Electrostatic sorting device

Abstract

An electrostatic sorting device according to the present disclosure comprises: a loading unit into which materials to be sorted, including multiple kinds of objects having different charging characteristics, are loaded; a charging unit for charging the multiple kinds of objects included in the materials to be sorted; an electrostatic separation unit having multiple electrodes to which predetermined voltages are applied, wherein the multiple kinds of objects falling between the multiple electrodes are pulled toward one of the multiple electrodes in accordance with the charged states thereof; a container disposed below the multiple electrodes and divided into multiple areas by partitions; a specific charge detection means for detecting a specific charge of each of the multiple kinds of objects in the materials to be sorted that have passed through the charging unit; and a voltage control unit for controlling the voltages on the basis of detection results of the specific charge detection means.

Description

Electrostatic Separation Device

[0001] The present disclosure relates to an electrostatic sorting device that electrostatically separates and sorts objects.

[0002] BACKGROUND ART A plastic electrostatic sorting device (Patent Document 1) is generally known that frictionally charges materials to be sorted, including multiple types of plastic pieces, and sorts the charged plastic pieces in an electrostatic field.

[0003] Plastic pieces become charged according to a triboelectric series (also called a triboelectric series). The triboelectric series is a ranking in which materials that tend to become positively charged when different materials are rubbed together are ranked higher and materials that tend to become negatively charged are ranked lower. For example, the triboelectric series of plastics, from those that tend to become positively charged to those that tend to become negatively charged, is ABS → PS → PE → PP → PET → PVC. "ABS" is a polymer of acrylonitrile, butadiene, and styrene, "PS" is polystyrene, "PE" is polyethylene, "PP" is polypropylene, "PET" is polyethylene terephthalate, and "PVC" is polyvinyl chloride.

[0004] The electrostatic separation device described in Patent Document 1 is composed of an input stocker, a drying furnace, an input hopper, an input feeder, a charging cylinder, an input feeder, a pair of electrodes, and a container.

[0005] The materials to be sorted are transferred to the input hopper and fed to the charging cylinder by an input feeder located below the input hopper. The input feeder vibrates to feed the materials into the charging cylinder, adjusting the speed at which the materials are fed into the charging cylinder. A fixed amount of material is fed into the charging cylinder per unit time. Inside the rotating charging cylinder, the various plastic pieces that make up the materials to be sorted rub against each other, and each plastic piece is charged with a polarity (positive or negative) and charge amount according to its triboelectric series. The charged materials pair together, with positively charged plastic pieces and negatively charged plastic pieces sticking together due to electrostatic force (Coulomb force). The materials exiting the charging cylinder are transferred to the input feeder. The input feeder dissolves the pairings of the materials by moving them up and down and pushing them forward with up-and-down pushing vibrations. The dissolve-paired materials are then dropped between a pair of electrodes (electrostatic field) to which a high DC voltage is applied. As a result, each plastic piece contained in the material to be sorted falls naturally, but is attracted to one of the pair of electrodes by electrostatic force depending on the polarity and amount of charge. As a result, each plastic piece falls while tracing a parabolic trajectory. The plastic pieces that fall along the parabolic trajectory are collected in a container located below the electrodes.

[0006] Therefore, by dividing the container appropriately with partitions, it is possible to collect plastic pieces by type in each section of the container. For example, if the materials to be sorted include ABS, PS, and PP, dividing the container into three sections—a negative electrode side, a positive electrode side, and a middle section—will allow ABS to be collected on the negative electrode side, and PS and PP to be collected on the positive electrode side. ABS, PS, and PP will be collected mixed in the middle section.

[0007] Patent No. 5630988

[0008] In general, it is believed that the higher the voltage applied to the pair of electrodes, the higher the accuracy of sorting of object pieces contained in the material to be sorted. However, after careful consideration, the inventors of the present application found that if the voltage is too high, the frequency of object pieces colliding with the multiple electrodes increases, which actually reduces the sorting accuracy.

[0009] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide an electrostatic sorting device that can suppress a decrease in sorting accuracy due to collision of object pieces with a pair of electrodes.

[0010] One aspect of an electrostatic separation device according to the present disclosure is an electrostatic separation device comprising: an input section for inputting a material to be sorted that includes multiple types of objects with different charge characteristics; a charging section for charging the multiple types of objects contained in the material to be sorted; an electrostatic separation section having multiple electrodes to which a predetermined voltage is applied and attracting the multiple types of objects that fall between the multiple electrodes to one of the electrodes depending on their charge states; a container disposed below the multiple electrodes and divided into multiple regions by partitions; a specific charge detection means for detecting the specific charge of each of the multiple types of objects in the material to be sorted that has passed through the charging section; and a voltage control section for controlling the voltage based on the detection results by the specific charge detection means, wherein the voltage control section increases the voltage when the specific charge detected by the specific charge detection means is below a threshold value for each of the multiple types of objects, and decreases the voltage when the specific charge detected by the specific charge detection means is above the threshold value.

[0011] According to the electrostatic sorting device of the present disclosure, it is possible to suppress a decrease in sorting accuracy that occurs due to collision of object pieces with multiple electrodes.

[0012] FIG. 1 is a conceptual diagram of an electrostatic separation device according to embodiment 1. FIG. 2 is a flowchart showing the function of the electrostatic separation device according to embodiment 1. FIG. 3 is a diagram explaining the threshold of the electrostatic separation device according to embodiment 1. FIG. 4 is a conceptual diagram of an electrostatic separation device according to embodiment 2. FIG. 5 is a flowchart showing the function of the electrostatic separation device according to embodiment 2. FIG. 6 is a conceptual diagram of an electrostatic separation device according to embodiment 3. FIG. 7 is a flowchart showing the function of the electrostatic separation device according to embodiment 3. FIG. 8 is a conceptual diagram of an electrostatic separation device according to embodiment 4. FIG. 9 is a flowchart showing the function of the electrostatic separation device according to embodiment 4. FIG. 10 is a conceptual diagram of an electrostatic separation device according to embodiment 5.

[0013] [First Embodiment] An electrostatic separation device 100 according to a first embodiment of the present disclosure will be described below with reference to FIG. 1. In the following description, a case where the material 101 to be separated is composed of multiple types of plastic pieces will be described as an example. However, common to all embodiments, the material 101 to be separated is not limited to plastic pieces. The material 101 to be separated that is not limited to plastic pieces may also be referred to as object pieces.

