Patent Application
20090145223
The present technical solution relates to measuring technique and can be used in the systems of stabilization of movement of transport means—vehicles (ground, air and sea); for navigation, piloting, ship navigation and other purposes.
For determining acceleration use is made of accelerometers. The accelerometers are considered to measure so-called apparent acceleration. Owing to the above, while tilting their axes of sensitivity from the axis along which the measurement of acceleration is made (in particular, a horizontal or vertical axis) there occur major errors being impermissible. Said errors are caused by the action of cross-axis accelerations (in particular, vertical acceleration when measuring horizontal acceleration or horizontal acceleration when measuring vertical acceleration).
For decreasing said errors, said accelerometers are located on a complicated, expensive, heavy and bulky stabilized (in a horizontal plane) gyro platform. In addition to that, said gyro platform possesses other considerable drawbacks and shortcomings as well: a long initial alignment (for an accurate alignment tens of minutes are required), the necessity of using very precise gyroscopes, considerable dependence on the action of vertical acceleration, vibrations and others. However, it is impossible to implement absolutely precise leveling of said platform. Practically always there is its tilting relative to a horizontal plane. And although said tilting is minor, its harmful influence is considered to be rather noticeable, since the output signal from the accelerometers is usually integrated.
Let's show the above by way of examples.
Let some flying vehicle be moving at constant speed at constant altitude and let the platform be tilted only by a constant angle (not only by value but also by sign), it being equal to 1′.
In this case, due to integration of the apparent acceleration when determining horizontal distance or the altitude of a flight, as well as the depth of sinking in water, there occurs an accumulation error being approximately equal to 300 m per every minute of work, which is unacceptable.
For eliminating said error the authors have developed devices [1], [2], and [3]. Moreover, for the operation of said devices no gyro platform is required. They can be located directly on the body of a moving object, which makes the constructions much simpler, lighter, less expensive, and smaller in size.
However, both in said accelerometer and in said devices [1], [2], [3] there occurs an error caused by the action of centrifugal (centripetal) accelerations. When the moving object is being rotating, by itself or around any instantaneous center of the rotation, above error can be intolerably big.
For eliminating said error the use of azimuth stabilization is required, which makes the construction considerably more complicated, and thus, increases its weight, cost and sizes.
Moreover, the azimuth stabilization does not fulfill its function even in a straight and level flight, it being because of centrifugal (centripetal) accelerations occurring due to the Earth's rotation and the rotation of a flying vehicle around the Earth's center, when moving in the Earth's sphere. This harmful influence is especially noticeable when determining the altitude of a flight.
Let's show the above by way of example.
Let said flying vehicle be moving along the Earth's equator in an east direction at constant altitude at constant speed being approximately equal to 2000 km/hr. In this case, even with the strict location of the axis of sensitivity of measuring vertical acceleration (along a vertical), because of integration, there occurs an accumulation error in determining the altitude of the flight being equal to approximately 10 m per every minute of the flight, which is unacceptable as well.
Due to the causes mentioned above determining vertical acceleration is not unreasonable considered to be unstable and is not practically used.
These are objects of the present technical solution to considerably increase the accuracy, accelerate the readiness for operation, and decrease weight, price and sizes.
To meet the above objects of the present invention there is provided a method and a device for determining axial linear acceleration. Said acceleration presents the projection of the vector of linear acceleration on a chosen axis. Said vector is known to be at a tangent to a trajectory of movement of a moving object. As said axis to be chosen choice can be made of any straight line, particularly, a vertical, a horizontal (i.e. a straight line located in a vertical plane or horizontal plane), or any axis of the mobile object.
Knowing said projection of each of two chosen mutually perpendicular axes located in a horizontal plane enables one to determine a linear acceleration vector being at a tangent to a horizontal trajectory of movement of the moving object. This matters for determining the location of the mobile object on the Earth's surface.
Knowing said projection of each of three chosen mutually perpendicular axes (in particular, a vertical along a η-axis and two mutually perpendicular horizontal axes: longitudinal ξ and transverse ζ) enables one to determine a linear acceleration vector at a tangent to a spatial trajectory of movement of the moving object. This matters for determining the location of the moving object in the space.
