Electric plug

A miniature multi-polar electric plug which can prevent the male contacts from being placed unprotected all the time is provided. An electric plug (10) has a plug housing (1), male contacts (2), a shutter (3), a shell (4), and a pair of compressed coil springs (5). The plug housing (1) has a header part (1a) and a frame part (1b). The header part (1b) protrudes from the frame part and has a mounting board (12) for mounting the male contacts (2) and the shutter (3). The compressed coil springs (5) move the shutter (3) to cover or uncover the male contact (2).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2003-048126 filed on Feb. 25th in 2003, the entire contents of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an electric plug for electrical connecting.

BACKGROUND OF THE INVENTION

The recent electronic devices such as cellular phones, micro video cameras, and portable information terminals use a connection base designated as a cradle (also referred to as a docking station) for sending and receiving data to and from desk top personal computers.

The cradle mounts a plug thereon and is connected with a cable via which the cradle and a desk top personal computer are connected to each other. On the other hand, electronic devices such as portable information terminals have a receptacle, and the receptacle provided on the electronic device can be connected with the plug provided on the cradle to secure high speed data transfer between the electronic device and the desk top personal computer. One of the simplest forms of the cradle is a charger for cellular phones.

Conventionally, this kind of cradle is unique to electronic devices connected with the cradle. However, highly versatile cradles equipped with a connector connectable with various kinds of connectors of cellular phones have been invented (Japanese Published Unexamined Patent Application No. H11-177670).

In the above-described invention, the cradle includes a holding rail for holding a cellular phone and a connector connected with a connector of the cellular phone. The connector of the cradle is held on the cradle in such a manner as to be movable up and down, back and forth and around via springs.

With this structure, even when there is a relative displacement between the connector of the cellular phone and the connector of the cradle, the connector of the cradle can freely move to be engaged with the connector of the cellular phone.

However, the provision of the above-described connector to the cradle increases the number of components of the cradle. It is simpler in structure to directly engage the receptacle connector provided on the electronic device with the plug connector provided on the cradle side.

The interface connector (or an I/O connector) mounted on such a cradle is generally a multi-polar dual in-line connector having two rows of contacts. In the dual in-line plug, the dual in-line contacts are surrounded by insulative fixed vertical walls protecting the contacts from being direct touched by a hand. Such a dual in-line plug is so-called four-wall shrouded, thereby having a large outer size.

However, electronic devices (micro video cameras, for example) to be connected with a cradle having a dual in-line plug are increasingly being reduced in size, which inevitably requires size reduction in a dual in-line receptacle provided for the above-described electronic devices. For this reason, it has been sought to miniaturize a dual in-line plug installed in the cradle, leaving almost no room for the formation of insulative fixed vertical walls surrounding the contacts (the so-called no wall header).

However, even if a dual in-line plug is miniaturized until there is no room left for insulative surrounding walls, when the contacts placed unprotected are subjected to dust or handling, it may become an indirect cause of a contact failure of the contacts. For this reason, dustproof measures have been sought for miniaturization of the dual in-line plug.

Furthermore, when security is taken into consideration, it is preferable to array dual in-line female contacts of fixed contacts in a dual in-line receptacle provided on an electronic device, and to array male contacts of flexible leaf springs in a dual in-line plug provided on a cradle, since the female contacts receive a contact pressure from the male contacts.

In other words, as compared with the fixed contacts which receive the contact pressure, the male contacts which give the contact pressure tend to be comparatively short-lived as a result of repeated insertion and removal of the connector. For this reason, it is not preferable to provide the short-lived male contacts to the connector mounted on the electronic device because it requires disassembling partially the electronic device in order to replace the connector.

Therefore, when the replacing the connector is taken into consideration, it is preferable to mount the dual in-line plug connector having male contacts of short-lived flexible leaf springs on the cradle. This holds true of cable connectors, without being limited to cradle connectors.

In order to solve the above-described problems, the present invention has an object of providing a miniature multi-polar electric plug which can prevent the contacts from being placed unprotected all the time.

SUMMARY OF THE INVENTION

The inventors have invented the following new electric connection plug to accomplish the above-mentioned object.

