JP7665484B2 - Hulling equipment - Google Patents

Description

The present invention relates to a rice hulling device, and in particular to a rice hulling device that can simplify the control of grain flow rate adjustment.

A rice hulling device is known that includes a first tank for storing rice grains, a rice huller that hulls the rice grains supplied from the first tank, a second tank for storing the grains (a mixture of brown rice and unhulled rice) after being hulled by the rice huller, and a trembling sorter that separates the grains supplied from the second tank into brown rice and unhulled rice. In this type of rice hulling device, there is technology for adjusting the amount of rice grains processed by the rice huller and the amount of grains processed by the trembling sorter depending on the amount of grains stored in the second tank.

For example, Patent Document 1 describes a technology in which a limit sensor S4 is provided at the top of the mixed rice tank 4 (second tank), an upper limit sensor S5 in the middle, and a lower limit sensor S6 at the bottom. With this technology, when the mixed rice tank 4 is nearly full and the limit sensor S4 turns ON, the opening/closing shutter 1a (shutter) of the rice tank 1 (first tank) is closed. This stops the supply of grains from the rice hulling device 2 (huller) to the mixed rice tank 4, preventing the amount of rice stored in the mixed rice tank 4 from exceeding the limit.

In addition, if the amount of grains stored in the mixed rice tank 4 decreases from an appropriate amount and the upper limit sensor S5 changes from ON to OFF, the opening of the feed amount adjustment plate 1c is increased to increase the amount of rice supplied from the rice tank 1 to the rice huller 2. On the other hand, if the amount of rice stored in the mixed rice tank 4 increases and the upper limit sensor changes from OFF to ON, the opening of the feed amount adjustment plate 1c is reduced to decrease the amount of rice supplied to the rice huller 2. This makes it easier to maintain an appropriate amount of grains stored in the mixed rice tank 4.

In addition, when the amount of grains stored in the mixed rice tank 4 approaches the lower limit and the lower limit sensor S6 turns OFF, the oscillating sorting device 5 (oscillating sorter) is stopped, preventing the mixed rice tank 4 from becoming empty.

In other words, the technology of Patent Document 1 makes it possible to adjust the amount of rice processed by the hulling device 2 and the amount of grains processed by the oscillating sorting device 5, i.e., the flow rate of grains in the hulling device, according to the amount of rice stored in the mixed rice tank 4.

JP-A-07-328459 (for example, paragraphs 0027 to 0032, FIG. 3)

However, in the conventional technology described above, the grain flow rate is adjusted by controlling the opening and closing of the shutter, the opening of the feed rate adjustment plate, and the start and stop of the oscillating sorter, which creates the problem of complex control over such flow rate adjustment.

The present invention has been made to solve the above-mentioned problems, and aims to provide a rice hulling device that can simplify the control of grain flow rate adjustment.

To achieve this objective, the rice hulling device of the present invention comprises a first tank in which rice grains are stored, a shutter that opens and closes the flow path of rice grains discharged from the first tank, a rice huller that hulls the rice grains supplied from the first tank when the shutter is open, a second tank in which the grains are stored after being hulled by the rice huller, an upper limit sensor and a lower limit sensor that detect the upper and lower limits of the amount of grains stored in the second tank, and an adjustment means that adjusts the opening of the shutter based on the detection results of the upper limit sensor and the lower limit sensor. The adjustment means reduces the opening of the shutter when grains are detected by the upper limit sensor, and increases the opening of the shutter when grains are not detected by the lower limit sensor.

According to the rice hulling device of claim 1, the opening of the shutter is reduced when grains are detected by the upper limit sensor, so that the amount of rice processed by the rice huller can be reduced when the amount of grains stored in the second tank is about to exceed the upper limit. Also, the opening of the shutter is increased when grains are not detected by the lower limit sensor, so that the amount of rice processed by the rice huller can be increased when the second tank is about to become empty. In this way, by adjusting the grain flow rate by controlling the opening and closing of the shutter, there is an effect that the control of such flow rate adjustment can be simplified compared to the conventional technology that controls each of the opening and closing of the shutter, the opening of the feed amount adjustment plate, and the start and stop of the oscillating sorter.

