EP2126610A2

EP2126610A2 - Method for detecting movement

Info

Publication number: EP2126610A2
Application number: EP08715989A
Authority: EP
Inventors: Vincent Spruytte
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-02-23
Filing date: 2008-02-22
Publication date: 2009-12-02
Also published as: WO2008101725A3; WO2008101725A2

Abstract

The present invention is related to a method for detecting movement within a mass on a spring system, comprising the steps of: measuring signals representative of vibrations on the mass, collecting data representative of the wind speed and the vibration of the ground in the area of the mass on the spring system, deriving an estimation of the vibration on the mass due to wind and ground from a statistical analysis of the collected data representative of wind speed and ground vibration, thereby taking into account information on the weight of the spring system, performing a statistical analysis of the signals representative of the vibrations on the mass, and taking a decision on movement based on the statistical analysis in the previous steps.

Description

METHOD FOR DETECTING MOVEMENT

Field of the Invention

[0001] The present invention generally relates to a method for detecting movement of sources within a vehicle like a trailer, train, car, cargo loader, fork lift and the more.

Background of the Invention

[0002] In first order a trailer or a vehicle can be modelled as a stiff lever on a fixed point, where this fixed point itself is placed on a suspension system where the primary components are a one-dimensional spring constant and the damping constant. [0003] The suspension system of a vehicle is normally low frequent. For example, the suspension system of a trailer normally produces vibrations at frequencies between 6 Hz and 9 Hz. The measured frequency on the lever will be between 4 Hz and about 7 Hz. More details can be found in patent document WO 92/10735, wherein a method for determining the dynamic properties of a vibration isolation pad is disclosed.

[0004] A person concealed in a vehicle or any external source mostly induces impacts on the system. Reference is also made to the introductory section of patent US-6370481-B1. This means that the system starts to vibrate on its natural frequency (about 4 Hz to about 7 Hz.) Due to the damping in the system this frequency is measured as a frequency band. The signal is very weak. To make it measurable, a geophone (i.e. a small instrument for measuring ground motion) with natural frequency of ca 1.5 to 2 times lower than the natural frequency (e.g. about 4.5 Hz) is used as an amplifier. As this probe has almost the same natural frequency as the trailer system, it amplifies the signals on its resonance frequency. [0005] Document US-6730481-B1 discloses an apparatus and method for human presence detection in vehicles. The main drawback of this method is that it only works in relatively calm situations. As a further drawback the detecting process is stopped or interrupted each time a disturbing signal (ground seismic signal, wind, ...) is found to exceed a certain threshold level . [0006] Patent document WO2006/007673-A1 proposes an improved system for detecting movements within a vehicle. Vehicle vibrations are sensed with a set of sensors positioned on the chassis of the vehicle. Simultaneously a number of external sources (wind, vibration, sound, ...) are measured. Next a set of correlation coefficients is determined between signals from signals measured on the vehicle and the signals indicative of the external sources. A statistical analysis of the set of correlation coefficients is performed and forms the basis for deciding on whether or not there is movement inside the vehicle. Although this approach works well, it is also limited by the disturbance levels. If those are too high, the measurement process has to be stopped and if there are no external forces, the process has to be stopped also. The problem is that, although the measurement itself is independent of the characteristics of the vehicle, the limits for stopping the measurement are dependent on the characteristics of the truck, especially the mass. This makes the calibration difficult when a range of types of truck is possible. Also the range of possible disturbance situations where a vehicle can be analysed is extended with this new algorithm.

[0007] Consequently, the present invention aims to provide an improved method for detecting movement from living objects or moving sources in general in the presence of external signals as ground vibrations, sounds, wind, ... without opening the vehicle or cargo loader and whereby the above-mentioned problems of the prior art solutions are overcome.

Summary of the Invention

[0008] The present invention relates to a method for detecting movement within a mass on a spring system, comprising the steps of :

- measuring signals representative of vibrations on the mass,

- collecting data representative of the wind speed and the vibration of the ground in the area of the mass on the spring system, - deriving an estimation of the vibration on the mass due to wind and ground from a statistical analysis of the collected data representative of wind speed and ground vibration, thereby taking into account information on the weight of the spring system, - performing a statistical analysis of the signals representative of the vibrations on the mass, and

- taking a decision on movement based on the statistical analysis in the previous steps. [0009] In a preferred embodiment the step of collecting data representative of the wind speed and the vibration of the ground in the area of the vehicle is performed by measurement.