[0014] The electrostatic separation device 100 includes an input stocker 111, a dryer 112, an input hopper 113, an input feeder 114, a charging cylinder 121, an input feeder 122, a plurality of electrodes 131, 132 (electrostatic separation section 130), a container 141, a specific charge detection means 151, and a voltage control section 133.

[0015] The input stocker 111 stores the materials to be sorted 101. The materials to be sorted 101 are input into the input stocker 111 as needed or periodically.

[0016] The material to be sorted 101 is fed from a feed stocker 111 into a dryer 112 and dried in the dryer 112 .

[0017] The material 101 to be sorted that has been dried in the dryer 112 is transferred to a charging hopper 113 and is supplied to a charging cylinder 121 by a charging feeder 114 provided below the charging hopper 113 .

[0018] The input feeder 114 vibrates to adjust the input speed of the materials 101 to the charging cylinder 121. A fixed amount of the materials 101 is input to the charging cylinder 121 per unit time.

[0019] The charging cylinder 121 rotates to agitate the materials to be sorted 101. The arrows shown on the charging cylinder 121 in FIG. 1 represent the rotation of the charging cylinder 121. Inside the charging cylinder 121, the various types of plastic pieces that make up the materials to be sorted 101 rub against each other, and each plastic piece becomes charged with a polarity (positive or negative) and charge amount according to the triboelectric charging sequence. The charging cylinder 121 is made of a material (e.g., ABS) that has specific charging characteristics, and the charging cylinder 121 itself is charged according to the triboelectric charging sequence. Here, the charging cylinder 121 and a charging cylinder rotation mechanism (not shown) that rotates the charging cylinder 121 may be collectively referred to as the charging unit 120.

[0020] The material 101 to be sorted that comes out of the charging cylinder 121 passes through a chute and is transferred to an input feeder 122. The charged material 101 to be sorted causes pairing, in which positively charged plastic pieces and negatively charged plastic pieces stick together due to electrostatic force.

[0021] The carry-in feeder 122 dissolves the pairing of the materials 101 to be sorted by vertical pushing vibrations that push the materials 101 forward while moving them up and down.

[0022] The feeder driving device 123 pushes the input feeder 122 up and down and vibrates it.

[0023] The voltage control unit 133 applies a high DC voltage to the negative electrode 131 and the positive electrode 132 that make up the multiple electrodes 131, 132 to create an electrostatic field between the electrodes. The voltage control unit 133 applies 60 kilovolts (kV) to the negative electrode 131 and the positive electrode 132, which are spaced apart by, for example, 20 centimeters (cm). In this case, the electric field strength between the electrodes is 3 kV / cm. Here, the multiple electrodes 131, 132 may be referred to as an electrostatic separator 130. The voltage control unit 133 can change the voltage applied to the multiple electrodes 131, 132. The multiple electrodes 131, 132 include negative electrodes 131 and positive electrodes 132, but the number of negative electrodes 131 and positive electrodes 132 does not have to be equal.

[0024] The material 101 to be sorted, which has been unpaired by the infeed feeder 122, is dropped between the electrodes (electrostatic field). Then, each plastic piece that makes up the material 101 to be sorted falls naturally while being attracted to one of the electrodes by an electrostatic force according to the polarity and amount of charge. In other words, each plastic piece follows a parabolic trajectory according to the polarity and amount of charge, and falls to a different position.

[0025] Below the negative electrode 131 and the positive electrode 132, a container 141 is installed, which is divided by partitions 142A and 142B into a negative electrode side container 141A, a positive electrode side container 141B, and a middle container 141C. Depending on the location where the plastic pieces fall, they are collected in the negative electrode side container 141A, the positive electrode side container 141B, or the middle container 141C. Among the plastic pieces contained in the sorted material 101, ABS tends to be positively charged and is therefore collected in the negative electrode side container 141A. PS and PP tend to be negatively charged and are therefore collected in the positive electrode side container 141B. A mixture of ABS, PS, and PP that are not sufficiently charged is collected in the middle container 141C. The negative electrode side container 141A and the positive electrode side container 141B are positioned so as to sandwich the middle container 141C. The number of regions is not limited to three and may be more than three.

[0026] Hereinafter, a group of ABS plastic pieces will be referred to as the "ABS group," a group of PS and PP plastic pieces will be referred to as the "PSPP group," and a group of plastic pieces that are a mixture of ABS, PS, and PP will be referred to as the "mixed group."

[0027] The ABS group, PSPP group, and mixed group collected in the container 141 are transported by a conveyor and stored in separate containers (not shown). The ABS group and PSPP group are recycled as resources (PSPP group is further sorted into PS group and PP group by a plastic electrostatic sorting device at the next stage, and is then recycled as resources).

[0028] The specific charge detection means 151 extracts a predetermined amount of plastic pieces charged by the charging tube 121 and detects the specific charge of each piece of the extracted plastic pieces. Here, "predetermined amount" refers, for example, to extracting 100 pieces of sorted material 101 from the input stocker 111 per lot. This means, for example, extracting a predetermined amount of plastic pieces at predetermined intervals and detecting the specific charge of each piece of plastic pieces with the specific charge detection means 151. The predetermined amount of plastic pieces extracted at one time is, for example, approximately 50 grams of plastic pieces, but is not necessarily limited to 50 grams. Here, the specific charge refers to the amount of charge per unit weight. Therefore, the specific charge detection means 151 includes a charge amount sensor 151a and a weight sensor 151b. The specific charge [nC / g] of each piece of plastic piece can be calculated by dividing the charge amount of each piece of plastic piece detected by the charge amount sensor 151a by the weight detected by the weight sensor 151b. The specific charge detecting means 151 is further provided with a plastic type sensor 151c, so that the specific charge can be obtained for each plastic type.

[0029] Here, when the plastic pieces fall from the infeed feeder 122 between the plurality of electrodes 131, 132 and are collected in the container 141, the position at which they fall within the container 141 is determined according to the specific charge of the plastic pieces.