(1) An electric plug comprising: an insulative plug housing having a frame part and a header part which has a mounting board and is formed integrally with the frame part to be protruded from the frame part and inserted into a mating receptacle; male contacts of flexible leaf springs each having a flexible top part, wherein the male contacts are arrayed in parallel on both surfaces of the mounting board for mounting the male contacts, and a pair of the flexible top parts of the male contacts opposed to each other with the mounting board disposed therebetween are raised towards opposite directions to each other; and a shutter which covers the male contacts when the header part is removed from the mating receptacle and is housed in the frame part by being pushed by the mating receptacle so as to expose the male contacts when the header part is inserted into the mating receptacle.

The invention described in (1), the shutter formed as thin walls surrounds the male contacts instead of insulative fixed vertical walls, thereby realizing miniaturization of the electric plug and a mating receptacle. When the electric plug is not inserted into the mating receptacle, the shutter covers the male contacts making it impossible to easily touch the male contacts. On the other hand, when the electric plug is inserted into the mating receptacle, the shutter is retracted to make the male contacts contact with female contacts of the mating receptacle which surrounds the male contacts, thereby making it impossible to easily touch the male contacts.

According to the invention described in (1), thin leaf springs are used for the male contacts instead of the conventional pin connection to connect the receptacle and the plug, thereby realizing miniaturization of the plug.

(2) The electric plug according to (1) further comprising an elastic member for pushing out the shutter to cover the male contacts when the header part is removed from the mating receptacle.

According to the invention described in (2), when the electric plug is not inserted in the mating receptacle, the shutter is moved by a force caused by the elastic member to shield the male contacts from outside, thereby protecting the male contacts from dust or handling. The elastic member can be a compressed coil spring, for example.

(3) The electric plug according to (1) or (2), wherein the mounting board has a top board, a distance between the flexible top parts opposed to each other with the mounting board disposed therebetween is slightly larger than a width of the top board to make the male contacts press female contacts of the mating receptacle.

(4) The electric plug according to any one of (1) to (3) wherein legs of the male contacts opposed to each other with the mating board disposed therebetween extend from the header part towards opposite directions to each other to be fixed on a printed-circuit board.

According to the invention described in (4), the contacts can be arrayed in a small pitch by mounting them in the positioning pattern on the surface of the printed-circuit board.

(5) The electric plug according to any one of (1) to (4) further comprising: a shell for covering the frame part; and pairs of soldering tabs arranged in edges of the shell to be fixed on the printed-circuit board.

The electric plug of the invention described in (5) can be mounted on the printed-circuit board like a surface mounting device.

(6) The electric plug according to any one (1) to (4), wherein the shell is formed of a metal thin plate, covers the frame part and has protruding pieces to cover a part of the header part.

According to the invention described in (6), the frame part is covered with the shell formed of the metal thin plate which reinforces the frame part structurally, and at the same time, shields the plug. Since the shell has the protruding pieces to partially cover the header part, when the plug is inserted into the mating receptacle, the mating receptacle and the plug are integrally shielded.

(7) The electric plug according to any one of (1) to (6), wherein the shutter has a first shutter wall and a second shutter wall which are opposed to each other with the male contacts disposed therebetween; each of the first shutter wall and the second shutter wall has a pair of restricting frames on both flanks thereof; each of the restricting frames has a groove, each of the surfaces of the mounting board for mounting the male contacts is provided with a pair of rails on opposite edges of the surface, and the rail is engaged with the groove in such a manner where the shutter can move back and forth.

According to the invention described in (7), the rails shaped in letter of L are engaged in the grooves shaped in letter of U, which secures the parallel movement of the shutter thereby preventing the shutter from opening unnecessary.

(8) An electric plug according to any one of (1) to (7) being installed in a cradle via the printed-circuit board.

(9) An electric plug according to any one of (1) to (7) being installed in a cable via the printed-circuit board.

(10) A receptacle capable of being connected with the electric plug according to any one of (1) to (9).

The “insulative plug housing” can be assumed to be a plug housing made from a material electrically isolated, and to have the feature of holding and protecting the male contacts with an electrically insulating member.

The phrase “the header part and the plug frame part are integrally formed” indicates that the plug housing can be integrally molded with an electrically insulative synthetic resin material. After the plug housing is integrally molded using a synthetic resin material, it can be processed mechanically in parts. Furthermore, the plug can be formed by cutting process.

