Patent Issued for Signal Processing Module, Navigation Device with the Signal Processing Module, Vehicle Provided with a Navigation Device and Method of Providing Navigation Data
The patent's inventor is Ruizenaar,
This patent was filed on
From the background information supplied by the inventors, news correspondents obtained the following quote: "The present invention relates to a signal processing module.
"The present invention further relates to a navigation device provided with a signal processing module.
"The present invention further relates to a vehicle provided with a navigation device.
"The present invention further relates to a method of providing navigation data.
"Nowadays GPS navigation facilities are available that can relatively accurately determine a position of a vehicle. However, in some circumstances alternative navigation methods are required as GPS-navigation signals are not always available, for example at locations below sea level and in buildings. One such alternative method is based on data obtained from inertial sensors. Inertial sensors comprise gyroscopes and accelerometers. Gyroscopes provide information about the orientation of the vehicle and accelerometers provide information about its acceleration. If the initial position and velocity of a vehicle are known, its momentaneous velocity and position can be estimated by numerical integration of the acceleration and orientation data obtained from the accelerometers and gyroscopes. Generally accelerometers have a systematic error, also denoted as bias, resulting in a drift in position indication, exponential in time. Accordingly, such navigation systems based on inertial sensors need to be calibrated periodically to measure and compensate the sensor biases. With low-cost sensors, and without bias compensation, the navigation solution becomes useless within minutes.
"A method to calculate a bias and a sensor signal compensated for bias is known as indexing. This method involves measuring acceleration at predetermined orientations, e.g. 0 and 180.degree. of the acceleration sensor and calculating the bias from the sum of the measurement results. The estimation of the bias obtained in this way can be used to correct the measurement result. This has the disadvantage that the acceleration measurement has to be periodically interrupted for calibration. Alternatively a bias compensated acceleration signal may be obtained by subtraction of the measurement results. This has the disadvantage that it is necessary to wait until the sensor has rotated over 180 degrees before a new bias compensated acceleration signal sample is available.
"U.S. Pat. No. 7,212,944 describes a method for determining bias comprising a plurality of sensors. Sequentially a different sensor is rotated, while the outputs of the other sensors are used to perform inertial calculations continuously through time. As each of the acceleration sensors is rotated from time to time, the effect of bias is averaged out. Although this allows for a continuous measurement of the acceleration, a relatively complex control of the acceleration sensors is required for sequentially rotating one of the sensors and for selecting the other sensors for determining the acceleration signal.
"Accordingly there is a need for a more simple device and method to determine bias and/or to provide for a bias free estimation of the acceleration."
Supplementing the background information on this patent, VerticalNews reporters also obtained the inventor's summary information for this patent: "According to a first aspect of the invention, a signal processing module is provided as claimed in claim 1.
"According to a second aspect of the invention, a navigation device is provided as claimed in claim 2.
"According to a third aspect of the invention, a method is provided as claimed in claim 12.
"Furthermore, according to a fourth aspect of the invention, a vehicle as claimed in claim 10 is provided.
"According to the invention a first and a second acceleration measurement vector signal are provided that respectively comprise a first and a second sequence of vector signal samples. The vector signal samples comprise at least a first and a second linearly independent acceleration measurement signal component. These signal components are preferably obtained by measurement of the acceleration along mutually orthogonal axes, but alternatively said axes may have a relative orientation of an angle differing from 90.degree., for example in a range of 20.degree. to 160.degree..
"An angle of rotation signal is provided that is indicative for the difference in orientation at which the sample of the first sequence and the corresponding sample of the second sequence were obtained.
"At least one difference signal is generated from the first and the second acceleration measurement vector signal, inverted matrix data is provided by inverting a matrix derived from the angle of rotation difference signal and subsequently a bias signal and/or an object state signal corrected for bias is estimated from the at least one difference signal and the inverted matrix data. The first and the second acceleration measurement vector signal may be subject to further operations before generation of the difference signal.
"According to the method and device according to the present invention acceleration measurement samples at different orientations are periodically sampled. Taking into account the difference in orientation at which the sample of the first sequence and the corresponding sample of the second sequence were obtained the contribution of bias to the measured signal samples and an estimation for the bias-compensated signal can be periodically obtained.
"It is noted that U.S. Pat. No. 7,066,004 discloses a MEM inertial sensor (e.g. accelerometer, gyroscope) having integral rotational means for providing static and dynamic bias compensation. The described sensor comprises a MEM inertial sense element disposed on a rotatable MEM stage. A MEM actuator drives the rotation of the stage between at least two predetermined rotational positions. Measuring and comparing the output of the MEM inertial sensor in the at least two rotational positions allows, for both static and dynamic bias compensation in inertial calculations based on the sensor's output. The known sensor requires operation in a static mode in order to be able to estimate the bias.
"In the signal processing module according to the first aspect of the invention the first and the second acceleration measurement vector signal (S1, S2) respectively comprise a first and a second sequence of vector signal samples that comprise at least a first and a second linearly independent acceleration measurement signal component. The vector signal samples represent a measurement result of an acceleration sensor having a variable orientation as a function of time, wherein samples in the first sequence have a corresponding sample in the second sequence. This feature results in the technical effect that the bias is estimated and/or corrected during normal operation of the device. Accordingly a separate static mode is superfluous.
