JP2004115247A - Spiral conveyor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spiral conveyor detecting breakout of a screw. <P>SOLUTION: The spiral conveyor arranges a spiral screw in a trough, rotates the screw with a motor, and conveys a material to be carried to one end side of an delivery side. The spiral conveyor comprises a detected part deployed at the delivery side of the screw, a rotation detection part for generating a detection signal when the detected part reaches inside the detection area by rotation of the screw, a status detection part for detecting abnormality of the screw based on a detection signal from the rotation detection part, and an alarm part for generating an alarm when abnormality of the screw is detected by the status detection part. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a spiral conveyor that conveys an object by rotating a helical screw.
[0002]
[Prior art]
A conventional spiral conveyor has a structure in which a spiral screw is arranged in a trough-shaped trough, the screw is rotated by a motor, and a conveyed object such as cake or powder is conveyed to a discharge unit side at one end. Had become.
By the way, when this conveyed object is conveyed, if the conveyed object is not normally discharged from the trough, the screw is overloaded, causing a breakage. In order to prevent this damage, conventionally, the torque applied to the motor is detected, and when the torque is equal to or more than a predetermined value, the driving of the motor is stopped.
Conventionally, there is a method in which a torque applied to a motor is detected, and when the torque is equal to or more than a predetermined value, the driving of the motor is reversely rotated (for example, see Patent Document 1).
[0003]
[Patent Document 1]
Japanese Utility Model Laid-Open No. 4-17039 (Page 1, FIG. 1)
[0004]
[Problems to be solved by the invention]
However, in the above-described related art, the screw may be broken even when the torque applied to the motor is equal to or less than a predetermined value, depending on the service life of the screw and the state of deterioration of the screw. If the screw breaks, it needs to be replaced. However, in a spiral conveyor that transports a distance of several tens of meters, the screw becomes longer, and the cost and time required for replacement are enormous.
Further, if the operation is continued with the screw broken, if the screw is not broken (portion connected to the motor), the conveyed object is conveyed, but from the broken portion to the discharge unit side, Since the conveyed object cannot be conveyed by the screw, the conveyed object is stored in the trough and the internal pressure increases, which may lead to breakage of the trough.
[0005]
Therefore, it is necessary to grasp the fracture of the screw as soon as possible and to prevent the screw itself from being fractured.
[0006]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a spiral conveyor capable of grasping that a screw has broken.
Another object of the present invention is to provide a spiral conveyor for preventing a screw from breaking.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a spiral conveyor in which a spiral screw is arranged in a trough, the screw is rotated by a motor, and a conveyed object is conveyed to a discharge unit at one end. A detection part provided on the discharge part side of the screw, a rotation detection part that outputs a detection signal when the detection part reaches a detection area by rotation of the screw, and a detection signal from the rotation detection part. And a warning unit that issues a warning when the state detection unit detects an abnormality in the screw, based on the condition detection unit.
[0008]
Further, the present invention is characterized in that, in the above-mentioned spiral conveyor, the state detection unit detects an abnormality when the detection signal output from the rotation detection unit is not detected at predetermined time intervals.
Further, the present invention is characterized in that, in the spiral conveyor described above, a motor control unit that stops driving the motor when an abnormality is detected by the state detection unit is provided.
[0009]
Further, in the spiral conveyor according to the present invention, the detected portion may be set to a predetermined length, and the rotation detecting portion may be provided on an outer peripheral portion of a trough in a rotation axis direction of the screw. Features.
Further, the present invention is characterized in that in the above-mentioned spiral conveyor, a guide is provided so as to be at a predetermined distance when the rotation detecting section detects the detected section.
[0010]
Further, the present invention is a spiral conveyor that arranges a spiral screw in a trough, rotates the screw by a motor, and conveys a conveyed object supplied from a supply unit side to a discharge unit side on one end side. A plurality of detected parts provided on the screw, and a rotation detecting part provided in correspondence with each of the detected parts, and outputting a detection signal when the detected part reaches a detection area by rotation of the screw. A state detection unit that detects an abnormality of the screw based on a detection signal output from each of the rotation detection units; and an alarm unit that issues an alarm when the state detection unit detects an abnormality in the screw. And characterized in that:
[0011]
Further, the present invention, in the above-mentioned spiral conveyor, wherein the state detection unit detects an abnormality of the screw when a time difference between detection signals output from the rotation detection unit is a predetermined value or more. Features.