The male contacts in this invention are preferably leaf springs so as to be arrayed in a small-pitch of about 0.5 mm. When a pin is used as the male contact instead of the leaf spring, a slit socket pin corresponding to the contact pin must have some outer diameter, which makes it difficult to array the male contacts in a small pitch of 0.5 mm or so.

The number of poles of the male contacts to be arrayed is preferably 40 or more when the electric plug is used as an interface connector. In other words, as many as 20 male contacts can be arrayed in parallel on one surface of the mounting board, and 13 male contacts can be arrayed in parallel on one surface to make 26 poles as a whole depending on the application of the plug connector.

The “insulative shutter” can be assumed to be a shutter made from a material electrically isolated, and to have a function of isolating the male contacts with an electric insulator. Unless when the plug is connected with the mating receptacle, the shutter can be assumed to cover the male contacts so as to isolate the male contacts from outside.

The shutter can be assumed to be integrally formed with first and second flange parts formed on both flanks of the shutter, and the integrally formed shutter can be assumed to be slidably engaged with an opening part formed in the frame part composing the plug housing.

Therefore, the shutter is housed in the frame part of the plug housing to be moved not fixed.

It can be assumed that the shutter is formed like a rectangular tube formed of a thin plate having slot grooves on its sides. There is some space between the frame part and the mounting board on which the male contacts are mounted; and the shutter moves to cover and uncover the male contacts via the space.

The structure of the shutter like this enables the plates composing the header part to be thinner, thereby allowing the mating receptacle to be reduced in size.

DETAILED DESCRIPTION OF THE PREFERRRED EMBODIMENT

The embodiments of the present invention will be described as follows, based on the drawings.

FIG. 1is a perspective view showing the structure of an electric plug of an embodiment of the present invention when partly disassembled. In the embodiment shown inFIG. 1, the electric plug10(hereinafter simply referred to as the plug10) is composed of a plug housing1, male contacts2, a shutter3, a shell4, and a pair of compressed coil springs5.

In the embodiment shown inFIG. 1, the plug housing1is made from an insulative material and has a header part1aand a frame part1b. The header part1aand the frame part1bare formed integrally, and the header part1aprotrudes from the frame part1b.

The male contacts2are made of flexible leaf springs and each has a flexible top part21. The male contacts2are arrayed in parallel on a mounting board12provided in the header part1a. The mounting board12has two rows of parallel arrayed male contacts2: one on a front surface and one on a rear surface of the mounting board12. Two male contacts opposed to each other across the mounting board12are disposed so that their flexible top parts21are raised towards opposite directions to each other.

The frame part1bis shaped like a square cylinder with a pair of long-side walls100aand100bopposed to each other and a pair of short-side walls110aand110bopposed to each other. In the frame part1b, a face (top face) from which the header part1aprotrudes and a face (bottom face) opposed to the top face are opened. Through the bottom face of the frame part1bis inserted the insulative shutter3to assemble the plug housing1. A space exists between an inner side of the frame part1band the mounting board12, and the shutter3is inserted into the space.

The shutter3is composed of a wall-shaped shutter part31which sandwiches the mounting board12, and a first flange33aand a second flange33bformed on both flanks of the shutter part31, the first and second flanges33aand33bbeing integrally formed with the shutter part31using an electric insulative material.

The flanges33aand33bare each shaped like a box with an open bottom and a top wall opposite to the bottom, and each of the top wall has a projection32for supporting one end of one of the compressed coil springs5inside thereof.

The shutter part31is composed of a first shutter wall31aand a second shutter wall31bopposed to each other across the mounting board12, and an opening part30formed between the first and second shutter walls31aand31bso as to cover the plural male contacts2. On both sides of the shutter part31are formed slot grooves31cand31dinto which mounting board12is inserted.

The shutter3with the above-mentioned structure is slidably engaged within the frame part1bof the plug housing1.

The shell4is integrally formed by bending a metal thin plate, and assembled from upper of the plug housing1so as to cover the outer side of the frame part1b. The compressed coil springs5which are elastic members are beforehand incorporated into the flanges33aand33bof the shutter3, and after the shell4and the plug housing1are assembled, bottom edges of the shell4are partially bent to make ribs provided on the bottom edges of the shell4, and the compressed coil springs5are disposed between the ribs and the projections32provided within the flanges33aand33b.