[0030] This will be explained in detail using Figure 3. Figure 3 shows the distribution of specific charges of a predetermined amount of plastic pieces when the plastic pieces contain resin A and resin B. Hereinafter, the distribution of specific charges shown in Figure 3 may be referred to as a distribution curve. The horizontal axis represents the unit of specific charge [nC / g]. The vertical axis represents the probability of existence. This can also be considered as a graph in which the number of resins A and B in the predetermined amount of plastic pieces taken out is arranged in order of the magnitude of the specific charges carried by resins A and B. These are obtained from the measurement results of the specific charge detection means 151. When the material to be sorted contains such resins A and B, resins A and B form the distribution curve shown in Figure 3 and are collected in container 141. This distribution curve may be a normal distribution. That is, resin A, which has a positive specific charge, is attracted to the negative electrode 131 side, and resin B, which has a negative specific charge, is attracted to the positive electrode 132 side, and resin A and resin B are mixed in the intermediate part and collected in container 141.

[0031] Therefore, in the container 141 shown in FIG. 1 , the region where resin A is abundant is designated as the negative electrode side container 141A, the region where resin B is abundant is designated as the positive electrode side container 141B, and the region where resin A and resin B are mixed is designated as the middle container (intermediate region) 141C, and these are separated by partitions 142A and 142B. This allows resin A and resin B to be efficiently recovered from the negative electrode side container 141A and the positive electrode side container 141B, respectively. The curve indicated by A in the container 141 in FIG. 1 is an image of the distribution of resin A recovered in large amounts in the negative electrode side container 141A of the container 141, and the curve indicated by B is an image of the distribution of resin B recovered in large amounts in the positive electrode side container 141B of the container 141. These images of the distribution of resin A and the distribution of resin B correspond to the distribution curves of the specific charges of resin A and resin B shown in FIG. 3. In other words, as described above, the positions at which the plastic pieces collected in container 141 fall within container 141 are determined according to the specific charge of the plastic pieces. Therefore, if the distribution curve of the specific charge of each plastic type of plastic piece can be obtained, the fall distribution of each plastic type of plastic piece in container 141 can be obtained, and conversely, if the fall distribution of each plastic type of plastic piece in container 141 is known, the distribution curve of the specific charge of each plastic type of plastic piece can be obtained. Note that when the number of regions is three or more, intermediate region 141C may not be a region where resin A and resin B are mixed.

[0032] Here, the specific charge detection means 151 and the voltage control unit 133 are electrically connected. Therefore, the specific charge and plastic type information detected or calculated by the specific charge detection means 151 are transmitted to the voltage control unit 133 and aggregated. The voltage control unit 133 receives and aggregates this information and sets a specific charge threshold for each plastic type. For example, if the voltage control unit 133 aggregates the specific charge information for each plastic type of plastic pieces transmitted from the specific charge detection means 151 to the voltage control unit 133 and determines that the specific charge distribution is the distribution shown in Figure 3, the threshold for resin A is set to the apex of the distribution curve for resin A. Similarly, the specific charge detection means 151 sets the threshold for resin B to the apex of the distribution curve. Hereinafter, the predetermined amount of plastic pieces removed when setting the threshold may be referred to as the "first predetermined amount of plastic pieces." The specific charge detection means 151 detects the specific charge for each plastic type of the first predetermined amount of plastic pieces, creates a distribution curve for each plastic type, and sets the threshold for each plastic type as described above. Here, the first predetermined amount of plastic pieces corresponds to the first of 100 times that the specific charge detection means 151 takes out the material to be sorted per lot, and the second and third predetermined amounts of plastic pieces described below correspond to the second and third of 100 times that the specific charge detection means 151 takes out the material to be sorted per lot, respectively.

[0033] When the voltage control unit 133 sets such a threshold, if the specific charge of resin A is detected particle by particle by the specific charge detection means 151 and found to be greater than the threshold, the voltage control unit 133 reduces the voltage applied to the multiple electrodes 131, 132. Similarly, if the specific charge of resin B is detected particle by particle by the specific charge detection means 151 and found to be greater than the threshold, the voltage control unit 133 reduces the voltage applied to the multiple electrodes 131, 132. This is performed each time the specific charge of the plastic pieces is detected particle by particle by the specific charge detection means 151.

[0034] On the other hand, after setting the specific charge threshold, if the specific charge of resin A is detected particle by particle by specific charge detection means 151, voltage control unit 133 increases the voltage applied to multiple electrodes 131, 132. Similarly, if the specific charge of resin B is detected by specific charge detection means 151 and is smaller than the threshold, voltage control unit 133 increases the voltage applied to multiple electrodes 131, 132.

[0035] In the above description, the cases where resin A and resin B are both larger and smaller than the threshold value have been described, but this is not limited to this. Each time the specific charge detection means 151 obtains a detection result for each of the second predetermined amount of plastic pieces, the voltage applied to the plurality of electrodes 131, 132 is increased or decreased depending on whether the specific charge is larger or smaller than the threshold value.

[0036] The greater the specific charge of the plastic pieces and the voltage between the multiple electrodes 131 and 132, the greater the electrostatic force acting on the plastic pieces passing through the multiple electrodes 131 and 132. The specific charge can vary depending on the condition of the plastic pieces (e.g., mixing ratio, humidity, etc.). Therefore, when the specific charge detected by the specific charge detection means 151 falls below a predetermined threshold, the voltage control unit 133 increases the voltage between the multiple electrodes 131 and 132, thereby suppressing fluctuations in the electrostatic force acting on the plastic pieces and stabilizing sorting accuracy. Furthermore, since excessive voltage can lead to increased power consumption, when the specific charge exceeds a predetermined threshold, the voltage control unit 133 reduces the voltage between the multiple electrodes 131 and 132, thereby suppressing excessive power consumption. Furthermore, the greater the voltage, the greater the electrostatic force acting on the plastic pieces. Therefore, it is generally believed that increasing the voltage will allow plastic pieces to fall into the desired area depending on their type. However, if the voltage is too high, the electrostatic force will become too large, causing the plastic pieces to collide with the electrodes 131 and 132 and fall off to positions outside the desired area more frequently.

[0037] Therefore, the voltage control unit 133 determines whether the specific charge of the second predetermined amount of plastic pieces is larger or smaller than the set threshold value, and changes the voltage applied to the multiple electrodes 131, 132 depending on the determination result.

