JP2020020704A - Sensor output conversion circuit and seat - Google Patents

Abstract

To enable the output characteristics of a sensor to be changed and thereby suppress the degradation of the accuracy of detecting a physical quantity by the sensor.SOLUTION: A sensor output conversion circuit 40 comprises: a sensor-side resistor Rfsr built in a sensor (pressure sensor PS1) and changed in resistance value in accordance with a change in physical quantity of a measurement object; a first resistor Rm connected in series to the sensor-side resistor Rfsr between a power supply EP and a ground GND; an operational amplifier OP having a non-inverted input terminal (+) to which a wiring W between the sensor-side resistor Rfsr and the first resistor is Rm connected; and a negative feedback circuit 41 for connecting the output terminal and an inverted input terminal (-) of the operational amplifier OP. The first resistor Rm comprises a plurality of adjusting resistors R1-R4 and switches SW1-SW4 for switching the connecting states of the plurality of adjusting resistors R1-R4, and the switches SW1-SW4 are switchable on the basis of a signal from a control device 100.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a sensor output conversion circuit for converting an output of a sensor, and a seat including the sensor output conversion circuit.

  2. Description of the Related Art Conventionally, there has been known a device that mounts a pressure sensor on a seat on which a seated person sits and estimates a seated posture of the seated person (Patent Document 1).

JP-A-11-064131

  However, in the related art, since a circuit for changing the output characteristics of the pressure sensor is not provided, the output characteristics of the pressure sensor are constant, so when various occupants with different weights sit on the seat, The pressure applied to the pressure sensor changes greatly for each occupant, and the pressure sensor may not be able to accurately detect the pressure. Specifically, for example, when the pressure sensor has output characteristics such that the response is high when the pressure is low and the response is low as the pressure increases, a seated person with a large weight sits on the seat. In such a case, the accuracy of the pressure detection by the pressure sensor may deteriorate.

  Therefore, an object of the present invention is to suppress deterioration in the physical quantity detection accuracy of a sensor by making it possible to change the output characteristics of the sensor.

In order to solve the above-described problem, a sensor output conversion circuit according to the present invention is built in a sensor, and a sensor-side resistor whose resistance value changes according to a change in a physical quantity of a measurement target, between a power supply and a ground, A first resistor connected in series with the sensor-side resistor, an operational amplifier having a wiring between the sensor-side resistor and the first resistor connected to a non-inverting input terminal, and an output terminal and an inverting input terminal of the operational amplifier. A negative feedback circuit.
The first resistor includes a plurality of adjustment resistors and a switch that switches a connection state of the plurality of adjustment resistors, and the switch is switchable based on a signal from a control device.

  According to this configuration, the output value output from the operational amplifier can be changed by sending a signal from the control device to the switch, switching the switch, and switching the connection state of the plurality of adjustment resistors, so that the output value of the sensor can be changed. The output characteristics can be changed, and deterioration of the physical quantity detection accuracy of the sensor can be suppressed.

  Further, the switch may be provided in each of the plurality of adjustment resistors.

  According to this, the resistance value of the first resistor, that is, the pattern of the combined resistance value of the plurality of adjustment resistors can be increased as compared with a configuration in which the number of switches is smaller than the number of adjustment resistors, for example.

  Further, the switch may be a transistor.

  According to this, the switch can be favorably switched by the signal from the control device.

  Further, the first resistor may be connected to a ground.

  Further, the plurality of adjusting resistors may have different resistance values.

  According to this, the resistance value of the first resistor, that is, the pattern of the combined resistance value of the plurality of adjustment resistors can be increased as compared with a configuration in which the plurality of adjustment resistors have the same resistance value, for example.

When the number of the adjusting resistors is n, the resistance value of the k-th adjusting resistor among the n adjusting resistors may be a value obtained by multiplying the smallest resistance value by 2 ^k−1. Good.

  According to this, since the resistance values of the plurality of adjustment resistors sequentially shift twice from the smallest resistance value, the resistance value of the first resistor can be changed within an appropriate range.

