JP5416642B2 - Finger structure of robot hand - Google Patents

Description

  The present invention relates to a finger structure of a robot hand that grips and conveys an article.

  Conventionally, industrial robots have been used in production sites to automate the picking and handling of parts. Robot hands with various structures for gripping and transporting parts of various sizes and shapes are available. Proposed. Generally, the finger of such a robot hand is subjected to a so-called knurling process in which a pattern is engraved so that the gripping surface is difficult to slip, or an elastic sheet such as rubber or resin is attached.

  In addition, since a particularly large gripping force is required for a robot used for assembling or disassembling parts, for example, in the robot hand described in Patent Document 1, a leaf spring-like member having a slit is wound around a finger and fixed. . In this way, when the object is gripped by the finger, it is pressurized by the gripped object, and a part of the leaf spring-like member is deformed, and a slit between the undeformed part adjacent to this opens, and its edge is It comes to be strongly pressed against the surface of the grasped object.

  Further, in Patent Document 2, a large number of sleeve pins that can be projected and retracted are embedded in mutually facing surfaces of at least two fingers (finger), and the sleeve pins are urged to protrude to increase the gripping force. The robot hand described above is described.

  Patent Document 3 discloses a mechanical universal hand that can hold an object appropriately only by mechanical operation without depending on friction of a gripping surface. The robot hand shown in FIG. 8 of this document includes a plurality of joints in each of the three finger units arranged so as to surround the object, and is bent so that they wrap around the object. It is held so as to be wrapped.

JP 2004-268147 A Japanese Patent Laid-Open No. 2-185389 JP 2006-198748 A

  By the way, in the conventional method of attaching an elastic sheet, the friction coefficient of the finger gripping surface can be set freely, and there is no fear of damaging the object, but such an elastic sheet is usually worn. It is difficult to secure sufficient durability as a robot hand because it is easy to peel off and often peels off. On the other hand, the knurling process has a difficulty in that it is relatively expensive, and it is inevitable that the anti-slip effect is deteriorated if it is used for a long period of time.

  Further, in a finger wound with a leaf spring-like member having a slit as in Patent Document 1, the edge of the slit of the leaf spring-like member is strongly pressed against the surface of the gripped object, and the position of this edge Is fixed in the longitudinal direction of the finger, a strong force is applied locally even if a slight impact is applied during conveyance, and there is a concern that the surface of the grasped object may be damaged.

  In this regard, even in the finger described in Patent Document 2, the position of the sleeve pin protruding from the facing surface is fixed in the longitudinal direction of the finger, so there is a concern similar to that in Patent Document 1. In addition, a structure in which a large number of sleeve pins are embedded in individual fingers must be complicated and cannot be said to be inexpensive.

  In addition, the mechanical universal hand provided with the multi-joint finger unit as in Patent Document 3 is very expensive with a complicated structure, and if it is bent when holding the object as described above, the joint of the finger unit Since the portion protrudes outside, it is difficult to use in a narrow environment, for example, when the part stored in the box is taken out and interferes with the surrounding wall.

  The present invention has been made in view of such circumstances, and the object thereof is to obtain a required gripping performance stably with a simple structure that is relatively inexpensive, ensuring sufficient durability, and being narrow. It is to provide an excellent finger structure that is easy to use even in an environment.

  In order to achieve the above object, the present invention provides a robot hand that grips an object with a plurality of fingers, a coil spring is wound around the outer periphery of the fingers, and windings at intermediate portions excluding at least both ends thereof are the longitudinal directions of the fingers. It is attached so as to be displaced in the direction.

  In the above structure, the coil spring wound around the outer periphery of the finger of the robot hand can produce an anti-slip effect, for example, like a knurled pattern, and the surface of the object is sandwiched between the windings. Thus, since the displacement in the longitudinal direction of the finger is allowed and restrained to some extent, the gripping state of the object is stabilized and there is little fear of scratching the surface. Moreover, it is a simple structure which only attaches a coil spring, and there is little fall of the anti-slip effect by wear like knurling. Even if the anti-slip effect is reduced, it can be easily recovered by replacing the coil spring.

  Preferably, at least three fingers surround the object (that is, the three fingers extend in approximately the same direction and each point in contact with the surface of the object when viewed in this direction. This is advantageous in stabilizing the gripping state of the object by the fingers.