[0012]
Further, according to the present invention, in the above-mentioned spiral conveyor, the state detection unit may be configured such that a time difference between detection signals output from the rotation detection unit is equal to or greater than a predetermined value, and the time difference is equal to or greater than a predetermined value. In a case where a certain number of times occur, an abnormality of the screw is detected.
[0013]
Further, the present invention is a method for detecting an abnormality of a screw in a spiral conveyor in which a spiral screw is disposed in a trough, the screw is rotated by a motor, and a conveyed object is conveyed to a discharge unit at one end. When the detected part provided in the screw reaches the detection area, a detection signal is output from the rotation detection part, and based on the detection signal, an abnormality of the screw is detected. When detected, an alarm is issued.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a spiral conveyor according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic block diagram showing a configuration of a spiral conveyor according to one embodiment of the present invention. In this figure, 1 is a cylindrical trough. In this figure, the trough 1 has a cylindrical shape, but this shape is not limited to a cylindrical shape as long as the object can be transported by the screw 2, and may be a gutter shape, a trough shape, or the like. Reference numeral 2 denotes a spiral screw, which is disposed in the trough 1 and is connected to a drive shaft of a motor 3 provided on one end side of the trough, and is driven to rotate by driving the motor 3. The motor 3 is driven at a rotation speed according to a control signal from the motor control unit 15 and stops driving in response to a drive stop control signal.
The supply unit 4 supplies an object to be transported supplied from a transport device in a preceding stage into the trough 1. The object to be conveyed here is one that can be conveyed by rotating the screw 2 and includes, for example, a powdery or muddy material (such as a cake), and a fluid or sticky material. The discharge unit 5 discharges the conveyed object supplied from the supply unit 4 and conveyed when the screw 2 is rotationally driven by the drive of the motor 3.
[0015]
The detection bar 11 is provided at an end of the screw 2 on the discharge section 5 side. The detection bar 11 corresponds to the above-described detected portion.
The proximity switch 12 detects whether or not the detection bar 11 is within the detection area in a non-contact manner. In particular, when the detection bar 11 reaches the detection area due to the rotation of the screw 2, the detection signal is transmitted to the motion detector 13. Output to This proximity switch 12 corresponds to the above-described rotation detection unit.
The motion detector 13 detects an abnormality of the screw 2 based on a detection signal from the proximity switch 12. The motion detector 13 detects an abnormality when the detection signal output from the proximity switch 12 is not detected at predetermined time intervals. When the detection signal from the proximity switch 12 cannot be detected at a predetermined time interval and the motor 3 is driving, the motion detector 13 gives an alarm by the alarm unit 14 and stops the driving of the motor 3. In order to make the motor control unit 15 output a control signal for stopping the driving of the motor 3 to the motor control unit 15. The motion detector 13 corresponds to the above-described state detection unit.
[0016]
The alarm unit 14 gives an alarm when an abnormality is detected in the screw 2 by the motion detector 13. This warning is performed by outputting a warning sound, turning on a warning lamp, outputting a warning message to a display device such as a display, or the like. The motor control unit 15 controls the driving of the motor 3 and stops the driving, and when the motion detector 13 detects an abnormality, stops the driving of the motor 3.
[0017]
Next, the detection bar 11 and the proximity switch 12 will be further described with reference to the drawings. FIG. 2 is a side view of the spiral conveyor, and FIG. 3 is a diagram for explaining a relationship between the detection bar 11 and the proximity switch 12 as viewed from a direction from the discharge unit 5 toward the supply unit 4.
In FIG. 2, the detection bar 11 is attached to the end 50 of the screw 2 (the tip of the screw 2), so that the proximity switch 12 can detect the detection bar 11 every time the screw 2 rotates. Pass through.
A top liner 16 is provided in the trough 1 near the detection bar 11 so that the distance is such that the detection bar 11 passes through the detection area of the proximity switch 12 and does not contact the proximity switch 12. I have. As the top liner 16, a material that is softer than the screw 2 even when it comes into contact with the screw 2 is applied. This is because the screw 2 and the top liner 16 come into contact with each other when the screw 2 is rotationally driven by the motor 3, so that the contact reduces wear of the screw 2 with respect to the top liner 16. The top liner 16 corresponds to the above-described guide.
