WO2025169494A1 - Resin type estimation device and resin type estimation method - Google Patents

Abstract

This resin type estimation device comprises: an electromagnetic-wave generation unit that generates terahertz waves; an electromagnetic-wave incidence unit that causes the terahertz waves to be incident on resin waste; a transmitted-wave detection unit that detects transmitted waves transmitted through the resin waste and emitted; a reflected-wave detection unit that detects reflected waves reflected from the resin waste and emitted; a thickness estimation unit that estimates the thickness of the resin waste on the basis of reflected waves detected by the reflected-wave detection unit; and a resin type estimation unit that estimates the material of the resin waste on the basis of the intensity of the transmitted waves detected by the transmitted-wave detection unit and the thickness of the resin waste estimated by the thickness estimation unit.

Description

Resin type estimation device and resin type estimation method

This disclosure relates to a resin type estimation device and a resin type estimation method for estimating the type of resin.

Solid waste (e.g., waste plastic, etc.) is sorted based on the materials that make up the solid waste, and each material is reused. Therefore, for example, when solid waste is reused by generating materials from it, if the solid waste is sorted with high precision, the purity of the generated materials can be increased.

For this reason, estimation devices that estimate the materials that make up solid waste are known. For example, the estimation device described in Patent Document 1 discloses a method in which terahertz waves are incident on solid waste, and the terahertz waves that are reflected by the solid waste and emitted, or the terahertz waves that have passed through the solid waste and emitted, are detected, and the material is estimated based on the intensity of the detected terahertz waves.

Japanese Patent Application Laid-Open No. 2021-120625

On the other hand, Patent Document 1 discloses a method of using terahertz waves of multiple frequencies to estimate the material based on the detected intensity of each, but this method has the problem of requiring multiple detection units.

The present disclosure has been made to solve the above-mentioned problems, and aims to provide a resin type estimation device and a resin type estimation method that can estimate the materials of resin waste using a simple method.

A resin type estimation device according to one disclosure includes an electromagnetic wave generation unit that generates terahertz waves, an electromagnetic wave incidence unit that incidents the terahertz waves onto resin waste, a transmitted wave detection unit that detects transmitted waves that have passed through the resin waste and are emitted, a reflected wave detection unit that detects reflected waves that have been reflected and emitted from the resin waste, a thickness estimation unit that estimates the thickness of the resin waste based on the reflected waves detected by the reflected wave detection unit, and a resin type estimation unit that estimates the material of the resin waste based on the intensity of the transmitted waves detected by the transmitted wave detection unit and the thickness of the resin waste estimated by the thickness estimation unit.

A resin type estimation method according to one disclosure includes the steps of generating terahertz waves, directing the terahertz waves at resin waste, detecting transmitted waves that have passed through the resin waste and are emitted, detecting reflected waves that have been reflected from the resin waste and are emitted, estimating the thickness of the resin waste based on the detected reflected waves, and estimating the material of the resin waste based on the intensity of the detected transmitted waves and the estimated thickness of the resin waste.

The resin type estimation device and resin type estimation method disclosed herein make it possible to estimate the material of resin waste in a simple manner.

FIG. 1 is a diagram illustrating an estimation device 10 according to a first embodiment. FIG. 4 is a flowchart illustrating an operation of the estimation device 10 according to the first embodiment. FIG. 10 is a diagram illustrating arrival time difference information according to the first embodiment. 10A and 10B are diagrams illustrating changes in the intensity of electromagnetic waves according to the thickness of the resin waste 2 according to the first embodiment. FIG. 10 is a diagram illustrating the transmittance of 0.5 THz electromagnetic waves in various plastics according to the first embodiment. FIG. 10 is a diagram illustrating a resin type estimation table according to the first embodiment.

The following describes the embodiments with reference to the accompanying drawings. In the following description, identical parts are designated by the same reference numerals. Since their names and functions are also the same, detailed descriptions of them will not be repeated.

