JP3677161B2

JP3677161B2 - lift device

Info

Publication number: JP3677161B2
Application number: JP35585198A
Authority: JP
Inventors: 稔之清水; 茂伊藤; 正大内
Original assignee: Oki Denki Bohsai Co Ltd; Matsushita Electric Works Ltd
Current assignee: Panasonic Electric Works Co Ltd; Oki Denki Bohsai Co Ltd
Priority date: 1998-12-15
Filing date: 1998-12-15
Publication date: 2005-07-27
Anticipated expiration: 2018-12-15
Also published as: JP2000177995A

Description

【０００１】
【発明の属する技術分野】
本発明は、天井面に取着される電気機器を昇降させる昇降装置に関するものである。
【０００２】
【従来の技術】
この種の昇降装置としては、天井面に取着される昇降装置本体と、該昇降装置本体から繰り出し及び巻き取られるワイヤを介して、昇降装置本体に昇降自在に吊り下げられる昇降体とを備え、昇降体に取り付けられた照明器具への給電用の接点を昇降装置本体および昇降体の対向面にそれぞれ設け、昇降装置本体から昇降体を介して照明器具に給電するものがあった。
【０００３】
【発明が解決しようとする課題】
上記構成の昇降装置では、昇降体に取り付けられた照明器具に数Ａ程度の負荷電流が流れるため、昇降装置本体と昇降体との間を電気的に接続する接点に給電用の接点が用いられていた。したがって、接点間の電気抵抗が大きく、照明器具の代わりに照明器具に比べて負荷電流の遙かに小さい煙感知器などの電気機器を昇降体に取り付けた場合、接点間の電気抵抗が大きいために接点間での電気的接触の信頼性を確保することができず、信頼性が要求される煙感知器を昇降装置に取り付けることができないという問題があった。
【０００４】
本発明は上記問題点に鑑みて為されたものであり、その目的とするところは、負荷電流の小さい電気機器を取り付けることができる昇降装置を提供することにある。
【０００５】
【課題を解決するための手段】
上記目的を達成するために、請求項１の発明では、天井面に取着される昇降装置本体と、該昇降装置本体から繰り出し及び巻き取られるワイヤを介して、昇降装置本体に昇降自在に吊り下げられる昇降体とを備え、昇降体に取り付けられた電気機器への給電用の接点を昇降装置本体および昇降体の対向面にそれぞれ設け、昇降装置本体から昇降体を介して電気機器に給電する昇降装置において、両接点の内、昇降装置本体に設けた接点には、弾性を有し、略Ｕ字状であって先端ほど互いに近付く向きに傾斜するばね片が形成されるとともに、昇降体に設けた接点には、略平板状であってばね片の先端の間に挿入される突片が形成され、各接点の少なくとも接触部位は、微少電流用の接点に用いられる電気抵抗の小さい材料から形成されることを特徴とし、各接点の接触部位は微少電流用の接点に用いられる電気抵抗の小さい材料から形成されているので、両接点間の電気抵抗を一般に給電用に用いられる接点に比べて小さくでき、負荷電流の小さい煙感知器などの電気機器を昇降体に取り付けた場合でも、接点間の接触の信頼性を確保することができるから、負荷電流の小さい煙感知器などの電気機器を昇降体に取り付けて使用することができる。また両接点の接触時に、昇降装置本体側の接点に設けられたばね片と、昇降体側の接点に設けられた突片とが互いに摺接するので、両接点の接触面に付着した電気抵抗を増加させる要因となる汚れを除去することができ、接点間の電気抵抗が増加するのを防止して、接触の信頼性を確保することができる。
【０００６】
