Overload protection device and motor

Abstract

To provide an overload protection device that makes it possible to protect an overload on a motor, etc., without being affected from external environments.SOLUTION: The overload protection device comprises a coupling for connecting an output end of a motor shaft of a motor and an input part of the device to be driven. The coupling includes a drive member fixed to the output end of the motor shaft, and a follower member magnetically coupled to the drive member and fixed to the input part of the device being driven. The coupling is constituted so that the torque of the motor shaft is transmitted to the device being driven by a magnetic force between the drive member and the follower member. When the load on the motor shaft exceeds the maximum permissible torque that the coupling can transmit, the drive member runs idle with respect to the follower member, and the connection between the motor shaft and the device being driven is cut off.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an overload protection device that suppresses excessive loads on a driven device and a motor and prevents damage to the driven device and the motor, and a motor provided with the overload protection device.

Background Art

[0002] Conventionally, when driving a driven device such as a conveyor device with a motor (or a geared motor), if the load suddenly increases due to foreign matter being caught or the like, and the motor continues to be driven in this overload state, one or both of the motor and the driven device may be physically damaged. In response, an overload protection device has been developed that detects the overload of the motor and prevents damage to the motor and the driven device by cutting off or restricting the power supply to the motor.

[0003] For example, Patent Document 1 discloses an overload protection device that prevents damage to a geared motor and an industrial machine. Hereinafter, in this paragraph, the reference numerals of Patent Document 1 are shown in parentheses. The overload cutoff device (4) selects a predetermined current value less than the rated current value of the motor (2) as the current designated value (6), and selects the predetermined time during which current flows at an overload current value (5) exceeding the current designated value (6) as the designated value of the overload current time (7) by a designated value setting means (14), an overcurrent detection means (15) that detects an overload current value (5) and an overload current time exceeding the current designated value (6) selected by the designated value setting means (14), and a power supply cutoff means (19) that cuts off the power supply to the motor (2) when the overcurrent detection means (15) detects that the overload current time has exceeded the designated value of the overload current time.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Conventional overload protection devices such as Patent Document 1 read an increase in the value of the current flowing through the motor, and when the measured current value exceeds the specified value of the current, they detect an overload and cut off the power supply to the motor. However, in conventional overload protection devices, when the power supply is unstable, current fluctuations in the equipment (for example, the occurrence of power supply voltage imbalance due to the use of a specific single-phase power supply, etc.) or noise from mechanical devices (for example, voltage fluctuations and noise generation due to acceleration and deceleration of a large-capacity servo motor) are large, and the device is used in the installation environment, there is a problem that the overload protection device is electrically affected by the external environment, reads an incorrect current value, and is likely to malfunction. Therefore, there is a risk that the overload protection device will stop the motor unnecessarily, or will not be able to stop the motor appropriately despite an overload, resulting in damage to the motor or the like.

[0006] The present invention has been made to solve the above problems, and an object thereof is to provide an overload protection device capable of protecting a motor or the like from an overload without being affected by the external environment, and a motor with an overload protection device.

Means for Solving the Problems

[0007] The overload protection device according to one embodiment of the present invention is an overload protection device that is connected to a motor that drives a driven device and operates to protect the motor from an overload, comprising a coupling that connects an output end of a motor shaft of the motor and an input portion of the driven device, the coupling including a driving member fixed to the output end of the motor shaft and a driven member magnetically coupled to the driving member and fixed to the input portion of the driven device, the coupling being configured to transmit the torque of the motor shaft to the driven device by the magnetic force between the driving member and the driven member, When the load on the motor shaft exceeds the maximum allowable torque that can be transmitted by the coupling, the driving member idles with respect to the driven member, and the connection between the motor shaft and the driven device is disconnected.

[0008] The overload protection device of the present invention couples the motor shaft and the input portion of the driven device so as to be able to transmit torque by a coupling using magnetic force. When the load on the motor shaft exceeds the maximum allowable torque that can be transmitted by the coupling, the driving member idles with respect to the driven member, so that the coupling (torque transmission) between the motor shaft and the driven device is forcibly disconnected. As a result, a torque exceeding the maximum allowable torque of the coupling is not applied between the motor shaft and the input portion of the driven device, and it is possible to surely prevent an overload state from occurring. That is, the overload protection device of the present invention can protect against overloads to motors and the like without being affected by electrical influences from the external environment.

