Patent Description:
In a plant or factory, there are cases in which a reaction step of accelerating a chemical reaction of raw materials or an stirring step of mixing raw materials of various types is performed to obtain a predetermined product or an intermediate material. In such a step, a chemical reaction of raw materials is accelerated or a degree of mixing of raw materials is made uniform by rotating a rotating shaft to which rotary blades are attached using an electric motor. Here, an acceleration status of the chemical reaction and a mixing status are estimated by measuring a viscosity of the product or intermediate material.

Currently, a rotational viscometer has been mainstream for viscometers for measuring a viscosity. This rotational viscometer measures a viscosity by detecting a reaction torque acting on a rotating shaft in case that the rotating shaft is rotated and converting the detection result into a viscosity. In case that such a rotational viscometer is applied to online measurement, for example, a strain gauge (torque sensor) attached to the rotating shaft for detecting a reaction torque and a calculator converting a detection result of the strain gauge into a viscosity are thought to be necessary.

Further, the following Non-Patent Literature <NUM> discloses a conventional method for detecting a reaction torque acting on a rotating shaft. Specifically, in the method disclosed in Non-Patent Literature <NUM> below, a reaction torque received by the rotating shaft is detected on the basis of an angular response of the rotating shaft. Patent Literature <NUM> discloses a method for detecting rotary speed by which it is possible to obtain the rotary speed of the rotating shaft of the induction motor without employing a measuring instrument. Patent Literature <NUM> discloses a reaction solution viscosity detector which includes a power detection means, a current detection means, a voltage detection means, a rotational speed detection means for detecting speed of the rotational shaft, and a frequency detection means for detecting inverter output frequencies, and performs a specific operation based on values of detection output obtained in the respective processes, thus calculating precise rotary torque and further detecting reaction solution viscosity based on the rotary torque detection value. Patent Literature <NUM> discloses a stirring device having a stirring vane which is provided in a container main body, wherein a current value for an electric motor to rotate the stirrer with a predetermined rotational frequency is measured as a load, and a viscosity is measured on the basis of the measured current value.

Incidentally, in case that a rotational viscometer is applied to online measurement, as described above, a strain gauge for detecting a reaction torque acting on a rotating shaft needs to be attached to the rotating shaft. Here, since a strain gauge is liable to deteriorate due to high temperatures, it may not be usable depending on an environmental temperature. Also, since existing equipment may need to be disassembled or processed for attaching a strain gauge, it may be difficult to attach the strain gauge to a rotating shaft.

Some preferred aspects of the present invention have been made in view of the above circumstances, and an objective thereof is to provide a viscosity estimation device and a viscosity estimation method that can estimate a viscosity without using a strain gauge and can be applied to online measurement of viscosity.

To solve the above-described problem, , a viscosity estimation device and a viscosity estimation method as defined in the appended claims have been developed. Thus, a viscosity estimation device according to one aspect of the present invention is a viscosity estimation device (<NUM>, <NUM>) which estimates a viscosity of a substance stirred by a rotation of a rotating shaft (AX) rotationally driven by an induction motor (IM), wherein the viscosity estimation device includes: a current detector (<NUM>) detecting a drive current supplied to the induction motor; a rotation detector (<NUM>, 20A) detecting rotation of the rotating shaft; and a calculator (<NUM>, 30A) obtaining a viscosity correlation value (ST), which is a value having a correlation with a viscosity of the substance, using a detection result of the current detector and a detection result of the rotation detector.

In addition, in the viscosity estimation device of the present invention, the calculator includes: a slip ratio calculator (<NUM>) obtaining a slip ratio of the rotating shaft using the detection result of the current detector and the detection result of the rotation detector; an effective value calculator (<NUM>) obtaining an effective value of the drive current from the detection result of the current detector; and a viscosity correlation value calculator (<NUM>) obtaining the viscosity correlation value using a calculation result of the slip ratio calculator and a calculation result of the effective value calculator.

In addition, in the viscosity estimation device of the present invention, the calculator includes a frequency calculator (<NUM>) obtaining a frequency of the drive current from the detection result of the current detector, and the slip ratio calculator obtains a slip ratio of the rotating shaft using a calculation result of the frequency calculator and a rotation speed of the rotating shaft obtained from the detection result of the rotation detector.

In addition, in the viscosity estimation device of the present invention, the calculator includes a rotation speed calculator (<NUM>) obtaining a rotation speed of the rotating shaft from the detection result of the rotation detector.