[0018]
With this top liner 16, when the detection bar 11 passes near the proximity switch 12, as shown in FIG. 3, it is possible to maintain a predetermined distance (symbol A) and pass without contact.
[0019]
Next, FIG. 4 is a diagram for explaining an attached state of the detection bar 11 when viewed from a direction from the discharge unit 5 side to the supply unit 4 side.
In FIG. 4A, the detection bar 11 is attached to an attachment member 11A fixed to an end of the screw 2 by an attachment member 11B. This detection bar does not necessarily have to be attached to the tip (symbol B) of the screw 2. Further, the detection bar 11 may be attached by welding the detection bar 11 and the screw 2 without using the attachment members 11A and 11B.
[0020]
In FIG. 4B, the detection bar 11 is attached substantially parallel to the rotation axis of the screw 2 and has a predetermined length in the extension direction of the rotation axis of the screw 2 (corresponding to the case where the screw 2 expands and contracts). (Length C) and attached (symbol C). In this case, the proximity switch 12 is preferably provided not on the outer peripheral portion of the trough 1 on the plane perpendicular to the rotation axis direction of the screw 2 but on the outer peripheral portion of the trough 1 in the rotation axis direction of the screw 2. Accordingly, even when the length of the screw 2 is expanded or contracted, the detection bar 11 can pass through the detection area of the proximity switch 12, and the proximity switch 12 normally moves the detection bar 11. Can be detected.
[0021]
Next, the operation of the spiral conveyor will be described with reference to the flowchart of FIG. Here, the description will be made on the assumption that the rotation speed of the motor 3 is 60 rotations per hour.
First, when the operator presses the operation button to start the operation, the motor control unit 15 drives the motor 3 to rotate at a predetermined rotation speed (step S1), and outputs a motor drive control signal to the motion detector 13. . When the motor 3 rotates, the screw 2 connected to the motor 3 rotates. The conveyed object supplied from the supply unit 4 is conveyed in the trough 1 from the supply unit 4 side to the discharge unit 5 side by the rotation of the screw 2, and is discharged from the discharge unit 5 to the outside of the trough 1.
[0022]
On the other hand, the motion detector 13 detects whether or not a detection signal is received from the proximity switch 12 at every predetermined time (every 60 seconds) (Step S2). When the detection signal has been received at predetermined time intervals, that is, when the screw 2 is rotating normally without breaking, the motion detector 13 sends a control signal indicating “no abnormality” to the motor control unit 15. Output. When a control signal indicating "no abnormality" is output from the motion detector 13, the motor control unit 15 detects whether or not an operation stop instruction has been input from the operator (step S3), and the operation stop instruction has been input. If not, the process proceeds to step S2.
On the other hand, when the operation stop instruction is input from the operator, the motor control unit 15 stops driving the motor 3 and stops the operation of the spiral conveyor (step S4).
[0023]
On the other hand, when the detection signal is not received at every predetermined time, that is, when the screw 2 is broken and the end of the screw 2 is not driven to rotate, the motion detector 13 outputs a control signal indicating “abnormal”. The alarm is output to the motor control unit 15 and an alarm is issued by the alarm unit 14 (step S5).
When the control signal indicating "abnormal" is output from the motion detector 13, the motor control unit 15 detects whether the motor 3 is being driven (step S6). When the motor 3 is being driven, the motor control unit 15 stops the rotation of the motor 3 (step S7) and stops the operation of the spiral conveyor. On the other hand, when the motor 3 is not driven, the motor control unit 15 stops the operation of the spiral conveyor without outputting a control signal for stopping the rotation of the motor 3.
[0024]
According to this embodiment, whether or not the motor 3 is driven is detected in step S6. Therefore, the stop switch is not pressed by an operator who visually confirms the breakage of the screw 2 without pressing the stop switch. Even during the operation, the driving of the motor 3 can be stopped.
