JP7797992B2 - Magnetostrictive torque sensor - Google Patents

Description

The present invention relates to a magnetostrictive torque sensor.

Conventionally, magnetostrictive torque sensors have been known that use magnetostrictive materials with magnetostrictive properties, whereby the magnetic permeability changes when torque (rotational torque) is applied, and detect the change in the magnetic permeability of the magnetostrictive material when torque is applied by detecting the change in inductance of a detection coil.

Conventional magnetostrictive torque sensors have a sensor section in which four detection coils are bridge-connected, and detect the torque applied to a shaft with magnetostrictive properties based on the change in impedance of each detection coil due to the application of torque (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2020-160088

However, detection coils contain resistance components, and there is variation in this resistance component. In particular, when detection coils are constructed using wiring patterns formed on a substrate, there is inevitably a certain degree of error in the thickness and width of the wiring pattern, resulting in variation in the resistance component of the detection coil. When variation in the resistance component of a detection coil occurs, a phenomenon known as offset occurs, in which output is generated even when no torque is being applied. Furthermore, because the offset caused by variation in this resistance component changes significantly with temperature, there is a risk of reduced detection accuracy.

The present invention aims to provide a magnetostrictive torque sensor that can improve detection accuracy even when there is variation in the resistance component of the detection coil.

In order to solve the above-mentioned problems, the present invention provides a magnetostrictive torque sensor that detects torque transmitted by a magnetostrictive material having magnetostrictive properties. The sensor unit has a bridge circuit including a first detection coil having a first linear portion inclined at a predetermined angle relative to the axial direction of the magnetostrictive material, and a second detection coil having a second linear portion inclined at the predetermined angle in the opposite direction to the first linear portion relative to the axial direction of the magnetostrictive material; a drive unit that applies an AC drive voltage to the bridge circuit; and a voltage measurement unit that measures the voltage output from the bridge circuit, wherein the voltage measurement unit is configured to measure the voltage when the current flowing through the bridge circuit becomes zero.

This invention provides a magnetostrictive torque sensor that can improve detection accuracy even when there is variation in the resistance component of the detection coil.

1 is a perspective view showing the appearance of a magnetostrictive torque sensor according to an embodiment of the present invention; 2A is a perspective view of FIG. 1 with the resin molded portion omitted, and FIG. 2B is a cross-sectional view showing the laminated structure of the flexible substrate and the magnetic ring. 3A to 3C are diagrams illustrating an example of wiring patterns formed on each wiring layer of a flexible substrate. FIG. 2 is a diagram showing the circuit configuration of a sensor unit and a voltage measurement unit. 5 is a time chart showing changes in voltage and current at each part in FIG. 4; FIG. 10 is a diagram showing the circuit configuration of a sensor section and a voltage measurement section of a magnetostrictive torque sensor according to another embodiment of the present invention.

[Embodiment]
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

Figure 1 is a perspective view showing the appearance of a magnetostrictive torque sensor according to this embodiment. Figure 2(a) is a perspective view of Figure 1 with the resin molded portion omitted, and Figure 2(b) is a cross-sectional view showing the layered structure of a flexible substrate and a magnetic ring. Figure 3 is a diagram showing an example of a wiring pattern formed on each wiring layer of the flexible substrate.

(Magnetostrictive material 2)
As shown in FIGS. 1 to 3, a magnetostrictive torque sensor (hereinafter simply referred to as torque sensor) 1 is a sensor that detects torque (rotational torque) applied to a magnetostrictive material 2, and is attached to the periphery of the magnetostrictive material 2.

The magnetostrictive material 2 is a cylindrical member to which torque is applied in the circumferential direction. The magnetostrictive material 2 in the torque sensor 1 is, for example, a shaft used to transmit torque in a vehicle's powertrain system, or a shaft used to transmit torque in a vehicle's engine. The magnetostrictive material 2 can be, for example, a base material made of chromium steel containing chromium, such as chromium steel, chromium molybdenum steel, or nickel chromium molybdenum steel, which has been carburized, quenched, and tempered, and then shot peened.

