Sensor device

Abstract

The present invention provides a sensor device capable of detecting disconnection of a sensor electrode.　The sensor device comprises: a sensor electrode; a drive circuit that outputs, to the sensor electrode, a drive signal which includes an alternating current component; an electrostatic detection circuit that detects capacitance between the sensor electrode and an object, and a resistive component of the sensor electrode; a first resistor that is inserted in series on a first line which connects a first part of the sensor electrode and the electrostatic detection circuit; and a second resistor that is inserted in series on a second line which connects a second part of the sensor electrode and the electrostatic detection circuit.

Description

Sensor Device

[0001] The present disclosure relates to a sensor device.

[0002] A conventional capacitance detection device detects capacitance between a detection electrode arranged close to a shield electrode and an object, and includes an AC voltage output unit that outputs an AC voltage to the shield electrode via a plurality of first wirings; a first detection signal generation unit that has a plurality of detection nodes connected one-to-one to the detection electrodes via a plurality of second wirings arranged close to the first wirings, and supplies electric charge from the detection nodes to the detection electrodes via the second wirings so that the voltage of the detection nodes oscillates in accordance with the AC voltage, and generates a plurality of first detection signals in accordance with the electric charge supplied from each of the plurality of detection nodes; a plurality of first filters provided on a plurality of first paths that branch from an AC output node to which the AC voltage output unit outputs the AC voltage to each of the plurality of first wirings; and at least one phase difference signal generation unit that generates a phase difference signal in accordance with the phase difference between one of the first detection signals and the AC voltage (see, for example, Patent Document 1).

[0003] International Publication No. 2022 / 074963

[0004] Conventional capacitance detection devices (sensor devices) can determine when a portion of a plurality of first wirings connected to a shield electrode is broken, but they do not detect when a detection electrode (sensor electrode) is broken.

[0005] Therefore, an object of the present invention is to provide a sensor device that can detect disconnection of a sensor electrode.

[0006] A sensor device according to an embodiment of the present disclosure includes a sensor electrode, a drive circuit that outputs a drive signal including an AC component to the sensor electrode, an electrostatic detection circuit that detects the resistance component of the sensor electrode as well as the capacitance between the sensor electrode and an object, a first resistor inserted in series into a first line connecting a first location of the sensor electrode to the electrostatic detection circuit, and a second resistor inserted in series into a second line connecting a second location of the sensor electrode to the electrostatic detection circuit.

[0007] A sensor device capable of detecting disconnection of a sensor electrode can be provided.

[0008] It is a figure which shows typically a steering wheel which mounts the sensor device of the embodiment. It is a figure which shows an example of a circuit configuration of the sensor device of the embodiment. It is a figure which shows an example of a circuit configuration around the sensor electrode of the sensor device of the embodiment. It is a figure which explains the failure judgment of the sensor electrode of the sensor device of the embodiment. It is a figure which shows an example of a circuit configuration of the sensor device by the modified example of the embodiment.

[0009] Hereinafter, an embodiment to which the sensor device of the present disclosure is applied will be described.

[0010] 1 is a diagram schematically illustrating a steering wheel 10 equipped with a sensor device 100 according to an embodiment. The sensor device 100 includes a sensor electrode 110, a heater driving circuit 120, an electrostatic detection circuit 130, and a control circuit 140. The control circuit 140 is an example of a control unit.

[0011] The steering wheel 10 is mounted on a vehicle, and a sensor electrode 110 of the sensor device 100 is mounted on the inside of the surface of the rim 11. The sensor electrode 110 can operate as a heating element. The sensor device 100 determines whether the driver's hand is in contact with the rim 11 of the steering wheel 10. The sensor device 100 also warms the steering wheel 10 by supplying power for heating to the sensor electrode 110. In other words, the sensor device 100 has both the functions of HOD (Hands On Detect) and a steering heater. A hand is an example of an object. The rim 11 of the steering wheel 10 is an example of a fixed part to which the sensor electrode 110 is fixed. The surface 11A of the rim 11 is an example of a contact part that can come into contact with a detection object.

[0012] Hereinafter, the driver of the vehicle will be referred to as the operator of the sensor device 100. The operator's touching the rim 11 of the steering wheel 10 on which the sensor electrode 110 is provided will be referred to as the operator's operation.

[0013] The steering wheel 10 has a rim 11, a hub 12, and spokes 13. The rim 11, hub 12, and spokes 13 shown in Figure 1 are core metal portions of the rim 11, hub 12, and spokes 13. In Figure 1, the surface 11A of the rim 11 is shown separated from the rim 11 in order to show the sensor electrode 110. Also, covers that cover the hub 12 and spokes 13 are omitted from Figure 1.

[0014] The ground terminal of the steering wheel 10 is electrically connected to a core metal that is provided around the entire circumference of the rim 11 of the steering wheel 10. By connecting the core metal to the ground terminals of the heater drive circuit 120, the electrostatic detection circuit 130, and the control circuit 140 via connectors (not shown), the ground potentials of the heater drive circuit 120, the electrostatic detection circuit 130, and the control circuit 140 become equal to the ground potential of the steering wheel 10.

[0015] <General Configuration of Sensor Device 100> The sensor device 100 includes, as its main components, a sensor electrode 110, a heater driving circuit 120, an electrostatic detection circuit 130, and a control circuit 140. The control circuit 140 may be an ECU (Electronic Control Unit). While Fig. 1 shows a simplified diagram of the connections among the sensor electrode 110, the heater driving circuit 120, the electrostatic detection circuit 130, and the control circuit 140, the control circuit 140 is also connected to the heater driving circuit 120 via cables, connectors, and the like (not shown).