  Further, the plurality of adjusting resistors may be connected in parallel.

  According to this, for example, when the switch is a transistor, even if the number of output ports is small, the resistance value of the first resistor, that is, the plurality of adjusting resistors Can be increased in the pattern of the combined resistance value.

  Further, the number of the adjusting resistors may be four.

  Further, the resistance values of the four adjustment resistors may be 200Ω, 400Ω, 800Ω, and 1600Ω.

  According to this, the resistance value of the first resistor can be changed in the range of 106 to 1600Ω.

Further, the seat according to the present invention is a seat provided with the sensor output conversion circuit, and includes a seat body having a seat surface for supporting a seated person.
The sensor is a pressure sensor arranged on the seat surface side of the seat body.

  According to this, it is possible to change the output characteristics of the pressure sensor provided on the seat body, so that it is possible to suppress the deterioration of the pressure detection accuracy of the pressure sensor due to the difference in the weight of the occupant.

  According to the present invention, it is possible to change the output characteristics of the sensor, so that it is possible to suppress deterioration of the physical quantity detection accuracy of the sensor.

  Further, by providing a switch for each of the plurality of adjustment resistors, for example, the resistance value of the first resistor, that is, the combined resistance value of the plurality of adjustment resistors, is reduced compared to a configuration in which the number of switches is smaller than the number of adjustment resistors. Pattern can be increased.

  Further, when the switch is a transistor, the switch can be favorably switched by a signal from the control device.

  Further, by setting the resistance values of the plurality of adjustment resistors to different values, for example, the resistance value of the first resistor, that is, the synthesis of the plurality of adjustment resistors, is compared with a configuration in which the plurality of adjustment resistors have the same resistance value. The pattern of the resistance value can be increased.

In addition, by setting the resistance value of the k-th adjustment resistor among the n adjustment resistors to a value obtained by multiplying the smallest resistance value by 2 ^k−1 , the resistance values of the plurality of adjustment resistors become the most. Since the resistance value is shifted by two times in order from the smaller resistance value, the resistance value of the first resistor can be changed within an appropriate range.

  Further, by setting the resistance values of the four adjustment resistors to 200Ω, 400Ω, 800Ω, and 1600Ω, the resistance value of the first resistor can be changed in the range of 106 to 1600Ω.

  In addition, by applying the sensor output conversion circuit to the pressure sensor provided on the seat, it is possible to suppress a decrease in accuracy of pressure detection by the pressure sensor due to a difference in the weight of the occupant.

FIG. 2 is a diagram illustrating a configuration of a sheet according to an embodiment. It is a circuit diagram showing a sensor output conversion circuit. 4 is a graph showing a relationship between a pressure applied to a pressure sensor, an output voltage, and a resistance value of a first resistor. FIG. 4 is a circuit diagram showing a configuration in which a plurality of adjustment resistors are connected in series. 9 is a table showing a relationship between an output state of an output port and a combined resistance value in a form of series connection. 9 is a table showing a relationship between an output state of an output port and a combined resistance value in a form of parallel connection. 9 is a graph showing a relationship between an actual combined resistance value and a pattern (output state of an output port) in a form of parallel connection. 5 is a graph showing a relationship between an actual combined resistance value and a pattern (output state of an output port) in a form of series connection.

Next, an embodiment of the present invention will be described in detail with reference to the drawings as appropriate.
As shown in FIG. 1, the vehicle seat S of the present embodiment is an example of a seat, and is configured as, for example, a vehicle seat installed in a vehicle. The vehicle seat S includes a seat body S0, a control device 100, and a sensor output conversion circuit 40 (see FIG. 2).

  The seat body S0 has a seat cushion S1 and a seat back S2. The seat cushion S1 and the seat back S2 include a cushion pad 20 and a skin 10 that covers the cushion pad 20. The cushion pad 20 is made of urethane foam or the like, and is supported by a frame (not shown). The outer skin 10 is made of synthetic leather, cloth, or the like. The outer surface of the skin 10 is a seat surface for supporting a seated person.

