JP2006347490A - Sitting crew detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-price crew physique judging system which uses an EF technology. <P>SOLUTION: A switch in a sitting crew detector is set so that an electrode CH1 on a seat can perform charge/discharge action and the other electrode CH2 is fixed to a certain voltage or at the grounding point. Then a voltage change is given and the capacity value at the electrode CH1 is found. The same measurement is carried out also for the other electrode CH2 and the capacity is measured. Also, the switch in the detector is set so that the switches CH1 and CH2 can perform charge/discharge action to measure the capacity. Further, a voltage change is given to the electrode CH1 and the other electrode CH2 is fixed at a certain voltage or at the grounding point. Then a voltage change is given, the resistance value at the electrode CH1 is found. The same measurement is also carried out for the other electrode CH2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

 The present invention relates to an occupant seat distance detection device that detects a distance between an occupant seated on a vehicle seat and the seat.

 As a conventional technique, an occupant detection system using a weak electric field (EF) technique shown below is known (for example, see Patent Document 1). The relative permittivity of the human body is large, and when viewed at a frequency of about 100 kHz, it can be considered that it is almost a conductor. In addition, there is capacitive coupling between various parts of the body and the ground. When one or more electrodes are placed on the seat, an AC voltage is applied to one of them, and an occupant sits on the electrode, the body and the body are as if they were facing the electrode. A displacement current flows between the surfaces. That is, a capacitance is formed between the electrode and the body surface, and the size of the displacement current is determined by the size of the area where the body surface of the occupant covers each electrode on the seat. By detecting the magnitude of the displacement current, there is a technique for determining the seating area of a person who is seated, and for estimating the seating position when there are a plurality of electrodes.

When there is a distance between the occupant and the seat, such as when the occupant lays a seat cushion, the measurement capacity appears to be small, and the measurement becomes inaccurate. As an occupant physique detection technique in such a case, by arranging a plurality of electrodes, for example, in two layers, the linear distance between the electrode and the body surface is measured from two different locations. A technique is known in which only the seating area is obtained regardless of the distance between the two. However, in order to actually perform measurement using two layers of electrodes, it is necessary to maintain a certain distance between the electrodes even if a person is seated on the seat by putting something between the two layers of electrodes. In addition, in order to improve sitting comfort between the two-layer electrodes, it is necessary to always grasp the distance between the two-layer electrodes when a soft object is sandwiched. This complicates the sensor structure and has been a problem in terms of cost.
JP 2004-123087 A

 The present invention has been made to solve the above-described problems, and provides a device that enables a distance determination between an electrode and an occupant body surface with a one-layer electrode structure, and realizes a low-cost occupant seat distance detection device. For the purpose.

 The present invention has been made to solve the above problems, and the invention according to claim 1 is characterized in that a plurality of electrodes arranged on a seat, voltage applying means for applying a voltage to the electrodes, A plurality of switch means connected to each of a plurality of electrodes, each of which switches between connecting each electrode to a voltage applying means, connecting to a ground point or a point of a constant potential, and one switch among the plurality of switch means Means connects one electrode of the plurality of electrodes to the voltage applying means, and another switch means of the plurality of switch means connects the other electrode of the plurality of electrodes to a ground point or A first mode for controlling all of the plurality of electrodes to be connected to a point of a constant potential, and a second mode for controlling the plurality of switch means to connect the plurality of electrodes to the voltage applying means. Have Switch control means, connected to one end of the switch means, capacitance measuring means for measuring a capacitance value between each of the plurality of electrodes and the ground, and the first measured by the capacitance measuring means From the storage means for storing the measurement capacity of the mode and the measurement capacity of the second mode, and the capacity stored in the storage means, the sum of the measurement capacities of the first mode, the sum and the second A seating occupant detection device comprising: a calculation unit that calculates a quotient of the measured capacity of the mode of the first mode; and a seating status determination unit that determines a passenger seating status from a calculation result of the calculation unit. is there.

