Device for regulating stiffness

A device for regulating stiffness has a rotary shaft coupled to the driven member to rotate the driven member, a rotational connection body coupled to the rotary shaft to freely rotate thereon and rotating by a driving power of the driving motor, and an elastic connection body fixed to the rotary shaft and extending in the length direction of the rotary shaft to connect to the rotational connection body, wherein the elastic connection body gives an elastic force in a direction opposite to the rotating direction of the rotational connection body to interrupt free rotation of the rotational connection body with respect to the rotary shaft, and wherein if the rotational connection body rotates by the driving motor, the elastic force of the elastic connection body acts as spring so that the rotating force of the rotational connection body is transmitted to the rotary shaft.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Korean Patent Application No. 10-2012-0150471, filed on Dec. 21, 2012, and all the benefits accruing therefrom under 35 U.S.C. §119, the contents of which in its entirety are herein incorporated by reference.

BACKGROUND

The present disclosure relates to a device for regulating stiffness, and more particularly, to a device for regulating stiffness by transmitting a rotational driving power of a driving motor to a rotary shaft connected to a driven member while maintaining predetermined stiffness.

2. Description of the Related Art

A rotating structure, which includes a driven member connected to a rotary shaft and a driving motor for rotating the rotary shaft so that the driven member is rotated, is used in various fields.

For example, the rotating structure may be easily found at a robot manipulator or the like and also used for treatment such as joint rehabilitation when a joint is damaged by an accident or the like.

FIG. 1is a schematic view showing an example of a conventional rotating structure.

As shown inFIG. 1, if a joint portion4of the leg1of a patient is damaged and needs to be rehabilitated, a support member5is fixed to the thigh2, and a driven member6hinged by the support member5is fixed to the calf3. At this time, a hinge connection portion7between the support member5and the driven member6is fixed to the corresponding location of the joint portion4.

A rotary shaft (not shown) is formed at one end of the support member5located at the hinge connection portion7, and a driving motor8is connected to the rotary shaft.

If the rotary shaft rotates by the driving motor8, the driven member6rotates on the hinge connection portion7with respect to the support member5by means of the rotating force of the rotary shaft. If the driven member6is rotated, the calf3fixed to the driven member6also rotates on the joint portion4accordingly.

If the driven member6is repeatedly rotated in clockwise and counterclockwise directions by adjusting a driving direction of the motor8, the motion of bending and spreading the leg1may be performed repeatedly, and this motion helps rehabilitation of the damaged joint portion4.

However, as shown inFIG. 1, if the rotating force of the driving motor8is directly transmitted to the rotary shaft which rotates the driven member6, the rotating movement of the driven member6is entirely restricted by the driving power of the driving motor8, which is called a rigidly coupling state. In other words, if the driving motor8starts driving, the driven member6also instantly rotates, and unless the driving motor8stops driving, a rotating force is continuously applied to the driven member6.

The joint portion4of a person is an organ which operates by soft muscle contraction. If the joint portion4of a person moves by using a rotating structure in a rigidly coupling state as described above, the joint portion4may not follow the movement of the driven member6, which may run the risk and damage the joint portion4.

In addition, the damaged joint portion4may be hardened and immovable in a moment. At this time, unless the driving power of the driving motor8is intercepted instantly, the rotating force of the driving motor8may move the joint portion4constrainedly and give a great damage to the joint portion4. The above phenomenon may also occur when the calf3cannot rotate any more due to an obstacle or the like.

Meanwhile, even when the above rotating structure is used for a robot manipulator (when the support member and the driven member are respectively robot arms), if the safety of the robot is considered, the stiffness of the rotary shaft and the driving motor for rotating a driven member needs to be suitably adjusted, as well known in the art.

As described above, when transmitting power of the driving motor and the rotary shaft, their stiffness should be suitably adjusted. For this, a stiffness generating device capable of generating desired stiffness may be used for adjusting the stiffness.

However, a conventional stiffness generating device changes stiffness by using an electromagnetic configuration as disclosed in Patent Literature 1, which however has a complicated design and is not easily controlled.

SUMMARY

The present disclosure is directed to providing a device for regulating stiffness, which may adjust stiffness in a rapid and easy way with a simple structure by using a mechanical configuration.