[0009] The overload protection device according to a further aspect of the present invention further includes detection means for detecting idling of the coupling, and when detecting the idling state of the coupling based on an output signal from the detection means, determining that the motor is in an overload state, and a control unit that controls the motor to stop power supply to the motor. That is, by detecting the idling of the coupling using the output signal from the detection means and the control unit stopping the power supply to the motor in the idling state, it is possible to prevent the motor from being driven uselessly.

[0010] The overload protection device according to a further aspect of the present invention is characterized in that the detection means includes a magnetic sensor that measures the magnetic force of a detected portion provided on the coupling over time, and detects the idling state of the coupling based on a change in magnetic force when the coupling shifts from a coupled state to an idling state. That is, the overload protection device detects the idling state of the coupling by using a magnetic sensor that measures the magnetic force of the detected portion of the coupling over time, so that the idling state can be quickly detected and the motor can be effectively stopped.

[0011] A further form of the overload protection device of the present invention further includes a user interface that receives an input from a user, notifies the user of an overload state, and requests confirmation of the removal of the load cause. After the control unit stops the power supply to the motor, when the user inputs confirmation of the removal of the load cause via the user interface, the power supply to the motor can be turned on. That is, by notifying the user of the overload state via the user interface and requesting confirmation of the removal of the load cause, it is possible to prevent the user from turning on the power while the load cause remains, and to further improve the safety of the device.

[0012] A further form of the overload protection device of the present invention further includes a relay configured to receive a stop signal for stopping the power supply from the control unit to the motor, and to switch the relay contacts upon reception of the stop signal to cut off the power supply to the motor. That is, the relay that receives the power supply stop signal mechanically switches the relay contacts to cut off the power supply to the motor on the mechanical device side, so that overload protection can be more reliably performed without being affected by the electrical environment of the external environment.

[0013] A further form of the overload protection device of the present invention is characterized in that the coupling and the magnetic sensor are housed in a peripheral wall portion surrounding an output end of the motor shaft protruding externally from a housing of a motor body of the motor. That is, the overprotection load device is easily retrofittable to an existing motor.

[0014] In a further form of the overload protection device of the present invention, the maximum allowable torque that can be transmitted by the coupling is determined to be equal to or greater than the rated torque of the motor and less than the stall torque of the motor. That is, by forcibly disconnecting the coupling, it is possible to prevent the motor from operating beyond a predetermined torque (torque threshold) that is equal to or greater than the rated torque and less than the stall torque. Thereby, the motor and the driven device can be reliably protected.

[0015] A motor according to an embodiment of the present invention is characterized by including the above overload protection device. That is, the motor of the present invention can exhibit the effects of the above overload protection device as a motor.

[0016] A further form of the motor of the present invention is a geared motor including a speed reduction mechanism that outputs power to the driven device. That is, the motor of the present invention can exhibit the effects of the above overload protection device as a geared motor.

Advantages of the Invention

[0017] The overload protection device of the present invention enables protection of a motor or the like from overload without being affected by electrical influences from the external environment.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the shapes of the respective figures referred to in the following description are conceptual diagrams or schematic diagrams for explaining suitable shapes, and the dimensional ratios etc. do not necessarily match the actual dimensional ratios. That is, the present invention is not limited to the dimensional ratios in the drawings.

[0020] FIG. 1 is a schematic diagram exemplarily showing a motor 11 according to an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line A-A of the motor 11 in FIG. 1. FIG. 3 is a block diagram showing the configuration of an overload protection device 100 according to an embodiment of the present invention.

[0021] As shown in FIG. 1, the motor 11 of the present embodiment includes a motor body 12, a motor shaft 13 provided on the motor body 12, a terminal box 14 electrically connected to the motor body 12, and an overload protection device 100 introduced into the motor body 12. The motor body 12 is composed of a general motor, and a detailed description thereof will be omitted. Also, according to FIG. 1, a speed reducer 16 is connected to the output side of the motor 11. In the present embodiment, the input portion (shaft) 16a of the speed reducer 16 constitutes the input portion of the driven device.