"Likewise the method according to the third aspect of the invention is characterized in that the step of providing the first and the second acceleration measurement vector signal respectively comprises providing a first and a second sequence of vector signal samples that comprise at least a first and a second linearly independent acceleration measurement signal component, and that the angle of rotation signal is indicative for a difference in orientation at which the sample of the first sequence and the corresponding sample of the second sequence were obtained.
"In a first embodiment the inertial sensor unit comprises a first and a second inertial sensor that provide the first and the second acceleration measurement vector signal respectively, as well as a rotation facility that causes a relative rotation between the first and the second inertial sensor. The relative rotation may be generated for example in that each of the inertial sensors is independently rotated by a respective actuator at a mutually different rotational speed. Preferably, however, only one of the sensors is rotated, while the other has a fixed orientation. In this embodiment, the device has a difference signal generating module that comprises integration and subtraction facilities. The difference signal generating module is arranged for determining at least a difference between an n.sup.th order integrand of the first and the second acceleration measurement vector signal and a difference between an m.sup.th order integrand of the first and the second acceleration measurement vector signal wherein m and n are mutually different integers greater or equal than 0. The inverse calculation module comprises integration facilities that derive the matrix from the angle of rotation signal.
"Preferably the value for m and n differs by one to minimize the number of integrations. Preferably the values of m and n are 1 and 2 respectively. This implies that a difference in velocity and a difference in position are estimated from the sensor signals. In an alternative embodiment a difference in acceleration and a difference in velocity are estimated from the sensor signals. However, this embodiment is relatively sensitive for the influence of the rotation imposed on the sensor(s). Accordingly a more accurate estimation of bias and the bias compensated acceleration signal is obtained by a selection of the values 1 and 2 for m and n respectively. It is assumed that a higher order integration does not further improve accuracy noticeably.
"Instead of using a first and a second inertial sensor in this embodiment, a larger plurality of sensors may be used. In that case the bias and/or the bias compensated acceleration signal may be determined with an improved precision.
"The angle of rotation signal, indicative for a difference in orientation at which the sample of the first sequence and the corresponding sample of the second sequence were obtained, may be derived in various ways. For example the relative orientation of the acceleration sensors may be measured by optical encoding means. Alternatively the orientation of each of the sensors may be measured by a respective angular sensor, e.g. a gyroscope with integration means or a compass. Alternatively an actuator that imposes a relative rotation upon the sensors may issue a signal indicative for the momentaneous angle between the first and the second inertial sensor.
"In a second embodiment of a navigation device according to the invention the inertial sensor unit comprises a single acceleration sensor for generating a single acceleration measurement vector signal. A signal splitting facility derives the first and the second acceleration measurement vector signals from the single acceleration measurement vector signal, for example by alternately assigning a sample of the single acceleration measurement vector signal as a sample of the first and as a sample of the second acceleration measurement vector signal. The angle of rotation signal of the orientation signal generation unit is indicative for an orientation of the acceleration sensor. The single acceleration sensor may be rotated controllably by an actuator, but may otherwise be passively rotated by movements of a vehicle at which the sensor is mounted or by a combination of both. The angle of rotation signal, indicative for a difference in orientation at which the sample of the first sequence and the corresponding sample of the second sequence were obtained, may be derived in various ways e.g. by a gyroscope with integration means or a compass mechanically coupled to the single acceleration sensor.
"In this second embodiment, the navigation device comprises a difference signal generating module with a delay facility for delaying the samples of the first acceleration measurement signal for synchronization with corresponding samples of the second acceleration measurement signal. It further comprises a rotation compensation facility for compensating for a difference in orientation of the acceleration sensor between the moment of sampling a sample for the first acceleration measurement signal vector and the moment of sampling a corresponding second sample for the second acceleration measurement signal vector. The compensation facility is controlled by the angle of rotation signal.
"The second embodiment is advantageous in that only a single acceleration sensor is required and in that it is not necessary to actively rotate the single sensor. It is sufficient that naturally occurring rotations, e.g. caused by a vehicle at which the sensor is mounted are present. Signals obtained by a conventional acceleration sensor may be used. This is advantageous in that the invention can be applied to vehicles provided with such a conventional acceleration sensor by processing the acceleration sensor signal with a signal processing module according to the invention. This embodiment is particular suitable if the momentaneous rotation frequency is relatively high in comparison with the bandwidth with which the acceleration sensor is sampled. If the average rotation frequency of naturally occurring rotations is too low the acceleration sensor may still be actively rotated by an additional actuator.
"The navigation device may be used as a standalone device, for a fireman may carry the device to navigate within a building obscured by smoke.
"The invention relates further to a vehicle provided with a navigation device according to the invention. The vehicle is for example a bicycle, car, motorcycle, train, ship, boat, or aircraft. Preferably the vehicle comprises a drive and steering mechanism controlled by the navigation device. The vehicle may comprise a further navigation facility such as a GPS receiver, or an odometer, for providing information relating to a state of the vehicle, the state comprising at least one of a position, a velocity and an acceleration and an orientation of the vehicle. A combination facility may be present for combining the object-state signal of the navigation device with the information provided by the further navigation facility. The combination facility may for example select the most reliable information for navigation.
"It should be noted that the signal processing can be implemented in hardware, software, or a combination of both."
For the URL and additional information on this patent, see: Ruizenaar,
Keywords for this news article include: Electronics, Signal Processing, Nederlandse Organisatie voor toegepast--natuurwetenschappelijk onderzoek TNO.
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