In one aspect, there is provided a device for regulating stiffness for transmitting a driving power of a driving motor to a driven member while maintaining predetermined stiffness, the device including: a rotary shaft coupled to the driven member to rotate the driven member; a rotational connection body coupled to the rotary shaft to freely rotate thereon and rotating by a driving power of the driving motor; and an elastic connection body fixed to the rotary shaft and extending in the length direction of the rotary shaft to connect to the rotational connection body, wherein the elastic connection body gives an elastic force in a direction opposite to the rotating direction of the rotational connection body to interrupt free rotation of the rotational connection body with respect to the rotary shaft, and wherein if the rotational connection body rotates by the driving motor, the elastic force of the elastic connection body acts as spring so that the rotating force of the rotational connection body is transmitted to the rotary shaft.

The elastic connection body may include a leaf spring; and a support body fixed to the rotary shaft and fixing the leaf spring in the length direction of the rotary shaft, wherein the elastic force is generated as the leaf spring is bent in the rotating direction of the rotational connection body by using the support body as a support point.

The rotational connection body may be connected to the rotary shaft and the leaf spring to be linearly movable in the length direction of the rotary shaft, and the stiffness may be adjusted as the rotational connection body makes a linear movement so that a distance between the rotational connection body and the support body changes.

The device for regulating stiffness may further include a rotating body fixed to the rotary shaft to free rotate thereon, wherein the rotating body may be connected to the rotational connection body by a link, and as the rotating body rotates, the rotational connection body linearly may move in the length direction of the rotary shaft.

The link may have one end joint-connected to the rotating body and the other end joint-connected to the rotational connection body and may be formed by a link arm disposed with a slant with respect to the rotary shaft.

The link arm may have one end connected to a universal joint connected to the rotating body and the other end connected to the rotational connection body by a ball joint.

A plurality of link arms may be disposed radially based on the rotary shaft.

The rotating body may include a first rotating body and a second rotating body disposed with the rotational connection body being interposed therebetween; the driving motor may include a first driving motor and a second driving motor respectively connected to the first rotating body and the second rotating body to rotate the first rotating body and the second rotating body independently; the first rotating body and the second rotating body may be respectively connected to the rotational connection body by the link; when the first driving motor and the second driving motor respectively rotate the first rotating body and the second rotating body in opposite directions based on the rotary shaft, the rotational connection body may not rotate with respect to the rotary shaft but linearly move in the length direction of the rotary shaft; and when the first driving motor and the second driving motor respectively rotate the first rotating body and the second rotating body in the same direction based on the rotary shaft, the rotational connection body may not linearly move in the length direction of the rotary shaft but rotate with respect to the rotary shaft.

The support body may be coupled to the rotary shaft to freely rotate thereon, and the support body may be selectively fixed to or separated from the rotary shaft by means of a fixing member so as to rotate integrally with the rotary shaft or freely rotate separately from the rotating body.

The fixing member may include: a second cam member linearly movable on the rotary shaft and having a coupling protrusion formed thereon; a first cam member coupled to the support body and having a coupling groove formed therein so as to be coupled with the coupling protrusion; and a spring connected to the male cam member to press the male cam member toward the first cam member.

The first cam member may be coupled to the support body in a direction opposite to the direction in which the leaf spring is fixed.

The support body may include a plurality of support units extending in a radial direction with respect to the rotary shaft, and a leaf spring may be fixed to each of the plurality of support units.

DETAILED DESCRIPTION

Hereinafter, an embodiment of the present disclosure capable of implementing the above object will be described with reference to the accompanying drawings. Though the present disclosure is described with reference to the embodiments depicted in the drawings, the embodiments are just examples, and the spirit of the present disclosure and its essential configurations and operations are not limited thereto.

FIG. 2is a perspective view showing a device10for regulating stiffness (hereinafter, also referred to as a stiffness regulating device10) according to an embodiment of the present disclosure,FIG. 3is a perspective view showing the stiff regulating device10ofFIG. 2, observed at a different angle, andFIG. 4is an exploded perspective view showing the stiff regulating device10ofFIG. 2. InFIG. 4, a third frame800is not depicted.

As shown inFIGS. 2 to 4, the stiffness regulating device10includes a rotary shaft100, a rotational connection body200formed on the rotary shaft100, a first rotating body300and a second rotating body400formed on the rotary shaft100with the rotational connection body200being interposed between them, an elastic connection body500located between the first rotating body300and the second rotating body400and coupled to the rotational connection body200, a first frame600and a second frame700formed with the first rotating body300and the second rotating body400being interposed between them, a third frame800for fixing the first frame600and the second frame700to each other, and a first driving motor910and a second driving motor920respectively connected to the first frame600and the second frame700.