Embodiment 1.
FIG. 1 is a diagram illustrating an estimation device 10 according to a first embodiment. Referring to FIG. 1 , the estimation device 10 estimates the materials constituting the resin waste 2. The estimation device 10 estimates the materials constituting the resin waste 2 based on terahertz waves, which are electromagnetic waves in the frequency band of 100 GHz to 10 THz. The estimation device 10 includes an electromagnetic wave generation unit 11 that generates terahertz waves, an electromagnetic wave incidence unit 12 that directs the terahertz waves toward the resin waste 2, a transmitted wave detection unit 13 that detects transmitted waves that have passed through the resin waste 2 and are emitted, a reflected wave detection unit 16 that detects reflected waves that have been reflected from the resin waste 2, a thickness estimation unit 17 that estimates the thickness of the resin waste 2 based on the reflected waves detected by the reflected wave detection unit 16, and a resin type estimation unit 15 that estimates the material of the resin waste 2 based on the intensity of the transmitted waves detected by the transmitted wave detection unit 13 and the thickness of the resin waste 2 estimated by the thickness estimation unit 17. The estimation device 10 further includes a memory unit 14 that stores various data used by the resin type estimation unit 15. The resin type estimation unit 15 includes an intensity correction unit 18 that corrects the intensity of the transmitted wave detected by the transmitted wave detection unit 13 based on the thickness of the resin waste 2 estimated by the thickness estimation unit 17, and a material estimation unit 19 that estimates the material of the resin waste 2 based on the intensity of the corrected transmitted wave.

There is a strong correlation between the materials that make up the resin waste 2 and the propagation characteristics of electromagnetic waves having frequencies between 100 GHz and 10 THz in the resin waste 2. In this example, the propagation characteristics include at least one of the following: the property of transmitting electromagnetic waves, the property of reflecting electromagnetic waves, and the property of absorbing electromagnetic waves.

The estimation device 10 allows the electromagnetic waves emitted from the resin waste 2 to reflect the propagation characteristics of the electromagnetic waves in the resin waste with high accuracy. Therefore, the materials that make up the resin waste 2 can be estimated with high accuracy based on the intensity of the electromagnetic waves emitted from the resin waste 2.

The estimation device 10 estimates the materials that make up the resin waste 2. For example, the resin waste 2 includes containers, bags, plastic wrap, film, home appliance parts, automobile parts, or wire coating, all of which are made of materials whose main component is plastic. For example, the containers are bottles, tubes, packs, cups, trays, cases, etc. For example, the plastics are polystyrene, polypropylene, acrylonitrile butadiene styrene, etc.

The estimation device 10 estimates whether the material constituting the resin waste 2 is primarily composed of polystyrene, polypropylene, or acrylonitrile butadiene styrene.

The electromagnetic wave generating unit 11 generates terahertz waves, which are electromagnetic waves with a frequency between 100 GHz and 10 THz. The electromagnetic wave generating unit 11 includes a GUNN diode, an IMPATT (Impact Avalanche and Transit Time) diode, or a resonant tunneling diode (RTD). The electromagnetic wave generating unit 11 may also include an oscillator using a CMOS (Complementary Metal-Oxide-Semiconductor) and a frequency multiplier (e.g., a phase-locked loop) that multiplies the frequency of the electromagnetic waves generated by the oscillator by n (n is a real number greater than or equal to 1). The electromagnetic wave generating unit 11 generates pulse waves.

The electromagnetic wave incident unit 12 incidents the electromagnetic waves generated by the electromagnetic wave generation unit 11 onto the resin waste 2. The electromagnetic wave incident unit 12 is equipped with an optical system including at least one of a lens and a parabolic mirror. The electromagnetic wave incident unit 12 converts the electromagnetic waves generated by the electromagnetic wave generation unit 11 into parallel light that is parallel to a predetermined incident direction passing through the electromagnetic wave generation unit 11 and the resin waste 2. The electromagnetic wave incident unit 12 may focus the electromagnetic waves generated by the electromagnetic wave generation unit 11 at a focal position within the resin waste 2.