[0010] Advantageously, the step of collecting data representative of the wind speed and the ground vibration is performed simultaneously with the step of measuring signals representative of vibrations on the vehicle.

[0011] The information on the weight of the spring system preferably comprises an approximation of the weight of the suspended part of the spring system.

[0012] The spring system is typically a cargo loader, a trailer or a vehicle. [0013] In a preferred embodiment the method further comprises a step of determining a statistical prediction of the vibration level on the mass based on the statistical analysis. The step of taking a decision is then performed by comparing said statistical prediction with said measured signals.

[0014] In another aspect the invention relates to a program, executable on a programmable device containing instructions, which when executed, perform the method as in any of the previous claims.

Brief Description of the Drawings

[0015] Fig. 1 represents a model of a vehicle as a stiff lever.

[0016] Fig. 2 illustrates a typical frequency response of a geophone sensor on a truck to an impulse. The X axis represents the frequency in Hz.

[0017] Fig. 3 illustrates the influence of the ground vibration on the vibration speed on the vehicle. [0018] Fig. 4 illustrates the influence of the vehicle mass on the vibration speed on the vehicle.

[0019] Fig. 5 illustrates the effect of internal damping on the vehicle vibration level. [0020] Fig. 6 illustrates the influence of the wind speed on the vehicle vibration level. .

[0021] Fig. 7 illustrates the embodiment with the cargo loader.

Detailed Description of Embodiment(s)

[0022] The present invention discloses a method for detecting movements, heart beats, breathing,... from living objects or other moving sources within a mass on a spring system in the presence of external signals as vibrations, sounds, wind, .... whereby it is not needed to open the mass. The mass on the spring system can be a vehicle (trailer, truck, car, train, ....), a cargo loader or fork lift on a suspension system or other spring system.

[0023] The scheme in Fig.1 represents the complete model. The measurements are performed with geophone sensors. The signal measured by a geophone sensor is strongly non-linear due to the resonance phenomena. Therefore the first order harmonic in the signal is measured, which gives a much more linear signal. This measurable signal contains the information about the presence of vibration sources (moving sources) in the vehicle. The measured signal is proportional with the vibration speed. Two possible kinds of forces act on the system. On the one hand there are internal forces in the vehicle (e.g. hidden persons) and on the other hand external forces like vibrations on the ground, wind, .... [0024] The mathematical representation of the system can be described by four differential equations of second order with eight initial conditions, as given below. Hereby k_g denotes the spring constant of the soil, ζ_g the damping coefficient of the soil, rrig is the mass acting on the soil. Two possible kinds of forces act on the system. The variables z_s, z_t, Z_b and z_g are indicated in Fig.1. On the one hand there are internal forces in the vehicle (e.g. hidden persons) and on the other hand external vibrations on the ground. F(t) denotes the force on the vehicle and G(t) the force on the ground. = 0 Z₅(O) = O s O z_s,(0) = O g(0) = : 0

Zg₁(O) = O

Zb(O) = O Z₁J₁(O) = O

m_s - ±_h(Δ

^■* ^{+ ~ζs} (i^ ^" dt^zs(t))]

m_s (z^Ct) - ZJ₅(I)) - ζ_s - iz_g(t) j

[0025] From this set of differential equations the impulse response (and thus the frequency response) to an excitation can be calculated. Fig.2 shows a typical shape of the measured sensor frequency response. [0026] Now the influence of various external sources on the vehicle vibration is discussed. Fig.3 shows the influence of the ground vibration on the simulated system for different masses of the vehicle. The ground vibration is the signal from the sensor on the ground. The vehicle vibration is the signal on the vehicle. Both signals are vibration speeds. From Fig.3 can easily be seen that log(vibration speed) is proportional to log(ground vibration), hence it is concluded that the following relation holds (with a a positive value) :

Vvehicle ~~ Vg

[0027] Fig.4 illustrates the influence of the mass m_veh of the vehicle on the vibration level sensed on the vehicle. Again taking into account the logarithmic scale, it is clear that this relation can be approximated by the expression (whereby b denotes a positive value):

^vehicle "" Wveh

[0028] Fig.5 shows the effect of damping on the suspension of the vehicle for different masses of the vehicle. One can conclude that this influence is marginal within realistic margins.

