Ordnance arming switch knob assembly

An improved ordnance arming knob assembly. An arbor is secured to a switch shaft. A knob is keyed to the arbor to move in an axial direction relative to the arbor while preventing rotation between the knob and the arbor. A pin on the knob extends in a direction parallel to the switch shaft axis into a stationary hole located, for example, on a panel on which the switch is mounted. The knob must be pulled in an axial direction against the force of one or more springs to withdraw the pin from the hole prior to turning to actuate the arming switch.

TECHNICAL FIELD 
The invention relates to switch control knobs and more particularly to an 
improved ordnance arming switch knob assembly which requires two distinct 
actions in the proper sequence in order to arm an explosive ordnance. 
BACKGROUND ART 
Most ordnance arming devices used with explosives require at least two 
distinct enabling features to prevent accidental arming. For example, some 
systems require actuation of two separate switches for arming an 
electrically triggered explosive. In other systems, a cover must be moved 
to obtain access to an arming switch. In still another type of system, a 
key must be inserted into the switch before it can be actuated. 
DISCLOSURE OF INVENTION 
According to the invention, a knob assembly which requires two distinct 
actions is provided for arming explosive ordnance. A knob on the assembly 
must be pulled against a substantial spring force before it can be rotated 
to actuate a rotary ordnance arming switch. An arbor is secured to the 
shaft of a rotary switch. The knob is keyed to the arbor for limited axial 
movement relative to the arbor. A spring between the arbor and the knob 
urges the knob to an axial position wherein a pin on the knob engages a 
stationary hole. The hole may be, for example, in a panel on which the 
switch is mounted. While the pin is positioned in the hole, the knob and 
the arbor cannot rotate to actuate the switch. In order to actuate the 
switch, the knob must be pulled against the force of the spring to 
withdraw the pin from the hole and the knob then must be rotated to turn 
the arbor and the attached switch shaft. 
Accordingly, it is an object of the invention to provide a switch knob 
assembly which requires pulling prior to rotating in order to arm an 
ordnance. 
Other objects and advantages of the invention will be apparent from the 
following detailed description of preferred embodiments thereof and the 
accompanying drawings.

BEST MODES FOR CARRYING OUT THE INVENTION 
Referring to FIGS. 1 and 2 of the drawings, a cross sectional view is shown 
through a knob assembly 10 according to one embodiment of the invention 
for actuating a rotary switch 11 (shown in fragmentary). The switch 11 is 
mounted in a keyed opening 12 through a panel 13. The opening 12 is keyed 
to prevent rotation of the switch 11 relative to the panel 13. The switch 
11 is mounted on the panel 13 with a washer 14 and a nut 15. A rotary 
switch shaft 16 projects past the nut 15. The switch 11 may be connected, 
for example, to arm an explosive ordinance (not shown). Or, the switch 11 
may be connected in any other electric circuit in which accidental 
actuation of the switch 11 must be prevented. 
The knob assembly 10 generally consists of an arbor 17 and a knob 18. The 
arbor 17 has a blind opening 19 for receiving the shaft 16. A cone point 
setscrew 20 is threaded into an opening 21 in the arbor 17 and engages a 
conical detent 22 in the shaft 16 for securing the arbor 17 to the shaft 
16. A hole 23 in the knob 18 aligns with the arbor hole 21 to facilitate 
insertion of the setscrew 20. The arbor 17 is generally cylindrical and 
has a stepped outer diameter with an upper section 24 having a slightly 
smaller diameter than a lower section 25. An annular surface 26 is formed 
between the surfaces 24 and 25. Opposite the setscrew 20, a keyway 27 is 
formed in the lower section 25 to extend parallel to the rotational axis 
of the switch shaft 16 and the attached arbor 17. 
The knob 18 has a stepped axial bore including a lower section 28 which 
slides over the lower arbor section 25, a lower intermediate section 29 
which slides on the upper arbor section 24, an upper intermediate section 
30 which is coaxial with and spaced from the upper arbor section 24, and a 
larger diameter upper section 31. An annular surface 32 is formed between 
the lower bore section 28 and the lower intermediate bore section 29 and 
an annular surface 33 is formed between the lower intermediate bore 
section 29 and the upper intermediate bore section 30. A helical 
compression spring 34 is positioned over the upper arbor section 24 and 
extends between the annular knob surface 33 and a spring retainer 35 
secured to the arbor 17. The spring retainer 35 may be in the form of an 
annular washer which is secured to the arbor 17 by bending an annular lip 
36 on the arbor 17 over the spring retainer 35. After the spring retainer 
35 is secured to the arbor 17 during manufacture of the knob assembly 10, 
a cover plate 37 is secured to the knob 18 to cover the upper knob bore 
section 31. The cover plate 37 is secured to the knob 18 by bending an 
annular lip 38 over a perimeter 39 of the cover plate 37. 
