Abstract:
A reliable and secure activation of an access based on a detection of movement in a remote access system by providing a secure method for opening/closing of an access in hands-free access mode. The detection of movement relates to the displacement of a lower member of a user by a remote access system, this access system including at least two elements of detection which each emit a signal whose variations ( 31, 33, 35 ) are analyzed. The detection of a movement of a lower member is validated by the application of a double verification step according to parameters (dAsA, dAsB) of a criterion for identification (tA, tB; dAsA, dAsB) of a form of variation (F 2;  A, B) of each signal ( 31, 33, 35 ) with a model form of the movement, and according to a criterion for simultaneity of detection of the forms of variation (F 2 ) identified on the two signals.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a method for opening/closing of an access by detection of movement of a lower member of a user, allowing a secure hands-free access. 
         [0002]    The main, but non-exclusive, application of this invention relates to the opening of vehicle trunks, in order to allow the authorized user to open a trunk with only a foot movement, the user being identified by a badge or a key that he/she is carrying by means of a BCM control module (initials for “body control module”) situated in the vehicle. 
       BACKGROUND OF THE INVENTION 
       [0003]    Currently, hands-free access requests mainly consists of the need to position a hand in order to confirm a request for opening/closing an access to a vehicle, and this process comprises two main steps: recognition of a key or a badge authorized to open or close the vehicle near to the access by the BCM of the access system and, in the case of a request for opening, detection of the presence of the hand on a handle. 
         [0004]    The implementation of this method necessitates antennas for the detection of authorized keys or badges, contact sensors in the handles, in general capacitive sensors, for the detection of a hand, together with a centralized system for management of the hands-free access requests, which may for example be a computer wholly or partially dedicated to this function. 
         [0005]    With regard to the use of the foot for contactless opening, one known application relates to the opening of an operating theater door for hospital staff. The utility model CN 202 143 044 for example provides for the door to be equipped with an inductive sensor for detection of a foot. People wishing to enter or to exit from the theater extend their foot near to the sensor and the signal detected by the sensor is transmitted to a device for controlling a mechanism for opening/closing of the door. 
         [0006]    Use of the foot for a hands-free access to the trunk of an automobile is presented in the international patent application WO 2012/052210. This document provides the detection of a movement of a part of the body of the user, for example the foot, by a capacitive detection assembly with two elongated electrodes. These electrodes run horizontally under the trunk, the longer underneath the shorter, and are coupled to a control and evaluation device. The variations of capacitance are monitored with respect to a reference potential, and when the movement is in the detection range, an activation is triggered, for example the opening of the trunk. 
         [0007]    The management of the accesses to a vehicle in the framework of the requests for hands-free access using hand detection has been improved in order to combat various interference effects. For example, the patent document FR 2 827 064 aims to identify the interference effects generated by the metallic paints of automobiles by a module for logical interpretation of the durations of the signals received. 
         [0008]    One solution provided to the problem of electromagnetic interference is described in the patent document FR 2 915 331. A time-related filtering is provided for the signals coming from the sensors in the access handles, in order to validate or otherwise the presence of a hand on a handle prior to validating a request for opening. 
         [0009]    The system for hands-free opening/closing of the prior art therefore offers an appreciable comfort for users, with a confirmation of opening/closing of an access given by the presence of a hand or by a foot movement. However, false detections such as those resulting from interference effects caused by atmospheric phenomena, in particular rain, or other types (electromagnetic interference, objects passing under the bumper, etc.) are not identified and unexpectedly trigger a spurious request for opening. Solutions exist for overcoming certain interference effects for opening/closing operations using the hand, but no reliable solution exists for foot movement detection systems. Even if, in the latter case, the detection system is based on two sensors per access, the system has not been made sufficiently reliable in a noisy environment. 
       SUMMARY OF THE INVENTION 
       [0010]    The invention aims to provide a solution to the need for a reliable and secure activation of an access based on a detection of movement of a lower member of a user, even in an environment with interference effects. For this purpose, the invention provides a comparison of the form and of the behavior over time of the signals received by the electrodes in question in order to discriminate the useful signals from the signal variations due to noise. 
         [0011]    More precisely, the subject of the present invention is a method for opening/closing of an access in hands-free access mode made secure by detection of a leg/foot, referred to as lower member, movement of a user by a remote access system. This access system comprises at least two means of detection. The detection means each emit a signal whose variations are analyzed. The detection of a movement of a lower member is validated by the application of a double verification step according to a criterion for identification of a form of variation of each signal with a model form of said movement, and according to a criterion for simultaneity of detection of the forms of variation identified on the signals. 