[0016] The sensor device 100 has two modes: a heat generation mode in which power for generating heat is supplied from the vehicle power supply to the sensor electrode 110, and a non-heat generation mode in which no power for generating heat is supplied. The control circuit 140 switches the mode of the sensor device 100 in a time-division manner. That is, the control circuit 140 has times when the sensor device 100 is in the heat generation mode and times when the sensor device 100 is in the non-heat generation mode.

[0017] <Sensor Electrode 110> The sensor electrode 110 is provided around the rim 11 of the steering wheel 10 while being insulated from a core metal that is provided around the rim 11 of the steering wheel 10. The sensor electrode 110 is connected to the heater drive circuit 120, the electrostatic detection circuit 130, and the control circuit 140 via signal lines or the like. The sensor electrode 110 is a long, thin, sheet-like, strip-shaped electrode that is provided around the rim 11, and can be made, for example, by applying a conductor such as silver paste to the surface of a resin film. Alternatively, the sensor electrode 110 may be made of a metal cloth woven with metal threads or a conductive cloth made by plating a fiber cloth with a metal.

[0018] <Heater Drive Circuit 120> The heater drive circuit 120 is connected to the sensor electrode 110, and supplies power for heating to the sensor electrode 110 from the vehicle power supply in the heat generation mode.

[0019] <Electrostatic Detection Circuit 130> The electrostatic detection circuit 130 is connected to the sensor electrode 110, and detects the electrostatic capacitance between the sensor electrode 110 and the operator's hand.

[0020] <Control Circuit 140> The control circuit 140 is realized by a computer including a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), an input / output interface, an internal bus, etc. The control circuit 140 switches the mode of the sensor device 100 between a heat generation mode and a non-heat generation mode. In the heat generation mode, the control circuit 140 heats the sensor electrode 110 to warm the rim 11 of the steering wheel 10. In the non-heat generation mode, the control circuit 140 determines whether a hand is touching the rim 11 of the steering wheel 10 based on the output of the electrostatic detection circuit 130. Details of the control performed by the control circuit 140 in the non-heat generation mode and the heat generation mode will be described later.

[0021] <Circuit configuration of sensor device 100> Fig. 2 is a diagram showing an example of the circuit configuration of the sensor device 100. Fig. 2 shows a power supply V1 of the vehicle 1 on which the sensor device 100 is mounted. The power supply V1 is, for example, a battery of the vehicle 1. In Fig. 2, the power supply V1 is described as being a battery, but the power supply V1 may also include a generator, a regenerative device, or the like of the vehicle 1 in addition to the battery. The output voltage of the power supply V1 is V1.

[0022] 3 is used to illustrate the circuit configuration around the sensor electrode 110 of the sensor device 100. Fig. 3 is a diagram showing an example of the circuit configuration around the sensor electrode 110 of the sensor device 100, and is an enlarged view of the portion within the dashed-dotted rectangular frame shown in Fig. 2. The sensor electrode 110 is a thin, long, strip-shaped sheet electrode.

[0023] In addition to the sensor electrode 110, the heater driving circuit 120, the electrostatic detection circuit 130, and the control circuit 140, the sensor device 100 includes a first line 111, a second line 112, a first resistor R1, and a second resistor R2, as shown in FIG. 3.

[0024] The second resistor R2, the first line 111, and the second line 112 are provided to determine a fault in the sensor electrode 110. Determining a fault in the sensor electrode 110 means detecting a disconnection in the sensor electrode 110. The disconnection is not limited to a case where the sensor electrode 110 is completely separated between both ends in the longitudinal direction, but also includes a state where the sensor electrode 110 is partially separated in the lateral direction (width direction) and has a portion connecting the ends. In a normal state, one ends (on the input terminal 130A side) of the first resistor R1 and the second resistor R2 are connected to each other, and the other ends of the first resistor R1 and the second resistor R2 are connected to each other via the sensor electrode 110. When the sensor electrode 110 is completely separated between both ends in the longitudinal direction, the other ends of the first resistor R1 and the second resistor R2 are no longer connected to each other, and the resistance component on the sensor electrode 110 side as viewed from the input terminal 130A changes. Furthermore, if there is a part that is partially divided in the short direction (width direction) and connects both ends, the resistance component between the other ends of the first resistor R1 and the second resistor R2 becomes larger, and the resistance component on the sensor electrode 110 side as seen from the input terminal 130A changes.

[0025] <Sensor electrode 110 and surrounding circuits> The sensor electrode 110 is provided on the steering wheel 10. As shown in Fig. 3, the sensor electrode 110 has a first end 110A and a second end 110B. The first end 110A and the second end 110B are opposite ends in the longitudinal direction of the sensor electrode 110. The first end 110A is an example of a first location, and the second end 110B is an example of a second location.

[0026] 3, one end of a first line 111 is connected to the first end 110A, and one end of a second line 112 is connected to the second end 110B. The other ends of the first line 111 and the second line 112 are connected to an input terminal 130A of the electrostatic detection circuit 130.

[0027] The first line 111 and the second line 112 are wires connected to the first end 110A and the second end 110B, which are both ends of the sensor electrode 110, and form a loop circuit together with the sensor electrode 110.

[0028] A portion of the first line 111 between the first end 110A and the first resistor R1 is connected to a node 125 of the heater driving circuit 120 by a line branching off from the first line 111. In addition, the second end 110B of the sensor electrode 110 is connected to the drain of the low-side MOSFET 122 by a line branching off from the second line 112.

[0029] The first resistor R1 is inserted in series in the first line 111, and the second resistor R2 is inserted in series in the second line 112.