According to the rice hulling device of claim 2, in addition to the effect of the rice hulling device of claim 1, the following effect is achieved. The opening degree of the shutter is decreased when the period during which grains are detected by the upper limit sensor exceeds a predetermined threshold, and the opening degree of the shutter is increased when the period during which grains are not detected by the lower limit sensor exceeds a predetermined threshold. This makes it possible to reduce the frequency of adjusting the opening degree of the shutter compared to a configuration in which the opening degree of the shutter is immediately decreased or increased when grains are detected by the upper limit sensor or when grains are no longer detected by the lower limit sensor. This has the effect of simplifying the control of grain flow rate adjustment.

According to the rice hulling device of claim 3, in addition to the effect of the rice hulling device of claim 2, the following effect is achieved. When the period during which grains are not detected by the upper limit sensor and grains are detected by the lower limit sensor exceeds a predetermined threshold, the amount of grains stored in the second tank is maintained at an appropriate amount, and the flow rate of rice and post-hulled grains is in an appropriate state. In this state, the opening of the shutter is not adjusted, which has the effect of simplifying the control of grain flow rate adjustment.

The rice hulling device according to claim 4 has the following effect in addition to the effect of the rice hulling device according to claim 2 or 3. The rice hulling device is provided with a winnower that separates the grains hulled by the rice huller into brown rice and unhulled grains, and the grains selected as brown rice by the winnower are supplied to the second tank. Therefore, if the husking rate (the ratio of brown rice obtained from unhulled grains) in the rice huller is low, the grains selected as brown rice by the winnower, i.e., the grains supplied from the winnower to the second tank, will decrease. In other words, if the amount of grains stored in the second tank decreases, the husking rate may be reduced. In this state, even if the grains in the second tank are separated into brown rice and unhulled grains by the oscillating sorter, the grains selected as brown rice by the oscillating sorter are also likely to have a low husking rate.

In contrast, in claim 4, when the period during which grains are not detected by the lower limit sensor exceeds a predetermined threshold and the amount of grains stored in the second tank decreases, some of the grains selected as brown rice by the oscillating sorter are returned to the second tank. This has the effect of preventing the second tank from becoming empty, while allowing grains with a low husking rate to be selected again by the oscillating sorter.

On the other hand, if the amount of grains stored in the second tank has not decreased, it means that many grains selected as brown rice by the winnowing machine are being supplied to the second tank, and it can be determined that the husking rate in the rice huller is high. Therefore, in claim 4, if the period during which grains are detected by the lower limit sensor exceeds a predetermined threshold value and the amount of grains stored in the second tank has not decreased, the return of grains selected as brown rice by the oscillating sorter to the second tank is blocked. This has the effect of suppressing the inefficient circulation in which grains with a high husking rate are supplied again to the oscillating sorter.

According to the rice hulling device of claim 5, in addition to the effect of the rice hulling device of any one of claims 1 to 4, the following effect is achieved. By gradually decreasing the opening degree of the shutter when grains are detected by the upper limit sensor, and gradually increasing the opening degree of the shutter when grains are not detected by the lower limit sensor, the amount of rice supplied to the rice huller can be gradually increased or decreased. This has the effect of allowing fine adjustment of the flow rate of grains.

1 is a schematic diagram of a rice hulling device according to one embodiment of the present invention; FIG. 2 is a partially enlarged cross-sectional view of the rice hulling device, showing an enlarged cross-sectional view of part II in FIG. 1 . 13 is a flowchart of a flow rate adjustment process.

Below, a preferred embodiment of the present invention will be described with reference to the attached drawings. First, the overall configuration of the rice hulling device 1 will be described with reference to FIG. 1. FIG. 1 is a schematic diagram of the rice hulling device 1 in one embodiment of the present invention.

As shown in FIG. 1, the rice hulling device 1 is equipped with a bucket conveyor 2a that delivers rice grains in fixed amounts, and the rice grains delivered from the bucket conveyor 2a are supplied to a first tank 3 through a flow path A. The first tank 3 is a container that can store a predetermined amount of rice grains, and the rice grains stored in the first tank 3 are supplied to a rice huller 4 for hulling. The detailed configuration of the rice huller 4 will be described later with reference to FIG. 2.

The grains hulled by the rice huller 4 (a mixture of brown rice, unhulled rice, and rice husks) are supplied to the winnower 5. A known configuration can be used for the winnower 5, so a detailed description will be omitted. However, the winnower 5 removes the husks from the grains processed by the rice huller 4 (see flow path B) and separates the grains into unhulled rice and brown rice (see flow paths C and D). An example of a known configuration for the winnower 5 is the winnowing section of JP 2014-208321 A.