  A plurality of pressure sensors PS1 to PS6 are provided below the skin 10 in the seat cushion S1 and the seat back S2. The pressure sensors PS <b> 1 to PS <b> 6 are sensors that acquire measurement values for specifying the motion of the occupant sitting on the seat body S <b> 0. The pressure sensors PS1 to PS6 are arranged so as to be able to detect the state of the seat surface facing the seated person sitting on the seat body S0, and acquire pressure values from the seated person sitting on the seat body S0.

Each of the pressure sensors PS1 to PS6 is arranged on the seat surface side of the seat body S0. Specifically, each of the pressure sensors PS1 to PS6 is arranged between the cushion pad 20 and the skin 10. Each pair of pressure sensors PS1 to PS6 is provided symmetrically with respect to the left and right centers of the vehicle seat S.
Specifically, pressure sensors PS1 to PS3 are provided on the seat cushion S1. The pressure sensor PS1 and the pressure sensor PS2 are arranged at positions corresponding to the seated person's buttocks in the seat cushion S1. The pressure sensor PS1 and the pressure sensor PS2 constitute a first cushion sensor SC1 that measures the pressure from the buttocks of the seated person. The pressure sensor PS2 is arranged slightly before the pressure sensor PS1. Note that the first cushion sensor SC1 may include only one of the pressure sensor PS1 and the pressure sensor PS2.

  The pressure sensor PS3 is located below the thigh of the seated person. The pressure sensor PS3 constitutes a second cushion sensor SC2 that measures a pressure value from the thigh of the seated person. The pressure sensor PS3 is disposed far away from the pressure sensor PS1 and the pressure sensor PS2.

  Pressure sensors PS4 to PS6 are provided in the seat back S2. The pressure sensor PS4 is provided at a position corresponding to the back of the seated person's waist. The pressure sensor PS5 is disposed slightly above the pressure sensor PS4. Both the pressure sensor PS4 and the pressure sensor PS5 constitute a first back sensor SB1 that measures the pressure from the waist of the seated person. Note that the first back sensor SB1 may include only one of the pressure sensor PS4 and the pressure sensor PS5.

  The pressure sensor PS6 is disposed far above the pressure sensors PS4 and PS5. The pressure sensor PS6 is located corresponding to the upper part of the back of the seated person. The pressure sensor PS6 constitutes a second back sensor SB2 that measures a pressure value from above the back of the seated person.

  The pressure sensors PS1 to PS6 are, for example, elements whose electric resistance changes according to external pressure. As the pressure value increases, the voltage of the detection signal increases (or decreases). As the pressure sensors PS1 to PS6, for example, as the input pressure increases, the contact area between the pair of electrodes increases and the resistance value decreases, and as the input pressure increases, the resistance strain increases. Thus, a strain gauge or the like having a large resistance value can be used. However, it is desirable to use a pressure-sensitive sensor because the amount of change in the resistance value with respect to the pressure change is larger than that of the strain gauge.

  Each of the pressure sensors PS1 to PS6 is incorporated in a sensor output conversion circuit 40 (see FIG. 2) described later, and is connected to the control device 100 via the sensor output conversion circuit 40. Note that one sensor output conversion circuit 40 is provided for each of the plurality of pressure sensors PS1 to PS6 provided in the seat body S0.

  A paint 31 serving as a position display unit is applied to positions on the outer surface of the skin 10 corresponding to the pressure sensors PS1 to PS6. The paint 31 is applied to the outer surface 10 </ b> A of the skin 10 so as to be exposed outside the skin 10. The color of the paint 31 is different from the color of the outer surface 10 </ b> A of the skin 10. Specifically, for example, when the outer surface 10A of the skin 10 is black, the color of the paint 31 can be a color that stands out from black such as yellow.