[0030] The parasitic capacitance between the sensor electrode 110 and the ground potential point is Crgl, and the parasitic capacitance between the hand H is Chg. The parasitic capacitance Chg changes significantly depending on whether the hand H is touching the sensor electrode 110. The parasitic capacitance between Crgl, the sensor electrode 110, and the ground potential point, and between the parasitic capacitance Chg, the sensor electrode 110, and the hand are shown by dashed lines because there are no wirings in these areas.

[0031] Note that, although the embodiment in which the first end 110A and the second end 110B are both ends of the sensor electrode 110 will be described here, the first end 110A and the second end 110B may be portions closer to the center in the longitudinal direction than both ends of the sensor electrode 110. However, the first end 110A and the second end 110B may be portions of the sensor electrode 110 that are different from each other.

[0032] <Heater driving circuit 120> The heater driving circuit 120 has a high-side MOSFET 121, a low-side MOSFET 122, a decoupling MOSFET 123, a resistor 124, and a node 125. The high-side MOSFET 121 is an example of a first switch, the low-side MOSFET 122 is an example of a second switch, and the decoupling MOSFET 123 is an example of a decoupling switch.

[0033] The high-side MOSFET 121, low-side MOSFET 122, and decoupling MOSFET 123 are configured as N-channel MOSFETs. N-channel MOSFETs have a smaller on-resistance than P-channel MOSFETs, and therefore have the advantage of making it easier to reduce power consumption. Note that Coss of the high-side MOSFET 121, low-side MOSFET 122, and decoupling MOSFET 123 is a schematic representation of parasitic capacitance.

[0034] The high-side MOSFET 121 has a drain connected to the power supply V1, a source connected to the source of the decoupling MOSFET 123, and a gate connected to the control circuit 140. The voltage V1 of the power supply V1 is supplied to the drain of the high-side MOSFET 121. The high-side MOSFET 121 is driven by a PWM gate drive signal supplied to its gate from the control circuit 140.

[0035] The low-side MOSFET 122 has a drain connected to the second end 110B of the sensor electrode 110, a source connected to a reference potential point (V2), and a gate connected to the control circuit 140. The reference potential point is the ground potential point, and the voltage of the reference potential point is V2 (GND). The low-side MOSFET 122 is provided between the sensor electrode 110 and the reference potential point, and is driven by a PWM gate drive signal supplied to its gate from the control circuit 140.

[0036] The decoupling MOSFET 123 is provided between the high-side MOSFET 121 and the first end 110A of the sensor electrode 110. The drain of the decoupling MOSFET 123 is connected to the node 125, the source is connected to the source of the high-side MOSFET 121, and the gate is connected to the control circuit 140. The point where the source of the decoupling MOSFET 123 and the source of the high-side MOSFET 121 are connected is a connection point 123A. The connection point 123A is the connection point between the high-side MOSFET 121 and the decoupling MOSFET 123. The decoupling MOSFET 123 is driven by a PWM gate drive signal supplied to its gate from the control circuit 140.

[0037] In the heat generation mode, the control circuit 140 sets the gate voltages of the high-side MOSFET 121, the decoupling MOSFET 123, and the low-side MOSFET 122 to an H (High) level, thereby turning the high-side MOSFET 121, the decoupling MOSFET 123, and the low-side MOSFET 122 on. When switching to the non-heat generation mode, the control circuit 140 first sets the gate voltages of the high-side MOSFET 121 and the decoupling MOSFET 123 to an L (Low) level, thereby turning the high-side MOSFET 121 and the decoupling MOSFET 123 off. Next, the control circuit 140 sets the gate voltage of the low-side MOSFET 122 to a L (Low) level, thereby turning the low-side MOSFET 122 off. When switching to the non-heat generation mode, a period of time is provided during which the high-side MOSFET 121 and the decoupling MOSFET 123 are off and the low-side MOSFET is on, thereby setting the potential of the sensor electrode 110 to the reference potential (GND) in the non-heat generation mode.

[0038] The gate drive signals that drive the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 are not limited to PWM signals. When the sensor electrode 110 is not to generate heat, each gate drive signal may be held at an L level. The body ECU may also adjust the temperature of the sensor electrode 110 (heating element) by changing the voltage of the power supply V1. In this case, the control circuit 140 may fix the time for which the gate drive signal is set to an H (High) level and the time for which it is set to an L (Low) level.

[0039] The resistor 124 is inserted in series with the line 123B connecting the node 123A and the reference potential point. The line 123B is connected to the source of the low-side MOSFET 122 on the reference potential side. The resistor 124 is a high-resistance resistor that can maintain the node 123A at the reference potential in the non-heat-generation mode. In the heat-generation mode, almost no current flows through the resistor 124, allowing current to flow from the high-side MOSFET 121 through a path passing through the decoupling MOSFET 123, the sensor electrode 110, and the low-side MOSFET 122, thereby generating heat in the sensor electrode 110. However, to reduce the power consumed by the resistor 124 in the heat-generation mode, the resistance value of the resistor 124 is set to greater than 1 kΩ. Furthermore, to shorten the time it takes for the voltage at the node 123A to reach V2 when switching to the non-heat-generation mode, the resistance value of the resistor 124 is set to less than 100 kΩ.

[0040] An N-channel MOSFET may be used instead of resistor 124. The drain of the MOSFET is connected to connection point 123A, the source is connected to a reference potential point, and the gate is connected to control circuit 140. A gate drive signal is supplied from control circuit 140 to the gate of this MOSFET, so that it is always open (off) in the heat generation mode and always conductive (on) in the non-heat generation mode.

[0041] Node 125 is a node between the drain of decoupling MOSFET 123 and the first end 110A of the sensor electrode 110. A voltage V3 is supplied to node 125. The voltage of node 125 is higher than the voltage of reference potential point V2. Node 125 is located between the drain of decoupling MOSFET 123, the first end 110A of the sensor electrode 110, and the input terminal 130A of the electrostatic detection circuit 130.

