Pneumatic clamping device

A pneumatic clamping device used to clamp a plurality of sheets together includes a cylinder with a guide element at one end defining a pneumatic chamber within the cylinder and a piston having an elongated shaft, a cylindrical head on one end of the shaft and a clamping foot on an opposite end of the shaft. The piston head is movable within the cylinder chamber, while the piston shaft extends through the guide element and positions the piston foot for insertion through aligned holes in the sheets when the shaft is substantially extended from the cylinder. A coil spring is positioned in the cylinder chamber between one side of the piston head and an end of the cylinder opposite from its one end for biasing the shaft to its extended position. Pressurized air for a source thereof may be supplied to the cylinder chamber at an opposite side of the piston head for overcoming the bias force of the coil spring, resulting in retraction of the piston shaft and clamping of the sheets together between the foot and the cylinder.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention broadly relates to techniques for clamping various 
types of structures during manufacturing thereof and, more particularly, 
is concerned with a pneumatic device for clamping parts of structures 
together while fastener holes are drilled through the structures. 
2. Description of the Prior Art 
Several approaches are disclosed in the prior art for clamping various 
structures, such as a pair of metal sheets, together. One approach employs 
a clamping mechanism 10 comprised by a collet 12 and a mandrel 14 shown in 
FIG. 1 which is used in conjunction with and as an integral part of a 
machine assembly called a drillmotor (not shown). The collet 12 must be 
inserted through a previously drilled hole to a depth so that the flanges 
16 at the base of the collet are through the hole. A clamping force is 
applied when the tapered mandrel 14 is drawn upward into the slotted 
section of the collet. The force exerted by the mandrel 14 spreads the 
collet 12 to fill the hole and presses upward so that the collet flanges 
16 bear against the lower surface of the part through which the collet was 
inserted. One such device is manufactured by Omark Industries and is known 
as a Spacematic Drillmotor. 
Another approach utilizes a hand operated mechanical clamping device which 
exerts varying degrees of clamping force depending upon the torque applied 
to the device. This device is commonly referred to as a "cleeco" clamping 
device. Patents to Finkle, U.S. Pat. No. 2,280,403; Rossman, U.S. Pat. No. 
2,371,470; Mooy, U.S. Pat. No. 2,388,603; Van Sittert, U.S. Pat. No. 
2,397,892; Cole, U.S. Pat. No. 2,561,098; and Jones, U.S. Pat. No. 
3,096,679, show clamping devices of the "cleeco" type. 
Several disadvantages are inherent in these existing clamping approaches 
and deleterious effects result therefrom. The size of the collet and 
drillmotor assembly plus a template foot and tail pad which are integral 
parts of the assembly make the assembly unwieldly and restrict use of the 
assembly to large, open and uniformly contoured surfaces. An additional 
disadvantage to this device is that the collet grip ranges are limited and 
collets must be changed as various thicknesses of material are encountered 
during assembly operations. Disadvantages to the "cleeco" device are that 
the mechanical operations for its installation and removal are time 
consuming. Also, in most instances the device is not capable of applying a 
constant clamping force and frequently must be retorqued after initial 
installation to apply desired clamping force. A further disadvantage to 
the "cleeco" device is that the small footprint provided by this device at 
the point where the clamping force is applied to the understructure can 
inflict damage to the understructure if the "cleeco" device is 
overtorqued. 
Therefore, a need exists for an improved device for clamping structures 
together which is easy to handle, has substantially universal application 
in not being limited by the shape of the structures, and will quickly and 
simply provide a constant, controlled clamping force. 
SUMMARY OF THE INVENTION 
The present invention provides a pneumatic clamping device designed to 
satisfy the aforementioned needs. The device is preferably portable, can 
be installed at a previously drilled fastener hole very quickly and is 
capable of exerting a constant controlled force for clamping two or more 
plies or sheets of material, such as metal, together. The constant 
clamping force is sufficient to prevent or minimize the formulation and 
disposition of chips and burrs of metal at the interface of two or more 
parts when fastener holes are drilled through the parts adjacent to the 
region of application of the clamping force. The pneumatic device is 
small, independently operated, quick acting, and easily installed. It can 
be operated on "shop air" (readily available pressurized air). The air 
pressure can be regulated to deliver a constant clamping force even when 
the parts to be clamped are assembled with a viscous sealant material 
applied to their faying surfaces. 