  Such a paint 31 displays the positions of the pressure sensors PS1 to PS6 from outside the seat body S0 in a visible manner before the occupant sits on the vehicle seat S.

  The control device 100 is connected to the pressure sensors PS1 to PS6 so that pressure values can be obtained from the pressure sensors PS1 to PS6. The control device 100 can transmit information detected by each of the pressure sensors PS1 to PS6 to a target device, for example, a smartphone SP.

  The control device 100 and the smartphone SP have a CPU, a ROM, a RAM, a rewritable nonvolatile memory, and the like (not shown), and execute a program stored in advance. Note that the smartphone SP further includes a display DSP.

  A short-range communication device 3A that enables short-range wireless communication such as Bluetooth (registered trademark) or Wi-Fi (registered trademark) is connected to the control device 100. The control device 100 is capable of communicating with the smartphone SP via the short-range communication device 3A, providing a predetermined screen or sound to the smartphone SP in cooperation with an application installed in the smartphone SP, and inputting the screen by the smartphone SP. Data can be obtained.

  In such a system including the seat body S0, the control device 100, and the smartphone SP, for example, a game of 100 m running can be provided on the smartphone SP. In this case, the control device 100 outputs a signal for performing an operation for running the character in the game displayed on the display DSP by the seated person alternately raising and lowering the left and right legs on the seat body S0.

  In playing such a game, the seated person can visually recognize the position of the paint 31 applied to the seat body S0 before sitting on the seat body S0, so that the position of each of the pressure sensors PS1 to PS6 can be determined. It can be easily confirmed. Thereby, the seated person can appropriately set his or her left and right thighs on the left and right pressure sensors PS3, and can enjoy the game by effectively using each pressure sensor PS3.

  As shown in FIG. 2, the sensor output conversion circuit 40 includes a sensor-side resistor Rfsr, a first resistor Rm, an operational amplifier OP, and a negative feedback circuit 41. The sensor-side resistor Rfsr is a resistor that is built in the pressure sensor PS1 and changes its resistance value according to a change in pressure as a physical quantity to be measured. In the following description, the sensor output conversion circuit 40 corresponding to the pressure sensor PS1 will be described as a representative, and the other sensor output conversion circuits 40 corresponding to the pressure sensors PS2 to PS6 have the same structure. The description is omitted.

  The first resistor Rm is connected in series with the sensor-side resistor Rfsr between the power supply EP and the ground GND. Specifically, an end of the first resistor Rm opposite to the sensor-side resistor Rfsr is connected to the ground GND, and an end of the sensor-side resistor Rfsr opposite to the first resistor Rm is connected to the power supply EP. ing.

The first resistor Rm includes four adjusting resistors R1 to R4 and four switches SW1 to SW4 for switching the connection state of the adjusting resistors R1 to R4. The four adjustment resistors R1 to R4 are connected in parallel and have different resistance values. Specifically, the resistance value of the k-th adjustment resistor among the four adjustment resistors R1 to R4 is a value ^obtained by multiplying the smallest resistance value by 2 ^k−1 . In the present embodiment, when the adjustment resistors R1 to R4 are arranged in ascending order of resistance value, the order is R1, R2, R3, and R4. Therefore, in the present embodiment, the resistance value of the first adjustment resistor R1 becomes the smallest value, the resistance value of the second adjustment resistor R2 is twice as large as R1, and the resistance value of the third adjustment resistor R3 is four times that of R1. The resistance value of the fourth adjustment resistor R4 is eight times that of R1. Specifically, in the present embodiment, the resistance value of the first adjustment resistor R1 is 200Ω, the resistance value of the second adjustment resistor R2 is 400Ω, the resistance value of the third adjustment resistor R3 is 800Ω, The resistance value of the adjusting resistor R4 is 1600Ω.

