IMPROVED HOLD-DOWN APPARATUS

Abstract: A hold-down apparatus for securing a component chassis (20) onto a supporting rack (22). The apparatus is provided with a drive mechanism (28) which engages a mounting toe (26) secured to the front panel (24) of the chassis. The mechanism further includes a knob (34) and threaded spindle (32) driven by the knob. The threaded spindle (32) is received by a threaded nut (44), the nut being pivotally mounted on a hinge assembly (30) fastened to the rack. The chassis (20) is secured in place by first engaging the drive mechanism with the mounting toe (26) and manually rotating the knob (34). The spindle is thereby threaded into the pivotally-mounted nut causing the chassis to be driven toward the rear of the rack (22) until the rear electrical connector halves mounted on the chassis and rack are fully mated. The chassis is thus secured in place. An anti-rotation mechanism (58) is provided on the nut which prevents the hold-down from releasing the chassis under vibration.

Description: IMPROVED HOLD-DOWN APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the mounting of electronic equipment and more particularly to a space- saving apparatus for securing a unit of electronics onto a rack or shelf. 2» Description of the Prior Art There exists various devices for securing electronic modules or "black boxes" onto supporting racks or shelves. Such hold-down devices sometimes serve the additional function of extracting the modules from the racks or shelves. U.S. Patent Nos. 3,640,141 and 4,018,091, issued on February 8, 1972 and April 19, 1977, respectively, disclose devices which serve the dual function of holding down and extracting. Both of these patents are hereby fully incorporated herein by reference. Single function and dual function devices will be collectively referred to herein as "hold-downs." Prior art hold-downs typically include a threaded spindle which is pivotely coupled to the rack or shelf. The spindle carries a body member having a nut which threadably engages the spindle. The body member is provided with a mechanism for engaging a bracket or hook (commonly referred to as a "toe") which is mounted on the front panel of the box. In many hold-down applications, space is severely limited. This is especially true in avionic installations. The prior art hold-downs possess a serious drawback inasmuch as they require a substantial amount of space. When a box is in a secured position, the spindle extends a considerable distance away from the front panel of the box. In addition, the protruding spindle presents a serious safety hazard to persons in the area. For example, it is not uncommon for a person walking near an avionic rack to strike the relatively sharp spindle or to catch an article of clothing on the spindle. The present invention overcomes the above-noted shortcomings of the prior art hold-downs. The hold-down disclosed herein is provided with a spindle which extends away from the front panel a minimal distance. Thus, the subject hold-down requires substantially less space than prior art hold-downs and eliminates the safety hazard presented by such prior art devices. Moreover, many prior art hold-downs can be easily modified to incorporate the principles of the subject invention. These and other advantages of the subject invention will become apparent from a reading of the following Detailed Description of the Invention together with the drawings. SUMMARY OF THE INVENTION A hold-down apparatus for securing a component chassis onto a supporting rack is disclosed. The appara- tus includes a body portion having a fluted knob for driving a threaded spindle. The body portion further includes appropriate mechanism for engaging a hook or mounting toe secured to the front panel of the chassis. The threaded spindle is received by a nut assembly having a threaded bore extending therethrough. The nut assembly is pivotally mounted on a hinge assembly which is to be secured to the supporting rack. In OMPI VvTPO 1 operation, the body portion is pivoted upwards to engage 2 the toe of the chassis. The body portion is then manually 3 rotated, thereby causing the spindle to thread into the 4 nut assembly. Further rotation causes the chassis to be 5 driven by the body portion until the rear electrical 6 * connector half of the chassis has fully mated with the 7 rack-mounted connector half. At this point the rotation £ is terminated and the chassis is secured in place. 