(Sensor unit 10)
The torque sensor 1 includes a sensor section 10 provided to surround the magnetostrictive material 2. The sensor section 10 includes a detection coil 3 provided around the magnetostrictive material 2, and a magnetic ring (magnetic ring, back yoke) 4 provided to surround the detection coil 3. In this embodiment, the sensor section 10 includes first to fourth detection coils 31 to 34.

As shown in Figures 1 and 2(a), the sensor unit 10 includes a cylindrical bobbin 5 arranged coaxially and spaced apart from the magnetostrictive material 2, a flexible substrate 6 wrapped around the outer surface of the bobbin 5, and a resin molded portion 7. In this embodiment, the detection coil 3 is composed of a wiring pattern (wiring layer 60, described below) formed on the flexible substrate 6. The bobbin 5 is made of a non-magnetic material such as resin, and has a flange 51 that protrudes radially outward and is integrally formed at one axial end thereof. The magnetic ring 4 is provided to cover the periphery of the flexible substrate 6.

(Resin molded portion 7)
As shown in FIG. 1 , the resin molded portion 7 is intended to protect the flexible substrate 6 and the magnetic ring 4, and is formed by molding resin so as to cover the periphery of the bobbin 5, flexible substrate 6, and magnetic ring 4. The resin molded portion 7 integrally includes a main body portion 71 that covers the periphery of the bobbin 5, flexible substrate 6, and magnetic ring 4, and a flange portion 72 formed to protrude outward from the main body portion 71. A through-hole 71a is formed in the main body portion 71 for passing the magnetostrictive material 2 through. A retaining hole 74 is formed in the flange portion 72, penetrating the flange portion 72 and holding a short cylindrical collar 73 made of metal. The flange portion 72 is fixed to surrounding members (members that do not rotate with the rotation of the magnetostrictive material 2) using bolts or the like.

(Flexible substrate 6)
2B, the flexible substrate 6 has four wiring layers 60: a first wiring layer 61, a second wiring layer 62, a third wiring layer 63, and a fourth wiring layer 64. However, the number of layers of the wiring layers 60 is not limited to this, and may be two or more.

The first wiring layer 61 is formed on the surface of a first base resin layer 65a made of polyimide, and the back surface of the first base resin layer 65a is adhesively fixed to the second wiring layer 62 via an adhesive layer 66b. A first coverlay layer 67a made of polyimide is provided on the surface of the first wiring layer 61 via an adhesive layer 66a and is insulating treated. Double-sided tape 68a is affixed to the surface of the first coverlay layer 67a, and the flexible substrate 6 is adhesively fixed to the bobbin 5 via this double-sided tape 68a.

The second wiring layer 62 is formed on the surface of a second base resin layer 65b made of polyimide, and a third wiring layer 63 is formed on the back surface of the second base resin layer 65b.

The fourth wiring layer 64 is formed on the back surface of a third base resin layer 65c made of polyimide, and the surface of the third base resin layer 65c is adhesively fixed to the third wiring layer 63 via an adhesive layer 66c. A second coverlay layer 67b made of polyimide is provided on the surface of the fourth wiring layer 64 via an adhesive layer 66d, and is insulatingly treated. Double-sided tape 68b is affixed to the second coverlay layer 67b, and the flexible substrate 6 and magnetic ring 4 are adhesively fixed via this double-sided tape 68b.

The second wiring layer 62 and third wiring layer 63, which form the inner layers of the flexible substrate 6, are made of rolled copper foil. The first wiring layer 61 and fourth wiring layer 64, which form the outer layers of the flexible substrate 6, are made of electrolytic copper foil that has been copper-plated. As will be described in more detail below, the torque sensor 1 requires the formation of vias (through holes) in the flexible substrate 6, so the outer layers, the first and fourth wiring layers 61 and 64, are plated.

Figure 3 is a diagram showing an example of the wiring pattern formed on each wiring layer 60 of the flexible substrate 6. Figure 3 schematically shows the wiring pattern of each wiring layer 60 when the flexible substrate 6 is unfolded into a flat surface.