  The switches SW1 to SW4 are transistors, and can be switched based on signals from output ports p1 to p4 of the control device 100. The switches SW1 to SW4 are provided for each of the four adjustment resistors R1 to R4. More specifically, the first switch SW1 is connected in series to the first adjusting resistor R1, and is connected to the ground GND. Similarly, the second switch SW2, the third switch SW3, and the fourth switch SW4 are connected in series to the corresponding second adjustment resistor R2, third adjustment resistor R3, and fourth adjustment resistor R4, respectively, and are each connected to the ground GND. It is connected to the.

  The operational amplifier OP is an amplifier having a non-inverting input terminal (+), an inverting input terminal (-), and one output terminal. The non-inverting input terminal (+) is connected to a wiring W between the sensor-side resistor Rfsr and the first resistor Rm. The output voltage Vout output from the output terminal is fed back to the inverting input terminal (−) via the negative feedback circuit 41 and is output to the control device 100.

  The negative feedback circuit 41 is a circuit that connects the output terminal of the operational amplifier OP and the inverting input terminal (-). Note that, in the present embodiment, the negative feedback circuit 41 is configured only with wiring, but the present invention is not limited to this, and the negative feedback circuit 41 may be provided with a resistor. That is, the output terminal of the operational amplifier OP may be connected to the inverting input terminal (-) via the resistor.

In the sensor output conversion circuit 40, when the control device 100 controls the power supply EP and applies the voltage Vpp to the sensor-side resistor Rfsr and the first resistor Rm connected in series, the voltage Vpp becomes equal to the sensor-side resistor Rfsr and the first resistor Rfsr. The voltage is divided by one resistor Rm. Thus, the potential between the sensor-side resistor Rfsr and the first resistor Rm, that is, the voltage Vin applied to the first resistor Rm is expressed by the following equation (1).
Vin = {Rm / (Rfsr + Rm)} · Vpp (1)

When the voltage Vin is input to the non-inverting input terminal (+) of the operational amplifier OP, the output voltage Vout is output to the control device 100 from the output terminal of the operational amplifier OP. Here, since the negative feedback circuit 41 includes only wiring, the output voltage Vout is represented by the following equation (2).
Vout = Vin = {Rm / (Rfsr + Rm)}. Vpp (2)

Here, the resistance value of the first resistor Rm changes to various values by switching the switches SW1 to SW4. The resistance value of the first resistor Rm is represented by the following equation (3).
_{Rm = 1 / (p 1 /} R1 + p 2 / R2 + p 3 / R3 + p 4 / R4) ··· (3)
p _{1 to} p ₄ : 0 or 1

Here, p _{1 to} p ₄ are values indicating output states (HIGH / LOW) of signals output from the output ports p _{1 to} p ₄ to the switches SW 1 to SW ₄ , and correspond to ON / OFF of the switches SW 1 to SW 4. ing. In this circuit, when the outputs of the output ports p1 to p4 are set to HIGH, the switches SW1 to SW4 are turned ON, and the adjusting resistors R1 to R4 are connected to the ground GND. When the outputs of the output ports p1 to p4 are set to LOW, the switches SW1 to SW4 are turned off, and the connection between the adjustment resistors R1 to R4 and the ground GND is cut off. In the equation (3), 0 is substituted into p _{1 to} p ₄ when the switches SW1 to SW4 are OFF, and 1 is substituted when the switches SW1 to SW4 are ON.

  In this embodiment, each of the adjustment resistors R1 to R4 is set to 200Ω, 400Ω, 800Ω, and 1600Ω. Therefore, the combined resistance value of the adjustment resistors R1 to R4, that is, the resistance value of the first resistor Rm is set in the range of 106 to 1600Ω. You can switch with.

  By switching the resistance value of the first resistor Rm in this way, the characteristics of the output voltage Vout, which is the output value of the pressure sensor PS1, can be switched as shown in FIG. FIG. 3 is a graph in which the horizontal axis represents the pressure applied to the pressure sensor PS1, and the vertical axis represents the output voltage Vout.