  In that case, it is particularly preferable that the three or more fingers are substantially linear and arranged so as to extend in parallel with each other in order to prevent interference with the surroundings. In addition, a receiving portion that expands the diameter of the finger so that the tip of the coil spring comes into contact with the tip of the fingers is provided to prevent the coil spring from falling off, and a tapered portion that is tapered integrally with the receiving portion. If formed, it can function as a guide when the finger is inserted into a narrow space.

  Further, the clearance between the outer periphery of the finger and the inner periphery of the coil spring surrounding the finger is preferably set within a predetermined range (for example, about several hundred microns to at most several millimeters). As long as the clearance with the coil spring falls within the predetermined range on the end side, a constricted portion may be provided at the intermediate portion in the longitudinal direction of the finger. In this way, when gripping a relatively large object, the shape of the constricted portion of the finger matches the convex shape of the surface, and the contact point may increase.

  Still further, at least one of the coil springs wound around each of the plurality of fingers may be right-handed and at least one may be left-handed. In this way, it can be expected that dropping of the object is suppressed.

  In addition, coil springs having different winding thicknesses and pitches in the longitudinal direction may be used. In this way, a plurality of objects having different dimensions and shapes can be suitably held by one coil spring. There is sex.

  As described above, according to the finger structure of the robot hand according to the present invention, although it is a simple structure in which a coil spring is wound around the outer periphery of the finger, a gripping performance equivalent to or higher than that of knurling can be stably obtained. In addition, sufficient durability that is difficult to achieve with an elastic sheet is also obtained. Further, for example, the cost is lower than that of a robot hand provided with articulated fingers, and it is easy to use even in a narrow environment.

It is a perspective view showing an example of a robot equipped with a robot hand according to the present invention. It is a perspective view which expands and shows the robot hand. It is explanatory drawing which shows an example of the drive mechanism of the robot hand. It is explanatory drawing of the holding | grip of components by the robot hand. FIG. 5B is a view corresponding to FIG. 4B according to another embodiment in which a constriction is provided in the middle of the finger. FIG. 5 is a view corresponding to FIG. 4 according to another embodiment using a so-called unequal pitch coil spring, and shows a state in which a relatively small component is gripped on the tip side of a finger having a narrow winding pitch. FIG. 2 is a view corresponding to FIG. 2 according to another embodiment in which a suction pad is provided at the tip of a finger, and FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a perspective view showing an embodiment of a robot according to the present invention, and FIG. 2 is an enlarged view of the robot hand of FIG. FIG. 3 is an explanatory diagram showing an example of a mechanism for operating the fingers of the robot hand.

  The robot 1 shown in FIG. 1 is a so-called multi-joint type, a fixed portion 2 fixed to a floor or the like, a base portion 3 capable of turning (shown by an arrow A) around a vertical axis a at the upper portion thereof, First and second arm portions 4 and 5 are sequentially attached to the upper portion of the base portion 3, and a robot hand 7 is attached to a distal end portion 5 a of the second arm portion 5 via a wrist portion 6. ing. That is, a pair of left and right support wall portions 3a is provided on the upper portion of the base portion 3, and the base end portion of the first arm portion 4 is supported so as to be rotatable around the horizontal axis b while being sandwiched between them. Has been. Thereby, the first arm portion 4 can be tilted up and down as indicated by an arrow B.

  The first arm portion 4 has a bifurcated distal end portion, and supports the base end portion of the second arm portion 5 so as to be rotatable around the axis c between them, thereby the second arm portion. 5 can also be tilted up and down (arrow C). A bifurcated tip portion 5a is provided at the tip of the second arm portion 5 so as to be rotatable (arrow D) around an axis d in the longitudinal direction, and a columnar wrist portion 6 is provided therebetween. Is supported so as to be rotatable (arrow E) around the axis e. And the robot hand 7 is attached to the front-end | tip of the wrist part 6, ie, the edge part near the front left side of the figure, so that rotation (arrow F) is possible around the axis line f.

  As shown in FIG. 2, the robot hand 7 includes a box portion 70 corresponding to a palm, and a rod 71 and fingers 72 corresponding to fingers. The box portion 70 is rectangular in plan view, and is relatively short in the direction of the axis f of the wrist portion 6 (the Y direction shown in FIG. 2 and hereinafter also referred to as the front-rear direction of the robot hand 7), and is orthogonal thereto. It is relatively long in the X direction (left-right direction). In the example shown in the figure, the dimension in the Z direction which is the vertical direction, that is, the thickness of the palm is smaller than the length before and after that.

