JP7798348B2 - Material mixing method and mixing device - Google Patents

Description

The present invention relates to a mixing method for mixing materials using a mixer equipped with stirring blades, and a mixing device equipped with a mixer and a control device.

Mixers equipped with stirring blades are well known and are described, for example, in Patent Document 1. The type of mixer described in Patent Document 1 includes a container into which materials are poured, a rotating shaft located within the container, and multiple stirring blades attached to the rotating shaft. The rotating shaft is rotated by an electric motor and reducer located outside the container, allowing the stirring blades to rotate within the container. In other words, the materials can be mixed.

Some mixers, such as the mixer described in Patent Document 1, have a chopper installed inside the container. The chopper consists of a drive shaft that protrudes a certain length into the container and multiple metal plates attached to the drive shaft; when the drive shaft rotates, these metal plates rotate at high speed. When the material hits the chopper rotating at high speed, a strong dispersion force is applied, resulting in efficient mixing.

Japanese Patent Application Laid-Open No. 2008-229461

The mixer described in Patent Document 1 excels by efficiently mixing materials using multiple rotating mixing blades and a chopper. However, the optimal mixing state for each material depends on its intended use and the type of material. Insufficient mixing may not be suitable for the intended purpose, while excessive mixing can alter the physical properties of the material. Therefore, mixers must be operated appropriately to achieve the appropriate mixing state. For example, a set operating time is used to operate the mixer. The set operating time is determined based on empirical results of achieving the desired mixing state when the mixer is mixed with the type and weight of the target materials. However, the mixing state will change if environmental conditions such as room temperature and humidity vary, or if the properties of the materials differ. In other words, setting an operating time and operating the mixer does not guarantee that the desired mixing state will be achieved. Another method involves detecting changes in the torque of the electric motor that rotates the mixing blades to estimate the mixing state of the materials, rather than relying on operating time, and stopping mixing when the appropriate torque is reached. However, torque changes do not necessarily correlate highly with the mixing state, making it difficult to achieve the appropriate mixing state.

The present invention aims to solve these problems, specifically to provide a material mixing method that can mix materials to a desired mixture state. It also aims to provide a mixing device that is equipped with such a mixing method.

The present invention relates to a mixing method in which materials are fed into a mixer equipped with an agitating blade and mixed. During mixing, the vibration of the mixer is detected while the agitating blade is rotating, and changes in vibration acceleration are monitored. A time pattern is defined as a time-dependent change in the vibration acceleration, in which the vibration acceleration takes on minimum and maximum values over time depending on the mixing state of the materials, and mixing is completed when the vibration acceleration reaches a specific pre-set time pattern. According to another invention, the vibration acceleration monitored is the vibration acceleration for one or more frequency components of the vibration that are 1, 2, 3, ... , 6 times the rotational frequency of the agitating blade.

When mixing materials, the vibration acceleration changes over time, and this vibration acceleration correlates with changes in the mixed state of the materials. In other words, by monitoring changes in vibration acceleration, the mixed state of the materials can be inferred. This invention is configured to complete mixing when the vibration acceleration forms a specific, pre-set time pattern. In other words, when the change in the vibration acceleration over time forms a specific pattern, mixing is stopped. This allows the desired mixed state to be achieved. Another invention monitors the vibration acceleration for one or more frequency components of the vibration that are 1, 2, 3, ... times the rotational frequency of the mixing blades. These frequency components have characteristic patterns, as will be explained below. Therefore, the timing to stop mixing can be detected with high accuracy, and the desired mixed state can be achieved.

1 is a front cross-sectional view showing a mixing device according to an embodiment of the present invention. 2 is a side cross-sectional view of the mixing device according to the present embodiment, taken along the line XX in FIG. 1. FIG. 1 is a graph showing the relationship between mixing time and degree of mixing achieved when test materials are mixed. 10 is a graph showing the change in vibration acceleration of the X-axis component with respect to mixing time when the test material is mixed. 10 is a frequency spectrum obtained by frequency analysis of vibration acceleration at a predetermined timing when the test material is mixed. 10 is a graph showing the change over mixing time in vibration acceleration of a frequency component of a sixth harmonic wave, with the rotation frequency of the mixer as the fundamental wave, when a test material is mixed.

This embodiment will be described below. The material mixing method according to this embodiment can be performed using various types of mixing devices and is not limited to a specific type of mixing device. However, this description will focus on the mixing device 1 according to this embodiment, as shown in Figure 1.

