Cutting device
The cutting device employs a torque detection system to identify single-blade abnormalities by analyzing drive current fluctuations, ensuring accurate detection and preventing damage, thus enhancing operational safety.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- MAX CO LTD
- Filing Date
- 2025-12-03
- Publication Date
- 2026-06-11
Smart Images
Figure JP2025042221_11062026_PF_FP_ABST
Abstract
Description
Cutting device 【0001】 This disclosure relates to a cutting device. 【0002】 Conventionally, there is a cutting device described in Patent Document 1 below. This cutting device includes two cutting blades that sandwich and cut an object to be cut, and a driving unit that operates the cutting blades by the driving force of an electric motor. 【0003】 Japanese Patent Application Laid-Open No. 2024-94218 【0004】 In the cutting device described in Patent Document 1, when a single-blade abnormality occurs in which one of the two cutting blades is damaged for some reason, there is a possibility that an operator may use the cutting device without noticing it. In such a case, only the other cutting blade that is not damaged contacts the object to be cut, which may cause an unintended malfunction in the cutting device. In order to avoid such a situation, there is a need for a cutting device that can detect such a single-blade abnormality when it occurs. 【0005】 This disclosure has been made in view of such a situation, and its object is to provide a cutting device that can more appropriately detect a single-blade abnormality. 【0006】A cutting device that solves the above problems comprises a first cutting blade, a second cutting blade, a toggle link mechanism, a drive unit, a torque detection unit, and a control unit. The first cutting blade is rotatably supported with a first shaft as a pivot point and has a blade forming portion at its tip. The second cutting blade is rotatably supported with a second shaft as a pivot point and has a blade forming portion at its tip. The toggle link mechanism has a first link member whose tip is rotatably connected to the base end of the first cutting blade, a second link member whose tip is rotatably connected to the base end of the second cutting blade, and a movable member connected to the base end of the first link member and the base end of the second link member. The drive unit is equipped with an electric motor and opens and closes the first cutting blade and the second cutting blade via the first link member and the second link member by moving the movable member with the power of the electric motor. The torque detection unit detects the output torque of the electric motor. The control unit controls the electric motor. After driving the electric motor, the control unit determines that a single-blade malfunction has occurred, if it detects that the output torque of the electric motor detected by the torque detection unit has a predetermined fluctuation pattern, indicating that an abnormality has occurred in either the first cutting blade or the second cutting blade. 【0007】 This configuration makes it possible to more accurately detect whether or not a single-edged abnormality has occurred in the first cutting blade and the second cutting blade. 【0008】 The cutting device of this disclosure makes it possible to detect single-edged abnormalities more appropriately. 【0009】A perspective view showing the perspective structure of the cutting device of the first embodiment. A cross-sectional view showing the partially fractured cross-sectional structure along the line II-II in Figure 1. A front view showing the front structure around the tip of the cutting device of the first embodiment. A cross-sectional view showing an example of operation of the cutting device of the first embodiment. A cross-sectional view showing an example of operation of the cutting device of the first embodiment. A block diagram showing the electrical configuration of the cutting device of the first embodiment. A cross-sectional view showing an example of operation of the cutting device of the first embodiment. A graph showing the changes in drive current Im and drive current change ΔIm with respect to the rotation angle θm of the electric motor when the cutting blade is normal in the cutting device of the first embodiment. A graph showing the changes in drive current Im and drive current change ΔIm with respect to the rotation angle θm of the electric motor when a single-blade abnormality occurs in the cutting device of the first embodiment. A flowchart showing the procedure of processing executed by the control unit of the first embodiment. A flowchart showing the procedure of processing executed by the control unit of the first modified example of the first embodiment. A flowchart showing the procedure of processing executed by the control unit of the second modified example of the first embodiment. A flowchart showing the procedure of processing executed by the control unit of the second embodiment. A graph showing the change in rotational speed ωm with respect to the rotational angle θm of the electric motor in the second embodiment. 【0010】 The following describes an embodiment of the cutting device with reference to the drawings. To facilitate understanding of the explanation, the same reference numerals are used for identical components in each drawing whenever possible, and redundant explanations are omitted. 【0011】 <First Embodiment> First, a first embodiment of the cutting device 10 will be described. Figure 1 is a perspective view showing the oblique structure of the cutting device 10 of this embodiment. The cutting device 10 is an electric cutting device used, for example, to cut reinforcing bars that make up mesh reinforcement at a construction site. Figure 2 is a cross-sectional view showing a partially fractured cross-section structure along the line II-II in Figure 1. 【0012】As shown in Figure 2, the cutting device 10 includes a pair of cutting blades 20a and 20b for cutting objects such as reinforcing bars, a drive unit 30 that generates power to open and close the pair of cutting blades 20a and 20b, and a toggle link mechanism 40 that transmits the power from the drive unit 30 to the pair of cutting blades 20a and 20b. Also, as shown in Figure 1, the cutting device 10 includes a pair of guide plates 50a and 50b provided adjacent to the pair of cutting blades 20a and 20b, and a housing 60 provided to surround the outer circumference of the drive unit 30. 【0013】 As shown in Figure 2, the cutting blade 20a is formed in the shape of a long plate, and its central portion is rotatably supported by a shaft portion 59a fixed to the main frame 70. The main frame 70 is fixed to the housing 60. A blade forming portion 21a is provided at the tip of the cutting blade 20a. As shown in Figure 1, the blade forming portion 21a is positioned to be exposed to the outside from the tip of the housing 60. As shown in Figure 2, the cutting blade 20b is similarly rotatably supported by a shaft portion 59b and also has a blade forming portion 21b at its tip. As the cutting blades 20a and 20b rotate around the shaft portions 59a and 59b as pivot points, the respective blade forming portions 21a and 21b open and close in the Y direction in the figure. In this embodiment, the Y direction is an example of the opening and closing direction. Also, the cutting blade 20a is an example of a first cutting blade, and the cutting blade 20b is an example of a second cutting blade. Furthermore, shaft portion 59a is an example of a first shaft portion, and shaft portion 59b is an example of a second shaft portion. 