As shown in FIG. 3, the first to fourth detector coils 31 to 34 are formed on the wiring layer 60 of the flexible substrate 6. The first and third detector coils 31, 33 have first linear portions 31a, 33a inclined at a predetermined angle relative to the axial direction of the magnetostrictive material 2, and the second and fourth detector coils 32, 34 have second linear portions 32a, 34a inclined at a predetermined angle in the opposite direction to the first linear portions 31a, 33a relative to the axial direction of the magnetostrictive material 2.

In the torque sensor 1, the change in magnetic permeability when torque is applied to the magnetostrictive material 2 is greatest in the ±45 degree direction relative to the axial direction. Therefore, by forming the first linear portions 31a, 33a so that they are inclined at +45 degrees relative to the axial direction, and the second linear portions 32a, 34a so that they are inclined at -45 degrees relative to the axial direction, detection sensitivity can be improved.

In this torque sensor 1, the wiring patterns of the wiring layer 60 forming the first detector coil 31 and the wiring layer 60 forming the fourth detector coil 34 are partially interchanged, so that the first and fourth detector coils 31, 34 are formed across two wiring layers 60 (first and second wiring layers 61, 62). Similarly, the wiring patterns of the wiring layer 60 forming the second detector coil 32 and the wiring layer 60 forming the third detector coil 33 are partially interchanged, so that the second and third detector coils 32, 33 are formed across two wiring layers 60 (third and fourth wiring layers 63, 64). The wiring layers 60 are electrically connected via vias.

By forming each detection coil 3 across two wiring layers 60, it is possible to suppress the effects of differences in the characteristics of the two wiring layers 60. As a result, it is possible to suppress measurement errors caused by differences in the characteristics between the wiring layers 60 and improve measurement accuracy.

In this embodiment, the wiring patterns formed on the first wiring layer 61 and the third wiring layer 63, and the second wiring layer 62 and the fourth wiring layer 64 are substantially the same. Furthermore, the currents flowing in the wiring patterns formed on the first wiring layer 61 and the third wiring layer 63, and the second wiring layer 62 and the fourth wiring layer 64 are arranged to flow in the same direction. In FIG. 3, the current direction is indicated by outline arrows. Also, in FIG. 3, the input electrodes of the first through fourth detection coils 31-34 are indicated by reference numerals 31b, 32b, 33b, and 34b, and the output electrodes are indicated by reference numerals 31c, 32c, 33c, and 34c. Furthermore, the reference numerals a-y and A-Y in FIG. 3 conveniently indicate the connection relationship via vias, and the same reference numerals indicate that the same reference numerals are electrically connected via vias. The wiring patterns of each wiring layer 60 shown in FIG. 3 are merely examples, and the specific structure of the wiring patterns is not limited to these.

(Circuit configuration of sensor unit 10 and voltage measurement unit 9)
Fig. 4 is a diagram showing the circuit configuration of the sensor unit 10 and the voltage measurement unit 9. As shown in Fig. 4, the torque sensor 1 includes the sensor unit 10 having a bridge circuit 10a, a drive unit 8 that applies an AC drive voltage to the bridge circuit 10a, and a voltage measurement unit 9 that measures the voltage output from the bridge circuit 10a.

The sensor unit 10 is composed of a bridge circuit 10a in which the first, second, third, and fourth detection coils 31-34 are connected in a sequential circular pattern. The driver 8 is configured to apply a drive voltage between the connection point a of the first and fourth detection coils 31, 34 and the connection point b of the second and third detection coils 32, 33.

The voltage measurement unit 9 is configured to measure the voltage between the connection c of the first and second detection coils 31, 32 and the connection d of the third and fourth detection coils 33, 34. In this embodiment, the voltage measurement unit 9 is configured to measure the voltage when the current I _coil flowing through the bridge circuit 10 a becomes zero.

More specifically, the voltage measurement unit 9 includes a pulse generation circuit 93 that outputs a pulse at the timing when the current I _coil flowing through the bridge circuit 10 a becomes zero, and a sample-and-hold circuit 96 that holds the output voltage of the bridge circuit 10 a when the pulse is input from the pulse generation circuit 93.

In this embodiment, the voltage measurement unit 9 further includes a current detection resistor 91a connected in series to the bridge circuit 10a, and a comparator 91b that compares the voltage across the current detection resistor 91a. The output of the comparator 91b is either high or low depending on the direction of the current I _coil . That is, the output is high when the current I _coil flows in one direction, and low when the current I coil flows in the other direction.