[0038] In the above example, the voltage applied to the plurality of electrodes 131, 132 is increased or decreased relative to the threshold value each time the specific charge of each plastic type in the second predetermined amount of plastic pieces is detected, but this is not limiting. For example, the voltage applied to the plurality of electrodes 131, 132 may be increased or decreased based on whether the peak of the distribution curve of the specific charge of each plastic type obtained from the detection results of the specific charge of each plastic type in the second predetermined amount of plastic pieces is greater or smaller than the peak of the distribution curve of the specific charge of each plastic type shown in Figure 3 obtained from the detection results of the specific charge of each plastic type in the first predetermined amount of plastic pieces.

[0039] That is, if the peak of the distribution curve of specific charge for resin A obtained from the detection results for each plastic type of the second predetermined amount of plastic pieces is larger than the peak of the distribution curve of specific charge for resin A shown in Figure 3 obtained from the detection results for the specific charge for each plastic type of the first predetermined amount of plastic pieces, it is determined that resin A has a specific charge larger than the threshold, and the voltage control unit 133 reduces the voltage applied to the multiple electrodes 131, 132. In this case, if the peak of the distribution curve of specific charge for resin B obtained from the detection results for the second predetermined amount of plastic pieces is larger than the peak of the distribution curve of specific charge for resin B shown in Figure 3 obtained from the detection results for the specific charge for each plastic type of the first predetermined amount of plastic pieces, it is determined that resin B has a specific charge larger than the threshold, and the voltage control unit 133 reduces the voltage applied to the multiple electrodes 131, 132. On the other hand, if the peak of the distribution curve of the specific charge of resin A detected from the second predetermined amount of plastic pieces is smaller than the peak of the distribution curve of resin A shown in Figure 3, it is determined that resin A has a specific charge smaller than the threshold, and the voltage control unit 133 increases the voltage applied to the multiple electrodes 131, 132. In this case, if the peak of the distribution curve of the specific charge of resin B detected from the second predetermined amount of plastic pieces is smaller than the peak of the distribution curve of resin B shown in Figure 3, it is determined that resin B has a specific charge smaller than the threshold, and the voltage control unit 133 increases the voltage applied to the multiple electrodes 131, 132. Here, if the distribution curve of the specific charge for each plastic type detected from the second predetermined amount of plastic pieces is larger than the threshold for resin A and smaller than the threshold for resin B, or if the specific charge for resin A is smaller than the threshold for resin A and larger than the threshold for resin B, the voltage control unit 133 does not need to change the voltage applied to the multiple electrodes 131, 132.

[0040] The function of the electrostatic separation device 100 can be explained using the flowchart shown in Figure 2. Specifically, in step S1, the specific charge detection means 151 detects the specific charge of each plastic type in a first predetermined amount of material 101 (plastic pieces), and the voltage control unit 133 creates a distribution curve of the specific charge for each plastic type and sets a threshold value for each plastic type. In step S2, the voltage control unit 133 determines whether the specific charge for each plastic type in a second predetermined amount of material 101 (plastic pieces) detected by the specific charge detection means 151 is greater than or less than the threshold value. In step S3, if the specific charge is greater than the threshold value, the voltage control unit 133 reduces the voltage of the multiple electrodes 131 and 132. In step S4, if the specific charge is less than the threshold value, the voltage control unit 133 increases the voltage of the multiple electrodes 131 and 132.

[0041] According to the electrostatic separation device 100 having the above-described configuration, the specific charge detection means 151 detects the specific charge of each plastic type in the first predetermined amount of plastic pieces, and the voltage control unit 133 aggregates the detection results to create a distribution curve of the specific charge of each plastic type and set a threshold value for each plastic type. The voltage control unit 133 determines whether the detection result of the specific charge of each plastic type in the second predetermined amount of plastic pieces by the specific charge detection means 151 is larger or smaller than the threshold value and varies the voltage applied to the multiple electrodes 131, 132.

[0042] The types of plastic pieces constituting the material 101 fed into the feeding hopper 113 are not constant over time but change from moment to moment. Therefore, with the electrostatic separation device 100 configured as described above, it is possible to apply to the multiple electrodes 131, 132 a voltage that most efficiently sorts and recovers the material 101 in accordance with the latest state of the plastic pieces contained in the material 101, which changes from moment to moment.

[0043] In the above explanation, the threshold value of the specific charge for each plastic type is set to the peak of the distribution curve of the specific charge of resin A for resin A, and to the peak of the distribution curve of the specific charge of resin B for resin B. However, this is not a limitation. For example, the threshold value for resin A may be set to a range with a predetermined width on both the positive and negative sides from the peak of the distribution curve of the specific charge of resin A. This predetermined width may be set appropriately for resin A, for example, to 10% of the maximum width of the peak of the distribution curve for resin A shown in Figure 3, and for resin B, for example, to 10% of the maximum width of the peak of the distribution curve for resin B shown in Figure 3.

[0044] Here, the specific charge detection means 151 detects the specific charge of each plastic type of a first predetermined amount of plastic pieces, the voltage control unit 133 creates a distribution curve for each plastic type and sets a threshold for each plastic type, and then the specific charge detection means 151 detects the specific charge of each plastic type of a second predetermined amount of plastic pieces, and the voltage control unit 133 determines whether the specific charge is greater than or equal to the threshold and increases or decreases the voltage applied to the multiple electrodes 131, 132. However, the threshold does not need to be fixed once it is set. For example, the specific charge detection means 151 may detect the specific charge of each plastic type of a second predetermined amount of plastic pieces, and the voltage control unit 133 may create a distribution curve for each plastic type and set a new threshold for each plastic type. In this case, the specific charge detection means 151 detects the specific charge of each plastic type of a third predetermined amount of plastic pieces, and the voltage control unit 133 determines whether the specific charge is greater than or equal to the newly set threshold and increases or decreases the voltage applied to the multiple electrodes 131, 132. At the same time, the specific charge detection means 151 may detect the specific charge of each plastic type of the third predetermined amount of plastic pieces, and the voltage control unit 133 may create a distribution curve for each plastic type and set a new threshold value. By repeating this process thereafter, it is possible to set a threshold value that corresponds to the latest state of the material to be sorted 101, which changes from moment to moment. The method of setting the threshold value is the same in embodiments other than embodiment 1 described below.