[0042] As an example, a voltage regulator that converts voltage V1 supplied from power supply V1 into voltage V3 may be connected to node 125. Voltage V3 is lower than voltage V1. Alternatively, voltage V1 may be converted into voltage V3 using a voltage divider resistor instead of the voltage regulator. A diode may be provided between the voltage regulator and node 125 to prevent backflow to the voltage regulator.

[0043] <Electrostatic Detection Circuit 130> The electrostatic detection circuit 130 includes a charge amplifier 131, an AC signal source 132, an amplitude adjustment circuit 133, a first ADC (Analog to Digital Converter) 134A, a second ADC 134B, a first multiplier 135A, a second multiplier 135B, a first phase adjustment circuit 136A, a second phase adjustment circuit 136B, a 90-degree delay circuit 137, a first LPF (Low Pass Filter) 137A, and a second LPF 138B. The electrostatic detection circuit 130 detects the electrostatic capacitance of the sensor electrode 110 using a self-capacitance method. The AC signal source 132 is an example of a drive circuit. The first multiplier 135A is an example of a first multiplier, and the second multiplier 135B is an example of a second multiplier. The first phase adjustment circuit 136A is an example of a first phase adjustment circuit. The 90-degree delay circuit 137 is an example of a phase changer and an example of a 90-degree delay circuit. The first LPF 138A is an example of a first low-pass filter, and the second LPF 138B is an example of a second low-pass filter.

[0044] The electrostatic detection circuit 130 detects electrostatic capacitance by self-capacitance, which can improve the sensitivity of the electrostatic capacitance at the sensor electrode 110. The electrostatic detection circuit 130 may detect the electrostatic capacitance by self-capacitance of the sensor electrode 110 only in the non-heat generation mode.

[0045] <Charge Amplifier 131> The charge amplifier 131 has a non-inverting input terminal (+) connected to the output terminal of the amplitude adjustment circuit 133, an inverting input terminal (-) connected to the first phase adjustment circuit 136A via a capacitor C1, and output terminals connected to the input terminals of the first ADC 134A and the second ADC 134B. The charge amplifier 131 is a differential amplifier that amplifies the difference between the input to the non-inverting input terminal (+) and the input to the inverting input terminal (-) to output an output signal. The first phase adjustment circuit 136A is connected to the first end 110A of the sensor electrode 110 via a first resistor R1. The first phase adjustment circuit 136A is also connected to the second end 110B of the sensor electrode 110 via a second resistor R2. The first phase adjustment circuit 136A matches the phase of the signal input to the inverting input terminal (-) of the charge amplifier 131 with the phase of the signal input to the non-inverting input terminal (+).

[0046] <AC Signal Source 132> The AC signal source 132 is connected to the amplitude adjustment circuit 133 and to the first end 110A of the sensor electrode 110 via a capacitor Crs and a first resistor R1. The AC signal source 132 outputs an AC signal (e.g., a sine wave signal) to drive the sensor electrode 110. The AC signal source 132 may stop outputting the AC signal in the heat generation mode. The AC signal is an example of a drive signal having an AC component. The AC signal output by the AC signal source 132 is input to the sensor electrode 110 via the first resistor R1 and the second resistor R2. The AC signal output by the AC signal source 132 is also input to the non-inverting input terminal (+) of the charge amplifier 131 via the amplitude adjustment circuit 133. In addition, the AC signal output by the AC signal source 132 is input to the first multiplication unit 135A via the second phase shift adjustment circuit 136B, and is also input to the second multiplication unit 135B via the second phase shift adjustment circuit 136B and the 90-degree delay circuit 137.

[0047] <Amplitude Adjustment Circuit 133> When the hand H, which is an object, is not present near the sensor electrode 110 (when the parasitic capacitance Crg is zero), the amplitude adjustment circuit 133 eliminates the difference between the inverting input terminal (-) and the non-inverting input terminal (+), and adjusts the amplitude so that the output voltage of the charge amplifier 131 becomes extremely small.

[0048] A DC isolation capacitor for blocking DC components may be inserted in series between the input terminal of the electrostatic detection circuit 130 and the branch point of the capacitors C1 and Crs.

[0049] <First ADC 134A> The first ADC 134A has an input terminal connected to the output terminal of the charge amplifier 131 and an output terminal connected to one of the input terminals of the first multiplication unit 135A. The first ADC 134A digitally converts the output of the charge amplifier 131 and outputs the digital signal to the first multiplication unit 135A.

[0050] <Second ADC 134B> The second ADC 134B has an input terminal connected to the output terminal of the charge amplifier 131 and an output terminal connected to one of the input terminals of the second multiplication unit 135B. The second ADC 134B digitally converts the output of the charge amplifier 131 and outputs the digital signal to the second multiplication unit 135B.

[0051] <First multiplication unit 135A> The first multiplication unit 135A has an input terminal connected to the output terminal of the first ADC 134A, an input terminal connected to the AC signal source 132 via the second phase adjustment circuit 136B, and an output terminal connected to the input terminal of the first LPF 138A. The first multiplication unit 135A multiplies the output of the first ADC 134A by the output of the second phase adjustment circuit 136B, and outputs the result to the first LPF 138A.

[0052] <Second multiplication unit 135B> The second multiplication unit 135B has an input terminal connected to the output terminal of the second ADC 134B, an input terminal connected to the AC signal source 132 via the 90-degree delay circuit 137 and the second phase adjustment circuit 136B, and an output terminal connected to the input terminal of the second LPF 138B. The second multiplication unit 135B multiplies the output of the second ADC 134B by the output (AC signal) of the AC signal source 132 whose phase has been delayed by the second phase adjustment circuit 136B and the 90-degree delay circuit 137, and outputs the result to the second LPF 138B.