The pulse generating circuit 93 is configured to output a pulse in response to the output from the comparator 91b. In this embodiment, two pulse generating circuits 93 are provided: a first pulse generating circuit 93a and a second pulse generating circuit 93b. The output of the comparator 91b is directly connected to the input of the first pulse generating circuit 93b. The output of the comparator 91b is also connected to the input of the second pulse generating circuit 93b via an inverting circuit (NOT circuit) 94. Both pulse generating circuits 93a and 93b have the function of outputting a pulse when a high signal is input (when the input changes from low to high). In other words, in this embodiment, a pulse is output from the pulse generating circuit 93 when the direction of the current I _coil flowing through the bridge circuit 10a changes and the output of the comparator 91b changes, i.e., when the current I _coil becomes zero. When the current I _coil changes from positive to negative, a pulse is output from the first pulse generating circuit 93a, and when the current I _coil changes from negative to positive, a pulse is output from the second pulse generating circuit 93b. The output of the first pulse generating circuit 93a is connected to the clock input of a first sample and hold circuit 96a. The output of the second pulse generating circuit 93b is connected to the clock input of a second sample and hold circuit 96b.

On the other hand, the voltage between the connection points c and d to be detected is amplified by a first differential amplifier circuit 95 and input to two sample and hold circuits 96, namely, first and second sample and hold circuits 96a and 96b. When a high signal is input to the clock input of the sample and hold circuit 96, the sampling switch turns on and the input signal (the amplified voltage _Vs between the connection points c and d) is output as is. When the clock input goes low, the sampling switch turns off and the state immediately before the sampling switch was switched is maintained. Note that if the pulse width of the pulse output by the pulse generation circuit 93 (the time during which the voltage is high) is long, the timing at which the current I _coil becomes zero will be off, so it is preferable that the pulse width of the pulse output by the pulse generation circuit 93 be sufficiently short.

Since the clock input of the first sample and hold circuit 96a receives a pulse from the first pulse generating circuit 93a, the first sample and hold circuit 96a holds the voltage _Vs at the timing when the current I _coil becomes zero as the current I _coil changes from positive to negative. And since the clock input of the second sample and hold circuit 96b receives a pulse from the second pulse generating circuit 93b, the second sample and hold circuit 96b holds the voltage _Vs at the timing when the current I _coil becomes zero as the current I _coil changes from negative to positive.

The outputs of both sample and hold circuits 96a, 96b are output to a second differential amplifier circuit 97, where the difference is amplified, passed through a low-pass filter 98 to remove high-frequency noise components, and then input to a voltage detection unit 99, where the voltage value is detected. In other words, the voltage detection unit 99 detects the voltage value obtained by amplifying the difference between the output voltages of the first and second sample and hold circuits 96a, 96b.

Fig. 5 is a time chart showing changes in voltage and current at each point in Fig. 4. Fig. 5 shows time charts for the voltage _V0 at the connection point a, the current _Icoil flowing through the bridge circuit 10a, the output voltage _Vtp of the first pulse generating circuit 93a, the output voltage _Vtn of the second pulse generating circuit 93b, and the output voltage _Vs of the first differential amplifier circuit 95. The time chart for the output voltage _Vs of the first differential amplifier circuit 95 also shows the output voltage _Vhp of the first sample and hold circuit 96a and the output voltage _Vhn of the second sample and hold circuit 96b.

As shown in FIG. 5 , when the polarity of the voltage _V0 applied to the bridge circuit 10a is reversed, the polarity of the current _Icoil is also reversed after a predetermined time td. When the direction of the current _Icoil changes from positive to negative, a pulse is output from the first pulse generating circuit 93a (see the time chart of the output voltage _Vtp ), and the output voltage _Vs of the first differential amplifier circuit 95 at that time is held in the first sample-and-hold circuit 96a as the output voltage _Vhp . When the direction of the current _Icoil changes from negative to positive, a pulse is output from the second pulse generating circuit 93b (see the time chart of the output voltage _Vtn ), and the output voltage _Vs of the first differential amplifier circuit 95 at that time is held in the second sample-and-hold circuit 96b as the output voltage _Vhn . The amplitude of the output voltage _Vs can be extracted by extracting the difference between these values using the second differential amplifier circuit 97. The amplitude (fluctuation range) of the output voltage _Vs changes depending on the torque applied to the magnetostrictive material 2, so the torque applied to the magnetostrictive material 2 can be determined based on the detected value of the amplitude (fluctuation range) of the output voltage _Vs.