In addition, in the viscosity estimation device according to one aspect of the present invention, in case that it is assumed that the viscosity correlation value is ST, a frequency of the drive current may be ω [rad/s] or [Hz], a rotation speed of the rotating shaft is ωm [rad/s] or [Hz], the effective value of the drive current is Ia, and the slip ratio of the rotating shaft is s [%], the viscosity correlation value calculator obtains the viscosity correlation value ST by performing a calculation shown in the following expression (<NUM>). <NUM>] <MAT>.

In addition, in the viscosity estimation device according to one aspect of the present invention, the drive current may have three phases, and the current detector may detect all phases of the three phases.

In addition, in the viscosity estimation device according to one aspect of the present invention, the drive current may have three phases, and the current detector may detect only one specific phase of the three phases.

In addition, in the viscosity estimation device according to one aspect of the present invention, in case that it is assumed that the slip ratio is s, a frequency of the drive current detected by the current detector is ω, and a rotation speed of the rotating shaft detected by the rotation detector is ωm, the slip ratio calculator may perform a calculation of s = (ω-ωm)/ω to obtain the slip ratio.

In addition, in the viscosity estimation device according to one aspect of the present invention, the frequency calculator may obtain a frequency of the drive current each time the rotating shaft rotates by a prescribed number of revolutions.

In addition, in the viscosity estimation device according to one aspect of the present invention, the effective value calculator may obtain the effective value of the drive current each time the rotating shaft rotates by the number of revolutions.

In addition, in the viscosity estimation device of the present invention, the calculator further includes a viscosity correlation value viscosity calculator (<NUM>) which converts the viscosity correlation value obtained by the viscosity correlation value calculator into a viscosity value of the substance.

In addition, in the viscosity estimation device according to one aspect of the present invention, the calculator further may include a filter calculator (<NUM>) which performs smoothing processing on the viscosity value converted by the viscosity correlation value viscosity calculator.

In addition, in the viscosity estimation device of the present invention, the rotation detector detects the rotation after the current detector has detected the drive current.

In the viscosity estimation device the present invention, the current detector may detect the drive current after the rotation detector has detected the rotation.

In addition, in the viscosity estimation device according to one aspect of the present invention, the current detector may perform processing of detecting the drive current in parallel with processing of detecting the rotation by the rotation detector.

In addition, in the viscosity estimation device according to one aspect of the present invention, the rotation detector may be an encoder.

In addition, in the viscosity estimation device according to one aspect of the present invention, the rotation detector may be a tachometer.

A viscosity estimation method of the present invention is a viscosity estimation method for estimating a viscosity of a substance stirred by a rotation of a rotating shaft (AX) rotationally driven by an induction motor (IM), the viscosity estimation method including: a detection step (S11) of detecting a drive current supplied to the induction motor; a rotation detection step (S14) of detecting rotation of the rotating shaft; and a calculation step (S17) of obtaining a viscosity correlation value, which is a value having a correlation with a viscosity of the substance, using a detection result of the current detection step and a detection result of the rotation detection step.

According to some preferred aspects of the present invention, there is an effect that a viscosity can be estimated without using a strain gauge and this is applicable to online measurement of viscosity.

Hereinafter, a viscosity estimation device and a viscosity estimation method according to one embodiment of the present invention will be described in detail with reference to the drawings. Hereinafter, an outline of the embodiment of the present invention will be described first, and then details of each embodiment of the present invention will be described.

In the embodiment of the present invention, a viscosity can be estimated without using a strain gauge and this can be applied to online measurement of viscosity. For example, the embodiment of the present invention makes it possible to continuously estimate a viscosity of a material in a device (for example, a reactor or stirring device) that stirs the material in a tank by rotating a rotating shaft having stirring blades with an induction motor online.

Here, in the Japanese Industrial Standards (JIS: Japanese Industrial Standards), viscometers are classified into six types (JIS Z <NUM>) including a capillary viscometer, a falling ball viscometer, a coaxial double cylindrical rotational viscometer, a single cylindrical rotational viscometer, a cone-and-plate rotational viscometer, and a vibrational viscometer. Such viscometers are generally used as a testing instrument used in a research laboratory, an experimental laboratory, or the like. Therefore, conventionally, in a plant or the like, quality control has been performed by removing a sample from a product or an intermediate material being manufactured and measuring a viscosity of the removed sample in a measuring room.