  And while the rear side of the said box part 70 is connected with the wrist part 6 so that rotation is possible, the rod 71 of a left-right pair of rectangular cross section is provided in the front side so that it may each extend ahead. Each of the rods 71 is provided with a pair of round bar-like fingers 72 so as to extend downward. The fingers 71 approach and separate from each other in the longitudinal direction of the rod 71, and the pair of rods 71 are adjacent to each other. It has come away.

  Specifically, as shown in a perspective view from above in FIG. 3, a screw shaft 73 is supported inside the box portion 70 so as to extend left and right in the vicinity of the center of the front and rear, and is provided at one end portion thereof. The driven gear 74 is meshed with the driving gear 76 of the electric motor 75. The screw shaft 73 is provided with a clockwise male screw on one side (left side) in the longitudinal direction, and provided with a counterclockwise male screw on the other side (right side), and a corresponding female screw is formed. A pair of nuts 77 are screwed together. The pair of nuts 77 are integrally provided at the base end portion of the rod 71, respectively.

  When the drive gear 76 and the driven gear 74 are rotated by the operation of the electric motor 75 and the screw shaft 73 rotates, for example, counterclockwise, the pair of nuts 77 move toward each other, while the screw shaft 73 moves to the right. If it rotates around, the nut 77 moves away from each other. That is, the pair of nuts 77 that respectively support the rod 71 are moved in the opposite direction in the longitudinal direction by the rotation of the screw shaft 73, so that the pair of rods 71 are close to each other as indicated by white arrows in the figure. , To come away.

  A similar drive mechanism is provided in each rod 71, and a pair of nuts 79 are screwed onto a screw shaft 78 extending in the longitudinal direction of the rod 71. It is fixed by fastening. Then, when the electric motor 80 connected to the rear end of the screw shaft 78 is operated, and the screw shaft 78 rotates, for example, clockwise, the nuts 79 move toward each other, while the screw shaft 78 rotates counterclockwise. The nut 79 moves away from each other. In this manner, the pair of fingers 72 are moved closer to and away from the longitudinal direction of the rod 71.

  That is, in the robot hand 7 of this embodiment, four straight fingers 72 are arranged in parallel, and are opened and closed by approaching and moving away from each other. Although details will be described later with reference to FIG. 4, the four fingers 72 of the robot hand 7 are inserted into the storage box B and positioned so as to surround the part P to be grasped (FIG. 4 (a)). The part P can be gripped by closing from ((b) of the figure). In the example shown in the figure, the storage box B is divided into four sections b1 each storing a part P.

-Finger structure-
In this embodiment, as a characteristic configuration, a coil spring 81 is wound around each of the four fingers 72 of the robot hand 7 so as to exhibit an anti-slip effect and to stabilize the gripping state of the object. It is That is, as shown in FIG. 2, the four fingers 72 are basically made of a metal round pipe, and although not shown, the upper end (base end) of the rod 71 is the same as described above. While being fixed to the nut 79 of the screw shaft 78, a resin plug 82 is attached to the lower end of the finger 72, that is, the front end so as to prevent the coil spring 81 from falling off.

  As shown in the exploded view of the finger 72 on the near side in FIG. 2, the plug 82 has a shaft portion 82b provided with a male screw on one side (the upper side in the figure) of the disk-like base portion 82a and on the opposite side. The tapered cone portions 82 c are integrally formed, and the shaft portion 82 b is screwed into the opening (not shown) at the lower end of the finger 72. That is, an internal thread is formed at least at the lower end on the inner periphery of the finger 72 made of a round pipe, and the external thread of the shaft portion 82b is screwed into the internal thread.

  Thus, the outer diameter of the disc-shaped base portion 82 a of the plug 82 attached to the lower end of the finger 72 is larger than the outer diameter of the finger 72, and the upper surface of the base portion 82 a is the lower end of the coil spring 81 on the distal end side of the finger 72 ( It becomes a receiving portion that contacts the tip) and receives it so as not to be displaced downward. On the other hand, the conical portion 82c of the plug 82 is a tapered portion that tapers downward, and functions as a guide when the finger 72 is inserted into the component storage box B or the like from its tip as described later.