A pin 40 is pressed into a radial hole 41 in the knob 18. The pin 40 
projects into the keyway 27 to limit relative motion of the knob 18 to the 
arbor 17 to linear motion in an axial direction. During rotation of the 
knob 18, the pin 40 engages the sides of the keyway 27 to simultaneously 
rotate the arbor 17 and the attached switch shaft 16. The knob 18 has a 
second pin 42 pressed into a hole 43. The hole 43 is formed in a bottom 
surface 44 on the knob 18 and extends in a direction parallel to the axis 
of the switch shaft 16 and of the knob assembly 10. The pin 42 has an end 
45 which projects from the bottom knob surface 44 into a hole 46 in the 
panel 13. 
In operation, the knob 18 can move in an axial direction between two 
positions. In one position, as is shown in FIG. 1, the spring 34 presses 
the knob 18, relative to the arbor 17, towards the panel 13. At this 
position, movement is limited by the annular knob surface 32 abutting the 
annular arbor surface 26. Since the pin end 45 is located in the 
stationary panel hole 46, the knob 18 and the attached arbor 17 and the 
switch shaft 16 are prevented from being rotated. In order to actuate the 
switch 11, the knob 18 must be pulled in an axial direction against the 
force of the spring 34 to a position wherein the pin end 45 is withdrawn 
from the panel hole 46. While the pin end 45 is held clear of the panel 
hole 46, the knob 18 is rotated to actuate the switch 11. For safety, the 
spring 34 may be sized to require a substantial force for withdrawing the 
pin end 45 from the panel hole 46. For example, a pulling force on the 
order of 6 pounds may be required. Axial motion of the knob 18 as it is 
pulled away from the panel 13 is limited by the spring retainer 35 
abutting an annular surface 47 between the upper intermediate bore section 
30 and the upper bore section 31 in the knob 18. 
FIGS. 3-5 illustrate a second embodiment according to the invention of a 
switch knob assembly 50 for arming explosive ordnance (not shown) or for 
other applications where accidental operation of a switch must be 
prevented. The assembly 50 includes an arbor 51 secured to a shaft 52 of a 
rotary switch 53 (shown in fragmentary) and a knob 54. The switch 53 is 
secured in a keyed opening 55 in a panel 56 with a washer 57 and a nut 58. 
The arbor 51 is attached to the switch shaft 52 with a cone point setscrew 
59 which is passed through an opening 60 in the knob 54 and is threaded 
into an opening 61 in the arbor 51. 
The arbor 51 is generally cylindrical and has three keyways 62-64 formed 
therein. The three keyways 62-64 each extend parallel to the rotational 
axis of the switch shaft 52 and to the axis of the arbor 51 and are spaced 
120.degree. apart. Each keyway 62-64 is open at an end surface 65 of the 
arbor 51 adjacent the nut 58 and is closed by an end 66 at an opposite end 
67 of the arbor 51. As best seen in FIG. 4, the keyway 62 has a generally 
semicircular cross sectional area 68 and has flared sides 69 and 70 which 
join with a cylindrical side 71 of the arbor 51. The keyways 63 and 64 
have similar cross sections. 
The knob 54 has a knurled or shaped top 72 to facilitate pulling and 
turning the knob 54. The knob has a central bore 73 which includes an 
upper end 74 sized to receive a cap 75, an intermediate section 76 and an 
enlarged lower end 77 which provides clearance for the nut 58. After the 
arbor 51 is inserted into the bore 73, the cap 75 is secured in the upper 
bore end 74 by an annular lip 78 on the knob 54 which is bent over the cap 
75. Three generally semicircular tabs 79-81 project from the knob 54 
radially inwardly into the intermediate bore section 76. The tabs 79-81 
are sized to be received by the keyways 62-64, respectively and function 
as a means for keying knob 54 to arbor 51. The tabs 79-81 slide in the 
keyways 62-64 when the knob 54 is moved in an axial direction, while 
preventing rotational motion between the knob 54 and the arbor 51. 
A helical compression spring 82 is located in the keyway 62. The axis of 
the spring 82 is parallel to the axis of the shaft 52 and the spring 82 is 
compressed between the keyway end 66 on the arbor 51 and the knob tab 79. 
A second helical compression spring 83 is located in the keyway 63 and is 
compressed between the keyway end 66 on the arbor 51 and the knob tab 80. 
Similarly, a third helical compression spring 84 is located in the keyway 
64 and is compressed between the keyway end 66 on the arbor 51 and the 
knob tab 81. The springs 82-84 urge the knob 54 towards the panel 56 until 
the arbor end 67 abuts the cap 75. When the knob 54 is in this position, 
as is shown in FIG. 3, a boss 85 integrally formed on the knob 54 projects 
into a hole 86 in the panel 56. So long as the boss 85 is located in the 
hole 86, the knob 50 is prevented from being rotated and, hence, the 
switch 53 cannot be actuated. 