[0022] Also, in this embodiment, the motor 11 is an induction motor. The induction motor has a characteristic that its rotational speed decreases as the load increases. The motor 11 has a rotational speed-torque characteristic according to each specification. FIG. 4 illustrates the rotational speed-torque characteristic of a typical motor. In particular, the motor 11 has a no-load rotational speed at which the rotational speed is maximum when the load is 0, and has a characteristic that the rotational speed decreases as the load on the motor shaft 13 increases. Also, as a general specification, a rated rotational speed and a rated torque (indicating the torque generated at the rated rotational speed) are set for the motor 11. Since heat generation rapidly increases when the motor 11 operates with a torque exceeding the rated torque, continuous operation below the rated torque is preferably performed. Further, up to a certain load, the load and the torque are balanced, but when the load exceeds the stall torque (the maximum torque that the motor can generate), the motor 11 is forcibly stopped, and the risk of damage to the motor 11 and the driven device increases.

[0023] Also, the terminal box 14 includes power terminals (U, V, W) connected to the three-phase power supply 18, motor terminals electrically connected to the motor 11, and external terminals for connecting to external devices. The power terminals are electrically connected to the motor terminals via a substrate. This terminal box 14 includes a substrate in which a processor, a communication circuit, a relay circuit, etc. are incorporated, and the substrate constitutes a part of the components (control unit 110) of the overload protection device (or overload protection system) 100. Note that the terminal box 14 may be configured such that an independent control power supply 19 (for example, a battery) that is not affected by the external power environment is supplied to the control unit 110 of the overload protection device 100 separately from the three-phase power supply 18. This control power supply 19 may be provided inside the terminal box 14 of the motor 11.

[0024] Then, by connecting the output end of the motor shaft 13 to the driven device via the coupling 101 of the overload protection device 100 (and further optionally via a speed reducer), the driven device can be driven. The driven device is, for example, a chip conveyor (not shown), and the output side of the motor shaft 13 of the motor 11 is directly or indirectly connected to the sprocket of the chip conveyor.

[0025] As shown in FIGS. 1 and 2, the overload protection device 100 includes a coupling 101 that connects the output end of the motor shaft 13 of the motor 11 and the input portion 16a of the driven device. The coupling 101 includes a driving member 102 fixed to the output end of the motor shaft 13 and a driven member 103 that is magnetically coupled to the driving member 102 via an air gap 106 and fixed to the input portion 16a of the driven device. The coupling 101 is configured to transmit the torque of the motor shaft 13 to the driven device by the magnetic force between the driving member 102 and the driven member 103.

[0026] Specifically, the driving member 102 is formed of a cylindrical body fitted onto the motor shaft 13 and has a driving magnet 102a on its outer periphery. On the other hand, the driven member 103 is formed of an annular body fitted onto the shaft-like input portion 16a and has a driven magnet 103a on the inner periphery of the annular portion. As shown in FIGS. 1 and 2, the driving member 102 is disposed inside the annular portion of the driven member 103. Then, as shown in FIG. 2, the driving magnet 102a of the driving member 102 and the driven magnet 103a of the driven member 103 face each other via the air gap 106 in the radial direction, forming a so-called in-out type magnetic coupling. Further, the driving magnet 102a and the driven magnet 103a are configured such that the N poles and the S poles are alternately continuous in the circumferential direction.

[0027] In the coupling 101, when the drive magnet 102a rotates together with the drive member 102 by the rotational drive of the motor shaft 13, the drive magnet 102a acts magnetically on the driven magnet 103a, and the driven member 103 rotates following the driven magnet 103a and rotates synchronously. That is, while the magnetic coupling between the drive magnet 102a and the driven magnet 103a is maintained, the drive member 102 and the driven member 103 rotate synchronously, and the torque of the motor shaft 13 can be transmitted to the input portion 16a. In the transmission state of this coupling 101, the torque of the motor shaft 13 and the load from the driven device are balanced, and the torque increases as the load increases. The coupling 101 has a maximum allowable torque T indicating the limit value at which torque transmission is possible as an inherent characteristic. That is, when the load (torque) applied to the coupling 101 is equal to or less than the maximum allowable torque T, the coupling 101 forms a transmission state (coupled state).

[0028] On the other hand, when the load (torque) exceeds the maximum allowable torque T that can be transmitted by the coupling 101, the coupling 101 goes out of tune, and the drive member 102 and the driven member 103 no longer synchronize. As a result, the coupling 101 shifts from a transmission state (synchronous state) that transmits torque to an idling state (out-of-tune state) that does not transmit torque. That is, when the load on the motor shaft 13 exceeds the maximum allowable torque T that can be transmitted by the coupling 101, the coupling 101 idles the drive member 102 with respect to the driven member 103, making it possible to forcibly disconnect the connection between the motor shaft 13 and the driven device.

