotational ellipsoid. One of the models is given by the standard model known as WGS-84 system defined by the Defense Mapping Agency. Conveniently, it would be a great advantage to measure the local gravity acceleration value to ensure application of an exact acceleration value of the gravity to increase the accuracy of inertial navigation.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method and a device to calibrate the scale factor of an angular measurement sensor. Therefore an accelerometer measurement device attached in a fixed way to the angular rate measurement sensor is used to determine values necessary for calibrating.
Another object of the present invention is to provide a method and a device to measure the current acceleration value of the locally sensed gravity simultaneously with the calibration process of an angular measurement sensor.
A further object of the present invention is to provide a device comprising an acceleration measurement device and units to perform the calibration method according to the present invention.
A further object of the present invention is to provide a device additionally using a transmission network for exchanging data due to the above described calibration method.
A further object of the present invention is to provide a system comprising at least one angular measurement sensor and a device for calibrating the angular measurement sensor including the possibility of remotely operating the calibration steps.
To solve the objects of the present invention, a method for easily calibrating an angular rate measurement sensor is provided accordingly.
To reach this and other advantages and in accordance with the purpose of the present invention the method comprises several steps to obtain data necessary for calibration. The angular measurement sensor is attached to the acceleration measurement device in any fixed way in order to ensure that both the angular measurement sensor and the acceleration measurement device are displaced simultaneously in the same way when the arrangement of both is displaced. In a first step the assembly of angular measurement sensor which shall be calibrated and the acceleration measurement device is placed in a stationary position, for example placed on an table. In this position the level plane is determined by the acceleration measurement device. Said level plane shall be understood as the locally plane perpendicular to the direction of the gravity vector. The initial value of the angular measurement sensor to be calibrated is set to a pre-defined initial value, but may be preferably set to zero. Correspondingly, it may be possible that a set of initial values of the angular measurement sensor may have to be set to a set of pre-defined initial values. The definition of the initial value may be necessary due to a following evaluation and calculation process of the measured values. In a next step the assembly of the angular measurement sensor and acceleration measurement device is displaced. The displacement may be performed in an adequate way with respect to the capabilities of the angular measurement sensor. Measured values are determined by the angular measurement sensor during displacement of the assembly. After displacement the assembly is placed back to the stationary position similar to that in the first calibration step. Again the level plane is determined using the acceleration measurement device. Now independent measurements of the displacement procedure are available and consequently, the change of the orientation is determined. The determination of the level planes allows to calculate an angle of displacement. The obtained measured values according to the angular measurement sensor allow calculation of a fu
Collin Jussi
Kappi Jani
Moller Richard A.
Nokia Corporation
Ware Fressola Van Der Sluys & Adolphson LLP
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