[0045] The voltage control unit 133 includes a processor such as a CPU (Central Processing Unit) and memory. The CPU performs arithmetic processing to execute the functions of the voltage control unit 133. The memory stores a rewritable program describing the functions executed by the CPU. In accordance with the program, the voltage control unit 133 creates a distribution curve for each plastic type based on the specific charge detected by the specific charge detection means 151 for a first predetermined amount of plastic pieces, and sets a threshold value. Furthermore, each time the specific charge detection means 151 detects a specific charge for each plastic type for a second predetermined amount of plastic pieces, the voltage control unit 133 compares the detected specific charge with the threshold value and controls the voltage applied to the multiple electrodes 131 and 132. At the same time, the voltage control unit 133 creates a new distribution curve for each plastic type based on the specific charge for each plastic type detected by the specific charge detection means 151 for the second predetermined amount of plastic pieces, and sets a new threshold value.

[0046] [Embodiment 2] An electrostatic separation device 200 according to embodiment 2 of the present disclosure will be described below with reference to Figure 4. In the following description, a case where the material to be separated 101 is multiple types of plastic pieces will be described as an example. Furthermore, similar components to those of the electrostatic separation device 100 according to embodiment 1 will be assigned similar reference numerals and their description will be omitted, and only the features that differ from those of the electrostatic separation device 100 according to embodiment 1 will be described.

[0047] The electrostatic separation device 200 differs from the electrostatic separation device 100 of the first embodiment in that a partition position control unit 160 is provided in addition to the electrostatic separation device 100 of the first embodiment.

[0048] The partition position control unit 160 is electrically connected to the specific charge detection means 151. Therefore, the specific charge of each plastic type of the first predetermined amount of plastic pieces and information on the plastic type detected or calculated by the specific charge detection means 151 are sent to the partition position control unit 160. The partition position control unit 160 receives this information and calculates the difference in specific charge between the plastic types.

[0049] If the difference in specific charge is small relative to the second threshold, the partitions 142A and 142B are moved to narrow the intermediate region, and if the difference in specific charge is large relative to the second threshold, the partitions 142A and 142B are moved to widen the intermediate region.

[0050] When the difference in specific charge between plastic types of plastic pieces falls below a predetermined second threshold, the electrostatic force acting on the plastic pieces is insufficient, increasing the proportion of pieces that do not move toward electrode 131 or electrode 132. Therefore, when the partition position control unit 160 determines that the difference in specific charge between plastic types of plastic pieces detected by the specific charge detection means 151 is smaller than the second threshold, the partition position control unit 160 moves the partitions 142A and 142B to narrow the intermediate region 141C. This narrows the intermediate region 141C, thereby preventing a decrease in the recovery rate of plastic pieces contained in regions other than the intermediate region 141C, even when movement toward electrode 131 or electrode 132 is insufficient. Conversely, when the difference in specific charge is greater than the second threshold, the partitions 142A and 142B are moved to widen the intermediate region 141C, thereby improving the recovery purity of appropriately sorted plastic pieces. Here, the second threshold for the difference in specific charge between multiple plastic types may be set, for example, such that if the difference in specific charge between two types of plastic pieces, resin A and resin B, is 10 nC / g or more, migration toward electrode 131 or electrode 132 is sufficient, and if it is less than 10 nC / g, migration toward electrode 131 or electrode 132 is insufficient. Since this difference in specific charge corresponds to the absolute amount of the difference in specific charge, it can also be set appropriately for the difference in specific charge between a plastic piece with a positive specific charge and a plastic piece with a negative specific charge. Even if there are three or more types of plastic, for example, if the difference in specific charge between two different types of plastic is 10 nC / g or more, migration toward electrode 131 or electrode 132 is sufficient, and if it is less than 10 nC / g, migration toward electrode 131 or electrode 132 is insufficient.

[0051] The electrostatic separation device 200 according to the second embodiment is configured by adding a partition position control unit 160 to the electrostatic separation device 100 according to the first embodiment. Therefore, similar to the electrostatic separation device 100 according to the first embodiment, the specific charge detection means 151 detects the specific charge of each plastic type in a first predetermined amount of plastic pieces, and the voltage control unit 133 aggregates the detection results to create a distribution curve of the specific charge for each plastic type, and sets a threshold value for each plastic type from this distribution curve. The voltage control unit 133 determines whether the detection result of the specific charge of each plastic type in a second predetermined amount of plastic pieces by the specific charge detection means 151 is greater or smaller than the set threshold value, and varies the voltage applied to the multiple electrodes 131, 132 accordingly. Furthermore, the partition position control unit 160 calculates the difference in specific charge between multiple plastic types based on information from the specific charge detection means 151, and moves the partitions 142A and 142B to narrow the intermediate region 141C when this difference in specific charge is smaller than the second threshold value, and to widen the intermediate region 141C when the difference in specific charge is larger than the second threshold value.

[0052] The function of the electrostatic separation device 200 can be explained using the flowchart shown in FIG. 5. Specifically, in step S1, the specific charge detection means 151 detects the specific charge of each plastic type in a first predetermined amount of sorted material 101 (plastic pieces), and the separation position control unit 160 creates a distribution curve of the specific charge for each plastic type and sets a threshold value for each plastic type. In step S2, the voltage control unit 133 determines whether the specific charge of each plastic type in a second predetermined amount of sorted material 101 (plastic pieces) detected by the specific charge detection means 151 is greater than or less than the threshold value. In step S3, if the specific charge is greater than the threshold value, the voltage control unit 133 reduces the voltage of the multiple electrodes 131 and 132. In step S4, if the specific charge is less than the threshold value, the voltage control unit 133 increases the voltage of the multiple electrodes 131 and 132. Furthermore, in step S5, the difference in specific charge between the multiple types of plastics is calculated and whether the difference in specific charge is greater than or less than a second threshold value. In step S6, if the difference in specific charge is greater than the second threshold, the partition position control unit 160 moves the partitions 142A and 142B to widen the intermediate region 141C, and in step S7, if the difference in specific charge is smaller than the second threshold, the partition position control unit 160 moves the partitions 142A and 142B to narrow the intermediate region 141C.