【0014】 The toggle link mechanism 40 comprises a pair of link members 41a and 41b, and a trunnion 42. 【0015】 The link member 41a is formed in a plate shape. A shaft portion 410a is provided at the tip of the link member 41a. The base end of the cutting blade 20a is rotatably connected to the shaft portion 410a. Similarly, the link member 41b is also provided with a shaft portion 410b to which the base end of the cutting blade 20b is rotatably connected. In this embodiment, the link member 41a is an example of a first link member, and the link member 41b is an example of a second link member. 【0016】The trunnion 42 is provided to be movable along a predetermined axis m10. In this embodiment, the direction along axis m10 is an example of the direction of movement of the trunnion 42. Hereinafter, the direction parallel to axis m10 will be referred to as the X direction. The X direction is perpendicular to the Y direction. In this embodiment, the X direction is an example of a predetermined direction. A shaft portion 420 is formed at the tip of the trunnion 42. The base ends of a pair of link members 41a and 41b are rotatably connected to the shaft portion 420. The shaft portion 420 is inserted into a guide groove 71 of the main frame 70, which is fixed to the housing 60. The guide groove 71 is formed to extend along axis m10. The trunnion 42 is supported so as to be able to reciprocate in the X direction by the shaft portion 420 being guided by the guide groove 71 of the main frame 70. The base end of the trunnion 42 is formed in a cylindrical shape around axis m10 and is connected to the drive unit 30. In this embodiment, the trunnion 42 is an example of a movable member. 【0017】 The drive unit 30 opens and closes the cutting blades 20a and 20b via the link members 41a and 41b by applying power in the X direction (axial direction) to the trunnion 42 of the toggle link mechanism 40. The drive unit 30 includes a ball screw mechanism 31, a reduction mechanism 32, and an electric motor 33. 【0018】 The ball screw mechanism 31 includes a nut portion 310 and a threaded portion 311. 【0019】 The nut portion 310 is formed in a cylindrical shape with an axis m10 and has an internal threaded portion on its inner circumference. The nut portion 310 is integrally connected to the trunnion 42 of the toggle link mechanism 40 by inserting its tip into the base end of the trunnion 42 and fixing it therein. 【0020】 The threaded portion 311 is formed in a rod shape so as to extend along the axis m10 and has a male thread on its outer surface. The male thread of the threaded portion 311 is screwed into the female thread of the nut portion 310. The base end of the threaded portion 311 is connected to the reduction mechanism 32. 【0021】The reduction mechanism 32 is connected to the output shaft of the electric motor 33. The reduction mechanism 32 reduces the rotation of the output shaft 330 of the electric motor 33 and transmits it to the screw portion 311. 【0022】 The electric motor 33 is, for example, a brushless DC motor. The electric motor 33 has an output shaft 330. The output shaft 330 is a substantially cylindrical member, and its central axis coincides with the axis m10. A part of the output shaft 330 protrudes to the reduction mechanism 32 and is connected to the reduction mechanism 32. The electric motor 33 is driven based on power supplied from a predetermined power supply device 34. The power supply device 34 is, for example, a storage battery such as a lithium-ion battery mounted on the cutting device 10. When power is supplied from the power supply device 34 to the coil of the electric motor 33, the electric motor 33 is driven and the output shaft 330 rotates about the axis m10. The rotation of the output shaft 330 is transmitted to the screw portion 311 via the reduction mechanism 32, causing the screw portion 311 to rotate about the axis m10. 【0023】 As shown in Figures 1 and 2, the cutting device 10 further includes an operating unit 100. When the operating unit 100 is turned ON by the operator, power is supplied to the electric motor 33, causing the electric motor 33 to rotate in the forward direction, which in turn causes the pair of cutting blades 20a and 20b to close. When the operating unit 100 is turned OFF by the operator, the electric motor 33 rotates in the reverse direction, causing the pair of cutting blades 20a and 20b to open, after which the power supply to the electric motor 33 is cut off. 【0024】As shown in Figure 1, the guide plates 50a and 50b are plate-shaped members that are exposed from the tip of the housing 60. The guide plates 50a and 50b are fixed to the main frame 70. The guide plates 50a and 50b are provided so as to sandwich the pair of cutting blades 20a and 20b in the Z direction. The Z direction is perpendicular to the X and Y directions. In this embodiment, the Z direction is an example of a direction perpendicular to the opening and closing direction of the cutting blades 20a and 20b. The guide plate 50a has a recess 51 formed therein that extends in the X direction from its outer edge to between the respective blade-forming portions 21a and 21b of the pair of cutting blades 20a and 20b. The guide plate 50b also has a similar recess 51 formed therein. The respective recesses 51 of the guide plates 50a and 50b are provided to guide the object to be cut between the respective blade-forming portions 21a and 21b of the pair of cutting blades 20a and 20b. In this embodiment, guide plates 50a and 50b are examples of guide parts. 【0025】 Next, an example of the operation of the cutting device 10 of this embodiment will be described. In the following, among the X directions, the direction from the drive unit 30 toward the cutting blades 20a and 20b, as shown in Figure 2, will be referred to as the Xa direction, and the opposite direction will be referred to as the Xb direction. 【0026】 In the cutting device 10 of this embodiment, when the operating unit 100 is not being operated, the blade forming portions 21a and 21b of the pair of cutting blades 20a and 20b are positioned spaced apart in the Y direction, as shown in Figures 1 and 2. Hereinafter, the position of the pair of cutting blades 20a and 20b shown in Figures 1 and 2 will be referred to as the fully open position. 【0027】When cutting an object using the cutting device 10, first, as shown in Figure 3, the object to be cut 110 is inserted into the respective recesses 51 of the guide plates 50a and 50b, positioning the object to be cut 110 between the respective blade forming portions 21a and 21b of the pair of cutting blades 20a and 20b. Next, when the operator operates the control unit 100, the electric motor 33 is driven, causing the output shaft 330 of the electric motor 33 to rotate. The torque of the output shaft 330 of the electric motor 33 is transmitted to the threaded portion 311 of the ball screw mechanism 31 via the reduction mechanism 32. As a result, when the threaded portion 311 rotates around the axis m10, the nut portion 310 is displaced in the Xa direction along the axis m10. Therefore, the trunnion 42 of the toggle link mechanism 40 is displaced in the Xa direction together with the nut portion 310. In this way, the drive unit 30 converts the torque output from the electric motor 33 into power along the axial direction of the trunnion 42 and applies it to the trunnion 42, causing the trunnion 42 to be displaced in the axial direction. Due to this displacement of the trunnion 42, as shown in Figure 4, the pair of link members 41a and 41b swing in the R1a and R1b directions, respectively, with the shaft portion 420 of the trunnion 