Medical device and method for controlling rotation thereof

Abstract

[Problem] To provide a medical device and a rotation control method for the same with which it is possible to suppress damage to a shaft part or biological tissue caused by rotational energy accumulated in a motor or strain energy accumulated in the shaft part. [Solution] This elongated medical device (10), which is inserted into a living body lumen, comprises: an elongated shaft part (20) which is rotationally driven; a motor (45) which rotates a proximal portion of the shaft part (20); a power supply which supplies current to the motor (45); a rotational structure part (30) which is connected to a distal portion of the shaft part (20) and is capable of rotating; a motor drive circuit (60) which drives the motor (45); and a control unit (50) which controls the motor drive circuit (60) and causes the motor drive circuit (60) to drive the motor (45), wherein the motor drive circuit (60) can switch circuits, and the control unit (50) can invert the direction of rotational force acting on the motor (45) as the motor drive circuit (60) switches circuits.

Description

[Technical Field]

[0001] The present invention relates to a medical device to be inserted into a body lumen and a method for controlling the rotation of the same. [Background technology]

[0002] When a thrombus forms in a biological lumen, it must be removed promptly. Examples of symptoms of thrombus formation in a biological lumen include deep vein thrombosis, in which a thrombus forms in a vein deep in the body, such as the femoral vein or the popliteal vein. Known treatment methods for deep vein thrombosis include inserting a long tubular body part of a medical device into a blood vessel and injecting a drug such as a thrombolytic agent into the embolic site to dissolve and remove the thrombus.

[0003] Treatments that involve injecting drugs to remove thrombi are associated with side effects such as bleeding. For this reason, the use of an atherectomy device has been proposed, which uses a rotating wire member attached to the distal end of a shaft inserted into a blood vessel to mechanically destroy emboli (thrombi, etc.) that come into contact with the member, thereby increasing the patency rate (the proportion of unoccluded areas in the cross section of the blood vessel) (see, for example, Patent Document 1). This makes it possible to avoid the use of drugs or to reduce the amount of drugs used.

[0004] The device described in Patent Document 1 uses an electrically powered motor to rotate a structure connected to the distal end of a shaft. When torque is applied to the shaft, the shaft winds up, accumulating torsion and causing the distal structure to rotate. Excessive torsion accumulated in the shaft can damage the shaft or biological tissue. Therefore, when the torque exceeds a certain threshold, the current is cut off, allowing the motor to rotate freely, thereby eliminating the distortion in the wound shaft and stopping its rotation. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 9,119,661 Summary of the Invention [Problem to be solved by the invention]

[0006] In the device described in Patent Document 1, the motor rotates freely immediately after the current is cut off, so there is a possibility that the rotational energy (kinetic energy) accumulated as inertia in the drive system in the direction of winding up the shaft may be further applied to the shaft, which may result in torque exceeding the threshold being applied to the shaft or biological tissue.

[0007] Furthermore, in the device described in Patent Document 1, when the wound shaft unwinds, it rotates freely until it stops rotating, which can lead to excessive winding of the shaft in the direction opposite to the direction of winding, and the resulting torque can damage the shaft or biological tissue.

[0008] The present invention has been made to solve the above-mentioned problems, and aims to provide a medical device and a method for controlling its rotation that can prevent damage to the shaft portion or biological tissue caused by the rotational energy accumulated in the motor or the strain energy accumulated in the shaft portion. [Means for solving the problem]

[0009] The medical device according to the present invention that achieves the above object is a long medical device that is inserted into a body lumen, and includes a long, rotationally driven shaft portion, a motor that rotates a proximal portion of the shaft portion, a power source that supplies current to the motor, a rotatable rotation structure that is connected to a distal portion of the shaft portion, a motor drive circuit that drives the motor, and a control unit that controls the motor drive circuit to cause the motor drive circuit to drive the motor so as to repeat a plurality of rotation cycles, the motor drive circuit having a circuit that can switch a flow of current, and the control unit reverses the direction of a rotational force acting on the motor by switching the circuit of the motor drive circuit. ,beforeAfter the reversal of the direction of the rotational force is released and before the motor is driven by the motor drive circuit for the next rotation cycle, Open both terminals of the motor. A reset stage is provided in which no current is supplied to the motor.

[0010] The rotation control method of the present invention for achieving the above object is a rotation control method for a medical device having a long, rotationally driven shaft portion, a motor that rotates a proximal portion of the shaft portion, a power source that supplies current to the motor, a rotatable rotation structure that is connected to a distal portion of the shaft portion, a motor drive circuit that drives the motor, and a control unit that controls the motor drive circuit to cause the motor drive circuit to drive the motor to repeat a plurality of rotation cycles, the motor drive circuit having a circuit that can switch the flow of current. The method includes the steps of controlling the motor drive circuit to accelerate the motor, controlling the motor drive circuit to switch the circuit to reverse the direction of a rotational force acting on the motor, and after the reversal of the direction of the rotational force is released and before the motor is driven by the motor drive circuit for the next rotation cycle, controlling the motor drive circuit to Open both terminals of the motor. and providing a reset phase in which no current is supplied to the motor. [Effects of the Invention]

[0011] The medical device and its rotation control method configured as described above can reverse the direction of the rotational force acting on the motor to generate a braking force on the motor. This allows the shaft and rotating structure to quickly decelerate or eliminate excessive force acting on the shaft or rotating structure. This effectively prevents damage to the shaft or biological tissue caused by rotational energy accumulated in the motor or torsional strain energy accumulated in the shaft. [Brief explanation of the drawings]

[0012] [Figure 1]FIG. 1 is a plan view showing a medical device according to an embodiment. [Figure 2] FIG. 1 is a block diagram illustrating a medical device. [Figure 3] FIG. 2 is a circuit diagram showing a motor drive circuit. [Figure 4] FIG. 1 is a circuit diagram showing the drive current generation circuit of the motor drive circuit, where (A) shows the state for clockwise rotation, (B) shows the state for counterclockwise rotation, (C) shows the state for release, and (D) shows the state for short-circuit braking. [Figure 5] FIG. [Figure 6] 1A and 1B are cross-sectional views showing the state inside a blood vessel, in which (A) shows the state in which the medical device has been inserted into the blood vessel, and (B) shows the state in which the rotating structure of the medical device is exposed inside the blood vessel. [Figure 7] 1 is a flowchart illustrating a method for controlling rotation of a medical device. [Figure 8] 1 is a graph showing rotation speed versus number of rotations of a medical device. [Figure 9] FIG. 10 is a circuit diagram showing a state in which a counterclockwise rotational force is applied to the motor by the drive current generating circuit while the motor is rotating clockwise. [Figure 10] FIG. 2 is a circuit diagram showing an operating state of a protection circuit for a motor drive circuit. [Figure 11] FIG. 3 is a circuit diagram showing the operating state of an emergency braking circuit of the motor drive circuit. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the size and proportions of each component in the drawings may be exaggerated for the sake of explanation and may differ from the actual size and proportions. In this specification, the side of the device that is inserted into the living body will be referred to as the "distal side," and the side that is operated will be referred to as the "proximal side."