At the top of the header part1aof the plug housing1is formed a cap-shaped top board11, from which the mounting board12extends downward. Since the top board11is shaped like a roof, the top board11and the mounting board12are integrally formed to have a vertical cross section shaped like the letter T. On two surfaces of the mounting board12are formed shallow grooves in striped into which the male contacts2are buried.

Furthermore, in order to support the top board11and the mounting board12, a pair of vertical supports13aand13bis formed on the frame part1b. The top board11, the upper part of the mounting board12, and the vertical supports13aand13bform the header part1awhich is inserted into a mating receptacle.

On an outer surface of the long-side wall100aof the frame part1bare formed triangular projections14band14d.Similarly, on an outer surface of the long-side wall100bopposed to the long-side wall100ais formed another triangular projection14a(not illustrated) on the position opposed to the triangular projection14b. Similarly, on the outer face of the long-side wall100bis formed a triangular projection14c(not illustrated) on the position opposed to the triangular projection14d. These triangular projections14ato14dare provided to lock the later-described holes43ato43dof the shell4.

Bent pieces42aand42bare formed on top of the shell and are opposed to each other, and each has a vertical cross section shaped like the letter S. Similarly, on top of the shell4are formed another bent pieces42cand42dwhich are opposed to each other and each has a vertical cross section shaped like the letter S.

A shell long-side wall400aof the shell4covering the long-side wall100aof the frame part1bis provided with rectangular holes43band43d. A shell long-side wall400bof the shell4covering the long-side wall100bis also provided with a hole43a(not illustrated) opposed to the hole43b, and a hole43c(not illustrated) opposed to the hole43d.

The area of the inner cross section of the shell4is formed slightly larger than that of the outer cross section of the frame part1b, and the plug housing1and the shell4are assembled by inserting the shell down to the plug housing1.

The bent pieces42aand42bcover the vertical support13ain such a manner as to be slightly above the vertical support13a. Similarly, the bent pieces42cand42dcover the vertical support13bin such a manner as to be slightly above the vertical support13b. The effects of the shell4and the bent pieces42ato42dwill be described later.

The shell4is installed so as to be in tight contact with the frame part1b. To be more specific, when the shell4is inserted into the plug housing1to some extent, the triangular projections14band14dare engaged with the rectangular holes43band43d, respectively. Similarly, the triangular projections14aand14care engaged with the rectangular holes43aand43c, respectively.

The structure of the plug10in the present embodiment will be further explained as follows.FIG. 2AtoFIG. 2Cshow the plug10when it is assembled;FIG. 2Ais a front view,FIG. 2Bis a plan view, andFIG. 2Cis a side view. The right half ofFIG. 2Bis a cross sectional view taken along the line X–X′ ofFIG. 2A.

FIG. 3Ais a cross sectional view taken along the line Z–Z′ ofFIG. 2B, andFIG. 3BandFIG. 3Care cross sectional views taken along the line Y–Y′ ofFIG. 2B.FIG. 3BandFIG. 3Cshow the male contacts2, which are composed of long contacts2aand short contacts2bhaving a different length from each other.FIG. 3Bshows the long contacts2aandFIG. 3Cshows the short contacts2b.

As shown inFIG. 3B, the long contacts2acomposed of flexible leaf springs are held on the mounting board12in such a manner where the flexible top parts21of each pair of long contacts2aopposed to each other across the mounting board12are raised towards opposite directions to each other. The long contacts2aare arrayed in parallel and a pair of rows of paralleled long contacts2ais opposed to each across the mounting board12.

Similarly, as shown inFIG. 3C, the short contacts2bmade of flexible leaf springs are held on the mounting board12in such a manner where the flexible top parts21of each pair of short contacts2bopposed to each other across the mounting board12are raised towards opposite directions to each other. The short contacts2bare arrayed in parallel and a pair of rows of paralleled short contacts2bis opposed to each across the mounting board12.

The difference between the long contacts2aand the short contacts2bis the length from the positions of ends of respective legs22to the positions of the flexible top parts21. Assuming that the length from the positions of the ends of the legs22of the long contacts2ato the positions of the flexible top parts21is T1and the length from the positions of the ends of the legs22of the short contacts2bto the positions of the flexible top parts21is T2, T1is longer than T2. In other words, the long contacts2ahave the longer length T1, whereas the short contacts2bhave the shorter length T2. The long contacts2aare arrayed in an electrical power line, for example, and the short contacts2bare arrayed in a signal line.