         [0012]    According to embodiments that are particularly advantageous, the method according to the invention may also include the following steps: 
         [0013]    the form to be verified being represented by a sharp point between two slopes of opposite signs of the V-shaped type, the form identification criterion comprises the detection of times of critical changes of variation in slope inclination of this form, corresponding to the detection of a sharp point and of a form exit, in order to acquire the values of the critical variations in slope inclination at the sharp point and at the form exit, the determination of the values of a ratio R of the variation in instantaneous amplitude and of duration EtA of travel of the form, together with comparisons of these values of critical variations in slope inclination, of the ratio R of variation in amplitude and of duration EtA of the form with predefines threshold values; 
         [0014]    the determination of the ratio of variation in instantaneous amplitude is carried out based on the variation in signal amplitude between a point of critical change in instantaneous inclination and a current point, divided by the duration of travel between these points; 
         [0015]    the form identification criterion comprises a test for strictly increasing slopes of the forms verified prior to validation; 
         [0016]    the criterion for simultaneity of the forms is verified when the difference Etmax between the times of detection of their sharp points is less than a predefined value, in particular less than 250 ms; 
         [0017]    an additional verification step consists in applying a coherence criterion by determining the ratio between the larger and the smaller of the variation amplitudes of a pair of forms from various signals, satisfying the identification and simultaneity criteria, and in validating this additional step when this ratio is substantially equal to or less than a predefined value, in particular less than or equal to 4; 
         [0018]    the variation amplitude of the forms satisfying the identification and simultaneity criteria is measured by the ratio of the amplitudes between the sharp point and the form exit. 
         [0019]    Thus, one of the advantages of the invention is to be able to compare, with determinant criteria, signals coming from at least two detection means, which allows all the noise effects to be eliminated. Another advantage of this method is that it allows a simplified implementation with a reduced memory requirement and a high speed in the calculations. 
         [0020]    Preferably, the verifications performed on the signals are preceded by a step for filtering the signals intended to eliminate the interference effects due to the high frequency variations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Other data, features and advantages of the present invention will become apparent upon reading the non-limited description that follows, with reference to the appended figures which show, respectively: 
           [0022]      FIG. 1 , various external views (diagram  1 A to  1 C) of a rear part of a vehicle equipped with two sensors of one example of a remote access system with a detection of leg/foot movements of a user (or kick from the lower member); 
           [0023]      FIGS. 2   a  and  2   b , diagrams of the measurements supplied by these two sensors in the form of variations of signals, respectively in the case of a noise-free environment and in the case of a noisy environment due to rain; 
           [0024]      FIG. 3 , diagrams of a detailed variation of a signal before and after filtering, together with the instantaneous slope of this signal, during a characteristic kick movement of the user; 
           [0025]      FIG. 4 , a block diagram of processing of the signals supplied by these two sensors based on form, simultaneity and amplitude comparison criteria, and 
           [0026]      FIG. 5 , one example of logic flow diagram for detection of movement characteristic of a foot kick according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    With reference to the external views in  FIG. 1  of a rear part of an automobile vehicle  100 , a remote access system comprises two electrodes forming sensors  1  and  2  for detection of a movement of a user lower member. These sensors (also respectively referred to as “upper” and “lower”) are arranged above one another in the rear bumper  101 , situated under the trunk  102  of the vehicle  100 . The sensors  1  and  2  are arranged at the level of a lower member, formed of a leg  3  and of a foot  4  of a user of average height. For symmetry reasons of access to the trunk  102 , the sensors are situated preferably in the plan of symmetry of the vehicle  100 . 
         [0028]    The diagrams  1 A,  1 B and  1 C show the movement of the lower member of the user in a back-and-forth motion referred to as “kick movement” under the trunk of the vehicle  100 . The convention for use of the remote access system allows the authorized user, by the identification of his/her badge, to open the trunk  102  by a forward movement (going from the diagram  1 A to diagram  1 B) then a reverse movement (going from the diagram  1 B to diagram  1 C) of the leg  3  and of the foot  4  under the trunk  102  of the vehicle  100 . This movement signals an order to open the mechanism of the trunk  102  by a suitable control command. 
         [0029]    In  FIGS. 2   a ,  2   b  and  3 , amplitudes of signals As as a function of the time “t” are plotted.  FIG. 2   a  illustrates the measurements supplied by the sensors  1  and  2  in the form of diagrams  5  and  6  of signal variations in the case of a noise-free environment. On the time “t” abscissa axis, the times of production of three successive foot kicks  7  are plotted. The signal amplitudes are measured and recorded periodically as a function of the time “t”. The elementary interval of time Δt between two measurements is defined experimentally. In this example, Δt is around 20 ms. 
         [0030]    When the foot kicks occur, the diagrams  5  and  6  show drops in level of the signals. In this noise-free environment, the signal/noise ratio is high, and the detection of each foot kick movement has a distinct “V” shape with, successively over time, a descending slope Pd then an ascending slope Pa, surrounding an sharp point P, situated at the low peak of the “V”. 