The rotary shaft100extends in a direction perpendicular to the first frame600and the second frame700. The rotary shaft100extends to have a length so that both ends thereof are exposed out of the first frame600and the second frame700. The rotary shaft100is not directly fixed by the first frame600and the second frame700, and the rotation of the rotary shaft100is not restricted by the first frame600and the second frame700.

One end or both ends of the rotary shaft100exposed out of the first frame600and the second frame700are coupled to a driven member (not shown) to be rotated by a driving motor. If the rotary shaft100rotates, the driven member rotates together.

The driven member of this embodiment is not limited to an elongated rod-shaped driven member as shown inFIG. 1, and it should be understood that any member rotatable by the rotary shaft100may be used as the driven member of this embodiment.

A support member is coupled to any one of the first to third frames to fix the stiff regulating device10.

Similar to the above, the support member is not limited to an elongated rod-shaped support member as shown inFIG. 1, and it should be understood that any member for fixing the stiff regulating device10at a specific location can be used as the support member.

A fixing drum610is coupled to the first frame600, and the fixing drum610rotatably fixes a first pulley620. The first pulley620is connected to a second pulley630, rotatably fixed to the first frame600, by a belt640, and the second pulley630is connected to the first driving motor910and rotates by the first driving motor910.

The first rotating body300is fixed to the first pulley620with the first frame600being interposed between them. The rotation of the first rotating body300is not restricted by the first frame600, and if the first pulley620rotates, the first rotating body300rotates together.

According to the above configuration, the first driving motor910rotates to make the second pulley630rotate, the rotation of the second pulley630makes the first pulley610rotate, and the rotation of the first pulley610makes the first rotating body300rotate.

A fixing drum710is coupled to the second frame700, and the fixing drum710rotatably fixes a first pulley720. The first pulley720is connected to a second pulley730, rotatably fixed to the second frame700, by a belt740, and the second pulley730is connected to the second driving motor920and rotates by the second driving motor920.

The second rotating body400is fixed to the first pulley720with the second frame700being interposed between them. The rotation of the second rotating body400is not restricted by the second frame700, and if the first pulley720rotates, the second rotating body400rotates together.

According to the above configuration, the second driving motor920rotates to make the second pulley730rotate, the rotation of the second pulley730makes the first pulley710rotate, and the rotation of the first pulley710makes the second rotating body400rotate.

The first rotating body300and the second rotating body400are connected to the rotary shaft100to freely rotate thereon, and are linked to the rotational connection body200respectively by means of a link arm310and a link arm410.

An elastic connection body500, which includes a leaf spring530extending in the length direction of the rotary shaft100and a support body520selectively fixed to or rotatably coupled to the rotary shaft100to support one end of the leaf spring530, is coupled to the rotary shaft100. The elastic connection body500is fixed to the rotary shaft100at ordinary time to rotate together with the rotary shaft100.

The rotational connection body200is connected to the rotary shaft100to freely rotate thereon and is formed on the rotary shaft100to be linearly movable in the length direction of the rotary shaft100.

A slit210is formed in the rotational connection body200to vertically perforate the rotational connection body200, and two rollers211facing each other are provided in the slit210.

The rotational connection body200and the elastic connection body500are coupled so that the leaf spring530is inserted between two rollers211.

The rotational connection body200is connected to the rotary shaft100to freely rotate thereon. However, since the leaf spring530of the elastic connection body500selectively fixed to or rotatable on the rotary shaft100is coupled through the rotational connection body200in the vertical direction, the free rotation of the rotational connection body200with respect to the rotary shaft100is restricted by an allowable bending angle of the leaf spring530. Meanwhile, the movement in the length direction on the rotary shaft100is not restricted by the leaf spring530.

FIG. 5is an exploded perspective view showing the rotary shaft100of the stiff regulating device10of this embodiment as well as the elastic connection body500, the rotational connection body200and the rotating bodies300,400connected thereto.

As shown inFIG. 5, a plurality of link arms310are coupled to the first rotating body300in the radial direction with respect to the center of the first rotating body300. One end320of the link arms310is connected to the first rotating body300by a universal joint, and the other end330is coupled to a ball212formed on the upper surface of the rotational connection body200and connected to the rotational connection body200by a ball joint.