An acceleration vector a of the moving object in general case consists of three vectors: a linear acceleration vector, centrifugal (centripetal) acceleration vector and vector of Coriolis acceleration.
Therefore, the projection of the vector a on an axis chosen in general case is equal to
a
a
=a
l
+a
c
+a
k (1)
where aa—projection of said vector a on an axis chosen.
Coriolis acceleration is considerably small (even for aircrafts it is not expected to be more than one hundredth parts of the value 1 m/sec2). Therefore, (and because of the fact that it is not considered to be dangerous) in the present application said Coriolis acceleration is neglected. However, in a special case Coriolis acceleration can be taken into account by means of technical implementation of a known mathematical formula for this acceleration. Moreover, since Coriolis acceleration is small enough, then for the compensation of said acceleration it is enough to know even approximate values being the components of said mathematical formula (the linear velocity of relative motion and angular velocity of transient motion, in particular, the angular velocity of the Earth being practically constant value).
It is known that considerable amount of accidents and crashes of ground vehicles, in particular, automobiles, takes place in the places of turning (turning around). They are because of the action of horizontal linear transverse acceleration al
However, it should be taken into account, that the provided technical solution is true for air and water transport and for any other axis chosen (in particular, not only vertical but horizontal as well).
In general case, radii of rotation (turning) are not known. So, for eliminating the necessity of knowledge of said radii the present solution has brought, for the first time, the differences of centrifugal (centripetal) accelerations of two points located along the axis chosen of the moving object (in particular, longitudinal or transverse axis of the moving object). Herewith, the distances between these two points are known. Let us mark said difference of centrifugal (centripetal) accelerations through Δav.
Let us call this difference of centrifugal accelerations axial differential centrifugal acceleration. This acceleration is determined in a horizontal plane.
In connection with the above, the provided method for determining axial linear acceleration comprises the following stages:
Device for implementation of the provided method is fastened on said moving object, which comprises mutually connected:
A horizontal axes and a vertical may be chosen as axes for measuring above mentioned accelerations.
As the axes chosen use also can be made of, in particular, the axes of the moving object, for example, its longitudinal, transverse and vertical axis, in particular, if the body of said object is used as a horizontal platform [4].
The axial differential centripetal acceleration sensor may comprise a pair of known identical centrifugal acceleration sensors (for example, with centrifugal weights), they being switched to the differential scheme, the output whereof the signal of axial differential centrifugal acceleration is taken.
However, each of said measuring sensors is known to have considerable drawbacks and shortcomings: presence of the threshold of sensitivity and considerable dependence on the tilt angle. Therefore, in the present application there is provided an axial differential centrifugal acceleration sensor, wherein the above considerable drawbacks and shortcomings are eliminated.
Each of said sensors included in the device provided has two sealed miniature vessels filled with flowing medium, in particular, liquid, and provided with pressure sensors. The distance between the point of determining pressure along the chosen axis of the moving object is known.
Let us mark this distance in the axial acceleration sensor, in particular, in a horizontal acceleration sensor, through b1, and in the axial differential centrifugal acceleration sensor—through b2, correspondingly.
The authors have found such a ratio between b1 and b2, wherewith any harmful influence of centrifugal (centripetal) accelerations is eliminated.
As a result the same signal of said axial differential centrifugal acceleration Δav=ω2b is being taken from the output of each said sensor, where ω—angular velocity of rotation, and the value of b varies when tilting. This ratio, in case of necessity, may be corrected by means of practice.
Therefore, the axial acceleration sensor determines, thanks to the ratio chosen between b1 and b2, a value al+ω2b, and the axial differential centrifugal acceleration sensor determines a value Δav=ω2b.
Since the outputs of said sensors are switched to a differential scheme, then from the output thereof (i.e. from the output of the provided device) the signal of the axial linear acceleration al, in particular, al
(al+Δav)−Δav=al, (2)
(al
For determining accelerations use is made of pressure sensors. As said pressure sensors use can be made of any known pressure sensors, predominantly, of semiconductor type, wherein under influence of pressure the changes of specific resistances take place.
The pressure sensors are switched to differential blocks. As differential scheme and differential block use can be made of a Wheatstone bridge, magnetic amplifier by differential scheme, scheme of difference of electrical parameters (currents, voltages, as well as active, capacitance, and inductive resistances).