[0053] <First Phase Adjustment Circuit 136A> One end of the first phase adjustment circuit 136 is connected to the first end 110A of the sensor electrode 110 via a first resistor R1 and to the second end 110B of the sensor electrode 110 via a second resistor R2. The other end of the first phase adjustment circuit 136A is connected to the inverting input terminal (-) of the charge amplifier 131 via a capacitor C1. The first phase adjustment circuit 136A imparts a first delay to the signal transmitted from the sensor electrode 110 and outputs the signal to the charge amplifier 131. The first delay is adjusted so that the output of the second LPF 138B is minimized when the sensor electrode 110 is in a normal state. The normal state of the sensor electrode 110 refers to a state in which the sensor electrode 110 is not damaged, such as broken or disconnected, and the impedance between the first end 110A and the second end 110B of the sensor electrode 110 is within a normal range.

[0054] <Second Phase Adjustment Circuit 136B> The second phase adjustment circuit 136B is provided between the AC signal source 132 and the first multiplication unit 135A and the 90-degree delay circuit 137. By adjusting the phase shift amount of the first phase adjustment circuit 136A and the phase shift amount of the second phase adjustment circuit 136B, when the sensor electrode 110 is in a normal state, the phase of the output of the charge amplifier 131 input to the first multiplication unit 135A and the phase of the output of the second phase adjustment circuit 136B are made to match.

[0055] <90-degree Delay Circuit 137> The 90-degree delay circuit 137 is provided between the second phase adjustment circuit 136B and the first and second multiplication units 135A and 135B. The 90-degree delay circuit 137 changes the second phase of the drive signal input from the second phase adjustment circuit 136B to the second multiplication unit 135B so that the second phase of the drive signal input from the second phase adjustment circuit 136B to the first multiplication unit 135A is delayed by 90 degrees relative to the first phase of the drive signal input from the second phase adjustment circuit 136B to the first multiplication unit 135A. Instead of the 90-degree delay circuit 137, a circuit that advances the phase by 90 degrees (or delays the phase by 270 degrees) may be provided between the second phase adjustment circuit 136B and the first multiplication unit 135A. In this case, too, the phase of the output of the charge amplifier 131 input to the first multiplication unit 135A is matched with the phase of the output of the second phase adjustment circuit 136B input to the first multiplication unit 135A via the circuit that advances the phase by 90 degrees.

[0056] <First LPF 138A> The first LPF 138A is provided in a subsequent stage of the first multiplication unit 135A. The input terminal of the first LPF 138A is connected to the output terminal of the first multiplication unit 135A, and the output terminal of the first LPF 138A is connected to the control circuit 140. The first LPF 138A removes high-frequency components from the output of the first multiplication unit 135A and outputs the output to the control circuit 140.

[0057] <Second LPF 138B> The second LPF 138B is provided at a stage subsequent to the second multiplication unit 135B. The second LPF 138B has the same cutoff frequency as the first LPF 138A. The input terminal of the second LPF 138B is connected to the output terminal of the second multiplication unit 135B, and the output terminal of the second LPF 138B is connected to the control circuit 140. The second LPF 138B removes high-frequency components from the output of the second multiplication unit 135B and outputs the output to the control circuit 140.

[0058] <Relationship Between Outputs of First Multiplier 135A and Second Multiplier 135B> An AC signal is input to the first multiplier 135A from the AC signal source 132 via the second phase adjustment circuit 136B. An AC signal is input to the second multiplier 135B from the AC signal source 132 via the second phase adjustment circuit 136B and the 90-degree delay circuit 137. That is, the phase of the AC signal input to the second multiplier 135B lags behind the phase of the AC signal input to the first multiplier 135A by 90 degrees.

[0059] Since the first multiplication unit 135A and the second multiplication unit 135B both receive the signal obtained by digitally converting the output of the charge amplifier 131 by the first ADC 134A and the second ADC 134B, the phases of the input signals of the first multiplication unit 135A and the second multiplication unit 135B are equal to each other.

[0060] Therefore, when the first multiplier 135A and the second multiplier 135B demodulate the input signal, the signal component extracted by the second multiplier 135B is a signal component whose phase is delayed by 90 degrees from the signal component extracted by the first multiplier 135A. When the first multiplier 135A extracts a capacitance component, the second multiplier 135B outputs a resistance component.

[0061] The output of the first multiplication unit 135A has high-frequency components removed by the first LPF 138A, and the output of the second multiplication unit 135B has high-frequency components removed by the second LPF 138B. When the first LPF 138A outputs the moving average of the capacitance component, the second LPF 138B outputs the moving average of the resistance component.

[0062] Control circuit 140 uses the output of first multiplier 135A and the output of second multiplier 135B, which are two signal components with a phase difference of 90 degrees, to determine whether hand H is approaching sensor electrode 110 and to determine a failure of sensor electrode 110. Details of this will be described later using FIG. 4.

[0063] <Control Circuit 140> The control circuit 140 determines whether the hand H is in proximity to the sensor electrode 110, determines whether the sensor electrode 110 has a malfunction, and controls the sensor electrode 110 to generate heat as a heater.

[0064] Here, the proximity of the hand H to the sensor electrode 110 means, for example, that the hand H is in contact with the operation surface that covers the sensor electrode 110 .

[0065] Furthermore, when making these determinations and controls, the control circuit 140 outputs gate drive signals to the gates of the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123, thereby controlling switching between a conductive state and an open state.

