JPH05256955A - Presence detecting apparatus - Google Patents

Abstract

PURPOSE:To detect that a passenger is seated by outputting a presence signal when the condition of the heartbeat data is satisfied and moreover, the satisfactory condition is repeated a predetermined number of times or more. CONSTITUTION:A piezoelectric element 2 of a live body data detecting means 1 converts various kinds of pressure changes impressed to a buried part, e.g. heartbeat of a passenger, etc., to electric signals. Thereafter, a filter circuit 3 filters the signals of the frequency band corresponding to the heartbeat. In the case of an automobile, since the vibration of the engine is transmitted to seats, signals of the frequency of at least 8-10Hz or higher are cut. An amplifier circuit 4 amplifies the electric signals passing the circuit 3. A smoothing circuit 5 rectifies and integrates the amplified signals. Then, a judging means 7 judges that a person is on the seat when the heartbeat data from a heartbeat means 6 is in the range of the ordinary heartbeat and the state is repeated a fixed number of times, thus outputting a presence detecting signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a seating detection device for detecting whether or not a passenger in a moving body is seated.

[0002]

2. Description of the Related Art Conventionally, as a technique for detecting a passenger's heartbeat, for example, a wristwatch-type heartbeat detector which can be attached to a measurement site with a binder as shown in Japanese Utility Model Laid-Open No. 213325/1990. There was a device.

Further, regarding the detection of the presence of a human body, there is a technique of detecting the presence of a person by changing the electrostatic capacitance between two electrodes of the seat, as disclosed in Japanese Patent Laid-Open No. 3-233391.

[0004]

In the above conventional method, the main body must be fixed to the arm with a band in order to detect the heartbeat, which is very troublesome for the user.

Further, when trying to detect a heartbeat in a moving body such as an automobile in a non-contact manner, noise that does not exist in the case of being detected in the bed, for example, noise generated by knocking or unevenness of the road surface is generated. At the same time, there was a possibility that the piezoelectric element would detect it.

On the other hand, there is also a problem that it is difficult to distinguish between an object and a human body when detecting the presence of a person.

The present invention is to solve the above problems. A first object of the present invention is to detect a passenger's heartbeat in a non-contact manner by embedding a sensor portion of a biological information detecting means in a seat in a vehicle, and the passenger is present. It is to detect that you are seated.

A second object is to cut signals other than heartbeat information as noise to obtain highly accurate heartbeat information.

[0009]

In order to solve the above-mentioned problems, an occupant detection apparatus of the present invention comprises a biometric information detecting means in which a sensor unit is embedded in a vehicle seat, and a signal from the biometric information detecting means indicates the occupant's A heartbeat calculating means for detecting heartbeat information and a condition that the heartbeat information from the heartbeat calculating means is received and the value of the heartbeat information is within a certain range are satisfied, and the satisfied condition is repeated a certain number of times or more. In this case, a judgment means for outputting a seating signal is provided.

Further, the heartbeat calculating means is an autocorrelation coefficient calculating means for calculating an autocorrelation coefficient of the signal from the biological information detecting means, and a basic cycle for calculating a basic cycle from the result of the autocorrelation coefficient calculating means. The calculation means and the calculation means for obtaining the cycle per unit time from the basic cycle are provided.

[0011]

With the above structure, the biometric information detecting means embedded in the seat detects a pressure change occurring at the contact surface between the passenger and the seat and converts it into an electric signal. This change in pressure includes that due to the passenger's heartbeat. The heartbeat calculating means calculates the heartbeat rate per unit time for the electric signal from the biological information detecting means. The determination means outputs a presence signal when the condition that the value of the heart rate is within a certain range is satisfied and the satisfied condition is repeated a certain number of times or more.

In the heartbeat calculating means, the autocorrelation coefficient calculating means calculates the autocorrelation coefficient for the input signal. The basic cycle calculating means calculates the basic cycle of the input signal from the autocorrelation coefficient. The calculation means calculates the number of cycles per unit time from the obtained basic cycle.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of the first embodiment of the present invention. The biological information detecting means 1 includes a piezoelectric element 2 as a sensor section,
Alternatively, the circuit section includes a filter circuit 3, an amplifier circuit 4, and a smoothing circuit 5, and is connected to the heartbeat calculating means 6. The heartbeat calculating means 6 is connected to the judging means 7.

The piezoelectric element 2 is embedded, for example, in a portion of the backrest of the seat near the passenger's heart. As the piezoelectric element 2, for example, thin film-processed polyvinylidene fluoride or the like is used.

Next, the operation of the first embodiment of the present invention will be described. In the biological information detecting means 1, the piezoelectric element 2 converts various pressure changes applied to the buried portion, such as the occupant's heartbeat, into electric signals. Next, the filter circuit 3 filters the signal in the frequency band corresponding to the heartbeat. In the case of automobiles, the vibration of the engine is transmitted to the seat, so that signals with a frequency of at least 8 to 10 Hz or higher are cut. The amplifier circuit 4 amplifies the electric signal that has passed through the filter circuit 3. The smoothing circuit 5 rectifies and integrates the amplified signal.