42 as the pivot point. As a result, the respective tips of the pair of link members 41a and 41b are displaced so that they are separated from each other in the Y direction. Due to this displacement of the pair of link members 41a and 41b, the pair of cutting blades 20a and 20b swing in the R2a and R2b directions, respectively, with the shaft portions 59a and 59b as pivot points. As a result, the blade-forming portions 21a and 21b of the pair of cutting blades 20a and 20b are displaced so that they move closer to each other in the Y direction, and the object to be cut 110 is sandwiched between the blade-forming portions 21a and 21b of the pair of cutting blades 20a and 20b. When the blade-forming portions 21a and 21b of the pair of cutting blades 20a and 20b are further displaced so that they move closer to each other in the Y direction, the blade-forming portions 21a and 21b bite into the object to be cut 110. When the pair of cutting blades 20a and 20b are displaced to the position where the blade-forming portions 21a and 21b are closest to each other as shown in Figure 5, the object to be cut 110 is cut by the blade-forming portions 21a and 21b. Hereafter, the position of the pair of cutting blades 20a and 20b shown in Figure 5 will be referred to as the fully closed position. 【0028】After the blade-forming portions 21a and 21b of the pair of cutting blades 20a and 20b are closest together, the electric motor 33 rotates in reverse, causing the blade-forming portions 21a and 21b of the pair of cutting blades 20a and 20b to automatically return to the positions shown in Figures 1 and 2. 【0029】 In the following, the rotation direction of the electric motor 33 that causes the pair of cutting blades 20a and 20b to close will be referred to as forward rotation, and the rotation direction of the electric motor 33 that causes the pair of cutting blades 20a and 20b to open will be referred to as reverse rotation. 【0030】 Next, the electrical configuration of the cutting device 10 will be described. 【0031】 As shown in Figure 6, the cutting device 10 further includes a rotation sensor 80, a current sensor 81, a voltage sensor 82, a home sensor 83, a trigger switch 84, a notification device 85, and a control device 90. 【0032】 The rotation sensor 80 detects the rotation angle θm of the output shaft 330 of the electric motor 33 and outputs a signal corresponding to the detected rotation angle θm. For example, the rotation sensor 80 is a sensor that outputs a pulse signal each time the output shaft 330 rotates by a predetermined angle. In this case, by counting the number of pulse signals output from the rotation sensor 80, the rotation angle θm of the output shaft 330 can be detected from the count and the predetermined angle. The rotation sensor 80 takes the rotation position of the output shaft 330 of the electric motor 33 when the cutting blades 20a and 20b are in the fully open position shown in Figure 2 as the initial position (θm = 0°) and detects the rotation angle θm from this initial position. Hereafter, the rotation angle θm of the output shaft 330 of the electric motor 33 will be referred to as the rotation angle θm of the electric motor 33. 【0033】 The current sensor 81 detects the drive current Im, which is the current flowing through the electric motor 33, and outputs a signal corresponding to the detected drive current Im. The voltage sensor 82 detects the drive voltage Vm, which is the voltage applied to the electric motor 33, and outputs a signal corresponding to the detected drive voltage Vm. 【0034】The origin sensor 83 is a sensor for detecting when the cutting blades 20a and 20b are in the fully open position shown in Figure 2. For example, when the cutting blades 20a and 20b are in the fully open position shown in Figure 2, the trunnion 42 of the toggle link mechanism 40 is also in the position shown in Figure 2. Taking advantage of this, the cutting device 10 uses a position sensor that detects the position of the trunnion 42 of the toggle link mechanism 40 as the origin sensor 83. The origin sensor 83 outputs a predetermined origin detection signal when the trunnion 42 of the toggle link mechanism 40 is in the position shown in Figure 2. If the trunnion 42 of the toggle link mechanism 40 deviates from the position shown in Figure 2 due to the opening and closing operation of the cutting blades 20a and 20b, the origin sensor 83 stops outputting the origin detection signal. Therefore, it is possible to detect whether the cutting blades 20a and 20b are in the fully open position based on whether or not the origin detection signal is output from the origin sensor 83. 【0035】 The trigger switch 84 turns ON and outputs an ON signal when the operating unit 100 shown in Figures 1 and 2 is being operated by the user, and turns OFF and outputs an OFF signal when the operating unit 100 is not being operated by the user. Therefore, it is possible to detect whether or not the operating unit 100 is being operated based on whether or not the trigger switch 84 is outputting an ON signal. 【0036】 The notification device 85 is a device for notifying the user of various states of the cutting device 10. As the notification device 85, for example, a lighting device that notifies the user of various states of the cutting device 10 by flashing, turning on, or turning off a light, a display device that displays the various states of the cutting device 10 on a display or the like, an acoustic device that notifies the user of various states of the cutting device 10 by buzzer sound or voice, and a vibration generating device that notifies the user of various states of the cutting device 10 by vibration. As for various states of the cutting device 10, for example, when an abnormality occurs in the cutting device 10, the notification device 85 notifies the user of that fact. 【0037】The control device 90 controls the operation of the entire cutting device 10, including the electric motor 33. The control device 90 is composed of, for example, a circuit board mounted on the cutting device 10. The control device 90 includes, for example, an inverter circuit for controlling the current supplied from the power supply device 34 to the electric motor 33, a microcomputer for controlling the switching operation of the inverter circuit, and a memory device for storing various programs. The control device 90 receives the output signals from the rotation sensor 80, current sensor 81, voltage sensor 82, origin sensor 83, and trigger switch 84. Based on the output signals from the rotation sensor 80, current sensor 81, voltage sensor 82, origin sensor 83, and trigger switch 84, the control device 90 controls the electric motor 33 and the notification device 85. The control device 90 includes a speed acquisition unit 91, a position acquisition unit 92, and a control unit 93. 【0038】 The speed acquisition unit 91 acquires the opening and closing speeds of the cutting blades 20a and 20b. In this embodiment, taking advantage of the correlation between the opening and closing speeds of the cutting blades 20a and 20b and the rotational speed ωm of the output shaft 330 of the electric motor 33, the speed acquisition unit 91 acquires the rotational speed ωm of the output shaft 330 of the electric motor 33 as an indicator of the opening and closing speeds of the cutting blades 20a and 20b. Specifically, if the rotation sensor 80 is a sensor that outputs a pulse signal each time the output shaft 330 rotates by a predetermined angle, the speed acquisition unit 91 acquires the rotational speed ωm of the output shaft 330 of the electric motor 33 based on the number of pulse signals output from the rotation sensor 80 per unit time. Hereafter, the rotational speed ωm of the output shaft 330 of the electric motor 33 will be referred to as the rotational speed ωm of the electric motor 33. 