Angle adjusting mechanism
BACKGROUND OF THE INVENTION 
     The invention relates to an angle adjusting mechanism that holds two members at a desired relative angular position. 
     A boom type microphone stand, which is shown in FIG. 6 hereof, provides one application or use for the invention. As shown in FIG. 6, the microphone stand comprises a main stand S, an arm A on which a microphone is installed, and a boom 80 which connects the stand S and the arm A to be freely adjustable in terms of their relative rotation angle. 
     As is shown in FIGS. 7 and 8, a conventional angle adjusting mechanism for the boom 80 comprises a fixed member 81 that is installed on the main stand S and a movable member 82 that is installed on the arm A. Two friction plates 83 on opposite sides of the member 82 are compressively tightened by tightening the fixed member 81 and spaced apart parallel, upstanding support walls 86 by means of a cooperating tightening bolt 84 and a nut 85, thereby fixing the tilt angle of the movable member 82 A metal washer 87 is disposed beneath the nut 85. 
     However, this conventional mechanism suffers bending from the upper side 88 of the support walls 86, at the end of the fixed member 81 when the tightening bolt 84 and the nut 85 are tightened. When the friction plates 83 are made of a substance like rubber, etc. having compressibility, what is then the upper side of the friction plate 83A is more strongly compressed than the lower side of that plate, as shown in FIG. 9. The uneven compression of the friction plate 83A causes a one-sided tightening of the movable member 82 and causes asymmetrical wearing of the friction plate 83A, which speeds up the aging process of the rubber material of the plate. 
     A friction plate made of a non-compressible material, like a plastic, is shown in FIG. 10, which also illustrates a conventional design. When a tightening force is applied to the top part 89 of both friction plates 83B, the tightening force is applied partially and insufficiently against the movable part 82. Much wearing of the top part 89 occurs, because of the eccentric load that is applied to the friction plates 83B. As the wearing of the top part 89 becomes greater, a greater tightening force on the nut 85 will be required to obtain the same amount of tightening force on the friction plates 83B. This decreases the durability of the friction plates and of the tightening nut. At the same time, cracks and ruptures may develop in the fixed member. 
     When the arm A is long or its weight is great, further, a larger tightening force is required to prevent the arm A from sagging down. This requires that the angle adjusting mechanism itself be made larger in size, which creates problems not only in terms of its over large outside appearance but also in terms of its functional ability. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an angle adjusting mechanism which has a superior holding force, a compact outside appearance, which is smoothly operable and has high durability. 
     An angle adjusting mechanism of the invention includes a first member having a first support wall into which a tightening bolt is inserted and a second support wall for receiving a nut which is screwed onto the tightening bolt. A second member of the angle adjusting mechanism has a third holding wall which is disposed between the first and second support walls of the first member. A friction plate is provided on both sides of the third holding wall of the second member. A holding fitting, preferably made of non-yielding material, like metal, is provided inside the second support wall of the first member. That holding fitting includes a compressive part that compressively tightens the friction plate, which the holding fitting engages, due to the tightening of a support wall tightening means, in the form of a bolt and nut. The tightening means draws the support walls together and compresses the other elements between them. 
     Other objects and features of the invention are explained below with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a disassembled, exploded, perspective view of the angle adjusting mechanism according to the invention; 
     FIG. 2 is a cross section showing the assembled condition of the angle adjusting mechanism shown in FIG. 1; 
     FIG. 3 is a disassembled, exploded, perspective view of another embodiment of the angle adjusting mechanism of the invention; 
     FIG. 4 is a cross section showing the assembled condition of the angle adjusting mechanism; 
     FIG. 5 is a partly cut away, front view of the mechanism in FIG. 4; 
     FIG. 6 is a perspective view of a prior art microphone stand; 
     FIG. 7 is a front view of its essential parts; 
     FIG. 8 is a cross section thereof; 
     FIG. 9 shows the cross section in the tightened state; and 
     FIG. 10 is likewise a cross section of the same. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As is shown in FIGS. 1 and 2, the angle adjusting mechanism in this example comprises a first member 10 that ordinarily serves as the fixed side of the mechanism, a second member 20 that serves as the movable side of the mechanism, at least one, and preferably a pair, of friction plates 30 at opposite sides of the member 20 and a holding fitting 40, preferably stiff and of metal. 
     The first member 10 includes a main tubular body 11 that becomes the installation part for the stand. A first support wall 12 is formed integrally with and stands up from the tubular main body 11. A second support wall 13 extends parallel to and is spaced a distance away from the first wall 12 and stands up from the main body 11. In the first support wall 12, there is a hole 16 for receiving and passing through an inserted tightening bolt 50. In the second support wall, there is a bearing hole 14 for the insertion and passage through of the tightening bolt 50. A nut 51 is to be screwed onto the tightening bolt 50. 