  Further, an annular groove is formed on the outer periphery on the proximal end side of the finger 72, that is, the upper side in the figure, and a resin ring member 83 is fitted on the outer periphery. The ring member 83 is in contact with the upper end (base end) of the coil spring 81 so as not to be displaced further upward. Thus, the upper end is received by the ring member 83 and the lower end is received by the base portion 82a of the plug 82, and the coil spring 81 is pre-compressed by a predetermined amount. On the other hand, the winding 81 in the middle portion of the coil spring 81 excluding the upper and lower ends can be displaced in the longitudinal direction along the outer periphery of the finger 72.

  More specifically, the coil spring 81 is formed by spirally winding (coiling) a wire having a circular cross section as an example, and has a substantially circular shape when viewed in the axial direction of the coil. The inner diameter of the coil is set to be slightly larger than the outer diameter of the finger 72 (round pipe). Between the outer periphery of the finger 72 and the inner periphery of the coil spring 81 surrounding the finger 72, for example, the outer diameter of the finger 72 is set. When the diameter is 10 mm, a clearance of several hundred microns to several millimeters (˜9 mm) is provided. This clearance is set so that the winding of the coil spring 81 is smoothly displaced in the longitudinal direction along the outer periphery of the finger 72 as will be described later.

  In this embodiment, two of the four coil springs 81 (the foremost and the farthest in the example in the figure) are right-handed, and the other two coil springs 81 are left-handed. If all the coil springs 81 are right-handed, if the parts P gripped by the four fingers 72 are subjected to gravity via the coil springs 81, the coil springs 81 are wound from the respective coil springs 81. This is because a force that rotates counterclockwise along the line acts, and this may cause the component P to fall off while rotating counterclockwise.

-Robot hand operation and its effects-
Next, a state in which the egg-shaped component P is gripped by the fingers 72 of the robot hand 7 described above as an example will be described with reference to FIG. FIG. 5A schematically shows a state where the finger 72 is inserted into the storage box B for the component P, and FIG. 5B schematically shows a state where the component P is gripped.

  First, as shown in FIG. 2, the robot hand 7 is positioned above one section b1 of the storage box B, and the positions of the four fingers 72 are aligned with the four corners of the section b1, respectively. 1. The robot arm 7 is moved downward as indicated by an arrow in FIG. As a result, four fingers 72 are inserted into the four corners of the section b1 as shown in FIG. If the fingers 72 are to be inserted straight in this way, there should be a minimum gap in addition to the thickness of the fingers 72 at the four corners of the section b1 of the storage box B.

  Moreover, since the conical portion 82c of the plug 82 at the tip of each finger 72 functions as a guide when inserted in this way, the finger 72 can be stored in the compartment b1 of the storage box B even if the control accuracy of the robot hand 7 is not so high. Can be inserted along the four corners. Further, even if the peripheral wall of the section b1 and the coil spring 81 of the finger 72 are rubbed at this time, the shock is absorbed and alleviated by the bending of the coil spring 81. There is little worry that 72 will be damaged.

  Then, after inserting the four fingers 72 into the four corners of the compartment b1 of the storage box B and then closing and gripping the part P as shown in FIG. 5 (b), the parts enclosed by these fingers 72 The outer peripheral surface of each finger 72 comes into contact with the surface of P, and the movement in the horizontal direction is restricted. Further, the winding of the coil spring 81 wound around the finger 72 also comes into contact with the surface of the component P and is pushed away in accordance with the convex shape of the surface of the component P, so that it is exaggerated in the drawing. It is displaced up and down, that is, in the longitudinal direction of the finger 72.

  For this reason, on the surface of the part P surrounded by the four fingers 72, as shown by a circle C in the figure, effective contact points with the outer periphery of the finger 72 and the winding of the coil spring 81 tend to increase. Even if the frictional force at each contact point C is not so large, in other words, the component P can be stably gripped without requiring a very large gripping force. In addition, the winding of the coil spring 81 that has been pushed away and displaced in the longitudinal direction of the finger 72 as described above exerts an elastic force so as to sandwich the component P from above and below, and this also causes the gripping state to be held. Stabilize.