請求項２の発明では、請求項１の発明において、各接点の接触部位に、給電用に用いられる接点の電気抵抗に比べて電気抵抗の小さい金属からなる低抵抗接触部を設けたことを特徴とし、給電用の接点の電気抵抗に比べて電気抵抗の小さい金属からなる低抵抗接触部を介して両接点は電気的に接触するので、請求項１の発明と同様、負荷電流の小さい煙感知器などの電気機器を昇降体に取り付けた場合でも、接点間の接触の信頼性を確保することができ、負荷電流の小さい煙感知器などの電気機器を昇降体に取り付けて使用することができる。
【０００８】
【発明の実施の形態】
本発明の実施の形態を図面を参照して説明する。
【０００９】
（基本構成）
図１は本発明に係る昇降装置の基本構成を示し、天井２０に固定金具８を用いて取着される昇降装置本体１と、昇降装置本体１から繰り出し及び巻き取られるワイヤ３を介して、昇降装置本体１に昇降自在に吊り下げられる昇降体２とを備えており、昇降体２に取り付けられた負荷電流の小さい例えば煙感知器からなる電気機器４への給電用の接点５，６を昇降装置本体１および昇降体２の対向面にそれぞれ設け、昇降装置本体１から昇降体２を介して電気機器４に給電している。昇降装置本体１にはワイヤ３の繰り出し及び巻き取りを行う巻上装置７が設けられており、ユーザが昇降体２を引き下ろすと、巻上装置７からワイヤ３が繰り出されると共に、ユーザが昇降体２を持ち上げると、巻上装置７がワイヤ３を巻き上げることにより、昇降体２が昇降する。
【００１０】
図２は昇降装置本体１および昇降体２にそれぞれ設けられた接点５，６を示す図である。両接点５，６の表面には、一般に給電用の接点の材料として用いられる銅合金に比べて、電気抵抗の小さい例えば金や銀などの金属からなるめっき層５ａ，６ａが形成されているので、両接点５，６間の電気抵抗を給電用の接点に比べて小さくすることができる。すなわち、両接点５，６の少なくとも接触部位を、微少電流用の接点に用いられる電気抵抗の小さい材料（金や銀などの金属）から形成することによって、両接点５，６間の電気抵抗を一般に給電用に用いられる接点に比べて小さくでき、昇降体２に取り付けられる電気機器４に煙感知器のような負荷電流の小さい電気機器を用いた場合でも両接点５，６間の接触の信頼性を確保して、電気機器４へ確実に給電することができ、負荷電流の小さい電気機器４を昇降体２に取り付けて使用することができる。ここに、めっき層５，６から低抵抗接触部が構成される。
【００１１】
而して、常時は天井２０に固定された昇降体本体１に昇降体２を接続し、接点５，６を介して昇降体本体１と昇降体２との間を電気的に接続することにより、昇降体２に取り付けられた電気機器４を天井２０に取り付けられた状態で使用することができる。一方、電気機器４の点検時やメンテナンス時は、昇降体２を昇降体本体１から引き下ろして、昇降体２に取り付けられた電気機器４の点検やメンテナンスを行うことができ、点検やメンテナンスといった作業を安全且つ容易に行うことができる。
【００１２】
ところで、この昇降装置では両接点５，６の表面に、給電用の接点に比べて電気抵抗の小さいめっき層５ａ，６ａを形成することによって、両接点５，６間の電気抵抗を給電用の接点に比べて小さくしているが、図３に示すように、両接点５，６の接触面に給電用の接点に比べて電気抵抗の小さい例えば金や銀などの金属からなる低抵抗接触部としての接触板５ｂ，６ｂをそれぞれ溶着して、両接点５，６間の接触抵抗を給電用の接点に比べて小さくするようにしても良い。
【００１３】
（実施形態）
図４は本実施形態の昇降装置に用いる接点５，６を示す要部拡大図である。尚、接点５，６以外の構成は上述した図１の昇降装置と同様であるので、同一の構成要素についての説明は省略し、異なる部位について以下に説明する。
【００１４】
この昇降装置では、昇降体２に設けられた接点６の先端に略平板状の突片６ｃを突設するとともに、昇降装置本体１に設けられた接点５の先端に、略Ｕ字状であって先端ほど互いに近付く向きに傾斜する弾性を有するばね片５ｃ，５ｃを突設しており、両接点５，６の接触時に、昇降体２側の接点６に設けられた突片６ｃが、昇降装置本体１側の接点５に設けられたばね片５ｃ、５ｃ間に挿入され、接点５，６間が電気的に接続される。尚、両接点５，６は、基本構成の昇降装置と同様に給電用の接点に比べて電気抵抗の小さい微少電流用の接点から構成されているので、昇降体２に取り付けられる電気機器４に煙感知器のような負荷電流の小さい電気機器４を用いた場合でも両接点５，６間の接触の信頼性を確保して、電気機器４へ確実に給電することができ、負荷電流の小さい電気機器４を昇降体２に取り付けて使用することができる。