9 C BRIEF DESCRIPTION OF THE DRAWINGS 1 Figure 1 is an elevational view of a prior art hold-down apparatus with a portion of the apparatus cut away to show the details of the chassis front panel mounting top. Figure 2 is an elevational view of a first embodiment of the subject invention with a portion of the apparatus cut away to show the details of the chasis front panel mounting toe. Figure 3 is an elevational view of a second embodiment of the subject invention. Figure 4 is an exploded view of the nut assembly of the subject invention showing the details of the anti- rotation mechanism. Figure 5 is an elevational end view of the nut assembly. Figure 6 is an elevational end view of an alter- native nut assembly. Figure 7 is a perspective view of the hinge assembly of the subject invention. DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, an exemplary prior art hold-down may be seen in Figure 1. Reference is made to the previously-noted U.S. Patent Nos. 3,640,141 and 4,018,091 for details regarding the construction and operation of such hold-downs. Briefly, the depicted prior art hold-down is comprised of a body member, generally designated by the numeral 28, which is coupled to a hinge assembly 30 by way of a threaded spindle 32. The hinge assembly 30 is rigidly secured to the underside of the rack 22 which supports the module or black box, the box being generally designated by the numeral 20. Box 20 is provided with a front panel 24 which extends below the bottom of the box. Panel 24 carries a generally L-shaped hook or mounting toe 26 which is releasably captured by cooperating apparatus of the hold- down. Spindle 32 is pivotably secured to hinge assem- bly 30 by way of a pivot pin 36 which extends through and is secured within an opening (not shown) at the extreme end of the spindle. Pin 36 is carried in a pair of elongated openings 38 formed in the two sides of the hinge assembly and is retained therein by retaining washers 37 positioned at each end of the pin. The body member 28 is provided with an internal nut (not shown) which is coupled to a fluted knob 34 of the member. The nut threadably engages spindle 32. When knob 34 is manually rotated, the internal nut causes the body member to travel back and forth along spindle 32 with the direction of travel being determined by the direction of rotation. When knob 34 is rotated in a clockwise direc- tion, the body member 28 travels along spindle 32 towards the rack 22 so as to force the box onto the rack. The knob is rotated until the electrical connector halves (not shown) mounted on the rear of the box and on the rack have fully mated. The insertion force is limited by an inter- nal clutch mechanism which uncouples the knob 34 from the internal nut when a predetermined amount of force has been applied. The body mechanism 28 is further provided with an anti-rotation mechanism (not shown) whic prevents the Internal nut from rotating when subjected to vibration. As can be seen in Figure 1, when the box is so secured, the spindle extends a substantial distance past the body member 28 thereby occupying considerable space and pre- ' senting a safety hazard to persons in the area. The box is extracted by rotating knob 34 in a counterclockwise direction. Body member 28 moves away from the rack along spindle 32. Eventually, raised member 40 of body member 28 engages the bottom of the front panel 24 thereby applying an extracting force to the box. This extracting force causes the pivot pin to move from the position shown in Figure 1 to the opposite end of the opening which is closer to the supporting surface of rack 22. Thus, the angle of spindle 32 with respect to the rack supporting surface will be reduced during extrac- tion thereby reducing the undesirable tendency of the hold- down to lift the front of the box. Hinge 30 is also pro- vided with a shoulder or stop (not shown) which engages spindle 32 when the spindle is in the extracting position to further inhibit lifting. Referring now to Figure 2, a first embodiment of the subject invention may be seen. Those elements of the disclosed hold-down which are equivalent to those of the prior art hold-down have been identified with the same numeral. The hold-down includes a body portion 28 similar in construction to the body portion 28 of the prior art hold-down of Figure 1. The hold-down further includes a threaded spindle 42 which extends from one end of the body portion 28. Spindle 42, which is provided with at least one planar surface along its entire length, is secured to the internal nut of the body portion 28 by a roll pin or the like. Thus, the fluted knob 34 and spindle 42 rotate together. Threaded spindle 42 is received by a nut assembly, generally designated by the numeral 44 which is in turn mounted in a hinge assembly, generally designated by the numeral 46. As can best be seen in Figures 4 and 5, hinge assembly 44 is comprised of a cylindrical member 48 having an axial bore which extends entirely through the member and which is provided with threads 50 which cooperate with the threads of spindle 42. Nut assembly 44 further includes a pair of coaxial studs or pivot pins 52 which extend from opposite sides of member 48. Pivot pins 52 are positioned adjacent one end of member 48 and are aligned transverse to the major axis of the member. An anti-rotation mechanism is included in nut assembly 44 which prevents the hold-down from releasing when subjected to