As an inertial body choice is made of flowing medium (liquid, gas or their mixture), in particular, silicone oil, ligroin and etc. This flowing medium fills miniature sealed vessels, tightly fastened on one and the same base (platform), in particular, on the body of a moving object. The vessels of each corresponding, joint pair have been chosen to be located predominantly in the places with identical vibrations and temperature.
The inner cavities and contours of their cross-sections of the pair of the miniature vessels used for determining said axial acceleration (in particular, along a horizontal axis chosen ζ, marked through aζ), are chosen to be predominantly the same.
The inner cavities and the contours of their cross-section of the pair of the miniature vessels used for determining the axial differential centrifugal acceleration Δav are also chosen to be the same.
Own rotation of a moving object occurs around a pole, in particular, around the center of mass of the moving object. The location of said pole in the process of movement changes within known limits. For eliminating the influence of the location of the pole, the contours of the cross-sections of the inner cavities are located beyond said limits.
The contours are located in a plane passing through mutually perpendicular axes, one of which being the vertical axis of the moving object, and another one being the chosen axis of the moving object, in particular, its transverse axis.
By way of an example, the present application describes determination of the axial linear acceleration al
Said axial acceleration includes the axial linear acceleration al
In the sensor aζ each of said contours is asymmetrical (in particular, relative to the point of determining pressure) along the chosen horizontal axis ζ.
For determining the horizontal acceleration (i.e. said axial acceleration) of different polarity the asymmetrical contours of the inner cavities of the joint pair of the sealed vessels are counter-oriented (non-congruent).
Since said contours are identical and the points of determining pressure in the identical inner cavities are located identically, the cross-axis acceleration acting along a horizontal axis ζ being perpendicular to a horizontal axis ζ creates equal pressures in these points. Due to the above, the difference of the signals of said pressures is equal to zero. Therefore, said cross-axis acceleration will not cause any harmful influence on determining acceleration al
For eliminating any harmful influence of cross-axis acceleration aη (vertical acceleration acting along a vertical, i.e. along an axis η) in each of said contours there are extreme points, they being the most distant from the points of determining pressure. These points are counter-oriented on a line perpendicular to the chosen axis of the moving object, in particular, its transverse axis. If said transverse axis of the moving object is considered to be the chosen axis, then said extreme points are upper and lower. These points, when permissible tilting, in particular, of the transverse axis (at about up to 45°) remains along the vertical at the same, but changeable, distances from the points of determining pressure. Permissible tilts are those when said most distant points (A1 and B1, A2 and B2) remain as such (the most distant), in particular, along a vertical.
Therefore, the cross-axis acceleration aη with these tilts causes equal pressures in said points, as a result of the latter, said acceleration does not cause any harmful influence on determining horizontal acceleration, in particular, the axial horizontal transverse acceleration aζ, where aζ=al
In the axial differential centrifugal acceleration sensor use is made of a pair of identical contours, in particular, circle, wherein the points of determining pressure are identically located, particularly, at the centre of the circle. Therefore, in this sensor the vertical acceleration aη does not cause any harmful influence on determining the axis differential centrifugal acceleration Δav.
Thus, the vertical acceleration aη does not causes any harmful influence on determining the axial linear acceleration al
Since the acceleration aη does not causes any harmful influence on determining the acceleration al
With tilt angles over 45° (>45°) it is not the acceleration al
Thus, the axis of sensitivity of the provided device can either be strictly horizontal or strictly directed along a vertical.
For the columns of the flowing medium of similar length to act on the points of determining pressure along a horizontal (the axis in a horizontal plane) with said tilting by the angles υ, as the points of determining pressure in each said contour of the sensor aζ use is made of a common center of two spherical surfaces (inner cavity of the sealed vessel) of different radii (R and r). The contours of the cross-sections of said spherical surfaces present the arcs of circles of different radii (R and r) being counter-oriented.
The common centre (the point of determining pressure) of the arcs, as well as said extreme points are on the same straight line in each of the contours. The lines of the contours of the cross-sections of the inner cavities of both of the vessels are parallel.
Said contours of the inner cavities of the joint pair of the miniature sealed vessels designed for determining said axial acceleration, in particular, aζ are also counter-oriented. This counter-orientation is carried out by the location of spherical parts of the inner cavities of the sealed vessels of one and the same radius on either side from the centers of the spherical surfaces.