<Mixing device>
The mixing device 1 according to this embodiment is generally composed of a horizontal mixer 2 and a control device 3 that controls the mixer 2. The mixer 2 has a cylindrical container 5 into which materials are introduced and mixed, and this container 5 is fixed horizontally to a housing 6. The container 5 is provided with a material inlet 5a at its top and a material outlet 5b at its bottom.

Within the vessel 5, a rotating shaft 8 is located at the center of the cylinder. The rotating shaft 8 is horizontal and has three arms 10, 10, 10 attached to it, with stirring blades 11, 11, 11 fixed to the tip of each arm. As shown in Figure 2, the three stirring blades 11, 11, 11 are spaced 120 degrees apart from one another when viewed from the side. One end 8a of the rotating shaft 8 protrudes outward from the vessel 5. The housing 6 is provided with a drive mechanism 13, consisting of an electric motor, a reducer, etc., and the protruding end 8a of the rotating shaft 8 is connected to the drive mechanism 13. Therefore, when the drive mechanism 13 is driven, the rotating shaft 8 rotates, causing the stirring blades 11, 11, 11 to rotate. This means that the materials within the vessel 5 are mixed. The drive mechanism 13 is connected to and controlled by the control device 3.

Two choppers 14, 14 are also provided within the vessel 5. The choppers 14, 14 consist of drive shafts 16, 16 that protrude a predetermined length into the vessel 5, and multiple metal plates 17, 17, ... attached to the drive shafts 16, 16. Although the drive unit is not shown in Figures 1 and 2, when the drive unit rotates the drive shafts 16, 16, the metal plates 17, 17 rotate at high speed. This exerts a strong dispersion force on the materials within the vessel 5. These choppers 14, 14 can be driven or stopped when mixing the materials. The choppers 14, 14 are controlled by the control unit 3.

<Acceleration sensor>
To perform the material mixing method according to this embodiment, at least one acceleration sensor is required to detect vibrations of the mixer 2. The mixing device 1 according to this embodiment is provided with first and second acceleration sensors 19 and 20, as shown in FIGS. 1 and 2 . The first acceleration sensor 19 is provided in the upper portion of the housing 6, and the second acceleration sensor 20 is provided in the lower portion of the housing 6. The acceleration sensors 19 and 20 may be of any type as long as they can detect vibrations of the mixer 2. In this embodiment, however, a capacitive three-axis acceleration sensor (BMX055 manufactured by Bosch) is used. The first and second acceleration sensors 19 and 20 are capable of detecting vibration accelerations in three orthogonal directions, i.e., the x-, y-, and z-directions. The first and second acceleration sensors 19 and 20 are connected to the control device 3, and the measured vibration accelerations are monitored by the control device 3.

Indicators for understanding the state of vibration include not only vibration acceleration, but also vibration amplitude and vibration energy. However, evaluating the state of vibration using vibration amplitude or vibration energy is essentially equivalent to evaluating it using vibration acceleration. This is because vibration acceleration is closely related to vibration energy, vibration amplitude, etc. In the material mixing method according to the present embodiment, which will be explained next, the mixing state is estimated by monitoring vibration acceleration, but even if the mixing state is estimated by monitoring vibration amplitude and vibration energy, this essentially amounts to monitoring vibration acceleration.

<Material Mixing Method According to the Present Embodiment>
The material mixing method according to this embodiment is implemented by the control device 3. In short, the method estimates the mixing state of the materials by monitoring the vibration acceleration detected by the acceleration sensors 19 and 20 when the mixer 2 is operated to mix the materials, and determines whether mixing is complete based on this information. The vibration acceleration changes over time when the materials are mixed. The pattern of change in this vibration acceleration over time, i.e., the time pattern, has a strong correlation with the mixing state of the materials. The material mixing method according to this embodiment utilizes this correlation. In other words, when the vibration acceleration conforms to a specific time pattern during mixing of the materials, it is determined that the desired mixing state has been achieved, and mixing is complete.

The time pattern of vibration acceleration required to determine the completion of mixing varies depending on the type of material. In other words, the time pattern of vibration acceleration when mixing one material cannot be used for a different type of material. Therefore, it is necessary to obtain in advance the relationship between the time pattern of vibration acceleration and the mixed state depending on the type of material being mixed. This can be obtained through a preparation process in which the target materials are mixed on a trial basis. Next, the preparation process will be explained using experimental materials as an example.