vibration and the like. The mechanism includes a cylindrically-shaped housing 54 which is positioned on member 48 adjacent the end of the member opposite pivot pins 52. Housing 54 is provided with a co- axial bore 55 (Figure 5) which extends through the entire length of the housing end which is in communication with the threaded bore of cylindrical member 48. The diameter of bore 55 is reduced in the area adjacent member 48 so as to form a annular shoulder 56. The anti-rotation mechanism further includes a spindle-contacting element, generally deisgnated by the numeral 58. Element 58 is provided with a hemispherical surface 60 and an annular flange 62. The diameters of surface 60 and flange 62 are such that element 58 is free to move within bore 55 of housing 54 until the flange 62 contacts shoulder 56, with the hemispherical surface 60 of the element extending into the threaded bore of cylindri- cal member 48. The anti-rotation mechanism further includes a spring 64 and a set screw 66. The spring is positioned adjacent spindle-contacting element 58 and is held in place by set screw 66 which engages cooperating threads formed in bore 55. * As can best be seen in Figure 5, when one of the planar surfaces of threaded spindle 42 is contacting ele- ment 58, the flange 62 of the element is contacting or almost contacting shoulder 56 of housing 54. If the spin- die 42 is manually rotated, the circular surface of the spindle engages element 58 thereby causing the element to be forced back into housing 54 so as to slightly compress spring 66. As the spindle is further rotated, the planar surface of the spindle again engages element 58 thereby permitting the element to return to its original position with flange 62 engaging or almost engaging shoulder 56. Thus, a rotational resistance is created which can be overcome by manually rotating knob 34, but which is suffi- ciently great to prevent the hold-down from releasing the box under vibration. Referring to Figure 7, the details of the hinge assembly 46 may be seen. The assembly is preferably machined from a block of aluminum so as to minimize weight. Assembly 46 is provided with a cavity for receiving nut assembly 44 together with spindle 42. The width of the hinge assembly cavity is slightly larger than the diameter of cylindrical member 48 of the nut assem- bly 44. A cavity of width of 0.328 inches, to accommodate a cylindrical member 48 having a diameter of 0.325 inches, has been found to be suitable. The cavity extends straight through the forward portion of the hinge assembly to form a rectangular U-shaped opening or cut out 70. The dimensions of the cavity are reduced at the rear of the assembly to form a smaller circular U-shaped opening on cut out 72. The upper portion of hinge assembly 46 is provided with two mounting screw holes 74 which extend from the top planar surface 78 of the assembly down into the central cavity. Holes 74 are each provided with taped steel helicoil inserts for threadably receiving a pair of * mounting screws which extend through the supporting shelf 22. The side walls of hinge assembly 46 are each provided with an elongated opening 76. Openings 76 receive the pivot pins 52 of the nut assembly 44, with the width of the openings being somewhat greater than the diameter of the pivot pins 52. An opening width of approximately 0.18 inches to accommodate pin diameters of .156 has been found suitable. The angle of the major axis of the elongated openings 76 with respect to the top planar surface 78 together with the length of the openings are dictated by two primary considerations. First, the openings should be dimensioned to ensure that the spindle pivot point for extraction and the pivot point for insertion of the box are optimum. Second, the dimensions should be such that the nut assembly 48 can be properly installed within the hinge assembly 46. With respect to the first requirement, open- ings 76 should be dimensioned to enable the pivot point of spindle 42 to switch between the holding-down and extrac- tion positions. This is the sole function of the elon- gated openings 38 in the prior art hold-down of Figure 1. If the angle of openings 76 is too small, the difference in the the distance of the two pivot points from the planar surface 78 will be inadequate. Conversely, if the angle is too great, there will be a tendency for the pivot pins 52 to shift during the extraction process from the desired extraction position along the length of the openings downwards towards the insertion position at the opposite end of the opening. Any angle on the order of 33° is preferred although angles ranging from 15° to 45° are acceptable. With respect to the second requirement, elongated openings 76 should be of sufficient length to permit the nut assembly 44 to be installed within the hinge assembly 46. Installation is accomplished by first positioning the nut assembly inside the hinge assembly cavity with the axis defined by the pair