JP3682446B2 - Torque sensor - Google Patents

Description

従って、トルクの変化に対するインダクタンスＬの変化により発振周波数fcが変化し、トルクの検出を行うことができる。また、温度変化によるコイル５５の内部抵抗値の変化は帰還率に多少は影響するが、実質的に問題はない。しかも、検出回路５６の消費電力を少なくでき、また、構成も簡単となる。
この場合、第２の参考例として示す図８のように、増幅器５７の入出力間にはコイル５５及びコンデンサ５８に加え負の温度・抵抗特性をもつ感熱素子６４を直列に接続する構成としても良い。この第２の参考例によると、感熱素子６３により温度変化に対する帰還率をほぼ一定化できて、温度変化によるトルク検出精度の低下をなくすことができる。
【００２５】
【発明の効果】
本発明は以上の説明から明らかなように、周囲温度が変化してもトルク検出精度の低下をなくすことができる。
【図面の簡単な説明】
【図１】 本発明の第１の実施例における検出回路を示す図
【図２】 （ａ）は検出回路の地点ａの電圧波形図、（ｂ）は検出回路の地点ｂの電圧波形図
【図３】 機械的構成部分の概略正面図
【図４】 本発明の第２の実施例を示す検出回路の概略図
【図５】 本発明の第３の実施例を示す図４相当図
【図６】 第１の参考例を示す図３相当図
【図７】 検出回路を示す図
【図８】 第２の参考例を示す検出回路の図
【図９】 従来例を示す図３相当図
【図１０】 図４相当図
【図１１】 コイルの等価回路図
【符号の説明】
２１はトルク伝達軸、２２は第１の磁歪膜、２３は第２の磁歪膜、２５は第１のコイル、２６は第２のコイル、２７は検出回路、２８はブリッジ回路、３３は差動増幅器、３５は定電流供給回路（定電流供給手段）、４３はスイッチング回路（スイッチング手段）、５１、５２、５３は感熱素子、５４は磁歪膜、５５はコイル、５６は検出回路、５７は増幅器、５８はコンデンサ、６４は感熱素子を示す。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a torque sensor including a magnetostrictive film formed on an outer peripheral surface of a torque transmission shaft and a coil for detecting a change in permeability of the magnetostrictive film.
[0002]
[Problems to be solved by the invention]
FIG. 9 shows simplified mechanical components in the torque sensor. A plurality of first magnetostrictive films 2 having a strip shape are formed on the outer peripheral surface of the torque transmission shaft 1 in an inclined state (parallel to each other) by 45 ° with respect to the shaft center. A plurality of second magnetostrictive films 3 are formed in a state (parallel to each other) shifted by 90 ° from the first magnetostrictive film 2. As a result of such an arrangement, in a state where torque is applied to the torque transmission shaft 1, a compressive force is applied to one of the magnetostrictive films 2 and 3, and a tensile force is applied to the other. As a result, magnetostriction is caused by the inverse magnetostrictive effect. The permeability of one of the films 2 and 3 increases and the permeability of the other decreases. Actually, the magnetostrictive films 2 and 3 are formed at a higher density than the state shown in FIG.
[0003]
In order to detect such a change in permeability, a known sensor head 4 is provided. The sensor head 4 includes a first coil 5 disposed coaxially with a predetermined gap around the first magnetostrictive film 2 and a second magnetostrictive film 3 around the first magnetostrictive film 3. And a second coil 6 arranged coaxially with a predetermined gap.
[0004]
FIG. 10 shows a configuration of a detection circuit 7 for detecting torque from the change in magnetic permeability. The detection circuit 7 includes a bridge circuit 11 in which a series circuit 8 of the first coil 5 and a resistor 7 and a series circuit 10 of the second coil 6 and a resistor 9 are connected in parallel, and the bridge circuit. Switching means 12 that intermittently switches a current flowing through the bridge circuit 11 and flows a high-frequency current through the bridge circuit 11.
[0005]
The switching means 12 includes a switching element 12a and a driving circuit 12b that drives the switching element 12a at a high frequency.
The voltages at the midpoints 8a and 10a of the series circuits 8 and 10 of the bridge circuit 11 are differentially amplified by the differential amplifier 13 and rectified by the rectifier circuit 14. A signal Ts (voltage level) output through the rectifier circuit 14 is a signal corresponding to the torque.