The transmitted wave detection unit 13 detects electromagnetic waves that have passed through the resin waste 2 and are emitted. The reflected wave detection unit 16 detects electromagnetic waves that have been reflected from the resin waste 2 and are emitted. The transmitted wave detection unit 13 and the reflected wave detection unit 16 are equipped with Schottky barrier diodes and use the Schottky barrier diodes to detect electromagnetic waves.

In this example, the electromagnetic waves emitted from the resin waste 2 are electromagnetic waves that are incident on the resin waste 2 by the electromagnetic wave incident section 12 and that pass through the resin waste 2 (in other words, transmitted waves), and electromagnetic waves that are reflected by the resin waste 2 (in other words, reflected waves).

The transmitted wave detection unit 13 detects the intensity of the electromagnetic waves emitted from the resin waste 2 by passing through the resin waste 2. The reflected wave detection unit 16 measures the arrival time of the electromagnetic waves emitted from the resin waste 2 by being reflected by the resin waste 2.

The memory unit 14 stores various data used by the resin type estimation unit 15. Specifically, it stores a resin type table. The resin type table is a table of information on the intensity of terahertz waves transmitted according to the resin type. In this regard, materials and transmission intensities are stored as information that corresponds to each other. Transmission intensity is the intensity of electromagnetic waves transmitted by terahertz waves through the resin waste 2.

The memory unit 14 stores arrival time difference information regarding the reflected waves detected by the reflected wave detection unit 16. The arrival time difference information is information that correlates the time difference between when the electromagnetic waves reflected by the surface of the resin waste 2 reach the reflected wave detection unit 16 and when the electromagnetic waves reflected by the bottom surface of the resin waste 2 reach the reflected wave detection unit 16 with the thickness of the resin waste 2.

The propagation characteristics of the electromagnetic waves of the resin waste 2 are affected by the thickness of the resin waste 2, so in order to estimate the materials that make up the resin waste 2 with high accuracy, it is desirable to correct the intensity of the electromagnetic waves detected by the transmitted wave detection unit 13 using the thickness of the resin waste 2. Among the estimation devices 10, those that are incorporated into resin sorting machines that require high-speed, large-volume processing must process large amounts of resin waste at high speed, so it is preferable to estimate the thickness of each piece of resin waste 2 within the estimation device 10. Using terahertz waves, the thickness is estimated by using the difference in arrival time of the electromagnetic waves reflected by the surface and bottom of the resin waste 2 to the reflected wave detection unit 16.

To estimate thickness from the difference in arrival times, it is generally necessary to also input the refractive index. However, since the refractive indices of various plastics in the terahertz region are close to each other, even if the refractive index, which actually varies depending on the type of plastic, is assumed to be the same value, the error in the estimated thickness is small. Therefore, the estimation device 10 according to the present disclosure assumes that the refractive index is the same value.

FIG. 2 is a flowchart illustrating the operation of estimation device 10 according to the first embodiment.
2 , the electromagnetic wave generating unit 11 generates terahertz waves (step S2). Next, the electromagnetic wave incident unit 12 incidents the terahertz waves generated by the electromagnetic wave generating unit 11 onto the resin waste 2 (step S4). A portion of the electromagnetic waves incident onto the resin waste 2 by the electromagnetic wave incident unit 12 passes through the resin waste 2, while another portion of the electromagnetic waves is reflected by the resin waste 2.

The transmitted wave detection unit 13 detects the intensity of the electromagnetic waves transmitted through the resin waste 2 (step S6). The reflected wave detection unit 16 detects the electromagnetic waves reflected from the surface and bottom of the resin waste 2 (step S8). The reflected wave detection unit 16 measures the arrival time difference between the electromagnetic waves reflected from the surface and bottom. The thickness estimation unit 17 estimates the thickness of the resin waste 2 based on the arrival time difference measured by the reflected wave detection unit 16 and the arrival time difference information stored in the memory unit 14 (step S10).

