JP2024048044A - Gripping state detection device and control method thereof - Google Patents

Abstract

To accurately determine whether a device is in a gripped or non-gripped state even if a change in capacitance occurs due to disturbance.
[Solution] A CPU 21 determines that the state is a non-gripped state/gripped state when a measurement value S is within/outside a predetermined range based on a reference threshold value TH0 stored in a storage unit 25. When the CPU 21 determines that the state is a gripped state, it acquires an increased measurement value SA and an increase amount Δ1, determines an update threshold value based on these, and updates the reference threshold value TH0 to the determined update threshold value.
[Selected figure] Figure 3

Description

This technology relates to a grip state detection device that detects the grip state of a vehicle steering wheel and a control method thereof.

Conventionally, a device has been proposed that determines whether the steering wheel is being gripped or not based on changes in capacitance detected by a capacitance sensor attached to the steering wheel of a vehicle operated by a driver.

For example, the device in Patent Document 1 compares a threshold value for judgment with the capacitance to judge whether the steering wheel is being held or released (not being held). The threshold value for judgment is updated when the state changes from being held to being released.

Patent No. 6489091

However, the detected capacitance changes due to disturbances such as temperature. In the device of Patent Document 1, the judgment threshold is not updated even if a disturbance acts. Therefore, there is room for improvement in terms of increasing the accuracy of judging whether the object is being grasped or not by taking disturbances into account.

The aim of this technology is to accurately determine whether the device is gripped or not, even if changes in capacitance occur due to external disturbances.

In order to achieve the above object, the grip state detection device of the present technology has a measurement unit that measures capacitance that changes depending on the state of grip of the steering wheel of the vehicle by the driver and outputs it as a measurement value, a storage unit that stores a reference threshold value, a determination unit that determines that the steering wheel is in an unheld state where the driver is not gripping the steering wheel if the measurement value output by the measurement unit is within a predetermined range based on the reference threshold value stored in the storage unit, and determines that the steering wheel is in a gripped state where the driver is gripping the steering wheel if the measurement value is outside the predetermined range, an acquisition unit that acquires the measurement value output by the measurement unit as an increased measurement value when the determination unit determines that the steering wheel is in a gripped state, and acquires an increase in the increased measurement value relative to the measurement value last output in the unheld state, and an update unit that determines an update threshold value based on the increased measurement value and the increase amount after the increase amount is acquired by the acquisition unit, and updates the reference threshold value stored in the storage unit to the determined update threshold value.

This technology makes it possible to accurately determine whether the device is gripped or not, even if a change in capacitance occurs due to an external disturbance.

1 is a front view of a steering wheel to which a grip state detection device is applied; 2 is a block diagram of a main part of a steering switch device. FIG. 13 is a timing chart of a gripping/non-gripping determination process. 13 is a flowchart showing a gripping/non-gripping determination process. 5 is a continuation of the flowchart in FIG. 4 .

Below, an embodiment of this technology will be explained with reference to the drawings.

Figure 1 is a front view of a steering wheel to which a grip state detection device according to one embodiment of the present technology is applied.

This grip state detection device is configured as a steering switch device 100, for example. The steering switch device 100 is mounted on the steering wheel 90 of the vehicle, for example, and can be electrically connected to the vehicle's ECU (not shown).

The steering wheel 90 includes a steering spoke 91L that protrudes to the left when viewed from the driver's side, a steering spoke 91R that protrudes to the right, and a steering spoke 91C that protrudes downward. The steering wheel 90 also includes a circular steering wheel 92 that is connected to each end of the steering spokes 91L, 91R, and 91C, and is substantially concentric with a steering column (not shown). The driver can change the direction of travel of the vehicle by operating the steering wheel 92. A horn pad 93 is provided between the steering spokes 91L and 91R. The horn pad 93 is positioned so as to overlap with the center of rotation of the steering wheel 90.

The steering switch device 100 is a device capable of detecting the state of grip when a driver (person) grips a steering wheel 92 with the left or right hand. The steering switch device 100 includes a switch unit 96 capable of operating the drive of vehicle equipment, a steering switch case 94 in which the switch unit 96 is housed, and a substrate 28 provided within the steering switch case 94. The substrate 28 is provided with a measuring unit according to the present technology. The measuring unit further includes a sensor member and a processing member. The switch unit 96 and measuring unit are arranged in pairs on the left and right sides via a horn pad 93. Below, the switch unit 96 and measuring unit on the left side of the left and right sides will be described as a representative example.