[0014] The medical device 10 according to this embodiment is inserted into a blood vessel and used in a procedure to destroy and remove a thrombus. Note that the object to be removed is not necessarily limited to a thrombus, and may be any object that may exist in a biological lumen.

[0015] As shown in Figures 1 and 2, the medical device 10 comprises a long, rotatably driven shaft portion 20, a guidewire tube 21 into which a guidewire 100 can be inserted, an outer sheath 25 that can accommodate the shaft portion 20, a rotating structure portion 30 that is rotated by the shaft portion 20, and an operating portion 40 that is arranged in the proximal portion of the shaft portion 20.

[0016] The proximal end of the shaft portion 20 is disposed in the operating portion 40. The shaft portion 20 is capable of reciprocating in the circumferential direction by the operating portion 40. However, the shaft portion 20 is not limited to being reciprocating, and may be unidirectionally rotating.

[0017] The shaft portion 20 preferably has a structure that suppresses twisting. As an example, as shown in FIG. 5 , the shaft portion 20 is formed of a metal circular tube 26 and a resin cover tube 29 that covers the outside of the circular tube 26. The circular tube 26 is formed of a metal material, such as stainless steel or a Ni-Ti alloy, to provide high torque transmission, and has a spiral slit 27 formed therein to allow for flexible bending. The circular tube 26 has a plurality of hook structures 28 formed in the slit 27 that engage with each other to prevent the slit width from widening, providing high strength against twisting in the direction in which the slit width widens. The cover tube 29 covers the outside of the circular tube 26 with a small clearance, limiting radial deformation of the circular tube 26. Therefore, the cover tube 29 can appropriately maintain the shape of the slit 27 so that the circular tube 26 can exhibit high torque transmission and flexibility. The configuration of the shaft portion 20 is not limited to this. For example, the shaft portion 20 may have a structure in which two or more coils with different winding directions are stacked in layers in the radial direction.

[0018] The guidewire tube 21 is disposed inside the hollow interior of the shaft portion 20, and has a hub 22 connected to its proximal end. The guidewire tube 21 has a guidewire lumen into which the guidewire 100 can be inserted.

[0019] The outer sheath 25 is coaxially disposed on the outside of the shaft portion 20. The inner cavity of the outer sheath 25 can accommodate the contracted rotating structure portion 30. A Y connector, for example, may be connected to the proximal portion of the outer sheath 25. This allows a suction force to be applied to the outer sheath 25 from a side branch of the Y connector, or a thrombolytic agent to be injected.

[0020] The rotating structure 30 is connected to a distal portion of the shaft portion 20. The rotating structure 30 includes a plurality of wire rods 31. Both axial ends of each wire rod 31 are connected to the shaft portion 20, and the central portion protrudes radially away from the shaft portion 20. The shape of each wire rod 31 is not particularly limited, and may be formed, for example, in a spiral shape. The number of wire rods 31 is also not particularly limited. The proximal end of each wire rod 31 is fixed to a sliding portion 23 that is slidable relative to the shaft portion 20. The distal end of each wire rod 31 is fixed to a fixing portion 24 that is fixed to the shaft portion 20. The fixing portion 24 is disposed distal to the sliding portion 23. The fixing positions of each wire rod 31 relative to the fixing portion 24 and the sliding portion 23 are aligned in the circumferential direction. Furthermore, the approximate central portions of each wire rod 31 in the curved axial direction are aligned in the circumferential direction at a position radially away from the shaft portion 20. As a result, the rotating structure 30 has a uniform bulge in the circumferential direction as a whole. When the shaft portion 20 rotates, the rotating structure 30 also rotates accordingly, which can crush thrombi in blood vessels or agitate the crushed thrombi.

[0021] The wire 31 constituting the rotating structure 30 is made of a flexible thin metal wire. The rotating structure 30 is housed inside the outer sheath 25 until it reaches the target location in the blood vessel. To house the wire 31 in the outer sheath 25, the outer sheath 25 is moved distally relative to the shaft 20, and the distal end of the outer sheath 25 is pressed against the proximal portion of the rotating structure 30. This causes the sliding portion 23 to move proximally along the shaft 20, and the wire 31 is reduced in diameter and housed inside the outer sheath 25. After the shaft 20 is inserted into the blood vessel until it reaches the target location in the blood vessel, the outer sheath 25 is moved proximally relative to the shaft 20. The rotating structure 30 is exposed to the outside of the outer sheath 25 and expands due to its own elastic force. At this time, the sliding portion 23 moves distally along the shaft 20.

[0022] The fixing portion 24 may be disposed proximally of the sliding portion 23. In this case, when the wire 31 is housed in the outer sheath 25, the outer sheath 25 is moved distally relative to the shaft portion 20, and the distal end of the outer sheath 25 is pressed against the proximal portion of the rotating structure portion 30. This causes the sliding portion 23 to move distally along the shaft portion 20, and the wire 31 is reduced in diameter and housed inside the outer sheath 25. After the shaft portion 20 is inserted to the target site in the blood vessel, when the outer sheath 25 is moved proximally relative to the shaft portion 20, the rotating structure portion 30 is exposed to the outside of the outer sheath 25 and expands due to its own elastic force. At this time, the sliding portion 23 moves proximally along the shaft portion 20.

[0023] The wire 31 is preferably made of a material with shape memory properties so that it can be elastically deformed to a large extent. Suitable materials for the wire 31 include, for example, a shape memory alloy or stainless steel that can be given a shape memory effect or superelasticity by heat treatment. Suitable shape memory alloys include Ni-Ti, Cu-Al-Ni, Cu-Zn-Al, and combinations thereof.