[0066] <Operation in Heat Generation Mode> In addition, in the heat generation mode, the control circuit 140 outputs PWM gate drive signals synchronized at the same frequency and at H level to the gates of the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123. As a result, the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 are turned on. As a result, current flows from the power supply V1 through the high-side MOSFET 121, the decoupling MOSFET 123, the sensor electrode 110, and the low-side MOSFET 122 toward the reference potential point. As a result, the sensor electrode 110 generates heat and functions as a heater.

[0067] The duty ratio of the PWM gate drive signal (PWM signal) may be determined by the control circuit 140 through feedback control based on the target temperature of the heater of the steering wheel 10, the current temperature of the heater of the steering wheel 10, etc. The temperature of the heater of the steering wheel 10 may be measured by a temperature sensor provided in the steering wheel 10. The power supply V1 itself may be driven by PWM, and in the heat generation mode, an H-level signal may be continuously applied to the gates of the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 to keep the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 continuously in a conductive state (ON).

[0068] <Operation in Non-Heat Generation Mode> <Determination of Approach of Hand H to Sensor Electrode 110> In the non-heat generation mode, the control circuit 140 outputs an L-level gate drive signal to the gates of the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123.

[0069] As a result, in the non-heat generation mode, the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 are in an open state (off). With the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 in an open state (off), the sensor electrode 110 becomes equivalent to a state in which the power supply V1 is not present. Even when the power supply V1 itself is driven by PWM, the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 are kept in an open state (off).

[0070] Based on the output of first LPF 138A, control circuit 140 determines whether hand H is in proximity to sensor electrode 110. Control circuit 140 may determine whether hand H is in proximity to sensor electrode 110 only in a non-heat generating state.

[0071] <Fault Determination of Sensor Electrode 110> The control circuit 140 determines whether or not there is a fault in the sensor electrode 110. This will be described with reference to Fig. 4. Fig. 4 is a diagram illustrating the fault determination of the sensor electrode 110. In Fig. 4, the horizontal axis is the first axis, and the vertical axis is the second axis.

[0072] Here, the phases of the first phase adjustment circuit 136A and the second phase adjustment circuit 136B are adjusted so that changes in the capacitance of the sensor electrode 110 are reflected in the output of the first LPF 138A. Changes in the resistance of the sensor electrode 110 are reflected in the output of the second LPF 138B. A first axis (horizontal axis) is defined such that its value varies with changes in the output of the first LPF 138A. The second axis extends in a direction 90 degrees different from the first axis. Therefore, in FIG. 4 , the value of the first axis (horizontal axis) varies with the output of the first LPF 138A, and the value of the second axis (vertical axis) varies with the output of the second LPF 138B.

[0073] Furthermore, since the capacitance of the sensor electrode 110 also changes with temperature, for example, a coordinate P0 determined by the output of the first LPF 138A (value on the horizontal axis) and the output of the second LPF 138B (value on the vertical axis) in the initial state at a reference temperature is set to the origin (the intersection of the first and second axes) in Fig. 4. The initial state is a state in which the hand H is not close to the sensor electrode 110 and there is no break in the sensor electrode 110. The reference temperature is, for example, 20°C, but may be any temperature.

[0074] In this case, when the hand H approaches the sensor electrode 110, the output of the first LPF 138A changes along the first axis (horizontal axis), and therefore, by setting a threshold value on the first axis (horizontal axis), it is possible to determine that the hand H has approached the sensor electrode 110. For example, when the coordinate determined by the outputs of the first LPF 138A and the second LPF 138B moves to P1 at the reference temperature, the amount of movement along the first axis from the origin exceeds the threshold value, and therefore it is possible to determine that the hand H has approached the sensor electrode 110.

[0075] Furthermore, when the temperature changes from the reference temperature (when the temperature changes), it is assumed that the coordinate determined by the outputs of the first LPF 138A and the second LPF 138B in the initial state shifts to P0A. In this case, if the coordinate determined by the outputs of the first LPF 138A and the second LPF 138B moves to P1A, it is possible to determine that the hand H has approached the sensor electrode 110 because the amount of movement along the first axis from the coordinate P0A exceeds the threshold value.

[0076] Furthermore, when the resistance value between both ends of the sensor electrode 110 changes, the output of the second LPF 138B changes along the second axis (vertical axis). Therefore, by setting a threshold value on the second axis (vertical axis), it is possible to determine whether a fault has occurred in the sensor electrode 110. For example, if, at a reference temperature, the coordinate determined by the outputs of the first LPF 138A and the second LPF 138B moves to P2 in the lower left and the amount of movement exceeds the threshold, it is possible to determine whether an open circuit has occurred in the sensor electrode 110. Note that, when the active shield electrode 150 is provided as shown in FIG. 5 , the output of the second LPF 138B increases when the sensor electrode 110 is open at two or more locations, resulting in a sensor electrode 110 that is not connected to both the first end 110A and the second end 110B. When the parasitic capacitance Crgl decreases and the output waveform of the charge amplifier 131 saturates, the coordinate shifts to the upper left. By setting thresholds for fault determination on the positive and negative sides of both the first axis (horizontal axis) and the second axis (vertical axis), it is possible to determine multiple types of faults. For example, as shown in Figure 4, a determination area representing a horizontally long rectangular shape is set, and if the coordinates correspond to the inside of the determination area, it is determined to be normal, and if the coordinates correspond to the outside of the determination area, it is determined to be fault.