【0039】The position acquisition unit 92 acquires the positions of the cutting blades 20a and 20b. In this embodiment, by utilizing the correlation between the positions of the cutting blades 20a and 20b and the rotation angle θm of the electric motor 33, the position acquisition unit 92 acquires the rotation angle θm of the electric motor 33 as an indicator of the positions of the cutting blades 20a and 20b. Specifically, the position acquisition unit 92 detects whether the cutting blades 20a and 20b are in the fully open position based on the output signal of the origin sensor 83. If the position acquisition unit 92 detects that the cutting blades 20a and 20b are in the fully open position, it determines that the output shaft 330 of the electric motor 33 is in the initial position (θm = 0°). After detecting that the output shaft 330 of the electric motor 33 is in the initial position, the position acquisition unit 92 acquires the rotation angle θm of the electric motor 33 from the initial position by counting the number of pulse signals output from the rotation sensor 80. The rotation angle θm represents the direction in which the electric motor 33 rotates in the positive direction from the initial position as a positive value. Therefore, when the electric motor 33 is rotating in the forward direction, the rotation angle θm increases, and when the electric motor 33 is rotating in the reverse direction, the rotation angle θm decreases. 【0040】 The control unit 93 controls the electric motor 33 and the notification device 85. For example, the control unit 93 controls the opening and closing operation of the cutting blades 20a and 20b by controlling the current supplied to the electric motor 33 using PWM (pulse width modulation) control. The control unit 93 also controls the braking operation of the cutting blades 20a and 20b by performing so-called short-circuit brake control, which involves short-circuiting the multiple coils of the electric motor 33. 【0041】 Furthermore, the control unit 93 monitors whether a single-edged abnormality has occurred, such as damage to either the cutting blade 20a or 20b, during the period when the electric motor 33 is driven to cut the workpiece 110. If the control unit 93 detects that a single-edged abnormality has occurred, it performs braking control of the cutting blades 20a and 20b to stop them, and so on. 【0042】 Next, the method for detecting a single-edged blade abnormality by the control unit 93 will be described. 【0043】As shown in FIG. 4, when the workpiece 110 is cut by a pair of cutting blades 20a and 20b, reaction forces F1a and F1b in the figure are applied from the workpiece 110 to each of the pair of cutting blades 20a and 20b. As a result, forces F2a and F2b as shown in FIG. 4 are applied to the link members 41a and 41b of the toggle link mechanism 40. At this time, in the shaft portion 420 of the trunnion 42, the Y-direction component of the force F2a and the Y-direction component of the force F2b cancel each other out. As a result, only the X-direction component of the force F2a and the X-direction component of the force F2b are applied to the shaft portion 420 of the trunnion 42. That is, only a force in the X direction, or in other words, only an axial force, is applied to the shaft portion 420 of the trunnion 42. 【0044】 In such a cutting device 10, if the cutting blade 20b is damaged and an operator operates the operation unit 100 without noticing it, there is a possibility that a single-blade abnormality may occur in which only the cutting blade 20a performs a closing operation. At this time, as shown in FIG. 7, since the workpiece 110 is sandwiched between the cutting blade 20a and the inner wall surfaces of the concave portions 51 of the guide plates 50a and 50b, only the reaction force F1a is applied to the cutting blade 20a. In this case, only the force F2a shown in FIG. 7 is applied to the shaft portion 420 of the trunnion 42. Therefore, not only the X-direction component of the force F2a but also the Y-direction component of the force F2a is applied to the shaft portion 420. The Y-direction component of the force F2a applied to this shaft portion 420 may act on the ball screw mechanism 31 and the main frame 70, causing damage to them. 【0045】 On the other hand, when the inventor experimentally measured the waveform of the output torque of the electric motor 33 when the cutting blades 20a and 20b are normal as shown in FIG. 4 and the waveform of the output torque of the electric motor 33 when a single-blade abnormality occurs in the cutting blades 20a and 20b as shown in FIG. 7, it was confirmed that their waveforms are different. In the experiment, the drive current Im of the electric motor 33 detected by the current sensor 81 was used as an index indicating the output torque of the electric motor 33, utilizing the correlation between the output torque of the electric motor 33 and the drive current Im of the electric motor 33. 【0046】Specifically, when the cutting blades 20a and 20b are functioning correctly, the drive current Im of the electric motor 33 when cutting a predetermined workpiece 110 exhibits a waveform as shown by the solid line L10 in Figure 8. The solid line L10 in Figure 8 is a graph showing the relationship between the rotation angle θm of the electric motor 33 on the horizontal axis and the drive current Im of the electric motor 33 on the vertical axis. The dashed line L20 in Figure 8 is a graph showing the relationship between the rotation angle θm of the electric motor 33 on the horizontal axis and the change in the drive current Im per unit angle ΔIm / Δθ on the vertical axis. The change in drive current ΔIm / Δθ is the derivative of the drive current Im of the electric motor 33. Hereafter, the change in drive current ΔIm / Δθ will be abbreviated as ΔIm. 【0047】 As shown in Figure 8, when the rotation angle θm of the electric motor 33 increases from 0° to cut the workpiece 110, the drive current Im of the electric motor 33 decreases, and then the rotation angle θm of the electric motor 33 is maintained at a nearly constant value. After that, when the rotation angle θm of the electric motor 33 reaches angle θ11, the drive current Im of the electric motor 33 increases and then decreases. The rotation angle θ11 corresponds to the rotation angle θm of the electric motor 33 when the cutting blades 20a and 20b come into contact with the workpiece 110 and the workpiece 110 begins to be cut. Then, when the rotation angle θm of the electric motor 33 reaches angle θ13 and the workpiece 110 is cut, the stop control of the electric motor 33 is executed and the drive current Im of the electric motor 33 decreases sharply. At this time, the change in drive current ΔIm is approximately "0" before the rotation angle θm of the electric motor 33 reaches angle θ11, as shown by the dashed line L20 in Figure 8. It increases once after the rotation angle θm of the electric motor 33 reaches angle θ11, and then decreases again after the rotation angle θm of the electric motor 33 reaches angle θ12. 