200936908 九、發明說明 【發明所屬之技術領域】 本發明是關於利用層積型壓電元件，構成可解除作用 於電動機輸出軸等的旋轉軸的夾緊力或制動力的夾緊裝置 【先前技術】 眾知作爲將夾緊力或制動力施加於電動機的輸出軸等 @ 的旋轉軸的夾緊裝置或制動裝置有利用依電磁鐵的磁性吸 收力的無激磁動作型磁韌等。又，在專利文獻1提案著代 替磁性吸引力而利用層積型壓電元件的伸縮，俾將夾緊力 或制動力施加於旋轉軸的制動裝置。在揭示於該專利文獻 1的制動裝置，如繪製於其第8圖至第16圖所示地，被推於 外側鼓輪的內周面的內側鼓輪的韌塊，爲當伸張層積型壓 電元件，則利用內側鼓輪的變形而從圓筒構件的內周面離 開而朝內側引拉，藉此，制動力成爲被開放。 © 專利文獻1:日本特開2004-60746號公報 【發明內容】 本發明的課題是在於提案從旋轉軸的外側利用層積型 壓電元件而在該旋轉軸可施加及解放夾緊力或制動力的小 型又精巧的夾緊裝置。 爲了解決上述課題，本發明是一種夾緊裝置，係使用 層積型壓電元件俾解除藉由可撓性筒部朝半徑方向翹曲而 -4- 200936908 作用於旋轉軸的夾緊力或制動力的夾緊裝置，其特徵爲： 上述可撓性的筒部，是在該軸線方向的後端形成有朝 半徑方向的外方擴展的安裝用凸緣，該軸線方向的前端側 部分的斷面形狀爲多角形， ' 配置有環狀部成爲圍著上述筒部的上述前端側部分的 • 狀態， 上述環狀部隨著上述層積型壓電元件的伸縮把徑擴大 φ 及縮小的方式，上述層積型壓電元件被組裝於上述環狀部 > 上述環狀部與上述筒部的上述前端側部分之間，是在 此些的周方向的至少兩處部位被連結，藉由把上述層積型 壓電元件伸張而朝外側擴展的上述環狀部，朝外側引拉著 上述筒部的上述前端側部分，使得該前端側部分的斷面形 狀從多角形變形成爲真圓或接近真圓的形狀， 上述筒部的上述前端側部分的內周面周長，是比上述 Ο 旋轉軸的圓形外周面的周長還要長。 在本發明的夾緊裝置中，把筒部的多角形斷面的前端 側部分被固定於旋轉軸的外周。亦即，旋轉軸配置成貫通 筒部的狀態，藉由圓形斷面的旋轉軸使得多角形斷面的前 端側部分被翹曲成大約圓形。結果，筒部的前端側部分的 彈性復原力對於旋轉軸的外周面形成有作用作爲夾緊力或 制動力的狀態。 在該狀態中，當將電壓施加於層積型壓電元件而伸張 該層積型壓電元件，則環狀部會擴展，而被連結於該環狀 -5- 200936908 部的前端側部分的部位也朝外側被引拉，把該前端側部分 變形成真圓或接近於真圓的形狀。該前端側部分的內周面 的周長是比旋轉軸的圓形外周面的周長還長之故，因而當 該前端側部分變形成真圓或接近於真圓的狀態，則該前端 側部分與旋轉軸的機械性卡合狀態實質上被解除，而被施 ^ 加於旋轉軸的夾緊力或制動力被解除。該結果，旋轉軸被 ' 切換成旋轉自如的狀態。 當解除對於層積型壓電元件的電壓施加，則環狀部縮 0 小於內側而將筒部的前端側部分朝外側引拉的拉力被解除 。該結果，該筒部的前端側部分欲復原成多角形斷面的彈 性復原力恢復成再作用於旋轉構件的外周面的夾緊狀態或 制動狀態。 在此，將上述筒部的前端側部分的斷面形狀作爲正多 角形，對於旋轉軸的外周面從外側均等地施加夾緊力或制 動力較佳。此時，上述環狀部是對應於上述正多角形的角 數的個數的上述層積型壓電元件與連結片交互地沿著周方 〇 向被連結，而被設定成各層積型壓電元件的伸縮方向成爲 該環狀部的周方向較佳。又，各連結片分別被連結於上述 筒部的上述前端側部分的正多角形的角間的部位就可以。 又，將圓形斷面的內筒以翹曲成多角形斷面的狀態嵌 入於上述筒部的上述前端側部分的內側，而將旋轉軸貫通 於該內側也可以。在該情形，將上述內筒的內周面的周長 作成比上述旋轉軸的圓形外周面的周長還要長就可以。 在本發明的夾緊裝置中，藉由將旋轉軸貫穿於事先形 -6 - 200936908 成於多角形斷面的筒部的前端側部分，或是藉由將旋轉軸 貫穿於嵌入在筒部的前端側部分內側的內筒，俾將該前端 側部分強制地翹曲成爲圓形於半徑方向的外側，藉由此， 發生對於旋轉軸的夾緊力或制動力。又，當伸張層積型壓 電元件，則配置於圍著前端側部分的狀態的環狀部朝外側 ' 擴展，使得前端側部分朝外方被引拉，而對於旋轉軸的夾 緊力或制動力被開放或減低。 φ 在本發明的夾緊裝置中，嵌入於旋轉軸的筒部（或是 筒部及內筒），及配置成圍著該筒部的狀態的層積型壓電 元件所組裝的環狀部僅配置於旋轉軸外周側就可以。又， 環狀部是配置於用以將筒部固定於固定構件側的安裝用凸 緣的外徑尺寸內的部位就可以，因此旋轉軸的徑向的佔有 空間也可以較少。因此，可實現小型又精巧的構成的夾緊 裝置。 Ο 【實施方式】 以下，參照圖式，將適用本發明的夾緊裝置的實施形 態加以說明。 第1圖是表示本實施形態的夾緊裝置的主要部分的槪 略立體圖，表示其夾緊狀態。第2圖是表示其槪略俯視圖 ，第3圖是表示其槪略斷面圖。參照此些圖式加以說明， 夾緊裝置1是具有被固定於夾緊對象的旋轉軸2的圓形外周 面2a的大孔帽狀的金屬製制動環3。制動環3是具備：朝半 徑方向可翹曲的筒部4，及從該筒部4的後端開口緣4a朝半 200936908 徑方向外方擴展的圓盤狀安裝用凸緣部5’及配置成圍著 筒部4的前端開口緣4b側的外周的狀態的環狀部6。 在此，第5圖是表示安裝於旋轉軸2之前的保護環3的 槪略俯視圖。如該圖所不地’筒部4是後端開口緣4 a側被 視作爲圓形斷面，而前端側部分4(：是作爲整體被視作爲正 四方形斷面，而在該四個各角部分4d具圓弧狀。又，從筒 部4的圓形斷面的後端開口緣4a到正四方斷面的前端側部 分4c之間的部位，是斷面形狀徐徐地從圓形移行至正四方 0 形。筒部4的周長是被設定成對旋轉軸2的圓形外周面2 a的 周長還要稍長。 因此，如第2圖所示地，在將旋轉軸2嵌入於筒部4的 狀態下，筒部4的前端側部分4c藉由旋轉軸2的圓形外周面 2a被彈性變形成接近真圓的狀態，而在該前端側部分4c的 4個角部分4d稍留下間隙的狀態下，使得該前端側部分4c 被推向旋轉軸2的圓形外周面2a。結果，在旋轉軸2藉由該 前端側部分4c形成有施加所定夾緊力或制動力的夾緊狀態 © 〇 之後，連續於該形狀的筒部4的後端開口'緣4a的安裝 用凸緣部5 ’是沿著該外周緣部分以一定角度間隔形成有 螺孔5a。如第3圖所示地，藉由固定螺絲7，該安裝用凸緣 部5是被固定在固定側的構件8。 環狀部6是配置成同軸狀態地圍著筒部4的正四方斷面 的前端側部分4c。環狀部6是具備：形成細長長方體形狀 的4個層積型壓電元件11，及夾住此些4個層積型壓電元件 -8- 200936908 11，而被連續於周方向的4個金屬製的連結片12。各連結 片12是同一形狀者，具備：彎曲成大約90度的一定厚度的 圓弧部分12a，及從該圓弧部分12a的內周面中央朝圓弧中 心延伸的胳膊部分12b。該胳膊部分12b的前端（內端）爲 連結或連結於筒部4的前端部分4c的4個角部分4d的中間位 置。 在此，層積型壓電元件11是朝環狀部6的周方向伸縮 ❹ 。當將電壓施加於各層積型壓電元件11，則各層積型壓電 元件1 1伸張，使得環狀部6作爲整體朝外側擴展。亦即， 夾著各層積型壓電元件11而連結著各連結片12之故，因而 當層積型壓電元件11伸張，則僅對應於伸張量的合計分量 會擴展環狀部6的直徑。 第4圖是表示將電壓施加於各層積型壓電元件U而予 以伸張的狀態，當層積型壓電元件1 1伸張，則環狀部6作 爲整體而朝外側擴展，而該構成零件的各連結片1 2朝半徑 G 方向的外方稍微移動。結果，被連結或一體化於各連結片 12的筒部4的正四方形的前端側部分4c的各角部分4d之間 的部位朝外側被引拉而會彈性變形。藉此，正四方形的前 端側部分4c是作爲整體被翹曲成大約真圓的狀態。前端側 部分4c的內周面周長，是比旋轉軸2的圓形外周面2a的周 長還要稍大。因此，被翹曲成圓的前端側部分4(；與旋轉軸 2的圓形外周面2a之間的機械性卡合爲實質上被解除，使 得從前端側部分4c作用於旋轉軸2的夾緊力或制動力實晳 上成爲零的鬆開狀態。 -9 - 200936908 如此地，在夾緊裝置中，在各層積型壓電元件11未施 加電壓的狀態，藉由旋轉軸2被翹曲的筒部4的前端側部分 4c位在作用著夾緊力或制動力於旋轉軸2的夾緊狀態。當 將電壓施加於各層積型壓電元件11，而伸張此些時，則環 狀部6作爲整體而擴展，使得被連結於此的前端側部分4c ' 朝外側被引拉而被彈性變形成大約真圓。結果，前端側部 · 分4c與旋轉軸2的機械性卡合被解除，而被切換成作用於 旋轉軸2夾緊力或制動力被解除鬆開狀態。 @ (其他的實施形態） 在上述的例子中，將筒部4的前端側部分4c形成正四 方形，惟當然也可作成正六方形、正八方形等的正多方形 。在該情形，若夾著對應於角數的個數的層積型壓電元件 11來構成環狀部6，則欲將層積型壓電元件予以伸張時， 就可將正多角形的前端側部分4c容易地變形成真圓。 又，代替將制動環3的筒部4的前端側部分4c直接地抵 〇 接於旋轉軸2的圓形外周面2a，而將圓形斷面的可撓性內 筒嵌入於該前端側部分4c的內側，俾將該內筒抵接於旋轉 軸2也可以。在該情形，內筒功能作爲制動環，使得圓形 斷面的內筒被嵌入在正四方形斷面的筒部4的前端側部分 4c內而被翹曲成正四方形狀，在該狀態的內筒內貫通旋轉 軸2就可以。 【圖式簡單說明】 -10- 200936908 第1圖是表示適用本發明的夾緊裝置的主要部分的槪 略立體圖，表示該夾緊狀態。 第2圖是表示第1圖的夾緊裝置的槪略俯視圖。 弟3圖是表示第1圖的夾緊裝置的槪略斷面圖。 第4圖是表示第1圖的夾緊裝置的鬆開狀態的槪略俯視 ' 圖。 第5圖是表示第1圖的夾緊裝置的制動環初期形狀的俯 ❹ 視圖。 【主要元件符號說明】 1 :夾緊裝置 2 :旋轉軸 2 a :圓形外周面 3 :制動環 4 ’·筒部 4a :後端開口緣 4b :前端開口緣 4c :前端側部分 4d :角部分 5 :安裝用凸緣部 5a :螺孔 6 :環狀部 7 :固定螺絲 8 :固定側構件 -11 - 200936908 1 1 :層積型壓電元件 1 2 :連結片 1 2 a :圓弧部分 12b :胳膊部分200936908 IX. EMBODIMENT OF THE INVENTION [Technical Field] The present invention relates to a clamping device that can eliminate a clamping force or a braking force acting on a rotating shaft of a motor output shaft or the like by using a laminated piezoelectric element. It is known that a clamping device or a brake device that applies a clamping force or a braking force to a rotating shaft of an output shaft of a motor or the like has a non-exciting type magnetic toughness or the like that utilizes a magnetic absorbing force of an electromagnet. Further, Patent Document 1 proposes to apply a clamping force or a braking force to a braking device of a rotating shaft by using the expansion/contraction of the laminated piezoelectric element instead of the magnetic attraction force. In the brake device disclosed in Patent Document 1, as shown in FIGS. 8 to 16 , the tough mass of the inner drum pushed to the inner circumferential surface of the outer drum is a stretched laminate type. The piezoelectric element is separated from the inner circumferential surface of the cylindrical member by the deformation of the inner drum, and is pulled inward, whereby the braking force is opened. [Patent Document 1] JP-A-2004-60746 SUMMARY OF THE INVENTION An object of the present invention is to provide a laminated piezoelectric element from the outside of a rotating shaft, and to apply and release a clamping force or the like on the rotating shaft. Powerful small and compact clamping device. In order to solve the above problems, the present invention is a clamping device that uses a laminated piezoelectric element to release a clamping force acting on a rotating shaft by a flexible cylindrical portion that is warped in a radial direction. In the power-clamping device, the flexible tubular portion is formed with a mounting flange that expands outward in the radial direction at the rear end in the axial direction, and the distal end side portion in the axial direction is broken. The surface shape is a polygonal shape, and the annular portion is disposed so as to surround the distal end side portion of the tubular portion, and the annular portion is enlarged and reduced in accordance with the expansion and contraction diameter of the laminated piezoelectric element. The laminated piezoelectric element is assembled to the annular portion. Between the annular portion and the distal end portion of the tubular portion, at least two locations in the circumferential direction are connected by The annular portion extending outwardly of the laminated piezoelectric element and extending outwardly pulls the distal end side portion of the tubular portion outward so that the cross-sectional shape of the distal end side portion is deformed from a polygonal shape to a true circle or Close Rounded shape, the inner circumferential surface of the distal end side portion of the circumference of the cylindrical portion, a circumference of the circular outer peripheral surface of the rotary shaft than the Ο much longer. In the clamp device of the present invention, the front end side portion of the polygonal cross section of the tubular portion is fixed to the outer circumference of the rotary shaft. That is, the rotating shaft is disposed in a state of penetrating the cylindrical portion, and the front end side portion of the polygonal cross section is warped to be approximately circular by the rotation axis of the circular cross section. As a result, the elastic restoring force of the front end side portion of the tubular portion forms a state in which the outer peripheral surface of the rotating shaft acts as a clamping force or a motive force. In this state, when a voltage is applied to the laminated piezoelectric element to stretch the laminated piezoelectric element, the annular portion expands and is coupled to the front end side portion of the annular-5-200936908 portion. The portion is also pulled toward the outside, and the front end side portion is deformed into a true circle or a shape close to a true circle. The circumference of the inner peripheral surface of the front end side portion is longer than the circumference of the circular outer peripheral surface of the rotating shaft, and thus the front end side is formed when the front end side portion is deformed into a true circle or a state close to a true circle. The mechanically engaged state of the portion and the rotating shaft is substantially released, and the clamping force or the braking force applied to the rotating shaft is released. As a result, the rotation axis is switched to a state in which it is rotatable. When the voltage application to the laminated piezoelectric element is released, the pulling force at which the annular portion is smaller than the inner side and the distal end portion of the tubular portion is pulled outward is released. As a result, the elastic restoring force of the front end side portion of the tubular portion to be restored to the polygonal cross section is restored to the clamped state or the braked state that acts on the outer peripheral surface of the rotating member. Here, the cross-sectional shape of the distal end side portion of the tubular portion is a regular polygonal shape, and it is preferable to uniformly apply a clamping force or a motive force to the outer peripheral surface of the rotating shaft from the outside. In this case, the annular portion is such that the number of the number of the angles of the regular polygonal shape is connected to the connecting piece in the circumferential direction, and is set to each laminated type. The direction in which the electric component expands and contracts is preferably the circumferential direction of the annular portion. Further, each of the connecting pieces may be connected to a portion between the corners of the regular polygonal shape of the distal end side portion of the tubular portion. Further, the inner cylinder having a circular cross section may be fitted inside the front end side portion of the tubular portion in a state of being warped into a polygonal cross section, and the rotation shaft may be inserted through the inner side. In this case, the circumferential length of the inner circumferential surface of the inner cylinder may be longer than the circumferential length of the circular outer circumferential surface of the rotating shaft. In the clamp device of the present invention, the rotary shaft is inserted through the front end side portion of the cylindrical portion of the polygonal cross section through the pre-form -6 - 200936908, or the rotary shaft is inserted through the tubular portion. The inner cylinder on the inner side of the front end side portion forcibly warps the front end side portion to be circularly outward in the radial direction, whereby a clamping force or a braking force with respect to the rotating shaft occurs. Further, when the laminated piezoelectric element is stretched, the annular portion disposed in the state surrounding the distal end side portion is expanded outward so that the distal end side portion is pulled outward, and the clamping force for the rotating shaft or The braking force is opened or reduced. φ In the clamp device of the present invention, the tubular portion (or the tubular portion and the inner cylinder) that is fitted into the rotating shaft, and the annular portion that is assembled by the laminated piezoelectric element that is disposed around the tubular portion It can be placed only on the outer circumference side of the rotary shaft. Further, the annular portion may be disposed in a portion for fixing the tubular portion to the outer diameter of the mounting flange on the side of the fixing member. Therefore, the space occupied by the radial direction of the rotating shaft may be small. Therefore, a small and compact clamping device can be realized. [Embodiment] Hereinafter, an embodiment of a clamp device to which the present invention is applied will be described with reference to the drawings. Fig. 1 is a schematic perspective view showing the main part of the clamp device of the embodiment, showing the clamped state. Fig. 2 is a schematic plan view showing a schematic view thereof, and Fig. 3 is a schematic cross-sectional view showing the same. Referring to the drawings, the clamp device 1 is a metal-shaped brake ring 3 having a large-hole cap shape that is fixed to the circular outer peripheral surface 2a of the rotary shaft 2 to be clamped. The brake ring 3 includes a tubular portion 4 that is warped in the radial direction, and a disk-shaped mounting flange portion 5' that extends outward from the rear end opening edge 4a of the tubular portion 4 in the radial direction of the semi-200936908. The annular portion 6 in a state in which the outer periphery of the front end opening edge 4b side of the tubular portion 4 is formed. Here, Fig. 5 is a schematic plan view showing the guard ring 3 before being attached to the rotary shaft 2. As shown in the figure, the tubular portion 4 is a rear end opening edge 4a side which is regarded as a circular cross section, and the front end side portion 4 (: is regarded as a square cross section as a whole, and in each of the four The corner portion 4d has an arc shape. Further, a portion from the rear end opening edge 4a of the circular cross section of the tubular portion 4 to the front end side portion 4c of the regular square cross section is a cross-sectional shape that gradually moves from the circular shape. The circumference of the tubular portion 4 is set to be slightly longer than the circumference of the circular outer peripheral surface 2 a of the rotating shaft 2. Therefore, as shown in Fig. 2, the rotating shaft 2 is In the state of being embedded in the tubular portion 4, the distal end side portion 4c of the tubular portion 4 is elastically deformed to a state close to a true circle by the circular outer peripheral surface 2a of the rotary shaft 2, and at the four corner portions of the distal end side portion 4c. In the state in which the gap is slightly left, the front end side portion 4c is pushed toward the circular outer peripheral surface 2a of the rotary shaft 2. As a result, the rotary shaft 2 is formed with the predetermined clamping force or the system by the front end side portion 4c. After the clamping state of the power ©, the mounting flange portion 5' of the rear end opening 'edge 4a of the cylindrical portion 4 of the shape is continuous along the outer The rim portion is formed with a screw hole 5a at an angular interval. As shown in Fig. 3, the mounting flange portion 5 is a member 8 fixed to the fixed side by a fixing screw 7. The annular portion 6 is configured The front end side portion 4c of the regular square cross section of the tubular portion 4 is coaxially arranged. The annular portion 6 is provided with four laminated piezoelectric elements 11 having an elongated rectangular parallelepiped shape, and sandwiching the four laminated layers The piezoelectric element -8-200936908 11 is connected to four metal connecting pieces 12 in the circumferential direction. Each of the connecting pieces 12 has the same shape, and has a circular arc portion 12a bent to a certain thickness of about 90 degrees. And an arm portion 12b extending from the center of the inner peripheral surface of the circular arc portion 12a toward the center of the circular arc. The front end (inner end) of the arm portion 12b is connected or joined to the four corner portions of the front end portion 4c of the tubular portion 4. Here, the laminated piezoelectric element 11 is expanded and contracted toward the circumferential direction of the annular portion 6. When a voltage is applied to each of the laminated piezoelectric elements 11, the laminated piezoelectric elements 1 1 are stretched. So that the annular portion 6 as a whole expands outward, that is, sandwiches each layer type Since the electric component 11 is connected to each of the connecting pieces 12, when the laminated piezoelectric element 11 is stretched, only the total component corresponding to the amount of stretching expands the diameter of the annular portion 6. Fig. 4 is a view showing application of a voltage. In a state where the laminated piezoelectric element U is stretched, when the laminated piezoelectric element 1 1 is stretched, the annular portion 6 is expanded outward as a whole, and the respective connecting pieces 1 2 of the constituent parts face the radius G As a result, the outer side of the direction slightly moves. As a result, the portion between the corner portions 4d of the square front end side portion 4c of the tubular portion 4 that is connected or integrated with each of the connecting pieces 12 is pulled outward and elastically deformed. Thereby, the front end side portion 4c of the square shape is warped as a whole in a state of approximately true circle. The circumferential length of the inner peripheral surface of the distal end side portion 4c is slightly larger than the circumferential length of the circular outer peripheral surface 2a of the rotary shaft 2. Therefore, the mechanical engagement between the front end side portion 4 that is warped into a circle (the circular outer peripheral surface 2a of the rotary shaft 2) is substantially released, so that the front end side portion 4c acts on the clamp of the rotary shaft 2 In the clamping device, in the state in which the voltage is not applied to each of the laminated piezoelectric elements 11, the rotation shaft 2 is warped in the clamping device. The front end side portion 4c of the tubular portion 4 is in a clamped state in which a clamping force or a braking force acts on the rotary shaft 2. When a voltage is applied to each of the laminated piezoelectric elements 11, and the extension is performed, the ring is annular. The portion 6 is expanded as a whole, so that the front end side portion 4c' joined thereto is pulled outward to be elastically deformed into a substantially true circle. As a result, the mechanical engagement between the front end side portion 4c and the rotary shaft 2 is When it is released, it is switched to the clamping force acting on the rotating shaft 2 or the braking force is released. @ (Other embodiment) In the above example, the front end side portion 4c of the tubular portion 4 is formed into a square shape, Of course, it can also be made into a positive square with a square, a square, etc. In this case, when the annular portion 6 is formed by sandwiching the laminated piezoelectric element 11 corresponding to the number of corners, the front end of the regular polygon can be formed when the laminated piezoelectric element is to be stretched. The side portion 4c is easily deformed into a true circle. Further, instead of directly contacting the front end side portion 4c of the tubular portion 4 of the brake ring 3 to the circular outer peripheral surface 2a of the rotary shaft 2, the circular cross section can be The flexible inner cylinder is fitted inside the front end side portion 4c, and the inner cylinder may be abutted against the rotating shaft 2. In this case, the inner cylinder functions as a brake ring so that the inner cylinder of the circular cross section is embedded in The front end side portion 4c of the tubular portion 4 having a square cross section is warped into a square shape, and the rotating shaft 2 can be passed through the inner cylinder in this state. [Simplified Explanation] -10-200936908 Fig. 1 A schematic perspective view showing a main portion of a clamp device to which the present invention is applied, showing the clamped state. Fig. 2 is a schematic plan view showing the clamp device of Fig. 1. Fig. 3 is a view showing the clamp of Fig. 1. A schematic cross-sectional view of the device. Fig. 4 is a view showing the released state of the clamping device of Fig. 1. Fig. 5 is a top view showing the initial shape of the brake ring of the clamp device of Fig. 1. [Description of main components] 1 : Clamping device 2: Rotary shaft 2 a : Circular outer peripheral surface 3: brake ring 4'·tubular portion 4a: rear end opening edge 4b: front end opening edge 4c: front end side portion 4d: corner portion 5: mounting flange portion 5a: screw hole 6: annular portion 7: fixing screw 8 : fixed side member-11 - 200936908 1 1 : laminated piezoelectric element 1 2 : connecting piece 1 2 a : circular arc portion 12b: arm portion
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