Next, the resin type estimation unit 15 estimates the material that makes up the resin waste 2 based on the intensity of the electromagnetic waves detected by the transmitted wave detection unit 13, the reflection intensity information stored in the memory unit 14, and the thickness of the resin waste 2 estimated by the thickness estimation unit 17 (step S14). Then, the process ends (END).

FIG. 3 is a diagram illustrating arrival time difference information according to embodiment 1. Referring to FIG. 3, this example shows the relationship between the thickness of the resin waste 2 and the arrival time difference. The estimated thickness changes according to the arrival time difference. This example explains the case where the thickness is estimated from the arrival time difference and the intensity of the transmitted wave is corrected using the estimated thickness.

Here, the refractive indexes of various plastics for 0.5 THz electromagnetic waves were 0.95 for acrylonitrile butadiene styrene, 1.01 for polypropylene, and 1.09 for polystyrene. Therefore, because the refractive indexes of various plastics in the terahertz region are close to each other, even if the refractive index, which actually varies depending on the type of plastic, is assumed to be the same value, the error in the estimated thickness is small. Therefore, the refractive index of all plastics is assumed to be 1, and the thickness is calculated using the following formula.

Here, n is the refractive index, d is the thickness [m], c is the speed of light [m/s], and Δt is the arrival time difference [s]. Using this formula to estimate the thickness of three types of plastic, the thickness of 0.6mm acrylonitrile butadiene styrene is calculated to be 0.6mm, that of 2mm polypropylene is 1.9mm, and that of 1.5mm polystyrene is 1.6mm, with a small error in thickness.

Figure 4 is a diagram illustrating the change in electromagnetic wave intensity according to the thickness of the resin waste 2 according to embodiment 1. Referring to Figure 4, a case is shown in which the intensity of the electromagnetic wave decreases as the thickness increases.

Here is a specific example of how to correct the intensity of transmitted waves due to thickness. The following formula is used, which shows the relationship between the intensity reduction due to absorption of electromagnetic waves by matter.

Here, I is the intensity of the electromagnetic wave transmitted through the material, I ₀ is the intensity of the electromagnetic wave incident on the material, and μ is the absorption coefficient [1/m].

As an example, we will explain the case where estimation is performed using the estimation device 10 of the present disclosure on a 0.6 mm thick acrylonitrile butadiene styrene resin waste 2.

The transmitted wave detection unit 13 detected an intensity I = 5 of the electromagnetic wave (transmitted wave) emitted from the actual resin waste 2.

The reflected wave detection unit 16 detected an arrival time difference Δt = 3.8 × 10-12 [s] of the electromagnetic waves (reflected waves) emitted from the actual resin waste 2.

The thickness estimation unit 17 calculates the thickness d using equation (1), where n is 1, Δt is 3.8×10 ⁻¹² [s], and the speed of light c is 3×10 ⁸ [m/s]. The thickness estimation unit 17 calculates the thickness d to be 0.6 [mm].

The intensity correction unit 18 of the resin type estimation unit 15 corrects the transmittance to a 1 mm equivalent using equation (2). Here, for the 0.6 mm thick acrylonitrile butadiene styrene resin waste 2, I = 5 and I ₀ = 10, so exp(-μd) is 0.5. Since the thickness estimation unit 17 estimated d to be 0.6 [mm], the resin type estimation unit 15 can convert I to 1 [mm] and perform the calculation as follows:

Figure 5 is a diagram illustrating the transmittance of 0.5 THz electromagnetic waves through various plastics according to embodiment 1. Referring to Figure 5, transmittance indicates the ratio of the electromagnetic wave intensity detected by the transmitted wave detection unit 13 after passing through the resin waste 2, with the electromagnetic wave intensity immediately after generation by the electromagnetic wave generation unit 11 being set to 1.