【0048】On the other hand, when a single-edge abnormality occurs in the cutting edges 20a and 20b, when a predetermined workpiece 110 is cut, the drive current Im and the drive current change amount ΔIm of the electric motor 33 exhibit waveforms respectively shown by a solid line L11 and a dashed-dotted line L21 as shown in FIG. 9. As shown in FIG. 9, when the rotation angle θm of the electric motor 33 increases from 0°, the drive current Im of the electric motor 33 decreases and then is maintained at a substantially constant value. After that, after the rotation angle θm of the electric motor 33 reaches the angle θ21, the drive current Im of the electric motor 33 gradually increases while repeating increases and decreases. The rotation angle θ21 corresponds to the rotation angle θm of the electric motor 33 when either one of the cutting edges 20a and 20b contacts the workpiece 110. After that, even when the rotation angle θm of the electric motor 33 reaches the angle θ23, the workpiece 110 is not cut and the stop control of the electric motor 33 is executed, and the drive current Im of the electric motor 33 rapidly decreases. At this time, as shown by the dashed-dotted line L21 in FIG. 9, the drive current change amount ΔIm indicates substantially "0" before the rotation angle θm of the electric motor 33 reaches the angle θ21, and after the rotation angle θm of the electric motor 33 reaches the angle θ21, the drive current change amount ΔIm pulsates by repeating increases and decreases a plurality of times. 【0049】 As shown in FIGS. 8 and 9, the waveforms of the drive current Im and the drive current change amount ΔIm of the electric motor 33 are different between the case where the cutting edges 20a and 20b are normal and the case where a single-edge abnormality occurs in the cutting edges 20a and 20b. Therefore, the control unit 93 of the present embodiment monitors the drive current change amount ΔIm after driving the electric motor 33, and when the drive current change amount ΔIm has a fluctuation pattern as shown in FIG. 9, determines that a single-edge abnormality has occurred in the cutting edges 20a and 20b. 【0050】 Next, referring to FIG. 10, the procedure of the process executed by the control unit 93 will be described. The process shown in FIG. 10 is executed when the trigger switch 84 is turned on by the user operating the operation unit 100. 【0051】As shown in Figure 10, the control unit 93 first starts driving the electric motor 33 by supplying power to the electric motor 33 from the power supply unit 34, and starts the cutting operation of the cutting blades 20a and 20b (step S10). Next, the control unit 93 obtains the current rotation angle θm of the electric motor 33 from the position acquisition unit 92 (step S11). The control unit 93 also obtains the drive current Im of the electric motor 33 from the current sensor 81 (step S12). In this embodiment, taking advantage of the correlation between the output torque of the electric motor 33 and the drive current Im of the electric motor 33, the control unit 93 uses the drive current Im of the electric motor 33 detected by the current sensor 81 as an indicator of the output torque of the electric motor 33. Thus, in this embodiment, the current sensor 81 is an example of a torque detection unit that detects the output torque of the electric motor 33. 【0052】 Furthermore, since the output torque of the electric motor 33 is correlated with the rotational speed ωm of the electric motor 33, the control unit 93 may use the rotational speed ωm of the electric motor 33 as an indicator of the output torque of the electric motor 33. Also, since the output torque of the electric motor 33 is correlated with the drive voltage Vm of the electric motor 33, the control unit 93 may use the drive voltage Vm of the electric motor 33 detected by the voltage sensor 82 as an indicator of the output torque of the electric motor 33. In this case, the voltage sensor 82 is an example of a torque detection unit. 【0053】 Next, the control unit 93 determines whether the drive current Im of the electric motor 33 has a predetermined fluctuation pattern (step S13). For example, while monitoring the amount of change ΔIm per unit angle of the drive current Im of the electric motor 33, the control unit 93 determines whether, after the amount of change ΔIm of the drive current showed "0", the slope of the amount of change ΔIm of the drive current showed a positive value greater than a predetermined value a1 (>0), then a negative value less than a predetermined value a2 (<0), and then a positive value greater than the predetermined value a1. Alternatively, the control unit 93 determines whether the pattern of the amount of change ΔIm of the drive current showing "0", then the slope of the amount of change ΔIm of the drive current showing a positive value greater than a predetermined value a1, and then a negative value less than a predetermined value a2 has been repeated multiple times. 【0054】 The control unit 93 determines that the drive current Im of the electric motor 33 does not have a predetermined fluctuation pattern if the slope of the drive current change amount ΔIm shows a positive value greater than a predetermined value a1, then a negative value less than a predetermined value a2, and does not show a positive value greater than a predetermined value a1 (step S13: NO). In this case, the control unit 93 determines whether the pair of cutting blades 20a and 20b have reached the fully closed position (step S14). Specifically, the control unit 93 determines whether the current rotation angle θm of the electric motor 33 has reached the rotation angle corresponding to the fully closed position of the pair of cutting blades 20a and 20b. Note that in the process of step S14, the control unit 93 may use the position of the pair of cutting blades 20a and 20b just before reaching the fully closed position instead of the fully closed position. 【0055】 If the pair of cutting blades 20a and 20b have not reached the fully closed position (step S14: NO), the control unit 93 returns to the process of step S11. That is, after driving the electric motor 33, the control unit 93 acquires the rotation angle θm and drive current Im of the electric motor 33 during the period until the pair of cutting blades 20a and 20b reach the fully closed position, and monitors whether a predetermined fluctuation pattern occurs in the drive current Im of the electric motor 33. 【0056】 If the control unit 93 detects that the drive current Im of the electric motor 33 has a predetermined fluctuation pattern before the pair of cutting blades 20a and 20b reach the fully closed position (step S14: NO), it determines that a single-blade malfunction has occurred in the cutting blades 20a and 20b. In this case, the control unit 93 executes fail-safe control (step S15) and then terminates the process shown in Figure 10. As fail-safe control, the control unit 93 executes at least one of the following: stop control of the electric motor 33, open control of the cutting blades 20a and 20b, and notification processing. 【0057】The stop control of the electric motor 33 is, for example, a short brake control. The control unit 93 may change the braking force applied to the cutting blades 20a and 20b by PWM control of the short brake. Alternatively, the control unit 93 may apply braking force to the cutting blades 20a and 20b by controlling the electric motor 33 to rotate in reverse as a stop control. The open control is a control that not only applies braking force to the cutting blades 20a and 20b by controlling the electric motor 33 to rotate in reverse, for example, but also actually opens the cutting blades 20a and 20b. The notification process is a process in which the notification device 85 notifies the user that an abnormality has occurred. 