<Preparation process>
The materials used in the experiment were calcium carbonate (SUPER 1500, manufactured by Maruo Calcium) and ferric oxide (Todacolor 140ED, manufactured by Toda Kogyo). These materials become darker in brightness as mixing progresses and the ferric oxide particles become smaller in diameter, making them suitable for evaluating the degree of progress in the mixing state. Note that the degree of progress in the mixing state does not necessarily have to be evaluated by particle size, and can also be evaluated by other indicators such as viscosity.

The first step in the preparation process is to determine the relationship between mixing time and the degree of mixing achieved. 24.0 kg of calcium carbonate and 1.263 kg of ferric oxide are added to container 5 of mixer 2 and mixed. Mixing is stopped at an appropriate time, the brightness is measured with a brightness meter, and the mixed state is obtained. Mixing is started again, stopped at an appropriate time, the brightness is measured, and the mixed state is obtained. This process is repeated. The results obtained are shown in Figure 3. Note that graph 31 shows the changes when mixing is performed by driving not only mixing blades 11, 11, 11 but also choppers 14, 14, while graph 32 shows the changes when mixing is performed by driving only mixing blades 11, 11, 11 with choppers 14, 11, 14 stopped.

In the second stage of the preparation process, the relationship between mixing time and changes in vibration acceleration is obtained. The same amount of material as added in the first stage is added to container 5 of mixer 2 and mixed. During mixing, the vibration acceleration detected by acceleration sensors 19 and 20 is recorded. Figure 4 shows the relationship between mixing time and the vibration acceleration of the x-direction component of first acceleration sensor 19. In this embodiment, the x-direction is the direction parallel to rotation axis 8. Graph 35 shows the changes when mixing is performed by driving not only mixing blades 11, 11, 11 but also choppers 14, 14, while graph 36 shows the changes when mixing is performed by stopping choppers 14, 14 and driving only mixing blades 11, 11, 11.

Figure 5 shows a frequency spectrum obtained by frequency analysis of vibration acceleration measured at a certain timing. In the frequency spectrum, reference numeral 41 indicates the frequency component corresponding to the rotational frequency of the agitator blades 11, 11, 11. Similarly, reference numerals 42, 43, 44, 45, and 46 indicate the second, third, fourth, fifth, and sixth harmonics of the fundamental frequency of the agitator blades 11, 11, 11. The vibration acceleration of such nth-harmonic frequency components also exhibits a characteristic change over time. Figure 6 shows a graph illustrating the relationship between mixing time and vibration acceleration for the sixth-harmonic frequency component during the second stage of the preparation process. Graph 51 shows the change when mixing is performed by driving not only the agitator blades 11, 11, 11 but also the choppers 14, 14, while graph 52 shows the change when mixing is performed by driving only the agitator blades 11, 11, 11 with the choppers 14, 14 stopped.

<Regular operation>
As shown in graphs 35 and 36 in Figure 4 and graphs 51 and 52 in Figure 6, the vibration acceleration changes over time. That is, the time pattern of the vibration acceleration changes as the mixed state of the materials changes. When mixing materials, if the vibration acceleration is monitored and a specific time pattern is detected and mixing is stopped, the materials can be mixed in a desired state. An example of this operation will be described.

The following procedure is used to mix materials by driving both the mixing blades 11, 11, 11 and the choppers 14, 14. For example, suppose mixing is to be completed when the mixing reaches 90%. Graph 31 in Figure 3 (mixing blades 11, 11, 11 and choppers 14, 14 driven) indicates that the mixing time required to reach 90% mixing is approximately 1200 seconds. Graph 35 in Figure 4 (mixing blades 11, 11, 11 and choppers 14, 14 driven) shows that the mixing time reaches a minimum value, indicated by reference numeral 61, just before approximately 1200 seconds, and then begins to increase. In other words, the time pattern is one in which the mixing reaches a minimum value and then begins to increase. The time pattern indicated by reference numeral 61 is stored in the control device 3. When the mixing blades 11, 11, 11 and choppers 14, 14 are driven in the mixer 2 to mix the materials, the control device 3 monitors the x-direction component of the vibration acceleration. Mixing is stopped when the time pattern indicated by reference numeral 61 is detected. This allows mixing to be completed at 90% mixing completion.