【００１５】
また、両接点５，６の接触時に、昇降装置本体１側の接点５に設けられたばね片５ｃと、昇降体２側の接点６に設けられた突片６ｃとが互いに摺接するので、両接点５，６の接触面に付着した電気抵抗を増加させる要因となる汚れを除去することができ、接点５，６間の電気抵抗が増加するのを防止して、接触の信頼性を確保することができる。ここに、ばね片５ｃおよび突片６ｃから摺接部が構成される。
【００１６】
なお、本実施形態では、昇降体２側の接点６に突片６ｃを設けるとともに、突片６ｃが挿入されるばね片５ｃ，５ｃを昇降装置本体１側の接点５に設けているが、昇降装置本体１側の接点５に突片を設けるとともに、昇降体２側の接点６に突片が挿入されるばね片を設けても良い。また図５は、両接点５，６の接触面に摺接部としての傾斜面５ｄ，６ｄを形成した参考例であり、両接点５，６の接触時に接点５，６が接触方向と略直交する方向にずれて、接点５，６の傾斜面５ｄ，６ｄが互いに摺接し、傾斜面５ｄ，６ｄに付着した汚れを除去することができ、上述と同様に接点５，６間の電気抵抗が増加するのを防止して接触の信頼性を確保することができる。
【００１７】
【発明の効果】
上述のように、請求項１の発明は、天井面に取着される昇降装置本体と、該昇降装置本体から繰り出し及び巻き取られるワイヤを介して、昇降装置本体に昇降自在に吊り下げられる昇降体とを備え、昇降体に取り付けられた電気機器への給電用の接点を昇降装置本体および昇降体の対向面にそれぞれ設け、昇降装置本体から昇降体を介して電気機器に給電する昇降装置において、両接点の内、昇降装置本体に設けた接点には、弾性を有し、略Ｕ字状であって先端ほど互いに近付く向きに傾斜するばね片が形成されるとともに、昇降体に設けた接点には、略平板状であってばね片の先端の間に挿入される突片が形成され、各接点の少なくとも接触部位は、微少電流用の接点に用いられる電気抵抗の小さい材料から形成されることを特徴とし、各接点の接触部位は微少電流用の接点に用いられる電気抵抗の小さい材料から形成されているので、両接点間の電気抵抗を一般に給電用に用いられる接点に比べて小さくでき、負荷電流の小さい煙感知器などの電気機器を昇降体に取り付けた場合でも、接点間の接触の信頼性を確保することができるから、負荷電流の小さい煙感知器などの電気機器を昇降体に取り付けて使用できるという効果がある。また両接点の接触時に、昇降装置本体側の接点に設けられたばね片と、昇降体側の接点に設けられた突片とが互いに摺接するので、両接点の接触面に付着した電気抵抗を増加させる要因となる汚れを除去することができ、接点間の電気抵抗が増加するのを防止して、接触の信頼性を確保することができる。
【００１８】
請求項２の発明は、請求項１の発明において、各接点の接触部位に、給電用に用いられる接点の電気抵抗に比べて電気抵抗の小さい金属からなる低抵抗接触部を設けたことを特徴とし、給電用の接点の電気抵抗に比べて電気抵抗の小さい金属からなる低抵抗接触部を介して両接点は電気的に接触するので、請求項１の発明と同様、負荷電流の小さい煙感知器などの電気機器を昇降体に取り付けた場合でも、接点間の接触の信頼性を確保することができ、負荷電流の小さい煙感知器などの電気機器を昇降体に取り付けて使用できるという効果がある。
【図面の簡単な説明】
【図１】基本構成の昇降装置を示す概略の構成図である。
【図２】同上の昇降装置に用いる接点を示す要部拡大図である。
【図３】同上の昇降装置に用いる別の接点を示す要部拡大図である。
【図４】本実施形態の昇降装置に用いる接点を示す要部拡大図である。
【図５】参考例の接点を示す要部拡大図である。
【符号の説明】
１昇降装置本体
２昇降体
３ワイヤ
４電気機器
５，６接点
２０天井[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lifting device that lifts and lowers an electric device attached to a ceiling surface.