At this time, the output voltages _Vhp and _Vhn of both sample and hold circuits 96a and 96b are voltage values when the current _Icoil is zero, and are therefore not affected by the resistance components of the detection coils 31 to 34. This makes it possible to ignore the effects of variations in the resistance components of the detection coils 31 to 34 and fluctuations in the resistance components due to temperature changes, making it possible to accurately detect the torque applied to the magnetostrictive material 2.

(Modification)
In this embodiment, two pulse generating circuits 93 and two sample and hold circuits 96 are used, but this is not limiting, and one pulse generating circuit 93 and one sample and hold circuit 96 may be used. In other words, the second pulse generating circuit 93b and the second sample and hold circuit 96b can be omitted. In this case, the torque applied to the magnetostrictive material 2 can be found based on the voltage value of the output voltage _Vhp of the first sample and hold circuit 96a.

Furthermore, in this embodiment, four detection coils 31 to 34 are used, but this is not limiting. For example, the third and fourth detection coils 33 and 34 can also be replaced with resistive elements.

(Functions and Effects of the Embodiments)
As described above, in the torque sensor 1 according to this embodiment, the voltage measurement unit 9 is configured to measure the voltage when the current flowing through the bridge circuit 10a becomes zero. This suppresses the influence of the resistance components of the detection coils 31 to 34, making it possible to virtually ignore the influence of variations in the resistance components of the detection coils 31 to 34 and fluctuations in the resistance components due to temperature changes. As a result, it is possible to accurately detect the torque applied to the magnetostrictive material 2. In other words, according to this embodiment, even if there are variations in the resistance components of the detection coils 31 to 34, it is possible to reduce temperature fluctuations and improve detection accuracy. This embodiment is particularly effective when the detection coils 31 to 34 are configured using wiring patterns whose width and thickness are prone to change.

(Other embodiments)
Fig. 6 is a diagram showing the circuit configuration of a sensor unit and a voltage measurement unit of a torque sensor 1 according to another embodiment of the present invention. The circuit configuration shown in Fig. 6 is basically the same as the circuit configuration in Fig. 4, except for the method of extracting the timing at which the current I _coil becomes zero.

In the example of Figure 6, the drive unit 8 has a clock generation circuit 81 that generates a clock signal with a predetermined period, and an amplifier circuit 82 that amplifies the clock signal output from the clock generation circuit 81 and outputs it as a drive voltage. The voltage measurement unit 9 has a delay circuit 92 that receives the clock signal from the clock generation circuit 81 and delays and outputs the input clock signal. The pulse generation circuit 93 is configured to output a pulse in response to the output from the delay circuit 92.

As shown in FIG. 5 , the polarity of the current I _coil changes with the change in polarity of the voltage V ₀ applied to the bridge circuit 10a. However, the change in polarity of the current I _coil is delayed relative to the change in polarity of the voltage V ₀ depending on the material of the magnetostrictive material 2 and the configuration of the detection coils 31-34. Therefore, if the delay of the change in polarity of the current I _coil relative to the clock signal generated by the clock generation circuit 81 (the time corresponding to time td in FIG. 5 ) can be determined by experiment, calculation, or the like, the timing at which the current I _coil becomes zero can be extracted by delaying the clock signal by the obtained delay time. In other words, the delay circuit 92 delays the clock signal generated by the clock generation circuit 81 so that the timing of the clock signal's high-to-low transition coincides with the timing at which the polarity of the current I _coil changes. The clock signal delayed by the delay circuit 92 has exactly the same waveform as the output of the comparator 91b in FIG. 4 .