The signals of pressures in two said centers (the points of determining pressure) are supplied to the differential block, from the output whereof a signal al+Δav is taken, in particular, a signal al
In the axial differential centrifugal acceleration sensor the contours of the inner cavities of the two miniature sealed vessels filled also with the flowing medium are congruent (identical and superposedly-oriented). Congruency means that with imaginable parallel transferring, these contours are superposed. In particular, the inner cavities are used in the form of spheres. The center of each of said sphere is the point of determining pressure.
The signals of pressures in these points are supplied to their own differential block, from the output whereof the signal Δav=ω2b of the axial differential centrifugal acceleration is taken.
It is natural, that the axis of sensitivity of the axial differential centrifugal acceleration sensor is also horizontal irrespective of tilting.
No other accelerations but centrifugal (centripetal) ones directed along an axis ζ does not cause any changes of the output signal of the axial differential centrifugal acceleration sensor.
The signals of said axial acceleration and said axial differential centrifugal acceleration are supplied to the differential scheme, from the output whereof the signal of axial linear acceleration al, in particular, the signal of linear transverse acceleration al
Owing to the application of differential scheme and differential blocks any harmful influence, besides cross-axis accelerations, and other disturbance factors (vibrations, temperature and others) is eliminated.
Under the influence of pressure of filling the flowing medium into the sealed vessels and the pressure acted on each point of determining pressure by the vertical column of the flowing medium, it being located above said point, each pressure sensor is always in permanent readiness for operation (overcoming the zone of non-sensitivity is not required). That means that the threshold of sensitivity of every pressure sensor is equal to zero.
Each vessel can be provided with a screw with a thread in its wall and the body of said screw is partially located in the inner cavity. It sets conditions for the opportunity of calibration (adjustment), in particular, before putting into practice. With screwing, the pressure in the vessel is increasing and with unscrewing—decreasing, correspondingly.
The places of fastening said vessels on the body of the moving object or on some stabilized platform should be chosen, if possible, with equal vibrations and temperature. It should be taken into account that the provided device is influenced, unlike in the prior art, not by vibrations and temperature changes but by the difference of the vibrations and difference of the temperature changes in the places of fastening the vessels, which sets conditions for the opportunity of eliminating any harmful influence of said disturbance factors.
It is necessary to bear in mind that the provided device may be used for the first time to solve the task of stable precise determination of axial linear vertical acceleration.
Herewith, any harmful influence of not only horizontal but also of any centrifugal (centripetal) accelerations is eliminated, including those occurring due to the rotation of the Earth and the rotation of the moving object around the Earth's center.
The present technical solution is illustrated by the accompanying drawings.
FIG. 1—a structural (functional) scheme for determining axial linear acceleration is shown, it acting along a horizontal axis, in particular, transverse axis ζ. In this drawing there are not vessels and the wall thickness whereof shown, but there are cross-sections of inner cavities of vessels shown, and there are not pressure sensors shown, but the points (L1 and L2, L3 and L4) of determining pressure by means of said sensors are shown.
FIG. 2—shows an inner cavity of the vessel of the axial acceleration sensor.
FIG. 3—shows the inner cavity of the vessel of the axial differential centrifugal acceleration sensor.
Determination of linear acceleration (vector whereof being at a tangent to a trajectory of movement of a moving object) is based on determining of the projection of said vector on each of three chosen mutually perpendicular axes. Said projection is called axial linear acceleration.
The provided method for determining axial linear acceleration on the chosen axis comprises the following mutually connected stages:
By way of an example, in the present application consideration is given to the determination of axial linear acceleration along a horizontal axis denoted by the letter ζ (called a horizontal transverse axis).
The device implementing the provided method of determining axial linear acceleration comprises (
The sensor 1 comprises two miniature sealed vessels filled with flowing medium, in particular, liquid, and provided with pressure sensors determining pressures in points L1 and L2.
In
The pressure signals in the points of determining pressure L1 and L2 are supplied to a differential block 6, from the output whereof a signal aζ is outputted. This signal is supplied to the differential scheme 3.
