Grip detection device and computer program

Abstract

The present invention provides a hands-on detection device and a computer program with which an improvement in the speed of determining hands-on or hands-off and an improvement in the accuracy of the determination can be attained at the same time. Provided is a hands-on detection ECU that runs a current to a sensor electrode provided in a rim to perform hands-on detection with respect to the rim, in which the hands-on detection is performed using two modes with different currents for the hands-on detection.

Description

[Technical Field]

[0001] The present invention relates to a grip detection device and a computer program. This application claims priority from Japanese Application No. 2022-001220, filed January 6, 2022, and incorporates by reference all of the contents of said Japanese application. [Background technology]

[0002] 2. Description of the Related Art Conventionally, a technology has been widely used that uses a sensor provided on a steering wheel to monitor whether a driver is gripping the rim portion.

[0003] For example, Patent Document 1 discloses a contact detection sensor that uses a switched capacitor method to recognize events other than the object to be detected, that is, a human hand, touching or approaching the door handle, as noise events, and is therefore not affected even when the door handle is heavily wet, and can reliably determine the detection of a human hand by detecting an increase in capacitance value. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-129762 Summary of the Invention [Problem to be solved by the invention]

[0005] In the switched capacitor method described above, a current is passed through a capacitance connected to a sensor electrode to charge it, and when the electrode voltage of the sensor electrode reaches a certain voltage, the charging is stopped and an index related to the time constant associated with the charging (or discharging) of the charge is measured. The measured values ​​when gripping and when not gripping (hereinafter referred to as non-grip measured values) differ, and furthermore, the measured values ​​when gripping with gloves (hereinafter referred to as gloved measured values) differ from the measured values ​​when gripping with a bare hand (hereinafter referred to as bare hand measured values).

[0006] Generally, in the switched capacitor method, the non-grip measurement value increases in this order: the non-grip measurement value, the gloved measurement value, and the bare hand measurement value. Furthermore, the non-grip measurement value and the gloved measurement value are close to each other, while the bare hand measurement value is significantly different from the non-grip measurement value and the gloved measurement value. That is, in the case of bare hand gripping, the measurement time is longer than in the case of non-gripping or gripping with gloves, and there is a problem that the sensor cannot respond during such a long measurement time, resulting in a lack of responsiveness.

[0007] This problem can be solved by increasing the current used for charging and shortening the measurement time. However, since the non-gloved and gloved measurements are close to each other, increasing the current will bring the non-gloved and gloved measurements closer together, making accurate discrimination more difficult.

[0008] Patent Document 1 does not devise a solution to such a problem and is unable to solve it.

[0009] The present invention has been made in consideration of the above circumstances, and its purpose is to provide a grip detection device and a computer program that can simultaneously improve the speed of determining whether an object is being gripped or not and the accuracy of such determination. [Means for solving the problem]

[0010] The grip detection device of the present invention is a grip detection device that detects gripping of a rim portion by passing an electric current through an electrode provided on the rim portion, and performs the grip detection using two modes that use different electric currents for the grip detection.

[0011] The computer program of the present invention causes a computer that performs grip detection of the rim portion by passing an electric current through an electrode provided on the rim portion to execute a process of performing the grip detection using two modes that use different electric currents for the grip detection.

[0012] In the present invention, when the grip detection is performed, one of the two modes is appropriately selected and grip detection is performed in that mode, thereby improving both the speed and accuracy of the determination of grip / non-grip. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a grip detection device and a computer program that can simultaneously improve the speed of determining whether an object is being gripped or not and the accuracy of such determination. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a block diagram showing an example of the configuration of a steering wheel device according to an embodiment of the present invention; [Figure 2] 1 is a front view of a steering wheel of a steering wheel device according to an embodiment of the present invention; [Figure 3] 3 is an explanatory diagram for explaining detection of capacitance by a capacitance measuring circuit of the steering wheel device; FIG. [Figure 4] 4 is an equivalent circuit corresponding to FIG. [Figure 5] FIG. 2 is a block diagram showing the configuration of a control unit of the steering wheel device according to the present embodiment. [Figure 6] 10 is a graph illustrating the required time T in the first mode and the second mode. [Figure 7] 5 is a flowchart illustrating a grip detection process in the steering wheel device according to the present embodiment. [Figure 8] 5 is a flowchart illustrating a grip detection process in the steering wheel device according to the present embodiment. [Figure 9] 10A and 10B are diagrams illustrating a modified example of the grip detection process in the steering wheel device according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, a grip detection device according to an embodiment of the present invention will be described in detail with reference to the drawings.