Since an influence of measurement variation needs to be reduced in case that measuring a viscosity, viscosity measurements are performed a plurality of times by a tester having specialized knowledge. Therefore, viscosity measurement for a product requires a certain amount of time, and this has been a hindrance to productivity improvement and quality improvement. Here, a device for continuously measuring a viscosity online has also been realized, but it is expensive, requires special design for installation, and requires frequent maintenance to maintain the performance thereof. Therefore, it is the current situation that a device for continuously measuring a viscosity online has a limited field of application.

Currently, rotational viscometers are mainstream for viscometers for measuring a viscosity. In case that such a rotational viscometer is applied to online measurement, for example, a strain gauge (torque sensor) attached to a rotating shaft for detecting a reaction torque and a calculator converting a detection result of the strain gauge into a viscosity are thought to be necessary. Here, since the strain gauge is liable to deteriorate due to high temperatures, it may not be usable depending on an environmental temperature. Also, since existing equipment may need to be disassembled or processed for attaching a strain gauge, it may be difficult to attach the strain gauge to a rotating shaft.

In the embodiment of the present invention, a drive current supplied to an induction motor that rotationally drives a rotating shaft stirring a substance whose viscosity is a target to be estimated is detected, rotation of the rotating shaft is detected, and a detection result of the drive current and a detection result of the rotation of the rotating shaft are used to obtain a viscosity correlation value which is a value having a correlation with a viscosity of the substance. Thereby, a viscosity can be estimated without using a strain gauge, and this can be applied to online measurement of viscosity.

<FIG> is a block diagram showing a configuration of a main part of a viscosity estimation device <NUM> according to one embodiment of the present invention. As shown in <FIG>, the viscosity estimation device <NUM> of the present embodiment includes a current transformer <NUM> (also referred to as a current detector), an encoder <NUM> (also referred to as a rotation detector), and a calculator <NUM>. The viscosity estimation device <NUM> having such a configuration estimates a viscosity of a substance that is stirred by rotation of a rotating shaft AX that is rotationally driven by an induction motor IM. Further, the substance stirred by rotation of the rotating shaft AX may be an arbitrary substance.

Here, the induction motor IM includes a stator having a coil and a rotor having, for example, a cage-shaped structure, and the rotor is rotated by a rotating magnetic field formed by the coil of the stator. The induction motor IM may be driven by a single-phase alternating current or may be driven by a three-phase alternating current. In the present embodiment, a case in which the induction motor IM is driven by a three-phase alternating current will be described.

The rotating shaft AX is, for example, a columnar (rod-shaped) member, and is rotationally driven by rotation of the rotor of the induction motor IM. The rotating shaft AX may be connected to the rotor of the induction motor IM via a speed reducer having a prescribed speed reduction ratio. In a case in which such a speed reducer is provided, for example, in case that a drive current at a predetermined frequency (for example, <NUM> [Hz]) is supplied to the induction motor IM, the rotating shaft AX rotates at a predetermined number of revolutions (for example, <NUM> [rpm]) in a state of no load. Further, the rotating shaft AX may be directly attached to and coaxial with the rotor of the induction motor IM. Also, stirring blades may be provided on the rotating shaft AX.

The current transformer <NUM> detects a drive current supplied to the induction motor IM. Further, the current transformer <NUM> may detect all phases (three phases) of the drive current supplied to the induction motor IM or may detect only one specific phase. In the present embodiment, the current transformer <NUM> is assumed to detect only one specific phase of the three phases. A detection result of the current transformer <NUM> is output to the calculator <NUM>.

The encoder <NUM> detects rotation of the rotating shaft AX. Specifically, the encoder <NUM> detects an amount of rotation (or a rotational position) of the rotating shaft AX and outputs the number of pulses corresponding to a detection result thereof. The encoder <NUM> may be of a mechanical rotary encoder or may be of an optical rotary encoder. The detection result of the encoder <NUM> is output to the calculator <NUM>.

The calculator <NUM> includes a frequency calculator <NUM>, a rotation speed calculator <NUM>, a slip ratio calculator <NUM>, an effective value calculator <NUM>, an ST calculator <NUM> (also referred to as a viscosity correlation value calculator), an ST viscosity calculator <NUM>, and a filter calculator <NUM>. The calculator <NUM> having such a configuration obtains a viscosity correlation value ST (also referred to as a slip torque coefficient), which is a value having a correlation with a viscosity of a substance, using the detection result of the current transformer <NUM> and the detection result of the encoder <NUM>, and estimates a viscosity of the substance on the basis of the viscosity correlation value ST.