[0025]
Further, in the above-described embodiment, as shown in FIG. 6A, the case where the motion detector 13 detects whether or not the detection signal is output from the proximity switch 12 at every predetermined timing (every 60 seconds). As described above, as shown in FIG. 6 (b), if a detection signal is detected within a predetermined range of error time with respect to a predetermined timing even if the timing is not a predetermined timing, "no abnormality" It may be. For example, when the predetermined timing is every 60 seconds, when the error time is set to plus or minus 1 second, if a detection signal is detected between 59 seconds and 61 seconds after receiving the previous detection signal, The operation is continued as "No abnormality".
[0026]
Further, in the above-described embodiment, since the top liner 16 is provided in the trough 1, when the screw 2 is driven to rotate due to deformation, aging, or the like, the locus of rotation becomes elliptical (eccentric motion). Even so, when the screw 2 approaches the proximity switch 12, it is pushed down by the top liner 16, whereby the detection bar 11 can be operated without contacting the proximity switch 12.
[0027]
In this embodiment, the motion detector 13 issues an alarm in step S5. However, the motion detector 13 detects whether the motor 3 is driven and issues an alarm when the motor 3 is driven. Is also good.
[0028]
Next, a spiral conveyor according to a second embodiment will be described. FIG. 7 is a schematic configuration diagram of a spiral conveyor according to the second embodiment. In this figure, parts corresponding to the respective parts in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.
A plurality of detection bars 11 are provided on the screw 2. Here, three detection bars 11 are provided at a position near the supply unit 4 of the screw 2, a position near the discharge unit 5, and substantially at the center of the screw 2.
The same number (three) of the proximity switches 12 as the number of the detection bars 11 provided on the trough 1 is provided. The position at which the detection bar 11 is provided is provided so as to correspond to the position at which the detection bar 11 is provided (the position near the supply unit 4 of the screw 2, the position near the discharge unit 5, and the approximate center of the screw 2).
Here, the positions of the detection bar 11 and the proximity switch 12 are set such that the detection signals output from the respective proximity switches 12 are output at the same timing. For example, the detection bar 11 is provided at a position near the supply unit 4 of the screw 2, a position near the discharge unit 5, substantially at the center of the screw 2, and at each position, the screw 2 at the same position as viewed from the axis of the screw 2. Provided. The proximity switch 12 is located at a position near the supply unit 4 of the screw 2, at a position near the discharge unit 5, substantially at the center of the screw 2, and the same when viewed from the axis of the screw 2. It is provided in the trough 1 which is a position.
[0029]
The motion detector 13 detects an abnormality of the screw 2 based on detection signals output from the three proximity switches 12, respectively. Here, the motion detector 13 detects an abnormality based on a time difference between detection signals output from the respective proximity switches 12.
[0030]
In this figure, when the operation of the spiral conveyor is started, the motor 3 is driven to rotate, and the screw 2 is driven to rotate, each proximity switch 12 outputs a detection signal to the motion detector 13. The motion detector 13 compares the time at which the detection signal is output from each of the proximity switches 12 based on the detection signal output from each of the proximity switches 12, and determines the difference between the times by a predetermined value (hereinafter, “first”). Is greater than or equal to the predetermined value), an abnormality is detected and an alarm is issued. Specifically, assuming that the three proximity switches 12 are a proximity switch 12 (first), a proximity switch 12 (second), and a proximity switch 12 (third), respectively, as shown in FIG. When the respective detection signals of the switches 12 (first) to (third) are simultaneously detected at the time t1, it is detected that there is no abnormality.
[0031]
On the other hand, when the detection signals of the proximity switches 12 (first) to (third) are not simultaneously detected at the time t3, the motion detector 13 detects a difference (code C) of the times, and detects the difference of the time. If the difference (code C) is less than the first predetermined value, it is detected that there is no abnormality.
On the other hand, as shown at time t4, when the respective detection signals of the proximity switches 12 (first) to (third) are not detected at the same time, a difference (code D) between the times is detected, and the difference between the times is detected. If (code D) is equal to or greater than the first predetermined value, it is detected that "abnormality exists".