[0024] The operating section 40 includes a connection unit 41 in which the proximal portion of the shaft section 20 is disposed, and a drive unit 42 connectable to the connection unit 41. The connection unit 41 has a driven gear 43 connected to the proximal portion of the shaft section 20.

[0025] The drive unit 42 is a component that supplies drive force to the connection unit 41. The drive unit 42 can be connected to and disconnected from the connection unit 41. The drive unit 42 has a battery 44, a motor 45 connected to a power source, a motor drive circuit 60 that controls the rotation of the motor 45, a drive gear 47 that can mesh with a driven gear, and a gearbox 46 that connects the motor 45 and the drive gear 47. The drive unit 42 further has an execution switch 48 that starts and stops drive, a tachometer 49 that detects the number of rotations of the shaft portion 20 (or the motor 45), and a control unit 50 that controls the motor drive circuit 60.

[0026] By connecting the drive unit 42 to the connection unit 41, the drive gear 47 meshes with the driven gear 43. The drive gear 47 is driven to rotate by the motor 45, and can rotate the driven gear 43. The rotation of the driven gear 43 causes the proximal portion of the shaft portion 20 to rotate, and the rotation structure portion 30 connected to the distal portion of the shaft portion 20 can be rotated.

[0027] The gearbox 46 connects the rotating shaft of the motor 45 to a drive gear 47 at a predetermined gear ratio. The power source is a battery 44 disposed in the drive unit 42, but it may also be the facility's power source. The execution switch 48 is used by the surgeon to start and stop the operation of the medical device 10. When the execution switch 48 is turned on, the operation of the medical device 10 starts, and when the execution switch 48 is turned off, the operation of the medical device 10 stops.

[0028] The motor 45 is a DC motor that rotates using a direct current. Because the motor 45 is a DC motor, short-circuit braking can be generated by short-circuiting the terminals. Note that the configuration for short-circuiting the terminals of the motor 45 is not limited to a configuration in which the terminals are directly connected, and may be a configuration in which a resistor, a capacitor, or the like is interposed between the terminals to limit the flowing current for purposes such as circuit protection.

[0029] The tachometer 49 detects the rotation speed of the shaft portion 20 or the motor 45. The tachometer 49 is, for example, an ammeter that detects the current flowing through the motor 45. The tachometer 49 detects the rotation speed of the shaft optically, magnetically, or electrically, but the detection method is not particularly limited. When the tachometer 49 is an ammeter, the position where the tachometer 49 is disposed is not particularly limited as long as it can detect the current flowing through the motor 45, and it is connected in series to one of the terminal sides of the motor 45. The rotation speed of the shaft portion 20 can be converted from the rotation speed of the motor 45.

[0030] The control unit 50 controls the motor drive circuit 60. The control unit 50 is, for example, a microcontroller, but the configuration of the control unit 50 is not limited as long as it is capable of performing control. For example, the control unit 50 may be a computer equipped with a CPU (Central Processing Unit) and a memory circuit, or a semiconductor equipped with a logic circuit (a combination of flip-flop circuits, CPLD, etc.) for responding to the rotation state or user operations. The memory circuit stores programs executed by the control unit 50 and various parameters.

[0031] The control unit 50 is supplied with current from the battery 44, and is started up by the execution switch 48. The control unit 50 controls the current supplied to the motor 45 by the motor drive circuit 60 so that the rotating structure unit 30 rotates at a preset rotation speed. The control unit 50 receives a signal indicating the rotation speed of the motor 45 from a tachometer 49. The control unit 50 may also receive a signal indicating the rotation speed of the motor 45 from the motor 45 and convert it into the rotation speed of the shaft unit 20.

[0032] The motor drive circuit 60 includes a drive current generation circuit 70 that generates a current to drive the motor 45, an emergency braking circuit 80 that applies emergency braking to the motor 45, and a protection circuit 90 that protects the circuit.

[0033] The drive current generation circuit 70 is configured with an H-bridge circuit. The drive current generation circuit 70 has a first switch S1 and a second switch S2 connected in series, as well as a third switch S3 and a fourth switch S4 connected in series. The first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are all switching elements that can switch the flow of current on and off.

[0034] One terminal of the first switch S1 is grounded, and the other terminal is connected to the second switch S2. One terminal of the second switch S2 is connected to the battery 44, and the other terminal is connected to the first switch S1. One terminal of the third switch S3 is grounded, and the other terminal is connected to the fourth switch S4. One terminal of the fourth switch S4 is connected to the battery 44, and the other terminal is connected to the third switch S3. A first terminal T1 of the motor 45 is connected between the first switch S1 and the second switch S2, and a second terminal T2 of the motor 45 is connected between the third switch S3 and the fourth switch S4.

[0035] 4(A), the drive current generating circuit 70 of the motor drive circuit 60 is controlled by the control unit 50 to turn on the second switch S2 and the third switch S3 and turn off the first switch S1 and the fourth switch S4, thereby allowing current from the battery 44 to flow from the second switch S2 to the third switch S3 via the motor 45. At this time, current flows from the first terminal T1 to the second terminal T2 of the motor 45, causing the shaft portion 20 to rotate clockwise (CW).

[0036] 4(B), the drive current generating circuit 70 is controlled by the control unit 50 to turn on the first switch S1 and the fourth switch S4 and turn off the second switch S2 and the third switch S3, thereby allowing current from the battery 44 to flow from the fourth switch S4 to the first switch S1 via the motor 45. At this time, current flows from the second terminal T2 to the first terminal T1 of the motor 45, causing the shaft portion 20 to rotate counterclockwise (CCW).

[0037] As shown in FIG. 4(C), the drive current generating circuit 70 is controlled by the control unit 50 to turn off the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4, so that the first terminal T1 and the second terminal T2 of the motor 45 are in an open state.

[0038] As shown in Figure 4(D), the drive current generating circuit 70 is controlled by the control unit 50 to turn on the first switch S1 and the third switch S3 and turn off the second switch S2 and the fourth switch S4, thereby shorting the first terminal T1 and the second terminal T2 of the motor 45.