[0029] The maximum allowable torque T that the coupling 101 can transmit is determined by the magnetic attraction or repulsion between the driving magnet 102a and the driven magnet 103a. This maximum allowable torque T can be designed to be the desired value by those skilled in the art, for example, by adjusting the magnetic force intensity (selection of magnetic materials) and / or the configuration of the magnets (size, shape, number of poles, distance of the air gap), etc. In this embodiment, the maximum allowable torque T that the coupling 101 can transmit is determined based on the motor-specific rotational speed-torque characteristics shown in FIG. 4. Preferably, as shown in FIG. 4, the maximum allowable torque T is set to be equal to or greater than the rated torque of the motor 11 and less than the stall torque of the motor 11. Thereby, it is possible to prevent the motor 11 from operating beyond a predetermined torque that is equal to or greater than the rated torque and less than the stall torque. Also, preferably, the maximum allowable torque T is set to be the same as the rated torque of the motor 11. Thereby, it is possible to prevent the motor 11 from operating beyond the rated torque and effectively suppress the heat generation of the motor 11. Alternatively, the maximum allowable torque T may be set to be less than or equal to the rated torque of the motor 11 according to the operable torque of the driven device. Thereby, it is possible to more reliably suppress damage to the driven device according to the specifications of the driven device.

[0030] Further, the overload protection device 100 further includes a detection means for detecting the idling state of the coupling 101, and a control unit (MCU) 110 that receives the output signal from the detection means and determines that the motor 11 is in an overload state when detecting the idling of the coupling 101 based on the output signal, and controls the motor 11 to stop the power supply to the motor 11.

[0031] The detection means includes a magnetic sensor 104 that measures the magnetic force of the detected portion 105 provided on the coupling 101 over time. The detected portion 105 is a magnet or a magnetic body formed on the outer periphery of the driven member 103 of the coupling 101. The magnetic sensor 104 is arranged at a position where it can read the magnetic force of the detected portion 105 that rotates during operation. And the control unit 110 analyzes or calculates the output signal from the magnetic sensor 104, and is configured to detect the idling of the coupling 101 based on the change in the magnetic force in the detected portion 105 when the coupling 101 shifts from the transmission state to the idling state. Note that, instead of the magnetic sensor 104, the detection means may be configured to constantly measure the rotational speed of the motor shaft 13 and / or the driving member 102 and the rotational speed of the input portion 16a and / or the driven member 103, and detect the idling state of the coupling 101 when a difference occurs between them.

[0032] In the present embodiment, the coupling 101 and the magnetic sensor 104 are accommodated in a peripheral wall portion 107 that surrounds the output end of the motor shaft 13 protruding outward from the housing of the motor body 12 of the motor 11. That is, since the physical components of the overload protection device 100 are provided outside the motor body 12, it is easy to retrofit an existing motor.

[0033] As shown in FIG. 3, the overload protection device 100 is provided with a relay 111 as power cut-off means. The relay 111 is directly or indirectly connected to the control unit 110 and the three-phase power supply 18. The relay 111 is configured to receive an instruction from the control unit 110, control the three-phase power supply 18, and cut off the power supply from the three-phase power supply 18 to the motor 11. In the present embodiment, the relay 111 operates by mechanical switching of relay contacts. In the overload protection device 100 of the present embodiment, when the control unit 110 receives an output signal indicating the idling state of the coupling 101 from the detection means (magnetic sensor 104), it determines or detects that the motor 11 is in an overload state, controls the relay 111 to cut off the power, and stops the power supply to the motor 11.

[0034] In addition, as shown in FIG. 3, the overload protection device 100 is provided with a user interface 113 that enables interaction between the user and the system. The user interface 113 can be selected from any means such as a display, a touch panel, and audio input / output means, which is connected to the control unit 110. The user interface 113 can receive input from the user and enable operations and settings of the motor 11. Further, the user interface 113 may notify the user that the motor 11 is in an overload state when the overload state of the motor 11 is detected. Furthermore, after the power supply to the motor 11 is stopped based on the detection of the overload state, the user interface 113 may operate to request confirmation (safety confirmation) of the removal of the load cause. In this case, the user can input via the user interface 113 that the load cause has been removed, thereby releasing the power supply stop state of the motor 11 and enabling the motor 11 to be restarted. In other words, if there is no input confirming the removal of the load cause, the power supply to the motor 11 is restricted.