In this example, the transmittance of 0.6 mm thick acrylonitrile butadiene styrene, 2 mm thick polypropylene, and 1.5 mm thick polystyrene is shown.

As shown in the figure, the transmittance of the three types of plastic before correction is the same value (0.5), making it difficult to estimate the resin type based solely on the intensity of the electromagnetic waves detected by the transmitted wave detection unit 13.

Meanwhile, the thickness estimation unit 17 estimates the thickness using the difference in arrival time between the wave reflected from the front surface of the resin waste 2 and the wave reflected from the back surface, measured by the reflected wave detection unit 16. The intensity correction unit 18 corrects the intensity of the electromagnetic wave detected by the transmitted wave detection unit 13.

After correction, the transmittance (calculated as a 1mm thickness) is 0.31 for acrylonitrile butadiene styrene, 0.69 for polypropylene, and 0.65 for polystyrene. Therefore, differences in transmittance for each resin type become apparent, making it possible to estimate the resin type.

Figure 6 is a diagram illustrating a resin type estimation table according to embodiment 1. Referring to Figure 6, the resin type estimation table is stored in memory unit 14. The resin type estimation table is a table of the transmittance of various plastics when converted to a thickness of 1 mm. In this example, the transmittance of acrylonitrile butadiene styrene (ABS), polypropylene (PP), and polystyrene (PS) when converted to a thickness of 1 mm is shown. Note that in this example, a table of transmittance based on a thickness of 1 mm has been described, but the table is not limited to this and the reference value may be changed to another value.

Specifically, the registered transmittance values are 0.31 for acrylonitrile butadiene styrene (ABS), 0.69 for polypropylene (PP), and 0.65 for polystyrene (PS).

The estimation device 10 of the present disclosure estimates the thickness of the resin waste 2 in the thickness estimation unit 17 using the arrival time difference between the reflected wave from the front surface of the resin waste 2 and the reflected wave from the back surface, measured by the reflected wave detection unit 16. The intensity correction unit 18 corrects the intensity of the electromagnetic wave detected by the transmitted wave detection unit 13 based on the thickness estimated by the thickness estimation unit 17. The material estimation unit 19 calculates the transmittance per 1 mm of thickness based on the corrected intensity of the electromagnetic wave. The material estimation unit 19 also references a resin type estimation table to estimate the resin type that is closest to the calculated transmittance.

In this way, the estimation device 10 of the present disclosure is able to cancel out the effect of thickness from the intensity of the reflected waves from the detected resin waste 2, making it possible to estimate the materials that make up the resin waste 2 with high accuracy.

Therefore, when resin waste 2 is reused by generating materials from it, such as in chemical recycling or material recycling, the purity of the generated materials can be increased by using the estimation device 10 to estimate with high accuracy the materials that make up the resin waste 2.

Furthermore, with the estimation device 10 according to the present disclosure, there is no need to check the thickness in advance, and both thickness estimation and resin type estimation are possible within the sorting process, making it possible to handle high-speed, large-volume processing. Furthermore, with the estimation device 10 according to the present disclosure, there is no need to provide multiple detection units using terahertz waves of multiple frequencies, and it is possible to estimate the materials that make up the resin waste 2 with high accuracy based on the reflected waves and transmitted waves of the detected resin waste 2 using terahertz waves of a single frequency, making it possible to estimate the materials that make up the resin waste 2 using a simple method.

When resin is used in products, glass fiber is often added to increase its strength, and titanium oxide is often added as a pigment to make it white, and these additives may also be included in solid waste collected for recycling. Because the refractive index of glass fiber and titanium oxide is higher than that of resin alone, the refractive index of the solid waste as a whole increases. However, because the majority of solid waste is still resin, the rate of change in refractive index is small. Therefore, even with resins containing these additives, it is possible to prevent a decrease in estimation accuracy by using the estimation device 10 according to the present disclosure.