[0006]
Incidentally, the first and second coils 2 and 3 generally formed of a copper wire have an internal resistance R0 as can be seen from FIG. 11 showing an equivalent circuit thereof. In the circuit of FIG. 10 that supplies current, the resistance value of the resistor R0 increases as the temperature increases, the supply current decreases, and the level of the output signal Ts of the detection circuit 14 decreases.
As described above, the conventional torque sensor has a problem that the torque detection accuracy is deteriorated in an environment where there is a temperature change.
[0007]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a torque sensor in which the torque detection accuracy does not decrease even when the ambient temperature changes.
[0008]
[Means for Solving the Problems]
According to the first aspect of the present invention, the first and second magnetostrictive films are formed on the outer peripheral surface of the torque transmission shaft, the first and second magnetostrictive films having the magnetic permeability changing in opposite directions in the torque acting state. In the first coil and the second coil that detect the magnetic permeability change of the film, the first coil and the second coil are provided, and the detection circuit detects the torque from the magnetic permeability change.
The detection circuit includes:
A bridge circuit in which a series circuit of the first coil and a resistor and a series circuit of the second coil and a resistor are connected in parallel;
Constant current supply means for detecting the current flowing in the bridge circuit and making the current constant;
Switching means for intermittently switching a current flowing through the bridge circuit and causing a high-frequency current to flow through the bridge circuit;
It is characterized by comprising a differential amplifier that differentially amplifies the voltage at the midpoint of each series circuit of the bridge circuit and outputs a signal corresponding to the torque.
[0009]
In the first aspect of the invention, since the current flowing through the bridge circuit is detected and the current flowing through the bridge circuit is made constant, the internal resistance values of the first and second coils change due to changes in the ambient temperature. However, a constant current always flows through the bridge circuit, so that the torque detection accuracy does not deteriorate even if the ambient temperature changes.
[0010]
According to a second aspect of the present invention, the first and second magnetostrictive films are formed on the outer peripheral surface of the torque transmission shaft, the first and second magnetostrictive films having the magnetic permeability changing in opposite directions in the torque acting state. In the first coil and the second coil that detect the magnetic permeability change of the film, the first coil and the second coil are provided, and the detection circuit detects the torque from the magnetic permeability change.
The detection circuit includes:
A bridge circuit in which a series circuit of the first coil and a resistor and a series circuit of the second coil and a resistor are connected in parallel;
Switching means for intermittently switching a current flowing through the bridge circuit and causing a high-frequency current to flow through the bridge circuit;
A differential amplifier that differentially amplifies the voltage at the midpoint of each series circuit of the bridge circuit and outputs a signal corresponding to the torque;
It is characterized by comprising a thermal element having a negative temperature / resistance characteristic interposed between the switching means and the midpoint of each series circuit of the bridge circuit.
[0011]
In the second aspect of the invention, since the thermal element having negative temperature / resistance characteristics is interposed between the switching means and the midpoint of each series circuit of the bridge circuit, the ambient temperature rises. Even if the internal resistance values of the first and second coils increase, the resistance value of the thermosensitive element decreases, so that a constant current always flows through the bridge circuit, and the torque detection accuracy may decrease. Absent.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. First, in FIG. 3, the mechanical components of the torque sensor are shown in a simplified manner. A plurality of first magnetostrictive films 22 having a strip shape are formed on the outer peripheral surface of the torque transmission shaft 21 in an inclined state (parallel to each other) by 45 ° with respect to the shaft center. A plurality of second magnetostrictive films 23 formed are formed in a state (parallel to each other) that is shifted from the first magnetostrictive film 22 by 90 °. As a result of such an arrangement, in a state where torque is applied to the torque transmission shaft 21, a compressive force is applied to one of the magnetostrictive films 22 and 23, and a tensile force is applied to the other. As a result, magnetostriction is caused by the inverse magnetostrictive effect. The permeability of one of the films 22 and 23 increases, and the permeability of the other decreases. In practice, the magnetostrictive films 22 and 23 are formed at a higher density than the state shown in FIG.
[0015]
In order to detect such a change in magnetic permeability, a known sensor head 24 is provided. The sensor head 24 includes a first coil 25 and a second magnetostrictive film 23 which are coaxially arranged around the first magnetostrictive film 22 with a predetermined gap therebetween. And a second coil 26 arranged coaxially with a predetermined gap.
