JPH02287232A - Torque detection method - Google Patents

Abstract

PURPOSE:To achieve a higher temperature characteristic by a method wherein a parallel LC resonance circuit is composed of a capacitance of a capacitor and an inductance portion of a winding and an AC excitation is performed at a frequency near a resonance frequency to measure a phase difference between an excitation voltage and an excitation current. CONSTITUTION:A capacitor 4 is connected in parallel to a winding 1 and a parallel LC circuit is composed of a capacitance C of the capacitor 4 and an inductance L of the winding 1. An AC excitation is performed at a frequency near a resonance frequency thereof to measure a phase difference between an excitation voltage and an excitation current thereof. Here, when a torque is applied to a shaft 3 to be measured, a magnetostrictive film 2 deposited on the shaft 3 to be measured stretches to vary a magnetic characteristic (magnetic permeability). In other words, as the inductance L of the winding 1 would on the shaft 3 to be measured changes, a phase difference between the excitation voltage and the excitation current of the parallel LC resonance circuit varies and this change in the phase difference can be detected as change in torque.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a non-contact torque detection method that utilizes the magnetostrictive effect of a magnetic material, such as the joint torque of a robot or the torque of a motor used in a machine tool. Regarding the method of detecting.

[Conventional technology]

The magnetostrictive torque detection method is used for boat fishing, as shown in FIG. It consists of both excitation and detection windings 11 and 12 wound around the measurement axis 3 (Japanese Patent Laid-Open No. 6119532).
(See Publication No. 3).

Conventionally, a multi-by-break system has been used as the signal processing section, as seen in, for example, Japanese Patent Application Laid-Open No. 62-220821.

Typically, these methods measure changes in the magnetic properties of a magnetostrictive film deposited on the measured shaft due to a torque applied to the measured shaft.
As shown in FIG. 13, this is captured as a frequency change using the multi-by-break method and processed by f/V conversion.

[Problem to be solved by the invention]

However, this method requires two windings, one for excitation and one for detection, which increases the number of parts and complicates the circuit. In addition, when the circuit is incorporated into a motor etc., the temperature of the torque sensor section also rises, but with this method, due to the effects of excitation, temperature rise of the detection winding, temperature sensitivity of the transistor, etc., 0 point (no load) time) drift is very large. The characteristics shown by the broken line in Figure 6 show the characteristics due to the winding temperature change from 20°C to 80°C (60°C), but in this case, even though no torque is applied, the A detection error of approximately 90% of the rated torque occurs.

The present invention has been made in view of these conventional problems, and aims to simplify the detection circuit and improve the temperature characteristics.

[Means to solve the problem]

In order to achieve this object, the present invention uses a non-contact torque detection method that utilizes the magnetostrictive effect of a magnetic material. A parallel LC resonant circuit is constituted by the capacitance of and the inductance of the winding,
It is characterized in that torque is detected by performing alternating current excitation at a frequency near the resonance frequency and measuring the phase difference between the excitation voltage and excitation current.

In this torque detection method, the decrease in detection sensitivity due to the skin effect of the windings and the increase in high frequency resistance due to the eddy current flowing in the magnetic film and the shaft to be measured is calculated by multiplying the excitation current by the excitation voltage by a certain gain. Compensation can be performed by measuring the phase difference between the subtracted compensation excitation voltage and the excitation current.

〔Example〕

Hereinafter, the present invention will be specifically explained based on Examples.

FIG. 1 shows an embodiment of the present invention, in which the axis to be measured 3
A magnetic film 2 having a magnetostrictive effect is deposited in a plurality of strips at regular intervals so as to form a constant angle with the axis direction of the magnetic film 2, thereby forming a magnetic circuit in which the axis to be measured 3 is part of the magnetic path. A torque sensor is formed by winding a single winding 1 around a shaft 3 to be measured with a certain gap.

In this torque sensor, as shown in Fig. 2, a capacitor 4 is connected in parallel to the winding 1, and the capacitance C of the capacitor 4 and the inductance L of the winding 1 constitute a parallel LC resonant circuit. AC excitation is performed at a frequency close to the frequency, and the phase difference between the excitation voltage and excitation current is measured. In the figure, 5 is a resistor for exciting current detection. When this parallel LC resonant circuit is subjected to AC excitation at a frequency near the resonant frequency, its detection characteristic has a linear portion in the phase difference Δθ in the minute displacement section ΔL of the inductance, as shown in FIG. In this method, linearity of torque and phase difference is ensured by utilizing this straight section.

When torque is applied to the shaft 3 to be measured, the magnetostrictive film 2 deposited on the shaft 3 to be measured expands and contracts, and its magnetic properties (magnetic permeability) change. That is, since the inductance L of the winding l wound around the shaft 3 to be measured changes, the phase difference between the excitation voltage and the excitation current of the parallel LC resonant circuit changes. This method detects changes in this phase difference as changes in torque.