     The second member 20 includes a third holding wall 21 that is provided between the first support wall 12 and the second support wall 13. A tubular part 22 extends along the plane of the holding wall 21 and above that wall. The tubular part 22 serves as an installation part for the boom pipe of a microphone or as the support for any other object supported by the stand. 
     The third holding wall 21 has a bolt hole 23 through it in alignment with the bolt hole 16 and through which the tightening bolt 50 is inserted. 
     There is a friction plate 30 on one side of the holding wall 21 toward the support wall 13 or there are friction plates on both sides of the holding wall 21. Each friction plate 30 has a ring shape. The tightening bolt 50 is inserted through the hole 31 through the plate 30. A friction plate 30 is provided on both opposite sides of the third holding wall 21 of the second member 20. 
     The holding metal fitting 40 is also annular. It has a central insertion hole 41 for passage of the tightening bolt 50 through it. The fitting 40 comprises a tubular part 43 that engages with the bearing hole 14 of the second support wall 13. It also has a flange shaped compressive part 42 which is provided on the tubular part 43. The fitting 40 is provided at the inside of the second support wall 13 and contacts the friction plate 30 that is at that side of the third holding wall 21. 
     In this example, there are a plurality of convex splines 44, each of which engages a correspondingly shaped and circumferentially located cutout 15 that is formed on the border of the bearing hole 14 of the second support wall 13. The splines in the cutouts connection holds the fitting 40 so that it is capable of sliding only in the axial direction of the tightening bolt 50, as in a splined structure. 
     The tightening bolt 50 is inserted from outside the first support wall 12 of the first member 0 and the nut 51 is screwed onto the threaded shank of the bolt 50 from outside the second support wall 13, and the nut is tightened for drawing the first and second support walls 12 and 13 toward each other and integrally tightening together the various members. 
     Since the holding metal fitting 40 is able to slide in the axial direction of the tightening bolt 50 at this time, the friction plate 30 that contacts the fitting 40 is compressively tightened over the entire annular surface of the compressive part 42 of the holding metal fitting 40. At the same time, it presses its plate surface vertically. This applies a uniform surface pressure on the friction plate 30, which, in turn, applies a large friction force on the third holding wall 21 and on the contact surface 33. This produces a force that tightens to the holding wall 21 of the second member 20 evenly and strongly. 
     The frictional force that is applied to the contact surface 33 can be adjusted by selecting the size of the friction plate 30. This makes it possible to set the holding force which is necessary for positioning the second member 20. 
     In addition, it is possible to set the necessary tightening torque by inserting a spring metal washer 19 between the holding metal fitting 40 and the nut 51. This friction engaging washer enables adjustment of the angle by moving the movable side of the boom part, etc. without loosening the nut 51. 
     In FIGS. 3 and 4, the same reference numbers as in FIG. 1 indicate the same parts. FIGS. 3 and 4 show an embodiment employing a plurality of clawed friction plates 60. A claw part 61 projects from the periphery of each friction plate. A plurality of first friction plates 60A include claws that extend down to engage the stopping part 18 of the first member 10. A plurality of second friction plates 60B include claws that extend up to engage the stopping part 28 of the second member 20. The friction plates 60A and 60B are arranged alternately along the bolt 50. It is possible and desirable for the first friction plates 60A and the second friction plates 60B to be of the same construction, and to be inverted when installed. 
     The first member 10 and the various other members are integrally tightened together from both sides by means of the tightening bolt 50 and the nut 51. 
     In this embodiment, a friction force is produced on the facing contact surfaces of the various friction plates. As a consequence, the holding force against the second member 20 is further strengthened and its relative position is held accurately. 
     It is preferable to fix the claw parts 61 to the various stopping parts in slots in the first and second members with stopping screws 29, as shown in FIGS. 3 and 5, so that the friction plates 60A and 60B may not develop backlash inside the stopping part 18 of the first member 10 and the stopping part 28 of the second member 20. 
     The tightening force that is produced when the tightening bolt 50 and tightening nut 51 are tightened is converted into a force that compresses the friction plates 30 or 60 through the holding metal fitting. Accordingly, it becomes possible to press against the holding surface of the second member over the entire surface of the friction plate(s), which produces a large compressive and tightening force so as to accurately hold the installed items. 
     In addition, the tightening force may be made to withstand a greater load by changing the size and/or the number of the friction plates. 
     Because there is not a one sided or top side load on the friction plates, as occurs with the conventional structure described above, it is possible to prevent asymmetric wear of the friction plates and of the first and second members 10 and 20, improving their durability. 
     If necessary, angular adjustment can be set smoothly to a desired angle by shifting the movable side without operating the tightening nut, in view of the presence of the washer 19. 
     The invention offers a highly practical angle adjusting mechanism which is compact in outside appearance, superior in holding force, capable of smoother operation and extremely effective. 
     Although the present invention has been described in connection with a plurality of preferred embodiments thereof, many other variations and modifications will now become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.