Grains sorted as unhulled by the winnower 5 are returned to the bucket conveyor 2a through flow path C, while grains sorted as brown rice (mixed rice consisting of brown rice and unhulled rice) are supplied to the second tank 6 through flow path D. The second tank 6 is a container capable of storing a predetermined amount of grains, and is provided with an upper limit sensor 60 and a lower limit sensor 61. The upper limit sensor 60 and the lower limit sensor 61 are sensors for detecting the presence or absence of grains in the second tank 6, and are composed of, for example, a capacitance sensor or a pressure sensor.

The upper limit sensor 60 is disposed at the upper end of the second tank 6 (above the center in the vertical direction), and the lower limit sensor 61 is disposed at the lower end of the second tank 6. Therefore, when grains are detected by the upper limit sensor 60, it can be determined that the amount of grains stored in the second tank 6 is nearly full, and when grains are no longer detected by the lower limit sensor 61, it can be determined that the amount of grains stored in the second tank 6 is nearly empty.

The grains stored in the second tank 6 are supplied in fixed amounts to the oscillating sorter 7, where they are sorted into unhulled rice, mixed rice, and brown rice (see flow paths E to G). The oscillating sorter 7 can be of a known configuration, so a detailed description will be omitted, but an example of a known configuration is the sorting device disclosed in JP 11-114501 A.

The grains selected as unhulled by the oscillating sorter 7 are returned to the bucket conveyor 2a through the flow path E. Therefore, the grains selected as unhulled by the winnower 5 or the oscillating sorter 7 are supplied again to the huller 4 via the first tank 3 and hulled.

The grains selected as mixed rice by the oscillating sorter 7 are supplied to the bucket conveyor 2b through flow path F, and the grains (mixed rice) sent out from the bucket conveyor 2b are returned to the second tank 6 through flow path H. Therefore, the grains selected as mixed rice by the oscillating sorter 7 are selected again by the oscillating sorter 7.

The grains selected as brown rice by the oscillating sorter 7 are supplied to the bucket conveyor 2c through flow path G, and the grains (brown rice) sent out from the bucket conveyor 2c are supplied to a subsequent process (not shown) through flow path I to become a product. The bucket conveyor 2c is provided with a switching damper 8 for returning some of the grains selected as brown rice by the oscillating sorter 7 to the second tank 6. Details of this switching damper 8 will be described later.

In this way, the rice hulling device 1 is configured so that a portion of the grains hulled by the rice huller 4 are circulated, and a mechanism for adjusting the flow rate of the grains is provided between the first tank 3 and the rice huller 4. This configuration will be described with reference to Figure 2. Figure 2 is a partially enlarged cross-sectional view of the rice hulling device 1, which is an enlarged cross-sectional view of part II in Figure 1.

As shown in FIG. 2, a flow path 30 that connects to the housing 40 of the rice huller 4 is formed at the bottom of the first tank 3, and a shutter 31 is provided in this flow path 30. The shutter 31 is driven by a driving means (such as a stepping motor) not shown, and is configured so that the flow path area of the flow path 30 can be changed by the opening degree of the shutter 31. Therefore, by changing the opening degree of the shutter 31, the amount of rice supplied from the first tank 3 to the rice huller 4 can be finely adjusted.

At the upper end (upper side in Fig. 2) of the housing 40 of the rice huller 4, a receiving port 41 is formed to receive rice supplied from the first tank 3 through the flow path 30. An inclined plate 42 extends downward from the edge of the receiving port 41 (the end on the left side in Fig. 2), and a delivery roller 43 is disposed in a position adjacent to the lower end of this inclined plate 42.

The delivery roller 43 is a rotary valve having multiple vanes 43b arranged around its rotation axis 43a (circumferential direction). This delivery roller 43 can have a known configuration, so the detailed configuration is not shown, but an example of a known configuration is the rotary valve disclosed in JP 2017-064660 A.

The delivery roller 43 has multiple disk-shaped partition plates 43c arranged in the axial direction of the rotating shaft 43a (perpendicular to the paper surface of FIG. 2). The partition plates 43c and the blades 43b define a space 43d for delivering a fixed amount of rice at a time.

Approximately half of the outer periphery of the discharge roller 43 on the side where rice grains are supplied from the inclined plate 42 (the right side in Fig. 2) is covered by a cover 44. The rice grains supplied from the inclined plate 42 to the flow path between the discharge roller 43 and the cover 44 are stored in the space 43d of the discharge roller 43, and the rice grains stored in the space 43d are sent out in fixed amounts by the multiple blades 43b as the discharge roller 43 rotates in one direction (clockwise in Fig. 2) and are unwound from the tip of the cover 44.