The heartbeat calculating means 6 calculates the heartbeat rate per unit time from the signal from the biological information detecting means 1. This can be realized by an A / D conversion circuit and a microcomputer.

The judging means judges that the person is present when the heartbeat information from the heartbeat calculating means is within the normal human heart rate range and the state is repeated a certain number of times, Outputs the presence detection signal.

Although the heart rate is detected in this embodiment, respiration other than the heartbeat may be used as the biological information. At this time, the frequency band to be filtered in the filter circuit 3 is further lowered.

FIG. 2 is a block diagram of the second embodiment of the present invention. In the heartbeat calculating means 6, the autocorrelation coefficient calculating means 8
Is connected to the basic period calculation means 9. The basic period calculation means 9 is connected to the calculation means 10. The autocorrelation coefficient calculating means 8, the basic period calculating means 9, and the calculating means 10 can be incorporated as software of a microcomputer.

FIG. 3 is a flow chart showing an algorithm for calculating the fundamental frequency using the autocorrelation coefficient. When obtaining the autocorrelation coefficient, the autocorrelation function is first obtained.
The autocorrelation function is the value at a certain time and the arbitrary time τ
It is a function that represents the correlation with the value at a time point (called a lag). In this embodiment, it is assumed that discrete data is obtained at a sampling rate of 20 Hz. Therefore τ
Can be expressed as p · Δt. p represents the number of sampling data, and Δt represents the sampling period. The maximum value τmax of the lag must be set within a range not exceeding N · Δt. When M = N−τmax, generally, the autocorrelation function C (p) is

[0021]

[Equation 1]

It is calculated by However, in this embodiment, since the original waveform is subjected to the rectification and integration processing in the smoothing circuit 5, the direct current component is included in date (i).

[0023]

[Outer 1]

Since it can be considered that the
It is better to obtain C (p) as follows.

[0025]

[Equation 2]

[0026]

[Equation 3]

The autocorrelation coefficient R (p) is obtained by the following equation. R (p) = C (p) / C (0) Next, the means for obtaining the fundamental frequency from the autocorrelation coefficient will be described. FIG. 4 is a graph of the obtained autocorrelation coefficient. The autocorrelation coefficient theoretically takes a maximum value when τ is a fundamental period. Therefore, the point that becomes the maximum point is first obtained. In FIG. 4, points a, b, c, d, and e are set as maximum points.
However, since a point that happens to be a maximum point due to an error is also included, a threshold function is set and only points that exceed this are treated as maximum points. Here, the points c, d, and e are the elements of the maximum point set. Next, the cycle corresponding to the maximum value e of these is set as a temporary basic cycle. Since this may be an integral multiple of the true fundamental period, a search is made for an element of the second maximum point set in the vicinity of the period of 1 / integer. In the third embodiment, the point c corresponds to this, so the point corresponding to the point c is the basic cycle T.

When the basic period T is obtained, the heart rate per unit time can be calculated. The heart rate HR per minute is obtained at HR = 60 · sampling frequency / T 2. The heart rate is set to 0 when no passenger is present. Also, without calculating the heart rate per unit time,
The presence determination may be made based only on the value of the basic cycle.

[0029]

As described above, since the seating detection apparatus of the present invention can detect the heartbeat of a passenger who is seated, the seating of a passenger can be detected separately from an object.

Further, since the heartbeat is calculated using the autocorrelation coefficient, there is an effect that it is resistant to noise mixed in other than the heartbeat and an accurate heartbeat can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an occupancy detection device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of a heart rate calculation means of the same apparatus according to the second embodiment of the present invention.

FIG. 3 is a flowchart of a heartbeat calculation algorithm in the device.

FIG. 4 is a graph of an autocorrelation coefficient in the same apparatus as the second embodiment.

[Explanation of symbols]

 1 biometric information detecting means 6 heartbeat calculating means 7 judging means 8 autocorrelation coefficient calculating means 9 basic period calculating means 10 calculating means

Claims (2)

[Claims] 1. A biometric information detecting means in which a sensor unit is embedded in a seat in a vehicle, a heartbeat calculating means for detecting heartbeat information of an occupant from a signal from the biometric information detecting means, and heartbeat information from the heartbeat calculating means. Is received and the condition that the value of the heartbeat information is within a certain range is satisfied and the satisfied condition is repeated a certain number of times or more, a seating signal indicating that the passenger is in the seat is output. An occupancy detection device having a determination means. 2. The heartbeat calculating means includes an autocorrelation coefficient calculating means for calculating an autocorrelation coefficient of a signal from the biological information detecting means,
The presence detection apparatus according to claim 1, further comprising: a basic cycle calculating means for calculating a basic cycle from a result of the autocorrelation coefficient calculating means; and a calculating means for calculating a cycle per unit time from the basic cycle.