[0039] As shown in FIG. 3 , the emergency braking circuit 80 is controlled by the control unit 50 to apply emergency braking to the motor 45, for example, when an excessive torque load is detected. The emergency braking circuit 80 includes a fifth switch S5 and a sixth switch S6. One terminal of the fifth switch S5 is grounded, and the other terminal is connected to a first terminal T1 of the motor 45. One terminal of the sixth switch S6 is grounded, and the other terminal is connected to a second terminal T2 of the motor 45. The fifth switch S5 and the sixth switch S6 are both switching elements that can switch current flow on and off. During normal operation when emergency braking is not being performed, the fifth switch S5 and the sixth switch S6 are switched off by the control unit 50. When emergency braking is to be performed, the emergency braking circuit 80 switches the fifth switch S5 and the sixth switch S6 on by the control unit 50, shorting the first terminal T1 and the second terminal T2, thereby generating short-circuit braking.

[0040] The protection circuit 90 is a circuit that protects the motor drive circuit 60 from the back electromotive force of the motor 45. The protection circuit 90 has a diode 91, a capacitor 92, a Zener diode 93, and a seventh switch S794. The anode of the diode 91 is connected to the input from the battery 44, and the cathode is connected to the input terminal T3 (the second switch S2 and the fourth switch S4) of the drive current generation circuit 70 via the seventh switch S7. One terminal of the capacitor 92 is connected to the input terminal T3 of the drive current generation circuit 70 via the seventh switch S7, and the other terminal is grounded. One terminal of the Zener diode 93 is connected to the input terminal T3 of the drive current generation circuit 70 via the seventh switch S7, and the other terminal is grounded. One terminal of the seventh switch S7 is connected to the cathode of the diode 91, the capacitor 92, and the Zener diode 93, and the other terminal is connected to the input terminal T3 of the drive current generation circuit 70. The seventh switch S7 is a switching element that can switch the flow of current on and off. The diode 91, the capacitor 92, and the Zener diode 93 are not limited to these, and may be circuits having similar functions.

[0041] The connection unit 41 and the drive unit 42 may be integrally formed.

[0042] Next, the rotation control method of the medical device 10 according to the embodiment will be described with reference to the flowchart shown in FIG. 7, taking as an example the case where a thrombus B in a blood vessel is destroyed and aspirated.

[0043] First, the medical device 10 is prepared in a state in which the distal portion of the shaft portion 20, including the rotating structure portion 30, is housed in the outer sheath 25. Next, the proximal end of the guidewire 100, which has been percutaneously inserted into a blood vessel and is located outside the body, is inserted into the guidewire lumen of the guidewire tubular body 21 of the medical device 10. Next, as shown in FIG. 6(A), the medical device 10 is brought to the vicinity of the thrombus B along the guidewire 100. Thereafter, when the outer sheath 25 is moved proximally relative to the shaft portion 20, the rotating structure portion 30 is exposed to the outside of the outer sheath 25 and expands due to its own elastic force, as shown in FIG. 6(B). At this time, the sliding portion 23 moves distally relative to the shaft portion 20.

[0044] Next, the surgeon operates the execution switch 48 shown in FIGS. 1 and 2 to activate the medical device 10 (step S10). This causes the control unit 50 to determine the rotation direction of the motor 45 (step S11) and control the motor drive circuit 60 to set the circuit to the clockwise state shown in FIG. 4(A) (step S12). During normal operation when emergency braking is not being performed, the control unit 50 switches the fifth switch S5 and sixth switch S6 of the emergency braking circuit 80 off and switches the seventh switch S7 of the protection circuit 90 on. This causes the motor 45 to start rotating, and the rotational force is transmitted to the shaft portion 20 via the gearbox 46, the drive gear 47, and the driven gear 43. This causes the shaft portion 20 and the rotating structure 30 to start rotating. Here, the direction in which the shaft portion 20 is initially rotated is clockwise (CW), but the rotation direction can also be reversed. 8, the control unit 50 gradually accelerates the shaft unit 20 and the rotating structure unit 30 driven by the motor 45 (step S13). This phase of the medical device 10 is referred to as an acceleration phase Ph1.

[0045] The control unit 50 receives a signal from the tachometer 49 and monitors the rotation speed of the shaft unit 20. When the rotation speed of the shaft unit 20 reaches a target peak speed range TA (step S14), the control unit 50 maintains the rotation speed of the shaft unit 20 (step S15). The target peak speed range TA is not particularly limited, but is 2500 to 3500 rpm in this embodiment. The control unit 50 controls the current input to the motor 45 to maintain the target peak speed range TA. This phase of the medical device 10 is designated as the target peak speed phase Ph2. The rotating structure unit 30 that has reached the target peak speed range TA has a high speed, so it can effectively crush thrombus B adhered to blood vessels and thrombus B floating within blood vessels. Therefore, it is preferable that there is a time during which the rotating structure unit 30 rotates within the target peak speed range TA. Note that there may be no time during which the rotating structure unit 30 rotates within the target peak speed range TA without reaching the target peak speed range TA.

[0046] When the rotating structure 30 rotates within the blood vessel, it crushes the thrombus B. The blood in the blood vessel and the crushed thrombus B rotate due to the force applied by the rotating structure 30. Therefore, the rotational speed of the blood and thrombus B in the blood vessel increases with a delay from the rotational speed of the rotating structure 30.

[0047] When the rotational speed of the rotating structure 30 becomes substantially constant within the target maximum speed range TA, the blood and crushed thrombus B, which are rotating under the force of the rotating structure 30, gradually approach and substantially match the rotational speed of the rotating structure 30. That is, the control unit 50 maintains the rotational speed of the rotating structure 30 constant until the rotational speed of the blood and crushed thrombus B substantially matches the rotational speed of the rotating structure 30. As the rotational speed of the blood and crushed thrombus B reaches the rotational speed of the rotating structure 30, the relative speed between the rotating structure 30 and the blood and crushed thrombus B increases when the rotating structure 30 subsequently rotates in the reverse direction. This allows the rotating structure 30 to effectively crush the thrombus B.

[0048] When the rotation speed of the rotating structure part 30 and the rotation speed of the thrombus B become approximately the same, the thrombus B rotates together with the rotating structure part 30. As a result, the rotating structure part 30 cannot crush the thrombus B floating in the blood vessel. For this reason, it is preferable to stop the rotation of the rotating structure part 30 promptly after the rotation speed of the rotating structure part 30 and the rotation speed of the thrombus B become approximately the same.