[0016]
FIG. 1 shows a configuration of a detection circuit 27 for detecting torque from the change in magnetic permeability. In this detection circuit 27, the bridge circuit 28 is configured by connecting a series circuit 30 of the first coil 25 and a resistor 29 and a series circuit 32 of the second coil 26 and a resistor 31 in parallel. ing. The midpoints 30a and 32a of the series circuits 30 and 32 of the bridge circuit 28 are connected to the input terminals of the differential amplifier 33. The differential amplifier 33 is connected to the midpoint 30a of the series circuits 30 and 32. , 32a are differentially amplified and output. This output is rectified by the rectifier circuit 34. A signal Ts (voltage level) output through the rectifier circuit 34 is a signal corresponding to the torque.
[0017]
The bridge circuit 28 is supplied with a constant current from a constant current supply circuit 35 which is a constant current supply means. In the constant current supply circuit 35, a detection resistor 36 for detecting a current flowing through the bridge circuit 28 is connected between the bridge circuit 28 and the ground, and the voltage ( The point a) has the waveform shown in FIG. The detected voltage is smoothed and averaged by the resistor 37 and the capacitor 38 (the waveform (point b) is shown in FIG. 2B), and this smoothed voltage is applied to the inverting input terminal (−) of the operational amplifier 39. The operational amplifier 39 compares the smoothed voltage with the set voltage from the reference voltage setting circuit 40 input to the non-inverting input terminal (+), and operates so that the difference between the two is always close to zero. The base current of the PNP transistor 42 is controlled by controlling the collector current of the NPN transistor 41. As a result, the supply current Id, which is the collector current of the transistor 42, is controlled to a constant value and operates as a constant current power source.
[0018]
The supply current Id is converted to a high frequency current by the switching circuit 43 serving as switching means and supplied to the bridge circuit 28. The switching circuit 43 includes a PNP transistor 44 and a driving circuit 45 as switching elements. The drive circuit 45 includes an NPN-type transistor 46 that controls on / off of the transistor 44. The transistor 46 operates by inputting a rectangular wave frequency signal (clock) to the base to control the on / off of the transistor 46. To do.
[0019]
According to the present embodiment, the constant current supply circuit 35 is provided to detect the current flowing through the bridge circuit 28, and the current flowing through the bridge circuit 28 is made constant. Even if the internal resistance values of the second coils 25 and 26 change, a constant current always flows through the bridge circuit 28, and the torque detection accuracy does not deteriorate.
[0020]
FIG. 4 shows a second embodiment of the present invention. In this embodiment, the configuration of the detection circuit 50 is different from that of the first embodiment. That is, the switching circuit 43, the thermal element 51, and the bridge 28 are connected in order between the DC power source Vd and the ground. The differential amplifier 33 and the switching circuit 43 are schematically shown. The thermal element 51 is composed of a thermistor having negative temperature / resistance characteristics, and the resistance value decreases as the temperature increases.
[0021]
According to the second embodiment, the thermal element 51 having negative temperature / resistance characteristics is interposed between the switching circuit 43 and the midpoints 30a and 32a of the series circuits 30 and 32 of the bridge circuit 26. Therefore, even if the ambient temperature rises and the internal resistance values of the first and second coils 25 and 26 increase, the resistance value of the thermal element 51 decreases, so that a substantially constant current always flows through the bridge circuit 28. Thus, the torque detection accuracy does not decrease.
[0022]
As shown in FIG. 5 showing the third embodiment of the present invention, a thermal element 52 having a negative temperature / resistance characteristic is interposed between the coil 25 and the midpoint 30a, and the negative temperature / resistance is also the same. The heat sensitive element 53 having characteristics may be interposed between the coil 26 and the midpoint 32a. Also in this embodiment, the same effect as in the second embodiment can be obtained. That is, the thermal element may be configured to be interposed between the switching circuit 43 and the midpoints 30a and 32a of the series circuits 30 and 32 of the bridge circuit 26.
[0023]
6 and 7 show a first reference example . In the first reference example , a magnetostrictive film 54 is formed on the outer peripheral surface of the torque transmission shaft 21, and one coil 55 for detecting a change in permeability of the magnetostrictive film 54 is provided. The detection circuit 56 is composed of an oscillation circuit. That is, the coil 55, the capacitor 58, and the gain adjusting resistor 59 are connected in series between the input and output of the inverting amplifier 57, and another gain adjustment is provided between the input and output of the amplifier 57. 60 are connected. Capacitors 61 and 62 are respectively connected between both ends of the series circuit of the coil 55 and the capacitor 58 and the ground. Further, an inverting amplifier 63 is connected to the output side of the amplifier 57. The detection circuit 56 is configured as an oscillation circuit that outputs a signal Sf having an oscillation frequency corresponding to the torque by series resonance that is fed back from the output of the amplifier 57 to the input.