  That is, as described above, the contact with the winding of the coil spring 81 is geometrically or with the frictional force at the contact point C while restraining the movement of the part P in the longitudinal direction of the finger. When an external force is applied, the coil spring 81 is bent, and the contact point C with the winding is displaced in the finger longitudinal direction. For this reason, it is possible to prevent the contact state between the component P and the finger 72 (including the coil spring 81) from being changed even if an impact is applied due to interference with surrounding objects or the like, and the component P or the finger 72 caused by the impact is changed. Alternatively, damage to the robot hand 7 and the robot 1 is reduced.

  Further, in order to smoothly displace the winding of the coil spring 81 in the longitudinal direction of the finger 72 as described above, in this embodiment, the clearance between the outer periphery of the finger 72 and the winding of the coil spring 81 surrounding the finger 72 is set as described above. Therefore, it is set to an appropriate range that is not too small and not too large. That is, if the clearance is too small, the winding of the coil spring 81 is difficult to slide along the outer periphery of the finger 72. If the clearance is too large, the winding is greatly bent in the radial direction of the coil, that is, not in the longitudinal direction of the finger 72 while holding the component P, and the finger 72 including the coil spring 82 is bent. There is a problem that the existence area is apparently enlarged.

  Further, in order to suitably grip the surface of the component P by the winding of the coil spring 81 pushed away when the component P is gripped as described above, the dimension and shape of the component P, particularly the bent shape of the component surface, are used. There is a preferable relationship between the winding thickness and pitch of the coil spring 81. For example, the winding interval has a preferable range that is neither too wide nor too narrow corresponding to the convex shape of the surface of the component P.

  Therefore, it is preferable to select the thickness and pitch of the winding of the coil spring 81 according to the size and shape of the part P to be gripped, particularly the bent shape of the surface of the part, so that a gripping state suitable for the part P can be obtained. Can be realized. In other words, in this embodiment, each of the parts having various sizes and shapes can be suitably gripped simply by replacing the coil spring 81 attached to the finger 72 mainly by the size and shape of the part P to be gripped. Is something that can be done.

  Furthermore, although not shown in the figure, when the part P gripped as described above is taken out from the storage box B, the fingers 72 inserted in the four corners of the section b1 may interfere with the surrounding walls. In addition, even if there is interference with surrounding equipment or the like while the part P is being transported or when it is stored in another box, the impact caused by this is due to the bending of the coil spring 81 as described above. Since it is absorbed and relaxed, the gripping state of the component P is stable, and damage to the component P, the finger 72, and the like due to the impact is small.

  Therefore, according to the robot hand 7 according to this embodiment, the contact point C with the component P is simple in structure in which the coil spring 81 is wound around each of the four fingers 72 holding the component P, and the cost is relatively low. Can be expected to increase the anti-slip effect. Therefore, high gripping performance can be stably obtained without increasing the frictional force at these contact points.

  In addition, there is little fear that the anti-slip effect is reduced due to wear as in the knurling process, and even if the coil spring 81 sags due to long-term use, it can be easily recovered simply by replacing it.

  Furthermore, since the coil spring 81 is merely wound around the finger 72, the finger 72 itself does not become so thick. For example, when the component P is gripped like a multi-joint finger, the joint portion does not protrude outward. The robot hand 7 having four fingers 72 as a whole is difficult to increase in size and is easy to use even in a narrow environment.

-Other embodiments-
The description of the above-described embodiment is merely an example, and does not limit the present invention, its application, or its use. For example, in the above-described embodiment, the finger 72 of the robot hand 7 is configured by a straight round pipe, but this may be configured by a rod-shaped member instead of a pipe, or may be bent to some extent. I do not care. When inserted into a narrow place, straight is advantageous, but if the egg-shaped part P as described above is gripped, it may be advantageous to have a gently curved shape so as to wrap it. Basically, the tip portion may be slightly bent while having a straight shape.

  In addition, the cross-sectional shape of the finger 72 is not limited to a perfect circle, and may be an ellipse or an ellipse, or a rectangle with rounded corners. In this case, the coil spring 81 may be elliptical, oval, or rectangular so that a required clearance is provided between the outer periphery of the finger 72, particularly the gripping surface. In addition, the cross-sectional shape of the winding of the coil spring 81 is not limited to a circle, and for example, a so-called square spring having a rectangular cross-section of the winding may be used.