The configurations exemplified as the above-mentioned embodiments are examples of the configurations of the present disclosure, and may be combined with other known technologies, or may be modified, such as by omitting some parts, without departing from the spirit of the present disclosure. Furthermore, the above-mentioned embodiments may also be implemented by appropriately adopting the processes and configurations described in other embodiments.

The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present disclosure is indicated by the claims, not the above description, and is intended to include all modifications that are equivalent in meaning to and within the scope of the claims.

2. Resin waste, 10. Estimation device, 11. Electromagnetic wave generation unit, 12. Electromagnetic wave incidence unit, 13. Transmitted wave detection unit, 14. Memory unit, 15. Resin type estimation unit, 16. Reflected wave detection unit, 17. Thickness estimation unit, 18. Intensity correction unit, 19. Material estimation unit.

Claims (12)

an electromagnetic wave generating unit that generates terahertz waves;
an electromagnetic wave incidence unit that causes the terahertz waves to be incident on the resin waste;
a transmitted wave detection unit that detects a transmitted wave that has passed through the resin waste and is emitted;
a reflected wave detection unit that detects a reflected wave reflected from the resin waste;
a thickness estimation unit that estimates a thickness of the resin waste based on the reflected wave detected by the reflected wave detection unit;
A resin type estimation device comprising: a resin type estimation unit that estimates the material of the resin waste based on the intensity of the transmitted wave detected by the transmitted wave detection unit and the thickness of the resin waste estimated by the thickness estimation unit. The resin type estimation device described in claim 1, wherein the reflected wave detection unit estimates the thickness of the resin waste based on the difference in arrival time between the reflected waves reflected on the surface and bottom surfaces of the resin waste. The resin type estimation unit
an intensity correction unit that corrects the intensity of the transmitted wave detected by the transmitted wave detection unit based on the thickness of the resin waste estimated by the thickness estimation unit;
The resin type estimation device according to claim 1 , further comprising a material estimation unit that estimates the material of the resin waste based on the intensity of the corrected transmitted wave. The resin type estimation device described in claim 3, wherein the material estimation unit estimates the material of the resin waste based on the corrected transmitted wave intensity using a resin type estimation table containing information regarding the transmitted wave intensity corresponding to each of multiple resin types relative to a reference thickness. The resin type estimation device described in claim 1, wherein the resin waste is a material whose main component is plastic. The resin type estimation device described in claim 5, wherein the resin waste is primarily composed of one of polystyrene, polypropylene, and acrylonitrile butadiene styrene. generating terahertz waves;
a step of irradiating the terahertz wave onto resin waste;
detecting a transmitted wave that has passed through the resin waste and is emitted;
detecting a reflected wave reflected from the resin waste;
estimating a thickness of the resin waste based on the detected reflected waves;
A resin type estimation method comprising a step of estimating the material of the resin waste based on the intensity of the detected transmitted wave and the estimated thickness of the resin waste. The resin type estimation method described in claim 7, wherein the step of estimating the thickness of the resin waste estimates the thickness of the resin waste based on the difference in arrival time between reflected waves reflected at the surface and bottom surfaces of the resin waste. The step of estimating the material of the resin waste includes:
a step of correcting the intensity of the detected transmitted wave based on the estimated thickness of the resin waste;
The resin type estimation method according to claim 7, further comprising the step of estimating the material of the resin waste based on the intensity of the corrected transmitted wave. The resin type estimation method described in claim 9, wherein the step of estimating the material of the resin waste estimates the material of the resin waste based on the corrected transmitted wave intensity using a resin type estimation table containing information regarding the transmitted wave intensity corresponding to each of a plurality of resin types for a reference thickness. The resin type estimation method described in claim 7, wherein the resin waste is a material whose main component is plastic. The resin type estimation method according to claim 11, wherein the resin waste is primarily composed of one of polystyrene, polypropylene, and acrylonitrile butadiene styrene.