[0016] 1 is a block diagram showing an example of the configuration of a steering wheel device 100 according to this embodiment. The steering wheel device 100 includes a steering wheel 2 and a grip detection ECU (Electronic Control Unit) 1. The grip detection ECU 1 (grip detection device) is communicatively connected to in-vehicle devices such as a driving assistance ECU 3 via an in-vehicle network provided in the vehicle.

[0017] 2 is a front view of the steering wheel 2 of the steering wheel device 100 according to this embodiment. The steering wheel 2 includes a sensor electrode 21, which is provided inside the rim portion 10.

[0018] The grip detection ECU 1 performs grip detection. Specifically, it determines whether the steering wheel 2 (rim portion 10) is in a gripped state or an un-grip state based on the capacitance coupled to the sensor electrode 21. Here, the gripped state is a state in which the driver is gripping the steering wheel 2, and the un-grip state is a state in which the driver is not gripping the steering wheel 2 and has let go. The grip detection ECU 1 also determines whether an abnormality has occurred.

[0019] The grip detection ECU 1 includes a control unit 11 (grip detection unit), a storage unit 12, a communication unit 13, and a capacitance measurement circuit .

[0020] The storage unit 12 includes memory elements such as RAM (Random Access Memory) and ROM (Read Only Memory), and stores programs, data, etc. required for the control unit 11 to execute processes such as grip detection. The storage unit 12 also temporarily stores data, etc. required for the control unit 11 to execute processes. The storage unit 12 also stores thresholds 121 used for grip detection. The thresholds 121 include thresholds TS1 and TS2 used for grip determination, which will be described later, and a threshold TS3 used for abnormality determination, which will be described later.

[0021] The communication unit 13 is a communication interface for transmitting and receiving information to and from other in-vehicle devices via an in-vehicle network. The communication unit 13 is connected to a communication line (LAN) provided in the vehicle, and transmits and receives information to and from the driving assistance ECU 3, etc. The communication unit 13 transmits the result of the grip determination by the control unit 11 to the driving assistance ECU 3.

[0022] The driving assistance ECU 3 is an ECU that executes processing related to the advanced driving assistance system. The driving assistance ECU 3 receives a signal indicating the result of the grip determination by the control unit 11 via the communication unit 13, and executes predetermined processing related to the advanced driving assistance system according to the result of the grip determination. For example, during autonomous driving, if the control unit 11 receives a grip determination result indicating that the steering wheel 2 is not gripped, the driving assistance ECU 3 terminates the autonomous driving. Note that the processing of the driving assistance ECU 3 is not limited to autonomous driving, and may be, for example, lane keep assist, parking assist, etc.

[0023] The capacitance measuring circuit 14 is connected to the sensor electrode 21 and is an electric circuit for detecting the capacitance coupled to the sensor electrode 21. The capacitance measuring circuit 14 can detect the capacitance between the sensor electrode 21 and the vehicle ground GND (see FIG. 3).

[0024] Fig. 3 is an explanatory diagram for explaining the detection of capacitance by the capacitance measuring circuit 14 of the steering wheel device 100. For convenience, the timing unit 142 is not shown in Fig. 3. The sensor electrode 21 is interposed between the covering layer 22 of the steering wheel 2 and the urethane layer 23 that covers the core metal (not shown).

[0025] As described above, the capacitance measuring circuit 14 is connected to the sensor electrode 21 of the steering wheel 2. The reference of the capacitance measuring circuit 14 is the vehicle ground GND. The driver is not directly connected to the vehicle ground GND, but is capacitively coupled to it.

[0026] Figure 4 is an equivalent circuit corresponding to Figure 3. In Figure 4, Ch is the capacitance of the driver, and Cl is the capacitance formed by the driver's hand 200 and the sensor electrode 21. That is, the capacitance measurement circuit 14 is connected to the ground GND via the capacitance Cl and the capacitance Ch.

[0027] At this time, the detected capacitance (combined capacitance) Cm is "(Cl × Ch) / (Cl + Ch)". Generally, since Cl << Ch, the detected capacitance Cm is approximately equivalent to the capacitance Cl. The capacitance Ch has almost no influence on the capacitance Cm, and the capacitance Cm depends on the capacitance Cl.

