Abstract:
A compact rotary attenuator comprises a housing ( 1 ), a terminal board ( 3 ) having input and output terminals ( 20 A and  20 B) and electronic components connected between the input and output terminals, a driving shaft ( 13 ) attached to the terminal board ( 3 ) at right angles therewith within the housing ( 1 ), input and output contact shoes ( 11  and  12 ) for spring contact with the input and output terminals ( 20 A and  20 B), and input and output coaxial connectors ( 9  and  10 ) each having a central conductor extending into the housing ( 1 ), wherein the input and output contact shoes ( 11  and  12 ) make contact with the input and output terminals ( 20 A and  20 B) on different sides of the terminal board ( 3 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a rotary attenuator device. 
     2. Description of the Related Art 
     This type of device has been publicly known, for example as disclosed in Japanese Unexamined Patent Publication No. 2000-294410. This device has been often used as illustrated in the accompanied figure, FIG. 5, by arranging a plurality of devices  50  in one electronic device. Each rotary attenuator device  50  has a disk-shaped terminal board  52  which can rotate in a housing  51 . The disk-shaped terminal board is driven by stepwise rotational movement for a specified angle through operating a dial (not illustrated) mounted at a driving shaft  53  which protrudes outside of the housing  51 . Plural pairs of input and output terminals are locally arranged on one side of the terminal board  52 . Also, an input coaxial connector  54  and an output coaxial connector  55  are provided on a side of the housing  52 , which is opposite to the side where the driving shaft  53  is provided. 
     As illustrated in FIG. 6, contact shoes  56  and  57  respectively contact with input terminal  58  and output terminals  59  of a pair in the housing, and come to respectively contact with input terminals  58 ′ and output terminals  59 ′ of another pair once the terminal board rotates stepwise in one direction or another direction. Here, the contact shoes  56  and  57  are respectively connected to the central conductor of the connectors  54  and  55 . The contact shoes  56  and  57  of the input and output coaxial connectors  54  and  55  are made similar each other. 
     As illustrated in FIG. 7, the contact shoe  56 , for example, is made by bending a metal sheet band, such that the sheet surface of the bent part is parallel to the surface of the non-bent part. Therefore, it looks like a U-shape skid for the shaft  56 A, which is connected to the central conductor. The contact shoe  54  extends along circumferential direction on the terminal board, e.g. a direction towards its adjacent input terminal  58 ′. The contact shoe  54  elastically contacts with the input terminal by its elasticity, and comes to contact with the adjacent input terminal with its rounded end, e.g. the rounded bottom part of the U-shape. Such contact shoe is also provided to the output coaxial connector. 
     As described above, in the publicly known device, since the pair of input and output terminals  58  and  59  respectively contact with the contact shoes  56  and  57  at one side of the terminal board, e.g. on the same side of the terminal board  52 , the pair of the input and output terminals  58  and  59  cannot be provided too close to each other. Therefore, the input and output coaxial connectors  54  and  55  need to be arranged in more distant positions. Accordingly, the distance between the input terminal and the output terminal needs to be set relatively large. If plural pairs of both terminals are arranged along the circumference on the terminal board  52 , the terminal board  52  becomes large. Consequently, if a plurality of the rotary attenuator devices  50  are arranged as illustrated in FIG. 5, the total width L becomes extremely large. That is, it is not avoidable that the electronic device, in which this rotary attenuator device is used, becomes even larger. 
     Moreover, since the possible elastic displacement of the conventional contact shoe of FIG. 7 is small, the allowable amount for errors in the displacement is small. In other words, it is hard to stabilize the contact. Furthermore, because of its shape, the contact shoe smoothly contacts with the terminal when the terminal board rotates in one rotational direction, but when the terminal board rotates in the opposite direction, the contact shoe is often caught by the terminal and also, the contact tends to be unstable. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a compact rotary attenuator which does not make the electronic device large when it is used in plural. 
     According to the invention there is provided a compact rotary attenuator which comprises the terminal board, on which plural pairs of input and output terminals are provided along its circumference and an electronic part including resistance are provided between the input and output terminals of each pair; the driving shaft which is joined to the center of the terminal board in the housing to be vertical to the surface of the terminal board and held so as to rotate; input and output contact shoes which elastically contact with input and output terminals of each pair by its freely sliding movement, and input and output coaxial connectors being held by the housing and having the central conductor extending to the inside of the housing. 
     In the rotary attenuator of the present invention, the first aspect of the invention is featured by that the input contact shoe and the output contact shoe are provided on different sides of the terminal board to contact with corresponding input terminal and output terminal. 
     According to the first aspect of the invention, since the input terminal and the output terminal are provided on the opposite side of the terminal board to the other, both can be arranged in adjacent position along the circumference of the terminal board, no matter with the size of its head portion. Therefore, the distance along the circumferential direction can be short when the plural pairs of the input terminal and the output terminal are arranged. Accordingly, the distance in a radial direction for the arrangement on the circuit board can be small. As a result, the terminal board can be small in its size, and also the attenuator device can be small in its size. 