The frequency calculator <NUM> obtains a frequency ω [rad/s] or [Hz] of the drive current supplied to the induction motor IM from the detection result of the current transformer <NUM>. For example, the frequency calculator <NUM> may be configured to obtain the frequency ω of the drive current supplied to the induction motor IM each time the rotating shaft AX rotates by a prescribed number of revolutions N (N is an integer of <NUM> or more). Further, a timing or a period for obtaining the frequency ω of the drive current supplied to the induction motor IM by the frequency calculator <NUM> can be arbitrarily set.

The rotation speed calculator <NUM> obtains a rotation speed ωm [rad/s] or [Hz] of the rotating shaft AX from the detection result of the encoder <NUM>. For example, the rotation speed calculator <NUM> may be configured to obtain the rotation speed ωm of the rotating shaft AX every time a prescribed time (for example, <NUM> [s]) elapses. Further, a timing or a period for obtaining the rotation speed ωm of the rotating shaft AX by the rotation speed calculator <NUM> can be arbitrarily set.

The slip ratio calculator <NUM> obtains a slip ratio of the rotating shaft AX using the detection result of the current transformer <NUM> and the detection result of the encoder <NUM>. Specifically, the slip ratio calculator <NUM> obtains the slip ratio of the rotating shaft AX using the frequency ω of the drive current obtained by the frequency calculator <NUM> using the detection result of the current transformer <NUM> and the rotation speed ωm of the rotating shaft AX obtained by the rotation speed calculator <NUM> using the detection result of the encoder <NUM>. More specifically, the slip ratio calculator <NUM> performs the calculation shown in the following expression (<NUM>) to obtain a slip ratio s [%] of the rotating shaft AX. [Math <NUM>] <MAT>.

The effective value calculator <NUM> obtains an effective value Ia [A] of the drive current supplied to the induction motor IM from the detection result of the current transformer <NUM>. For example, the effective value calculator <NUM> may be configured to obtain the effective value Ia of the drive current each time the rotating shaft AX rotates by the prescribed number of revolutions N as in the frequency calculator <NUM>. Further, a timing or a period for obtaining the effective value Ia of the drive current by the effective value calculator <NUM> can be arbitrarily set.

The ST calculator <NUM> obtains a viscosity correlation value ST using a calculation result of the slip ratio calculator <NUM> and a calculation result of the effective value calculator <NUM>. Specifically, the ST calculator <NUM> performs the calculation shown in the following expression (<NUM>) to obtain the viscosity correlation value ST by using the frequency ω of the drive current obtained by the frequency calculator <NUM>, the rotation speed ωm of the rotating shaft AX obtained by the rotation speed calculator <NUM>, the effective value Ia of the drive current obtained by the effective value calculator <NUM>, and the slip ratio s of the rotating shaft AX obtained by the slip ratio calculator <NUM>. <NUM>] <MAT>.

Here, a case in which a model of the induction motor IM in a stationary coordinate system (αβ coordinate system) is converted into a dq coordinate system may be conceived. In case that it is assumed that the number of poles of the induction motor IM is P, a mutual inductance between the stator and the rotor is M, a maximum value of a current on a d-axis is Id, and a direct current (DC) resistance value of the rotor is Rr, a generated torque τe in a steady state of the induction motor IM is represented by the following expression (<NUM>). <NUM>] <MAT>.

Also, in case that it is assumed that a braking coefficient (= viscosity) is Rm and Coulomb friction is T<NUM>, a generated torque τe in a steady state of the induction motor IM is represented by the following expression (<NUM>). <NUM>] <MAT>.

The following expression (<NUM>) can be obtained from the above expressions (<NUM>) and (<NUM>). <NUM>] <MAT>.

Now, in case that the mutual inductance M between the stator and the rotor, the DC resistance value Rr of the rotor, and the Coulomb friction Tl are assumed to be constant, the following two conditions are assumed.

Then, the above expression (<NUM>) is represented by the following expression (<NUM>). <NUM>] <MAT>.

From the above expression (<NUM>), it can be ascertained that the braking coefficient Rm indicating the viscosity is proportional to the product of a value obtained by dividing the frequency ω of the drive current by the rotation speed ωm of the rotating shaft AX, the square of the effective value Ia of the drive current, and the slip ratio s of the rotating shaft AX. Therefore, the viscosity correlation value ST, which is a value having a correlation with a viscosity of the substance, can be represented as in the above expression (<NUM>).