[0049] When the number of rotations reaches a predetermined number or the torque load exceeds a threshold (step S16), the control unit 50 controls the motor drive circuit 60 to place the circuit in a short-circuit braking state shown in FIG. 4(D) (step S17). Note that the number of rotations does not have to be an integer. The control unit 50 can calculate the torque load from the output of the ammeter. This short-circuits the first terminal T1 and the second terminal T2 of the motor 45, resulting in short-circuit braking. This causes the current in the circuit applied to the motor 45 to flow backward. Here, "backward" refers to the current flowing in the opposite direction to the current applied to the motor 45 in a phase before braking begins (e.g., the target maximum speed phase Ph2). As a result, the kinetic energy of the motor 45 is converted into thermal energy, decelerating the motor 45 and the shaft portion 20. This phase of the medical device 10 is referred to as the decelerating phase Ph3, as shown in FIG. 8. The motor 45 and the shaft portion 20 decelerate faster than when they rotate freely due to short-circuit braking of the motor 45. The rotational behavior of the freely rotating shaft portion 20 is indicated by the outline arrows in FIG.

[0050] The control unit 50 continues short-circuit braking until the clockwise (CW) rotation of the motor 45 and the proximal portion of the shaft portion 20 reaches zero and reverses to a counterclockwise (CCW) rotation. The control unit 50 continues short-circuit braking until a predetermined time has elapsed since the deceleration phase Ph3 began. When a predetermined time has elapsed since the deceleration phase Ph3 began (step S18), the control unit 50 controls the motor drive circuit 60 to place the circuit in the idling state shown in FIG. 4(C) (step S19). This allows the motor 45 and shaft portion 20, which have begun rotating counterclockwise (CCW), to idling without being forcibly braked, and to prepare for the next rotation. This phase of the medical device 10 is referred to as the reset phase Ph4, as shown in FIG. 8. The predetermined time from the deceleration phase Ph3 until the short-circuit braking is released is set based on the results of experiments and simulations so that the rotational energy stored in the motor 45 and the torsional strain energy stored in the shaft portion 20 are sufficiently reduced. It is possible that the rotation of the motor 45 and the shaft portion 20 may not be reversed when a predetermined time has elapsed since the deceleration stage Ph3 was entered.

[0051] Note that the control unit 50 does not have to release the short-circuit braking and put the motor drive circuit 60 into an idling state when a preset time has elapsed since the deceleration stage Ph3 was entered. For example, the control unit 50 may monitor a signal from an ammeter and release the short-circuit braking after detecting that the clockwise (CW) rotation of the motor 45 and the shaft unit 20 has reached zero and has switched to the counterclockwise (CCW) rotation.

[0052] Alternatively, the control unit 50 may monitor the signal from the ammeter and release the short-circuit braking when it detects that the current value has fallen below a predetermined value before it becomes zero (before the rotation reverses).

[0053] Alternatively, the control unit 50 may monitor the signal from the ammeter and release the short-circuit braking when it detects that the current value has reached a predetermined value after it has become zero (after the rotation has reversed).

[0054] Furthermore, in the deceleration stage Ph3, while the motor 45 continues to rotate clockwise (CW) while decelerating, the control unit 50 may control the circuit of the motor drive circuit 60 to the state shown in FIG. 9 instead of the short-circuit braking state shown in FIG. 4(D). As a result, a current that generates a counterclockwise (CCW) rotational force acts on the motor 45, which continues to rotate clockwise (CW). This applies a strong braking force to the motor 45, allowing the motor 45 to rapidly decelerate. Furthermore, in the deceleration stage Ph3, the control unit 50 may perform both the short-circuit braking (see FIG. 4(D)) and the braking (see FIG. 9) that applies a rotational force to the motor 45 in the direction opposite to the rotational direction of the motor 45, at different timings (e.g., alternately). Furthermore, the braking that applies a rotational force to the motor 45 in the direction opposite to the rotational direction of the motor 45 does not necessarily have to be performed by the drive current generation circuit 70, but may be performed by a circuit other than the drive current generation circuit 70 of the motor drive circuit 60. Furthermore, the control unit 50 may reverse the current in the circuit applied to the motor 45 in order to eliminate twisting of the shaft unit 20 and the rotating structure unit 30 when the motor 45 is stopped.

[0055] In the reset stage Ph4, the motor 45 is not supplied with current, so it freely rotates together with the shaft portion 20, gradually decelerating and stopping. Note that the reset state Ph4 does not have to be provided. That is, the deceleration stage Ph3, in which short-circuit braking is performed, may continue until the motor 45 and the shaft portion 20 stop.

[0056] After the motor 45 and the shaft unit 20 have stopped, the control unit 50 performs counterclockwise (CCW) operation as shown by the two-dot chain line in Fig. 8. The control unit 50 can perform the same operation as the clockwise (CW) operation described above, with only the rotation direction reversed.

[0057] The rotational phase of the rotating structure 30, located at the distal portion of the shaft 20, lags behind that of the motor 45 due to the torsion of the shaft 20. For this reason, it takes a certain amount of time for the rotation of the rotating structure 30 to stop after the rotation of the motor 45 has stopped. For this reason, by providing a deceleration phase Ph3 and a reset phase Ph4 in the operation by the control unit 50, the torsion of the shaft 20 can be quickly reversed, and the rotating structure 30 can be quickly restored to a state desirable for crushing.

[0058] It should be noted that the next rotational movement may be initiated before the rotation of the motor 45 and the proximal portion of the shaft portion 20 reaches completely zero.

[0059] When the control unit 50 determines from the detection result of the tachometer 49 that the rotation speed of the motor 45 has become zero or is approaching zero, it ends the reset stage Ph4 (step S20). Note that the control unit 50 may determine that the reset stage Ph4 has ended when the elapsed time from a predetermined stage reaches a preset time, rather than from the detection result of the tachometer 49. The end of the reset stage Ph4 may be determined based on the elapsed time from the start of the acceleration stage Ph1, the elapsed time from the start of the target maximum speed stage Ph2, the elapsed time from the start of the deceleration stage Ph3, or the elapsed time from the end of the deceleration stage Ph3.