[0028] When the steering wheel 2 is in the non-gripped state, the sensor electrode 21 is capacitively coupled electrically to the vehicle ground GND via the air in the vehicle interior. When the steering wheel 2 is in the gripped state, that is, when the driver's hand 200 is in contact with the rim portion 10, by approaching the driver's hand 200, the distance d between the sensor electrode 21 and the driver's hand 200 becomes shorter, and the sensor electrode 21 is capacitively coupled to the driver's body. When the sensor electrode 21 is capacitively coupled to GND, that is, in the non-gripped state, due to the capacitive coupling with the ground plane, the capacitance becomes very small.

[0029] Also, the capacitance Cl varies depending on the distance d and is inversely proportional to the distance d. When gripping the steering wheel 2 while wearing gloves compared to when gripping it with bare hands, the distance d increases, so the capacitance Cl becomes smaller.

[0030] [[ID=IS]] That is, the capacitance Cm is the smallest in the non-gripped case and the largest in the case of gripping with bare hands. When gripping while wearing gloves, the capacitance Cm is larger than in the non-gripped case and smaller than in the case of gripping with bare hands.

[0031] On the other hand, the capacitance measurement circuit 14 detects the capacitance coupled to the sensor electrode 21 by a so-called switched capacitor method. In the switched capacitor method, a current is passed through the capacitance Cl connected to the sensor electrode 21 to charge it, and charging stops when the electrode voltage of the sensor electrode 21 reaches the target voltage. The rate at which the voltage rises (required time) is related to the current (amount) used for charging and the capacitance, and can be expressed by the formula "T = (Ce × Ve) / Ic." Here, Ce is the capacitance, Ve is the target voltage, T is the time required to reach the target voltage Ve, and Ic is the current. From this equation, the required time T is proportional to the capacitance Ce, and since the current Ic and the target voltage Ve are known, the capacitance Ce can be calculated by measuring the required time T using a timer 142 described below.

[0032] As described above, when gripping with gloves, the capacitance Cm is larger than when not gripping and smaller than when gripping with bare hands, so the time T required when gripping with gloves is larger than when not gripping and smaller than when gripping with bare hands. In other words, the relationship is "time T required when not gripping < time T required when gripping with gloves < time T required when gripping with bare hands."

[0033] The capacitance measurement circuit 14 measures the capacitance in two modes in which the magnitude of the current Ic flowing through the capacitance Cl (sensor electrode 21) differs. The two modes include a first mode in which a first current is used as the current Ic, and a second mode in which a second current larger than the first current is used. As will be described later, in the first mode, a gripping determination is made as to whether the state is gripped or not, and in the second mode, an abnormality determination is made as to whether an abnormality has occurred.

[0034] The capacitance measurement circuit 14 has a current control unit 141. The current control unit 141 controls the magnitude of the current Ic when measuring the capacitance using the switched capacitor method. Specifically, the current control unit 141 outputs the first current in the first mode and outputs the second current in the second mode.

[0035] Furthermore, the capacitance measuring circuit 14 has a timer 142. When detecting capacitance using the switched capacitor method, the timer 142 measures the required time T in the first mode and the second mode. The required time T may be expressed as a time, a counter number, or a frequency. Furthermore, the timer 142 measures the elapsed time Tm from when the current starts to flow in the first mode and the second mode. The results of the timing by the timer 142 (required time T, elapsed time Tm) are sent to the control unit 11.

[0036] FIG. 5 is a block diagram showing the configuration of the control unit 11 of the steering wheel device 100 according to this embodiment. The control unit 11 includes an arithmetic processing unit (not shown), such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). The control unit 11 performs various information processing or control processing related to the grip detection ECU 1. As described above, the control unit 11 determines whether the steering wheel 2 is in a gripped state or an ungripped state based on the capacitance coupled to the sensor electrode 21 (hereinafter referred to as grip determination). The control unit 11 also determines whether an abnormality has occurred that prevents the grip determination from being performed normally (hereinafter referred to as abnormality determination).

[0037] The control unit 11 has a grip determination unit 111, a switching unit 112, a stop determination unit 113, an abnormality determination unit 114, and a counting unit 115. The grip determination unit 111, the switching unit 112, the stop determination unit 113, the abnormality determination unit 114, and the counting unit 115 may be configured by hardware logic, or may be constructed by software by the CPU executing a predetermined program.