[0077] Although the above description has been given of a configuration in which the sensor device 100 includes the decoupling MOSFET 123, the sensor device 100 does not necessarily have to include the decoupling MOSFET 123. For example, in a heat generation mode in which the sensor electrode 110 is heated, the high-side MOSFET 121 and the low-side MOSFET 122 are made conductive while a voltage V3 (V2<V3<V1) is applied to the node 125, and power is supplied to the sensor electrode 110 from the power supply V1. In a non-heat generation mode (detection mode) in which the electrostatic capacitance is detected by the electrostatic detection circuit 130, the high-side MOSFET 121 and the low-side MOSFET 122 are opened while a voltage V3 (V2<V3<V1) is applied to the node 125, and the electrostatic capacitance of the sensor electrode 110 can be detected by the electrostatic detection circuit 130. The sensor device 100 can also be applied to products that are not integrated with a heater drive circuit. That is, the present invention can be applied to a product that does not have the power supply V1, the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123, and the current flowing from the power supply V1 to the reference potential V2 does not pass through the sensor electrode 110.

[0078] 5, the sensor device 100 may include an active shield electrode 150. Fig. 5 is a diagram showing an example of a circuit configuration of a sensor device according to a modified example of the embodiment.

[0079] The sensor device 100M has a configuration in which an active shield electrode 150 is added to the sensor device 100 shown in FIG.

[0080] The active shield electrode 150 is disposed on the rear side of the sensor electrode 110, in the vicinity of the sensor electrode 110. The rear side of the sensor electrode 110 means the side opposite to the side of the sensor electrode 110 that the hand H approaches. Additionally, the vicinity of the sensor electrode 110 means that the sensor electrode 110 and the active shield electrode 150 are close enough to be capacitively coupled. The capacitance between the sensor electrode 110 and the active shield electrode 150 is denoted by Csa.

[0081] The active shield electrode 150 is connected to an AC signal source 132 and is driven by a signal containing an AC component of the same frequency and phase as the AC component contained in the signal supplied to the sensor electrode 110. The amplitude of the AC component of the signal supplied to the active shield electrode 150 is greater than the amplitude of the AC component of the signal supplied to the sensor electrode 110.

[0082] The active shield electrode 150 is provided to shield the sensor electrode 110 from noise and to suppress the effects of parasitic capacitance. The active shield electrode 150 is arranged near the sensor electrode 110 at a predetermined distance so as to be able to shield the sensor electrode 110 from noise mainly from a reference potential point such as the ground and to suppress the effects of parasitic capacitance between the sensor electrode 110 and the reference potential point.

[0083] The amplitude adjustment circuit 133 adjusts the current flowing from the active shield electrode 150 through the capacitance Csa to the sensor electrode 110 and the current flowing from the sensor electrode 110 through the parasitic capacitance Crgl to the reference potential point so as to cancel each other out. That is, in a state where the hand H, which is an object close to the sensor electrode 110, is not present (a state where the parasitic capacitance Crg is zero), the amplitude is adjusted so that the drive current flowing through the sensor electrode 110 becomes zero.

[0084] The sensor device 100M of the modified embodiment includes an active shield electrode 150 arranged in the vicinity of the sensor electrode 110, thereby reducing the effects of noise and parasitic capacitance in the sensor electrode 110 and also reducing the effects of noise and parasitic capacitance in the wiring, etc. included in the electrostatic detection circuit 130.

[0085] <Effects> The sensor device 100 includes a sensor electrode 110, an AC signal source 132 (drive circuit) that outputs a drive signal including an AC component to the sensor electrode 110, an electrostatic detection circuit 130 that detects the resistance component of the sensor electrode 110 as well as the capacitance between the sensor electrode 110 and an object, a first resistor R1 inserted in series into a first line 111 that connects a first location on the sensor electrode 110 to the electrostatic detection circuit 130, and a second resistor R2 inserted in series into a second line 112 that connects a second location on the sensor electrode 110 to the electrostatic detection circuit 130. When the sensor electrode 110 breaks, the resistance component on the sensor electrode 110 side as viewed from the input terminal 130A changes. Therefore, the sensor device 100M can detect the change in resistance component to determine whether the sensor electrode 110 has failed.

[0086] Therefore, it is possible to provide the sensor device 100 that can detect disconnection of the sensor electrode 110 .

[0087] The first location may be one of the ends of the sensor electrode 110, and the second location may be the other of the ends of the sensor electrode 110. Any break occurring between the ends of the sensor electrode 110 can be detected.

[0088] The electrostatic detection circuit 130 may also include a charge amplifier 131 that outputs a voltage corresponding to the charge of the sensor electrode 110, a first multiplication unit 135A that is connected downstream of the charge amplifier 131 and receives a drive signal from an AC signal source 132, a second multiplication unit 135B that is connected downstream of the charge amplifier 131 and receives a drive signal from the AC signal source 132, and a phase change unit (90-degree delay circuit 137) that changes the first phase or the second phase so that the first phase of the drive signal input from the AC signal source 132 to the first multiplication unit 135A is different from the second phase of the drive signal input from the AC signal source 132 to the second multiplication unit 135B. When the sensor electrode 110 is disconnected, the ratio of the capacitance to the resistance of the sensor electrode 110 changes from when a hand H is close to the sensor electrode 110. Therefore, when the signal corresponding to the charge of the sensor electrode 110 is demodulated using the drive signal, the first phase and the second phase are different, so that signal components with different phases can be extracted from the output of the charge amplifier 131, making it possible to distinguish changes in the resistance value of the sensor electrode 110, and a sensor device 100 can be provided that can detect breaks in the sensor electrode 110 with high accuracy.