[0032]
According to this embodiment, whether or not the screw 2 is abnormal is detected based on the difference between the detection signals from the plurality of proximity switches 12 provided. As a result, when the screw 2 is normal, a detection signal is simultaneously detected from each of the proximity switches 12, but a difference between the detection signals in the vicinity of the supply unit 4 and the vicinity of the discharge unit 5 occurs. In this case, since the detection signal is output from each proximity switch 12 at a different time, it is possible to detect that the screw 2 is twisted or elongated, and to stop the alarm and the operation before the screw 2 is broken. It is possible to prevent the screw 2 from breaking.
[0033]
The proximity switch 12 serving as a reference may be any of the proximity switches 12 (first) to (third), but when twisting or elongation is accurately detected, the proximity switch closest to the supply unit 4 is used. It is desirable to use 12 (first) as a reference.
[0034]
Next, a third embodiment will be described. The configuration of the spiral conveyor in this embodiment is the same as that of FIG. 7, but only the function of the motion detector 13 is different. Therefore, the function of the motion detector 13 will be described.
In this embodiment, the motion detector 13 determines that the time difference between the detection signals output from the respective proximity switches 12 is equal to or greater than a predetermined value (hereinafter, referred to as a second predetermined value) and the time difference is equal to the second predetermined value. If the number of occurrences is equal to or more than the predetermined value, the abnormality of the screw 2 is detected. This second predetermined value is set shorter than the first predetermined value in the second embodiment when the second embodiment and the third embodiment are simultaneously realized.
[0035]
In this embodiment, when the time difference equal to or more than the second predetermined value occurs a predetermined number of times, the motion detector 13 detects that the screw 2 is abnormal, issues an alarm with the alarm unit 14, and sets the motor control unit as an alarm. A control signal for stopping the driving of the motor 3 is output to 15.
[0036]
According to this embodiment, when the difference between the detection signals output from the respective proximity switches 12 is equal to or more than the second predetermined value and the number of times when the difference is equal to or more than the second predetermined value is equal to or more than the predetermined number of times. Warning that the screw 2 is extended (or contracted) due to deterioration over time, etc., compared to when the use of the screw 2 is started, and maintenance of the screw 2 is required. Can be grasped. Thereby, maintenance can be performed before the screw 2 is broken.
[0037]
In the above-described embodiment, by using a magnetic detection element as the proximity switch 12 and applying a magnet (static magnetic field) as the detection bar 11, a change in magnetic flux when the detection object (the detection bar 11) approaches is used. It is possible to detect the rotational drive of the screw 2 by detecting the rotational drive of the screw 2 in a non-contact manner. The detection bar 11 may be detected by transmitting / receiving a signal, or the detection bar 11 may be detected by either reflection of visible or invisible light or light shielding.
[0038]
As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to the embodiments, and includes a design and the like without departing from the gist of the present invention.
[0039]
【The invention's effect】
As described above, according to the present invention, when the detected portion provided on the screw reaches the detection area, the rotation detection portion outputs a detection signal, and based on the detection signal, the abnormality of the screw is determined. Since the detection is performed, it is possible to detect that the screw has been broken.
[0040]
Further, according to the present invention, when an abnormality is detected by the state detection unit, the driving of the motor is stopped, so that the portion where the screw is not broken (the portion connected to the motor) is covered. The conveyed object is conveyed and the conveyed object cannot be conveyed by the screw on the discharge side from the broken part, the conveyed object is stored in the trough, the internal pressure rises, and the trough breakage is damaged Can be prevented.
[0041]
Further, according to the present invention, the detected portion is set to a predetermined length, and the rotation detecting portion is provided on the outer peripheral portion of the trough in the rotation axis direction of the screw. The effect that the detection part can detect the detected part normally can be obtained.
[0042]
Further, according to the present invention, since the guide is provided so as to be at a predetermined distance when the rotation detecting unit detects the detected portion, the screw can follow the locus of the ellipse with respect to the axis. Even in the case of eccentric movement as described, an effect is obtained that it is possible to prevent the detected portion from contacting the rotation detecting portion and damaging the detected portion and the rotation detecting portion.
[0043]
Further, according to the present invention, whether or not the screw has an abnormality is detected based on a difference between detection signals from a plurality of rotation detection units. This makes it possible to detect the occurrence of twisting or elongation of the screw, stop the alarm and stop the operation before the screw breaks, and prevent the screw from breaking.