Since the link arm310is coupled with a slant with respect to the center of the first rotating body300, the link arm310is formed with a slant with respect to the rotary shaft100which passes through the center of the first rotating body300. The plurality of link arms310are formed to have the same direction and angle and disposed to be wound around the rotary shaft100.

A plurality of link arms410are also provided to the second rotating body400in the radial direction with respect to the center of the second rotating body400. One end420of the link arm410is connected to the second rotating body400by a universal joint, and the other end430is coupled to a ball213formed on the lower surface of the rotational connection body200and connected to the rotational connection body200by a ball joint.

Since the link arm410is also coupled with a slant with respect to the center of the second rotating body400, the link arm410is formed with a slant with respect to the rotary shaft100which passes through the center of the second rotating body400. The plurality of link arms410are formed with the same direction and angle and disposed to be wound around the rotary shaft100.

FIG. 6is an exploded perspective view showing the rotary shaft100of the stiff regulating device10of this embodiment as well as the elastic connection body500and the rotational connection body200connected thereto.

As shown inFIG. 6, three slits210are formed in the rotational connection body200between two adjacent balls212.

The support body520of the elastic connection body500is made of rigid material which does not bend and includes three support units extending in the radial direction with respect to the rotary shaft100. Three leaf springs530are respectively fixed to the three support units. One end of the leaf spring530not fixed by the support body520will be a free end. As described later, if the rotational connection body200rotates, the leaf spring530having one free end is bent with the support body520serving as a support point and gives an elastic force to the rotational connection body200.

FIG. 7is an exploded perspective view showing the rotary shaft100and the elastic connection body500of the stiff regulating device10of this embodiment.

As shown inFIG. 7, the rotary shaft100includes a first large-diameter portion110coupled to the first rotating body300, a small-diameter portion120extending from the rear end of the first large-diameter portion110, and a second large-diameter portion130connected to the small-diameter portion120and coupled with the second rotating body400.

A straight chamfering121is formed at the rear end of the cylindrical small-diameter portion120. Accordingly, the rear end of the small-diameter portion120has an approximately hexagonal sectional shape. A hole having a hexagonal sectional shape is formed at the front end of the second large-diameter portion130so that the rear end of the small-diameter portion120may be inserted therein. Since the rear end of the small-diameter portion120is inserted into the hole of the second large-diameter portion130with a hexagonal sectional shape, the first large-diameter portion110and the second large-diameter portion130rotate integrally.

A support body520of the elastic connection body500is coupled to the small-diameter portion120so as to closely adhere to the joint between the first large-diameter portion110and the small-diameter portion120. The support body520may freely rotate on the small-diameter portion120.

However, the free rotation of the support body520is restricted by the fixing member. The fixing member of this embodiment includes a first cam member140fixed to the support body520in a direction opposite to the extending direction of the leaf spring530, a second cam member150having a coupling protrusion151which may be coupled to a coupling groove141formed in the first cam member140, and a spring160disposed between the second cam member150and the front end of the second large-diameter portion130.

The rotary shaft100and the elastic connection body500are coupled to each other by inserting the support body520of the elastic connection body500into the small-diameter portion120, subsequently inserting the first cam member140into the small-diameter portion120to be coupled to the support body520, then inserting the second cam member150and the spring160into the small-diameter portion120, and then finally inserting the second large-diameter portion130into the rear end of the small-diameter portion120.

According to the above configuration, the elastic connection body500may be selectively fixed to or separated from the rotary shaft100by means of the fixing member, so that the elastic connection body500may rotate integrally with the rotary shaft100or freely rotate separately from the rotating body100. This will be described in detail later.

Hereinafter operations of the stiff regulating device10of this embodiment will be described with reference toFIGS. 8 to 12.

FIGS. 8 to 10are diagrams for illustrating a stiffness adjusting operation by using the stiff regulating device10according to this embodiment.

In a state shown inFIG. 8, the first driving motor910and the second driving motor920are respectively driven with the same power so that the first rotating body300and the second rotating body400rotate together in the counterclockwise direction (based on the state shown inFIG. 1). Since the first rotating body300and the second rotating body400face each other, the first rotating body300and the second rotating body400rotate in opposite directions based on the rotary shaft100.