The sensor 2 also comprises two miniature sealed vessels filled with flowing medium, in particular, liquid, and provided with pressure sensors determining pressures in the points L3 and L4.
In
The signals of pressures in the points of determining pressure L3 and L4 are supplied to a differential block 9, from the output whereof a signal Δav=ω2b is outputted, where ω-angular velocity, and b—varies when tilting. This signal is also supplied to the differential scheme 3.
By the letter b1 we shall mark the distance between the points L1 and L2, and by the letter b2—between the points L3 and L4, correspondingly. Herewith, the ratio between b1 and b2 is chosen so that the difference Δav to be contained in the signal of the sensor 1, being supplied to the differential scheme 3, and the signal of the sensor 2 be equal by value to ω2b. This equation, when required, is implemented by means of practice.
The inner cavity of each vessel of the sensor 1 consists of two semispheres (
In each contour 4 and 5 there are extreme (the most distant along a vertical from the points of determining pressure) points being counter-oriented on a vertical axis of the moving object: an upper (A1 and A2) and lower point (B1 and B2). Said points (A1 and A2, B1 and B2) are located on the circles (
A cross-axis horizontal acceleration, in particular, aξ (perpendicular to the acceleration aζ) also does not make any harmful influence on determining the acceleration aζ to be measured, since the inner cavities of both vessels of the sensor 1 are identical, as a consequence thereof, the points L1 and L2 are acted upon in a horizontal plane by the columns of the flowing medium of equal lengths herewith.
At the same time, the horizontal acceleration aζ (said axial acceleration) causes in the point L1 the pressure P1=ρaζR (where R—radius of a bigger semisphere) and in the point L2 the pressure P2=ρaζr (where r—radius of a smaller semisphere). So, from the differential block 6 there is a signal ΔP (irrespective of tilting) supplied to the differential scheme 3 equal to
ΔP=P1−P2=ρaζ(R−r), (4)
The points L1 and L2 are acted upon by the influence of the axial linear transverse acceleration al
So, aζ=al
The sensor 2 comprises also two miniature sealed vessels filled with flowing medium, in particular, liquid, and provided with pressure sensors determining the pressures in the points L3 and L4.
Unlike the sensor 1, the contours of the cross-sections of the inner cavities of the vessels in the sensor 2 are superposedly oriented and, since they are identical, they are considered to be congruent. In particular, use is made of the inner cavities of the vessels in the sensor 2 in the form of spherical surfaces (hollow spheres with equal radii
The points of determining pressure L3 and L4 present the centers of these contours (the circles) 7 and 8.
Since the signal Δav=ω2b is outputted from the differential block 9, from the output of the differential scheme 3 the signal of difference is taken
a
l
=(al
From (3) it is seen that in the provided technical solution determination is made of the axial linear acceleration, irrespective of tilting and acting of cross-axis and centrifugal (centripetal) accelerations.
The contours 4 and 5, 7 and 8 are located in a plane passing through two mutually perpendicular axes, one of which being a vertical axis of the moving object, and another one—a transverse axis of the object.
In conformity with Pascal's law there are lots of places possible for fixing a pressure sensor, since, in particularly, with rotating this sensor in a horizontal plane round the point of determining pressure, its output signal is not changing.
In each vessel used for the initial calibration there is provided a screw 11 shown by way of an example on the contour 4. The body of the screw is partially located in the inner cavity of the vessel. When screwing said screw, the pressure is increasing, when unscrewing, it is decreasing, accordingly.
As the differential scheme and each differential block, use can be made of a Wheatstone bridge, magnetic amplifier by differential scheme, electrical scheme of difference of electrical parameters (currents, voltages, as well as active, capacitance and inductive resistances).
As each pressure sensor, use can be made of any known pressure sensor, preferably with a semiconductor sensitive element, which is known to have changes of specific resistance when the pressure changes.
In the provided device the pressure sensors operate with the sensitivity threshold being practically equal to zero. It is explained by the fact that they are acted upon by the pressure of filling the flowing medium, in particular, liquid, into the vessels and the pressures which are caused by the columns of the medium located above them.