[0029] Fig. 6 illustrates the influence of the wind speed on the vehicle vibration.

It can be concluded that a relation of the following form holds :

Vvehicle ~~ Vwind The force of the wind F(t) is deducted from the measurement of the wind speed.

[0030] As can be understood from what precedes, the signal on the vehicle is a summation of the response on the vehicle of a force on the vehicle and of the reaction of the vehicle of a force on the soil. Hence, one can write :

V_Veh,cle(t) = Vperson(t) + + V_wιnd(t)

From this it is clear that the minimum signal on the vehicle is the signal from the soil and the wind.

[0031] When the ground vibration v_g, the wind speed Vwmd and the weight of the vehicle can be measured or if in another way data on the wind speed or vehicle weight is available, it is possible to predict the vibration level of the vehicle due to these influences.

[0032] When the measured level on the vehicle is equal or smaller than the predicted level, there is no additional source to cause vibrations; when the measured level on the vehicle is larger than the predicted value, there is a source, other than the ground vibrations or the wind that excites the vehicle. This is probably caused by an intruder. [0033] The measured speeds v_g, Vw and vt are evaluated with statistical levels

L_N ^S defined by: the statistical level L_N ^S is the level where N% of the time the signal S is higher. The calculation of these statistical levels is based on a cumulative distribution. [0034] In first order, a trailer or vehicle can be modelled as a stiff lever on a fixed point, where this fixed point itself is placed on a suspension system where the primary components are a one-dimensional spring constant and the damping constant. The suspension system of a vehicle is normally low frequent. The mass in the mass-spring system is the combined weight of the parts of the truck on top of the suspension system and the load in the truck. The weight of the suspension system, the axes and the wheels, i.e. the structure under the suspension system, is normally relatively small as compared to the weight on top of the suspension system. In this case, the weight can be approximated by the total weight of the trailer or of the truck. This is easily measured on a weigh bridge or on an axe weigher. [0035] A cargo loader is a structure that is fixed to the ground. The cargo is placed on top of a lift. The lift consists of four beams with a pneumatic or hydraulic system to lift the cargo. The system operates as a spring system. Due to the fact that these are pneumatic or hydraulic, their natural frequency is low and the system acts as a spring mass system.

[0036] A person in the cargo (on top of the platform) or any external source mostly induces impacts on the system, which means that the system starts to vibrate on its natural frequency. Again, this frequency is measured as a frequency with a width due to the damping in the system. Also in this situation the signal is very small. To make the signal measurable, a geophone with natural frequency between 50% and 200 % of this natural frequency is used as an amplifier. As this probe has almost the same natural frequency as the system, the signals are amplified on the system's resonance frequency. The weight used in the calculations is the total weight of all elements on top of the lift. This is the weight of the cargo and the weight of the platform itself.

[0037] Fig.7 illustrates the working principle for the specific embodiment wherein a cargo loader is used. The cargo is transferred on the platform when it is on ground level. On the bridge, an operator may be present or not. On the original stacker (in front of the platform and not shown in the Figure), on the cargo or on an intermediate system the weight is measured. On some systems, the bridge and the transfer platform are one and the same. When the load is on the platform, the vibration level of the platform is measured with one to four sensors, depending on the dimensions of the platform.