When mixing materials by stopping choppers 14 and driving only agitator blades 11, 11, 11, the process is as follows. For example, suppose you want to complete mixing when the mixing level reaches 60%. Graph 33 in Figure 3 (only agitator blades 11, 11, 11 driven) indicates that the mixing time required to achieve 60% mixing is approximately 200 seconds. Graph 51 in Figure 6 (only agitator blades 11, 11, 11 driven) shows that the mixing time reaches a maximum value at approximately 200 seconds, as indicated by reference numeral 62, and then begins to decrease. In other words, the time pattern is one in which the value reaches a maximum value and then begins to decrease. The time pattern indicated by reference numeral 62 is stored in control device 3. When mixer 2 is driving only agitator blades 11, 11, 11 to mix, control device 3 monitors the frequency component of the sixth harmonic of the vibration acceleration. When control device 3 detects the time pattern indicated by reference numeral 62, mixing is completed when the mixing level reaches 60%.

While only two examples of this operation have been explained, the time pattern to be monitored can be freely selected to match the desired degree of mixing achieved. In the above explanation, the x-direction component of vibration acceleration and the frequency component of the sixth harmonic wave were explained, but vibration acceleration can also be monitored for the y-direction component, z-direction component, or for nth harmonic wave frequency components other than the sixth harmonic wave. Alternatively, the x-direction component of vibration acceleration and the frequency component of the nth harmonic wave can be monitored simultaneously, and mixing can be completed when it is detected that a specific time pattern has been reached for each.

REFERENCE SIGNS LIST 1 Mixing device 2 Mixer 3 Control device 5 Container 6 Housing 8 Rotating shaft 10 Arm 11 Stirring blade 13 Driving mechanism 14 Chopper 16 Driving shaft 17 Metal plate 19, 20 Acceleration sensor

Claims (9)

A mixing method in which materials are mixed by being introduced into a mixer equipped with stirring blades,
The vibration of the mixer during rotation of the stirring blade is detected as vibration acceleration,
A time pattern is a pattern of change in the time direction in which the vibration acceleration takes on a minimum value or a maximum value over time depending on the mixing state of the material,
A material mixing method in which mixing is completed when it is detected that the vibration acceleration has formed a predetermined specific time pattern. 2. The material mixing method according to claim 1, wherein the vibration acceleration to be monitored is a vibration acceleration for one or more frequency components of the vibration that are 1, 2, 3, ... , 6 times the rotation frequency of the stirring blade among the frequency components of the vibration. The mixing method includes a preparation step of setting the specific time pattern,
3. The material mixing method according to claim 1, wherein the preparation step comprises: feeding equivalent materials into the mixer, mixing the materials, observing changes in the mixed state of the materials, detecting a time pattern of the vibration acceleration when a desired mixed state is reached, and determining the specific time pattern. The material mixing method according to claim 1 or 2, wherein the vibration acceleration monitored is the vibration acceleration for each of three mutually orthogonal components of the vibration: the x-direction, y-direction, and z-direction. The material mixing method described in claim 1 or 2, wherein the mixer is provided with a chopper that disperses the materials, and the chopper is driven in parallel with the rotation of the stirring blades. a mixer into which the material is fed;
a rotating stirring blade provided in the mixer;
a vibration detection means provided in the mixer;
a control device;
The control device, when rotating the stirring blades, obtains vibration acceleration from the vibration of the mixer detected by the vibration detection means and monitors changes in the vibration acceleration, and determines a time pattern as a change in the time direction in which the vibration acceleration takes on minimum and maximum values over time depending on the mixing state of the materials, and stops the stirring blades when it detects that the vibration acceleration has become a specific time pattern that is preset in the control device. 7. The mixing device according to claim 6, wherein the vibration acceleration monitored by the control device is a vibration acceleration for one or more frequency components of the vibration that are 1, 2, 3, ... , 6 times the rotational frequency of the stirring blade among the frequency components of the vibration. The mixing device described in claim 6 or 7, wherein the vibration acceleration monitored by the control device is the vibration acceleration for each of three mutually orthogonal components of the vibration: the x-direction, the y-direction, and the z-direction. The mixing device described in claim 6 or 7, wherein the mixer is provided with a chopper that disperses the material, and the chopper is driven by the control device in parallel with the rotation of the stirring blades.