[0038] The grip determination unit 111 performs grip determination based on the required time T. In the first mode, the grip determination unit 111 determines the non-gripping state and the gripping state using a threshold value TS1. The threshold value TS1 is between the required time T1 corresponding to the non-gripping state and the required time T2 (first required time) corresponding to the gripping state while wearing gloves (see FIG. 6). The required times T1 and T2 can be obtained by experimentation or the like.

[0039] The switching unit 112 switches between the first mode and the second mode based on the elapsed time Tm obtained from the timer unit 142. For example, the switching unit 112 switches the mode based on the decision of the cancellation decision unit 113, and also switches the mode based on the decision of the abnormality determination unit 114.

[0040] The cancellation determination unit 113 determines to cancel the grip determination based on the elapsed time Tm. When the elapsed time Tm is equal to or greater than TS2 (first threshold) in the first mode, the cancellation determination unit 113 determines to cancel the grip determination. The threshold TS2 is between the required time T2 and the required time T3 (second required time) corresponding to gripping with bare hands (see FIG. 6A). The required time T3 can be obtained by experiment or the like. Based on the determination of the cancellation determination unit 113, the switching unit 112 switches from the first mode to the second mode.

[0041] The abnormality determination unit 114 determines whether an abnormality has occurred. When the cancellation determination unit 113 determines that the grip determination is to be cancelled, the abnormality determination unit 114 performs the abnormality determination. That is, the abnormality determination unit 114 performs the abnormality determination by comparing the elapsed time Tm after switching to the second mode with a threshold value TS3 (second threshold value). The threshold value TS3 is a time longer than the required time T4 (third required time) corresponding to gripping with a bare hand in the second mode (see FIG. 6B). The required time T4 can be obtained by experiment or the like. The switching unit 112 switches from the second mode to the first mode based on the determination result of the abnormality determination unit 114.

[0042] The counting unit 115 counts the number of times that the cancellation of the grip determination is decided by the cancellation deciding unit 113. When the cancellation deciding unit 113 decides to cancel multiple times, the switching unit 112 switches from the first mode to the second mode.

[0043] As shown in Fig. 2, the steering wheel 2 includes a circular rim portion 10 and a hub portion 4 located in the center of the rim portion 10. The hub portion 4 houses, for example, an airbag (not shown).

[0044] The rim portion 10 is covered with a covering layer 22 such as leather, and the hub portion 4 and spokes 3 are covered with, for example, a resin material. Sensor electrodes 21 are provided on the inside of the rim portion 10 along the circumferential direction of the rim portion 10. The rim portion 10 is divided into three equal parts in the circumferential direction, and a sensor electrode 21 is provided inside each of these parts. The number of sensor electrodes 21 is not limited to three, and may be two or less, or four or more.

[0045] In the following, an example in which the rim portion 10 has a circular ring shape will be described, but the present invention is not limited to this. The rim portion 10 may also have a non-circular shape (for example, a D-shape or a C-shape).

[0046] The hub portion 4 is connected to the rim portion 10 by three spokes 3. In other words, if the top and bottom positions are the 12 o'clock and 6 o'clock directions and the left and right positions are the 9 o'clock and 3 o'clock directions in the circumferential direction of the rim portion 10, just like a clock, the spokes 3 are located at the 3 o'clock, 6 o'clock, and 9 o'clock positions clockwise.

[0047] Of the three spoke parts 3, for example, the resin parts of the spoke part 3 at the 9 o'clock position and the spoke part 3 at the 3 o'clock position are each provided with an operation panel 20 having multiple operation buttons so that the driver can operate on-board devices such as audio while driving.

[0048] On the other hand, from the formula "capacitance Cm = (Cl × Ch) / (Cl + Ch)", when the coating layer 22 is very thin or conductive, Cl >> Ch, so "capacitance Cm = Ch". Also, when the driver grips the sensor with his bare hands, Cl does not exist, so "capacitance Cm = Ch". However, when gripping with gloves on, a small Cl is formed due to the thickness of the gloves, so "capacitance Cm = Cl".

[0049] Therefore, in order to improve the accuracy of the grasp judgment, it is necessary to consider not only grasping with bare hands but also grasping with gloves, and to configure the device to be able to handle the cases where "capacitance Cm = Cl" and "capacitance Cm = Ch."