[0002]
[Prior art]
This type of lifting device includes a lifting device main body attached to the ceiling surface, and a lifting body that can be lifted and lowered to the lifting device main body via a wire that is drawn out and wound up from the lifting device body. In some cases, a contact point for supplying power to the lighting fixture attached to the lifting body is provided on each of the lifting device body and the opposing surface of the lifting body, and power is supplied from the lifting device body to the lighting fixture through the lifting body.
[0003]
[Problems to be solved by the invention]
In the lifting device configured as described above, since a load current of about several A flows through the lighting fixture attached to the lifting body, a contact for power feeding is used as a contact point for electrically connecting the lifting device body and the lifting body. It was. Therefore, if the electrical resistance between the contacts is large and an electrical device such as a smoke detector, which has a much smaller load current than the lighting fixture, is attached to the elevator instead of the lighting fixture, the electrical resistance between the contacts is large. In addition, the reliability of electrical contact between the contacts cannot be ensured, and there is a problem that a smoke detector that requires reliability cannot be attached to the lifting device.
[0004]
The present invention has been made in view of the above problems, and an object of the present invention is to provide an elevating device to which an electric device having a small load current can be attached.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, a lifting / lowering device main body attached to the ceiling surface and a wire that is fed out and wound up from the lifting / lowering device main body are suspended up and down freely on the lifting / lowering device main body. A lifting body that is lowered, and provided with contact points for feeding power to the electrical equipment attached to the lifting body on the lifting device body and the opposing surface of the lifting body, respectively, to feed power to the electrical equipment from the lifting device body through the lifting body In the lifting device, the contact provided on the lifting device main body among the two contacts is elastic, and is formed with a spring piece that is substantially U-shaped and tilts toward the ends toward each other. The provided contact is formed with a projecting piece that is substantially flat and inserted between the tips of the spring pieces, and at least the contact portion of each contact is made of a material with low electrical resistance used for a contact for minute current. Formed As a feature, the contact part of each contact is made of a material with low electrical resistance used for contacts for minute currents, so the electrical resistance between both contacts can be made smaller than the contact generally used for power feeding, and the load Even when an electrical device such as a smoke detector with a small current is attached to the lifting body, the reliability of contact between the contacts can be secured, so an electrical device such as a smoke detector with a low load current is attached to the lifting body. Can be used. In addition, when both the contacts are in contact, the spring piece provided at the contact on the lifting device body side and the projecting piece provided on the contact on the lifting body side are in sliding contact with each other, thereby increasing the electrical resistance attached to the contact surface of both contacts. It is possible to remove the dirt that becomes a factor, prevent an increase in electrical resistance between the contacts, and ensure the reliability of the contact.
[0006]
The invention of claim 2 is characterized in that, in the invention of claim 1, a low resistance contact portion made of a metal having a smaller electrical resistance than that of the contact used for power feeding is provided at the contact portion of each contact. Since both the contacts are in electrical contact via a low resistance contact portion made of a metal having a smaller electrical resistance than that of the contact for power supply, smoke detection with a small load current is performed as in the first aspect of the invention. Even when an electrical device such as a detector is attached to the lifting body, the reliability of contact between the contacts can be ensured, and an electrical device such as a smoke detector with a low load current can be attached to the lifting body and used. .
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings.
[0009]
(Basic configuration)
FIG. 1 shows a basic configuration of a lifting device according to the present invention, and a lifting device body 1 attached to a ceiling 20 using a fixing bracket 8 and a wire 3 fed out and wound up from the lifting device body 1. The lifting device body 1 includes a lifting body 2 that can be freely lifted and lowered, and power supply contacts 5 and 6 that are attached to the lifting body 2 and that have a small load current, such as a smoke detector, are provided. Provided on opposite surfaces of the lifting device main body 1 and the lifting body 2, respectively, and feeds electric power from the lifting device body 1 to the electrical equipment 4 via the lifting body 2. The lifting device body 1 is provided with a hoisting device 7 for feeding and winding the wire 3. When the user pulls down the lifting body 2, the wire 3 is fed from the hoisting device 7 and the user moves up and down. When the body 2 is lifted, the hoisting device 7 winds up the wire 3, so that the elevating body 2 moves up and down.