[0035] Furthermore, the overload protection device 100 may include a communication circuit as a means for communicating with the outside. The communication circuit connects the control unit 110 and an external server, enabling data transmission and reception between them. By using the external server, the user can obtain a lot of data regarding the motor characteristics for each type of motor, and moreover, the setting and update / correction of the device become easy. Also, the external server may store the logs of various data output via the communication circuit by the control unit 110 during motor drive. Alternatively, a storage unit for storing various data may be incorporated as a recording medium such as a memory or a hard disk on the substrate inside the terminal box 14.

[0036] In addition, the communication circuit may optionally connect the control unit 110 and the user terminal. The user terminal is a terminal operable by the user, such as a control panel, a smartphone, a personal computer, etc. By using this user terminal, the operation of the motor 11 can be monitored and displayed on a monitor, or device settings can be remotely input to the control unit 110. The connection between the communication circuit and the above external device may be either wired or wireless. Examples of the wireless connection means include WiFi (registered trademark), Bluetooth (registered trademark), etc.

[0037] Next, with reference to the flowchart of FIG. 5, the operation of the motor 11 with the overload protection device 100 will be described. First, the user turns on the power supply of the motor 11. Thereby, the power supply is supplied from the three-phase power supply 18 to the motor 11. Next, when the user turns on the control power supply 19 and inputs an instruction to start operation via the user interface 113, the operation of the motor 11 starts. During operation, in the case of a normal load where the overload protection device 100 does not detect an overload state, the motor 11 operates normally, and the operation ends by stopping the motor 11 by the user's operation. On the other hand, when an overload occurs during operation and the load applied to the motor shaft 13 increases until it exceeds the maximum allowable torque T of the coupling 101, the magnetic coupling in the coupling 101 is disconnected, and the coupling 101 enters an idling state. As a result, the measured magnetic force by the magnetic sensor 104 changes rapidly according to the transition from the transmission state to the idling state. The control unit 110 receives the output signal from the magnetic sensor 104 and detects the idling state of the coupling 101 based on the change in the magnetic force. That is, the overload protection device 100 detects or determines that the motor 11 is in an overload state. Then, the control unit 110 transmits a stop signal to the relay 111. The relay 111 mechanically switches its relay contacts upon receiving the stop signal. By this switching of the relay contacts, the power supply from the three-phase power supply 18 to the motor 11 is cut off. The user receives a notification of motor power cut-off via the user interface 113. After the user removes the cause of the load, by inputting "confirmation of removal of load cause" (safety confirmation) via the user interface 113, the motor power cut-off is released, and it becomes possible to turn on the motor power supply.

[0038] FIG. 6 is a block diagram of the entire system including the motor 11 with the overload protection device 100. In the system shown in FIG. 6, the output side of the motor 11 equipped with the overload protection device 100 is connected to the speed reducer 16 via the coupling 101. In other words, in this system, the motor 11 with the overload protection device 100 and the speed reducer 16 are combined to form a geared motor. The three-phase power supply 18 supplies power to the motor 11. The control power supply 19 supplies control power to the overload protection device 100 (control unit 110). Also, the output shaft of the speed reducer 16 is connected to the chip conveyor 17 as the driven device. The system obtains a low rotational speed and high torque output at the output shaft of the speed reducer 16 to drive the chip conveyor 17. When the object being transported becomes overloaded or is jammed by foreign matter into the chip conveyor 17 during the driving of the chip conveyor 17, the coupling (torque transmission) between the motor shaft 13 and the chip conveyor 17 by the coupling 101 is forcibly disconnected, and the overload protection device 100 detects the idling state of the coupling 101. Then, by switching the relay contacts of the relay 111, the power supply to the motor 11 from the three-phase power supply 18 is cut off.

[0039] That is, the overload protection device 100 of this embodiment couples the motor shaft 13 and the input portion 16a of the driven device so that torque can be transmitted by the coupling 101 using magnetic force. When the load on the motor shaft 13 exceeds the maximum allowable torque T that can be transmitted by the coupling 101, the driving member 102 idles with respect to the driven member 103, thereby forcibly disconnecting the coupling (torque transmission) between the motor shaft 13 and the driven device. As a result, a torque exceeding the maximum allowable torque T of the coupling 101 is not applied between the motor shaft 13 and the input portion 16a of the driven device, and it is possible to surely prevent the occurrence of an overload state. That is, the overload protection device 100 of this embodiment can protect the motor 11 and the like from overload without being affected by electrical influences from the external environment.