[0050] However, when detecting capacitance Cm using the switched capacitor method, as mentioned above, the required time T is proportional to capacitance Ce, so when capacitance Cm=Ch, i.e., when the driver holds it with his bare hands, there is a problem that the required time T becomes long.

[0051] 6A and 6B are graphs illustrating the required time T in the first and second modes. Fig. 6A shows the first mode, and Fig. 6B shows the second mode. In Fig. 6A and Fig. 6B, the vertical axis represents the electrode voltage, and the horizontal axis represents the elapsed time Tm.

[0052] As shown in FIG. 6A, the time interval between the time required for gripping with gloves T2 and the time required for gripping with bare hands T3 is much larger than the time interval between the time required for non-gripping T1 and the time required for gripping with gloves T2.

[0053] In this way, when the driver grips the device with his bare hands, it takes time to make a grip determination, and the grip determination result is not obtained until the required time T3, resulting in a lack of responsiveness. This also affects other processes that use the grip determination result.

[0054] One possible approach to address this problem is to increase the magnitude of the current Ic flowing through the capacitance Cl to shorten the required time T. However, when the magnitude of the current Ic is increased, as shown in Fig. 6B, although the required time T4 corresponding to grasping with a bare hand is shortened, the time interval between the required time T1' corresponding to non-grasping and the required time T2' corresponding to grasping with gloves becomes shorter, which may result in an erroneous grasp determination.

[0055] The steering wheel device 100 according to this embodiment is configured to address such problems, as will be explained in detail below.

[0056] Fig. 7 is a flowchart illustrating the grip detection process in the steering wheel device 100 according to this embodiment. Fig. 7 shows the case of grip detection in the first mode.

[0057] For example, in response to transmission of an ignition signal, the control unit 11 selects the first mode as the mode used for detecting capacitance (step S101), and instructs the capacitance measuring circuit 14 to detect capacitance in the first mode.

[0058] In response to an instruction from the control unit 11, the capacitance measurement circuit 14 passes a first current through the sensor electrode 21 (capacitance Cl) (step S102). Then, the timing unit 142 starts timing (step S103). At this time, the counting unit 115 assigns 1 to "N," which indicates the number of times the cancellation decision unit 113 has decided to cancel the grip determination, and stores the result in the storage unit 12.

[0059] Immediately after starting the time measurement, the control unit 11 determines whether or not there has been a notification indicating the required time T from the capacitance measurement circuit 14 (step S104). For example, such a notification is an interrupt signal that the capacitance measurement circuit 14 sends to the control unit 11 when the target voltage Ve is reached after the current has flowed.

[0060] If the control unit 11 determines that a notification indicating the required time T has been received (step S104: YES), that is, if the required time T has been sent from the capacitance measurement circuit 14, the grip determination unit 111 determines whether the required time T is shorter than the threshold value TS1 (step S105).

[0061] If the grip determination unit 111 determines that the transmitted required time T is shorter than the threshold value TS1 (step S105: YES), it determines that the state is a non-gripped state (step S108). Thereafter, the processing proceeds to step S107. If the grip determination unit 111 determines that the transmitted required time T is not shorter than the threshold value TS1 (step S105: NO), that is, if the transmitted required time T is longer than the threshold value TS1, it determines that the state is a gripped state (step S106).

[0062] After the grasping determination unit 111 determines that the object is in a grasping state or a non-grasping state, the control unit 11 determines whether a predetermined time has elapsed since the start of timing based on the timing result of the timing unit 142 (step S107).

[0063] If the control unit 11 determines that the predetermined time has not elapsed since the start of timekeeping (step S107: NO), it repeats this determination. If the control unit 11 determines that the predetermined time has elapsed since the start of timekeeping (step S107: YES), the process returns to step S102.

[0064] On the other hand, if the control unit 11 determines in step S104 that there has been no notification indicating the required time T (step S104: NO), that is, if the required time T has not been sent from the capacity measurement circuit 14, it obtains the elapsed time Tm from the start of timing to the present time from the timing unit 142 and determines whether the elapsed time Tm is longer than or equal to the threshold value TS2 (step S109).

[0065] If the control unit 11 determines that the elapsed time Tm up to the present time is not longer than the threshold value TS2 (step S109: NO), that is, if the elapsed time Tm up to the present time is shorter than the threshold value TS2, the process returns to step S104. Also, if the control unit 11 determines that the elapsed time Tm up to the present time is longer than the threshold value TS2 (step S109: YES), the cancellation determination unit 113 decides to cancel the grip determination (step S110).