Accordingly, the present invention provides a pneumatic clamping device for 
clamping together a plurality of sheets of material undergoing some 
manufacturing operation. The device comprises the combination of: (a) a 
cylinder defining a pneumatic chamber therein and an elongated central 
bore; (b) a piston having an elongated shaft, a head on one end of the 
shaft and a clamping foot on an opposite end of the shaft, with the piston 
head disposed for translatory movement within the chamber, the piston 
shaft extending through and movable along the central bore of the cylinder 
upon movement of the piston head, and the piston foot disposed outside of 
the cylinder and movable toward and away from the cylinder upon 
corresponding movement of the piston head and shaft; (c) means disposed in 
the chamber at a first side of the piston head and biasing the head for 
movement in a first direction to a first position wherein the piston shaft 
is substantially extended from the cylinder and the piston foot is 
disposed remote from the cylinder, allowing sufficient clearance for 
insertion of the foot through aligned holes in the plurality of adjacent 
sheets of material; and (d) a source of pressurized air connected to the 
chamber of the cylinder at a second, opposite side of the piston head and 
actuatable for forcibly moving the piston head against the biasing means 
wherein the piston shaft is substantially retracted into the cylinder and 
the piston foot is disposed adjacent to, but spaced from, the cylinder, 
forcibly clamping the sheets therebetween. The device further includes a 
positioning pin attached to the cylinder adjacent the elongated piston 
shaft and extending generally parallel thereto outside of the cylinder.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings, and more particularly to FIGS. 2 through 4, 
there is shown the preferred embodiment of the pneumatic clamping device 
of the present invention, being generally designated 20. The pneumatic 
clamping device 20 includes a cylinder 22, a guide element 24, a bearing 
ring 26, a piston 28, a positioning pin 30, a coil spring 32, and a source 
of pressurized air 34. 
The cylinder 22 is formed by a hollow cylindrical housing 36 having a 
closed end 38 and an opposite open end 40. The guide element 24 is 
externally threaded and is installed into the complementarily internally 
threaded open end 40 of the housing 36. The guide element 24 in such 
location is spaced from the closed end 38 of the housing 36 such that a 
pneumatic chamber 42 is defined therebetween within the cylinder housing 
36. Also, the cylindrical guide element has a central bore or opening 44 
extending through it. 
The bearing ring 26 is attached to the guide element 24 and disposed 
outside of the cylinder housing 36. The ring 26 has a central opening 46 
which is aligned with the central opening 44 of the guide element 24. 
The piston 28 includes an elongated shaft 48, a cylindrical head 50 on one 
end of the shaft 48, and a clamping foot 52 on an opposite end of the 
shaft 48. The outer cylindrical surface 54 of the piston head 50 forms an 
air-tight seal with the interior cylindrical surface 56 of the cylinder 
housing 36, and furthermore is disposed for translatory, rectilinear 
sliding movement within the pneumatic chamber 42. The piston shaft 48 
extends through the aligned openings 44 and 46 of the guide element 24 and 
bearing ring 26, respectively, in an air-tight sealing relationship 
therewith. Also, the piston shaft moves relative to the guide element and 
bearing ring upon movement of the piston head within the chamber. The 
piston foot 52, which preferably defines an offset ledge 58, is disposed 
on the end of the piston shaft 48 which extends beyond the bearing ring 26 
outside of the cylinder 22. The foot is movable toward and away from the 
bearing ring upon corresponding movement of the piston head and shaft. 
The positioning pin 30 is attached outside of the cylinder 22 to, and 
extends downwardly from, the bearing ring 26 at a location adjacent to one 
side of the central opening 46 through the ring 26, as best seen in FIG. 
3. In such position, the pin 30 extends substantially parallel to the 
piston shaft 48 extending from the ring opening 46. 
The compressible coil spring 32 and the source of pressurized air 34 are 
provided for applying force to first and second opposing sides 60, 62 of 
the piston head 50 respectively for moving the piston 28 in opposite 
directions. On the one hand, the coil spring 32, which is disposed within 
the chamber 42 between the first side 60 of the piston head 50 and the 
closed end 38 of the cylinder housing 36, biases the piston 28 for 
movement in a first direction away from the closed cylinder end 38 and 
toward the guide element 24. On the other hand, through actuation of the 
pressurized air source 34, which is connected at orifice 64 to the 
cylinder chamber 42 between the guide element 24 and the second side 62 of 
the piston head 50, the piston 28 is forcibly moved against the coil 
spring 32 in an opposite second direction away from the guide element 24 
and toward the closed end 38 of the cylinder housing 36. 
The pressurized air source 34 is actuated and de-actuated by pressing down 
on and releasing a handle 66 which is pivotally mounted at 68 to a tab 70 
fixed to the cylinder housing 36. When the handle 66 is pressed downward, 
the stem 72 of a valve 74 moves downward to open the valve, allowing 
pressurized "shop" air to enter the cylinder chamber 42 from supply hose 
76. When the handle 66 is released, a compressed coil spring 78 which 
surrounds the valve stem 72 moves the latter upwardly to close the valve 
74 and block flow of pressurized air to the cylinder chamber 42. Instead, 
compressed air from the chamber 42 is now allowed to evacuate from the 
chamber to the atmosphere through a suitable passageway (not shown) in the 
valve stem 72. 
In using the pneumatic clamping device 20, it is desired that a clamping 
force applied to two or more sheets, plies or layers of material S such as 
steel sheet material, be sufficient to extrude a viscous faying surface 
sealant (not shown) from between the layers S to prevent metal chips or 
burrs from accumulating at their interface as the next fastener hole or 
the like is drilled through the sheets adjacent to the device 20. A 
prerequisite to the use of the clamping device 20 is that at least one 
fastener hole through each sheet or layer S must exist at the start. The 
clamping action necessary for drilling the first hole through the layers S 
without accumulating chips and burrs at their interface can be 
accomplished through use of prior art mechanical clamping devices such as 
C-clamps or toggle clamps which are commonly used in the manufacture of 
aircraft structures. 