[0010]
FIG. 2 is a view showing the contacts 5 and 6 provided on the lifting device main body 1 and the lifting body 2, respectively. Since the surfaces of both contacts 5 and 6 are formed with plating layers 5a and 6a made of a metal such as gold or silver having a lower electrical resistance than a copper alloy generally used as a material for contact for power feeding. The electrical resistance between the contacts 5 and 6 can be made smaller than that of the contact for power feeding. That is, by forming at least the contact portion of both the contacts 5 and 6 from a material having a low electrical resistance (metal such as gold or silver) used for the contact for minute current, the electrical resistance between the contacts 5 and 6 is reduced. Generally, it can be made smaller than the contacts used for power supply, and the reliability of contact between the contacts 5 and 6 can be achieved even when an electrical device 4 having a small load current such as a smoke detector is used for the electrical device 4 attached to the lifting body 2. Therefore, the electric device 4 can be reliably supplied with power, and the electric device 4 having a small load current can be attached to the elevator 2 for use. Here, the plating layers 5 and 6 constitute a low-resistance contact portion.
[0011]
Thus, the elevator body 2 is normally connected to the elevator body 1 fixed to the ceiling 20, and the elevator body 1 and the elevator body 2 are electrically connected via the contacts 5 and 6. The electric device 4 attached to the lifting body 2 can be used in a state attached to the ceiling 20. On the other hand, at the time of inspection or maintenance of the electrical equipment 4, the lifting body 2 can be pulled down from the lifting body body 1 so that the electrical equipment 4 attached to the lifting body 2 can be inspected or maintained. Can be performed safely and easily.
[0012]
By the way, in this lifting and lowering device , the plating layers 5a and 6a having a lower electrical resistance than the contact for power feeding are formed on the surfaces of the both contacts 5 and 6, thereby reducing the electrical resistance between the both contacts 5 and 6 for power feeding. As shown in FIG. 3, the contact surface of both contacts 5 and 6 has a low resistance contact portion made of a metal such as gold or silver having a lower electrical resistance than the contact for power feeding. The contact plates 5b and 6b may be welded to reduce the contact resistance between the contacts 5 and 6 as compared with the contact for power feeding.
[0013]
(Embodiment)
FIG. 4 is an enlarged view of a main part showing the contacts 5 and 6 used in the lifting device of this embodiment. Since the configuration other than the contacts 5 and 6 is the same as that of the lifting device of FIG. 1 described above , description of the same components is omitted, and different portions will be described below.
[0014]
In this lifting device, a substantially flat protruding piece 6 c is projected from the tip of the contact 6 provided on the lifting body 2, and is substantially U-shaped at the tip of the contact 5 provided on the lifting device body 1. The spring pieces 5c and 5c are elastically inclined so as to approach each other toward the tip, and the projecting piece 6c provided on the contact 6 on the lifting body 2 side is moved up and down when both the contacts 5 and 6 are in contact with each other. It is inserted between spring pieces 5c and 5c provided on the contact 5 on the apparatus main body 1 side, and the contacts 5 and 6 are electrically connected. Since both the contacts 5 and 6 are composed of contacts for minute current having a smaller electric resistance than the contact for power feeding as in the lifting device of the basic configuration , the contacts 5 and 6 are connected to the electrical equipment 4 attached to the lifting body 2. Even when an electric device 4 having a small load current such as a smoke detector is used, the contact reliability between both the contacts 5 and 6 can be ensured, and the electric device 4 can be reliably supplied with power, and the load current is small. The electric device 4 can be used by being attached to the lifting body 2.
[0015]
Further, when both the contacts 5 and 6 are in contact, the spring piece 5c provided on the contact 5 on the lifting device body 1 side and the protrusion 6c provided on the contact 6 on the lifting body 2 side are in sliding contact with each other. It is possible to remove dirt that causes an increase in electrical resistance attached to the contact surfaces of 5 and 6, and to prevent an increase in electrical resistance between the contacts 5 and 6, thereby ensuring contact reliability. Can do. Here, a sliding contact portion is constituted by the spring piece 5c and the protruding piece 6c.