[0066] Next, control unit 11 determines whether "N" is greater than 2 by referring to the contents stored in memory unit 12 (step S111). At this time, since 1 has been assigned to "N" stored in memory unit 12, control unit 11 determines that "N" is not greater than 2 (step S111: NO), and counting unit 115 assigns "N+1" to "N" and stores it in memory unit 12 (step S114). Thereafter, the process returns to step S102.

[0067] Furthermore, if the control unit 11 determines that "N" is greater than 2 (step S111: YES), that is, if the number of times the cancellation decision unit 113 decides to cancel the grasping judgment is three or more times, the grasping judgment unit 111 determines that the grasping state is present (step S112), the grasping judgment is canceled, and the switching unit 112 switches the mode from the first mode to the second mode (step S113).

[0068] As described above, in the first mode using a relatively small current, it takes time to determine whether the driver is gripping the steering wheel 2 with his bare hands. In this regard, if the elapsed time Tm up to the current point in time is equal to or greater than the threshold value TS2, there is a possibility that the driver is gripping the steering wheel 2 with his bare hands, and therefore, before the mode is switched by the switching unit 112, the grip determination unit 111 determines that the driver is in a gripping state (see step S112). After this, the first mode is interrupted and the second mode continues.

[0069] Fig. 8 is a flowchart illustrating the grip detection process in the steering wheel device 100 according to this embodiment. Fig. 8 shows the case of grip detection in the second mode.

[0070] After switching from the first mode to the second mode, the current control unit 141 of the capacitance measurement circuit 14 changes the current used from the first current to a larger second current. The second current flows through the sensor electrode 21 (capacitance Cl) (step S201). Then, the timer unit 142 starts timing (step S202).

[0071] Immediately after starting the time measurement, the control unit 11 determines whether or not a notification indicating the required time T has been received from the capacitance measurement circuit 14 (step S203). As described above, the notification is an interrupt signal that the capacitance measurement circuit 14 sends to the control unit 11 when the target voltage Ve is reached after the current has flowed.

[0072] If the control unit 11 determines that a notification indicating the required time T has been received (step S203: YES), that is, if the required time T has been sent from the capacitance measuring circuit 14, the switching unit 112 switches the mode from the current second mode to the first mode (step S204). After this, the process ends.

[0073] As described above, it takes time to determine whether the driver is holding the steering wheel 2 with his bare hands. However, if it takes time to determine whether the driver is holding the steering wheel 2 with his bare hands, it may be that the driver is holding the steering wheel 2 with his bare hands, or that a malfunction (abnormality) has occurred due to some reason.

[0074] Therefore, when a notification indicating the required time T is received, it is clear that the reason for the long time required for the grasping determination is not a malfunction but grasping with bare hands, so the mode is switched from the current second mode to the first mode. Furthermore, since the grasping state has already been determined before switching to the second mode (see step S112), accurate grasping determination is performed early on.

[0075] Furthermore, in step S203, if the control unit 11 determines that there has been no notification indicating the required time T (step S203: NO), the abnormality determination unit 114 performs an abnormality determination as to whether or not an abnormality has occurred.

[0076] That is, the abnormality determination unit 114 acquires the elapsed time Tm from the start of timekeeping to the present time from the timekeeping unit 142, and determines whether the elapsed time Tm is shorter than the threshold value TS3 (step S205).

[0077] If the abnormality determination unit 114 determines that the elapsed time Tm up to the present time is shorter than the threshold value TS3 (step S205: YES), the process returns to step S203. On the other hand, if the abnormality determination unit 114 determines that the elapsed time Tm up to the present time is not shorter than the threshold value TS3 (step S205: NO), that is, if the elapsed time Tm up to the present time is longer than or equal to the threshold value TS3, it determines that an abnormality has occurred (step S206).

[0078] That is, as described above, the threshold value TS3 is longer than the required time T4 corresponding to grasping with bare hands in the second mode (see Figure 6B), so if the elapsed time Tm up to the present time is longer than the threshold value TS3, it is clear that the reason it takes so long to determine the grasp is a malfunction.

[0079] In this way, when it is determined by the abnormality determination unit 114 that an abnormality has occurred, the control unit 11 stops the grip determination (step S207). When the grip determination is stopped, the control unit 11 may be configured to notify the driver of this.