of pivot pins 52 being aligned with the major axes of the elongated open- ings 76. Next, the nut assembly is twisted or rotated about the major axis of cylindrical member 48 until the pivot pins are positioned within the openings 76 as shown in Figure 2. Nut assembly 44 cannot be removed unless the assembly is rotated with the axis of cylindrical member 48 (or threaded spindle 42) is perpendicular with the major axis of openings 76. Inasmuch as spindle 42 is positioned within opening 70 of the hinge assembly 40 when the hold- down is in the holding-down position, the nut assembly will remain securely in place. In order to enable the nut assembly to be twisted into place as described above, the distance from an extreme end of one of openings 76 to the opposite extreme end of the other opening must be at least as great as the distance between the extreme ends of pins 52. If the distance between the opposite ends of opening 76 is too great, however, the nut assembly will have a tendency to disengage from the hinge assembly when the hold-down is out of the holding down position. Accordingly, it is preferable that the dimensions of nut and hinge assembly be such that a small amount of force is required to twist the nut assembly into place. Elongated openings approxi- mately 0.425 inches in length and 0.18 inches in width 1 have been found suitable. A compatible nut assembly would 2 have pins of 0.156 inches in diameter which extend 0.560 3 inches from end to end. 4 Operation of the subject hold-down is straight 5 forward. In order to insert a box, the fluted knob 34, {- ' and the threaded spindle 42 driven by the knob, are 7 rotated in a counter-clockwise direction. Such rotation 8 causes spindle 42 to unthread thereby causing the body 9 portion 28 to move away from nut and hinge assemblies. 0 Next, the body portion is lifted up to engage mounting 1 toe 26 of the box 20. When the body portion is secured to the toe, fluted knob 34 is rotated in a clockwise 3 direction thereby causing the spindle 42 to thread into the nut assembly 44. The body portion applies an inser- 5 tion force on the box thereby causing the rear connector 6 halves to mate. Rotation of the knob is continued until a 7 predetermined maximum insertion force is applied. Once 8 the maximum force is reached and the connector halves 9 fully mated, the internal clutching mechanism in the body 0 portion disengages the fluted knob 34 from the threaded 1 spindle 42. Thus, further rotation of knob 34 in the 2 clock-wise direction will no longer drive spindle 42. 3 As can be seen in Figure 2, when the subject invention is in the holding down position, the threaded 5 spindle extends down below the supporting shelf 22. 6 Accordingly, the spindle does not occupy precious space 7 and does not present a safety hazard. The anti-rotation mechanism prevents the threaded spindle from rotating due to vibration or the like. In order to ensure that the box is held securely in place, the hinge assembly 46 should be mounted on the rack relative to the mounting toe 26 of the box so that the spindle 42 is at an angle with respect to the rack surface of 17 plus or minus 8 degrees. 5 Referring now to Figure 3, a second embodiment of the subject invention may be seen. This embodiment is directed to a single function hold-down which is capable of securing a box in position but is not capable of performing the extraction function. The latter function must be accomplished by other means well-known in the art. Those elements of the second embodiment hold-down which are equivalent to those of the first embodiment hold-down are identified by the same numeral. The second embodiment hold-down is comprised of a body portion, generally designated by the numeral 80, which includes a fluted drive knob 82 and a ferrule 84. Ferrule 84 is rotably mounted on the drive knob. A threaded spindle 42 is rigidly secured to and extends from the body portion 80. Spindle 42 is received by a nut assembly 44 which is pivotably mounted within hinge assembly 46. The nut assembly 44 is provided with an anti- rotation mechanism similar to that of the first embodi- ent. Nut assembly 44, hinge assembly 46 and threaded spindle 42 cooperate in the same manner as do the corre- sponding components of the first embodiment hold-down. Elongated openings 76 of hinge assembly 46 are dimensioned such that the nut assembly can be installed in the hinge assembly in the same manner previously described regarding the first embodiment hold-down. The angle of openings 76 are not critical in this application inasmuch as the hold-down is not required to pivot between an extraction and a holding-down position. A box 20 is inserted by placing the box on the shelf with the connector halves positioned adjacent one another. Knob 82, and spindle 42 driven by the knob, are then rotated in a counter-clockwise direction. The body portion is thereby backed off, so that the hold-down can be pivoted upwards with the