[0024]
In this case, if the oscillation frequency fc is L, the inductance of the coil 55 and the capacitance of the capacitor 58 are C,
[Expression 1]

Therefore, the oscillation frequency fc is changed by the change of the inductance L with respect to the change of the torque, and the torque can be detected. In addition, a change in the internal resistance value of the coil 55 due to a change in temperature slightly affects the feedback rate, but there is substantially no problem. In addition, the power consumption of the detection circuit 56 can be reduced, and the configuration is simplified.
In this case, as shown in FIG. 8 shown as the second reference example , in addition to the coil 55 and the capacitor 58, a thermal element 64 having negative temperature / resistance characteristics may be connected in series between the input and output of the amplifier 57. good. According to the second reference example , the feedback factor with respect to the temperature change can be made substantially constant by the thermal element 63, and the decrease in the torque detection accuracy due to the temperature change can be eliminated.
[0025]
【The invention's effect】
As is apparent from the above description, the present invention can eliminate a decrease in torque detection accuracy even when the ambient temperature changes.
[Brief description of the drawings]
FIG. 1 is a diagram showing a detection circuit according to a first embodiment of the present invention. FIG. 2A is a voltage waveform diagram at a point a of the detection circuit, and FIG. 1B is a voltage waveform diagram at a point b of the detection circuit. FIG. 3 is a schematic front view of a mechanical component. FIG. 4 is a schematic diagram of a detection circuit showing a second embodiment of the invention. FIG. 5 is a diagram corresponding to FIG. 6 is a diagram corresponding to FIG. 3 showing a first reference example . FIG. 7 is a diagram showing a detection circuit. FIG. 8 is a diagram showing a detection circuit showing a second reference example . FIG. Fig. 10 Equivalent to Fig. 4 Fig. 11 Equivalent circuit diagram of coil
21 is a torque transmission shaft, 22 is a first magnetostrictive film, 23 is a second magnetostrictive film, 25 is a first coil, 26 is a second coil, 27 is a detection circuit, 28 is a bridge circuit, and 33 is differential. Amplifier 35, constant current supply circuit (constant current supply means), 43 switching circuit (switching means), 51, 52, 53 thermal element, 54 magnetostrictive film, 55 coil, 56 detection circuit, 57 amplifier , 58 are capacitors, and 64 is a thermal element.

Claims (2)

First and second magnetostrictive films are formed on the outer peripheral surface of the torque transmission shaft so that the magnetic permeability changes in the opposite direction to each other when the torque is applied, and changes in the magnetic permeability of the first and second magnetostrictive films are detected. The first coil and the second coil are provided, the first coil and the second coil are provided, and the first coil and the second coil are provided, and the detection circuit detects the torque from the change in the magnetic permeability.
The detection circuit includes:
A bridge circuit in which a series circuit of the first coil and a resistor and a series circuit of the second coil and a resistor are connected in parallel;
Constant current supply means for detecting the current flowing in the bridge circuit and making the current constant;
Switching means for intermittently switching a current flowing through the bridge circuit and causing a high-frequency current to flow through the bridge circuit;
A torque sensor comprising: a differential amplifier that differentially amplifies a voltage at a midpoint of each series circuit of the bridge circuit and outputs a signal corresponding to torque. First and second magnetostrictive films are formed on the outer peripheral surface of the torque transmission shaft so that the magnetic permeability changes in the opposite direction to each other when the torque is applied, and changes in the magnetic permeability of the first and second magnetostrictive films are detected. The first coil and the second coil are provided, the first coil and the second coil are provided, and the first coil and the second coil are provided, and the detection circuit detects the torque from the change in the magnetic permeability.
The detection circuit includes:
A bridge circuit in which a series circuit of the first coil and a resistor and a series circuit of the second coil and a resistor are connected in parallel;
Switching means for intermittently switching a current flowing through the bridge circuit and causing a high-frequency current to flow through the bridge circuit;
A differential amplifier that differentially amplifies the voltage at the midpoint of each series circuit of the bridge circuit and outputs a signal corresponding to the torque;
A torque sensor comprising: a thermosensitive element having negative temperature / resistance characteristics interposed between the switching means and a midpoint of each series circuit of the bridge circuit.

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