[0040] [Alternative Embodiments and Variations] The present invention is not limited to the above-described embodiments and can take various embodiments and modifications. Hereinafter, another embodiment and modification of the present invention will be described.

[0041] (1) In the above embodiment, the control unit of the overload protection device is integrated on the control board built in the terminal box of the motor. However, as long as each component can be controlled, it may be provided separately from the motor.

[0042] (2) In the above embodiment, the motor shaft of the motor is connected to the input part of the speed reducer which is a part of the driven device. However, the present invention is not limited to this. That is, the motor of the present invention may be a geared motor provided with a speed reduction mechanism for outputting power to the driven device. In this case, a coupling of the overload protection device is provided between the output end of the output shaft (motor shaft) of the geared motor and the input part of the driven device (for example, the sprocket of the chip conveyor).

[0043] (3) In the overload protection device of the above embodiment, an in-out type magnetic coupling is adopted. However, instead of this, a disk type magnetic coupling may be used.

[0044] (4) In the overload protection device of the above embodiment, the relay as the power-off means is configured to send a power-off signal to the power supply. However, the power-off means is arranged between the motor and the power supply, and the power supply may be cut off by opening and closing the switch. That is, the configuration of the above embodiment is only an example, and those skilled in the art can make various modifications under the technical idea of the present invention.

[0045] The present invention is not limited to the above-described embodiments and modifications, and can be implemented in various aspects as long as it belongs to the technical scope of the present invention.

Explanation of Reference Numerals

[0046] 11 Motor 12 Motor Body 13 Motor Shaft 14 Terminal Box 16 Reducer (Driven Device) 16a Input Section 17 Chip Conveyor (Driven Device) 18 Three-Phase Power Supply 19 Control Power Supply 100 Overload Protection Device 101 Coupling 102 Driving Member 102a Driving Magnet 103 Driven Member 103a Driven Magnet 104 Magnetic Sensor (Detection Means) 105 Detected Portion 106 Air Gap 107 Peripheral Wall 110 Control Unit (MCU) 111 Relay (Power Cut-off Means) 113 User Interface T Maximum Allowable Torque

Claims

1. An overload protection device that is connected to a motor for driving a driven device and operates to protect the motor from overload, comprising a coupling that connects an output end of a motor shaft of the motor and an input portion of the driven device, wherein the coupling includes a driving member fixed to the output end of the motor shaft and a driven member magnetically coupled to the driving member and fixed to the input portion of the driven device, the coupling is configured to transmit the torque of the motor shaft to the driven device by a magnetic force between the driving member and the driven member, and when a load on the motor shaft exceeds a maximum torque transmissible by the coupling, the driving member idles relative to the driven member, and the connection between the motor shaft and the driven device is disconnected. The overload protection device is characterized by this.

2. detection means for detecting idling of the coupling; and a control unit that determines that the motor is in an overload state when detecting the idling state of the coupling based on an output signal from the detection means, and controls the motor to stop power supply to the motor. The overload protection device according to claim 1 is characterized by further comprising this.

3. The detection means includes a magnetic sensor that measures the magnetic force of a detected portion provided on the coupling over time, and detects the idling state of the coupling based on a change in magnetic force when the coupling shifts from a transmission state to an idling state. The overload protection device according to claim 2 is characterized by this.

4. further comprising a user interface that receives an input from a user, notifies the user that there is an overload, and requests confirmation of removal of the load cause, and after the control unit detects that the motor is in an overload state and stops power supply to the motor, when the user inputs confirmation of removal of the load cause via the user interface, power supply to the motor can be turned on. The overload protection device according to claim 3 is characterized by this.

5. further comprising a relay configured to receive a stop signal for stopping power supply from the control unit to the motor, and to cut off power supply to the motor by switching a relay contact upon reception of the stop signal. The overload protection device according to claim 3 is characterized by this.

6. The overload protection device according to claim 3, wherein the coupling and the magnetic sensor are housed in a peripheral wall portion surrounding an output end of the motor shaft protruding externally from a housing of a motor body of the motor.

7. The overload protection device according to claim 3, wherein a maximum torque transmissible by the coupling is determined to be equal to or greater than a rated torque of the motor and smaller than a stall torque of the motor.

8. A motor comprising the overload protection device according to any one of claims 1 to 7.

9. The motor according to claim 8, wherein the motor is a geared motor including a speed reduction mechanism that outputs power to the driven device.

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