The long contacts2aand the short contacts2bare arrayed in parallel on the mounting board12, and the pair of rows of the male contacts2is opposed to each other with the mounting board12disposed therebetween, thereby forming a multi-polar dual in-line.

As shown inFIG. 3Bor3C, the respective legs22of the paired male contacts2opposed to each other across the mounting board12extend towards opposite directions to each other from the plug housing1. And the male contacts2arrayed on the same surface of the mounting board12are arranged in parallel. The legs22of the male contacts2can be fixed on a printed-circuit board (not illustrated).

As shown inFIG. 3Bor3C, the shutter part31of the shutter3covers both rows of the parallel arrayed male contacts2mounted on the both surfaces of the mounting board12.

As shown inFIG. 2B, the compressed coil springs5which are elastic members are disposed in a pair in the plug housing1. The inside of one end of each of the compressed coil springs5is inserted into the projection32in the flange33a(or33b) of the shutter3, and the inside of the other end of each of the compressed coil springs5is inserted into a rib41formed by bending a part of the shell4which extends toward inside of the plug housing1. In other words, the compressed coil springs5are arranged between the projection32in the shutter3and the rib41of the shell4.

The compressed coil springs5make a force to push out the shutter3within the plug housing1. In other words, the compressed coil springs5give a force to enable the shutter part31to move so as to cover each row of the parallel arrayed male contacts2arranged in pairs.

In addition, as shown inFIG. 2A, a pair of solderable tabs44band44dis provided in opposite directions to each other at bottom edges of the shell long-side wall400aof the shell4. The solderable tabs44band44dare to be fixed on a printed-circuit board. Similarly, a pair of solderable tabs44aand44cis provided in opposite directions to each other at bottom edges of the shell long-side wall400bof the shell4.

FIG. 4is a pattern layout showing the positioning pattern formed on the printed-circuit board on which to mount the plug10. The pattern layout ofFIG. 4corresponds to the plug10shown inFIG. 1.

As shown inFIG. 4, the printed-circuit board has positioning patterns6ato6dto which the tabs43ato43dof the shell4are soldered, and a positioning pattern group60to which the final ends of the male contacts2are soldered. The male contacts2are fixed on the positioning pattern group60and soldered, like a surface mounting device, to the printed-circuit board with which the plug10is intended to be connected.

The following is a description of the effects of the present invention.FIG. 5is an external appearance of the plug10, showing the state where the plug10is not inserted into the mating receptacle.FIG. 6is another external appearance of the plug10, showing the state where the plug10is inserted into the mating receptacle.

FIG. 5shows the shutter3covering the male contacts2. In the state shown inFIG. 5, the male contacts2are covered with the top board11and the shutter part31so as to be protected from handling or dust as shown also inFIG. 3BandFIG. 3C. Also, dust adhesion on the male contacts2is reduced.

The length L1between the flexible top parts21of the paired long contacts2aopposed to each other across the mounting board12is made to be slightly larger than the length L2of the vertical width of the top board11(FIG. 3B). Similarly, the length L1′ between the flexible top parts21of the paired short contacts2bopposed to each other across the mounting board12is made to be slightly larger than the length L′2of the vertical width of the top board11(FIG. 3C). Therefore, the long contacts2aand the short contacts2barrayed in pairs press female contacts of the mating receptacle providing a contact pressure to the mating receptacle.

The header part1aincluding the top board11and the vertical supports13aand13bis inserted into the mating receptacle. There is a key groove15formed on the top board11to guide a proper inserting direction. The mating receptacle has an inserting opening, and when the plug10is inserted into the mating receptacle, an apex of each of the shutter part walls31aand31bcomes into contact with front edge of the inserting opening.

When the plug10is inserted into the mating receptacle, the shutter walls31aand31bin contact with the front edge of the inserting opening cannot be inserted into the inserting opening of the mating receptacle, thereby being pushed back towards the frame part1b. This causes the male contacts2to be exposed as shown inFIG. 6and to press fixed female contacts of the mating receptacle, thereby making the male contacts2come into contact with the female contacts.

When the plug10is removed from the mating receptacle, the force caused by the compressed coil springs5moves the shutter3towards the top board11, thereby returning the shutter3to the state ofFIG. 5in which the shutter3covers the male contacts2.