The sensor member is a capacitance-type proximity sensor that detects the approach of the left hand to the steering wheel 92 by a change in capacitance. The processing member has an oscillation circuit, a detection circuit, and an output circuit (all not shown). The oscillation circuit is electrically connected to the sensor member and generates an electric field in the sensor member by high frequency waves. The detection circuit detects a change in the oscillation frequency of the oscillation circuit in response to the approach of the hand. The output circuit outputs the detection result of the detection circuit and transmits it to the ECU.

In a measurement unit configured in this way, when the hand is not present in the electric field of the sensor member, i.e., in the detection area, there is no change in the oscillation frequency of the oscillator circuit. On the other hand, when the hand enters the electric field of the sensor member, the hand is polarized due to the influence of the electric field, and a negative potential is generated on the hand, i.e., negative charges are unevenly distributed and accumulated. As a result, positive charges are unevenly distributed and accumulated on the sensor member. This increases the electrostatic capacitance, and the oscillation frequency of the oscillator circuit changes. The detection circuit can detect this change in oscillation frequency. The detection result of the detection circuit is then output from the output circuit as the detection result of the gripping condition of the left hand. There is no restriction on the configuration or arrangement of the measurement unit that can be adopted.

In this embodiment, the detection result of the gripping state includes a "gripped state" in which the steering wheel 92 is gripped by the driver, and a "non-gripped state" in which the steering wheel 92 is not gripped by the driver. The gripped state and non-gripped state may be determined separately for the left hand and the right hand. Alternatively, if a gripping state is determined for either the left or right hand, the whole state may be determined to be a gripped state.

Figure 2 is a block diagram of the main parts of the steering switch device 100. ROM 22, RAM 23, timer 24, memory unit 25, switch unit 96, display unit 27, board 28, and various I/Fs 29 are electrically connected to the CPU 21. Some of these components may be included in the ECU.

The CPU 21 controls the entire steering switch device 100. The ROM 22 stores programs executed by the CPU 21. The RAM 23 provides a work area when the CPU 21 executes the programs. The storage unit 25 is a non-volatile memory and stores various information. The switch unit 96 includes a touch panel or the like (not shown) and is a component that allows the user to input various instructions. The display unit 27 displays various information. The display unit 27 may also have a sound generation function. As described above, the sensor member measures the electrostatic capacitance that changes depending on the state of grip by the driver, and outputs the measured value S to the CPU 21. The various I/Fs 29 include various wireless or wired communication I/Fs.

Figure 3 is a timing chart of the grasping/non-grasping judgment process. The horizontal axis of Figure 3 represents the elapsed time, and the vertical axis represents the measured value S. Figure 3 shows the judgment process for the left hand as a representative example.

The initial value of the reference threshold value TH0 is stored in the memory unit 25 and can be updated during the grasping/non-grasping determination process. The upper limit value TH1 is the reference threshold value TH0 plus a predetermined value α, and the reference threshold value TH0 and the upper limit value TH1 define a threshold range for determining whether the state is grasping or non-grasping. Hereinafter, this threshold range is referred to as the "predetermined range" based on the reference threshold value TH0.

The period before time t10 is the period after the device is started and before it is determined that it is in a gripping state, or the period after it is determined that it has transitioned from a gripping state to a non-gripping state. The CPU 21 constantly monitors the measurement value S (at the acquisition timing that arrives at regular time intervals), and when the measurement value S falls outside the specified range (is no longer within the specified range), it determines that it has transitioned to a gripping state (time t10). Time t11 is the time when a specified time T0 has elapsed since time t10, when the measurement value S fell outside the specified range. The measurement value S output at time t11 is the increased measurement value SA.

The update timing occurs every time T1 after time t11. The interval between the update timings (time T1) is set to a value longer than the interval between the acquisition timings (fixed time interval).

Details will be described later with reference to Figures 4 and 5, but at the update timing, gripping/non-grip is determined according to the newly acquired measurement value S, and the reference threshold value TH0 and upper limit value TH1 can be updated. Note that the specified time T0 may or may not be equal to the time T1.