By using the circuit configuration shown in Figure 6, it is possible to omit the current detection resistor 91a, simplifying the circuit configuration and reducing costs. However, the circuit configuration shown in Figure 6 requires that the delay time be known. Therefore, if the delay time is unknown, it is preferable to use the more versatile circuit configuration shown in Figure 4.

Note that while the example in Figure 6 uses a delay circuit 92, this is not limiting and the operation of the delay circuit 92 may be configured to be performed by software. For example, the voltage measurement unit 9 may be provided with a control unit such as a microcomputer, and this control unit may perform the same operation as the delay circuit 92, i.e., delaying the clock signal. In this case, the clock generation circuit 81 of the drive unit 8 may be integrated into the control unit such as a microcomputer.

(Summary of the embodiment)
Next, the technical ideas grasped from the above-described embodiments will be described by using the reference numerals and the like in the embodiments. However, the reference numerals and the like in the following description do not limit the components in the claims to the members and the like specifically shown in the embodiments.

[1] A torque sensor for detecting torque transmitted by a magnetostrictive material (2) having magnetostrictive properties, comprising: a sensor unit (10) having a bridge circuit (10a) including a first detection coil (31) having a first linear portion (31a) inclined at a predetermined angle relative to the axial direction of the magnetostrictive material (2); and a second detection coil (32) having a second linear portion (32a) inclined at the predetermined angle in the opposite direction to the first linear portion (31a) relative to the axial direction of the magnetostrictive material (2); a drive unit (8) that applies an AC drive voltage to the bridge circuit (10a); and a voltage measurement unit (9) that measures the voltage output from the bridge circuit (10a), wherein the voltage measurement unit (9) is configured to measure the voltage when the current flowing through the bridge circuit (10a) becomes zero.

[2] The voltage measurement unit (9) of the magnetostrictive torque sensor (1) described in [1] includes a pulse generation circuit (93) that outputs a pulse when the current flowing through the bridge circuit (10a) becomes zero, and a sample-and-hold circuit (96) that holds the output voltage of the bridge circuit (10a) when a pulse is input from the pulse generation circuit (93).

[3] The voltage measurement unit (9) includes a current detection resistor (91a) connected in series with the bridge circuit (10a) and a comparator (91b) that compares the voltage across the current detection resistor (91a), and the pulse generation circuit (93) is configured to output a pulse in response to the output from the comparator (91b). [2] Magnetostrictive torque sensor (1).

[4] The magnetostrictive torque sensor (1) described in [3], wherein the pulse generating circuit (93) includes a first pulse generating circuit (93a) to which the output from the comparator (91b) is directly input, and a second pulse generating circuit (93b) to which the output from the comparator (91b) is input via an inverting circuit (94); the sample and hold circuit (96) includes first and second sample and hold circuits (96a, 96b) to which the output voltage of the bridge circuit (10a) is input; the first sample and hold circuit (96a) is configured to hold the output voltage when a pulse is input from the first pulse generating circuit (93a); the second sample and hold circuit (96b) is configured to hold the output voltage when a pulse is input from the second pulse generating circuit (93b); and the voltage measuring unit (9) includes a voltage detecting unit (99) that detects the difference between the outputs of the first and second sample and hold circuits (96a, 96b).

[5] The magnetostrictive torque sensor (1) described in [2], wherein the drive unit (8) has a clock generation circuit (81) and an amplifier circuit (82) that amplifies the clock signal output from the clock generation circuit (81) and outputs it as the drive voltage, the voltage measurement unit (9) has a delay circuit (92) that receives the clock signal from the clock generation circuit (81) and delays and outputs the input clock signal, and the pulse generation circuit (93) is configured to output pulses in accordance with the output from the delay circuit (92).

[6] The magnetostrictive torque sensor (1) described in [1], wherein the sensor unit (10) has a third detector coil (33) having the first linear portion (33a) and a fourth detector coil (34) having the second linear portion (34a), the bridge circuit (10a) is configured by sequentially connecting the first, second, third, and fourth detector coils (31-34) in a circular pattern, the driver (8) is configured to apply a drive voltage between the connection portion (a) of the first and fourth detector coils (31, 34) and the connection portion (b) of the second and third detector coils (32, 33), and the voltage measurement unit (9) is configured to measure the voltage between the connection portion (c) of the first and second detector coils (31, 32) and the connection portion (d) of the third and fourth detector coils (33, 34).