Below the unhulled rice section, a plate-shaped chute 46 is provided that slopes downward toward a pair of hulling rolls 45, and the unhulled rice that flows down along the flow surface (upper surface) of the chute 46 is supplied to the pair of hulling rolls 45. The pair of hulling rolls 45 are configured to rotate in opposite directions at different rotational speeds, and as the unhulled rice passes between the hulling rolls 45, the unhulled rice is husked and becomes brown rice. The husks and brown rice separated by the husking at the hulling rolls 45 are supplied to the winnowing machine 5 (see Figure 1) from a discharge outlet 47 formed at the lower end of the housing 40 (lower side in Figure 2).

In this manner, in this embodiment, the amount of hulling in the rice huller 4, i.e., the flow rate of rice and hulled grains, is adjusted by adjusting the opening of the shutter 31. This flow rate adjustment is based on the detection results of the upper limit sensor 60 and the lower limit sensor 61 (see FIG. 1) of the second tank 6. This process will be described with reference to FIG. 3. FIG. 3 is a flowchart of the flow rate adjustment process. The flow rate adjustment process in FIG. 3 is repeatedly executed by the control device (CPU) of the rice huller 1.

As shown in FIG. 3, the flow rate adjustment process first checks whether the time during which the upper limit sensor 60 is OFF and the lower limit sensor 61 is ON exceeds a predetermined threshold (e.g., 5 seconds) (S1). Specifically, the ON time and OFF time during which the upper limit sensor 60 and the lower limit sensor 61 are ON or OFF are stored in the memory (storage means) of the rice huller 1 for the past 10 seconds, and this memory is referenced to check whether the time during which the upper limit sensor 60 is OFF and the lower limit sensor 61 is ON during the past 10 seconds exceeds the threshold. If the time exceeds the threshold (S1: Yes), the amount of grain stored in the second tank 6 is appropriate, and the flow rate adjustment process is terminated.

On the other hand, if the time during which the upper limit sensor 60 is OFF and the lower limit sensor 61 is ON is less than or equal to the threshold (S1: No), then either the upper limit sensor 60 is ON or the lower limit sensor 61 is OFF, so it is checked whether the time during which the upper limit sensor 60 is ON exceeds a predetermined threshold (e.g., 5 seconds) (S2).

If the ON time of the upper limit sensor 60 exceeds the threshold value (S2: Yes), the amount of grain stored in the second tank 6 is nearly full, so the opening of the shutter 31 is decreased by one step (S3) and the process ends. This process of S3 reduces the amount of rice grains supplied from the first tank 3 to the rice huller 4, i.e., the amount of grains (brown rice and mixed rice) supplied from the rice huller 4 to the second tank 6.

On the other hand, if the ON time of the upper limit sensor 60 does not exceed the threshold (S2: No), it can be determined that the lower limit sensor 61 is OFF, and it is checked whether the OFF time of the lower limit sensor 61 exceeds a predetermined threshold (e.g., 5 seconds) (S4). If the OFF time of the lower limit sensor 61 exceeds the threshold (S4: Yes), the amount of grain stored in the second tank 6 is nearly empty, so the opening of the shutter 31 is increased by one step (S5), and the series of processes ends. This process of S5 makes it possible to increase the amount of rice supplied from the first tank 3 to the rice huller 4, i.e., the amount of grains (brown rice and mixed rice with rice) supplied from the rice huller 4 to the second tank 6.

As described above, this flow rate adjustment process is repeatedly executed by the control device of the rice huller 1, so if the upper limit sensor 60 remains ON or the lower limit sensor 61 remains OFF after the amount of rice supplied to the rice huller 4 is adjusted in steps S3 and S5, the opening of the shutter 31 is decreased or increased by one step again in steps S2 to S5.

In other words, the opening degree of the shutter 31 is repeatedly adjusted until the amount of grains stored in the second tank 6 becomes appropriate, preventing the amount of grains stored in the second tank 6 from exceeding the upper limit or preventing the second tank 6 from becoming empty. Furthermore, when grains are detected by the upper limit sensor 60 or the lower limit sensor 61, the shutter 31 is not closed or opened, but the opening degree is increased or decreased in stages, allowing fine adjustment of the flow rate of grains downstream of the rice huller 4.