【0058】 On the other hand, if the drive current Im of the electric motor 33 does not have a predetermined fluctuation pattern (step S13: NO) and the position of the pair of cutting blades 20a and 20b reaches the fully closed position (step S14: YES), the control unit 93 executes stop control for the electric motor 33 (step S16) and terminates the process shown in Figure 10. 【0059】 Next, the operation and effects of the cutting device 10 of this embodiment will be described. 【0060】 The cutting device 10 of this embodiment includes a current sensor 81 and a control unit 93. The current sensor 81 detects the drive current Im of the electric motor 33, which is correlated with the output torque of the electric motor 33. The control unit 93 controls the electric motor 33. After driving the electric motor 33, if the control unit 93 detects that the drive current Im of the electric motor 33 has a predetermined fluctuation pattern, it determines that a single-blade abnormality has occurred, which means that an abnormality has occurred in either the cutting blades 20a or 20b. Specifically, the control unit 93 determines whether the output torque of the electric motor 33 has a predetermined pulsation pattern as shown in Figure 9. The control unit 93 uses a fluctuation pattern as the predetermined pulsation pattern in which the change amount ΔIm of the drive current of the electric motor 33 increases, then decreases, and then increases again. 【0061】 This configuration makes it possible to more accurately detect whether a single-edged abnormality has occurred in the cutting blades 20a and 20b. 【0062】If the control unit 93 detects a single-edged blade abnormality, it notifies the user of this fact through the notification device 85. 【0063】 This configuration makes it easier for the user to recognize whether or not a single-edged blade malfunction has occurred. 【0064】 If the control unit 93 detects a single-edged blade abnormality, it executes a stop control for the electric motor 33. 【0065】 This configuration makes it possible to avoid the force F2a shown in Figure 7 becoming excessively large, thus reducing the likelihood of damage to the ball screw mechanism 31 and the main frame 70. 【0066】 (First Modified Example) Next, a first modified example of the cutting device 10 of the first embodiment will be described. 【0067】 When the cutting blades 20a and 20b are functioning normally, as shown in Figure 8, the change in the drive current ΔIm of the electric motor 33 is "0" before the rotation angle θm of the electric motor 33 reaches angle θ11, and then the drive current Im of the electric motor 33 begins to increase after the rotation angle θm of the electric motor 33 reaches θ11. In contrast, when a single-edged abnormality occurs in the cutting blades 20a and 20b, as shown in Figure 9, the change in the drive current ΔIm of the electric motor 33 is "0" before the rotation angle θm of the electric motor 33 reaches θ21, and then the drive current Im of the electric motor 33 begins to increase after the rotation angle θm of the electric motor 33 reaches θ21. There is a relationship between the rotation angle θ11 shown in Figure 8 and the rotation angle θ21 shown in Figure 9: "θ11 < θ21". 【0068】Using this, the control unit 93 of this modified example, as shown in Figure 11, detects that the drive current Im of the electric motor 33 has a predetermined fluctuation pattern (step S13: YES), and determines whether the rotation angle θms of the electric motor 33 is greater than or equal to a threshold angle θth when the drive current Im of the electric motor 33 begins to increase after the change in the drive current ΔIm of the electric motor 33 shows "0" (step S20). The threshold angle θth is set to satisfy the relationship "θ11 < θth < θ21" with respect to the rotation angle θ11 shown in Figure 8 and the rotation angle θ21 shown in Figure 9. For example, the control unit 93 determines that the drive current Im of the electric motor 33 has begun to increase when the change in the drive current ΔIm of the electric motor 33 becomes greater than or equal to a predetermined value a1 after the change in the drive current ΔIm of the electric motor 33 shows "0". 【0069】 Before the pair of cutting blades 20a and 20b reach the fully closed position (step S14: NO), the control unit 93 detects that the drive current Im of the electric motor 33 has a predetermined fluctuation pattern (step S13: YES), and if the rotation angle θms of the electric motor 33 when the drive current Im of the electric motor 33 begins to increase is greater than or equal to a threshold angle θth (step S20: YES), it determines that a single-edged abnormality has occurred in the cutting blades 20a and 20b. In this case, the control unit 93 executes fail-safe control (step S15) and then terminates the process shown in Figure 11. 【0070】 If the drive current Im of the electric motor 33 does not have a predetermined fluctuation pattern (step S13: NO), or if the rotation angle θms of the electric motor 33 when the drive current Im of the electric motor 33 begins to increase is smaller than the threshold angle θth (step S20: NO), the control unit 93 executes stop control for the electric motor 33 (step S16) when the position of the pair of cutting blades 20a and 20b reaches the fully closed position (step S14: YES), and terminates the process shown in Figure 11. 【0071】As described above, in the cutting device 10 of this modified example, the control unit 93 detects the rotation angle θms of the electric motor 33 when the change in the drive current ΔIm of the electric motor 33 becomes greater than or equal to a predetermined value a1, after the electric motor 33 has started to drive. In other words, the control unit 93 detects the rotation angle θms of the electric motor 33 when the change in the output torque per unit angle of the electric motor 33 becomes greater than or equal to a predetermined value, after the electric motor 33 has started to drive. The control unit 93 determines that a single-edged abnormality has occurred when it detects that the rotation angle θms of the electric motor 33 is greater than or equal to a threshold angle θth (a predetermined angle) and that the drive current Im of the electric motor 33 has a predetermined fluctuation pattern. Alternatively, the control unit 93 may determine that a single-edged abnormality has occurred when it detects that the rotation angle θms of the electric motor 33 satisfies "θth1 ≤ θms ≤ θth2" and that the drive current Im of the electric motor 33 has a predetermined fluctuation pattern, using two threshold angles θth1 and θth2 (θth1 < θth2). This configuration is effective in preventing the false detection of a single-edged abnormality when a small-diameter member is used as the material to be cut. 【0072】 This configuration makes it possible to more accurately detect abnormalities in one cutting edge. 【0073】 (Second Modification) Next, a second modification of the cutting device 10 of the first embodiment will be described. 【0074】When the cutting blades 20a and 20b are functioning normally, as shown in Figure 8, the integral value of the drive current Im of the electric motor 33 from when the rotation angle θm of the electric motor 33 reaches θ11 until the rotation angle θm of the electric motor 33 rotates by a predetermined angle θa, i.e., the work done by the electric motor 33 Wa, can be represented by the area of the region indicated by dot hatching in Figure 8. In contrast, when a single-edged abnormality occurs in the cutting blades 20a and 20b, as shown in Figure 9, the integral value of the drive current Im of the electric motor 33 from when the rotation angle θm of the electric motor 33 reaches θ21 until the rotation angle θm of the electric motor 33 rotates by a predetermined angle θa, i.e., the work done by the electric motor 33 Wb, can be represented by the area of the region indicated by dot hatching in Figure 9. There is a relationship between the work done by the electric motor 33 Wa shown in Figure 8 and the work done by the electric motor 33 Wb shown in Figure 9, where "Wa > Wb". 