  According to the graph of FIG. 3, in a range where the pressure applied to the pressure sensor PS1 is a small value such as 0 to F1, as the resistance value of the first resistor Rm increases, the slope of the output voltage Vout increases and the responsiveness and resolution increase. Will be higher. Further, in a range where the pressure applied to the pressure sensor PS1 is a medium value such as F1 to F2, the slope of the output voltage Vout is substantially constant regardless of the resistance value of the first resistor Rm. Then, in a range where the pressure applied to the pressure sensor PS1 is a large value such as F2 to F3, the smaller the resistance value of the first resistor Rm, the larger the slope of the output voltage Vout, and the higher the responsiveness and resolution.

  Therefore, for example, when the weight of the occupant is small, the control device 100 sets the resistance value of the first resistor Rm to 1600Ω by turning on the fourth switch SW4 and turning off the other switches SW1 to SW3. , The response of the pressure sensor PS1 can be increased. Further, for example, when the weight of the occupant is large, the control device 100 turns on all the switches SW1 to SW4 to set the resistance value of the first resistor Rm to 106 Ω, thereby improving the response of the pressure sensor PS1. Can be higher.

As described above, according to the sensor output conversion circuit 40 of the present embodiment, the following effects can be obtained.
By switching the connection state of the four adjustment resistors R1 to R4 with the switches SW1 to SW4, the output value of the pressure sensor PS1 output from the operational amplifier OP can be changed, so that the output characteristics of the pressure sensor PS1 are changed. Therefore, it is possible to suppress the deterioration of the pressure detection accuracy of the pressure sensor PS1.

  In particular, in the present embodiment, it is possible to change the output characteristics of the pressure sensors PS1 to PS6 provided on the seat body S0 used as a controller for operating a character in the game displayed on the smartphone SP. For this reason, it is possible to suppress a decrease in the accuracy of pressure detection by the pressure sensors PS1 to PS6 due to a difference in the weight of the seated person, and to provide equivalent operability to various seated persons having different weights.

  Since the switches SW1 to SW4 are provided for each of the four adjustment resistors R1 to R4, the resistance value of the first resistor Rm, that is, the four adjustment resistors Rm, for example, is smaller than the configuration in which the number of switches is smaller than the number of adjustment resistors. The pattern of the combined resistance value of the resistors R1 to R4 can be increased.

  Since the switches SW1 to SW4 are transistors, the switches SW1 to SW4 can be favorably switched by a signal from the control device 100.

  By setting the resistance values of the four adjustment resistors R1 to R4 to different values, for example, as compared with a configuration in which the four adjustment resistors have the same resistance value, the resistance value of the first resistor Rm, that is, the four adjustment resistors The pattern of the combined resistance value of R1 to R4 can be increased.

By setting the resistance value of the k-th adjustment resistor among the four adjustment resistors R1 to R4 to a value ^obtained by multiplying the smallest resistance value by 2 ^k−1 , the resistance values of the four adjustment resistors R1 to R4 are obtained. However, since the resistance value is shifted twice from the smallest resistance value in order, the resistance value of the first resistor can be changed within an appropriate range.

  Since the resistance values of the four adjustment resistors R1 to R4 are 200Ω, 400Ω, 800Ω, and 1600Ω, the resistance value of the first resistor Rm can be changed in the range of 106 to 1600Ω.

  Although the embodiments of the present invention have been described above, the present invention can be appropriately modified and implemented as shown in other embodiments below. In the following description, members having substantially the same structure as those of the above embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

  In the above embodiment, the plurality of adjusting resistors R1 to R4 are connected in parallel, but the present invention is not limited to this, and may be connected in series. For example, as shown in FIG. 4, five adjusting resistors R11 to R15 may be connected in series.