The ST viscosity calculator <NUM> converts the viscosity correlation value ST obtained by the ST calculator <NUM> into a viscosity value D. Specifically, the ST viscosity calculator <NUM> performs a calculation D = A·ST+B to convert the viscosity correlation value ST into the viscosity value D. Here, the variables A and B in the above expression may be stored in the ST viscosity calculator <NUM> in advance prior to measurement of a viscosity of the substance and may be input to the ST viscosity calculator <NUM> in case that measurement of a viscosity of the substance is performed. Further, the variable A in the above expression defines a scale factor (enlargement/reduction factor) of the viscosity correlation value ST, and the variable B in the above expression defines an offset of the viscosity correlation value ST.

The filter calculator <NUM> performs smoothing processing using a filter such as, for example, a primary delay filter (low-pass filter). In case that such smoothing processing is performed, since, for example, high frequency components are removed, a viscosity of the substance can be estimated with high accuracy. Data (for example, data indicating the viscosity) obtained by the smoothing processing performed in the filter calculator <NUM> is collected by a data collecting device or displayed on a display device via, for example, a network (not shown).

<FIG> is a flowchart showing a viscosity estimation method according to one embodiment of the present invention. The flowchart shown in <FIG> is repeated, for example, at a preset regular cycle time. Here, a state in which a drive current is supplied to the induction motor IM from a drive device (not shown), the rotating shaft AX is rotationally driven by the induction motor IM, and a predetermined substance is stirred by rotation of the rotating shaft AX is assumed.

In case that the processing of the flowchart shown in <FIG> is started, the current transformer <NUM> first detects a drive current supplied to the induction motor IM (step S11: also referred to as a current detection step). The current transformer <NUM> outputs the drive current detected by the current transformer <NUM> to the calculator <NUM>. Then, the frequency calculator <NUM> obtains the frequency ω of the drive current supplied to the induction motor IM from the detection result of the current transformer <NUM> (step S12). Also, the effective value calculator <NUM> obtains the effective value Ia of the drive current supplied to the induction motor IM from the detection result of the current transformer <NUM> (step S13).

Next, the encoder <NUM> detects rotation of the rotating shaft AX (step S14: also referred to as a rotation detection step). The encoder <NUM> outputs the detection result of the encoder <NUM> to the calculator <NUM>. Then, the rotation speed calculator <NUM> obtains the rotation speed ωm of the rotating shaft AX from the detection result of the encoder <NUM> (step S15).

Next, the slip ratio calculator <NUM> obtains a slip ratio of the rotating shaft AX by using the frequency ω of the drive current obtained by the frequency calculator <NUM> and the rotation speed ωm of the rotating shaft AX obtained by the rotation speed calculator <NUM> (step S16). Specifically, the slip ratio calculator <NUM> performs the calculation shown in the above-described expression (<NUM>) to obtain the slip ratio s [%] of the rotating shaft AX.

Next, the ST calculator <NUM> obtains the viscosity correlation value ST by using the frequency ω of the drive current obtained by the frequency calculator <NUM>, the rotation speed ωm of the rotating shaft AX obtained by the rotation speed calculator <NUM>, the effective value Ia of the drive current obtained by the effective value calculator <NUM>, and the slip ratio s of the rotating shaft AX obtained by the slip ratio calculator <NUM> (step S17: also referred to as a calculation step). Specifically, the ST calculator <NUM> performs the calculation shown in the above-described expression (<NUM>) to obtain the viscosity correlation value ST.

In case that the above-described processing is completed, the ST viscosity calculator <NUM> converts the viscosity correlation value ST obtained by the ST calculator <NUM> into the viscosity value D (step S18). Specifically, the ST viscosity calculator <NUM> performs the calculation D = A·ST+B to convert the viscosity correlation value ST into the viscosity value D. Then, the filter calculator <NUM> performs smoothing processing using a filter such as, for example, a primary delay filter (low-pass filter) (step S19). Then, data (for example, data indicating the viscosity) obtained by performing the smoothing processing is collected by a data collecting device or displayed on a display device via, for example, a network (not shown).

In the flowchart shown in <FIG>, for convenience of explanation, an example in which the processing of steps S14 and S15 are performed after completing the processing of steps S11 to S13 is shown. However, the processing of steps S14 and S15 may be performed before the processing of steps S11 to S13 or may be performed in parallel with the processing of steps S11 to S13.