The contents of the gripping/non-gripping judgment process will be outlined below. The CPU 21, which serves as the judgment unit, judges that the state is not gripped when the measurement value S output by the measurement unit is within a predetermined range, and judges that the state is gripped when the measurement value S is outside the predetermined range. For example, during the period in which the state is judged to be non-gripped (times t00 to t10, t40 onwards), the flag is set to "0", and during the period in which the state is judged to be gripped (times t10 to t40), the flag is set to "1".

At time t10, it is determined that the gripping state is established. At time t11, a predetermined time T0 has elapsed since time t10, the CPU 21, acting as the acquisition unit, acquires the newly output measurement value S as the increased measurement value SA. Furthermore, the CPU 21 calculates and acquires the increase amount Δ1 of the increased measurement value SA relative to the measurement value S last output in the non-gripping state, using SA-S.

At time t11, the CPU 21 as an update unit further determines an update threshold value TH0' based on the increase measurement value SA and the increase amount Δ1. The update threshold value TH0' is calculated and determined by the increase measurement value SA - the increase amount Δ1. Furthermore, the CPU 21 updates the reference threshold value TH0 stored in the memory unit 25 to the update threshold value TH0' determined above. At the same time, the CPU 21 also updates the upper limit value TH1' by adding a predetermined value α to the updated update threshold value TH0'. As a result, the predetermined range is also updated.

Here, the upper limit value TH1' is an upper limit value that is updated based on the update threshold value TH0'. The upper limit value TH1" is an upper limit value that is updated based on the additional update threshold value TH0" (described later).

The measurement value S output while the determination that the object is in the gripping state continues is specifically referred to as the "grip measurement value SB". The CPU 21 acquires the measurement value S output while the determination that the object is in the gripping state continues as the grip measurement value SB. After updating the reference threshold value TH0 to the update threshold value TH0', the CPU 21 as an update unit determines the additional update threshold value TH0" based on the grip measurement value SB and the increase amount Δ1, and updates the update threshold value TH0' to the additional update threshold value TH0". For example, at time t13, the CPU 21 acquires the measurement value S as the grip measurement value SB, determines the additional update threshold value TH0" based on the grip measurement value SB and the increase amount Δ1, and updates the update threshold value TH0' to the additional update threshold value TH0".

The CPU 21 acquires the measurement value S output while the determination of the gripping state is continuing as the gripping measurement value SB, and acquires the difference D between the previous value and the current value of the gripping measurement value SB. While the determination of the gripping state is continuing, the CPU 21 compares the absolute value of the difference D with the movement determination threshold value TH2 at the update timing. The movement determination threshold value TH2 is a fixed value and is stored in advance in the memory unit 25. Note that the movement determination threshold value TH2 may be a variable value that changes depending on the vehicle interior environment.

If the absolute value of the difference D > the movement determination threshold TH2 while the gripping state determination is continuing, the CPU 21 as the determination unit determines that a movement of the gripping position has occurred. After determining that a movement of the gripping position has occurred, the CPU 21 as the acquisition unit acquires the difference D that exceeds the movement determination threshold TH2 as the amount of change. Furthermore, the CPU 21 as the update unit determines the additional update threshold TH0" based on the gripping measurement value SB, the increase amount Δ1, and the amount of change. For example, the CPU 21 calculates and determines the additional update threshold TH0" by the gripping measurement value SB - (increase amount Δ1 + change amount). The update threshold TH0' is updated by this additional update threshold TH0".

If the absolute value of the difference D is not greater than the movement determination threshold TH2 while the grasped state is being determined, that is, if the absolute value of the difference D is equal to or less than the movement determination threshold TH2, for example, the CPU 21 as an update unit calculates and determines the additional update threshold TH0" using the grasped measurement value SB - the increase amount Δ1. The update threshold TH0' is updated by this additional update threshold TH0".

By performing the above process, even if a large change occurs in the measurement value due to a movement in the gripping position, the amount of change is used for calculation, so sudden fluctuations in the update threshold TH0' and additional update threshold TH0", as well as the reference threshold TH0, are avoided.

In other words, by subtracting changes in the measurement value due to hand movement, etc., it is possible to determine whether the device is in a gripping or non-grip state based only on changes in the measurement value caused by changes in the temperature environment inside the vehicle.

