Measuring and testing – Fluid flow direction – Relative to aircraft or watercraft
Reexamination Certificate
2002-11-18
2004-07-13
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Fluid flow direction
Relative to aircraft or watercraft
C073S865200, C073S384000, C342S122000
Reexamination Certificate
active
06761064
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an altimeter which detects the pressure of atmospheric air, and which obtains an altitude from the detected pressure value. More particularly, the present invention relates to a movement detecting type of (in other words, a stopped state detecting type of) altimeter which obtains an altitude while detecting movements in such a manner that the influence of variation in atmospheric pressure when there is no movement is minimized.
2. Description of the Prior Art
It is well known that an altitude is obtained from an atmospheric pressure detected with a pressure sensor by a standard pressure altitude conversion equation on the basis of a standard atmospheric pressure model which is formed by assuming that atmospheric air is an ideal gas, and in which a decrease by a 0.6 degree in temperature occurs with respect to every 100 m increase in altitude. It is also known that in actuality the pressure of atmospheric air is not constant and varies depending on weather, seasons, and time periods.
With respect to movement-detecting altimeters mounted on vehicles such as motor vehicles and bicycles, it is known that, by considering variations in atmospheric pressure depending on such factors, the influence of changes in atmospheric pressure is minimized in such a manner that while the altitude is obtained from atmospheric pressure by attributing a variation in the detected pressure value from a pressure sensor to a variation in altitude when the vehicle is moving, the altitude is regarded as constant even if the detected pressure value from the pressure sensor varies when the vehicle is stopped (e.g., JP 8-285582 A, JP 8-261755 A, and JP 2000-131061 A).
In this kind of movement-detecting altimeter, however, a variation in pressure in an atmosphere detected with the pressure sensor during moving is attributed to a change in altitude in practice, and, therefore, a variation in atmospheric pressure during moving is regarded as a change in altitude even when the atmospheric pressure itself varies, resulting in an error in measured altitude value. In many cases, the possibility of the influence of variation in atmospheric pressure being canceled out by averaging is high. In actuality, however, there is a possibility that errors resulting from variation in atmospheric pressure will be accumulated. For example, there is a certain degree of regularity in variation in atmospheric pressure in a day depending on the so-called sun effect. Therefore, errors can accumulate easily when there is a movement in a particular time period in a day. Similar error accumulation also occurs in a case where an atmospheric pressure change pattern and movement timing synchronize with each other.
Therefore, there is a possibility of peculiar accumulation of errors during a certain period in the movement-detecting altimeter operating as described above such that the altitude determined by the altimeter is largely different from the actual altitude. JP 2000-131061 refers to various efforts made to eliminate the influence of variation in atmospheric pressure. However, it is essentially difficult to solve similar problems as long as the difficulty in accurately detecting variation in atmospheric air in practice exists.
The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a movement-detecting altimeter designed so as to be capable of avoiding excessive accumulation of errors.
SUMMARY OF THE INVENTION
In order to attain the above-mentioned object, a movement-detecting altimeter according to the present invention includes pressure detection means for detecting pressure of atmospheric air, reference altitude computation means for computing a reference altitude from a pressure detected by the pressure detection means, movement detection means for detecting whether or not a moving condition is maintained, and movement dependent altitude updating means for updating an indicated altitude when the moving condition is maintained, the movement dependent altitude updating means ordinarily avoiding updating of the indicated altitude when the moving condition is not maintained, the movement dependent altitude updating means having: estimated altitude computation means for obtaining an estimated altitude by regarding as a change in altitude a variation in reference altitude obtained by reference altitude computation means from the latest detected pressure value and the preceding detected pressure value obtained by the pressure detection means when the moving condition is maintained; abnormality determination means for making a determination as to whether or not the estimated altitude is an abnormal value; and altitude indication setting means for setting, as an altitude to be indicated, a designated altitude based on the reference altitude when the abnormality determination means determines that the estimated altitude is an abnormal value, and for setting the estimated altitude as an altitude to be indicated when the abnormality determination means determines that the estimated altitude is not an abnormal value.
The movement-detecting altimeter in accordance with the present invention is provided with “estimated altitude computation means for obtaining an estimated altitude by regarding as a change in altitude a variation in reference altitude obtained by reference altitude computation means from the latest detected pressure value and the preceding detected pressure value obtained by the pressure detection means when the moving condition is maintained” and is therefore capable of practical real-time gasping of a change in altitude accompanying a move. The movement-detecting altimeter in accordance with the present invention is also provided, in particular, with “abnormality determination means for making a determination as to whether or not the estimated altitude is an abnormal value” and “altitude indication setting means for setting, as an altitude to be indicated, a designated altitude based on the reference altitude when the abnormality determination means determines that the estimated altitude is an abnormal value”. Therefore, if the accumulation of error becomes excessively large as the estimated altitude computation means repeats estimation to obtain estimated altitudes, a determination is made as to the existence of an abnormality value to check excessive accumulation of errors and to forcibly reset to the standard altitude at the corresponding time, thus grasping the altitude by removing the influence of an accumulated error. Therefore, while the advantage of the movement-detecting altimeter that the influence of variation in atmospheric pressure in a stationary condition is minimized is utilized, excessive accumulation of errors in indicated altitude peculiar to the movement-detecting altimeter (excessive accumulation of errors accompanying variation in atmospheric pressure during movement) can be avoided practically effectively.
The pressure detection means comprises a pressure sensor which is typically a piezoelectric element or a strain gage. The pressure sensor may be any transducer if the transducer is capable of directly or indirectly converting pressure into an electrical signal. Typically, the output signal from the pressure sensor is converted into a digital signal by an A/D converter by considering data processing. However, the output signal in the analog state may undergo data processing if necessary. Detection of pressure is performed at time intervals sufficiently shorter than the shortest time period in which variation in atmospheric pressure accompanying a change in altitude due to a move or variation in atmospheric pressure accompanying a change in weather, etc., can occur. Typically, detection of pressure is repeated at regular sampling intervals. If such a time interval requirement is satisfied, the pressure detection sampling (time) intervals may not be regular. The sampling intervals may be extremely short. However, for the purpose of minimizi
Adams & Wilks
Allen Andre
Lefkowitz Edward
Seiko Instruments Inc.
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