     According to the present invention, it can be designed that the input contact shoe and the output contact shoe are provided at one end of a respective elastic arm, which is formed like a cantilever, extends in the radial direction of the terminal board, and contacts with the central conductor of the coaxial connector and held at the other end. By doing this, since the contact shoe extends in a radial direction of the terminal board, only the size of the contact shoe needs to be considered in a circumferential direction of the terminal board. There is no need to secure space for elastic arm to hold the contact shoe, and the distance between the terminals can be small. For those reasons, the device can be small in its size even on this point. 
     In the present invention, the housing has a pair of flat outer surfaces, which are parallel and face each other. If each axis of the driving shaft, the input coaxial connector and the output coaxial connector is supposed to be in a surface parallel to the pair of outer surfaces, a plurality of the attenuators can be arranged by contacting the outer surfaces together, so that total width can be made shorter. 
     The second aspect of the invention is featured by that the housing has the pair of flat outer surfaces, which are parallel and face each other. And all the axes of the driving shaft, the input coaxial connector and the output coaxial connector are in one surface parallel to the pair of the outer surfaces. Since all the axes of the driving shaft, the input coaxial connector and the output coaxial connector are in one surface parallel to the pair of the outer surfaces, the attenuator can be made even smaller than the one in the first invention. Therefore, the total width in a direction of arranging the attenuators become extremely small when plural attenuators are arranged. Therefore, the device, in which the attenuator is used, can be also designed to be smaller. It can be made that the input contact shoe and the output contact shoe are provided on one end of respective elastic arm, which is formed like a cantilever and extends in a radial direction of the terminal board. Here, the elastic arm is connected with the central conductor of the coaxial connector and held thereby. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partially cutout, side view of a rotary attenuator according to an embodiment of the present invention, including input and output coaxial connectors and a driving shaft. 
     FIGS.  2 (A) and (B) are front and back views of a terminal board for the attenuator viewed in a direction of arrows A and B, respectively. 
     FIG. 3 is a perspective view of a contact shoe of the attenuator. 
     FIG. 4 is a perspective view of the attenuators that are arranged side by side. 
     FIG. 5 is a perspective view of the conventional rotary attenuators that are arranged side by side. 
     FIG. 6 is a side view of the terminal board and the contact shoe for the conventional attenuator. 
     FIG. 7 is a partially cross-section perspective view of the terminal and the contact shoe for the conventional attenuator. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, the rotary attenuator has a disk-type terminal board  3  in a hollow chamber  2  of a housing  1  which is a block-shaped metal. It is not illustrated in the figure, but the housing  1  itself can be disassembled into several parts, so that the attenuator device can be assembled by first placing the terminal board  3  in the hollow chamber  2 , as illustrated in FIG. 1, and then covering the terminal board. The housing  1  has outer surfaces  4 ,  5 , and  6 , which are respectively vertical to axes  4 A,  5 A, and  6 A. The axes  4 A,  5 A, and  6 A are vertical or parallel each other in a paper surface of FIG.  1 . Also, the housing  1  has a pair of flat outer surfaces  7 ,  8 , which are parallel to the paper surface of FIG. 1 (In FIG. 1, one of the flat outer surfaces  7  is illustrated, and the other outer surface  8  is located on the backside of the paper of the figure). Accordingly, the housing  1  has substantially rectangular parallelepiped block shape. In this invention, the outer surface does not have to be flat, and can be optionally any shape. 
     Coaxial connectors  9  and  10  are respectively attached to the outer surfaces  4  and  5  of the housing  1 . As for those coaxial connectors  9  and  10 , one is used as input coaxial connector, and the other is used as the output coaxial connector. The coaxial connectors  9  and  10  respectively have screw portions  9 A and  10 A, respectively, to connect with the coaxial cable outside the housing. Also, the coaxial connectors  9 ,  10  have central conductors  9 B,  10 B protruding into the housing. The central conductors  9 B,  10 B hold the contact shoes  11 ,  12 . The contact shoes are described below in detail. The driving shaft  13  extends outward from the outer surface  6  of the housing  1 , and the dial (not illustrated) can be attached outside the housing to rotationally drive the driving shaft  13  around the axis  6 A. The driving shaft  13  also protrudes into the housing  1 , and supports the terminal board  3  at its center position. The mutual positioning and attachment of the terminal board  3  and the driving shaft  13  are done by the spacer  14 , the nut  15 , and so on. The driving shaft  13  and the housing  1  are electrically connected by a spring washer  16  and a sliding member  17 . 