Figures 4 and 5 are flowcharts showing the gripping/non-grip determination process. This process is realized by the CPU 21 expanding a program stored in the ROM 22 into the RAM 23 and executing it. This process is started when the device is started. When this process is started, the CPU 21 executes a predetermined process as necessary. For example, the CPU 21 executes initialization. The CPU 21 can read the initial value of the reference threshold TH0 and the movement determination threshold TH2 stored in the memory unit 25, and further set the flag to "0". Therefore, at this point, it is determined that the state is non-grip. The CPU 21 also sets a "predetermined range" by the reference threshold TH0 + the predetermined value α. This sets the initial value of the "predetermined range" based on the reference threshold TH0. The predetermined range is a range equal to or greater than the reference threshold TH0 and equal to or less than the upper limit value TH1.

In step S101, the CPU 21 executes other processes. The other processes referred to here include, for example, termination processing of this process in response to a user instruction.

In step S102, the CPU 21 determines whether the acquisition timing has arrived. The acquisition timing arrives at regular time intervals after the device is started. If the acquisition timing has not arrived, the CPU 21 returns to step S101, and if the acquisition timing arrives, the CPU 21 proceeds to step S103. In step S103, the CPU 21 acquires the measurement value S output by the measurement unit and stores it in the RAM 23.

In step S104, the CPU 21 determines whether the measurement value S acquired in step S103 is within a predetermined range (TH0≦S≦TH1 holds). If the measurement value S is within the predetermined range, the CPU 21 returns to step S101. In this case, the determination result remains the non-grasping state. On the other hand, if the measurement value S is outside the predetermined range, the CPU 21 proceeds to step S105 and determines whether the measurement value S is less than the reference threshold value TH0 (S<TH0 holds).

If the measured value S is less than the reference threshold value TH0, the CPU 21 proceeds to step S111 and determines that there is an abnormality in at least one of the measurement unit, the memory unit 25, the acquisition unit, or the update unit. In step S112, the CPU 21 notifies the abnormality by displaying an abnormality on the display unit 27 or by issuing a voice message, and ends this process.

On the other hand, if the measured value S is not less than the reference threshold value TH0, the CPU 21 can determine that the measured value S exceeds the upper limit value TH1, and proceeds to step S106. In step S106, the CPU 21 determines that the hand is in a gripping state and sets the flag to "1" (time t10 in FIG. 3).

In step S107, when a predetermined time T0 has elapsed from time t10 when the measurement value S fell outside the predetermined range (time t11), the CPU 21 proceeds to step S108. In step S108, the CPU 21 acquires the measurement value S newly output by the measurement unit as the increased measurement value SA. Furthermore, the CPU 21 calculates and acquires the increase amount Δ1 of the increased measurement value SA relative to the measurement value S last output in the non-gripping state by "increase amount Δ1 = SA - S", and stores it in the RAM 23. Here, the latest measurement value S is always stored in the RAM 23. Therefore, the "measurement value S last output in the non-gripping state" is the measurement value S stored in the RAM 23 in step S103 immediately before proceeding to step S106.

In step S109, the CPU 21 determines the update threshold TH0' by "update threshold TH0' = increase measurement value SA - increase amount Δ1". In step S110, the CPU 21 updates the reference threshold TH0 stored in the memory unit 25 to the update threshold TH0' determined above, and also updates the upper limit value TH1' by "TH1' = TH0' + α". As a result, the predetermined range is also updated.

In step S201 of FIG. 5, when the update timing arrives, the CPU 21 proceeds to step S202. In step S202, the CPU 21 acquires the new measurement value S output by the measurement unit as the currently held measurement value SB.

In step S203, the CPU 21 determines whether the gripping measurement value SB acquired in step S202 is within a predetermined range (TH0' ≦ SB ≦ TH1' is satisfied). If the gripping measurement value SB is within the predetermined range, the CPU 21 determines in step S210 that the state is not being gripped, sets the flag to "0" (for example, time t40 in FIG. 3), and ends this process. In this case, the state returns to the state before time t10 in FIG. 3. Note that the period from step S106 until the non-gripping state is determined in step S210 is the period during which the determination that the state is being gripped continues.

On the other hand, if the gripping measurement value SB is outside the predetermined range, the CPU 21 proceeds to step S204 and determines whether the gripping measurement value SB is less than the update threshold value TH0' or less than the additional update threshold value TH0" (SB < [TH0' or TH0"] is true).