[0060] When the control unit 50 determines that the reset stage Ph4 has ended and one rotation cycle (steps S10 to S20) has been completed, it determines whether the execution switch 48 is on or off (step S10). If the execution switch 48 is still on, it determines the rotation direction of the motor 45 for the next rotation cycle (step S11). For example, the control unit 50 sets the rotation direction of the motor 45 to the opposite direction to the rotation direction of the motor 45 in the previous rotation cycle. The control unit 50 controls the motor drive circuit 60 to set the circuit in a counterclockwise (CCW) state as shown in FIG. 4B. Then, the control unit 50 gradually accelerates the shaft unit 20 and the rotating structure unit 30 driven by the motor 45 so that they reach the target maximum speed range TA, which is opposite in sign to the rotation in the previous rotation cycle (step S13). At this time, the sign of the current is also opposite in sign to the rotation before stopping. Thereafter, the control unit 50 controls the motor drive circuit 60 (steps S14 to S20) in the same manner as the clockwise (CW) control described above. Then, as long as the execution switch 48 remains on, the control unit 50 repeats steps S10 to S20 while switching the rotation direction of the motor 45. When the execution switch 48 is turned off by the operator, the control unit 50 stops the rotation of the motor 45 and ends the control (step S10). After stopping the operation of the medical device 10, the surgeon houses the rotating structure 30 in the outer sheath 25 and removes the medical device 10 from the blood vessel.

[0061] When the motor 45 is not disconnected from the battery 44, that is, when current can be supplied from the battery 44 to the motor 45, if excessive back electromotive force is generated in the motor 45, the reverse current caused by the back electromotive force does not pass through the diode 91 but is stored in the capacitor 92, and after the voltage of the protection circuit 90 exceeds the breakdown voltage, the reverse current flows to the Zener diode 93, as shown in Figure 10. This makes it possible to protect the motor drive circuit 60 from excessive back electromotive force.

[0062] During normal operation when emergency braking is not being performed, the control unit 50 switches off the fifth switch S5 and the sixth switch S6 of the emergency braking circuit 80 and switches on the seventh switch S7 of the protection circuit 90. The control unit 50 can perform emergency braking of the motor 45, for example, when an excessive torque load exceeding a threshold is detected by an ammeter or an excessive change in rotation speed exceeding a threshold is detected by a tachometer 49. When the control unit 50 determines that emergency braking is to be performed, as shown in FIG. 11 , the control unit 50 can switch on the fifth switch S5 and the sixth switch S6 of the emergency braking circuit 80, switch off the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 of the drive current generation circuit 70, and switch off the seventh switch of the protection circuit 90. This short-circuits the first terminal T1 and the second terminal T2 of the motor 45 via ground, resulting in short-circuit braking (short braking). This causes a current to act to generate a rotational force in the opposite direction to the rotational direction of the motor 45. Therefore, a braking force can be applied to the motor 45, and the motor 45 and the shaft portion 20 can be decelerated.

[0063] As described above, the medical device 10 according to the embodiment is a long medical device 10 that is inserted into a biological lumen, and includes a long, rotationally driven shaft portion 20, a motor 45 that rotates the proximal portion of the shaft portion 20, a power source (e.g., a battery 44) that supplies current to the motor 45, a rotating structure portion 30 that is connected to the distal portion of the shaft portion 20 and is rotatable, a motor drive circuit 60 that drives the motor 45, and a control unit 50 that controls the motor drive circuit 60 to cause the motor drive circuit 60 to drive the motor 45, and the motor drive circuit 60 is capable of switching circuits, and the control unit 50 is capable of reversing the direction of the rotational force acting on the motor 45 by switching the circuit of the motor drive circuit 60.

[0064] The medical device 10 configured as described above can generate a braking force on the motor 45 by reversing the direction of the rotational force acting on the motor 45. This allows the shaft portion 20 and the rotating structure portion 30 to quickly decelerate. Furthermore, if an excessive force such as torsion is acting on the shaft portion 20 or the rotating structure portion 30, this condition can be resolved. This effectively prevents the shaft portion 20 or the rotating structure portion 30 from coming into strong contact with biological tissue due to the rotational energy accumulated in the motor 45 or the torsional strain energy accumulated in the shaft portion 20, thereby preventing damage to the shaft portion 20 or the biological tissue.

[0065] The control unit 50 can also determine whether emergency braking of the motor 45 is necessary, and when it determines that emergency braking is necessary, the control unit 50 may control the motor drive circuit 60 to switch the motor 45 from a circuit connected to a power source (e.g., the battery 44) to a circuit disconnected from the power source, thereby reversing the direction of the rotational force acting on the motor 45. This allows the medical device 10 to apply a strong braking force to the motor 45, quickly decelerating the motor 45, the shaft unit 20, and the rotating structure unit 30. Furthermore, when emergency braking is required, disconnecting the motor 45 from the power source prevents the motor 45 from being rotationally driven by current from the power source, thereby improving safety.

[0066] Furthermore, the control unit 50 can determine whether emergency braking of the motor 45 is necessary, and when it determines that emergency braking is not necessary, the control unit 50 may control the motor drive circuit 60 to switch the motor 45 from a circuit connected to a power source (e.g., the battery 44) to a circuit disconnected from the power source, or may reverse the direction of the rotational force acting on the motor 45 without switching the motor 45 from a circuit connected to the power source. This allows the medical device 10 to apply a strong braking force to the motor 45, thereby quickly decelerating the motor 45, the shaft unit 20, and the rotating structure unit 30.

[0067] Furthermore, when the control unit 50 controls the motor drive circuit 60 to switch the motor 45 from a circuit connected to a power source to a circuit disconnected from the power source, the control unit 50 reverses the direction of the rotational force acting on the motor 45 by the back electromotive force (induced electromotive force) generated in the motor 45. This allows the medical device 10 to apply a strong braking force to the motor 45, thereby quickly decelerating the motor 45, the shaft unit 20, and the rotating structure unit 30.

[0068] Furthermore, the control unit 50 controls the motor drive circuit 60 to reverse the direction of the torque acting on the motor 45, and then cancels the reversal of the direction of the torque after a preset time has elapsed. This simplifies the control of the current in the circuit in the control unit 50, shortens the control calculation time, and enables stable operation.

[0069] The medical device 10 also has a tachometer 49 that detects the rotation of the motor 45 or the shaft portion 20, and the control unit 50 receives an output signal from the tachometer 49. This allows the control unit 50 to accurately detect the operating status of the shaft portion 20 driven by the motor 45 and accurately control the motor drive circuit 60.

[0070] Furthermore, the control unit 50 may cancel the reversal of the direction of the rotational force after controlling the motor drive circuit 60 to reverse the direction of the rotational force acting on the motor 45 and after detecting the reversal of the rotational direction of the motor 45 from a signal from the tachometer 49. This allows braking to be maintained until the torsion accumulated in the shaft portion 20 is eliminated, so that the rotation of the rotating structure portion 30 by the motor 45 can be repeated while suppressing damage to the shaft portion 20 or biological tissue.