According to the above operation, as shown inFIG. 9, the rotational connection body200moves toward the first rotating body300by the mechanical operation of the link arms310,410.

Contrarily, as shown inFIG. 10, in order to move the rotational connection body200toward the second rotating body400, the first driving motor910and the second driving motor920are respectively driven with the same power so that the first rotating body300and the second rotating body400rotate together in the clockwise direction (based on the state shown inFIG. 1). At this time, since the first rotating body300and the second rotating body400face each other, the first rotating body300and the second rotating body400also rotate in opposite directions based on the rotary shaft100.

According to the operations shown inFIGS. 8 to 10, the driving power of the first driving motor910and the second driving motor920is not transmitted to the rotary shaft100, and only the first rotating body300and the second rotating body400are used to freely rotate on the rotary shaft100.

In addition, since the first driving motor910and the second driving motor920move the first rotating body300and the second rotating body400with the same power, the rotational connection body200linked to the first rotating body300and the second rotating body400does not rotate with respect to the rotary shaft100but just moves in the length direction. Therefore, force is not applied to the leaf spring530by the rotational connection body200.

FIGS. 11 and 12are diagrams for illustrating an operation of rotating the rotary shaft100by using stiff regulating device10according to this embodiment.

In a state shown inFIG. 11, the first driving motor910and the second driving motor920are respectively driven with the same power so that their driving directions are opposite to each other, and therefore the first rotating body300rotates in the clockwise direction and the second rotating body400rotates in the counterclockwise direction (based on the state shown inFIG. 11). Since the first rotating body300and the second rotating body400face each other, the first rotating body300and the second rotating body400rotate in the same direction based on the rotary shaft100.

Since the first rotating body300and the second rotating body400rotate in the same direction, the rotational connection body200linked to the first rotating body300and the second rotating body400starts freely rotating with respect to the rotary shaft100together with the rotating bodies300,400. Since the first rotating body300and the second rotating body400rotate at the same speed, the rotational connection body200does not move in the length direction of the rotary shaft100.

Since the rotating path of the rotational connection body200is restricted by the leaf spring530of the elastic connection body500, the elastic connection body500rotates by the rotating force of the rotational connection body200, and accordingly the rotary shaft100fixed to the elastic connection body500rotates, which makes the driven member rotate.

InFIGS. 11 and 12, in order to show that the rotational connection body200is rotating, the link arms310,410are depicted distinguishably with reference symbols311,312,411,412.

If the driving motor is driven reverse to the above so that the first rotating body300rotates in the counterclockwise direction and the second rotating body400rotates in the clockwise direction, it will be understood that the rotational connection body200may rotate opposite toFIGS. 11 and 12and the rotary shaft100may rotate in a reverse direction.

As shown inFIG. 13, according to this embodiment, since the end of the leaf spring530of the elastic connection body500toward the first rotating body300is a free end, if the rotational connection body200applies force in the rotating direction M, the leaf spring530is bent. The bent leaf spring530has an elastic force to restore its original form, and the elastic force pushes the rotational connection body200in a direction S opposite to the rotating direction of the rotational connection body200so as to serve as stiffness when the driving power of the driving motors910,920is transmitted to the rotary shaft100.

In more detail, at the instant that the rotational connection body200rotates by the driving motors910,920, the leaf spring530is bent by the rotational connection body200, and the rotational driving power of the driving motors910,920is not directly transmitted to the rotary shaft100. In other words, even though the driving motors910,920rotate, the rotary shaft100does not rotate instantly but rotates with a time difference during which the leaf spring530is being bent.

According to the above configuration, the problem caused by perfect stiffness coupling between the driving motor and the rotary shaft may be solved.

Further, according to this embodiment, as shown inFIGS. 8 to 10, the magnitude of stiffness may also be adjusted by controlling the location of the rotational connection body200.

FIG. 14is a diagram for illustrating that stiffness may be adjusted by using the stiff regulating device10according to this embodiment.

As shown inFIG. 14, assuming that the distance from the support body520to a location where the rotational connection body200is positioned is I, the thickness of the leaf spring530is h, and the distance between the center of the rotary shaft100and the thickness center of the leaf spring530is r, the stiffness σ provided by the leaf spring530may be expressed according to Equation 1 below.

where E is a Young's modulus of the leaf spring.