If the gripping measurement value SB is less than the update threshold TH0' or less than the additional update threshold TH0", the CPU 21 proceeds to step S209 and determines that there is an abnormality in at least one of the measurement unit, the memory unit 25, the acquisition unit, or the update unit. In step S213, the CPU 21 executes a notification process similar to step S112 and ends this process. That is, as a notification process to notify of the abnormality, the CPU 21 displays an abnormality on the display unit 27 or issues a voice message. On the other hand, if the gripping measurement value SB is not less than the update threshold TH0' or less than the additional update threshold TH0", the CPU 21 proceeds to step S205 because it can be determined that the gripping measurement value SB exceeds the upper limit value TH1' or TH1" and the gripping state continues.

In step S205, the CPU 21 acquires the difference D between the previous and current values of the gripping measurement value SB. For example, if the current time is time t13, the difference D between the gripping measurement value SB acquired at time t12 and the gripping measurement value SB acquired at time t13 is acquired. The difference D is calculated by "difference D = current value - previous value". Therefore, the difference D is an amount whose sign is positive when the current value is greater than the previous value.

In step S206, the CPU 21 determines whether the absolute value of the difference D is greater than the movement determination threshold TH2 (movement determination threshold TH2<|difference D| holds). If movement determination threshold TH2<|difference D| does not hold (e.g., at time t13, t14), the CPU 21 proceeds to step S207, and if movement determination threshold TH2<|difference D| holds (e.g., at time t15, t18), the CPU 21 proceeds to step S211.

In step S211, the CPU 21 determines that a movement of the gripping position has occurred, and acquires the difference D as the amount of change (amount of change Δ2 at time t15, and a second amount of change Δ3 at time t18). Furthermore, the CPU 21 determines the value obtained by subtracting the increase amount Δ1 and the amount of change Δ2 from the measurement value during gripping SB as the additional update threshold TH0". In other words, the CPU 21 calculates and determines the additional update threshold TH0" by calculating "additional update threshold TH0" = measurement value during gripping SB - (increase amount Δ1 + amount of change)". If the second amount of change Δ3 has been acquired, the calculation formula "additional update threshold TH0" = measurement value during gripping SB - (increase amount Δ1 + amount of change Δ2 + second amount of change Δ3)" is used.

For example, if the current time is time t18, the amount of change Δ2 acquired at time t15 after it was determined that the state was gripped and the amount of change Δ3 acquired at time t18 are stored. Therefore, in the above calculation, the sum of the amount of change Δ2 acquired at time t15 and the second amount of change Δ3 acquired at the current time t18 is applied to the "amount of change". Alternatively, if the current time is time t15, there is no amount of change acquired and stored after it was determined that the state was gripped. Therefore, in the above calculation, only the amount of change Δ2 acquired at the current time t15 is applied to the "amount of change".

In step S212, the CPU 21 updates the update threshold TH0' stored in the memory unit 25 to the additional update threshold TH0" determined in step S211, and also updates the upper limit value TH1" by "TH1" = TH0" + α". As a result, the predetermined range is also updated. After that, the CPU 21 ends this process.

In step S207, the CPU 21 determines the additional update threshold TH0" by subtracting the increase amount Δ1 and the amount of change that has already been stored from the measured value during gripping SB. In other words, the CPU 21 calculates and determines the additional update threshold TH0" by calculating "additional update threshold TH0" = measured value during gripping SB - (increase amount Δ1 + amount of change)."

For example, if the current time is time t13, there is no change amount acquired and stored after the grasping state was determined. Therefore, in the above calculation, zero is applied to the "change amount". Alternatively, if the current time is time t16, there is one change amount acquired and stored at time t15. Therefore, in the above calculation, the change amount Δ2 acquired and stored at time t15 is applied to the "change amount".

In step S208, the CPU 21 updates the update threshold TH0' stored in the memory unit 25 to the additional update threshold TH0" determined in step S207, and also updates the upper limit value TH1" by "TH1" = TH0" + α". As a result, the predetermined range is also updated. After that, the CPU 21 ends this process.

According to this embodiment, when the measurement value S is within/outside a predetermined range based on the reference threshold value TH0, it is determined that the state is non-gripping/gripping, respectively. When it is determined that the state is gripping, an update threshold value TH0' is determined based on the increased measurement value SA and the increase amount Δ1, and the reference threshold value TH0 is updated to the update threshold value TH0' determined above (S109, S110). Then, the predetermined range (TH0', TH1') is updated.