[0016]
In addition, in this embodiment, while providing the protrusion 6c in the contact 6 by the raising / lowering body 2 side, the spring pieces 5c and 5c in which the protrusion 6c is inserted are provided in the contact 5 by the raising / lowering apparatus main body 1 side, While providing a protrusion on the contact 5 on the apparatus body 1 side, a spring piece on which the protrusion is inserted may be provided on the contact 6 on the lifting body 2 side. FIG. 5 is a reference example in which inclined surfaces 5d and 6d as sliding contact portions are formed on the contact surfaces of both contacts 5 and 6, and when the contacts 5 and 6 are in contact, the contacts 5 and 6 are substantially in the contact direction. The inclined surfaces 5d and 6d of the contact points 5 and 6 are slidably contacted with each other in a direction perpendicular to each other, and dirt attached to the inclined surfaces 5d and 6d can be removed. It is possible to prevent contact from increasing and to ensure the reliability of contact.
[0017]
【The invention's effect】
As described above, the invention according to claim 1 is a lifting device that can be lifted and lowered to the lifting device body through the lifting device body that is attached to the ceiling surface and the wire that is drawn out and wound from the lifting device body. A lifting device for supplying power to an electrical device from the lifting device body through the lifting body, the contact point for feeding power to the electrical device attached to the lifting body is provided on each of the opposing surfaces of the lifting device body and the lifting body. Of the two contacts, the contact provided on the lifting device body is elastic, and is formed with a spring piece that is substantially U-shaped and tilts toward the ends toward each other. Is formed with a projecting piece that is substantially flat and inserted between the tips of the spring pieces, and at least the contact portion of each contact is formed of a material having a low electrical resistance used for a contact for minute current. Each characterized by Since the point contact part is made of a material having a low electrical resistance used for a contact for minute current, the electrical resistance between the two contacts can be made smaller than that of a contact generally used for power supply, and smoke with a low load current can be obtained. Even when an electrical device such as a sensor is attached to the lifting body, the reliability of contact between the contacts can be ensured, so an electrical device such as a smoke detector with a small load current can be attached to the lifting body and used. effective. In addition, when both the contacts are in contact, the spring piece provided at the contact on the lifting device body side and the projecting piece provided on the contact on the lifting body side are in sliding contact with each other, thereby increasing the electrical resistance attached to the contact surface of both contacts. It is possible to remove the dirt that becomes a factor, prevent an increase in electrical resistance between the contacts, and ensure the reliability of the contact.
[0018]
The invention of claim 2 is characterized in that, in the invention of claim 1, a low resistance contact portion made of a metal having a smaller electric resistance than that of a contact used for power feeding is provided at the contact portion of each contact. Since both the contacts are in electrical contact via a low resistance contact portion made of a metal having a smaller electrical resistance than that of the contact for power supply, smoke detection with a small load current is performed as in the first aspect of the invention. Even when an electrical device such as an air conditioner is attached to the lifting body, the reliability of contact between the contacts can be ensured, and an electrical device such as a smoke detector with a low load current can be attached to the lifting body for use. is there.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a lifting device having a basic configuration .
FIG. 2 is an enlarged view of a main part showing a contact point used in the lifting device.
FIG. 3 is an enlarged view of a main part showing another contact used in the lifting device.
FIG. 4 is an enlarged view of a main part showing contacts used in the lifting device of the present embodiment .
FIG. 5 is an enlarged view of a main part showing a contact of a reference example .
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Lifting device main body 2 Lifting body 3 Wire 4 Electric equipment 5, 6 Contact 20 Ceiling

Claims

A lifting device body attached to the ceiling surface, and a lifting body that can be freely lifted and lowered from the lifting device body via a wire that is drawn out and wound up from the lifting device body. In the lifting device for supplying power to the electrical equipment from the lifting device body through the lifting body, contact points for power supply to the device are provided on the opposed surfaces of the lifting device body and the lifting body, respectively, and provided in the lifting device body among the two contacts. The contact is elastic and has a substantially U-shaped spring piece that is inclined in a direction approaching each other toward the tip. A projecting piece to be inserted between the tips of the pieces is formed , and at least a contact portion of each contact is formed of a material having a small electrical resistance used for a contact for minute current.

2. The lifting device according to claim 1, wherein a low resistance contact portion made of a metal having a smaller electric resistance than that of a contact used for power feeding is provided at a contact portion of each contact .