In this way, in this embodiment, the flow rate of rice and hulled grains (amount stored in the second tank 6) in the hulling device 1 is adjusted by controlling the opening and closing of the shutter 31. This simplifies the control of such flow rate adjustment compared to conventional technology that controls the opening and closing of the shutter, the opening of the feed rate adjustment plate, and the start and stop of the oscillating sorter.

In addition, when grains are detected by the upper limit sensor 60 or when grains are no longer detected by the lower limit sensor 61, the opening degree of the shutter 31 is not immediately increased or decreased, but is adjusted when the ON time of the upper limit sensor 60 or the OFF time of the lower limit sensor 61 exceeds a threshold value. This reduces the frequency of adjusting the opening degree of the shutter 31, simplifying the control of grain flow rate adjustment.

In addition, if the time during which the upper limit sensor 60 is OFF and the lower limit sensor 61 is ON exceeds the threshold (S1: Yes), the processes of S2 to S5, i.e., the adjustment of the opening degree of the shutter 31, are not performed. This makes it unnecessary to determine whether the ON time of the upper limit sensor 60 or the OFF time of the lower limit sensor 61 exceeds the threshold, or to change the opening degree of the shutter 31, simplifying the control of grain flow rate adjustment.

Returning to FIG. 1, as described above, among the grains hulled by the rice huller 4, the grains selected as brown rice by the wind sorter 5 are supplied to the second tank 6. Therefore, for example, when the husking rate (the proportion of brown rice obtained from rice husks) in the rice huller 4 is low, i.e., when the number of grains selected as brown rice by the wind sorter 5 is small, the amount of grains supplied to the second tank 6 via the flow path D decreases, and the amount of grains stored in the second tank 6 is likely to decrease. In other words, when the amount of grains stored in the second tank 6 decreases, the husking rate may have decreased. Even if the grains in the second tank 6 are selected by the oscillating sorter 7 in such a state, the grains selected as brown rice by the oscillating sorter 7 are also likely to have a low husking rate.

Therefore, in this embodiment, when there is a high possibility that the husking rate has decreased, a configuration is adopted in which a portion of the grains selected as brown rice by the oscillating sorter 7 is returned to the second tank 6 by the switching damper 8.

The switching damper 8 is configured to be able to divert the grains sent out from the bucket conveyor 2c into two directions, with one outlet of the switching damper 8 connected to the above-mentioned flow path I, and the other outlet connected to the flow path J leading to the second tank 6. The flow path of this switching damper 8 is switched based on the detection result of the lower limit sensor 61.

Specifically, when the OFF time of the lower limit sensor 61 exceeds a predetermined threshold (e.g., 5 seconds), i.e., when the husking rate in the rice huller 4 decreases and the amount of grains stored in the second tank 6 decreases, grains are sent out from each of the two flow paths I and J connected to the switching damper 8. That is, a portion of the grains selected as brown rice by the oscillating sorter 7 are returned to the second tank 6 through flow path J. This allows grains with a low husking rate to be selected again by the oscillating sorter 7, improving the quality of the grains (product) supplied to the subsequent process through flow path I. Furthermore, since grains can be returned to the second tank 6 when the amount of storage in the second tank 6 is decreasing, it is possible to prevent the second tank 6 from becoming empty.

On the other hand, if the amount of grains stored in the second tank 6 has not decreased, it means that a large amount of grains selected as brown rice by the winnower 5 are being supplied to the second tank 6, and it can be determined that the husking rate in the rice huller 4 is high. Therefore, in this embodiment, if the ON time of the lower limit sensor 61 exceeds the threshold value and the amount of grains stored in the second tank 6 has not decreased, the switching damper 8 is switched to send grains only from flow path I. In other words, the return of grains selected as brown rice by the oscillating sorter 7 to the second tank 6 is blocked. This makes it possible to improve the quality of the grains (products) supplied to the subsequent process through flow path I while suppressing the inefficient circulation in which grains with a high husking rate are supplied again to the oscillating sorter 7.

The present invention has been described above based on the embodiments, but the present invention is in no way limited to the above embodiments, and it can be easily imagined that various improvements and modifications are possible within the scope of the invention without departing from its spirit.

Although not described in the above embodiment, the shutter 31 may open and close the flow path 30 by rotating about a predetermined axis, or may open and close the flow path 30 by sliding displacement. Furthermore, one stage of the opening degree of the shutter 31 means, for example, rotating a stepping motor that drives the shutter 31 by a certain angle to displace the shutter 31 a predetermined amount (to the extent that it is neither closed nor fully open).