[0044]
According to this embodiment, a warning is issued when the difference between the detection signals output from the rotation detection unit is equal to or more than a predetermined value and the number of times when the difference is equal to or more than the predetermined value is equal to or more than the predetermined number. Therefore, it is possible to detect that the screw 2 is extended (or contracted) due to aging, etc., as compared with the time when the screw is started to be used, and it is possible to grasp that the maintenance of the screw 2 is necessary. it can. Thus, maintenance can be performed before the screw 2 is broken.
[Brief description of the drawings]
FIG. 1 is a schematic block diagram showing a configuration of a spiral conveyor according to an embodiment of the present invention.
FIG. 2 is a side view of the spiral conveyor.
FIG. 3 is a diagram for explaining a relationship between a detection bar 11 and a proximity switch 12 viewed from a direction from a discharge unit 5 side to a supply unit 4 side.
FIG. 4 is a diagram for explaining an attached state of the detection bar 11 when viewed from a direction from a discharge unit 5 side to a supply unit 4 side.
FIG. 5 is a flowchart for explaining the operation of the spiral conveyor.
FIG. 6 is a drawing for explaining a case where the motion detector 13 detects whether or not the screw 2 has an abnormality.
FIG. 7 is a schematic configuration diagram of a spiral conveyor according to a second embodiment.
FIG. 8 is a drawing for explaining a case where the motion detector 13 detects whether or not the screw 2 has an abnormality.
[Explanation of symbols]
Reference Signs List 1 trough 2 screw 3 motor 4 supply unit 5 discharge unit 11 detection bar 12 proximity switch 13 motion detector 14 alarm unit 15 motor control unit 16 top liner

Claims (9)

In a spiral conveyor that arranges a spiral screw in a trough, rotates the screw by a motor, and conveys an object to be conveyed to a discharge unit side at one end,
A detected part provided on the discharge part side of the screw;
A rotation detection unit that outputs a detection signal when the detected unit reaches the detection area due to rotation of the screw,
Based on a detection signal from the rotation detection unit, a state detection unit that detects an abnormality of the screw,
A spiral conveyer, comprising: an alarm unit for issuing an alarm when an abnormality is detected in the screw by the state detection unit. The spiral conveyor according to claim 1, wherein the state detection unit detects an abnormality when the detection signal output from the rotation detection unit is not detected at predetermined time intervals. The spiral conveyor according to claim 1 or 2, further comprising a motor control unit that stops driving of the motor when an abnormality is detected by the state detection unit. The detected portion is set to a predetermined length,
The spiral conveyor according to any one of claims 1 to 3, wherein the rotation detector is provided on an outer peripheral portion of a trough in a rotation axis direction of the screw. The spiral conveyor according to any one of claims 1 to 4, wherein a guide is provided so as to be at a predetermined distance when the rotation detecting section detects the detected section. In a spiral conveyor that arranges a spiral screw in a trough, rotates the screw by a motor, and conveys a conveyed object supplied from a supply unit side to a discharge unit side on one end side,
A plurality of detected parts provided on the screw;
A rotation detecting unit that is provided in correspondence with each of the detected units, and outputs a detection signal when the detected unit reaches a detection area by rotation of the screw;
A state detection unit that detects an abnormality of the screw based on detection signals output from the rotation detection unit,
A spiral conveyer, comprising: an alarm unit for issuing an alarm when an abnormality is detected in the screw by the state detection unit. The spiral conveyor according to claim 6, wherein the state detection unit detects an abnormality of the screw when a time difference between detection signals output from the rotation detection unit is equal to or greater than a predetermined value. The state detection unit is configured to, when the time difference of the detection signal output from the rotation detection unit is equal to or more than a predetermined value and the time difference is equal to or more than a predetermined value occur a predetermined number of times, and The spiral conveyor according to claim 6, wherein an abnormality of the spiral is detected. A screw screw is disposed in a trough, the screw is rotated by a motor, and a method for detecting an abnormality of the screw in a spiral conveyor that conveys an object to be conveyed to a discharge unit at one end,
A detection signal is output from the rotation detection unit when the detected part provided in the screw reaches the detection area,
Based on the detection signal, detecting an abnormality of the screw,
A screw abnormality detection method, wherein an alarm is issued when an abnormality is detected in the screw.

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