【0075】 Using this, the control unit 93 of this modified example, as shown in Figure 12, detects that the drive current Im of the electric motor 33 has a predetermined fluctuation pattern (step S13: YES), and determines whether the amount of work Wm of the electric motor 33 after the drive current Im of the electric motor 33 begins to increase after the change in the drive current ΔIm of the electric motor 33 shows "0" is less than or equal to the threshold Wth (step S30). The control unit 93 detects the rotation angle θms of the electric motor 33 when the drive current Im of the electric motor 33 begins to increase after the change in the drive current ΔIm of the electric motor 33 shows "0", and then calculates the amount of work Wm by calculating the integral value of the drive current Im of the electric motor 33 for the period until the rotation angle θm of the electric motor 33 changes from θms to "θms + θa". The threshold Wth is set to satisfy the relationship "Wb < Wth < Wa" with respect to the amount of work Wa shown in Figure 8 and the amount of work Wb shown in Figure 9. For example, the control unit 93 determines that the drive current Im of the electric motor 33 has started to increase when the drive current change amount ΔIm of the electric motor 33 becomes greater than or equal to a predetermined value a1 after the drive current change amount ΔIm of the electric motor 33 has shown "0". 【0076】Before the pair of cutting blades 20a and 20b reach the fully closed position (step S14: NO), the control unit 93 detects that the drive current Im of the electric motor 33 has a predetermined fluctuation pattern (step S13: YES), and if the amount of work Wm of the electric motor 33 after the drive current Im of the electric motor 33 begins to increase is less than or equal to the threshold Wth (step S30: YES), it determines that a single-edged abnormality has occurred in the cutting blades 20a and 20b. In this case, the control unit 93 executes fail-safe control (step S15) and then terminates the process shown in Figure 12. 【0077】 If the drive current Im of the electric motor 33 does not have a predetermined fluctuation pattern (step S13: NO), or if the amount of work Wm of the electric motor 33 after the drive current Im of the electric motor 33 has started to increase is greater than the threshold Wth (step S30: NO), the control unit 93 executes stop control of the electric motor 33 (step S16) when the position of the pair of cutting blades 20a, 20b reaches the fully closed position (step S14: YES), and terminates the process shown in Figure 10. 【0078】 As described above, in the cutting device 10 of this modified example, the control unit 93 calculates the amount of work Wm of the electric motor 33, which is the value obtained by integrating the drive current Im of the electric motor 33 with respect to the rotation angle θm of the electric motor 33, from the point when the change in the drive current ΔIm of the electric motor 33 becomes greater than or equal to a predetermined value a1 until the rotation angle θm of the electric motor 33 changes by a predetermined angle θa, after the electric motor 33 has started to drive. The control unit 93 determines that a single-edged abnormality has occurred when it detects that the amount of work Wm of the electric motor 33 is less than or equal to a threshold Wth (a predetermined value) and that the drive current Im of the electric motor 33 has a predetermined fluctuation pattern. Alternatively, the control unit 93 may determine that a single-edged abnormality has occurred when it detects that the amount of work Wm of the electric motor 33 satisfies "Wth1 ≤ Wm ≤ Wth2" and that the drive current Im of the electric motor 33 has a predetermined fluctuation pattern, using two thresholds Wth1 and Wth2 (Wth1 < Wth2). This configuration is effective in preventing the false detection of a single-edged abnormality when a small-diameter member is used as the material to be cut. 【0079】This configuration makes it possible to more accurately detect abnormalities in one cutting edge. 【0080】 <Second Embodiment> Next, a second embodiment of the cutting device 10 will be described. The following description will focus on the differences from the cutting device 10 of the first embodiment. 【0081】 In this embodiment, when the cutting device 10 performs stop control of the electric motor 33 as fail-safe control in step S15 shown in Figure 10, it controls the short brake by PWM control and changes the duty cycle D of the PWM control to stop the electric motor 33 more accurately. The duty cycle D indicates the percentage of time during which the short brake is effective relative to a predetermined period. The duty cycle D is set to a value in the range of "0% ≤ D ≤ 100%". For example, if the duty cycle D is 100%, it means that the short brake is effective for the entire duration of the predetermined period. If the duty cycle D is 50%, it means that the short brake is effective for only half the duration of the predetermined period. Therefore, the braking force applied to the electric motor 33 when the duty cycle is 50% is approximately half the braking force applied to the electric motor 33 when the duty cycle is 100%. 【0082】 When the control unit 93 performs stop control of the electric motor 33 as fail-safe control, it executes the process shown in Figure 13. 【0083】 As shown in Figure 13, the control unit 93 first executes a short brake control with a duty cycle value set to D1 for a predetermined time (step S40). D1 is set to, for example, "50%". Next, the control unit 93 first executes a short brake control with a duty cycle value set to D2 for a predetermined time (step S41). D2 is a value greater than D1, for example, "80%". Next, the control unit 93 executes a short brake control with a duty cycle value set to D3 until the electric motor 33 stops (step S42). D3 is a value greater than D2, for example, "100%". 【0084】Figure 14 shows an example of the operation of the electric motor 33 when the stop control shown in Figure 13 is performed. Figure 14 shows the change in the rotational speed ωm of the electric motor 33 when the rotation angle of the electric motor 33 changes from θ10 to θ13 when the stop control shown in Figure 13 is performed. During the period when the rotation angle θm of the electric motor 33 changes from θ10 to θ11, the duty cycle is set to D1. Also, during the period when the rotation angle θm of the electric motor 33 changes from θ11 to θ12, the duty cycle is set to D2. Furthermore, during the period when the rotation angle θm of the electric motor 33 changes from θ12 to θ13, the duty cycle is set to D3. 【0085】 Next, the operation and effects of the cutting device 10 of this embodiment will be described. 【0086】 In this embodiment, the control unit 93 drives the electric motor 33 and then stops the electric motor 33 by controlling a short-circuit brake, which short-circuits the coils of the electric motor 33, using PWM control. During the period in which the electric motor 33 is stopped, the control unit 93 changes the duty cycle of the PWM control of the short-circuit brake. 