(Additional Note)
Although the embodiments of the present invention have been described above, the invention according to the claims is not limited to the above-described embodiments. It should be noted that not all of the combinations of features described in the embodiments are necessarily essential to the means for solving the problems of the invention. Furthermore, the present invention can be appropriately modified and implemented within the scope of its spirit.

1...Magnetostrictive torque sensor (torque sensor)
2...Magnetostrictive material 3...Detection coil 31...First detection coil 32...Second detection coil 33...Third detection coil 34...Fourth detection coil 31a, 33a...First linear section 32a, 34a...Second linear section 8...Driver 81...Clock generating circuit 82...Amplifier circuit 9...Voltage measuring section 91a...Current detection resistor 91b...Comparator 92...Delay circuit 93...Pulse generating circuit 93a...First pulse generating circuit 93b...Second pulse generating circuit 95...First differential amplifier circuit 96...Sample and hold circuit 96a...First sample and hold circuit 96b...Second sample and hold circuit 97...Second differential amplifier circuit 98...Low pass filter 99...Voltage detection section 10...Sensor section 10a...Bridge circuit

Claims (6)

A torque sensor that detects torque transmitted by a magnetostrictive material having magnetostrictive properties,
a sensor unit having a bridge circuit including a first detection coil having a first linear portion inclined at a predetermined angle with respect to the axial direction of the magnetostrictive material, and a second detection coil having a second linear portion inclined at the predetermined angle in a direction opposite to the first linear portion with respect to the axial direction of the magnetostrictive material;
a drive unit that applies an AC drive voltage to the bridge circuit;
a voltage measuring unit that measures a voltage output from the bridge circuit,
The voltage measurement unit is configured to measure the voltage when the current flowing through the bridge circuit becomes zero.
Magnetostrictive torque sensor. The voltage measurement unit
a pulse generating circuit that outputs a pulse at the timing when the current flowing through the bridge circuit becomes zero;
a sample-and-hold circuit that holds the output voltage of the bridge circuit when a pulse is input from the pulse generating circuit,
2. The magnetostrictive torque sensor according to claim 1. The voltage measurement unit
a current detection resistor connected in series to the bridge circuit;
a comparator that compares the voltages across the current detection resistor;
the pulse generating circuit is configured to output a pulse in response to the output from the comparator.
3. The magnetostrictive torque sensor according to claim 2. the pulse generating circuit includes a first pulse generating circuit to which the output from the comparator is directly input, and a second pulse generating circuit to which the output from the comparator is input via an inverting circuit;
the sample and hold circuit includes first and second sample and hold circuits to which the output voltage of the bridge circuit is input;
the first sample-and-hold circuit is configured to hold the output voltage when a pulse is input from the first pulse generating circuit;
the second sample-and-hold circuit is configured to hold the output voltage when a pulse is input from the second pulse generating circuit;
the voltage measurement unit includes a voltage detection unit that detects a difference between outputs of the first and second sample-and-hold circuits;
4. The magnetostrictive torque sensor according to claim 3. the drive unit includes a clock generation circuit and an amplifier circuit that amplifies a clock signal output from the clock generation circuit and outputs the amplified clock signal as the drive voltage;
the voltage measurement unit has a delay circuit that receives a clock signal from the clock generation circuit, delays the input clock signal, and outputs the delayed clock signal;
The pulse generating circuit is configured to output a pulse in response to the output from the delay circuit.
3. The magnetostrictive torque sensor according to claim 2. the sensor unit includes a third detection coil having the first linear portion and a fourth detection coil having the second linear portion;
the bridge circuit is configured by sequentially connecting the first, second, third, and fourth detection coils in a circular fashion;
the drive unit is configured to apply a drive voltage between a connection portion of the first and fourth detection coils and a connection portion of the second and third detection coils;
the voltage measurement unit is configured to measure a voltage between a connection portion of the first and second detection coils and a connection portion of the third and fourth detection coils.
2. The magnetostrictive torque sensor according to claim 1.