As is shown in FIGS. 3 and 4, a pin such as cylinder 87 is located 
coaxially within the spring 82. When the knob 54 is pulled away from the 
panel 56 against the pressure of the springs 82-84, the knob 56 can move 
in an axial direction until an end 88 on the pin 87 abuts the keyway end 
66 and an end 89 on the pin 87 abuts the knob tab 79. Further axial motion 
of the knob 54 is prevented by the pin 87. It should be appreciated that 
although only one pin 87 is required, a separate pin may be positioned 
within each of the springs 82-84 and that the one or more pins may be 
either separate from the knob 54 and the arbor 51, as shown, or may be 
secured to or integrally formed with either the knob 54 or the arbor 51. 
In operation, the springs 82-84 normally position the knob 54 wherein the 
pin 85 is located in the panel opening 86 so that the switch shaft 52 
cannot be accidentally rotated. When the switch 53 must be actuated, the 
knob 54 first must be pulled against the force of the springs 82-84 until 
the pin 85 is withdrawn from the stationary panel hole 86 and while 
continuing to pull, the knob 54 must be rotated to actuate the switch 53. 
The springs 82-84 exert sufficient force on the knob 54 to prevent 
accidental operation of the switch 53. 
FIG. 6 is a cross sectional view of a third embodiment according to the 
invention of a switch knob assembly 92 for preventing accidental rotation 
of a shaft 93 on a rotary switch 94 (shown in fragmentary). The switch 94 
is shown mounted on a panel 95 with a washer 96 and a nut 97. The assembly 
92 includes an arbor 98 and a knob 99 which is keyed for limited axial 
movement on the arbor 98. The arbor 98 has an axial opening 100 in an end 
101 which receives the switch shaft 93. A conical point setscrew 102 
secures the arbor 98 to the switch shaft 93. The arbor 98 has a 
cylindrically shaped surface 103 and has an enlarged diameter flange 104 
adjacent an end 105. The arbor 98 further has an arcuate keyway 106 
adjacent the end 101. 
The knob 99 has a knurled rim 107 to facilitate pulling and rotating the 
knob 99 to actuate the switch 94. A stepped axial bore 108 extends through 
the knob 99. The bore 108 has a lower section 109 of a diameter for 
engaging the arbor surface 103 and an upper section 110 of a diameter for 
engaging the arbor flange 104. An annular surface 111 is located between 
the bore sections 109 and 110. A helical compression spring 112 is 
positioned coaxially around the arbor surface 103 to be compressed between 
the arbor flange 104 and the annular surface 111. After the arbor 98 and 
the spring 112 are assembled in the knob bore 108, a cap 113 is positioned 
in the knob bore 108 and secured by bending an annular lip 114 on the knob 
99 over the cap 113. The spring 112 urges the knob 99 relative to the 
arbor 98 to an axial position wherein the arbor end 105 abuts the cap 113. 
A pin 115 is pressed into a radially directed hole 116 in the knob 99 to 
project from the knob 99 into the keyway 106. The pin 115 restricts the 
knob 99 to limited axial movement relative to the arbor 98 and rotates the 
arbor 98 with the knob 99. A second pin 117 is pressed into a hole 118 in 
a bottom surface 119 of the knob 99. The pin 117 extends in a direction 
parallel to the axis of the knob 99, the arbor 98 and the shaft 93. The 
pin 117 has an end 120 which projects from the knob surface 119 and 
normally extends into a hole 121 in the panel 95. 
The switch knob assembly 92 functions similar to the above described switch 
knob assemblies 10 and 50. Normally, the spring 112 urges the knob 99 to a 
position relative to the arbor 98 wherein the projecting pin end 120 is 
located in the stationary hole 121 in the panel 95. This prevents rotation 
of the knob 99 to actuate the switch 94. In order to actuate the switch 
94, the knob 99 must be pulled against the force of the spring 112 until 
the pin 120 clears the panel hole 121. Once the pin end 120 is held clear 
of the hole 121, the knob 99 may be rotated to actuate the switch 94. 
The three described embodiments of a switch knob assembly each have a pin 
which engages a hole in a panel mounting a switch. It will be appreciated 
that the switch knob assembly will function equally well with any 
stationary hole positioned to be engaged by a projecting knob pin. For 
example, a positioning hole may be formed in a plate which has a mounting 
hole that slides over the switch shaft and is clamped between the nut, 
which secures the switch to a panel, and the panel. The mounting hole in 
the plate may be keyed, so as not to rotate relative to the switch, or it 
may be keyed to the panel, so as not to rotate relative to the switch. 
Although each of the above described knob assemblies has been described as 
engaging a single stationary hole, it should be noted that the knob 
assemblies may engage more than one hole. For example, two separate 
stationary holes may be located with one hole engaged when the rotary 
switch is in one position and the other hole engaged when the rotary 
switch is in another position. It will be appreciated that various other 
modifications and changes may be made to the above described switch knob 
assemblies without departing from the spirit and the scope of the 
following claims.