To use the device 20, the handle 66 must be in a released condition wherein 
the pressurized air is allowed to exhaust from the cylinder chamber 42 and 
coil spring 32 extends the piston shaft 48 when the spring forces the head 
50 of the piston 28 to a first position adjacent the guide element 24, as 
seen in FIG. 4. At such first position a spacer ring 80 within the chamber 
maintains the piston head 50 in a spaced relationship away from the guide 
element 50 so as not to block the orifice 64. The ring 80 has an opening 
82 aligned with the orifice 64. The offset piston foot 52 is now disposed 
remote or away from the positioning pin 30 which provides clearance 
therebetween sufficient to allow easy insertion of the piston foot and an 
adjacent portion of the piston shaft through the aligned holes H in the 
layers of material S. 
Once the foot 52 has been inserted, the positioning pin 30 approximately 
aligned with the holes H (it was misaligned with them during insertion of 
the foot due to the latter's offset relationship with the pin 30), and 
then inserted into the holes, the handle 66 may be depressed to open the 
valve 74 and supply pressurized air to the cylinder chamber 42. 
The air pressure within chamber 42 overcomes the biasing force of coil 
spring 32 and the piston is moved from its first position of FIG. 4 to a 
second position shown in FIG. 2. As the piston head 50 moves away from the 
guide element 24 and toward the closed end 38 of the housing 36 to the 
second position shown in FIG. 2, the piston shaft 28 is retracted into the 
cylinder 22 and the offset piston foot 52 becomes disposed adjacent to the 
positioning pin 30 such that its ledge 58 hooks the bottom one of the 
material plies or layers S and in conjunction with the pin 30, the portion 
of the piston shaft 28 adjacent to the foot 52 substantially fills the 
aligned holes H. Furthermore, in conjunction with the bearing ring 26, the 
ledge 58 of the foot 52 forcibly exerts a uniform pressure, clamping the 
sheets of material together. So long as the handle 66 is maintained 
depressed, as seen in FIG. 2, the clamping force will remain constant. 
When the handle is released, the clamping force is almost instantaneously 
removed from the sheets. A quick disconnect coupling 84 is provided to 
connect and disconnect the "shop air" supply hose 76 to and from the 
cylinder 22 of the device 20. 
As mentioned above, the clamping action will be exerted between the bearing 
ring 26 and the upper surface or ledge 58 of the offset foot 52. The 
diameter of the offset foot will be slightly less than the diameter of the 
existing hole H through which the offset foot 52 is installed. The piston 
shaft 48 and positioning pin 30 are configured so that when the clamping 
force is applied, the offset foot 52 is drawn toward the existing hole H 
and the combined cross-sections of shaft 48 and positioning pin 30 fill 
hole H and hold the offset foot 52 securely in the desired clamping 
position. 
A possible modification may be made to the valve 74 such that by squeezing 
handle 66 downward valve 74 opens and delivers "shop air" pressure into 
chamber 42. Valve 74 will remain open, even though handle 66 is released, 
until the handle 66 is squeezed downward a second time. This second motion 
will close the inlet port of the valve and open an exhaust port which will 
relieve the pressure in chamber 42 and allow the piston 28 to be moved 
downward by spring 32 and release the clamping force. 
Another modification to the preferred embodiment of the invention is shown 
in FIGS. 5 and 6. The hardware and operation of the clamping device is the 
same as that shown and described previously except the handle 66, valve 74 
and quick disconnect coupling 84 are replaced with a manual check valve 
86. The clamping device will be actuated by applying pressurized "shop 
air" at the check valve 86. The clamping force will remain until the 
supply of pressurized air is removed and pressure in chamber 42 is 
relieved by opening check valve 86. 
A further modification to the preferred embodiment could be accomplished by 
replacing the offset foot 52 and positioning guide or pin 30 with a collet 
and mandrel per se. This modification would provide a method for applying 
uniformly distributed bearing pressure around the periphery of the hole in 
cases where such a uniform distribution is considered advantageous. 
Thus, the clamping device of the present invention provides an improved 
composite unit composed of the combination of a pneumatic cylinder, a 
clamping foot (or collet and mandrel) and a system of inlet and exhaust 
valves for the control of pneumatic pressure within the cylinder. This 
clamping device provides substantial advantages over present methods 
because of the fact that this device can be installed and operated as a 
separate, portable and independently controlled clamping device as opposed 
to prior devices which are operated in conjunction with a drill-motor and 
which require an unwieldy template foot and tail pad. 
Although only the preferred embodiment of the device for carrying out the 
invention and several slight modifications thereof have been described 
above, it is not to be construed that this invention is limited to such 
embodiments. Other modifications may be made by those skilled in the art 
without departing from the spirit and scope of the invention defined 
below.