【0087】 When the stop control shown in Figure 13 is executed, the rotational speed ωm of the electric motor 33 gradually decreases as shown in Figure 14, and the electric motor 33 stops when the rotation angle θm of the electric motor 33 reaches θm13. This allows the electric motor 33 to be stopped smoothly and also shortens the rolling amount, which is the amount of change in the rotation angle θm of the electric motor 33 from the time the stop control is started until the electric motor 33 actually stops. 【0088】 <Other Embodiments> This disclosure is not limited to the above-described examples. 【0089】For example, the cutting device 10 may use a torque detection unit that detects any physical quantity correlated with the output torque of the electric motor, such as the power supply current supplied from the power supply unit 34 to the electric motor 33, or the power supply voltage supplied from the power supply unit 34 to the electric motor 33, rather than being limited to a current sensor 81 or a voltage sensor 82, as the torque detection unit for detecting the output torque of the electric motor. Alternatively, the cutting device 10 may use a torque sensor that directly detects the output torque of the electric motor 33 as the torque detection unit. 【0090】 Even the above-mentioned examples, with appropriate design modifications by those skilled in the art, are included within the scope of this disclosure, as long as they possess the features of this disclosure. The elements, their arrangement, conditions, shapes, etc., of each of the above-mentioned examples are not limited to those exemplified and can be modified as appropriate. The elements of each of the above-mentioned examples can be combined in different ways as appropriate, as long as no technical inconsistencies arise. 【0091】 Although various embodiments have been described above with reference to the drawings, it goes without saying that this disclosure is not limited to such examples. It is clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the claims, and these will naturally also fall within the technical scope of this disclosure. Furthermore, the components of the above embodiments may be combined in any way without departing from the spirit of the invention. 【0092】 This application is based on a Japanese patent application (Patent Application No. 2024-213782) filed on December 6, 2024, the contents of which are incorporated herein by reference. 【0093】 The cutting device of this disclosure makes it possible to detect single-edged abnormalities more appropriately. 【0094】10: Cutting device, 20a: Cutting blade (first cutting blade), 20b: Cutting blade (second cutting blade), 21a, 21b: Blade forming unit, 30: Drive unit, 33: Electric motor, 40: Toggle link mechanism, 41a: Link member (first link member), 41b: Link member (second link member), 42: Trunnion (moving member), 59a: Shaft (first shaft), 59b: Shaft (second shaft), 81: Current sensor (torque detection unit), 82: Voltage sensor (torque detection unit), 93: Control unit.
Claims
1. A first cutting blade rotatably supported on a first shaft and having a blade-forming portion at its tip; a second cutting blade rotatably supported on a second shaft and having a blade-forming portion at its tip; a toggle link mechanism having a first link member whose tip is rotatably connected to the base end of the first cutting blade, a second link member whose tip is rotatably connected to the base end of the second cutting blade, and a movable member connected to the base end of the first link member and the base end of the second link member; a drive unit equipped with an electric motor that moves the movable member by the power of the electric motor to open and close the first cutting blade and the second cutting blade via the first link member and the second link member; a torque detection unit that detects the output torque of the electric motor; and a control unit that controls the electric motor, wherein the control unit, after driving the electric motor, determines that a single-blade abnormality has occurred, in which an abnormality has occurred in either the first cutting blade or the second cutting blade, if the output torque of the electric motor detected by the torque detection unit has a predetermined fluctuation pattern. Cutting device.
2. The cutting apparatus according to claim 1, wherein the control unit determines that a single-blade abnormality has occurred when it detects that the output torque of the electric motor has a predetermined pulsation pattern as the predetermined fluctuation pattern.
3. The cutting apparatus according to claim 2, wherein the control unit uses a fluctuation pattern as the predetermined pulsation pattern in which the amount of change per unit angle of the output torque of the electric motor increases, then decreases, and then increases again.
4. The cutting apparatus according to claim 1, wherein the control unit, after starting to drive the electric motor, detects the rotation angle of the electric motor when the amount of change per unit angle of the output torque of the electric motor becomes greater than or equal to a predetermined value, and determines that the single-blade abnormality has occurred when it detects that the rotation angle of the electric motor is greater than or equal to a predetermined angle and that the output torque of the electric motor has the predetermined fluctuation pattern.
5. The cutting apparatus according to claim 1, wherein the control unit, after starting to drive the electric motor, calculates the amount of work done by the electric motor, which is the value obtained by integrating the output torque of the electric motor with respect to the rotation angle of the electric motor, for a period from the time when the amount of change per unit angle of the output torque of the electric motor becomes greater than or equal to a predetermined value until the rotation angle of the electric motor changes by a predetermined angle, and determines that the single-edged abnormality has occurred when it detects that the amount of work done by the electric motor is less than or equal to a predetermined value and the output torque of the electric motor has the predetermined fluctuation pattern.
6. The cutting device according to claim 1, wherein the torque detection unit detects, as the output torque of the electric motor, at least one of the following, which is correlated with the output torque of the electric motor: the drive current of the electric motor, the drive voltage of the electric motor, the rotational speed of the electric motor, the power supply current supplied to the electric motor from the power supply device, and the power supply voltage supplied to the electric motor from the power supply device.
7. The cutting device according to claim 1, wherein the control unit determines that a single-blade abnormality has occurred and notifies the user accordingly.
8. The cutting apparatus according to claim 1, wherein the control unit determines that a single-blade abnormality has occurred and executes a stop control for the electric motor.
9. The cutting device according to claim 8, wherein the control unit performs pulse width modulation control of a short brake that short-circuits the coils of the electric motor as the stop control, and changes the duty cycle of the pulse width modulation control during the period in which the stop control is being performed.
10. The cutting apparatus according to claim 1, wherein the waveform of the output torque of the electric motor when the first cutting blade and the second cutting blade are functioning normally is different from the waveform of the output torque of the electric motor when the single-blade malfunction occurs.