In the above embodiment, the opening degree of the shutter 31 is decreased when the ON time of the upper limit sensor 60 exceeds the threshold value, and the opening degree of the shutter 31 is increased when the OFF time of the lower limit sensor 61 exceeds the threshold value. However, this is not necessarily limited to this. For example, the opening degree of the shutter 31 may be immediately decreased or increased when the upper limit sensor 60 turns ON or the lower limit sensor 61 turns OFF.

In the above embodiment, a case has been described in which the opening degree of the shutter 31 is not adjusted when the period during which the upper limit sensor 60 is OFF and the lower limit sensor 61 is ON exceeds a threshold value (S1: Yes), but this is not necessarily limited to this. For example, a configuration may be adopted in which the process of S1 is omitted and a determination is made each time as to whether the ON time of the upper limit sensor 60 or the OFF time of the lower limit sensor 61 exceeds a threshold value (processing of S2 to S4).

In the above embodiment, the flow rate of unhulled rice and grains is adjusted by gradually increasing and decreasing the opening of the shutter 31, but this is not necessarily limited to this. For example, the shutter 31 may be closed when the ON time of the upper limit sensor 60 exceeds a threshold value, and the shutter 31 may be opened (fully open) when the OFF time of the lower limit sensor 61 exceeds a threshold value.

In the above embodiment, the switching damper 8 returns the grains to the second tank 6 when the OFF time of the lower limit sensor 61 exceeds the threshold, and the return is blocked when the ON time of the lower limit sensor 61 exceeds the threshold, but this is not necessarily limited to the above. For example, it may be configured such that when the OFF time of the lower limit sensor 61 exceeds the threshold, all of the grains sorted as brown rice by the oscillating sorter 7 are returned to the second tank 6.

Alternatively, the husking rate of the rice grains may be determined using other known techniques (e.g., JP 2021-053624 A), and if the husking rate is low, a portion of the grains may be returned to the second tank 6 by the switching damper 8, and if the husking rate is high, the return may be blocked. Alternatively, the switching damper 8 may be omitted, and all of the grains sorted as brown rice by the oscillating sorter 7 may be supplied to a subsequent process.

1 Rice hulling device 3 First tank 30 Rice flow path 31 Shutter 4 Rice huller 5 Wind sorter 6 Second tank 60 Upper limit sensor 61 Lower limit sensor 7 Swing sorter 8 Switching damper (return means)
S3, S4 Adjustment means

Claims (5)

A rice hulling device comprising: a first tank for storing rice grains; a shutter for opening and closing a flow path for rice grains discharged from the first tank; a rice huller for hulling the rice grains supplied from the first tank when the shutter is open; a second tank for storing grains after being hulled by the rice huller; an upper limit sensor and a lower limit sensor for detecting an upper limit and a lower limit of the amount of grains stored in the second tank; and an adjustment means for adjusting the opening of the shutter based on the detection results of the upper limit sensor and the lower limit sensor;
A rice hulling device characterized in that the adjustment means reduces the opening degree of the shutter when grains are detected by the upper limit sensor, and increases the opening degree of the shutter when grains are not detected by the lower limit sensor. The huller according to claim 1, characterized in that the adjustment means reduces the opening of the shutter when the period during which grains are detected by the upper limit sensor exceeds a predetermined threshold, and increases the opening of the shutter when the period during which grains are not detected by the lower limit sensor exceeds a predetermined threshold. The huller according to claim 2, characterized in that if the period during which no grains are detected by the upper limit sensor and the period during which grains are detected by the lower limit sensor exceeds a predetermined threshold, the adjustment means does not adjust the opening of the shutter. The rice huller includes a winnowing machine that separates the grains hulled by the rice huller into brown rice and unhulled grains, the second tank to which the grains separated as brown rice by the winnowing machine are supplied, a vibration sorting machine that separates the grains supplied from the second tank into brown rice and unhulled grains, and a return means that returns a portion of the grains separated as brown rice by the vibration sorting machine to the second tank,
The rice hulling device as described in claim 2 or 3, characterized in that the return means returns grains to the second tank when the period during which grains are not detected by the lower limit sensor exceeds a predetermined threshold, and blocks the return of grains to the second tank when the period during which grains are detected by the lower limit sensor exceeds a predetermined threshold. 5. The rice hulling apparatus according to claim 1, wherein the adjustment means gradually decreases or increases the opening degree of the shutter.

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