The improvement in temperature characteristics when the winding 1 is excited near the resonance frequency in this way will be explained. In Fig. 2, the inductance of the winding is divided, the resistance is R, and the capacitance of the capacitor is CaLl.

When an alternating current E (=V, /J'2) is applied to the circuit, the exciting current I is as follows.

I + =t / : ,,, c −JωCE■=
,E・−111−−−−−−− R+j ωL 17E−j ” B R2+(ωshi) R”+(ωL)
21 = I, +L = B 1j (ωc CIJ
L >aR2+(ωL)' R2
Value 1. )2 Therefore, the phase γ of the excitation current (2) with respect to the excitation voltage is expressed as follows.

If we calculate 2 for the temperature coefficient from equation (2), we get R2+(ωL)
2 For example, the frequency ω is ω=ω. =1/, rU-co, and R=R0(1+αt). Here, α represents the temperature coefficient of the resistance R, and t represents the temperature change.

On the other hand, the phase T' when the capacitor C is not connected as in the conventional case is as follows.

Here, the temperature coefficient is determined from equation (1).

Calculating the ratio of temperature coefficients, we get k 1/ ka = 1 / (ω, L/R,)”. Here, (ω. L/R0) 2 corresponds to the voltage rise ratio of the resonant circuit. Since this is usually set between 30 and 50, the temperature coefficient when the capacitor is connected is 1./1000, compared to the temperature coefficient of 2 for the conventional circuit without the capacitor connected. Therefore, the phase T with respect to temperature change
fluctuations become significantly smaller.

Figure 6 shows the temperature characteristics of torque detection using this method. Conventionally, when the applied torque is zero, when the temperature rises from 20°C to 80°C, an error equivalent to the rated torque occurs, as shown by the broken line, but with this method, compared to the conventional method, as shown by the solid line, the error is 0. Point drift is improved by nearly three orders of magnitude. Depending on how the detection coil is made, even greater improvements can be made.

FIG. 4 shows an example of a circuit for carrying out the torque detection method of the present invention, and FIG. 5 shows an operation waveform diagram of each part.

In the figure, 31 is a comparator that shapes the excitation AC voltage V into a rectangular wave, 32 is a comparator that shapes the excitation current I into a rectangular wave, and 33 is a clock oscillator that generates a clock pulse (see Figure 15 (a)). . Note that the excitation current can be detected as the voltage across the detection resistor R9 in FIG. The output of the comparator 31 (see FIG. 5(b)) and the clock pulse are input to an AND gate 34, which outputs the signal shown in FIG. 5(d). On the other hand, the output of the comparator 32 has the waveform shown in FIG. 5(C),
The inverter 35 inverts the phase (see FIG. 5(e)), and the AND gate 36 performs a logical product with the output of the AND gate 34 to generate the waveform shown in FIG. 5(f). This output pulse is counted by the counter 37 and latched at the rising edge pulse of the comparator 32, and the stored value of the latch 38 is outputted every cycle. This count output has a value corresponding to the phase difference between the excitation AC voltage V and the excitation current I.

In this way, the torque applied to the shaft 3 to be measured can be detected as an electrical signal.

By the way, in a torque sensor that utilizes the magnetostrictive effect as in the present invention, when torque is applied to the shaft to be measured, the magnetic properties of the magnetic film deposited on the shaft to be measured change, causing a change in the impedance of the winding. appear.

This change is detected as a phase change, as shown in Fig. 11(a).
.

As shown in the vector diagram of (3), if the current flowing through the resistance of the winding (III>IR') is large, even if the change in impedance is the same (ΔT, / 1.-Δ12'/1.
') The phase change becomes smaller (Δθ × Δθ').

Therefore, lowering the resistance of the winding portion leads to improved sensitivity. In fact, the direct current resistance of the winding can be lowered, but the current flowing through the winding becomes large due to high frequency resistance caused by the skin effect of the winding, magnetic film, eddy current flowing in the shaft under test, etc. Since the phase difference is measured including this phase difference, the sensitivity becomes low.

FIG. 7 shows an embodiment in which such problems are solved and the detection sensitivity is improved.

In this embodiment, the voltage V1 proportional to the excitation current I applied to the comparator 32 in FIG. 4 is compensated as follows. That is, the compensation circuit in FIG.
First, the excitation current VI = Rolosin (ω and ÷ ψ) is inverted in the negative-stage operational amplifier 41, and a certain gain K (gain (adjusted with the regulator 43), add them together, and invert them. As a result, the second stage operational amplifier 4
The output V' of 2 is V''' V+ K V = Rolnsin(ωt+ S') −KVosin
ωt= (LLcos %-KVo) sin cc+t
+RoLsinψcosωt= (Rolocos%
-KVo) + Rol, sin@) 5in (ω is 10) θ=jan' (Rnlosin 9'/(
R(II+IcOs 1i17-KVo) 'j. That is, the harmonic resistance component can be arbitrarily removed from the current flowing as the total impedance component of the winding.