[0071] Furthermore, after controlling the motor drive circuit 60 to reverse the direction of the rotational force acting on the motor 45, the control unit 50 may cancel the reversal of the direction of the rotational force when it detects from a signal from the tachometer 49 that the rotation speed of the motor 45 has reached a preset threshold. This makes it possible to maintain braking until the torsion accumulated in the shaft portion 20 is substantially eliminated, thereby making it possible to repeatedly rotate the rotating structure portion 30 by the motor 45 while suppressing damage to the shaft portion 20 or biological tissue.

[0072] Furthermore, the shaft portion 20 has a structure that suppresses torsion. This allows the braking force caused by a short circuit between the terminals of the motor 45 when the motor 45 decelerates to be effectively applied to the shaft portion 20, which is resistant to torsion, and enables the rotating structure portion 30 connected to the distal portion of the shaft portion 20 to be quickly decelerated. This effectively prevents the shaft portion 20 and the rotating structure portion 30 from continuing to rotate due to the rotational energy accumulated in the motor 45 and the torsional strain energy accumulated in the shaft portion 20, and effectively prevents damage to the shaft portion 20 and biological tissue.

[0073] Furthermore, the rotation control method for the medical device 10 in this embodiment is a rotation control method by the control unit 50 of the medical device 10, which includes a long, rotationally driven shaft portion 20, a motor 45 that rotates a proximal portion of the shaft portion 20, a power source (e.g., a battery 44) that supplies current to the motor, a rotatable rotating structure portion 30 that is connected to a distal portion of the shaft portion 20, a motor drive circuit 60 that drives the motor 45, and a control unit 50 that controls the motor drive circuit 60 to cause the motor drive circuit 60 to drive the motor 45. The rotation control method includes the steps of controlling the motor drive circuit 60 to accelerate the motor 45, and controlling the motor drive circuit 60 to switch the motor 45 from a circuit connected to a power source to a circuit disconnected from the power source, thereby reversing the direction of the rotational force acting on the motor 45. By reversing the direction of the rotational force acting on the motor 45, the rotation control method can generate a braking force on the motor 45. This allows the motor 45, the shaft portion 20, and the rotating structure portion 30 to quickly decelerate. Furthermore, if excessive force such as torsion is acting on the shaft portion 20 or the rotating structure portion 30, this state can be eliminated. As a result, it is possible to effectively prevent the shaft portion 20 or the rotating structure portion 30 from coming into strong contact with biological tissue due to the rotational energy accumulated in the motor 45 or the torsional strain energy accumulated in the shaft portion 20, thereby preventing the shaft portion 20 or the biological tissue from being damaged.

[0074] Furthermore, in the step of reversing the direction of the rotational force acting on the motor 45, the necessity of emergency braking of the motor 45 may be determined, and if it is determined that emergency braking is necessary, the direction of the rotational force acting on the motor 45 may be reversed by controlling the motor drive circuit 60 to switch the motor 45 from a circuit connected to a power source to a circuit disconnected from the power source. In this way, the rotation control method of the medical device 10 can apply a strong braking force to the motor 45 to quickly decelerate the motor 45, the shaft portion 20, and the rotating structure portion 30. Furthermore, when emergency braking is necessary, disconnecting the motor 45 from the power source prevents the motor 45 from being rotationally driven by current from the power source, thereby improving safety.

[0075] Furthermore, in the step of reversing the direction of the rotational force acting on the motor 45, the necessity of emergency braking of the motor 45 may be determined, and if it is determined that emergency braking of the motor 45 is not necessary, the motor drive circuit 60 may be controlled to switch the motor 45 from a circuit connected to a power source to a circuit disconnected from the power source, or the direction of the rotational force acting on the motor 45 may be reversed without switching the motor 45 from a circuit connected to a power source. In this way, the rotation control method for the medical device 10 can apply a strong braking force to the motor 45, thereby quickly decelerating the shaft portion 20 and the rotating structure portion 30.

[0076] Furthermore, in the step of reversing the direction of the rotational force, the motor drive circuit 60 may be controlled to switch the motor 45 from a circuit connected to a power source to a circuit disconnected from the power source, thereby reversing the direction of the rotational force acting on the motor 46 by the back electromotive force generated in the motor 45. In this way, the rotation control method for the medical device 10 can apply a strong braking force to the motor 45, quickly decelerating the shaft portion 20 and the rotating structure portion 30.

[0077] The rotation control method also includes a step of canceling the reversal of the direction of the rotational force after a predetermined time has elapsed since controlling motor drive circuit 60 to reverse the direction of the rotational force acting on motor 46. This simplifies the control of the current within the circuit in control unit 50, shortens the control calculation time, and enables stable operation.

[0078] Furthermore, the rotation control method may include a step of detecting the rotation speed of motor 45 or shaft portion 20 after the step of reversing the direction of the rotational force acting on motor 46, and canceling the reversal of the direction of the rotational force after detecting from the detection result that the rotational direction of motor 45 has been reversed. This allows braking to be maintained until the torsion accumulated in shaft portion 20 is eliminated, making it possible to repeatedly rotate rotating structure portion 30 by motor 45 while suppressing damage to shaft portion 20 or biological tissue.

[0079] Furthermore, the rotation control method may include, after the step of reversing the direction of the rotational force acting on the motor 46, a step of detecting the rotation speed of the motor 45 or the shaft portion 20, and canceling the reversal of the direction of the rotational force when the detected rotation speed reaches a preset threshold. This allows braking to be maintained until the torsion accumulated in the shaft portion 20 is substantially eliminated, thereby allowing the motor 45 to repeatedly rotate the rotating structure portion 30 while suppressing damage to the shaft portion 20 or biological tissue.

[0080] The present invention is not limited to the above-described embodiment, and various modifications can be made by those skilled in the art within the technical concept of the present invention. For example, the biological lumen into which the medical device 10 is inserted is not limited to a blood vessel, but may be, for example, a vascular tract, a ureter, a bile duct, a fallopian tube, a hepatic duct, etc. Therefore, the object to be destroyed does not have to be a thrombus B.