  Further, as shown in FIG. 5, for example, a constricted portion 72 a may be provided in the middle portion of the finger 72 in the longitudinal direction. As shown in the figure, the constricted portion 72a is formed by a smooth curved surface so that the outer diameter gradually changes over a predetermined range in the longitudinal direction of the finger 72, and the diameter is reduced most at the central portion. In this way, when gripping a relatively large component P as shown in the figure, the shape of the outer peripheral surface of the constricted portion 72a of the finger 72 is matched with the convex shape of the surface, so that both are along each other. May increase the number of contact points C.

  Further, as shown in FIG. 6, a so-called unequal pitch coil spring 84 in which the winding pitch is different in the longitudinal direction may be used. As shown in FIG. 5A, the winding pitch of the coil spring 84 is relatively narrow on the distal end side (lower end side in the figure) of the finger 72, while it is relatively wide on the proximal end side. . In the same figure (b) which shows the state which grasped comparatively small parts P in the part by the tip, the interval of the winding of the part pushed in contact with the surface of parts P has spread. Since the small part P usually has a small convex radius (curvature radius) on the surface, the one with a narrower winding pitch of the coil spring 84 is easier to grip between them.

  On the other hand, although not shown for relatively large components, the coil spring 84 can be suitably gripped at the proximal end portion of the finger 72 where the winding pitch of the coil spring 84 is large. Each of the two or more parts P having different sheath shapes can be suitably gripped. It should be noted that the thickness of the coil spring winding may be varied, for example, by narrowing the thickness where the winding pitch is narrow.

  Furthermore, as shown in FIG. 7, if a suction pad 85 is attached to the tip of the finger 72 instead of the plug 82, the component P or the like can be sucked and conveyed. The illustrated suction pad 85 has a cylindrical shaft portion 85b formed on the upper portion of a disk-like base portion 85a similar to the plug 82, and the inside thereof communicates with the inside of the finger 72 formed of a round pipe. On the other hand, a bellows-like suction cup 85c is formed below the base 85a instead of the conical part 82c. Although not shown, the lower end of the hose inserted into the finger 72 from above is connected to the shaft 85b. It can connect and negative pressure can be supplied to the suction cup part 85c.

  Further, the suction pad 85 to be mounted in this manner may be provided so as to be able to advance and retreat in the longitudinal direction of the finger 72 as shown in FIG. By doing so, the plurality of suction pads 85 that are in contact with the surface of the component P to be sucked advance and retreat, respectively, so that a suitable positional relationship along the surface shape of the component P is naturally obtained, so that the suction state becomes more stable. At this time, the coil spring 81 also functions to urge the suction pad 85 to advance.

  As described above, the finger structure of the robot hand according to the present invention is a simple structure that does not increase the cost so much that the required gripping performance and durability can be obtained, and it can be used in a narrow environment. For example, it is suitable for applications such as picking up industrial parts.

1 Robot 7 Robot Hand 72 Finger 72a Constricted Part 81 Coil Spring 82 Plug 82a Base (Receiving Part)
82c Conical part (tapered part)
P parts (objects to be gripped)

Claims (7)

A robot hand structure that grips an object with a plurality of fingers,
A finger structure for a robot hand, wherein a coil spring is wound around the outer periphery of each of the fingers, and at least the winding of the intermediate portion excluding both ends thereof can be displaced in the longitudinal direction of the fingers.   The finger structure according to claim 1, wherein at least three fingers are arranged so as to surround the object.   3. A receiving portion having an enlarged diameter so that the tip of the coil spring abuts is provided on a tip side of the finger, and a tapered portion integrally formed with the receiving portion is formed in any one of claims 1 and 2. Finger structure according to crab.   The finger structure according to any one of claims 1 to 3, wherein a clearance between the outer periphery of the finger and the inner periphery of the coil spring surrounding the finger is set within a predetermined range.   The finger structure according to any one of claims 1 to 4, wherein a constricted portion is formed at an intermediate portion in the longitudinal direction of the finger.   The finger structure according to any one of claims 1 to 5, wherein at least one of the plurality of coil springs is right-handed and at least one is left-handed.   The finger structure according to any one of claims 1 to 6, wherein the coil spring has different winding thicknesses and pitches in the longitudinal direction.

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