The relationship between θ and - in the above equation is expressed in a vector diagram as shown in FIG. As this figure shows, by appropriately selecting the value of K, it is possible to extract a large change in phase difference (θ
＞y＞.

Therefore, instead of taking the phase ψ of V and 1 to perform torque detection, in this embodiment, the phase θ of V and V' is taken to increase the sensitivity. As an example, K=Z'Rolo/Vo1
That is, the amplitude V0 of V' is R,! .

FIG. 9 shows the characteristics of the applied torque and phase difference in the case of A, together with the conventional example.

In this case, the sensitivity can be improved approximately twice as compared to the case without high frequency compensation.

FIG. 10 shows another embodiment. In this example, the center-tapped transformer 6 causes the current flowing through the resistance of the winding 1 to flow in the opposite direction to the detection resistor 5 and cancel it out, thereby increasing the sensitivity. In other words, the equivalent parallel resistance on the sensor winding 1 side is R7
Then, a resistor 7 having a resistance value of Rp/k is connected to the other side of the transformer 6 to cancel out the resistance current.

If =1/2 here, the torque-phase difference characteristic will be equivalent to the torque-phase difference characteristic shown in FIG.

〔Effect of the invention〕

As described above, in the present invention, in a non-contact torque detection method using the magnetostrictive effect, a parallel LC resonant circuit is created by connecting a capacitor in parallel with a winding wound around a magnetic material with a certain gap. Torque is detected by configuring the motor, excitation with alternating current at a frequency near its resonance frequency, and measuring the phase difference between the excitation voltage and the excitation current. By exciting the winding at a frequency close to the resonant frequency, the temperature characteristics are significantly improved compared to the oscillation method using multi-vibration, making it suitable for robots used in environments with large heat generation and temperature changes. It can be directly incorporated into the output shaft of a joint drive actuator or a machine tool drive motor. Furthermore, since only one winding is required around the axis to be measured, the number of parts is reduced and the device can be simplified.

The linearity of torque detection is largely influenced by the value of the winding current to the magnetostrictive film, but with this method, the current value can be freely set by changing the voltage applied to the winding.
It becomes possible to set the optimum operating point.

In addition, by measuring the phase difference between the compensation excitation voltage obtained by subtracting the excitation voltage multiplied by a certain gain from the excitation current and the excitation current, it is possible to compensate for an increase in the high frequency resistance of the winding. Sensitivity can be increased by suppressing the effects of the skin effect of the wire, magnetic film, eddy current flowing in the measured axis, etc., and noise resistance is enhanced. Therefore, it can be directly incorporated into the output shaft of a robot's joint drive actuator or the output shaft of a machine tool drive motor. Since the resistance component is removed, the temperature characteristics are improved.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of a winding for implementing the present invention, Fig. 2 is a circuit diagram showing an example of a detection circuit, Fig. 3 is a characteristic diagram showing a phase change in response to a torque change, and Fig. 4 is a diagram showing an example of a detection circuit. A block diagram showing an embodiment of the invention, FIG. 5 is a waveform diagram showing its operation, FIG. 6 is a temperature characteristic diagram of the present invention compared with a conventional example, and FIG. 7 is a circuit diagram showing an example of performing high frequency resistance compensation. , FIG. 8 is a diagram showing a comparison between the detection phase and the compensation phase, FIG. 9 is a characteristic diagram showing the relationship between applied torque and phase difference, and FIG. 10 is a circuit diagram showing another embodiment of high-frequency resistance compensation. FIG. 11 is a vector diagram showing the phase relationship between currents, FIG. 12 is a diagram showing an example of a conventional winding, and FIG. 13 is a circuit diagram showing an example of a conventional detection circuit. 1: Winding 2: Magnetic film 3: Axis to be measured 4: Capacitor 5: Detection resistor
6: Transformer 7: Resistor 31. 32: Comparator 33; Clock pulse generator 34. 36: AND gate 35: Inverter 37: Counter 38: Latch 41. 42: Operational amplifier
43 Nigain Regulator Patent Applicant Yasuyo Electric Manufacturing Co., Ltd. Representative Person Kobori Seedling Box Diagram Diagram Diagram Temperature Rise (deg) Diagram Diagram Diagram Diagram Diagram (a) (b) Δθ Δθ9

Claims (2)

[Claims] 1. In a non-contact torque detection method that utilizes the magnetostrictive effect of a magnetic material, a capacitor is connected in parallel to a winding wound around the magnetic material with a certain gap, and the capacitance of this capacitor and the inductance of the winding are Parallel L
A torque detection method comprising a C resonant circuit, AC excitation at a frequency near the resonant frequency, and torque detection by measuring the phase difference between the excitation voltage and the excitation current. 2. By measuring the phase difference between the compensation excitation voltage obtained by subtracting the excitation voltage multiplied by a certain gain from the excitation current and the excitation current, the torque that compensates for the increase in high frequency resistance of the winding is detected. The torque detection method according to claim 1, characterized in that: