JP3126690U

JP3126690U - Work mounting jig

Info

Publication number: JP3126690U
Application number: JP2006006916U
Authority: JP
Inventors: 正弘村松
Original assignee: 有限会社村松研磨工業
Priority date: 2006-08-25
Filing date: 2006-08-25
Publication date: 2006-11-02
Anticipated expiration: 2016-08-25

Abstract

【課題】特定の円筒状のワークについて、ワーク自体を回転させることなく、垂直方向にワークを吊るした場合にも落下することなく、さらに手軽にワークを固定することができる治具を提供すること。
【解決手段】円筒形状であり、かつ円筒形状の直径上の両端からに突出しているアームを有し、そのアームに孔を有する特定形状のワークについて、ワークの円筒部に治具本体の一部を挿入すると共に、突出部の孔を利用し、その孔に落下防止のためのボルトを挿入してなる治具の提供。
【選択図】図６PROBLEM TO BE SOLVED: To provide a jig capable of fixing a work more easily without rotating the work itself and dropping it even when the work is hung in the vertical direction with respect to a specific cylindrical work. .
A part of a jig body is formed on a cylindrical part of a workpiece having a cylindrical shape and having a projecting arm from both ends on the diameter of the cylindrical shape and having a hole in the arm. And a jig formed by inserting a bolt for preventing falling into the hole using the hole of the protruding portion.
[Selection] Figure 6

Description

本考案は、円筒状ワークの治具であって、特にバレル研磨等ワークに強い負荷がかかる場合に使用する治具に関する。 The present invention relates to a jig for a cylindrical workpiece, and particularly to a jig used when a heavy load is applied to a workpiece such as barrel polishing.

自動二輪車や自動車に使用される円筒状の部品例えばアウターチューブ等はその円筒状の半製品に穿孔、バリ取り、研磨作業等を施して完成品となるが、このような作業では、この円筒状のワークを治具に保持して行われる。これらの治具は、ボルト等を使用してワークを治具に締め付け固定することが一般的である。また、円筒状であることを利用して、円筒の内周面にフィンガーを圧接し固定する方法もある。前者での先行技術としては、穿孔やバリ取り等の複数の作業をするための治具として、径の異なる多種類の円筒形ワークを単一の治具で保持しうるようにしたもの（特許文献１）や旋盤加工時においてワークの外周より大きい内周を持つ円管の内部に複数の溝を設け内部のワークをねじで締め付けるもの（特許文献２）等が報告されている。また後者の先行技術文献としては、円筒形であることを利用してチャック機構により複数のフィンガーを内周面に圧接するもの（特許文献３）や円筒状ワークの内周面に風船体で圧接しワークと治具を固定するもの（特許文献４）等がある。 Cylindrical parts used in motorcycles and automobiles, such as outer tubes, are finished products by drilling, deburring, polishing, etc. in the cylindrical semi-finished product. This is done by holding the workpiece in a jig. In general, these jigs are fastened and fixed to a jig by using bolts or the like. Further, there is a method in which a finger is pressed against and fixed to the inner peripheral surface of the cylinder by utilizing the cylindrical shape. As the prior art in the former, as a jig for performing a plurality of operations such as drilling and deburring, a plurality of types of cylindrical workpieces having different diameters can be held by a single jig (patent Document 1) and the one in which a plurality of grooves are provided inside a circular pipe having an inner periphery larger than the outer periphery of the workpiece during lathe machining and the inner workpiece is tightened with screws (Patent Document 2) have been reported. Further, as the latter prior art document, a cylindrical mechanism is used to press a plurality of fingers against the inner peripheral surface by a chuck mechanism (Patent Document 3), or a cylindrical body is press-contacted with a balloon body. There is one that fixes the workpiece and the jig (Patent Document 4).

特許公開２０００−２１８４５４Patent Publication 2000-218454 実用新案公開平６−５８３５Utility model open hei 6-5835 特許公開平９−７７４５７Patent Publication 9-77457 特許公開平８−２８２９６４Patent Publication 8-282964

しかし、ボルト等を利用して治具とワークを締め付け固定する方法では、ワークごとにその作業をしなければならず手間がかかり、量産品では不向きである。またチャック機構等によるものでは、治具の構造が複雑でありコスト高となる。
また、バレル研磨等の作業ではワークに大きな負荷がかかり、ワークは治具と水平の位置だけでなく、治具に吊り下げられる状態にもなり治具とワークは強い締結力を必要とし前述のような治具では締結力の強度が不十分の場合もある。また、バレル研磨等では、ワークが円筒状の場合にはワークが治具に固定されにくく、ワークが研磨材と一緒に回転してしまい研磨に時間がかかるという問題点もある。 However, the method of tightening and fixing the jig and work using bolts or the like requires work for each work, which is not suitable for mass-produced products. Further, in the case of using a chuck mechanism or the like, the structure of the jig is complicated and the cost is increased.
Also, in the work such as barrel polishing, a large load is applied to the work, and the work is not only in a horizontal position with the jig, but is also suspended from the jig, and the jig and the work require a strong fastening force. In such a jig, the strength of the fastening force may be insufficient. Further, in barrel polishing or the like, when the workpiece is cylindrical, the workpiece is difficult to be fixed to the jig, and there is a problem that the workpiece rotates together with the abrasive and takes time for polishing.

解決しようとする問題点は、バレル研磨等の作業において、ワークを簡単な操作で取り付けることができる治具を提供し、さらにその治具を安価なものにすることにある。 A problem to be solved is to provide a jig capable of attaching a workpiece by a simple operation in an operation such as barrel polishing, and to make the jig inexpensive.

本考案は、ワークの形状を利用して、以下のような治具を提供するものである。 The present invention provides the following jigs using the shape of a workpiece.

すなわち、請求項１の考案は、円筒部を有し、かつ、円筒部の直径上の両端の外周壁より円筒部の延長線方向に沿って同じ長さの２つの突出部を有し、該突出部が円筒部より長く、該突出部には孔があいているワークにおいて、このワークの円筒部内に挿入し、かつ該突出部の長さに対応した長さを有する円柱状の治具本体と、該治具本体に、該治具本体の軸心と直交し、かつ、該突出部の側面の一方向から固定する留金をつけ、その留金の両端には該突出部の孔に嵌合する凸部を設け、ワークの円筒部への挿入と、留金の該突出部の側面からの固定と、該突出部の孔に嵌合する該留金の凸部とによりワークを固定する治具である。
請求項２の考案は、前記突出部の長さに対応させた治具本体において、突出部の孔の高さの位置に治具本体の直径方向に穿設して孔を貫通させ、その孔にスプリングとねじ溝をつけた丸棒とを挿入し、該丸棒延長上の一方にスライドコマ、ナット及び取手をつけ、丸棒の他の延長上に、留金及び留金を固定するナットをつけ留金の両端には、該突出部の孔と嵌合する大きさのボルトをつけ、スプリングの付勢により留金と治具本体の間に該突出部を挟みワークと治具を固定することを特徴とする請求項１の治具である。
請求項３の考案は、治具本体の前記孔を貫通する位置に留金、スライドコマを固定させるために、治具本体の軸心と直交し、かつ、留金及びスライドコマの大きさに合わせて治具本体の外周に互いに向き合う横溝を設けた治具本体を有する請求項２の治具である。
請求項４の考案は、複数のアームにより構成された治具取付アームに治具を取り付けるために、治具本体のワーク円筒部の挿入部とは反対側の頭部にねじ孔を設けた治具本体を有する請求項１ないし請求項３の治具である。
請求項５の考案は、複数のアームにより構成された治具取付アームの両端に請求項１ないし請求項４の治具をつけた複合治具である。 That is, the device of claim 1 has a cylindrical portion, and has two projecting portions having the same length along the extending line direction of the cylindrical portion from the outer peripheral walls at both ends on the diameter of the cylindrical portion, A columnar jig body that is inserted into the cylindrical portion of the workpiece and has a length corresponding to the length of the protruding portion in a workpiece having a protruding portion longer than the cylindrical portion and a hole in the protruding portion. A clasp that is orthogonal to the axis of the jig body and is fixed from one side surface of the projecting portion is attached to the jig body, and holes on the projecting portion are formed at both ends of the clasp. A convex part to be fitted is provided, and the work is fixed by inserting the work piece into the cylindrical part, fixing the clasp from the side surface of the projecting part, and the convex part of the clasp fitting into the hole of the projecting part. It is a jig to do.
The invention according to claim 2 is a jig main body corresponding to the length of the protruding portion, wherein the hole is drilled in the diameter direction of the jig main body at the height of the hole of the protruding portion, and the hole Insert a spring and a round bar with a thread groove into it, attach a slide piece, nut and handle on one side of the round bar extension, and fix the clasp and clasp on the other extension of the round bar At the both ends of the clasp, attach bolts of a size that fits into the holes in the protrusion, and the work and jig are fixed by sandwiching the protrusion between the clasp and the jig body by the spring force. The jig according to claim 1, wherein:
In order to fix the clasp and the slide piece at a position penetrating the hole of the jig main body, the invention of claim 3 is perpendicular to the axis of the jig main body and has a size of the clasp and the slide piece. The jig according to claim 2, further comprising a jig body provided with lateral grooves facing each other on the outer periphery of the jig body.
The invention of claim 4 is a jig in which a screw hole is provided in the head opposite to the insertion part of the work cylinder part of the jig body in order to attach the jig to the jig mounting arm constituted by a plurality of arms. 4. The jig according to claim 1, further comprising a tool body.
The invention of claim 5 is a composite jig in which the jigs of claims 1 to 4 are attached to both ends of a jig mounting arm constituted by a plurality of arms.

本考案の請求項１の考案は、円筒状の特定形状のワークにおいて、その形状を利用した治具を提供するものである。請求項２の考案は、治具本体に孔を貫通させ、その孔にスプリング等をつけさらに留金を設けることによりワークの取り付けを確実にすることができる治具を提供するものである。請求項３の考案は、ワークの把持をより確実にしてワークの回転を防ぐ治具を提供するものである。請求項４の考案は、複合治具を作製するためのものであり、請求項５の考案は、上記治具を用いてバレル研磨等を効率的にできる複合治具を提供するものである。 The invention of claim 1 of the present invention provides a jig utilizing a shape of a cylindrical workpiece having a specific shape. The invention of claim 2 is to provide a jig capable of ensuring the attachment of the workpiece by passing a hole through the jig body, attaching a spring or the like to the hole, and further providing a clasp. The invention of claim 3 provides a jig for more reliably holding the workpiece and preventing the rotation of the workpiece. The invention of claim 4 is for producing a composite jig, and the invention of claim 5 is to provide a composite jig that can efficiently perform barrel polishing using the jig.

本考案の実施例を以下に示す。 Examples of the present invention are shown below.

図１は、本考案の治具本体１の図である。本治具本体には横溝７が設けられている。図５に示すワーク１３の形状にあわせ、ワーク円筒部１６への挿入部１１及びワーク突出部１４とその孔１５及び取付アームへの締結ねじ溝部の高さに合わせ治具本体１を加工する。ワーク円筒部１６には、切削油や水が入っているため、ワーク円筒部への挿入部１１の径は、ワーク円筒部１６の径より約０．２ｍｍ細くして切削油や水をワーク円筒部より排出し易くしている。さらにワーク円筒部１６への挿入部１１は、図１のように挿入部の上部と下部にはその径に段差をつけてワーク円筒部に挿入しやすくするとともに切削油や水をワーク円筒部１６内に溜めておくこともできるようにしている。取付アームへの締結ねじ溝部９のある治具本体１の頭部の径は、図１のようにワーク円筒部への挿入部１１の径より太くし、取付アームへの締結ねじ溝部９を設けている。治具本体１のワーク円筒部１６へのワーク円筒部への挿入部１１をワークの円筒部１６に挿入した状態において、ワークの突出部の孔１５の高さにあわせ治具本体１に横溝７が設けられている。横溝の中央には治具本体の直径方向に貫通孔１０が設けられている。横溝７は留金２やスライドコマ５の寸法に合わせてその巾が決められる。図１の（１）は治具本体１の正面図であり、（２）は側面図である。
なお治具本体とは、ワークの円筒部内に挿入し、かつ該突出部の長さに対応した長さを有する円柱状のものをいうだけでなく、その径が円柱状の箇所により異なり段差があり、これに貫通孔１０や横溝７さらには取付アームへの締結ねじ溝部９等の加工を施したものも治具本体というものとする。 FIG. 1 is a diagram of a jig body 1 of the present invention. A lateral groove 7 is provided in the jig body. In accordance with the shape of the workpiece 13 shown in FIG. 5, the jig body 1 is machined according to the height of the insertion portion 11 and the workpiece protrusion 14, the hole 15, and the fastening screw groove to the mounting arm. Since the work cylinder portion 16 contains cutting oil and water, the diameter of the insertion portion 11 to the work cylinder portion is made approximately 0.2 mm thinner than the diameter of the work cylinder portion 16 so that the cutting oil and water are supplied to the work cylinder. It is easy to discharge from the part. Further, as shown in FIG. 1, the insertion portion 11 to the workpiece cylindrical portion 16 has a step in the diameter between the upper and lower portions of the insertion portion to facilitate insertion into the workpiece cylindrical portion, and at the same time, cutting oil or water is supplied to the workpiece cylindrical portion 16. It can also be stored inside. The diameter of the head of the jig body 1 having the fastening screw groove 9 to the mounting arm is made larger than the diameter of the insertion portion 11 to the work cylinder as shown in FIG. 1, and the fastening screw groove 9 to the mounting arm is provided. ing. In the state where the insertion portion 11 of the jig main body 1 to the work cylindrical portion 16 is inserted into the cylindrical portion 16 of the workpiece, the lateral groove 7 is formed in the jig main body 1 according to the height of the hole 15 of the protruding portion of the workpiece. Is provided. A through hole 10 is provided in the center of the lateral groove in the diameter direction of the jig body. The width of the lateral groove 7 is determined according to the dimensions of the clasp 2 and the slide piece 5. (1) of FIG. 1 is a front view of the jig body 1, and (2) is a side view.
The jig body is not only a columnar one that is inserted into the cylindrical portion of the workpiece and has a length corresponding to the length of the protruding portion, but also has a step that differs depending on the cylindrical portion. There is also a jig body that is processed with the through-hole 10, the lateral groove 7, and further the fastening screw groove 9 to the mounting arm.

図２は治具本体につける留金等の部品図である。ねじ溝をつけた丸棒３は治具本体の貫通孔１０に挿入されるものであり、貫通孔の径に合わせてその径が決められる。スプリング８は、その中にねじ孔をつけた丸棒３をとおして、貫通孔に挿入され、貫通孔の留金２とスライドコマ５により貫通孔に固定される。ねじ溝をつけた丸棒３は治具本体１を挟んで一方の側にはスライドコマ５とスライドコマを固定するナット６（図３のようにダブルナットとする場合もある。）及び取手４がつけられている。スライドコマ５、ナット６及び取手４にはその中心孔にはねじ溝があり、ねじ溝をつけた丸棒３と嵌合させている。 FIG. 2 is a component diagram such as a clasp attached to the jig body. The round bar 3 with a thread groove is inserted into the through hole 10 of the jig body, and its diameter is determined according to the diameter of the through hole. The spring 8 is inserted into the through hole through the round bar 3 having a screw hole therein, and is fixed to the through hole by the clasp 2 and the slide piece 5 of the through hole. The round bar 3 with a thread groove has a slide piece 5 and a nut 6 for fixing the slide piece on one side of the jig body 1 (a double nut may be used as shown in FIG. 3) and a handle 4. Is attached. The slide piece 5, the nut 6 and the handle 4 have a threaded groove in the center hole, and are fitted to the round bar 3 with the threaded groove.

留金２は、その中央には留金２の中心孔２２があり、ねじ溝をつけた丸棒３が通されナット６によって固定されている。留金２は、ワークの突出部の孔１５の間隔によりその長さが決められ、留金の両端には孔が開けられ、留金につけたボルト２１が取り付けられている。図２の（１）は留金の治具本体と反対側の面を示し、図２の（２）は治具本体側の面を示している。図２の（３）に示すように留金につけたボルト２１のねじ部分は、ワークの突出部の孔１５に挿入され治具からワークが脱落しないようにしている。また留金２はバレル研磨等の作業時にワーク自体が回転しないようにする役割も果たしている。 The clasp 2 has a central hole 22 of the clasp 2 in the center thereof, and a round bar 3 having a thread groove is passed through and fixed by a nut 6. The length of the clasp 2 is determined by the distance between the holes 15 in the protruding portion of the workpiece, holes are opened at both ends of the clasp, and bolts 21 attached to the clasp are attached. (1) in FIG. 2 shows the surface of the clasp opposite to the jig main body, and (2) in FIG. 2 shows the surface on the jig main body side. As shown in (3) of FIG. 2, the screw portion of the bolt 21 attached to the clasp is inserted into the hole 15 in the projecting portion of the workpiece so that the workpiece does not fall off from the jig. The clasp 2 also serves to prevent the workpiece itself from rotating during operations such as barrel polishing.

図３は、ねじ溝をつけた丸棒３に留金２、取手４、スライドコマ５、ナット６、スプリング８等をつけた図であり、図４は治具本体に留金等の部品を組み合わせた図である。治具本体と留金等の部品が組み合わされたものを治具と表現する。図４の（１）はその正面図であり、（２）は側面図である。なお、図３、図４において、スライドコマ５とナット６あるいは留金２とナット６が離れて描かれているが、これは各部品を明確にするためであり、使用時にはこの限りではない。重複するが図４ではダブルナットを採用している。 FIG. 3 is a view in which a clasp 2, a handle 4, a slide piece 5, a nut 6, a spring 8 and the like are attached to a round bar 3 having a thread groove. FIG. FIG. A combination of a jig body and clasp parts is expressed as a jig. 4A is a front view, and FIG. 4B is a side view. 3 and 4, the slide piece 5 and the nut 6 or the clasp 2 and the nut 6 are drawn apart from each other, but this is for the purpose of clarifying each part, and is not limited to this at the time of use. Although overlapping, a double nut is adopted in FIG.

図６は、ワークと治具の組み合わせ図であり、（１）は正面図、（２）は側面図である。治具本体１のワーク円筒部への挿入部１１をワークの円筒部１６に途中まで挿入する。途中までとしたのは、留金につけたボルト２１のねじ部がワーク突出部の先端にあたり途中で止まってしまうためである。次に取手４を治具本体側に押して、留金につけたボルト２１のねじ部がワーク突出部の先端にあたらないように留金を治具本体とは反対方向に移動させる。そして治具本体のワーク円筒部への挿入部１１全体をワークの円筒部１６に挿入し、取手４を放す。そこで貫通孔１０内にあるスプリング８の付勢により、留金２は治具本体１の横溝７に入り固定され、さらに留金につけたボルト２１のねじ部は、ワーク突出部の孔に挿入してワークの回転や落下を防ぐことができる。 FIG. 6 is a combination view of a workpiece and a jig, where (1) is a front view and (2) is a side view. The insertion part 11 to the work cylinder part of the jig body 1 is inserted into the work cylinder part 16 partway. The reason why it is halfway is that the threaded portion of the bolt 21 attached to the clasp hits the tip of the workpiece protruding portion and stops halfway. Next, the handle 4 is pushed toward the jig main body, and the clasp is moved in the direction opposite to the jig main body so that the screw portion of the bolt 21 attached to the clasp does not hit the tip of the workpiece protrusion. And the whole insertion part 11 to the workpiece | work cylindrical part of a jig | tool main body is inserted in the cylindrical part 16 of a workpiece | work, and the handle 4 is released. Therefore, by the bias of the spring 8 in the through hole 10, the clasp 2 enters the lateral groove 7 of the jig body 1 and is fixed, and the screw portion of the bolt 21 attached to the clasp is inserted into the hole of the workpiece protrusion. Can prevent the workpiece from rotating and dropping.

図７は、請求項５の複合治具を示したものである。複合治具１８とは、治具１２と治具取付アーム１７をボルト等で一体化したものを言う。バレル研磨等では、ワークをメディア内で回転させ、また大量に生産するため図７に示す治具取付アーム１７を回転機との結合孔１９により図示しない回転機に取り付けこれに本治具をつけて、ワークの研磨加工等をすることが多い。そこで、このアームの両端に治具本体１の治具取付アーム１７への締結ねじ溝部９に入るねじ部を設け、本治具を付け使用することによりワーク自体の回転や落下防ぎながら効率的にワークを研磨することができる。図７においては、治具取付アームとして互いに直行するアームを示したが、アームは４本とは限らず、６本あるいは８本となる治具取付アームとすることもできる。 FIG. 7 shows the composite jig of claim 5. The composite jig 18 refers to a jig in which the jig 12 and the jig mounting arm 17 are integrated with a bolt or the like. In barrel polishing or the like, a jig mounting arm 17 shown in FIG. 7 is attached to a rotating machine (not shown) through a coupling hole 19 with a rotating machine in order to rotate the workpiece in the medium and mass-produce the workpiece. In many cases, the workpiece is polished. Therefore, by providing a screw portion that enters the fastening screw groove portion 9 to the jig mounting arm 17 of the jig main body 1 at both ends of the arm, and using this jig, it is possible to efficiently prevent the workpiece itself from rotating and dropping. The workpiece can be polished. In FIG. 7, arms that are orthogonal to each other are shown as jig mounting arms, but the number of arms is not limited to four, and six or eight jig mounting arms may be used.

特定形状のワークを容易に治具に取り付けることができ、研磨作業等に広く採用することが可能である。 A workpiece having a specific shape can be easily attached to a jig, and can be widely used for polishing work and the like.

治具本体の正面図と側面図Front view and side view of jig body 治具本体につける留金等の部品図Part drawing such as clasp attached to jig body 各部品の組み合わせ図Combination diagram of each part 治具本体と各部品の組み合わせCombination of jig body and parts ワークの斜視図Perspective view of workpiece ワークと治具の組み合わせ図Combination diagram of workpiece and jig 治具と治具取付アームの複合治具Composite jig with jig and jig mounting arm

Explanation of symbols

１治具本体
２留金２１留金につけたボルト（凸部）２２留金の中心孔
３ねじ溝をつけた丸棒
４取手
５スライドコマ
６ナット
７（互いに向き合う）横溝
８スプリング
９取付アームへの締結ねじ溝部
１０貫通孔
１１ワーク円筒部への挿入部
１２治具
１３ワーク
１４（ワークの）突出部
１５（ワークの）突出部の孔
１６（ワークの）円筒部
１７治具取付アーム
１８複合治具
１９回転機との結合孔 DESCRIPTION OF SYMBOLS 1 Jig body 2 Clasp 21 Bolt (convex part) attached to clasp 22 Center hole of clasp
3 Round bar with thread groove 4 Handle 5 Slide piece 6 Nut 7 (Face each other) Horizontal groove 8 Spring 9 Fastening screw groove to mounting arm 10 Through hole 11 Insertion into work cylinder
DESCRIPTION OF SYMBOLS 12 Jig 13 Work 14 Projection part (work) 15 Hole of (work) projection 16 Cylindrical part (work) 17 Jig mounting arm 18 Composite jig 19 Joint hole with rotating machine

Claims

A cylindrical portion, and two protruding portions having the same length along the extending direction of the cylindrical portion from the outer peripheral walls at both ends on the diameter of the cylindrical portion, the protruding portion being longer than the cylindrical portion, A workpiece having a hole in the protruding portion, inserted into the cylindrical portion of the workpiece, and a columnar jig body having a length corresponding to the length of the protruding portion, the jig body, A clasp that is orthogonal to the axis of the jig body and is fixed from one side of the side surface of the protruding portion is provided, and convex portions that fit into the holes of the protruding portion are provided at both ends of the clasp, A jig for fixing the workpiece by inserting the clasp into the cylindrical portion, fixing the clasp from the side surface of the projection, and the convex portion of the clasp that fits into the hole of the projection.

In the jig body corresponding to the length of the protruding part, a hole is made in the diameter direction of the jig body at the height of the hole of the protruding part to penetrate the hole, and a spring and a screw groove are attached to the hole. A slide bar, nut and handle on one side of the round bar extension, and a nut for fixing the clasp and clasp on the other extension of the round bar. A bolt of a size that fits into the hole of the protruding portion is attached, and the workpiece and the jig are fixed by sandwiching the protruding portion between the clasp and the jig main body by biasing a spring. Item 1. The jig of item 1.

In order to fix the clasp and slide piece in a position penetrating the hole of the jig body, the outer periphery of the jig body is orthogonal to the axis of the jig body and matches the size of the clasp and slide piece. The jig according to claim 2, further comprising a jig body provided with lateral grooves facing each other.

2. A jig body having a screw hole in a head opposite to the insertion portion of the work cylinder portion of the jig body in order to attach the jig to a jig mounting arm constituted by a plurality of arms. The jig according to claim 3.

5. A composite jig in which the jigs according to claim 1 are attached to both ends of a jig mounting arm constituted by a plurality of arms.