ferrule 84 being positioned over the mounting toe 26 of the box. Next, knob 82 is rotated in a clockwise direction thereby forcing the box " back so as to cause the rear connector halves to engage. The knob is rotated until the connectors are fully mated. Care should be taken to avoid applying an excessive force. If desired, the hold-down force can be limited using an " internal clutch mechanism similar to that of the first embodiment hold-down. When the second embodiment hold-down is in the holding down position as shown in Figure 3, spindle 42 extends down below the rack 22 thereby conserving space and avoiding the creation of a safety hazard. As with the first embodiment hold-down, the hinge assembly of the second embodiment device should be mounted on the rack so as to achieve the desired spindle angle of 17 plus or minus 8 degrees. Referring now to Figure 6, an alternative embodiment nut assembly, generally designated by the numeral 82, may be seen. Nut assembly 82 includes a cylindrical member 48 having a threaded bore for receiving the threaded spindle 42. Pivot pins 84 and 86, which are positioned on opposite sides of member 48, are provided which have the same function as those of pins 52 of nut assembly 44. Nut assembly 82 is provided with an anti- rotation mechanism which is an integral part of pivot pin 86. The mechanism includes a spindle-contacting element 58 having a hemispherical surface, a spring 64 positioned adjacent element 58 and a set screw 66 which retains element 58 and spring 64 in place. Element 58, spring 64 and screw 66 cooperate together in the same manner as the corresponding elements of the Figure 5 embodiment in order to carry out the anti-rotation function. Pin 86 is somewhat longer than pin 84 for the purpose of accommodating the anti-rotation mechanism. In order to facilitate the installation of the alternative embodiment nut assembly 82 in the hinge assembly 46, pin 84 is provided with a removable end section 88 which is threadably secured to a base section 90. The nut assembly 82 is installed within the hinge assembly by first removing end section 88 from base section 90. Next, assembly 82 is placed within the cavity of the hinge assembly 46 with pin 86 positioned adjacent one of the openings 76. The assembly is then rotated thereby causing pin 86 to extend through the opening 76 and the base sec- tion 90 to extend slightly into the remaining opening 76. Finally, end section 88 is screwed onto the base section through the remaining opening 76 thereby securing the assembly in place. Thus, two embodiments of a novel hold-down have been disclosed. Although such embodiments have been described in some detail, it is to be understood that various changes can be made by one of ordinary skill which will fall within the spirit and scope of the invention as defined by the appended claims.

Claims: WHAT IS CLAIMED IS; 1. A hold-down apparatus for securing a component chassis onto a supporting rack comprising : a hinge assembly to be fastened to the supporting rack; a nut assembly pivotably mounted on said hinge assembly; a body portion for engaging the component chassis; and a spindle, coupled to said body portion, which is threadably received by said nut assembly. 2. The apparatus of Claim 1 wherein said nut assembly is provided with a threaded bore, which extend entirely through said nut assembly, for receiving said spindle. 3. The apparatus of Claim 2 wherein said nut assembly further includes anti-rotation means for resisting rotation of said spindle. 4. The apparatus of Claim 3 where said nut assembly includes a pair of opposing pins which are received by cooperating openings in said hinge assembly, 5. The apparatus of Claim 4 wherein said openings in said hinge assembly are elongated openings. 6. The apparatus of Claim 5 wherein said elongated openings are aligned at an angle of at least 15 degrees with respect to the supporting surface of the rack. 7. The apparatus' of Claim 6 wherein said anti- rotation means includes a spring-biased element for engaging said spindle. 8. The apparatus of Claim 7 wherein said anti- rotation means is incorporated into one of said opposing pins of said nut assembly. 9. A hold-down apparatus for securing a component chassis onto a supporting rack comprising: a body portion for engaging the component chassis; a threaded spindle driven by said body portion; a hinge assembly to be secured to the supporting rack, said hinge assembly being provided with a pair of elongated openings; and a nut assembly having a threaded bore extending entirely through said nut assembly which receives said threaded spindle, said nut assembly being provided with a pair of opposing mounting pins which are positioned within said elongated openings of said hinge assembly. OMPI

Inventors: HOLLINGSEAD ROBERT A, HOLLINGSEAD, ROBERT, A.
Applicants: HOLLINGSEAD INTERNATIONAL
Application year: 1983
Main classification: F16H27
IPC codes: B25B5, F16B5, H05K7