The increase amount Δ1 is the increase in the increased measurement value SA based on the last output measurement value S, so changes in capacitance due to disturbances such as temperature and humidity are compensated for. Therefore, even if a change in capacitance occurs due to disturbances, it is possible to accurately determine whether the sensor is gripped or not.

In addition, there is no need to install a temperature or humidity sensor to compensate for changes in capacitance due to disturbances such as temperature and humidity.

In addition, while the determination of the gripping state continues, the difference D between the previous value and the current value of the gripping measurement value SB is acquired. Then, if the difference D exceeds the movement determination threshold TH2 while the determination of the gripping state continues, it is determined that the gripping position has moved, and the difference D at that time is acquired as the amount of change, and the additional update threshold TH0" is determined based on the gripping measurement value SB, the increase amount Δ1, and the amount of change. For example, if the absolute value of the difference D becomes larger than the movement determination threshold TH2, the additional update threshold TH0" is determined based on the gripping measurement value SB, the increase amount Δ1, and the amount of change (S211). By basing it on the gripping measurement value SB, it is possible to follow the change over time of the measurement value due to disturbances such as temperature. By basing it on the amount of change, it is possible to respond to a sudden change in the measurement value S due to hand movement, etc. Therefore, an appropriate predetermined range (threshold range) can be set.

In particular, if a difference D whose absolute value is greater than the movement determination threshold TH2 is acquired multiple times while the grasping state is being determined, the value obtained by subtracting the increase Δ1 and the multiple differences D from the grasping measurement value SB is determined as the additional update threshold TH0". This makes it possible to set an appropriate predetermined range (threshold range) in response to multiple hand movements while the grasping state is being determined.

Furthermore, if the absolute value of the difference D never becomes greater than the movement determination threshold TH2, the additional update threshold TH0" is essentially determined based on the measurement value during gripping SB and the increase amount Δ1 (S207). This makes it possible to set an appropriate predetermined range (threshold range) in response to changes over time in the measurement value due to disturbances such as temperature.

In addition, when the measurement value S or the measurement value during gripping SB falls below the reference threshold value TH0, the update threshold value TH0', or the additional update threshold value TH0", an abnormality is determined to exist in at least one of the measurement unit, the memory unit 25, the acquisition unit, or the update unit, and a notification is issued. This prevents erroneous determinations.

In addition, when the state transitions from the gripped state to the non-gripped state and then transitions back to the gripped state, the increment Δ1 is newly acquired (S210 → S101 → → S108). This makes it possible to set the predetermined range (threshold range) for the next non-determined state with a value that follows the change over time of the measured value S.

In step S109, the increase amount Δ1 in "update threshold TH0' = increase measurement value SA - increase amount Δ1" does not have to be the increase amount Δ1 itself. For example, a value corresponding to the increase amount Δ1 (for example, a value smaller than the increase amount Δ1 by a predetermined value or a predetermined percentage) may be applied. Similarly, in the calculations in steps S207 and S211, a value corresponding to the increase amount Δ1 may be applied instead of the increase amount Δ1 itself.

Even while the grasping state is being determined, grasping/non-grasping may be determined based on the measurement value S, which is constantly monitored, regardless of the update timing.

After starting the device, it may be possible to specify whether or not to perform the grip/non-grip determination by operating the operation unit 26.

The present technology has been described above in detail based on preferred embodiments, but the present technology is not limited to these specific embodiments, and various forms that do not deviate from the gist of the technology are also included in the present technology.

The present technology can also be realized by supplying a program that realizes one or more of the functions of the above-described embodiments to a system or device via a network or a non-transitory storage medium, and having one or more processors of a computer in the system or device read and execute the program. The above-described program and the storage medium that stores the above-described program constitute the present technology. The present technology can also be realized by a circuit (e.g., an ASIC) that realizes one or more of the functions.