[0080] As described above, in the steering wheel device 100 according to this embodiment, grip determination is performed in the first mode using the first current smaller than the second current, and abnormality determination is performed in the second mode using the second current larger than the first current. That is, by using a smaller current, grip determination is performed in the first mode, which makes it possible to accurately distinguish between a non-grip case (required time T1) and a grip with gloves (required time T2). On the other hand, by using a larger current, abnormality determination is performed in the second mode, which makes it possible to quickly confirm gripping with a bare hand. As a result, the steering wheel device 100 according to this embodiment can achieve both improved grip determination speed and improved grip determination accuracy in grip detection.

[0081] Furthermore, in the steering wheel device 100 according to this embodiment, as described above, if the cancellation decision unit 113 makes multiple cancellation decisions, the mode is switched from the first mode to the second mode, thereby improving the responsiveness of the grip determination. In reality, the determination (result) of a non-grasping state is not made in the second mode, but only in the first mode. Therefore, by configuring the system so that switching from the first mode to the second mode is only performed when there are multiple cancellation decisions, the number of first mode, i.e., gripping determinations, can be increased, thereby making it possible to speed up the response to the gripping determination.

[0082] However, the present invention is not limited to this. It may be configured so that switching from the first mode to the second mode is performed even if the number of times the cancellation decision unit 113 decides to cancel is one. In this case, the number of times abnormality determination is performed in the second mode increases, thereby shortening the time until an abnormality is detected.

[0083] Although the above description has been given with reference to an example in which the current control unit 141 controls the first current and the second current, the present invention is not limited to this. For example, a variable resistance element may be provided in the circuit, and the first current and the second current may be adjusted by controlling the variable resistance element.

[0084] (Variation) The present invention is not limited to the above description, and can also be applied to an impedance measurement method.

[0085] 9 is a diagram illustrating a modified example of the grip detection process in the steering wheel device 100 according to the present embodiment. In the impedance measurement method according to the modified example, a sine wave is applied to the capacitive component (steering wheel 2), and the amount of current flowing into the sensor electrode 21 is measured and converted into a capacitance value. In the impedance measurement method according to the modified example, the mode is switched by manipulating the gain of the current / capacitance conversion unit. Hereinafter, the mode equivalent to the above-described first mode will be referred to as the first-equivalent mode, and the mode equivalent to the second mode will be referred to as the second-equivalent mode.

[0086] In the steering wheel device 100 according to the modified example, a grip detection ECU 1 is also connected to the steering wheel 2. The steering wheel 2 has a sensor electrode 21, a covering layer 22, and a urethane layer 23 that covers a core metal, and the sensor electrode 21 is interposed between the covering layer 22 and the urethane layer 23.

[0087] The grip detection ECU 1 includes a gain switching unit 141A, a signal generating circuit 14A, a control unit 11A, and a current measuring unit 15.

[0088] The current measuring unit 15 measures the current value by amplifying the current flowing through the sensor electrode 21 of the steering wheel 2. The current measuring unit 15 outputs the measured current value to the control unit 11A.

[0089] The gain switching unit 141A switches the gain related to the amplification of current in the current measurement unit 15. That is, the gain switching unit 141A switches the gain depending on whether the mode is the first equivalent mode or the second equivalent mode. For example, when switching from the first equivalent mode to the second equivalent mode is performed, the gain switching unit 141A reduces the gain. In other words, the gain switching unit 141A makes the gain in the first equivalent mode (hereinafter referred to as large gain) larger than the gain in the second equivalent mode (hereinafter referred to as small gain). The gain switching unit 141A corresponds to the current control unit 141 described above.

[0090] The signal generating circuit 14A applies a sinusoidal voltage to the steering wheel 2.

[0091] The control unit 11A performs the above-mentioned grip detection (grip determination and abnormality determination) in accordance with the output (measurement result) from the current measurement unit 15. That is, the control unit 11A corresponds to the control unit 11 described above.

[0092] As described above, the steering wheel device 100 according to the modified example is set to the large gain mode in the first equivalent mode, so that small current values ​​can be monitored in detail. That is, in the first-equivalent mode, a predetermined threshold value corresponding to the threshold value TS1 described above is used to determine whether the object is gripped or not. Furthermore, in the first-equivalent mode, if the object is gripped with a bare hand, the gain exceeds the tolerance level of the current measurement unit 15, causing clipping. That is, the output signal output to the control unit 11A is inaccurate, and the control unit 11A is unable to accurately detect gripping. Here, the tolerance level of the current measurement unit 15 corresponds to the threshold value TS2 described above. This state in which clipping occurs can be considered to be the same as the state in the switched-capacitor method in which the elapsed time Tm reaches the threshold value TS2 in the first mode and it is decided to stop gripping determination.