If the rotational connection body200moves toward the support body520, the distance I is decreased, which makes the stiffness σ increase. As shown inFIG. 10, if the rotational connection body200adheres to the support body520as close as possible, the driving power of the driving motors910,920is transmitted to the rotary shaft100as if it is perfect stiffness coupling. However, as shown inFIG. 9, if the rotational connection body200is located farthest from the support body520, the stiffness σ is minimized, and so the time difference increases as much when the driving power of the driving motors910,920is transmitted to the rotary shaft100.

Heretofore, it has been described that stiffness is adjusted by using the stiff regulating device10and the rotating force of the driving motor is transmitted to the rotary shaft100by using the adjusted stiffness.

Hereinafter, a configuration for preventing the stiff regulating device10from being broken or preventing an obstacle contacting a driven member from being broken when an external force is applied to the rotating driven member by the obstacle will be described.

A driven member (not shown) rotating by the rotary shaft100may contact an obstacle so that its rotation is interrupted. This case may correspond to a conventional example, described above, where the calf of a patient is interrupted by an obstacle or a joint portion is hardened and immovable when the stiff regulating device10is used for a link structure for rehabilitation training.

Referring toFIG. 11again, if an external force is applied to the driven member due to a circumstance as described above, the rotation of the rotary shaft100is interrupted. At this time, the driving motors910,920keep rotating the rotational connection body200regardless of the above situation. Therefore, a very large force is instantly applied to the elastic connection body500by the rotational connection body200, in comparison to ordinary time.

According to this embodiment, it is prevented that the driving power of the driving motor is continuously transmitted to the rotary shaft100, by using the fixing member described above.

FIGS. 15 to 17are diagrams for illustrating that the transmission of a driving power of the driving motor to the rotary shaft100is intercepted by using the fixing member.

FIGS. 15 and 16shows the rotary shaft100and the elastic connection body500of the stiff regulating device10, andFIG. 17is an enlarged view showing the A portion ofFIG. 16.

As described above, the elastic connection body500is coupled to the rotary shaft100to freely rotate thereon. However, at ordinary time, the free rotation of the elastic connection body500is prevented since the coupling protrusion151of the second cam member150not freely rotatable but fixed with respect to the rotary shaft100is coupled to the coupling groove141of the first cam member140which is coupled to the rear surface of the support body520of the elastic connection body500.

In more detail, as shown inFIG. 15, in a state where the coupling groove141and the coupling protrusion151are coupled to each other, the spring160does not rotate with respect to the rotary shaft100but strongly presses the second cam member150toward the first cam member140so that the elastic connection body500is fixed to the rotary shaft100.

However, as shown inFIGS. 16 and 17, if the elastic connection body500keeps rotating (namely, if the rotational connection body200keeps rotating by the driving motor) in a state where an external force is applied to the rotary shaft100and interrupts the rotation of the rotary shaft100, the coupling protrusion151with a slant deviates from the coupling groove141along the inclined surface of the coupling groove141.

FIG. 18is a diagram for illustrating a maximum yield force by which the coupling protrusion151deviates from the coupling groove141.

InFIG. 18, the coupling protrusion151is depicted just by half and the coupling groove141is exaggeratingly depicted, for convenience.

Referring toFIG. 18, the yield force P by which the coupling protrusion151deviates from the coupling groove141is expressed like Equation 2 below.

where Q represents a force of the spring160, α represents an inclined pressure angle of the coupling protrusion151, and μ represents a frictional coefficient between the coupling protrusion151and the coupling groove141.

Therefore, in a state where the rotation of the rotary shaft100is interrupted, if the rotating force of the rotational connection body200by the driving motor increases over the yield force P, the coupling protrusion151deviates from the coupling groove141.

If the coupling protrusion151deviates from the coupling groove141, the force restricting the free rotation of the elastic connection body500with respect to the rotary shaft100disappears. Therefore, the elastic connection body500freely rotates with respect to the rotary shaft100, and the driving power of the driving motors910,920is not transmitted to the rotary shaft100.

In this way, it is possible to prevent the stiff regulating device10from being broken or an obstacle interrupting rotation of the rotary shaft100from being broken since the driving power of the driving motor is continuously transmitted in a state where the rotation of the rotary shaft100is interrupted.

While the exemplary embodiments have been shown and described, it will be understood by those skilled in the art that various changes in form and details may be made thereto without departing from the spirit and scope of the present disclosure as defined by the appended claims.