The places of fastening the vessels on the body of the moving object or on some stabilized platform should be chosen, if possible, with equal vibrations and temperature. It should be taken into account that the provided device is influenced, unlike in the prior art, not by vibrations and temperature changes but by the difference of the vibrations and difference of the temperature changes in the places of fastening the vessels, which sets conditions for the opportunity of eliminating any harmful influence of said disturbance factors.
The operation of the provided device consists in determining the signals of pressures in the points L1 and L2, L3 and L4 and determining the differences of these pressures.
The provided application presents a group of inventions (a method and device) united by one inventive idea determining linear acceleration.
The present solution is the basis for an efficient solution of other important tasks, which are expected to be the basis of further patenting.
Knowing axial linear accelerations acting along mutually perpendicular horizontal axes ξ (longitudinal) and ζ (transverse) is expected, through the most optimum way, to enable one to carry out movement stabilization and piloting of flying vehicles, their navigation [4] , to determine their true meridian [5], ground speed, angle of drift of a moving object, wind speed vector and others.
Using the provided solution in the device [5] any harmful influence is eliminated of not only centrifugal (centripetal) accelerations caused by own rotations of the moving object but also by its turning around instantaneous centers of rotations.
Special attention should be paid to the movement stabilization of ground vehicles, in particular, automobiles.
For the stabilization, use is made of an accelerometer, which is considered to give out just the signal of axial transverse linear acceleration al
The roadway, even an asphalted one, is known to have tilting by some degrees. And a high-sensitivity accelerometer is known to react to the fractions of second of arc. So, even with unavoidable negligibly small transverse movements, said accelerometer gives out false signals.
Even with performing coordinated (proper) turns (i.e. whereby the axial transverse linear acceleration is equal to zero) said accelerometer reacts to centrifugal (centripetal) accelerations occurring herewith. In this case it gives out false signals being very dangerous.
Therefore, the designers are forced to bring sensors for measuring many other parameters up to gyroscopic devices into the system of movement stabilization and bring the system of comparing initial data (in particular, the places of turning and their radii) together with the actual data.
The above makes the system to be considerably more complicated, more expensive, much heavier and bulkier.
Despite this fact, the system is not efficient enough, and starts operating only after the object moves in a transverse direction (herewith, precious time is wasted). Moreover, the system does not enable one to perform safe turning at any speed (it provides just speed limit).
The provided device enables one to carry out movement stabilization at any speed of movement by one parameter since it is the presence of axial transverse linear acceleration that is the cause of movement destabilization. The signal of said acceleration appears already at the moment of the vehicle tending to move, which sets the condition for reliable quickness (signal into the brake system is supplied before possible movement) of its coming into action. Moreover, herewith, it is not required that the value of said acceleration be measured, but just the detection of its presence. Therefore, herewith, the provided device can be used with lower accuracy.
Thus, the provided solution will enable to implement the movement stabilization of ground vehicles in the most efficient, simplest, less expensive, lightest and small-sized way.
determining axial acceleration, including axial linear acceleration and axial differential centrifugal acceleration;
determining the axial differential centrifugal acceleration;
determining difference of said axial acceleration and said axial differential centrifugal acceleration.
for the first time a solution of precise determination of linear acceleration (the vector whereof being at a tangent to a trajectory of a moving object) is suggested;
for the first time the problem has been solved of the stable precise determination of vertical acceleration, (in airless space, including);
it is not required to perform horizontal and azimuth stabilization (the provided device can be fastened directly on the body of the moving object);
determination of axial linear acceleration presents the basis for efficient and accurate determination of the parameters of movement of the moving object;
it is not required that gyroscopes be used (the main sources of errors of inertial navigation systems);
quick readiness for operation and fast response;
the opportunity of an efficient and rather simple solution of movement stabilization of ground vehicles, particularly, automobiles, at any movement speed and at any form of their trajectory;
since the threshold of sensitivity of the provided device is practically equal to zero, there is no principal obstacles for achieving super high accuracy;
irrespective of permissible tilting (tens of degrees) the axis of sensitivity of the provided device can be either strictly horizontal, or strictly directed along a vertical;
since it is not required to have any stabilized gyro platform, the provided device turns out to be considerably simpler, lighter, less expensive and of smaller size compared to the prior art designed for the precise determination of acceleration.
| Number | Date | Country | Kind |
|---|---|---|---|
| 187 933 | Dec 2007 | IL | national |