     In FIGS.  2 (A) and (B), the terminal board  3  is disk-shaped, and has a D-shaped shaft hole  3 A at its center, in which the driving shaft  13  goes through. The driving shaft  13  is stopped in the circumferential direction by the straight inner area  3 A 1  of the D-shaped shaft hole. A plurality of holes  18  is provided along the circumference of the shaft hole  3 A, and used for putting wiring through from both sides of the terminal board if required. A plurality of pairs of terminal holes  19 A and  19 B are provided along the outer circumference of the terminal board  3 . The terminal  20 A is provided at one terminal hole  19 A, extruding outward from one side of the terminal board, while the terminal  20 B is provided at the other terminal hole  19 B, extruding outward from the other side of the terminal board. 
     Conductive surface areas  22 ,  23 , as illustrated by slanting lines in FIG. 2, are printed in areas on the terminal board, where the terminals  20 A,  20 B are to be attached. The conductive surface area  23  on a surface where the terminal  20 B is attached has an extension part  24 , which extends inward in a radial direction. Electronic part  29  required for an attenuator, such as resistance, is arranged and connects between the extension part  24  on the side of the terminal  20 B and the extension part  24  on the side of the terminal  20 A, and between the extension part  24  and the central conductive surface area  25 . Electrical properties, such as resistance, of the electronic parts arranged to each pair of terminals are different among the electronic devices, and the properties of the input/output terminals gradually change by stepwise rotation of the driving shaft  13  for every contact of the contact shoes with the pair of terminals. 
     In FIG. 3, the contact shoes  11 ,  12  held by the central conductors  9 B,  10 B of the coaxial connectors  9 ,  10  are attached to one end of the elastic arm  27 ,  28 , which extends in a radial direction of the terminal board, being angled from the surface of the terminal board. The other ends of the elastic arms  27 ,  28  are connected and retained to the central conductors  9 B,  10 B. The elastic arm  27  is positioned inward in the radial direction, and bent at its middle position such that one end is vertical to the other end (here, the elastic arm can be located outward in the radial direction). On the other hand, the elastic arm  28  is positioned outward in the radial direction, and slightly bent, but extends in the radial direction of the terminal board  3 . The contact shoes  11 ,  12  attached to one end of the elastic arms  27 ,  28  are the same each other. As illustrated in FIG. 3, the contact shoe  11  contacts with the terminal  20 A, and is shaped like a wave along the circumferential direction with its ends up in the circumferential direction. Because of this shape, the contact shoe can easily move onto the adjacent terminal at the time of moving towards the adjacent terminal. Accordingly, the contact shoe  11  surely contact with terminal even when the terminal to contact is changed by the stepwise rotational movement of the terminal board  3 , and stop at the normal contact position so as to maintain its contacting condition. The width of the contact length in the circumferential direction (distance between the ends  11 A) is larger than the diameter of the head part of the terminal, but is designed not to contact with the adjacent terminal when the lower surface of the dent  11 B contacts with one terminal at normal position. 
     For those reasons, the amount of attenuation can be selected by changing the resistance between the input/output terminals or the like through stepwise rotation of the driving shaft  13  under the condition where the input and output coaxial connectors  9 ,  10  are connected to coaxial cables. 
     According to the present invention, since a pair of the input and output terminals are arranged on two sides, the distance between those terminals is smaller than before, so that the radius of the terminal board can be smaller. That is, the width of the attenuator device can be smaller. Also, the width of the contact shoe in circumferential direction can be smaller by contacting the contact shoe with the terminal in the radial direction of the terminal board, so that device can be smaller even on this point. Furthermore, since the axes of the coaxial connectors and the driving shaft are supposed to be all located in one surface (hypothetical surface), the size in the above-described width direction can be smaller also in this point. The attenuator device of the present invention can be used alone, but it can be used combining several of them. In this case, the features of the present invention can be fully used. 
     As illustrated in FIG. 4, if a plurality of the attenuators are arranged by contacting the outer surfaces of the housing, from which the coaxial connectors  9 ,  10  and the driving shaft  13  protrude, the total width L is extremely small due to the narrow width of each attenuator, so that the electronic device, in which those attenuators are used, can be made small in the direction of arranging the attenuators. 
     As described above, in the present invention, since the input terminal and the output terminal are arranged on different side of the terminal board, the distance between the input terminal and the output terminal of the pair can be shorter. Moreover, if the contact shoe is designed to contact by extending in the radial direction of the terminal board, there is no space required for holding the contact shoe in the circumferential direction. And also, the distance between the pairs of the input terminal and the output terminal can be short when plural pairs of terminals are arranged on the terminal board, as well as the distance between the input terminal and the output terminal of the pair is maintained small. As a result, the size in the radial direction of the terminal board can be extremely small; therefore, the attenuator device can be made small. If all the axes of the input and output coaxial connectors and the driving shaft can be located in one surface, which is parallel to the flat outer surfaces of the housing, the size of the device can be even smaller. In a case that plural attenuators are arranged, a large effect can be expected if they are arranged by contacting each other by their outer surfaces.