[0053] According to the electrostatic separation device 200 of the second embodiment described above, the partition position control unit 160 moves the partitions 142A and 142B to narrow the intermediate region 141C when the difference in specific charge between the plastic types of the plastic pieces is smaller than the second threshold value, based on the detection result of the specific charge detection means 151, and to widen the intermediate region 141C when the difference in specific charge between the plastic types of the plastic pieces is larger than the second threshold value. Therefore, even when the difference in specific charge between the plastic types of the plastic pieces is small, a decrease in the recovery rate of the plastic pieces can be suppressed, and when the difference in specific charge between the plastic types of the plastic pieces is large, the recovery purity of the appropriately sorted plastic pieces can be improved.

[0054] The partition position control unit 160 includes a processor such as a CPU (Central Processing Unit) and memory. The CPU performs arithmetic processing to execute the functions of the partition position control unit 160. The memory stores a rewritable program that describes the functions executed by the CPU. In accordance with the program, the partition position control unit 160 calculates the difference in specific charge between plastic types based on the specific charge of each plastic type detected by the specific charge detection means 151 for a first predetermined amount of plastic pieces. Furthermore, the partition position control unit 160 compares whether the difference in specific charge is greater or smaller than a second threshold value and moves the partitions 142A and 142B accordingly. This is repeated for the first predetermined amount of plastic pieces, the second predetermined amount of plastic pieces, and the third predetermined amount of plastic pieces (and so on).

[0055] [Embodiment 3] An electrostatic separation device 300 according to embodiment 3 of the present disclosure will be described below with reference to Figure 6. In the following description, a case where the material to be separated 101 is multiple types of plastic pieces will be described as an example. Furthermore, similar components to those of the electrostatic separation device 100 according to embodiment 1 will be assigned similar reference numerals and their description will be omitted, and only the features that differ from those of the electrostatic separation device 100 according to embodiment 1 will be described.

[0056] The electrostatic separation device 300 differs from the electrostatic separation device 100 of the first embodiment in that an observation means 201 is provided in addition to the electrostatic separation device 100 of the first embodiment.

[0057] The observation means 201 observes whether or not plastic pieces collide with the plurality of electrodes 131 and 132. The observation means 201 is, for example, a camera.

[0058] The observation means 201 is electrically connected to the voltage control unit 133. When the observation means 201 detects that a plastic piece has collided with the plurality of electrodes 131, 132, a signal notifying the detection of the collision is input to the voltage control unit 133. Upon receiving the signal notifying the collision of a plastic piece with the plurality of electrodes 131, 132 input from the observation means 201 to the voltage control unit 133, the voltage control unit 133 reduces the voltage applied to the plurality of electrodes 131, 132.

[0059] Alternatively, if the observation means 201 does not confirm that plastic pieces have collided with the plurality of electrodes 131, 132 for, for example, a predetermined time, the voltage control unit 133 may increase the voltage applied to the plurality of electrodes 131, 132. Alternatively, if the frequency of plastic pieces colliding with the plurality of electrodes 131, 132 within a predetermined time increases, the voltage control unit 133 may reduce the voltage applied to the plurality of electrodes 131, 132. These settings can be appropriately configured by setting a program stored in the memory of the voltage control unit 133.

[0060] With such an observation means 201, when a plastic piece collides with the multiple electrodes 131, 132, the voltage applied to the multiple electrodes 131, 132 can be reduced, thereby preventing a decrease in sorting accuracy.

[0061] When the observation means 201 is a camera, it may be possible to determine using known image analysis or the like whether or not plastic pieces have collided with the plurality of electrodes 131, 132. When the observation means 201 is a camera, it is preferable that the camera constantly observes the plurality of electrodes 131, 132.

[0062] Furthermore, the observation means 201 is not limited to a camera, and may be, for example, an impact sensor provided on the plurality of electrodes. If the observation means 201 is an impact sensor provided on the plurality of electrodes 131, 132, the impact sensor may detect the impact generated when a plastic piece collides with the plurality of electrodes, and this detection signal may be input to the voltage control unit 133, which may then reduce the voltage applied to the plurality of electrodes 131, 132. Furthermore, if the impact sensor does not detect an impact for a predetermined time, the voltage control unit may increase the voltage applied to the plurality of electrodes. If the observation means 201 is an impact sensor, lighting for illuminating the plurality of electrodes 131, 132, which is required when taking pictures with a camera, is not required, thereby saving energy required for the sorting operation.

[0063] The electrostatic separation device 300 according to the third embodiment is configured by adding an observation means 201 to the electrostatic separation device 100 according to the first embodiment. Therefore, similar to the electrostatic separation device 100 according to the first embodiment, the specific charge detection means 151 detects the specific charge of each plastic type in a first predetermined amount of plastic pieces, and the voltage control unit 133 aggregates the detection results to create a distribution curve of the specific charge for each plastic type and sets a threshold value for each plastic type from the distribution curve. The voltage control unit 133 determines whether the detection result of the specific charge of each plastic type in a second predetermined amount of plastic pieces by the specific charge detection means 151 is greater or smaller than the threshold value, and varies the voltage applied to the multiple electrodes 131 and 132. At the same time, if the observation means 201 detects collision of plastic pieces with the multiple electrodes 131 and 132, the voltage control unit 133 reduces the voltage applied to the multiple electrodes 131 and 132.

[0064] The function of the electrostatic separation device 300 can be explained using the flowchart shown in FIG. 7 . Specifically, in step S1, the specific charge detection means 151 detects the specific charge of each plastic type in a first predetermined amount of material 101 (plastic pieces), and the voltage control unit 133 creates a distribution curve of the specific charge for each plastic type and sets a threshold value for each plastic type. In step S2, the voltage control unit 133 determines whether the specific charge for each plastic type in a second predetermined amount of material 101 (plastic pieces) detected by the specific charge detection means 151 is greater than or less than the threshold value. In step S3, if the specific charge is greater than the threshold value, the voltage control unit 133 reduces the voltage of the multiple electrodes 131 and 132. In step S4, if the specific charge is less than the threshold value, the voltage control unit 133 increases the voltage of the multiple electrodes 131 and 132. Furthermore, in step S7, the voltage applied to the multiple electrodes 131 and 132 is controlled based on the observation results obtained by the observation means 201.