[0089] The electrostatic detection circuit 130 further includes a first phase adjustment circuit 136A provided between the sensor electrode 110 and the charge amplifier 131, a first LPF 138A provided downstream of the first multiplication unit 135A, and a second LPF 138B provided downstream of the second multiplication unit 135B. The phase change unit is a 90-degree delay circuit 137 provided between the AC signal source 132 and the second multiplication unit 135B. The phase shift amount of the first phase adjustment circuit 136A may be adjusted so that the output of the second LPF 138B is minimized when the sensor electrode 110 is in a normal state, and the delay amount of the 90-degree delay circuit 137 may be adjusted so that the second phase is delayed by 90 degrees relative to the first phase. This can remove high-frequency components contained in the outputs of the first multiplication unit 135A and the second multiplication unit 135B. In addition, in a normal state where there is no break in the sensor electrode 110, the output of the second LPF 138B is at a minimum, and when a break occurs in the sensor electrode 110, the output of the second LPF 138B increases, making it easier to detect a break in the sensor electrode 110.

[0090] The sensor device 100 may further include a control circuit 140 that determines whether an object is approaching the sensor electrode 110 based on the output of the first LPF 138A, and that determines a fault in the sensor electrode 110 based on the outputs of the first LPF 138A and the second LPF 138B. This makes it possible to provide a sensor device 100 that can detect the proximity of an object to the sensor electrode 110 and a disconnection of the sensor electrode 110 using the control circuit 140.

[0091] The sensor device 100 may further include a high-side MOSFET 121 connected between the sensor electrode 110 and a power supply, and a low-side MOSFET 122 connected between the sensor electrode 110 and a reference potential point, the sensor electrode 110 being a heating element, and the high-side MOSFET 121 and the low-side MOSFET 122 may be conductive in a heating mode in which the sensor electrode 110 is made to generate heat, and the high-side MOSFET 121 and the low-side MOSFET 122 may be open in a non-heating mode in which the electrostatic capacitance is detected by the electrostatic detection circuit 130. A sensor device 100 may be provided that serves both as a heating element and a sensor electrode for proximity detection and is capable of detecting disconnection of the sensor electrode 110.

[0092] Furthermore, the sensor electrode 110 may be provided on the steering wheel 10. It is possible to provide a sensor device 100 that can detect a disconnection of the sensor electrode 110 with high accuracy while reducing the number of components attached to the steering wheel 10.

[0093] The above describes a sensor device according to an exemplary embodiment of the present disclosure. However, the present disclosure is not limited to the specifically disclosed embodiment, and various modifications and variations are possible without departing from the scope of the claims.

[0094] This international application claims priority based on Japanese Patent Application No. 2024-083103, filed on May 22, 2024, the entire contents of which are incorporated herein by reference.

[0095] 100 Sensor device 110 Sensor electrode 120 Heater drive circuit 121 High-side MOSFET (an example of a first switch) 122 Low-side MOSFET (an example of a second switch) 123 Decoupling MOSFET 123A Connection point 123B Line 124 Resistor 125 Node 126 Voltage regulator (an example of a voltage supply circuit) 130 Electrostatic detection circuit 132 AC signal source 133 Amplitude adjustment circuit 134A First ADC 134B Second ADC 135A First multiplication unit 135B Second multiplication unit 136A First phase adjustment circuit 136B Second phase adjustment circuit 137 90-degree delay circuit 138A First LPF 138B Second LPF 140 Control circuit 150 Active shield electrode

Claims

1. A sensor device comprising: a sensor electrode; an electrostatic detection circuit having a drive circuit that outputs a drive signal including an AC component to the sensor electrode and that detects the resistance component of the sensor electrode as well as the electrostatic capacitance between the sensor electrode and an object; a first resistor inserted in series into a first line connecting a first point of the sensor electrode and the electrostatic detection circuit; and a second resistor inserted in series into a second line connecting a second point of the sensor electrode and the electrostatic detection circuit.

2. The sensor device according to claim 1, wherein the first location is one of both ends of the sensor electrode, and the second location is the other of both ends of the sensor electrode.

3. The sensor device according to claim 1 or 2, wherein the electrostatic detection circuit comprises: a charge amplifier that outputs a voltage according to the charge of the sensor electrode; a first multiplication unit connected to a stage subsequent to the charge amplifier and to which the drive signal is input from the drive circuit; a second multiplication unit connected to a stage subsequent to the charge amplifier and to which the drive signal is input from the drive circuit; and a phase change unit that changes the first phase or the second phase so that the first phase of the drive signal input from the drive circuit to the first multiplication unit differs from the second phase of the drive signal input from the drive circuit to the second multiplication unit.

4. The sensor device described in claim 3, wherein the electrostatic detection circuit further comprises: a first phase adjustment circuit provided between the sensor electrode and the charge amplifier; a first low-pass filter provided downstream of the first multiplication unit; and a second low-pass filter provided downstream of the second multiplication unit; the phase change unit is a 90-degree delay circuit provided between the drive circuit and the second multiplication unit; the phase shift amount of the first phase adjustment circuit is adjusted so that the output of the second low-pass filter is minimized when the sensor electrode is in a normal state; and the delay amount of the 90-degree delay circuit is adjusted so that the second phase is delayed by 90 degrees relative to the first phase.

5. The sensor device described in claim 4, further comprising a control circuit that determines whether an object is in proximity to the sensor electrode based on the output of the first low-pass filter, and that determines whether the sensor electrode is faulty based on the outputs of the first low-pass filter and the second low-pass filter.

6. The sensor device according to claim 4 or 5, further comprising: a first switch connected between the sensor electrode and a power supply; and a second switch connected between the sensor electrode and a reference potential point, wherein the sensor electrode is a heating element; and in a heat generation mode in which the sensor electrode is heated, the first switch and the second switch are made conductive, and in a non-heat generation mode in which the electrostatic capacitance is detected by the electrostatic detection circuit, the first switch and the second switch are made open.

7. The sensor device according to claim 6, wherein the sensor electrode is provided on a steering wheel.

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