         [0031]    The simultaneity of the two diagrams  5  and  6  confirms the existence of foot kicks  7 . In a situation with no interference, the signal forms analysis supplied by the foot kicks from a sample of people, varying by their height or by their manner of kicking, allows a set of ranges of values to be validated. This set defines a model form of signal variation corresponding to a foot kick (see the complementary explanations with reference to  FIG. 4 ). 
         [0032]      FIG. 2   b  presents one example of the measurements supplied by the two sensors of the access system in the form of diagrams  10  and  12  of variations of signals, in the case of a noisy environment due to rain. On the time abscissa axis the times of production of the foot kicks  7  are plotted. At these times, the diagrams  10  and  12  show drops in signals level, as in a noise-free environment ( FIG. 2   a ). However, in a noisy environment, the foot kicks  7  are more difficult to identify on the variations of signals in the diagrams  10  and  12  owing to a lower signal/noise ratio. After analysis of the signals according to the identification and simultaneity criteria of the invention, as explained hereinafter, the variations of signals P 1 , P 2 , and P 3  will be validated as “V”-shaped forms corresponding to foot kicks. 
         [0033]    With reference to  FIG. 3 , diagrams  31  and  33  of detailed variations of the amplitudes As of a signal exhibiting a form F 1  corresponding to a “V”—resulting from a foot kick—are illustrated. The diagram  31  corresponds to the signal from the upper sensor  1 . The diagram  33  is the result of a low-pass filter being applied to the curve  31 : as the irregularities have been filtered out, the diagram  33  is shifted by the small delay due to the filtering. 
         [0034]    The diagram  35 , illustrated in the same figure, corresponds to the instantaneous variation dAs of the signal in the filtered diagram  33 . This variation dAs represents the derivative function of the signal in the filtered diagram  33  or, in other words, the instantaneous variation of the slope of this signal. The variation dAs takes a form F 2 , also “V”-shaped, defined between a minimum value dAsA at the sharp point A and a maximum value dAsB at the form exit B. Away from the form F 2 , the instantaneous level of signal variation forms an average base level Sm which oscillates substantially around zero. This level Sm results from the fact that the amplitude As of the signal  33  is substantially constant. 
         [0035]    The verification criteria for detection of a foot kick from an authorized user, according to the invention, utilize parameters for identification of the form of variation F 2 , namely: 
         [0036]    the critical changes in slope inclination at the times tA and tB correspond to the sharp point A and to the slope exit B, and are respectively determined by the minimum dAsB and the maximum dAsA of the instantaneous variation in slope of the signal As in the diagram  33 ; 
         [0037]    the amplitudes dAsA, dAsB are respectively greater (in absolute value) than thresholds Amin and Bmin, Amin and Bmin being equal (in relative values) to −5 and +5 units in the example; 
         [0038]    the dots “i” on this diagram  35  symbolize the measurements made at the times successively separated by the elementary intervals of time Δt around 20 ms; in the example, the period of time between the point A and the point B is longer than 300 ms and shorter than 1000 ms; 
         [0039]    the ratio between the difference of the amplitude variations at the points A and B of the form F 2  and the number of elementary periods Δt between these two points is, in the example, greater than 1. 
         [0040]      FIG. 4  shows one example of processing of the signals supplied by the sensors in the form of a block diagram, based on the analyses hereinabove, for verifying the form identification, simultaneity and amplitude comparison criteria according to the invention. The signals  20   a  and  20   b  supplied by the sensors are first of all (step  21 ) each subjected to a low-pass filter F with a coefficient equal to ⅙, used to filter out all the high-frequency variations due to noise. Then, at the form verification step  23 , each of the filtered signals  20 ′ a  and  20 ′ b  undergoes an analysis for verification of the variations of the signals after filtering and of their instantaneous variations  20 ″ a  and  20 ″ b.    
         [0041]    This verification analysis consists in applying a form identification criterion for “V”-shaped variation of the signals. This criterion comprises tests  23   t  for conformity with a model form that can indicate the existence of a foot kick. The “V”-shaped forms thus selected are validated provisionally at  23   v.    
         [0042]    The two following steps involve comparisons between the diagrams of instantaneous slope  20 ″ a  and  20 ″ b  coming from the measurements made by the two electrodes. 
         [0043]    At the step  25 , the simultaneity of the pair of forms selected on the two signals  20 ″ a  and  20 ″ b  is verified. The criterion consists in checking that the interval EtA between the times of detection of the sharp points of two forms selected, each form being on one signal, is shorter than a pre-established value Etmax, for example 180 ms. 