  Specifically, in the embodiment of FIG. 4, the first resistor Rm includes five adjusting resistors R11 to R15 and four switches SW1 to SW4 for switching the connection state of the adjusting resistors R11 to R15. The five adjusting resistors R11 to R15 are connected in series, and have the same resistance value, for example, 200Ω. Specifically, the first adjustment resistor R11 is connected in series to the sensor-side resistor Rfsr, the second adjustment resistor R12 is connected in series to the first adjustment resistor R11, and the third adjustment resistor R13 is connected to the second adjustment resistor R13. Is connected in series to the resistor R12. The fourth adjustment resistor R14 is connected in series with the third adjustment resistor R13, and the fifth adjustment resistor R15 is connected in series with the fourth adjustment resistor R14 and is also connected to the ground GND.

  The switches SW1 to SW4 are transistors and can be switched based on signals from output ports p1 to p4 of the control device 100. The first switch SW1 is connected to a wiring between the first adjustment resistor R11 and the second adjustment resistor R12, and is also connected to the ground GND. The second switch SW2 is connected to a wiring between the second adjustment resistor R12 and the third adjustment resistor R13, and is also connected to the ground GND.

  The third switch SW3 is connected to a wiring between the third adjustment resistor R13 and the fourth adjustment resistor R14, and is also connected to the ground GND. The fourth switch SW4 is connected to a wiring between the fourth adjustment resistor R14 and the fifth adjustment resistor R15, and is also connected to the ground GND.

In this embodiment, the resistance value of the first resistor Rm is represented by the following equation (4).
_{Rm = R11 + p 1 · [} R12 + p 2 · {R13 + p 3 · (R14 + p 4 · R15)}] ··· (4)
p _{1 to} p ₄ : 0 or 1

In the equation (4), the numerical values assigned to p _{1 to} p ₄ are opposite to those in the above embodiment. That is, in equation _(4), the p 1 ~p _4, when the switch SW1~SW4 is ON 0 is substituted, at the time of OFF 1 is substituted. According to this embodiment, as shown in FIG. 5, the resistance of the first resistor Rm depends on the output state (HIGH / LOW) of the signal of each output port p1 to p4, that is, ON / OFF of each switch SW1 to SW4. The value (combined resistance value) can be changed in proportion to 200Ω, 400Ω, 600Ω, 800Ω, 1000Ω.

  In the form of series connection, only five patterns of the resistance value (combined resistance value) of the first resistor Rm can be formed for the four output ports p1 to p4. Also, the number of adjusting resistors needs to be five.

On the other hand, in the case of the parallel connection, as shown in FIG. 6, 16 patterns of combined resistance values can be formed for the four output ports p1 to p4. Specifically, in the parallel connection mode, when the number of output ports is n, 2 ⁿ patterns of the combined resistance value can be created. You can do much. Furthermore, in the form of parallel connection, only four adjustment resistors are required, and cost reduction can be achieved. In the embodiment of FIG. 6, the resistance values of the adjusting resistors R1 to R4 are different from those of the above embodiment, and the range of the combined resistance value is 66.7 to 1 kΩ.

  However, in the case of the parallel connection, there are combined resistance values that are close to each other, such as the combined resistance values 125Ω and 111Ω of the patterns 9 and 10 shown in FIG. Therefore, as shown in FIG. 7, there is a possibility that a pattern in which the magnitude relation of the combined resistance value is reversed may occur depending on a manufacturing error of the adjustment resistors R1 to R4. Here, in FIG. 7, the graph shown by the solid line is a graph when the manufacturing error is substantially 0, and the graph shown by the broken line is a graph when there is the manufacturing error.

  On the other hand, in the form of series connection, as shown in FIG. 5, by shifting the combined resistance value of each pattern largely, for example, by 200Ω, the adjustment resistor R11 is shifted as shown in FIG. Even if a manufacturing error occurs in R15 to R15, the magnitude relationship of the combined resistance values does not reverse. Here, in FIG. 8, the graph indicated by the solid line is a graph when the manufacturing error is approximately 0, and the graph indicated by the broken line is a graph when the manufacturing error is present.

  In the above-described embodiment, the vehicle seat S used in a vehicle such as an automobile is exemplified as the seat. However, the present invention is not limited to this. Other seats, for example, a chair used in a room such as a house. It may be a child or a chair.