[0038] As explained before, the analysis of these signals and the analysis of the wind speed and ground vibration levels is performed to determine if a living person or object is present in the cargo. [0039] When the conditions wherein the system is used are relatively invariable, due to the fact that the system is always the same, it is possible to do the testing without measuring the weight or without measuring external influences. This will reduce the sensitivity of the system and probably the speed of measurement. [0040] When the range of the possible weights of the cargo is relatively small, it is possible to do the measurements without measuring the weight of the cargo and do the analysis taking into account a fixed weight. A sensitivity analysis on the obtained results can be performed to get an idea of the errors produced. [0041] The various parts of the system for detecting movements is now described. [0042] In its minimal configuration the system comprises only one geophone sensor of optimized characteristics to be positioned on the chassis of the vehicle. If a simultaneous measurement of the ground vibration is to be performed, at least a second geophone sensor is required. Note that for ground vibrations the sensor is advantageously placed near the wheel. The number of geophone sensors required in the system largely depends on the dimensions of the vehicle or trailer one is working on.

[0043] The system may further comprise a low frequency microphone to measure the wind speed. Another optional part of the system is a balance to measure the weight of the vehicle. [0044] Essential in the system is the central processing unit. The central processing unit takes care of the signal conditioning and the calculation of the different signals. It is arranged for comparing with the measured values of the vibration level on the mass. The processing unit may comprise a digital filter to filter the relevant part of the signal spectrum. The statistical engine comprised in the processor unit is arranged for calculating the different statistical levels and for deriving the statistical prediction of the vibration on the mass, based on the information regarding the ground vibration and the wind speed. [0045] The central processing unit may further also comprise a counter to count the number of measurement results before the statistical analysis starts and a statistical engine to calculate the different statistical levels.

[0046] One possible system to employ in order to implement the method of the present invention is the system described in WO2006/007673, possibly extended with a weighing system. [0047] With the method of the invention it is possible to give a good prediction of the two types of faults (no internal vibrations while there are internal sources and internal vibrations while there are no internal sources) where the distribution of both types of events and situations overlaps. The method also removes the influence of exceptional low and exceptional high values. [0048] Although the present invention has been illustrated by reference to specific embodiments, it will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied with various changes and modifications without departing from the spirit and scope thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. In other words, it is contemplated to cover any and all modifications, variations or equivalents that fall within the spirit and scope of the basic underlying principles and whose essential attributes are claimed in this patent application. It will furthermore be understood by the reader of this patent application that the words "comprising" or "comprise" do not exclude other elements or steps, that the words "a" or "an" do not exclude a plurality, and that a single element, such as a computer system, a processor, or another integrated unit may fulfil the functions of several means recited in the claims. Any reference signs in the claims shall not be construed as limiting the respective claims concerned. The terms "first", "second", third", "a", "b", "c", and the like, when used in the description or in the claims are introduced to distinguish between similar elements or steps and are not necessarily describing a sequential or chronological order. Similarly, the terms "top", "bottom", "over", "under", and the like are introduced for descriptive purposes and not necessarily to denote relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and embodiments of the invention are capable of operating according to the present invention in other sequences, or in orientations different from the one(s) described or illustrated above.

Claims

1. Method for detecting movement within a mass on a spring system, comprising the steps of : - measuring signals representative of vibrations on the mass,

- collecting data representative of the wind speed and the vibration of the ground in the area of the mass on the spring system,

- deriving an estimation of the vibration on the mass due to wind and ground from a statistical analysis of the collected data representative of wind speed and ground vibration, thereby taking into account information on the weight of the spring system,

- performing a statistical analysis of the signals representative of the vibrations on the mass, and

- taking a decision on movement based on the statistical analysis in the previous steps.

2. Method as in claim 1 , wherein the step of collecting data representative of the wind speed and the vibration of the ground in the area of the vehicle is performed by measurement.

3. Method as in claim 2, wherein the step of collecting data representative of the wind speed and the ground vibration is performed simultaneously with the step of measuring signals representative of vibrations on the vehicle.

4. Method as in any of claims 1 to 3, wherein the information on the weight of the spring system comprises an approximation of the weight of the suspended part of the spring system.

5. Method as in any of the previous claims, wherein the spring system is a cargo loader, a trailer or a vehicle.

6. Method as in any of the previous claims, further comprising a step of determining a statistical prediction of the vibration level on the mass based on said statistical analysis.

7. Method as in claim 6, wherein the step of taking a decision is performed by comparing said statistical prediction with said measured signals.

8. A program, executable on a programmable device containing instructions, which when executed, perform the method as in any of the previous claims.