[0065] According to the electrostatic separation device 300 of the third embodiment described above, when the observation means 201 detects a collision of plastic pieces with the plurality of electrodes 131, 132, the voltage control unit 133 reduces the voltage applied to the plurality of electrodes. This prevents the plastic pieces from being improperly sorted due to the collision of plastic pieces with the plurality of electrodes 131, 132. Furthermore, because the observation means 201 can observe the collision of plastic pieces with the plurality of electrodes 131, 132, it is possible to apply a voltage to the plurality of electrodes 131, 132 that is low enough to prevent the plastic pieces from colliding with the plurality of electrodes 131, 132. This allows separation to be performed without reducing the accuracy of separation of plastic pieces.

[0066] [Fourth Embodiment] An electrostatic separation device 400 according to a fourth embodiment of the present disclosure will now be described with reference to Figure 8. In the following description, a case where the material to be separated 101 is multiple types of plastic pieces will be described as an example. Furthermore, similar components to those of the electrostatic separation device 200 according to the second embodiment will be assigned the same reference numerals, and their description will be omitted. Only the features that differ from the electrostatic separation device 200 according to the second embodiment will be described.

[0067] The electrostatic separation device 400 differs from the electrostatic separation device 200 of the second embodiment in that an observation means 201 is provided in addition to the electrostatic separation device 200 of the second embodiment.

[0068] The function of the electrostatic separation device 400 can be explained using the flowchart shown in Figure 9. Specifically, in step S1, the specific charge detection means 151 detects the specific charge of each plastic type in a first predetermined amount of material 101 (plastic pieces), and the voltage control unit 133 and the partition position control unit 160 create a distribution curve of the specific charge for each plastic type and set a threshold value for each plastic type. In step S2, the voltage control unit 133 determines whether the specific charge of each plastic type in a second predetermined amount of material 101 (plastic pieces) detected by the specific charge detection means 151 is greater than or less than the threshold value. In step S3, if the specific charge is greater than the threshold value, the voltage control unit 133 reduces the voltage of the multiple electrodes 131, 132. In step S4, if the specific charge is less than the threshold value, the voltage control unit 133 increases the voltage of the multiple electrodes 131, 132. Furthermore, in step S5, the difference in specific charge between the multiple types of plastic is calculated and whether the difference in specific charge is greater than or less than a second threshold value. In step S6, if the difference in specific charges is greater than a second threshold, the partition position control unit 160 moves the partitions 142A and 142B to widen the intermediate region 141C, and in step S7, if the difference in specific charges is less than the second threshold, the partition position control unit 160 moves the partitions 142A and 142B to narrow the intermediate region 141C. Furthermore, in step S8, the voltages applied to the plurality of electrodes 131 and 132 are controlled based on the observation results obtained by the observation unit 201.

[0069] In the electrostatic separation device 400 according to the fourth embodiment, the electrostatic separation device 200 according to the second embodiment is provided with an observation means 201, and therefore, in addition to the effects obtained by the electrostatic separation device 200 according to the second embodiment, the effects obtained by the electrostatic separation device 300 according to the third embodiment can be obtained.

[0070] [Embodiment 5] An electrostatic separation device 500 according to embodiment 5 of the present disclosure will be described below with reference to Figure 10. In the following description, a case where the material to be separated 101 is multiple types of plastic pieces will be described as an example. Furthermore, similar components to those of the electrostatic separation device 400 according to embodiment 4 will be assigned similar reference numerals and their description will be omitted, and only the features that differ from the electrostatic separation device 400 according to embodiment 4 will be described.

[0071] The electrostatic separation device 500 differs from the electrostatic separation device 400 of embodiment 4 in that a central control unit 301 is provided between the specific charge detection means 151 and the voltage control unit 133, between the specific charge detection means 151 and the partition position control unit 160, and between the observation means 201 and the voltage control unit 133.

[0072] The central control unit 301 sets a threshold value and a second threshold value based on the detection result of the specific charge input from the specific charge detection means 151. The method of setting this threshold value and second threshold value is the same as the method of setting the threshold value of the voltage control unit 133 in the first embodiment and the method of setting the second threshold value of the partition position control unit 160 in the second embodiment.

[0073] That is, the central control unit 301 creates a distribution curve of the specific charge for each plastic type based on the detection results of the specific charge for each plastic type by the specific charge detection means 151 for the first predetermined amount of plastic pieces, sets a threshold for each plastic type, and calculates the difference in specific charge among multiple types of plastics. Thereafter, the central control unit 301 comprehensively evaluates the detection results of the specific charge for each plastic type by the specific charge detection means 151 for the second predetermined amount of plastic pieces, the difference in specific charge among multiple types of plastics calculated by the partition position control unit 160, information about collisions of plastic pieces with the multiple electrodes 131, 132 input from the observation means 201, and other information such as past operating records, and determines whether to increase or decrease the voltage applied to the multiple electrodes 131, 132 or to move the partitions 142A, 142B. The past operating records include the recovery rate of plastic pieces and the recovery purity of plastic pieces for a certain type of plastic pieces under the operating conditions (room temperature, humidity, mixing ratio with other plastic pieces, length of intermediate region 141C (position of partitions 142A, 142B), voltage applied to multiple electrodes 131, 132).

[0074] For example, if the detection result of the specific charge of each plastic type for the second predetermined amount of plastic pieces by the specific charge detection means 151 is greater than the threshold value, the electrostatic separation device 100 of embodiment 1 reduces the voltage applied to the plurality of electrodes 131, 132. However, the electrostatic separation device 500 of embodiment 5 also refers to past operating records, and compares the voltage applied to the plurality of electrodes 131, 132 and the length of the intermediate region 141C when a high recovery rate and high recovery purity were obtained under similar operating conditions in the past (type of plastic pieces, room temperature, humidity, mixing ratio with other plastic pieces), and makes a determination as to whether to reduce the amount of voltage reduction or not reduce the voltage, and whether to increase or decrease the length of the intermediate region 141C.

[0075] The central control unit 301 includes a processor such as a CPU (Central Processing Unit), a memory, and the like. The CPU executes arithmetic processing to execute the functions of the central control unit 301. The memory stores rewritable programs that describe the functions executed by the CPU. Note that the central control unit 301 may be an artificial intelligence.