[0093] As described above, when clipping of the current measuring unit 15 occurs in the first equivalent mode, the control unit 11A switches from the first equivalent mode to the second equivalent mode. In response to this, the gain switching unit 141A switches from the current large gain to the small gain. Thereafter, grip detection is performed in the small gain mode, i.e., the second equivalent mode, and large current values ​​can be monitored.

[0094] In the second equivalent mode, an abnormality is determined using a predetermined threshold value equivalent to the threshold value TS3 described above. That is, in the second equivalent mode, even if the device is gripped with a bare hand, clipping of the current measuring unit 15 does not occur, so it is easy to determine whether an abnormality has occurred or whether the device is being gripped with a bare hand. [Explanation of symbols]

[0095] 1 Grasp detection ECU 2 steering wheels 10 Rim 11, 11A Control unit (grasp detection unit) 12 Storage section 13 Communications Department 14 Capacitance measurement circuit 14A signal generation circuit 15 Current measurement section 21 Sensor electrode 100 Steering wheel device 111 Grip determination unit 112 Switching section 113 Cancellation Decision Section 114 Abnormality determination section 115 Counting Department 121 Threshold 141 Current control section 141A Gain switching section 142 Timing section

Claims

1. A grip detection device (1) that detects gripping of a rim portion (10) by passing a current through an electrode (21) provided on the rim portion (10), A grip detection device (1) that performs grip detection using two modes with different currents related to the grip detection.

2. The two modes differ in the current flowing through the electrode (21), A grip detection unit (11) that performs grip detection in the two modes; a switching unit (112) that switches modes based on the elapsed time since the current started to flow; The grip detection device (1) according to claim 1, comprising:

3. The gripping detection device (1) according to claim 2, wherein the two modes include a first mode in which a first current flows and a gripping determination is made as to whether the object is gripped or not, and a second mode in which a second current greater than the first current flows and an abnormality determination is made as to whether an abnormality has occurred.

4. A stop determination unit (113) that determines to stop the grip determination when the elapsed time is equal to or greater than a first threshold value in the first mode, The grip detection device (1) according to claim 3, wherein the switching unit (112) switches from the first mode to the second mode based on a decision made by the cancellation decision unit (113).

5. The gripping determination is performed based on the time required for the electrode voltage to reach a predetermined voltage, The grip detection device (1) according to claim 4, wherein the first threshold value is between a first required time when gripping with gloves and a second required time when gripping with bare hands.

6. When the cancellation decision unit (113) decides to cancel the grasping determination, the grasping detection unit (11) determines that the object is being grasped, The grip detection device (1) according to claim 4, wherein the switching unit (112) switches from the first mode to the second mode.

7. an abnormality determination unit (114) that performs the abnormality determination when it is determined that the grip determination is to be stopped; The grip detection device (1) according to claim 4 or 6, wherein the switching unit (112) switches from the second mode to the first mode based on a determination result of the abnormality determination unit (114).

8. The abnormality determination unit (114) determines that an abnormality has occurred when the elapsed time in the second mode is longer than a second threshold value, The grip detection device (1) according to claim 7, wherein the second threshold value is longer than a third time required for gripping with a bare hand in the second mode.

9. The grip detection device (1) according to claim 8, wherein the switching unit (112) switches from the second mode to the first mode when a notification is received indicating that the electrode voltage has reached a predetermined voltage within the second threshold.

10. The grip detection device (1) according to claim 4, 6, 7, 8 or 9, wherein the switching unit (112) performs the switching when the number of times the cancellation decision is made by the cancellation decision unit (113) is plural.

11. a current measuring unit (15) for measuring the current of the electrode (21); The two modes differ in the magnitude of the gain in the current measurement unit (15), A grip detection unit (11) that performs grip detection in the two modes; a switching unit (112) that switches modes based on the current value measured by the current measuring unit (15); The grip detection device (1) according to claim 1, comprising:

12. A computer (11) that detects gripping of the rim portion (10) by passing a current through an electrode (21) provided on the rim portion (10), The grip detection is performed using two modes in which the current related to the grip detection is different. A computer program for executing a process.

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