[0081] Furthermore, the rotation directions of the motor 45, the shaft portion 20, and the rotating structure portion 30 in each rotation cycle may be the same direction, rather than being opposite directions with a stop in between.

[0082] Furthermore, the configuration of the rotating structure 30 is not particularly limited, and for example, it does not have to be formed from wires 31. The rotating structure 30 only needs to be able to destroy objects within a biological lumen, and may, for example, be coated with an abrasive or have a sharp blade. Alternatively, the rotating structure 30 does not have to be able to destroy objects within a biological lumen. For example, the rotating structure 30 may be a spiral structure that can transport objects by rotating. [Explanation of symbols]

[0083] 10 Medical Devices 20 Shaft section 21 Guidewire tube 25 outer sheath 30 Rotating structure 40 Control section 41 Connection Unit 42 Drive unit 45 motor 49 Tachometer 50 control section 60 Motor drive circuit T1 Terminal 1 T2 Terminal 2

Claims

1. An elongated medical device to be inserted into a biological lumen, A long shaft portion that is driven to rotate; a motor for rotating a proximal portion of the shaft; a power supply that supplies current to the motor; a rotation structure coupled to a distal portion of the shaft portion and rotatable therewith; a motor drive circuit that drives the motor; a control unit that controls the motor drive circuit to drive the motor so as to repeat a plurality of rotation cycles, the motor drive circuit has a circuit capable of switching a current flow; The control unit reverses the direction of the rotational force acting on the motor by switching the circuit, and after the reversal of the direction of the rotational force is released and before the motor drive circuit drives the motor for the next rotation cycle, a reset step is provided in which both terminals of the motor are opened and no current is supplied to the motor.

2. The medical device of claim 1, wherein the control unit is capable of determining the need for emergency braking of the motor, and when it determines that emergency braking is necessary, controls the motor drive circuit to switch the motor from a circuit connected to the power supply to a circuit disconnected from the power supply, thereby reversing the direction of the rotational force acting on the motor.

3. The control unit is capable of determining whether emergency braking of the motor is necessary, and when it is determined that emergency braking is not necessary, controls the motor drive circuit to switch the motor from a circuit connected to the power supply to a circuit disconnected from the power supply, or reverses the direction of the rotational force acting on the motor without switching the motor from a circuit connected to the power supply. The medical device of claim 1 or 2.

4. The medical device according to any one of claims 1 to 3, wherein the control unit controls the motor drive circuit to reverse the direction of the rotational force acting on the motor by the back electromotive force generated in the motor when the motor is switched from a circuit connected to the power source to a circuit disconnected from the power source.

5. A medical device according to any one of claims 1 to 4, wherein the control unit controls the motor drive circuit to reverse the direction of the rotational force acting on the motor, and then cancels the reversal of the direction of the rotational force after a predetermined time has elapsed since the control unit reversed the direction of the rotational force acting on the motor.

6. a tachometer for detecting rotation of the motor or the shaft portion, The medical device according to any one of claims 1 to 5, wherein the control unit receives an output signal from the tachometer.

7. 7. The medical device of claim 6, wherein the control unit cancels the reversal of the direction of the rotational force after controlling the motor drive circuit to reverse the direction of the rotational force acting on the motor and detecting that the rotational direction of the motor has been reversed by a signal from the tachometer.

8. 7. The medical device of claim 6, wherein the control unit cancels the reversal of the direction of the rotational force when, after controlling the motor drive circuit to reverse the direction of the rotational force acting on the motor, it detects from a signal from the tachometer that the rotation speed of the motor has reached a predetermined threshold.

9. The medical device according to any one of claims 1 to 8, wherein the shaft portion has a structure that suppresses twisting.

10. A method for controlling rotation by a control unit of a medical device having a long shaft portion that is driven to rotate, a motor that rotates a proximal portion of the shaft portion, a power source that supplies current to the motor, a rotating structure that is rotatably connected to a distal portion of the shaft portion, a motor drive circuit that drives the motor, and a control unit that controls the motor drive circuit to cause the motor drive circuit to drive the motor so as to repeat a plurality of rotation cycles, wherein the motor drive circuit has a circuit that can switch the flow of current, the method comprising: controlling the motor drive circuit to accelerate the motor; controlling the motor drive circuit to switch the circuit, thereby reversing the direction of the rotational force acting on the motor; a reset step in which, after the reversal of the direction of the rotational force is released and before the motor is driven by the motor drive circuit for the next rotation cycle, the motor drive circuit is controlled to open both terminals of the motor and not supply current to the motor.

11. 11. The method for controlling rotation of a medical device according to claim 10, wherein in the step of reversing the direction of the rotational force, the necessity of emergency braking of the motor is determined, and if it is determined that emergency braking is necessary, the direction of the rotational force acting on the motor is reversed by controlling the motor drive circuit to switch the motor from a circuit connected to the power supply to a circuit disconnected from the power supply.

12. 12. The method for controlling rotation of a medical device according to claim 10 or 11, wherein in the step of reversing the direction of the rotational force, the necessity of emergency braking of the motor is determined, and if it is determined that emergency braking of the motor is not necessary, the motor drive circuit is controlled to switch the motor from a circuit connected to the power supply to a circuit disconnected from the power supply, or the direction of the rotational force acting on the motor is reversed without switching the motor from a circuit connected to the power supply.

13. A method for controlling rotation of a medical device according to any one of claims 10 to 12, wherein in the step of reversing the direction of the rotational force, the motor drive circuit is controlled to switch the motor from a circuit connected to the power supply to a circuit disconnected from the power supply, thereby reversing the direction of the rotational force acting on the motor by the back electromotive force generated in the motor.

14. The rotation control method according to any one of claims 10 to 13, further comprising the step of canceling the reversal of the direction of the rotational force after a predetermined time has elapsed since the direction of the rotational force acting on the motor is reversed by controlling the motor drive circuit.

15. A rotation control method according to any one of claims 10 to 14, further comprising the step of detecting the number of rotations of the motor or the shaft portion after the step of reversing the direction of the rotational force acting on the motor, and canceling the reversal of the direction of the rotational force after detecting that the rotational direction of the motor has been reversed from the detection result.

16. A rotation control method according to any one of claims 10 to 14, further comprising, after the step of reversing the direction of the rotational force acting on the motor, a step of detecting the rotation speed of the motor or the shaft portion, and canceling the reversal of the direction of the rotational force when the detected rotation speed reaches a preset threshold value.

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