[0076] In the electrostatic separation device 500 according to the fifth embodiment, the central control unit 301 is provided in the electrostatic separation device 400 according to the fourth embodiment, so it is possible to determine what to control to obtain the maximum effect by referring to past operating records, and therefore it is possible to recover plastic pieces with a higher recovery rate and recovery purity.

[0077] The technical scope of the present disclosure is not limited to the above-described embodiment, and various modifications can be made within the scope of the present disclosure defined in the claims.

[0078] For example, container 141 may be provided with a drop distribution sensor 151d capable of detecting the drop distribution of each plastic type. In this case, the voltage applied to the multiple electrodes 131, 132 and the positions of partitions 142A, 142B can be controlled taking into account the drop distribution of each plastic type of plastic pieces that actually fall into container 141. Also, input distribution sensor 151e capable of detecting the input distribution of each plastic type can be controlled taking into account the drop distribution of each plastic type of plastic pieces that actually fall from input feeder 122 into container 141. Furthermore, in embodiments 3 to 5, when the voltage applied to the multiple electrodes 131, 132 is maximized within a range in which the frequency of collisions of plastic pieces with the multiple electrodes 131, 132 does not exceed the collision frequency threshold, the plastic pieces can be attracted as strongly as possible toward the desired area, improving sorting accuracy while preventing a decrease in sorting accuracy due to collisions. The collision frequency threshold for plastic pieces with the multiple electrodes 131, 132 can be arbitrarily set by setting it to, for example, up to once every five seconds in the program stored in the memory of the voltage control unit 133. The collision frequency threshold can be appropriately set through prior experimentation. In this case, if the observation unit 201 does not confirm a collision of plastic pieces with the multiple electrodes 131, 132 within five seconds, the voltage control unit 133 increases the voltage applied to the multiple electrodes 131, 132. By maximizing the voltage applied to the multiple electrodes 131, 132 within the collision frequency threshold, the plastic pieces can be attracted as strongly as possible toward the desired area, improving sorting accuracy while preventing a decrease in sorting accuracy due to collisions. In the above-described first to fifth embodiments, the material to be sorted 101 is described as being plastic fragments, but the present invention is not limited to this case, and the material to be sorted 101 may contain metal fragments and / or organic fragments such as food. In this case, the material to be sorted 101 includes a plurality of types of objects, not limited to plastic fragments. As in the above-described first to fifth embodiments, the specific charge detection means 151 detects the specific charge and type of object for each of the plurality of types of object, creates a distribution curve for each of the plurality of types of object, and sets a threshold value.The partition position control unit 160 also calculates the difference in specific charge between multiple types of objects and determines the magnitude relationship with the second threshold, as in the above-described embodiments 2, 4, and 5. Therefore, even if the material 101 to be sorted contains metal pieces and / or organic pieces such as food, the material 101 to be sorted can be sorted in accordance with the description of the above-described embodiments 1 to 5. Although the voltage control unit 133, the partition position control unit 160, and the central control unit 301 are described as including a processor such as a CPU (Central Processing Unit) and memory, these functions may be realized using hardware (including circuitry) such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a GPU (Graphics Processing Unit). Alternatively, the functions of the voltage control unit 133, the partition position control unit 160, and the central control unit 301 may be realized by a combination of software and hardware.

[0079] 100, 200, 300, 400, 500 Electrostatic separation device 131, 132 Multiple electrodes 133 Voltage control unit 141 Container 151 Specific charge detection means 160 Partition position control unit 201 Observation means 301 Central control unit

Claims

1. A feeding section for feeding a material to be sorted containing a plurality of types of objects having different charging characteristics; A charging section for charging the plurality of types of objects contained in the material to be sorted; An electrostatic separation section having a plurality of electrodes to which a predetermined voltage is applied, and attracting the plurality of types of objects falling between the plurality of electrodes to either side of the plurality of electrodes according to their charged states; A container disposed below the plurality of electrodes and partitioned into a plurality of regions by partitions; Specific charge detection means for detecting the specific charge of each of the plurality of types of objects in the material to be sorted that has passed through the charging section; A voltage control section for controlling the voltage based on the detection result by the specific charge detection means, wherein the voltage control section increases the voltage when the specific charge detected by the specific charge detection means is lower than the threshold value for each of the plurality of types of objects, and decreases the voltage when the specific charge detected by the specific charge detection means is higher than the threshold value; An electrostatic sorting device that accommodates the plurality of types of objects that have fallen between the plurality of electrodes in the plurality of regions according to their charged states.

2. The electrostatic sorting device according to claim 1, further comprising a partition position control section for moving the position of the partition based on the detection result by the specific charge detection means, wherein the plurality of regions include an intermediate region and two or more regions sandwiching the intermediate region, and the partition position control section moves the partition so as to narrow the intermediate region when the difference in specific charge between the plurality of types of objects detected by the specific charge detection means is lower than a second threshold value, and moves the partition so as to widen the intermediate region when the difference in specific charge between the plurality of types of objects detected by the specific charge detection means is higher than the second threshold value.

3. The electrostatic sorting device according to claim 1 or 2, further comprising observation means for observing the collision of the objects with the plurality of electrodes, wherein the voltage control section controls the voltage based on the observation result by the observation means.

4. The electrostatic sorting device according to claim 3, wherein the observation means is a camera.

5. The electrostatic sorting device according to claim 3, wherein the voltage control section decreases the voltage when the frequency of collision of the objects with the plurality of electrodes increases based on the observation result by the observation means.

6. The electrostatic sorting device according to claim 3, wherein the voltage control section maximizes the voltage within a range where the frequency of collision of the objects with the plurality of electrodes does not exceed a collision frequency threshold value based on the observation result by the observation means.

7. An electrostatic separation unit having a plurality of electrodes, for attracting a plurality of types of objects included in a material to be sorted that falls between the plurality of electrodes to either side of the plurality of electrodes according to the charged state, a specific charge detection means for detecting the specific charge of the objects included in the material to be sorted, and a voltage control unit for controlling the voltage applied to the electrodes based on the detection result by the specific charge detection means. The electrostatic sorting device, wherein the voltage control unit lowers the voltage when the specific charge detected by the specific charge detection means exceeds a threshold value.