FIG. 7is a cross sectional view showing the state where the plug10is inserted into the mating receptacle. InFIG. 7, the header part1aof the plug10is inserted into the inserting opening90of the mating receptacle9, and a receptacle shutter91provided in the receptacle9is pushed back by the header part1aand retracted to the back of the inserting opening90.

As shown inFIG. 1, the shell4formed of a metal thin plate covers the frame part1band partially protrudes to form the bent pieces42ato42dfor partially covering the vertical supports13aand13bformed on both flanks of the header part1a. On the other hand, inFIG. 7, the receptacle shell94made of a metal thin plate covers the receptacle housing, and at the same time, bends towards the inserting opening90in such a manner as to have a U-shaped cross section, thereby covering parts of inner walls surrounds the inserting opening90.

InFIG. 7, the shell4made of a metal thin plate covers the frame part1bto structurally reinforce it, and also shields the plug.

Also, since a part of the shell4protrudes to partially cover the header part1a, a part of the header part1a(vertical supports13aand13b) is covered with the metal plate composing the shell4even inside the inserting opening90of the mating receptacle9. Therefore, when the plug10is inserted into the mating receptacle9, the mating receptacle9and the plug10are integrally shielded.

Next, the relationship between the first and the second shutter wall31aand31band the mounting board12of the plug housing1will be described as follows with the perspective view ofFIG. 8.

As shown inFIG. 8, the shutter part31is provided with the first shutter wall31aand the second shutter wall31bopposed to each other with the mounting board12disposed therebetween.

On both flanks of the first shutter wall31aare provided a pair of restricting frames34aand34b. Similarly, on both flanks of the second shutter wall31bare provided a pair of restricting frames34aand34b. Each of the restricting frames34aand34bis provided with a U-shaped groove35aor35b.

On the other hand, the mounting board12is provided with a pair of L-shaped rails12aand12bformed on both flanks in the width direction of the surface on which to mount the male contacts2(SeeFIG. 1). The pair of rails12aand12bis provided on each of the two surfaces of the mounting board12, so the mounting board12has two pairs of rails or a total of four rails.

As described above, the shutter3is assembled by being inserted from the bottom of the plug housing1, and as shown inFIG. 8the pairs of L-shaped rails12aand12bare engaged with the pairs of grooves35aand35b, respectively.

This combination of the first and second shutter walls31aand31band the mounting board12of the plug housing1secures parallel movement of the shutter3, and the pairs of rails12aand12bprevent the shutter3from being easily opened.

As described withFIG. 4, the plug10is mounted on the surface of the printed-circuit board which is installed in a cradle. This realizes an electric connection plug for miniature multi-polar cradles.

Furthermore, the printed-circuit board can be covered with a cable shell and electrically connected with the cable shell via a cable to provide an electric connection plug for cable connection.

The electric plug of the present invention thus directly engages the receptacle connector provided on the electric device with the plug connector provided on the cradle, without increasing the number of components of the cradle. The electronic device having a receptacle capable of being connected with the electric plug of the present invention can be reduced in size, at least without regard to of the external shape of the receptacle.

Also, in the embodiment shown in the perspective view ofFIG. 6, the plug10has a lateral width W1of 19.6 mm, a depth D1of 4.1 mm, and a height H1of 9.5 mm. The projecting part of the plug10has a lateral width W2of 14.7 mm, a depth D2of 2.4 mm, and a height H2of 3.2 mm. The contacts2have a pitch of 0.5 mm and 42 poles; however, two poles become unusable (not contactable) because of the key groove15, so the substantial number of poles is 40.

The electric plug of the present invention can protect the male contacts from dust or handling because the male contacts made of flexible leaf springs are covered by the shutter made of a thin plate when the plug is not connected with the mating receptacle.

Also, when the electric plug is connected with the mating receptacle, the shutter is pushed by the mating receptacle and retracted, making the plural male contacts exposed, thereby connecting the male contacts of the electric plug with the fixed female contacts of the mating receptacle.

Covering the male contacts with the thin plate shutter in this manner eliminates the need for the formation of an insulative cover housing to cover the male contacts, thereby realizing miniaturization of the electric plug or the mating receptacle.

Also, the electric plug of the present invention can be used for cradles and cables, and can further be used for printed-circuit boards and printed-circuit board connections, thereby resulting in a miniature dustproof plug with a wide application.