  In the embodiment, the sensor-side resistor Rfsr is connected to the power supply EP, and the first resistor Rm is connected to the ground GND. However, the present invention is not limited to this, and the arrangement of the first resistor Rm and the sensor-side resistor Rfsr is interchanged. , The first resistor Rm may be connected to the power supply EP, and the sensor-side resistor Rfsr may be connected to the ground GND.

  In the above-described embodiment, the pressure sensors PS1 to PS6 are illustrated as sensors, but the present invention is not limited to this. The sensor is a sensor having a sensor-side resistance whose resistance value changes according to a change in a physical quantity of a measurement target. Any sensor may be used as long as it is provided. For example, the sensor may be a temperature sensor having a sensor-side resistance whose resistance value changes according to a change in temperature.

In the above embodiment, the number of the adjusting resistors R1 to R4 is four, but the present invention is not limited to this, and may be, for example, two or three, or five or more. Is also good. Further, the number of switches may be appropriately changed according to the number of adjustment resistors. Further, the resistance values and the like of the adjustment resistors R1 to R4 can be arbitrarily set. When the number of adjustment resistors is n, the resistance value of the k-th adjustment resistor among the n adjustment resistors may be a value obtained by multiplying the smallest resistance value by 2 ^k−1 . Here, k: 1 to n.

  Further, the plurality of adjustment resistors may be connected in series, or may be connected in a combination of series and parallel.

  In the above-described embodiment, the switches SW1 to SW4 are configured by transistors. However, the present invention is not limited to this, and may be configured as long as the switches can be switched based on a signal from the control device. For example, an IC of a relay / FET / digital circuit (AND circuit, OR circuit, XOR circuit) may be used as the switch.

  The components described in the embodiment and the modified examples described above may be implemented in any combination.

Reference Signs List 40 sensor output conversion circuit 41 negative feedback circuit 100 control device EP power supply GND ground OP operational amplifier PS1 to PS6 pressure sensor R1 to R4 adjustment resistor Rfsr sensor side resistor Rm first resistor SW1 to SW4 switch

Claims (10)

A sensor-side resistor that is built into the sensor and whose resistance value changes according to a change in the physical quantity of the measurement target,
A first resistor connected in series to the sensor-side resistor between a power supply and ground;
An operational amplifier in which a wiring between the sensor-side resistor and the first resistor is connected to a non-inverting input terminal;
A sensor output conversion circuit comprising: a negative feedback circuit that connects an output terminal of the operational amplifier and an inverting input terminal;
The first resistor includes a plurality of adjustment resistors, and a switch that switches a connection state of the plurality of adjustment resistors,
The sensor output conversion circuit, wherein the switch is switchable based on a signal from a control device.   The sensor output conversion circuit according to claim 1, wherein the switch is provided for each of the plurality of adjustment resistors.   The sensor output conversion circuit according to claim 1, wherein the switch is a transistor.   4. The sensor output conversion circuit according to claim 1, wherein the first resistor is connected to a ground. 5.   The sensor output conversion circuit according to claim 1, wherein the plurality of adjustment resistors have different resistance values. When the number of the adjustment resistors is n, the resistance value of the k-th adjustment resistor among the n adjustment resistors is a value ^obtained by multiplying the smallest resistance value by 2 ^k−1. The sensor output conversion circuit according to claim 5.   The sensor output conversion circuit according to claim 1, wherein the plurality of adjustment resistors are connected in parallel.   The sensor output conversion circuit according to any one of claims 1 to 7, wherein the number of the adjusting resistors is four.   The sensor output conversion circuit according to claim 8, wherein the resistance values of the four adjustment resistors are 200Ω, 400Ω, 800Ω, and 1600Ω. It is a sheet | seat provided with the sensor output conversion circuit of any one of Claim 1 to 9, Comprising:
A seat body having a seat surface for supporting a seated person is provided,
The seat is a pressure sensor arranged on the seat surface side of the seat body.

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