<FIG> is a block diagram showing a configuration of a modified example of a viscosity estimation device <NUM> according to one embodiment of the present invention. As shown in <FIG>, the viscosity estimation device <NUM> according to the present modified example has a configuration in which the encoder <NUM> of the viscosity estimation device <NUM> shown in <FIG> is replaced with a tachometer 20A (rotation detector) and the calculator <NUM> is replaced with a calculator 30A. The tachometer 20A detects the rotation speed ωm [rad/s] or [Hz] of the rotating shaft AX. The tachometer 20A may be of a mechanical type or may be of an electric type.

The calculator 30A has a configuration in which the rotation speed calculator <NUM> of the calculator <NUM> shown in <FIG> is omitted, and a detection result of the tachometer 20A is directly input to the slip ratio calculator <NUM> of the calculator 30A. That is, since the tachometer 20A can directly detect the rotation speed ωm of the rotating shaft AX, the rotation speed calculator <NUM> for obtaining the rotation speed ωm of the rotating shaft AX from the detection result of the encoder <NUM> is omitted.

The flowchart showing the viscosity estimation method according to the present modified example is almost the same as the flowchart shown in <FIG>. Specifically, in the flowchart showing the viscosity estimation method according to the present modified example, the "detecting rotation of the rotating shaft" in step S14 in <FIG> is read as "detecting a rotation speed of the rotating shaft," and step S15 is omitted.

As described above, in the embodiment of the present invention, a drive current supplied to the induction motor that rotationally drives the rotating shaft stirring a substance whose viscosity is a target to be estimated is detected, rotation of the rotating shaft is detected, and the detection result of the drive current and the detection result of the rotation of the rotating shaft are used to obtain a viscosity correlation value which is a value having a correlation with a viscosity of the substance. Thereby, a viscosity can be estimated without using a strain gauge, and this can be applied to online measurement of viscosity.

Although the viscosity estimation device and the viscosity estimation method according to one embodiment of the present invention have been described above, the present invention is not limited to the above-described embodiment and can be freely changed within the scope of the present invention, as defined by the appended claims. For example, in the above-described embodiment, the viscosity correlation value ST, which is a value having a correlation with a viscosity of the substance, has been obtained using the detection result of the current transformer <NUM> and the detection result of the encoder <NUM> (or the tachometer 20A), and the viscosity of the substance estimated on the basis of the viscosity correlation value ST has been collected by a data collecting device or displayed on a display device via a network.

However, the detection result of the current transformer <NUM> and the detection result of the encoder <NUM> may be collected via a network, and the viscosity correlation value ST may be obtained and the viscosity may be estimated on the basis of the collected detection results. In this way, a viscosity of a substance can be estimated at a distant place away from an installation location of the induction motor IM and the rotating shaft AX.

Claim 1:
A viscosity estimation device (<NUM>, <NUM>) configured to estimate a viscosity of a substance stirred by a rotation of a rotating shaft rotationally driven by an induction motor, the viscosity estimation device comprising:
a current detector (<NUM>) detecting a drive current supplied to the induction motor;
a rotation detector (<NUM>, 20A) detecting rotation of the rotating shaft; and
a calculator (<NUM>, 30A) obtaining a viscosity correlation value, which is a value having a correlation with a viscosity of the substance, using a detection result of the current detector (<NUM>) and a detection result of the rotation detector (<NUM>, 20A),
wherein the calculator (<NUM>, 30A) comprises:
a slip ratio calculator (<NUM>) obtaining a slip ratio of the rotating shaft using the detection result of the current detector (<NUM>) and the detection result of the rotation detector (<NUM>, 20A);
an effective value calculator (<NUM>) obtaining an effective value of the drive current from the detection result of the current detector (<NUM>);
a frequency calculator (<NUM>) obtaining a frequency of the drive current from the detection result of the current detector (<NUM>);
a viscosity correlation value calculator (<NUM>) obtaining the viscosity correlation value using a calculation result of the slip ratio calculator (<NUM>), a calculation result of the effective value calculator (<NUM>), and a calculation result of the frequency calculator (<NUM>); and
a viscosity correlation value viscosity calculator (<NUM>) converting the viscosity correlation value obtained by the viscosity correlation value calculator (<NUM>) into a viscosity value of the substance, the conversion being performed based on a variable which defines a scale factor of the viscosity correlation value and a variable which defines an offset of the viscosity correlation value,
characterized in that
the viscosity correlation value calculator (<NUM>) is configured to obtain the viscosity correlation value by multiplying: a value obtained by dividing the frequency of the drive current by a rotation speed of the rotating shaft obtained by the detection result of the rotation detector (<NUM>, 20A); square of the effective value of the drive current; and the slip ratio of the rotating shaft.