 According to a second aspect of the present invention, a plurality of electrodes arranged on a seat, a voltage applying means for applying a voltage to the electrodes, and each of the plurality of electrodes are connected, and each electrode is connected to a voltage. A plurality of switch means for switching whether to connect to the application means, a ground point or a point of constant potential, and one switch means of the plurality of switch means, wherein one electrode of the plurality of electrodes is All of the plurality of electrodes are connected to the voltage applying means, and other switch means of the plurality of switch means connect other electrodes of the plurality of electrodes to a ground point or a point of a constant potential. Switch control means for controlling the resistance, resistance measuring means connected to one end of the switch means for measuring a resistance value between each of the plurality of electrodes and the ground, and measuring the resistance measuring means Storage means for storing measurement resistance; a calculation section for calculating a total sum of measurement resistance from the resistance stored in the storage section; and seating for determining a passenger seating situation from a calculation result of the calculation section A seat occupant detection device characterized by comprising a situation determination unit.

 In this device, the following two indices are used to determine the distance between the passenger and the electrode. The first indicator is that the switch in the device is set so that charge / discharge operation can be performed on one of the electrodes arranged on the car seat, and all the remaining electrodes are fixed at a constant voltage or grounding point. Set to Therefore, the capacitance value at the electrode to which the voltage change is applied is obtained. The same measurement is performed on each of the remaining electrodes, and the sum of the obtained capacities is taken as a sum A of capacity values. In addition, the switches in the apparatus are set so that the charge / discharge operation can be performed on all the electrodes of the plurality of electrodes, and the capacitance value B obtained at that time is set. The ratio (B / A) between the capacities A and B at this time is used as an index, and this is hereinafter referred to as a Cg ratio.

 Second, a voltage change or an alternating voltage is applied to one of a plurality of electrodes arranged on a car seat, and all the remaining electrodes are fixed to a constant voltage or a ground point. Therefore, the resistance value at the electrode to which a voltage change or an alternating voltage is applied is obtained. The same measurement is similarly performed on all the remaining electrodes of the plurality of electrodes arranged. The total resistance Rtotal, which is a value obtained by summing the resistance values obtained there, is used as an index. After obtaining the Cg ratio, it is also determined whether the distance between the occupant and the seat is long and the seating area is large from the measured capacity at each electrode and the capacity between the occupant and the vehicle body metal part obtained from the measurement. To do. When it is determined that the distance between the occupant and the seat is long and the seating area is large, the distance between the occupant and the seat is determined based on the total resistance Rtotal. By using the two indices obtained in the present invention, the distance between the electrode and the passenger can be determined. Therefore, when the distance between the electrode and the occupant is long, that is, when the occupant is sitting on the seat with a seat cushion or the like, prepare another occupant detection device dedicated to when the distance between the electrodes is far from the other occupants. be able to.

 In this invention, the measurement which calculates | requires the said Cg ratio, the measurement which calculates | requires the sum total of resistance, and the distance judgment of an electrode and a passenger | crew body surface are performed, and the distance judgment of an electrode and a passenger | crew body surface is carried out by 1 layer electrode structure. By enabling and eliminating the need for a sensor for grasping the distance between the two-layer electrodes, an inexpensive occupant detection device can be realized.

 Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration circuit diagram of the present embodiment. In this embodiment, a case where there are two electrodes will be described. In the figure, CH1 and CH2 are electrodes arranged on the seat. CL1 to CL3 are combined capacities that are the sum of the respective capacitance components between the electrodes CH1 to CH3 and the ground (vehicle body). RL1 to RL3 are combined resistances that are the sum of the resistance components between the electrodes CH1 to CH3 and the ground, respectively. The capacitors CL1 to CL3 and the resistors RL1 to RL3 will be described in detail later.

 The electrode CH1 is connected to the collector terminal of the transistor GND_TR_1. The emitter terminal of the transistor GND_TR_1 is grounded, and the electrode CH1 is switched between being grounded and not grounded with or without applying a signal to the base terminal of the transistor GND_TR_1. Similarly, the electrode CH2 is connected to the collector terminal of the transistor GND_TR_2, the emitter terminal of the transistor GND_TR_2 is grounded, and a signal is applied to the base terminal of the transistor GND_TR_2 to switch whether the electrode CH2 is grounded or not grounded. . The electrodes CH1 and CH2 are connected to one end of each of the measurement electrode selection switches CH_SEL_1 and CH_SEL_2 via the charging resistors Rc1 and Rc2. It is connected. The other end of the charge / discharge changeover switch CHG_SW is connected to a DC power supply (voltage E).

 The above-described one end of the charge / discharge changeover switch CHG_SW is connected to one end of each of the discharge resistors Rd1 and Rd2. The other end of the discharge resistor Rd1 is grounded, and the other end of the discharge resistor Rd2 is grounded via the discharge resistor changeover switch R_SEL. Further, one end of the charge / discharge switching switch CHG_SW is connected to the inverting input terminal of the comparator Comp, the non-inverting input terminal of the comparator Comp is grounded via a series connection circuit of the resistors Ra and Rb, and the resistors Ra and Rb A resistor Rc is connected between the connection point and the output terminal of the comparator Comp. A DC voltage of 5 V is applied to the connection point between the resistors Ra and Rb.

 Next, the operation of the above-described embodiment will be described. The distance determination process between the occupant and the electrode includes two processes, a determination process using the Cg ratio and a determination process using the total resistance Rtotal. In the determination process using the Cg ratio, two measurement modes are measured. The two measurement modes are called A mode and B mode, respectively. First, the two measurement modes of the determination process using the Cg ratio will be described in order.

 In the measurement of the A mode in the determination process using the Cg ratio, first, the control circuit (not shown) turns on the switch CH_SEL_1, turns off the switch CH_SEL_2, turns off the transistor GND_TR_1, turns on the transistor GND_TR_2, The switch R_SEL is turned off. Then, the switch CHG_SW is turned on for a certain time. When the switch CHG_SW is turned on, the output voltage E of the DC power source connected to the other end of the switch CHG_SW is supplied to the electrode CH1 through the switch CH_SEL_1 and the resistor Rc1, thereby charging the composite capacitor CL1. . Here, the combined capacitance CL1 is a combined capacitance in the on / off state of the above-described switches. Specifically, as shown in FIG. 2, the capacitance C1 between the electrode CH1 and the occupant Load, the grounded electrode This is a combined capacity of the capacity C2 between CH2 and the occupant load, and the capacity between the occupant load and the ground. And this synthetic | combination capacity | capacitance CL1 becomes a value corresponding to a passenger | crew's physique. Similarly, the combined resistance RL1 is a combined resistance. Note that I is a path of displacement current. Then, when the switch CHG_SW is turned on for a certain time, the combined capacitor CL1 is charged to the voltage E.

 Next, the control circuit turns off the switch CHG_SW and starts time measurement at the same time. When the switch CHG_SW is turned off, the electric charge of the combined capacitor CL1 is gradually discharged through the resistors Rc1 and Rd1, thereby gradually reducing the voltage at the inverting input terminal of the comparator Comp. Note that the discharge current of the combined capacitor CL1 also flows through the combined resistor RL1. When the voltage at the inverting input terminal of the comparator Comp is lowered to a certain voltage, the output of the comparator Comp rises to the “H (high)” level. The control circuit stops the above-described time measurement at this rise, and stores the measured time data (tda) in the memory. From this discharge time tda, the capacity component CL1 can be expressed as shown in Expression (1). In this equation, Vt is the voltage at the non-inverting input terminal of the comparator Comp. Rd1p is a parallel combined resistance of RL1 and (Rd1 + Rc1). E is a charging voltage.

 Next, the control circuit turns on the switch CH_SEL_2, turns off the switch CH_SEL_1, and selects the electrode CH2. The transistor GND_TR_1 is turned on, the transistor GND_TR_2 is shut off, and the electrode CH1 is grounded to GND. The same measurement is performed on the above setting, and the capacitance CL2 of the electrode CH2 when the electrode CH1 is grounded is obtained.

 Next, the B-mode measurement operation in the determination process using the Cg ratio will be described. In FIG. 1, switches CH_SEL_1 and CH_SEL_2 are turned on, and both electrodes CH1 and CH2 are selected. Further, the transistors GND_TR_1 and GND_TR_2 are cut off. Based on the above settings, the same measurement is performed to determine the capacitance Cmb. FIG. 3 is an explanatory diagram of the B mode. Here, the capacity | capacitances CL1, CL2, and Cmb obtained by each measurement mentioned above are represented using Formula (2)-(4). Here, when the Cg ratio used as an index for determining the distance between the occupant and the electrode is converted using Expressions (2) to (4), Expression (5) is obtained. Equation (5) is obtained by using the terms of capacitance values C1 and C2 between the electrodes CH1 and CH2 and the occupant's body surface and the sum Cg of the capacitance between the occupant and the vehicle body metal part. It is expressed as an expression.

 Here, the seating state is determined from the obtained Cg ratio, the capacities CL1 and CL2, and the capacity Cg obtained by combining the expressions (2) to (4). When the value of the index Cg ratio for determining the distance is large, it may be caused by the fact that it is caused by the presence of a small occupant such as a child or the large distance between the occupant and the seat. It is important to know if the sitting posture is the cause. Therefore, a case where the value of the index Cg ratio for determining the distance is large becomes a problem. The reason why the value of the index Cg ratio for determining the distance is large is mainly limited to the following four cases. 1) When the seat is empty or when the distance between the passenger and the seat is short and the seating area is small, for example, when a small child sits without laying anything underneath. 2) When the distance between the passenger and the seat is long and the seating area is small, for example, when a small child sits with a seat cushion. 3) A seated child touches the car body with his hand. 4) When the distance between the passenger and the seat is long and the seating area is large, for example, when an adult sits with a seat cushion.

 Among the above four cases, 1) and 2) can be separated from the remaining two cases because the capacitances CL1 and CL2 to be measured are very small. 3) Since the total sum Cg of the capacity between the occupant and the vehicle body metal part can be derived using the equations (2) to (4), it is erroneously determined by correcting the index Cg ratio for distance determination. Can be avoided and can be separated from the case of 4). As a result, in the case of the remaining 4), the distance between the occupant and the seat is determined in the determination process using the next total resistance Rtotal.

 Next, an embodiment of a determination process using the total resistance Rtotal will be described. In addition, when the parallel plate capacitor is considered between the occupant and the electrode, the value of the internal resistance of the parallel plate capacitor is inversely proportional to the capacitance value, so that the measured capacitance decreases as the distance between the occupant and the electrode increases. Thus, the internal resistance value is increased. Therefore, it can be seen that there is a strong correlation between the distance between the passenger and the electrode and the internal resistance value. In addition, when a pair of capacitive resistance parallel models after the electrodes as shown in FIG. 1, the resistance component value of this model is the change in the resistance value between the occupant and the vehicle body metal part, and the occupant and ground electrode. It can be seen that the influence of the change in the resistance value between the occupant and the measurement electrode is larger than the change in the resistance value during the period. Therefore, it turns out that there is a strong correlation between the resistance value between the occupant and the measurement electrode, and this is confirmed from actual measurement data. Therefore, the resistance component value of the model can be used as an index of the distance between the occupant and the electrode. Here, the resistance component of the capacitance-resistance parallel model is obtained for all of the plurality of electrodes on the seat, and the total resistance Rtotal measured at each electrode is used as a distance index.

 The determination process using the total resistance Rtotal will be described with reference to FIG. The control circuit turns on the switch CH_SEL_1, turns off the switch CH_SEL_2, and selects the electrode CH1. The transistor GND_TR_2 is turned on, the transistor GND_TR_1 is cut off, and the electrode CH2 is grounded to GND. The discharge resistance changeover switch R_SEL is turned off to select the discharge resistance Rd1. In the determination process using the Cg ratio, the two electrodes CH1 and CH2 are used, and the resistance components RL1 and RL2 are ignored.

 In the measurement operation, first, the charge / discharge switching switch CHG_SW is turned on, and a DC voltage is applied to the charging circuit. Here, the current output from the DC power source passes through the charge / discharge switching switch CHG_SW, the measurement electrode selection switch CH_SEL_1, the charging resistor Rc1, and the electrode CH1, flows to the capacitive component CL1 and the resistive component RL1, and charges the capacitive component CL1. Next, the charge / discharge switching switch CHG_SW is turned off to disconnect the charging path. Here, the current output from the capacitive component CL1 flows to the resistance component RL1 and the electrode CH1, and from the electrode CH1, flows to the charging resistor Rc1, the measurement electrode selection switch CH_SEL_1, and the discharging resistor Rd1. For this discharge, the discharge time td1 is measured. Next, the discharge resistance changeover switch R_SEL is turned on, and the discharge combined resistance Rdp (= Rd1 / Rd2) is selected. Then, measurement is performed in the same manner as described above, and the discharge time tdp is measured.

 The relational expressions of the discharge when the discharge voltages of the two discharge processes of this apparatus are at the comparator threshold Vt are expressed as Expressions (6) and (7), respectively. Here, td1 is a discharge time in the process of selecting the discharge resistor Rd1. tdp is a discharge time in the process of selecting the discharge resistance Rdp (= Rd1 / Rd2). Rd1p is a parallel combined resistance of RL1 and (Rd1 + Rc1). Rdp (= Rd1 // Rd2) is a parallel combined resistance of the discharge resistances Rd1 and Rd2. Rdpp is a parallel combined resistance of RL1 and (Rdp + Rc1). E is a charging voltage. Equations (6) and (7) are derived as equations (8) and (9), respectively, and the capacitance component CL1 is represented as equation (10).

 Also, this equation can be transformed from equation (10) as equation (11). Further, equation (11) is derived as in equation (12), and resistance component RL1 is expressed as in equation (13). Here, T (= td1 / tdp) is a discharge time ratio.

 Therefore, the resistance component RL1 can be obtained. The other electrodes CH2 are also measured in the same manner, and a total sum Rtotal = RL1 + RL2 of the obtained resistance values RL1 and RL2 is obtained and used as an index for determining the distance. Further, by using in combination with parameters of other related technologies other than the above two parameters, adults / children can be separated more effectively.

 The present invention is suitable for use in an occupant detection device for low-cost occupant physique discrimination using EF technology.

It is a circuit diagram showing the structure of the seat occupant detection device by one Embodiment of this invention. It is a circuit diagram of the A mode measurement of the determination process using Cg ratio in this embodiment. It is a circuit diagram of the B mode measurement of the judgment process using Cg ratio in this embodiment.

Explanation of symbols

CH1, CH2 ... Electrodes CH_SEL_1, CH_SEL_2 ... Measurement electrode selection switches GND_TR_1, GND_TR_2 ... Transistors

Claims (2)

A plurality of electrodes arranged on the seat;
Voltage applying means for applying a voltage to the electrode;
A plurality of switch means connected to each of the plurality of electrodes, for switching whether each electrode is connected to a voltage application means or to a ground point or a point of a constant potential;
One switch means of the plurality of switch means connects one electrode of the plurality of electrodes to the voltage application means, and the other switch means of the plurality of switch means is the plurality of electrodes. A first mode in which all of the plurality of electrodes are controlled to connect the other electrode to a ground point or a constant potential point, and the plurality of switch means connect the plurality of electrodes to the voltage applying means. Switch control means having a second mode for controlling to do,
A capacitance measuring means connected to one end of the switch means for measuring a capacitance value between each of the plurality of electrodes and the ground;
Storage means for storing the measured capacity of the first mode and the measured capacity of the second mode measured by the capacity measuring means;
An arithmetic unit that performs an operation for obtaining a sum of the measured capacities of the first mode and a quotient of the sum and the measured capacities of the second mode from the capacities stored in the storage unit;
A seated occupant detection device comprising: a seating status determination unit that determines a passenger seating status from a calculation result of the calculation unit. A plurality of electrodes arranged on the seat;
Voltage applying means for applying a voltage to the electrode;
A plurality of switch means connected to each of the plurality of electrodes, for switching whether each electrode is connected to a voltage application means or to a ground point or a point of a constant potential;
One switch means of the plurality of switch means connects one electrode of the plurality of electrodes to the voltage application means, and the other switch means of the plurality of switch means is the plurality of electrodes. Switch control means for controlling all of the plurality of electrodes so as to connect the other electrode to a ground point or a constant potential point;
Resistance measuring means connected to one end of the switch means for measuring a resistance value between each of the plurality of electrodes and ground;
Storage means for storing the measured resistance measured by the resistance measuring means;
A calculation unit for calculating a total sum of measured resistances from the resistance stored in the storage unit;
A seated occupant detection device comprising: a seating status determination unit that determines a passenger seating status from a calculation result of the calculation unit.

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