         [0044]    At the step  27 , the V-shaped forms of the signals  20 ″ a  and  20 ″ b,  verified by the identification and simultaneity criteria at the steps  23  and  25 , may advantageously be subjected to an additional amplitude coherence criterion. This criterion consists in comparing the amplitudes of the forms selected by establishing their ratio. The amplitude of each form is represented by the difference between the level of the form exit B and the level of the sharp point A. In particular, the ratio between the larger and the smaller of the amplitudes of the two forms selected is less than 4. 
         [0045]    In addition, the criterion for amplitudes comparison can advantageously provide for these amplitudes to remain lower than a predefined value. After this last amplitude verification, the foot kick is validated and this validation is subsequently transmitted (signal  20   v ) to the module  29  for remote control of the accesses. 
         [0046]      FIG. 5  shows one example of logic flow diagram for detection of a model foot kick movement according to the invention. This detection corresponds to the tests at the step  23  in  FIG. 4 . The start of the detection (step  41 ) begins when the remote access system is in a standby state. While still remaining in a standby state, the system calculates (step  45 ) the instantaneous slope inclination of the diagrams by the variations of signal amplitude at the times separated by the elementary intervals of time Δt. Then, a test for increase in slope (step  47 ) is carried out by comparing the instantaneous inclination with a predefined threshold value, in order to detect the sharp point of a V-shaped form corresponding to a model kick. 
         [0047]    If the response is NO to a first test for “increasing slope” (step  47 )—in other words “strictly increasing”—the process is looped back to the state for measuring the instantaneous inclination (step  45 ). When the slope satisfies this test, the signal has finished its decreasing trend and begins to increase, hence creating a minimum. This minimum is recorded (step  49 ) and corresponds, for example, to the sharp point “A” in  FIG. 3 . The point “A” corresponds to a critical change in the instantaneous slope inclination. 
         [0048]    The process continues with the calculation of instantaneous inclination (step  51 ), then a second test for “increasing slope” (comparison step  53 ). However, the conclusions of the step  53  are reversed with respect to the first test for “increasing slope” at the step  47 : if the slope is still increasing in the comparison step of  53 , the process is looped back to the inclination calculation (step  51 ), whereas if the slope ceases to be sufficiently increasing, an exit point “B” is recorded (step  55 ). This exit point corresponds to the end of slope “B” in  FIG. 4 . This exit point “B” also corresponds to a critical variation in the instantaneous slope inclination. 
         [0049]    Once the detection of the increasing slope of the “V”-shaped form is finished, the process (step  57 ) calculates the duration of travel of the V-shaped variation between the ends “A” and “B” of the increasing slope, based on the number of inputs points (dots “i” in  FIG. 3 ) during the detection process of this form. 
         [0050]    This number of input points is compared with values interval (step  59 ), so as to verify whether the travel duration of the increasing slope AB of the “V”-shaped form is really in the range between two predetermined time values, for example between 300 ms and 1000 ms. This step  59  performs the duration test of the “V”-shaped form. If the response is “NO” to this step, the “V”-shaped variation selected is not validated, and the process returns to the start (step  41 ). 
         [0051]    If the response is “YES”, the duration test is satisfied and a decision step (step  61 ) verifies whether the instantaneous variations of the slopes dAS ( FIG. 3 ) at the ends A and B have a value (in absolute value) greater than predetermined threshold values, for example 5 (in relative values: variations dAs at the point A lower than −5 and at the point B higher than +5 in the example). 
         [0052]    A final test (decision step  63 ) involves the monitoring by a ratio “R” defining the variation amplitude of the signal between a point of critical change in instantaneous inclination and a current point, divided by the unit of time (by dividing by the number of measurement points made during this variation). If the ratio R is less than a predefined threshold value Rmin, 1.5 in the example, the response “NO” sends the process back to the start (step  41 ). 
         [0053]    However, if the ratio R remains higher than the pre-established value Rmin, the selected form is provisionally validated at the step  65  (which corresponds to the validation step  23   v  in  FIG. 4 ). The selected form appears on each signal and the simultaneity criterion is subsequently applied to this pair of forms as explained hereinabove with regard to  FIG. 4 . If the pair of forms selected satisfies this simultaneity criterion, its validation is confirmed and the remote access system is made secure. 
         [0054]    In addition, the coherence criterion for amplitudes of the selected forms pair such as described with regard to  FIG. 4  may subsequently be applied in order to reinforce the validation as needs be. 
         [0055]    The invention is not limited to the exemplary embodiments described and shown. The remote access system can comprise more than one pair of sensors, for example two or even three pairs or more. Moreover, the invention may be applied to the opening of any access needing to have the possibility of being opened without contact by the legs, such as some doors of buildings (businesses, services receiving the public, hospitals, for example). This type of access, if its situation is exposed to various elements causing interference, must be able to have a system for management of the accesses that is robust and unaffected by noise signals.