21 CPU, 25 Memory unit, 28 Board, 92 Steering wheel, 100 Steering switch device, TH0 Reference threshold value, TH1 Upper limit value, S Measurement value, SA Increase measurement value, Δ1 Increase amount

Claims (12)

a measurement unit that measures a capacitance that changes depending on a state in which a driver grips a steering wheel of a vehicle, and outputs the capacitance as a measurement value;
A storage unit that stores a reference threshold value;
a determination unit that determines that the steering wheel is in an unheld state where the driver is not gripping the steering wheel when the measurement value output by the measurement unit is within a predetermined range based on the reference threshold value stored in the storage unit, and that the steering wheel is in a gripped state where the driver is gripping the steering wheel when the measurement value is outside the predetermined range;
an acquisition unit that acquires the measurement value output by the measurement unit as an increased measurement value when the determination unit determines that the device is in a gripped state, and acquires an increase in the increased measurement value relative to the measurement value last output in the non-grip state;
a gripping state detection device having an update unit that, after the increase amount is acquired by the acquisition unit, determines an update threshold value based on the increase measurement value and the increase amount, and updates the reference threshold value stored in the memory unit to the determined update threshold value. The gripping state detection device according to claim 1, wherein the update threshold is a value obtained by subtracting the increase amount from the increase measurement value. The acquisition unit acquires the measurement value output while the determination that the device is in the gripped state continues as a gripping measurement value,
The gripping state detection device according to claim 2, wherein after updating the reference threshold to the update threshold, the update unit determines an additional update threshold based on the measurement value during gripping and the increase amount, and updates the update threshold to the additional update threshold. The measuring unit is provided in a steering switch case disposed on the steering wheel,
The acquisition unit acquires a difference between a previous value and a current value of the during-holding measurement value,
The determination unit determines that a movement of the grip position has occurred when the difference exceeds a movement determination threshold while the determination that the grip state is continuing,
The acquisition unit acquires the difference exceeding the movement determination threshold as an amount of change in response to determining that a movement of the grip position has occurred,
The gripping state detection device according to claim 3 , wherein the update unit determines the additional update threshold based on the gripping measurement value, the increase amount, and the change amount after it is determined that a movement of the gripping position has occurred. The gripping state detection device according to claim 4, wherein, when the sign of the change amount is positive because the current value is greater than the previous value, the update unit determines a value obtained by subtracting the increase amount and the change amount from the gripping measurement value as the additional update threshold value. The gripping state detection device according to claim 5, wherein, when the change amount whose absolute value exceeds the movement determination threshold is acquired multiple times while the gripping state is being determined, the update unit determines a value obtained by subtracting the increase amount and the multiple change amounts from the gripping measurement value as the additional update threshold. The gripping state detection device according to claim 1, wherein when the measured value falls below the reference threshold value, the determination unit determines that at least one of the measurement unit, the storage unit, the acquisition unit, or the update unit is abnormal. The gripping state detection device according to claim 3, wherein when the gripping measurement value falls below the update threshold or the additional update threshold, the determination unit determines that at least one of the measurement unit, the storage unit, the acquisition unit, or the update unit is abnormal. The gripping state detection device according to claim 1, wherein the increase amount is newly acquired when the determination unit determines that the gripping state has been transitioned to the non-grip state after determining that the gripping state has been transitioned to the non-grip state. The gripping state detection device according to claim 1, wherein the increased measurement value is a measurement value output after a predetermined time has elapsed since the measurement value fell outside the predetermined range. a measurement step in which the measurement unit measures a capacitance that changes depending on a state in which the driver grips the steering wheel of the vehicle, and outputs the capacitance as a measurement value;
a determination step of determining that the steering wheel is in an unheld state, that is, not being gripped by the driver, when the measurement value output by the measurement unit is within a predetermined range based on a reference threshold value stored in a storage unit, and determining that the steering wheel is in a held state, that is, being gripped by the driver, when the measurement value is outside the predetermined range;
an acquisition step of acquiring a measurement value output by the measurement unit as an increased measurement value when the gripping state is determined by the determination step, and acquiring an increase in the increased measurement value with respect to the measurement value last output in the non-grip state;
a control step of determining an update threshold by subtracting the increase amount from the increase measurement value after the increase amount is acquired by the acquisition step, and updating the reference threshold value stored in the memory unit to the determined update threshold value. The acquisition step acquires the measurement value output while the determination that the device is in the gripping state continues as a gripping measurement value,
The control method for a gripping state detection device described in claim 11, wherein the update step determines an additional update threshold based on the gripping measurement value and the increase amount after updating the reference threshold to the update threshold, and updates the update threshold to the additional update threshold.

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